Bulletin of the American Physical Society
58th Annual Meeting of the APS Division of Plasma Physics
Volume 61, Number 18
Monday–Friday, October 31–November 4 2016; San Jose, California
Session JP10: Poster Session IV (High School/Undergraduate Research; Space Plasmas; DIII-D Tokamak; Low Temperature Plasma Science, Engineering and TechnologyPoster
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Room: Exhibit Hall 1 |
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JP10.00001: HIGH SCHOOL/UNDERGRADUATE RESEARCH |
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JP10.00002: An Overview of DPP's Education and Outreach Effort Paul Miller For more than 25 years, members of the American Physical Society's Division of Plasma Physics (DPP) have offered free plasma physics outreach to teachers and students at the location of the annual DPP meeting. This effort features two on-site events. Teachers Day is a day of workshops for secondary teachers. Each teacher attends ``Plasma 101'' and two more workshops based on interest. Plasma physics is presented not as a new topic to add, but rather a hook by which teachers can enhance topics they already teach. With the Plasma Sciences Expo, we offer a variety of interactive plasma and general science exhibits to busloads of local students. Learn more about our time-tested approach to outreach at this poster, and consider joining the team for next year's events in Milwaukee. [Preview Abstract] |
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JP10.00003: ALPhA Laboratory Immersion in Plasma Physics A. Dominguez, A. Zwicker, J.D. Williams According to the FESAC[1], as recently as 2014 there were a total of just 14 universities offering strong curricula in MFE sciences. Similarly, it was reported that 8 and 19 universities offer strong HEDPL and Discovery Plasma programs respectively. At the undergraduate level, there is also a lack of plasma physics in the curricula. This, regardless of its rich insights into the core subfields of physics, i.e., classical mechanics, electrodynamics, statistical mechanics and quantum phenomena. The coauthors have been leading a plasma physics workshop for the last 3 years directed at undergraduate physics professors and lecturers. The workshop is centered around a versatile and relatively inexpensive ($<\$10k$) plasma discharge experiment which lets students explore Panchen’s Law, spectroscopy and Langmuir probes. The workshop is part of the Advanced Laboratory Physics Association (ALPhA) Laboratory Immersions[2][3], and its objective is for the participants to become familiar with the experiments and incorporate them into their home institution’s curricula as junior labs, senior labs or independent student projects. [1] Assessment of the Workforce Development Needs for the FES. June, 21, 2014 [2] APS March Meeting 2011, Abstract #A14.011 [3] NSF grant #NSF DUE-1122993 [Preview Abstract] |
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JP10.00004: Growing a Science Internship One Year at a Time: Updates to the Science Undergraduate Laboratory Internship Program D. Ortiz-Arias, A. Dominguez, A. Zwicker, S. Greco Deedee Ortiz, Arturo Dominguez, Andrew Zwicker, Shannon Greco Between 1993-2014, the National Undergraduate Fellowship (NUF) program, sponsored by the DOE Office of Fusion Energy Sciences, provided summer research internships for outstanding undergraduate students from around the country. Since then, the NUF program was merged into the Science Undergraduate Laboratory Internship (SULI) program, sponsored by the DOE Office of Workforce Development for Teachers and Students. While there were many similarities between the two programs, the SULI program did not include the one-week introductory course in plasma physics or the opportunity for participants to present their summer research results at this meeting. In the past two years, working with representatives from both OFES and WDTS, we have again implemented some of the most important components of the NUF program. The week-long, introductory course in plasma physics is included and streamed live- especially important since most undergraduate physics students have not taken a plasma physics course before they begin their research. Students are again able to present their research to our community, a critical component of a full research experience and plans are underway to obtain additional funding to once again include universities as eligible host sites. [Preview Abstract] |
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JP10.00005: An Insider's View of the Role of Science and Scientists in Public Policy Andrew Zwicker In many ways, advances in fusion energy sciences and the amount of federal funding received are a case study of how the perception of a scientific endeavor can have a greater influence than actual scientific advances. Clearly, outreach by scientists to both legislators and the general public has a critical role in modifying this perception. This might include presenting current research results to the general public, advising an elected official on a piece of legislation, arguing for an increase in science funding, and more. As a new member of the NJ General Assembly, and as the first physicist ever elected to the NJ Legislature, I have had an opportunity to witness first hand how non-scientists judge science funding, scientists, and scientific advances. As expected, this can be based upon a lack of understanding of how science is conducted rather than results. There is no doubt that there is a clear need for scientists as policy advisors at all levels of government. I will discuss the importance of crosspollination between science and public policy and my experiences during my first year in public office, including my work to create a science fellowship similar to the APS/AAAS Congressional fellowship in the NJ Statehouse. [Preview Abstract] |
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JP10.00006: Addressing the Underrepresentation of Women in Physics at Multiple Levels Shannon Greco, Arturo Dominguez, Deedee Ortiz, Andrew Zwicker APS provides support to several universities and research institutions to host Conferences for Undergraduate Women in Physics (CUWiP). The goal of these Conferences is to provide practical tools and a community to help women persist in physics and STEM careers. This is particularly relevant for the DPP where women make up only 7{\%} of the membership. In January 2017, Princeton University and the Princeton Plasma Physics Laboratory (PPPL) will host a CUWiP. CUWiP and the Science Undergraduate Laboratory Internship (SULI) program expose undergraduates to the variety of possible careers in plasma physics and fusion energy in academia, government labs or private industry. We will report on the success of a number of PPPL programs to engage women at all levels in physics and highlight how programs such as CUWiP and SULI contribute to this goal. [Preview Abstract] |
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JP10.00007: Building an infrastructure at PICKSC for the educational use of kinetic software tools W. B. Mori, V. K. Decyk, A. Tableman, R. A. Fonseca, F. S. Tsung, Q. Hu, B. J. Winjum, L. D. Amorim, W. An, T. N. Dalichaouch, A. Davidson, A. Joglekar, F. Li, J. May, M. Touati, X. L. Xu, P. Yu One aim of the Particle-In-Cell and Kinetic Simulation Center (PICKSC) at UCLA is to coordinate a community development of educational software for undergraduate and graduate courses in plasma physics and computer science. The rich array of physical behaviors exhibited by plasmas can be difficult to grasp by students. If they are given the ability to quickly and easily explore plasma physics through kinetic simulations, and to make illustrative visualizations of plasma waves, particle motion in electromagnetic fields, instabilities, or other phenomena, then they can be equipped with first-hand experiences that inform and contextualize conventional texts and lectures. We are developing an infrastructure for any interested persons to take our kinetic codes, run them without any prerequisite knowledge, and explore desired scenarios. Furthermore, we are actively interested in any ideas or input from other plasma physicists. This poster aims to illustrate what we have developed and gather a community of interested users and developers. [Preview Abstract] |
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JP10.00008: Development of Active Learning Curriculum for CASPER's Microgravity Drop Tower. Jorge Carmona-Reyes, Li Wang, Judy York, Lorin Matthews, Rene Laufer, Mike Cook, Jimmy Schmoke, Truell Hyde As CASPER's new drop tower comes on line, plans for correlated educational research curricula are underway. CASPER's educational research team is working on developing curricula specific to the CASPER drop tower, modeled on a contest currently in use by (BEST) Robotics Inc. within central Texas independent school districts. The curricula integrates age specific use of computer programming software packages such as ``Scratch'' with industry standard communication protocols and augmented reality applications. Content is constructed around an earth and space science framework, covering subjects such as stars and galaxies, matter and energy, fusion and fission at a middle school level. CASPER faculty are partnering with the Region 12 Service Center; this combination provides a wide range of expertise that includes professional development, pedagogical methods, computational thinking in addition to microgravity and space science research expertise. The details of this work will be presented and samples of the manner in which it is impacting the CASPER research and educational outreach partnership will be discussed. [Preview Abstract] |
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JP10.00009: Applied plasma physics at Marquette University T. D. Tharp A new applied plasma physics laboratory is currently under construction at Marquette University. With emphases on both physics and engineering, our lab seeks to give undergraduates an opportunity to contribute to world-class research. Initially, our work will focus on the development of non-neutral plasma diagnostics for use on the ALPHA antimatter experiment at CERN. As our effort grows, we will also be seeking collaborative opportunities to involve students in industry and the quasineutral plasma research community. A description of planned research activities will be presented. [Preview Abstract] |
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JP10.00010: Measuring the parameters of a high flux plasma in Proto-MPEX C. Skeen, T.M. Biewer, C.L. Cantrell, J.C. Klemm, R.A. Musick, G. Nunley, J.S. Salazar Sanchez, D.J. Sawyer, H. Ray, G. Shaw, M. Showers The Prototype Material Plasma Exposure Experiment (Proto-MPEX) is a linear, magnetically confined plasma production device, utilizing a helicon antenna. The plasma column interacts with a material target at the end of the device, creating plasma-material interaction conditions that are relevant to the conditions that are expected in future fusion reactors. Moreover, helicon antenna plasma sources have been proposed as propulsion devices for spacecraft. It has been observed that in some circumstances the Proto-MPEX plasma exerts sufficient force on the target plate to cause the target to recoil. A ballistic probe has been designed to measure the force and heat flux profile of the plasma. The probe response has been calibrated, using scales, thermocouples, and fast camera imaging. The ballistic probe has been inserted into Proto-MPEX plasmas and the heat flux profile of the plasma has been measured. Also the maximum force that is exerted on the probe has been estimated. [Preview Abstract] |
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JP10.00011: Time-Domain Analysis of Higher Order Mode Properties in an Open Cavity Retaining Axial Symmetry S. Y. Lin, M. C. Lin Theoretical and computational research to accurately and efficiently determine higher order mode properties of an axially symmetrical open cavity has been pursued. Open cavities have been widely employed in gyrotrons for the generation of high-power millimeter, submillimeter, and THz waves. A standing wave forms in the main body of the cavity, and the open end allows the extraction of power generated by the electron beam wave interaction. On the other hand, microresonators, such as microspheres that have small effective volume of their whispering gallery modes (WGMs), high quality factors, and quasi insensitivity to conducting material boundaries can also be considered as open cavities since the WGMs are natural electromagnetic eigenmodes that are activated by external coherent signals. For these cavities, axial symmetry is usually retained. The CAVITY program developed by Professor K. R. Chu using Fortran allows the users to accurately and efficiently determine the resonant frequency, the quality factor, and the field profile for the TE modes of an open cavity. In this work, an extension of the CAVITY program using Mathematica, CAVITY-M, to perform time-domain analysis of higher order modes in open cavities retaining axial symmetry for wider applications such as those mentioned above has been carried out. The new CAVITY-M program developed using Mathematica is able to effectively analyze the higher order mode characteristics of a general open cavity with an axial symmetry, in addition to the traditional modes in a gyrotron cavity. [Preview Abstract] |
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JP10.00012: Mode conversion and heating in a UCLA-high schools collaborative experiment Miana Smith, Samuel Buckley-Bonnano, Patrick Pribyl, Walter Gekelman, Joe Wise, Bob Baker, Ken Marmie A small plasma device is in operation for use by undergraduates and high school students at UCLA. Magnetic field up to 100 G, with density $10^{8}\le n_{e} \le 10^{11}cm^{-3}$ and temperature $T_{e} <3eV$are available in a 50 cm diameter plasma 2 meters long. The plasma is generated by an ICP source at one end operating at about 500 kHz. For this experiment, a small plate located near the edge of the plasma column is used as an electrostatic launcher. High frequency waves $\omega_{ce} <\omega <3\omega_{ce} $are launched radially from the plate in the low-density region, with electric field perpendicular to B and to the density gradient. A Langmuir probe located some distance away axially measures plasma heating along a field line that passes several cm in front of the launcher, localized in radius with $\delta r\approx 1cm$ Absorption and strong electron heating are observed at the plasma resonant layer. We explore the ``double resonance condition at which $\omega_{pe} =2\omega_{ce} $. Here strong interaction with electron Bernstein waves is expected. The Bernstein waves are also launched at low power and their dispersion relation verified. [Preview Abstract] |
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JP10.00013: Development of Exploding Wire Plasma System for Studying Magnetic Reconnection Landry Horimbere, D. R. Stone, J. C. Rodgers, D. P. Lathrop We are developing an exploding wire plasma system to study magnetic field reconnection at high densities with a range of magnetic helicities. Magnetic helicity is a measure of the topological interlinkage of magnetic field loops and is conserved during reconnection. Magnetic reconnection plays a central role in energy transfer between magnetic fields and in the separation and merging of plasma structures. As a mode of magnetic energy dissipation, reconnection plays an important role in magnetic confinement devices for fusion research, in space weather phenomena such as solar flares, and in the energy transfer between the solar wind and earth’s magnetosphere. Past experiments exploring the interaction of plasmas arcs with various helicity configurations have, in the counter helical case1, yielded high soft X-ray fluxes and evidence of residual plasma structures. Our experiment will investigate higher particle, field and energy densities and as well as the effect of turbulent phase transition on the evolution of reconnecting plasmas. To reach this parameter space, our experimental plasma is produced using the exploding wire method combined with an externally applied quadrapole guiding field to produce a highly no liner screw pinch collision. We have constructed the experimental chamber and are in the process of constructing and testing the pulse power and diagnostic systems. [Preview Abstract] |
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JP10.00014: Measurement of argon neutral velocity distribution functions near an absorbing boundary in a plasma Zachary Short, Derek Thompson, Timothy Good, Earl Scime Neutral particle distributions are critical to the study of plasma boundary interactions, where ion-neutral collisions, e.g. via charge exchange, may modify energetic particle populations impacting the boundary surface. Neutral particle behavior at absorbing boundaries thus underlies a number of important plasma physics issues, such as wall loading in fusion devices and anomalous erosion in Hall thruster channels. Neutral velocity distribution functions (NVDFs) are measured using laser-induced fluorescence (LIF). Our LIF scheme excites the 1s4 non-metastable state of neutral argon with 667.913 nm photons. The subsequent decay emission at 750.590 nm is recorded synchronously with injection laser frequency. Measurements are performed near a grounded boundary immersed in a cylindrical helicon plasma, with the boundary plate oriented at an oblique angle to the magnetic field. NVDFs are recorded in multiple velocity dimensions and in a three-dimensional volume, enabling point-to-point comparisons with NVDF predictions from particle-in-cell models as well as comparisons with ion velocity distribution function measurements obtained in the same regions through Ar-II LIF. [Preview Abstract] |
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JP10.00015: Characterization of the detector for a low voltage, ultra-compact plasma spectrometer Julianne McIlvaine, Amy Keesee, Earl Scime Modern manufacturing techniques enable the production of wafer-scale plasma spectrometers which use low voltage power supplies. Mass production of low voltage, ultra-compact plasma spectrometers would provide for cost efficient geospace investigations requiring multiple spacecraft (constellations of up to 100 have been proposed) that obtain measurements across a region in space. These spectrometers consist of a collimating aperture, an energy analyzer, and a silicon solid state detector (SSSD). Early tests indicate that these units can detect ions of energies ranging from 3-20 keV simultaneously. Using a SSSD with thinned contacts, we can detect electrons with a lower energy limit of around 2 keV. We present the results of testing a four pixel low voltage silicon solid state detector. An electron beam was shot at the detector in an evacuated chamber to test the detection of these lower energies. Results will lead to improvements in the final design of an eight pixel SSSD with ASIC-based electronics. [Preview Abstract] |
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JP10.00016: Reduced Noise UV Enhancement of Etch Rates for Nuclear Tracks in CR-39 Rebecca Sheets, David Clarkson, Rubab Ume, Sean Regan, Craig Sangster, Stephen Padalino, James McLean The use of CR-39 plastic as a Solid State Nuclear Track Detector is an effective technique for obtaining data in high-energy particle experiments including inertial confinement fusion. To reveal particle tracks after irradiation, CR-39 is chemically etched in NaOH at 80$^{\circ}$C for 6 hours, producing micron-scale signal pits at the nuclear track sites. Using CR-39 irradiated with 5.4 MeV alpha particles and 1.0 MeV protons, we show that exposing the CR-39 to high intensity UV light before etching, with wavelengths between 240 nm and 350 nm, speeds the etch process. Elevated temperatures during UV exposure amplifies this effect, with etch rates up to 50\% greater than unprocessed conditions. CR-39 pieces exposed to UV light and heat can also exhibit heightened levels of etch-induced noise (surface features not caused by nuclear particles). By illuminating the CR-39 from the side opposite to the tracks, a similar level of etch enhancement was obtained with little to no noise. The effective wavelength range is reduced, due to strong attenuation of shorter wavelengths. Funded in part by a LLE contract through the DOE. [Preview Abstract] |
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JP10.00017: Bulk Etch Rate and Swell Rate of CR-39 David Clarkson, Rubab Ume, Rebecca Sheets, Sean Regan, Craig Sangster, Stephen Padalino, James McLean The use of CR-39 plastic as a Solid State Nuclear Track Detector is an effective technique for obtaining data in high-energy particle experiments including inertial confinement fusion. To reveal particle tracks after irradiation, CR-39 is chemically etched in NaOH at 80$^{\circ}$C, producing micron-scale signal pits at the nuclear track sites. The development of these pits depends on both the bulk etch rate and the faster etch rate along the track, and is complicated by swelling as water is absorbed. Contrary to common etching models, we find the bulk etch rate to be depth dependent within 15 \mu \)m of the surface, as revealed by swelling TASTRACK CR-39 pieces to their maximum capacity prior to etching. The bulk etch rate was measured using the standard mass method as well as the fission fragment track diameter method. Combining models of swelling and etching rates predicts the progress of bulk etching during a standard etch, without pre-swelling. This result has implications for the understanding the chemistry of the etch process, as well as the outcome of CR-39 surface preparation methods. Funded in part by a LLE contract through the DOE. [Preview Abstract] |
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JP10.00018: TNSA Heavy Ion Measurements using the Time-Resolved Tandem Faraday Cup M.K. Ginnane, B. Kousar, J. Slish, K. Palmisano, S. Mandanas, S.J. Padalino, T.C. Sangster, S. Regan, C. Mileham, C. Stoeckl The MTW Laser at LLE utilizes an ultra-intense laser to produce high-energy heavy ion pulses through Target Normal Sheath Acceleration (TNSA). Using the Time-Resolved Tandem Faraday Cup (TRTF) the total number of heavy ions produced by TNSA can be determined, which is needed for stellar nuclear reaction cross section measurements. TNSA heavy ions stop within the thin walled front cup, while light ions pass through it and deposit their remaining charge in the back cup. A two channel storage scope measures voltages produced by the beam currents collected in the cups, respectively. The charge state fraction of plasma ions is modified by passing the heavy ions through a charge-exchange foil at the TRTF entrance. While passing through the foil, ions equilibrate to known charge states based on their velocities. Using time of flight, the total heavy ion current can be normalized to the correct charge state fraction. A pair of dipole magnets deflect relativistic TNSA electrons from the cup’s entrance. They also prevent secondary electrons from escaping the front and back cups. Funded in part by a LLE contract through the DOE. [Preview Abstract] |
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JP10.00019: Heavy ion beams from an Alphatross source for use in calibration and testing of diagnostics R.J. Ward, G.M. Brown, D. Ho, B.F.O.F. Stockler, C.G. Freeman, S.J. Padalino, S.P. Regan Ion beams from the 1.7 MV Pelletron Accelerator at SUNY Geneseo have been used to test and calibrate many inertial confinement fusion (ICF) diagnostics and high energy density physics (HEDP) diagnostics used at the Laboratory for Laser Energetics (LLE). The ion source on this accelerator, a radio-frequency (RF) alkali-metal charge exchange source called an Alphatross, is designed to produce beams of hydrogen and helium isotopes. There is interest in accelerating beams of carbon, oxygen, argon, and other heavy ions for use in testing several diagnostics, including the Time Resolved Tandem Faraday Cup (TRTF). The feasibility of generating these heavy ion beams using the Alphatross source will be reported. Small amounts of various gases are mixed into the helium plasma in the ion source bottle. A velocity selector is used to allow the desired ions to pass into the accelerator. As the heavy ions pass through the stripper canal of the accelerator, they emerge in a variety of charge states. The energy of the ion beam at the high-energy end of the accelerator will vary as a function of the charge state, however the maximum energy deliverable to target is limited by the maximum achievable magnetic field produced by the accelerator's steering magnet. [Preview Abstract] |
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JP10.00020: Characterizing Neutron Diagnostics on the nTOF Line at SUNY Geneseo Hannah Harrison, Hannah Seppala, Hannah Visca, Praveen Wakwella, Kurt Fletcher, Stephen Padalino, Chad Forrest, Sean Regan, Craig Sangster Charged particle beams from SUNY Geneseo's 1.7 MV Tandem Pelletron Accelerator induce nuclear reactions that emit neutrons ranging from 0.5 to 17.9 MeV via $^{\mathrm{2}}$H(d,n)$^{\mathrm{3}}$He and$^{\mathrm{11}}$B(d,n)$^{\mathrm{12}}$C. This adjustable neutron source can be used to calibrate ICF and HEDP neutron scintillators for ICF diagnostics. However, gamma rays and muons, which are often present during an accelerator-based calibration, are difficult to differentiate from neutron signals in scintillators. To mitigate this problem, a new neutron time-of-flight (nTOF) line has been constructed. The nTOF timing is measured using the associated particle technique. A charged particle produced by the nuclear reaction serves as a start signal, while its associated neutron is the stop signal. Each reaction is analyzed event-by-event to determine whether the scintillator signal was generated by a neutron, gamma or muon. Using this nTOF technique, the neutron response for different scintillation detectors can be determined. Funded in part by a LLE contract through the DOE. [Preview Abstract] |
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JP10.00021: High Current, High Density Arc Plasma as a New Source for WiPAL Roger Waleffe, Doug Endrizzi, Rachel Myers, John Wallace, Mike Clark, Cary Forest The Wisconsin Plasma Astrophysics Lab (WiPAL) has installed a new array of nineteen plasma sources (plasma guns) on its 3 m diameter, spherical vacuum vessel. Each gun is a cylindrical, molybdenum, washer-stabilized, arc plasma source. During discharge, the guns are maintained at 1.2 kA across 100 V for 10 ms by the gun power supply establishing a high density plasma. Each plasma source is fired independently allowing for adjustable plasma parameters, with densities varying between $10^{18}-10^{19}$ m$^{-3}$ and electron temperatures of 5-15 eV. Measurements were characterized using a 16 tip Langmuir probe. The plasma source will be used as a background plasma for the magnetized coaxial plasma gun (MCPG), the Terrestrial Reconnection Experiment (TREX), and as the plasma source for a magnetic mirror experiment. Temperature, density, and confinement results will be presented. [Preview Abstract] |
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JP10.00022: Two Non-Invasive Optical Diagnostics for the Plasma Couette Experiment Megan Tabbutt, Ken Flanagan, Jason Milhone, Mark Nornberg, Fred Roesler, Cary Forest Two non-invasive optical diagnostics have been developed for the Plasma Couette Experiment Upgrade (PCX-U). PCX-U is capable of producing electron temperatures of 5 to 15 eV, densities between $10^{10}$and $5\times10^{11}$cm$^{-3}$, and ion temperatures between 0.5 eV to 2 eV. The first diagnostic described utilizes a low cost USB spectrometer for optical emission spectroscopy (OES). Combined with a modified coronal model, OES is used to measure electron temperature in Argon plasmas. A higher resolution spectrometer is used to image ion lines which can be analyzed to determine moments of the ion energy distribution function, particularly ion temperature and flow. Both optical diagnostics are mounted on a linear stage for scanning chords across the plasma volume. Abel transform techniques are used to create radial profiles of measured plasma properties. [Preview Abstract] |
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JP10.00023: Density Measurement of Compact Toroid with Mach-Zehnder Interferometer Lauren Laufman-Wollitzer, Doug Endrizzi, Matt Brookhart, Ken Flanagan, Cary Forest Utilizing a magnetized coaxial plasma gun (MCPG) built by Tri Alpha Energy, a dense compact toroid (CT) is created and injected at high speed into the Wisconsin Plasma Astrophysics Laboratory (WiPAL) vessel. A modified Mach-Zehnder interferometer from the Line-Tied Reconnection Experiment (LTRX) provides an absolute measurement of electron density. The interferometer is located such that the beam intersects the plasma across the diameter of the MCPG drift region before the CT enters the vessel. This placement ensures that the measurement is taken before the CT expand. Results presented will be used to further analyze characteristics of the CT. [Preview Abstract] |
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JP10.00024: Hardening of Metallic Materials Using Plasma Immersion Ion Implantation (PIII) Yufan Xu, Mike Clark, Ken Flanagan, Jason Milhone, Paul Nonn, Cary Forest A new approach of Plasma Immersion Ion Implantation (PIII) has been developed with the Plasma Couette Experiment Upgrade (PCX-U). The new approach efficiently reduces the duty cycle under the same average power for PIII. The experiment uses a Nitrogen plasma at a relatively high density of $10^{10}\sim10^{11}$ cm$^{-3}$ with ion temperatures of $<2$ eV and electron temperature of $ 5\sim 10$ eV. The pulser for this PIII experiment has a maximum negative bias greater than 20kV, with 60Hz frequency and a 8 $\mu$s on-time in one working cycle. The samples (Alloy Steel 9310) are analyzed by a Vicker Hardness Tester to study the hardness and X-ray Photoelectron Spectroscopy (XPS) to study implantation density and depth. Different magnetic fields are also applied on samples to reduce the energy loss and secondary emission. Higher efficiency of implantation is expected from this experiment and the results will be presented. [Preview Abstract] |
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JP10.00025: Search of the MRI Through Magnetic Field Measurement Using a Hall Probe Array Jacob Lynn, Ethan Peterson, Ken Flanagan, Cary Forest The Plasma Couette Experiment Upgrade (PCX-U) is capable of producing plasma with parameters ideal for the observation of a magnetorotational instability (MRI). PCX-U allows for the generation of plasma with Keplerian-like flow profiles, sufficiently weak magnetic fields, and suitable fluid and magnetic Reynolds numbers. Numerical simulations show that plasma with these parameters should excite the MRI. When the MRI is achieved, the plasma is expected to develop a poloidal field structure. To detect this field structure, an axial magnetic probe has been constructed. The probe consists of a 1 ft. long PCB containing a two-axis, 15 position hall probe array that can be inserted through the entire axial length of PCX-U. The hall probes used have a magnetic sensitivity of 28 mV/G and a bandwidth of 100kHz, which is sufficient to measure the predicted saturated state of the MRI. Initial magnetic results as well as details of the probe construction, calibration and implementation will be shown. [Preview Abstract] |
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JP10.00026: Boundary Condition Effects on Taylor States in SSX Jeremy Han, Jaron Shrock, Manjit Kaur, Michael Brown, David Schaffner Three different boundary conditions are applied to the SSX $0.15~m$ diameter plasma wind tunnel and the resultant Taylor states* are characterized. The glass walls of the wind tunnel act as an insulating boundary condition. For the second condition, a flux conserver is wrapped around the tunnel to trap magnetic field lines inside the SSX. For the last condition, the flux conserver is segmented to add theta pinch coils, which will accelerate the plasma. We used resistive stainless steel and copper mesh for the flux conservers, which have soak times of $3\mu s$ and $250\mu s$, respectively. The goal is to increase the speed, temperature, and density of the plasma plume by adding magnetic energy into the system using the coils and compressing the plasma into small volumes by stagnation. The time of flight is measured by using a linear array of magnetic pick-up loops, which track the plasma plume's location as a function of time. The density is measured by precision quadrature He-Ne laser interferometry, and the temperature is measured by ion Doppler spectroscopy. Speed and density without the coils are $30\ km/s$ and $10^{15}\ cm^{-3}$. We will reach a speed of $100\ km/s$ and density of $10^{16}\ cm^{-3}$ by adding the coil. *Gray, et al, PRL $\textbf{110}$, 085002 (2013) [Preview Abstract] |
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JP10.00027: Theta Pinch Coil Design for SSX J. E. Shrock, J. Han, M. Kaur, M.R. Brown, D.A. Schaffner We present the essential physics and design parameters behind a theta pinch coil used on SSX. The coil is used as an accelerator to drive flux behind a Taylor plume traveling about 30 km/sec. Operating between 25 and 40 kV on a time scale $<10$ $\mu s$, the design focuses on minimizing the quarter cycle rise time ($\frac{\pi}{2}\sqrt{LC}$) of the coil while maintaining the necessary precautions for working at high voltage. Our design works with 1.1 and 3.3 $\mu F$ capacitors and a maximum stored electrical energy of $U=\frac{1}{2}CV^2\simeq 880$ $J$ (at the lower capacitance). This electrical energy is converted into kinetic energy in the plume. Each plume has a mass greater than 30 $\mu g$, giving an initial kinetic energy of at least $14~J$. At perfect efficiency, the upper bound of the plume velocity will be 240 km/sec using the lower capacitance circuit. [Preview Abstract] |
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JP10.00028: Time of Flight Measurements of a Plasma Plume in a Glass Tube With and Without a Metal Liner C. Fiedler Kawaguchi, D. A. Schaffner, M. R. Brown, M. Kaur, H. K. Johnson Researchers have yet to attain a self-sustaining fusion reaction in which the amount of energy put in is less than that being produced. A novel approach for the compression and heating of plasma is under development at Swarthmore College with collaboration from Bryn Mawr College through the ARPA-E ALPHA program. Two acceleration modules are being designed to accelerate and compress plasma plumes using pulsed copper rings outside of a glass chamber (module one) and inside of a stainless steel chamber (module two). Measurements of plasma velocity are made using a time of flight technique using Hall probes and magnetic pickup probes (B-dot) probes to measure magnetic field at an array of spatial locations along the chamber. Results shows that the response time of the Hall probe chip used was too slow to register the fast changing fields. B-dot probes were shown to have a fast enough response. Time of flight measurements of field are made in the glass tube using cross correlation methods, with and without a stainless steel liner. Preliminary results show an average increase in the plasma plume velocity, from 38 km/s to 45 km/s, when the glass chamber is lined. [Preview Abstract] |
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JP10.00029: Effect of Metal Proximity on a Pulsed Copper Coil H. K. Johnson, D. A. Schaffner, M. R. Brown, M. Kaur, C. Fiedler-Kawaguchi Generating and accelerating plasma in a stainless steel chamber affects the magnetic fields inside. These effects will decrease the field due to a pulsed coil (which will later be used to accelerate plasma) inside the chamber. This work is being done in conjunction with the Swarthmore Spheromak Experiment. Both facilities are collaborating in an attempt to accelerate and compress plasma as part of ARPA-E's Accelerating Low-Cost Plasma Heating and Assembly (ALPHA) program. Measurements of the impact of the chamber on the coil's magnetic fields were made using a B-dot probe inside the coil, which was placed at incremental distances from a metal plate. As the coil is moved from the plate, the plate's interference with the field was seen to exponentially decay. This process was repeated for stainless steel, aluminum, and copper, and a range of voltages (500-800V). At least seventy percent of the original signal was recovered within two inches. Pulsing the coil inside the stainless steel chamber resulted in signals about one third the strength of those measured outside of the chamber. The results of this experiment will be used to guide development of the stainless steel pulse-coil system for the Swarthmore ALPHA project. [Preview Abstract] |
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JP10.00030: Experimental Investigation of Temperature Measurement Techniques in a Toroidal Pure Electron. Albert Marshall, Benjamin Tomhave, Matthew Stoneking In the Lawrence Non-neutral Torus II (LNT II), a purely toroidal magnetic field (R$_{\mathrm{0}}=$18 cm, B \textless 1 kG) cofines electron plasma for several seconds at densities near 10$^{\mathrm{7}}$ /cm$^{\mathrm{3}}$. The experiment can be operated as a variable-length partial torus or a full torus trap. Trapped charge and density are determined from the frequencies of the lowest order diocotron modes, but as yet, no simple temperature measurement technique has been developed for the LNT II. We report on two strategies for determining the temperature: thermal excitation of Trivelpiece-Gould modes and plasma expansion into a vacuum region past a time varying electrostatic barrier. Besides its being a fundamental plasma parameter, temperature is expected to determine the maximum confinement time in a toroidal plasma due to magnetic pumping transport. [Preview Abstract] |
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JP10.00031: Experimental Investigation of Trapped Particle Modes in a Toroidal Electron Plasma Without End Effects Benjamin Tomhave, Albert Marshall, Matthew Stoneking Electron plasma is confined using a purely toroidal magnetic field (R$_{\mathrm{o\thinspace }}=$ 18 cm, B \textless 1 kG) for times ($\sim $4 s) that are much longer than any of the dynamical timescales of the system. The experiment can be operated as a variable length partial torus or a fully toroidal closed-field trap. Plasma dynamics are observed by monitoring the image charge on isolated wall sectors. In addition, the plasma is controlled or perturbed by application of time-varying potential to isolated wall sectors. Phase-space separatrices are ubiquitous in magnetically confined plasma and the resulting interactions between trapped and passing particles lead to many important effects. We introduce a phase-space separatrix in a closed field (fully-toroidal trap) by applying an electric squeeze to toroidally localized wall sectors in order to study trapped particle modes in a full torus. These experiments provide a comparison with similar experiments in cylindrical traps, but without end effects. [Preview Abstract] |
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JP10.00032: Ion-Neutral Collision effects on Streaming Instabilities in the Pre-Sheath of Low Temperature Plasmas Patrick Adrian, Scott Baalrud, Trevor Lafleur Ion-ion streaming instabilities are present in the pre-sheaths of multi-ion-species plasmas and have been theorized to cause an anomalous frictional force that merges ion flow speeds together.[1] If the neutral pressure is sufficiently high, ion-neutral collisions will damp the two stream instability and decrease the frictional force felt by ions. We present different models for the ion velocity near the sheath - pre-sheath boundary taking into account both two stream instabilities and neutral collisions. We consider different ion-neutral collision models for the collision term, $\frac{\partial f}{\partial t}|_c$, in the kinetic equation, which yield modifications to the linear dielectric response function of the plasma. We present new PIC-MCC simulations and compare with theoretical predictions for: (1) the presence of instability, (2) the observed growth rates , (3) and the flow speeds of the ions through the pre-sheath. \\ [4pt][1] Baalrud S D, Hegna C C and Callen J D 2009 Phys. Rev. Lett. 103 205002 [Preview Abstract] |
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JP10.00033: Measurement of Thermal Effects in the Dispersion Relation of the Dust Acoustic Wave Joshua Hoyng, Jeremiah Williams A complex or dusty plasma is a four-component plasma system composed of ions, electrons, neutral particles and charged microparticles. The presence of these charged microparticles reveals different plasma phenomena, including a new wave mode known as the dust acoustic, or dust density, wave (DAW). The DAW is a low frequency, longitudinal mode that propagates through the microparticle component of the dusty plasma system and is self-excited by the energy from the ions streaming through this component. In recent years the DAW has been the subject of intense study and has provided a way to examine the thermal properties of the microparticle component. In this presentation, we report the results of an experimental study examining the thermal effects in the dispersion relation of this wave mode over a range of neutral gas pressures. [Preview Abstract] |
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JP10.00034: Dust particle circulation and vortices in a dc glow discharge dusty plasma Ayden Kish, Edward Thomas Complex, or dusty, plasmas introduce a new charged species - dust grains of up to a few microns in diameter - to the dynamics of a background plasma discharge. While the size of these dust grains allow us to observe many plasma phenomena macroscopically, their presence also results in the generation of other processes that are unique to dusty plasmas. This presentation reports the observations of a recent study of toroidally-shaped dust clouds in a direct-current Argon plasma discharge. These dusty plasma clouds are formed by placing a conducting ring on a lower electrode while generating the plasma using an upper, biased electrode. Dust particles become suspended in the plasma between the two electrodes and, under the correct pressure and discharge conditions, the toroidally-shaped cloud is formed. This work reports on a variety of experimental configurations used to generate the clouds, measurements of particle flow and rotation using particle image velocimetry (PIV), and initial characterization of the plasma conditions that lead to the formation of these structures. [Preview Abstract] |
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JP10.00035: First absolutely calibrated on-axis ion flow measurements in MST. B. Schott, M. Baltzer, D. Craig, D.J. Den Hartog, T. Nishizawa, M.D. Nornberg Improvements in absolute calibration techniques allow for the first direct measurements of the flow profile in the core of MST. We use both active charge exchange recombination spectroscopy and passive emission near 343 nm to measure ion temperature and flow. It is generally assumed that O VI is the brightest passive emission source. However, we show that there are cases, such as high temperature, pulsed poloidal current drive (PPCD) plasmas where the passive emission is dominated by C VI. Differences in the fine structure for O VI and C VI result in a systematic velocity error of about 12 km/s if the wrong model is assumed. Active measurements, however, are relatively insensitive to background model choice. The dominant source of error in active velocity measurements remains the systematic errors in calibration. The first absolutely calibrated, localized toroidal velocity measurements were obtained using an updated calibration technique. During PPCD, the on-axis ion flow is up to 40 km/s larger than both the n $=$ 6 mode velocity and the line-averaged ion velocity. These measurements provide the first direct look at the flow profile in the core of MST. This work has been supported by the US DOE and the Wheaton College summer research program. [Preview Abstract] |
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JP10.00036: Effects of Resistivity and Viscosity on m$=$0 Rise and Fall Time in the RFP A.M. Futch, D. Craig, R. Hesse, C.M. Jacobson In the reversed field pinch (RFP), poloidal mode number m$=$0 fluctuations are driven in a sawtooth cycle via nonlinear coupling with unstable m$=$1 tearing modes. We explore how the rise and fall time of these m$=$0 fluctuations depends on resistivity and viscosity in visco-resistive MHD simulations using the DEBS code. Both the Lundquist number (S) and magnetic Prandtl number (Pr) affect the rise/fall time. Analysis of MST experimental data also shows that both the rise and fall times of the m$=$0 amplitude vary with S. The variation observed in experiment is consistent with simulation results for rise time, but shows some differences for fall time. Rise time is insensitive to the resistivity profile but depends slightly on the viscosity profile. Fall time is strongly correlated with the duration of the crash which depends on both resistivity and viscosity profiles. These results suggest that the rise and fall time of the m$=$0 modes at the sawtooth crash is not strongly influenced by the local resistivity near the resonant surface but instead is primarily determined by the overall dynamics of the entire sawtooth cycle. The role of viscosity is less clear though the edge viscosity affects the m$=$0 evolution more than the core. This work has been supported by the U.S.D.O.E. [Preview Abstract] |
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JP10.00037: Experimental studies of the effect target geometry on the evolution of laser produced plasma plumes. Cuyler Beatty, Austin Anderson, Jeremy Iratcabal, Eric Dutra, Aaron Covington The expansion of the laser plumes was shown to be dependent on the initial target geometry. A 16 channel framing camera was used to record the plume shape and propagation speeds were determined from analysis of the images. Plastic targets were manufactured using different methods including 3D printing, CNC machining and vacuum casting. Preliminary target designs were made using a 3D printer and ABS plastic material. These targets were then tested using a 3 J laser with a 5 ns duration pulse. Targets with a deep conical depression were shown to produce highly collimated plumes when compared to flat top targets. Preliminary results of these experiments will be discussed along with planned future experiments that will use the indented targets with a 30 J laser with a 0.8 ns duration pulse in preparation for pinched laser plume experiments at the Nevada Terawatt Facility. Other polymers that are readily available in a deuterated form will also be explored as part of an effort to develop a cost effective plasma plume target for follow on neutron production experiments. [Preview Abstract] |
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JP10.00038: Improved Temperature Diagnostic for Non-Neutral Plasmas with Single-Electron Resolution Sabrina Shanman, Lenny Evans, Joel Fajans, Eric Hunter, Cheyenne Nelson, Carlos Sierra, Jonathan Wurtele Plasma temperature diagnostics in a Penning-Malmberg trap are essential for reliably obtaining cold, non-neutral plasmas. We have developed a setup for detecting the initial electrons that escape from a trapped pure electron plasma as the confining electrode potential is slowly reduced. The setup minimizes external noise by using a silicon photomultiplier to capture light emitted from an MCP-amplified phosphor screen. To take advantage of this enhanced resolution, we have developed a new plasma temperature diagnostic analysis procedure which takes discrete electron arrival times as input. We have run extensive simulations comparing this new discrete algorithm to our existing exponential fitting algorithm. These simulations are used to explore the behavior of these two temperature diagnostic procedures at low $N$ and at high electronic noise. [Preview Abstract] |
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JP10.00039: Construction of an Alpha Particle Spark Detector and Fusor for research in plasma physics and radiation detection Olorunsola Akinsulire, Fabrice Fils-aime, Jake Hecla, Michael Short, Anne White This project delves into the realms of plasma physics and nuclear engineering by exploring systems used to generate plasmas and detect radiation. Basic plasma processes can be explored using inertial electrostatic confinement, in a device commonly called a ``fusor''. The fusor will generate neutrons and x-rays. The breakdown of air within a spark gap can be achieved with alpha particles and the avalanche effect; and constitutes an Alpha Particle Spark Detector (APSD), relevant for studies of basic nuclear processes and detectors. In the fusor, preliminary data was collected on breakdown voltage versus pressure in an air plasma to see how well the current system and geometry match up with expectations for the Paschen curve. A stable plasma was observed, at voltages roughly consistent with expectations, and it was concluded that a more controlled gas introduction system is needed to maintain a steady plasma over wider pressure ranges, and will allow for introduction of D2 gas for the study of neutron and x-ray producing plasmas. This poster will discuss the design, construction, and initial operation of the Alpha Particle Spark Detector and the fusor as part of an Undergraduate Research Opportunity (UROP) project. [Preview Abstract] |
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JP10.00040: Imaging Measurements of Plasma Fluctuations in a Multi-Instability Regime Atit Bashyal, Muhammad Mujtaba, Saikat Chakraborty Thakur, George Tynan, Adam Light The purpose of this research is to look for signatures of certain instabilities using visible light emitted from a cylindrical argon plasma column. The Controlled Shear Decorrelation Experiment (CSDX) was built to demonstrate drift-wave/shear-flow interaction, but recent work indicates that multiple instabilities emerge as the background magnetic field is increased. Visible light from ArI and ArII line emission is collected at high frame rates using a fast digital camera. The imaging data is used to construct plots of spectral density against frequency and wavenumber. These ''dispersion plots'' can be compared to theoretical dispersion curves to make a tentative identification of the active instabilities. We present here the radial localization of various fluctuations, as well as progress on identifying the underlying instabilities. [Preview Abstract] |
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JP10.00041: A second-order Grad-Shafranov solver with accurate derivative computation Iraj Eshghi, Lee Ricketson, Antoine Cerfon We present progress on a fast Grad-Shafranov and Poisson solver that uses the finite element method with linear elements to find equilibria of the electro-magnetic potentials inside tokamaks. The code converges with second-order errors, and we introduce a module which can take derivatives of the potential at no increase in error. Thus, this code can be much faster than most higher-order finite element solvers, while still retaining a sufficiently small error margin in the physically relevant quantities. [Preview Abstract] |
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JP10.00042: ABSTRACT WITHDRAWN |
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JP10.00043: Implementation Of External Magnetic Fields To Create Pressure High Density Plasmas On The Helicon Plasma Experiment (HPX) Phil Azzari, Jordan Hopson, Jordan Frank, Paul Crilly, Royce James, Jackson Karama, Omar Duke-Tinson, Richard Paolino, Eva Sandri, Justin Sherman, Erin Wright, Jeremy Turk HPX Plasmas are created by imparting directed energy into a Pyrex tube preloaded with Ar gas at fill pressures on the order of 10$^{\mathrm{-4}}$ mTorr utilizing an RF power supply and matching box that can deliver about 250 W of power in the 20 MHz to 100 MHz frequency range. It has been demonstrated [1] that a uniform magnetic field in lower energy level plasmas can facilitate a decrease in inertial effects, which promotes energy conservation within the plasma to provide the necessary external energy in the plasma's magnetic field required to reach the Helicon Mode. This uniform magnetic field will be created by a set of electromagnets capable of producing 1000 gauss. These electromagnets, provided by Princeton Plasma Physics Laboratory will facilitate W-mode production. After reaching the Helicon Mode, the plasma must be forced along the Pyrex tube by an acceleration coil in order to come in contact with several diagnostic probes and to be propelled into a viewing port so Thompson Scattering can be conducted. The progress on the development of the acceleration coil and electromagnets will be presented. [Preview Abstract] |
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JP10.00044: Progress on Langmuir Probe, Data Analysis, Acquisition and Optimization Innovations at the Coast Guard Academy Plasma Lab (CGAPL) Erin Wright, John Frank, Phil Azzari, Royce James, Jordan Hopson, Omar Duke-Tinson, Richard Paolino, Eva Sandi, Justin Sherman, Jeremy Turk CGAPL houses four major plasma experiments that span large temperature, density, energy and functionality regimes. Often automation and remote operation of intelligent devices are required in adverse operating environments for digital and analogue systems. Plasma data collected by a multitude of diagnostics and sensors (to include Langmuir probes) over long timescales mandates CGAPL's 40-channel Data Acquisition (DAQ) system that collects and stores data plus controls CGAPL. The ability to remotely control and operate lab diagnostics then collect and store data through a LabView collective Graphic User Interface (GUI) currently under construction, enable users to remotely control, collect, and store CGAPL experimental data. Innovative solutions to optimize data collection and apparatus command and control, will enhance the ability to run experiments remotely, improve the validity of results, and advance participation in fusion grade diagnostic development. Instrument automation, optimization, and data collection obstacles, solutions, and procedures will be reported. [Preview Abstract] |
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JP10.00045: Spectrometer Development in Support of Thomson Scattering Investigations for the Helicon Plasma Experiment (HPX) Eva Sandri, Richard Davies, Phil Azzari, John Frank, Jackson Frank, Royce James, Jordon Hopson, Omar Duke-Tinson, Richard Paolino, Justin Sherman, Erin Wright, Jeremy Turk Now that reproducible plasmas have been created on the Helicon Plasma Experiment (HPX) at the Coast Guard Academy Plasma Laboratory (CGAPL), a high-performance spectrometer utilizing volume-phase-holographic (VPH) grating and a charge coupled device (CCD) camera with a range of 380-1090 nm and resolution of 1024x1024 is being assembled. This spectrometer will collect doppler shifted photons created by exciting the plasma with the first harmonic of a 2.5 J Nd:YAG laser at a wavelength of 1064 nm. Direct measurements of the plasma's temperature and density will be determined using HPX's Thomson Scattering (TS) system as a single spatial point diagnostic. TS has the capability of determining plasma properties on short time scales and will be used to create a robust picture of the internal plasma parameters. A prototype spectrometer has been constructed to explore the Andor CCD camera's resolution and sensitivity. Concurrently, through intensive study of the high energy TS system, safety protocols and standard operation procedures (SOP) for the Coast Guard's largest and most powerful Laser have been developed. The current status of the TS SOP, diagnostic development, and the collection optic's spectrometer will be reported. [Preview Abstract] |
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JP10.00046: DSMC simulations of vapor transport toward development of the lithium vapor box divertor concept Christopher Jagoe, Jacob Schwartz, Robert Goldston The lithium vapor divertor box concept attempts to achieve volumetric dissipation of the high heat efflux from a fusion power system. The vapor extracts the heat of the incoming plasma by ionization and radiation, while remaining localized in the vapor box due to differential pumping based on rapid condensation. Preliminary calculations with lithium vapor at densities appropriate for an NSTX-U–scale machine give Knudsen numbers between 0.01 and 1, outside both the range of continuum fluid dynamics and of collisionless Monte Carlo. The direct-simulation Monte Carlo (DSMC) method, however, can simulate rarefied gas flows in this regime. Using the solver contained in the OpenFOAM package, pressure-driven flows of water vapor will be analyzed. The use of water vapor in the relevant range of Knudsen number allows for a flexible similarity experiment to verify the reliability of the code before moving to tests with lithium. The simulation geometry consists of chains of boxes on a temperature gradient, connected by slots with widths that are a representative fraction of the dimensions of the box. We expect choked flow, sonic shocks, and order-of-magnitude pressure and density drops from box to box, but this expectation will be tested in the simulation and then experiment. [Preview Abstract] |
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JP10.00047: Comparison of Compressional Alfv\'{e}n Eigenmodes in NSTX-U with Simulation Using the CAE3B Eigenmode Solver N Geiser, N A Crocker, H Smith, E D Fredrickson In fusion research devices like the NSTX-U, compressional Alfv\'{e}n eigenmodes (CAEs) occur at a discrete set of frequencies, or eigenmodes, and can be classified by three mode numbers. The code CAE3B [H M Smith, PPCF 075001 (2009)] simulates a Hall-MHD plasma with realistic geometry, allowing predictions of CAE frequency and structure for experimental plasmas. We compare CAE3B results with experimentally observed modes in NSTX plasmas in order to validate the physics of CAE3B. To make comparisons, it is necessary to develop techniques to determine which simulated modes should be compared to the experimental modes. Two techniques will be assessed: (1) mapping based on patterns of frequency clustering and (2) mapping based on similarity of long-term frequency evolution as plasma parameters change. Preliminary comparisons for an NSTX discharge at a single time show that high-n experimental modes (e.g. n$=$6) have frequencies significantly lower than the lowest predicted eigenmodes, suggesting that these experimental modes are not CAEs, but global Alfv\'{e}n eigenmodes. Low-n experimental modes (e.g. n$=$3), however, have frequencies higher than the lowest predicted eigenmodes, suggesting that the modes are CAEs with higher poloidal or radial quantum numbers than the lowest eigenmode. [Preview Abstract] |
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JP10.00048: Statistics of magnetic moment jumps in collision-less mirror machines Christopher Ferri, Alexander Glasser, Alan Glasser, Samuel Cohen The magnetic moment adiabatic invariant $\mu$ has long been known to be "conserved to all orders," and is taken to be constant in many models used to predict plasma behavior. However, in high magnetic curvature or weak field systems, the lack of a proper small parameter renders $\mu$ conservation very weak. For example, since the 1950's it has been known that in magnetic mirrors, many charged particles experience jumps in $\mu$ as they cross the axial midplane. Such changes in $\mu$ affect mirror confinement. The detailed statistics of these jumps determine whether confinement increases or decreases. We present extensive studies, performed with a Hamiltonian code, of $\mu$ jumps. The jump in $\mu$ is measured by comparing $\mu$ values at successive axial turning points. Using statistical methods, we characterize these $\mu$ jumps and examine their distributions and trends, segregated by initial phase-space position, and speculate on the effects that such jumps in $\mu$ might have on the population of trapped mirror particles. We further consider the harmonic behavior of (zeroth-order) $\mu$ near the axial turning points. [Preview Abstract] |
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JP10.00049: Calculating Pressure-Driven Current Near Magnetic Islands for 3D MHD Equilibria Dhanush Radhakrishnan, Allan Reiman In general, 3D MHD equilibria in toroidal plasmas do not result in nested pressure surfaces. Instead, islands and chaotic regions appear in the equilibrium. Near small magnetic islands, the pressure varies within the flux surfaces, which has a significant effect on the pressure-driven current, introducing singularities. Previously, the MHD equilibrium current near a magnetic island was calculated, including the effect of "stellarator symmetry," wherein the singular components of the pressure-driven current vanish [A. H. Reiman, Phys. Plasmas 23, 072502 (2016)]. Here we first solve for pressure in a cylindrical plasma from the heat diffusion equation, after adding a helical perturbation. We then numerically calculate the corresponding Pfirsch-Schluter current. At the small island limit, we compare the pressure-driven current with the previously calculated solution, and far from the island, we recover the solution for nested flux surfaces. Lastly, we compute the current for a toroidal plasma for symmetric and non-symmetric geometries. [Preview Abstract] |
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JP10.00050: Empirical scalings and modeling of error field penetration thresholds in tokamaks C. Schaefer, M.J. Lanctot, O. Meneghini, S.P. Smith, N.C. Logan, S. Haskey Recent experiments in several tokamaks show that applied n=2 fields can lead to disruptive n=1 locked modes at field thresholds similar to those found for n=1 fields. This has important implications for the allowable size of error fields in next-step devices. In order to extrapolate field thresholds to ITER, an error field database (EFDB) is being developed under the OMFIT integrated modeling framework. The initial phase of development involves analysis of the applied 3D field, detection of island onset, characterization of island structure, reconstruction of the plasma equilibrium, determination of measurable plasma parameters at the relevant rational surfaces, and archiving in a dedicated MDSplus tree. The EFDB is both an extension of previous data assembly efforts and a means of documenting the parametric dependencies of error field penetration thresholds for a variety of tokamaks, across different plasma regimes, and for arbitrary applied field configurations. Through analysis of available data, empirical scalings for n=1 and n=2 fields are resolved. The trends are compared to functional dependencies predicted by drift-MHD models. [Preview Abstract] |
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JP10.00051: Development of a Digital Control for the Phase Contrast Imaging Alignment Feedback System M. Hirata, A. Marinoni, J.C. Rost, E.M. Davis, M. Porkolab The Phase Contrast Imaging diagnostic is an internal reference interferometer that images density fluctuations on a 32-element linear detector array. Since proper operation of the system requires accurate alignment of a CO2 laser beam on a phase plate, beam motion due to vibrations of the DIII-D vessel need to be compensated up to 1 kHz. The feedback network controlling the steering mirrors currently uses a linear analog controller, but a digital controller can provide improved stability performance and flexibility. A prototype was developed using an Arduino Due, a low-cost microcontroller, to assess performance capabilities. Digital control parameters will be developed based on the measured frequency and phase response of the physical components. Finally, testing of the digital feedback system and the required revisions will be done to achieve successful performance. This upgrade to the linear analog controller is expected to be used routinely on similar diagnostics in fusion devices, especially in view of restricted access to the machine hall. [Preview Abstract] |
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JP10.00052: Wall Conditioning Characterization in NSTX-U D. Caron, V. Soukhanovskii, F. Scotti, M. Weller Impurities in tokamak plasmas can lead to disruptive instabilities due to radiative energy loss which impede access to high-confinements mode. One source of impurities in NSTX-U are water molecules trapped in graphite plasma facing components (PFCs), which make up the walls and divertors. Hydrogen and oxygen impurities are released into the plasma due to plasma surface interactions. Extreme ultraviolet (EUV) and visible spectrometers are used in conjunction with a residual gas analyzer (RGA) to characterize the source and amount of released impurities. A high resolution visible spectrometer measured H/D Balmer-$\alpha $ intensity ratio on the inner wall, the upper and lower divertors, and provided a hydrogen time history for shot-to-shot trends. The RGA provided partial pressure trends of masses 2 (H$_{\mathrm{2}})$, 16 (O$_{\mathrm{2}})$, and 18 (H$_{\mathrm{2}}$O). Trends of O VIII and C VI spectral line intensities from the core plasma were obtained from the EUV spectrometer. The trends are correlated with wall conditioning, namely helium glow discharge cleaning and boronization. Using these trends, impurity content monitoring and recommendations for wall conditioning can be implemented. [Preview Abstract] |
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JP10.00053: Dependence of Edge Profiles and Stability on Neutral Beam Power in NSTX P. Travis, G.P. Canal, T.H. Osborne, R. Maingi, S.A. Sabbagh Studying the effect of neutral beam injected (NBI) power on edge plasma profiles and magnetohydrodynamic (MHD) stability is central to the understanding of edge-localized modes (ELMs). Higher heating power should quicken the development of pressure and current-driven peeling-ballooning modes. NSTX ELMy H-mode discharges with NBI power of 4, 5 and 6 MW were analyzed with a python-based set of analysis tools [1] that fit plasma profiles, compute kinetic equilibria, and evaluate the MHD stability with the code ELITE. Electron density and temperature from Thomson scattering measurements, and ion density, temperature, and rotation from Charge Exchange Recombination Spectroscopy were inputs to the kinetic equilibrium fits. The power scan provides an opportunity to compare the stability calculations from the ELITE (ideal) and M3D-C1 (resistive) codes. Preliminary analysis shows that edge pressure profiles for the 5 and 6 MW discharges are comparable, suggesting they both reach a stability boundary. The 4 MW case shows lower edge pressure, which is likely limited by edge transport below the edge stability boundary. [1] T. Osborne et al., J. Conf. Phys. Series 123 (2008) 012014. [Preview Abstract] |
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JP10.00054: Temperature Dependence of Lithium Reactions with Air Roman Sherrod, C.H. Skinner, Bruce Koel Liquid lithium plasma facing components (PFCs) are being developed to handle long pulse, high heat loads in tokamaks. Wetting by lithium of its container is essential for this application, but can be hindered by lithium oxidation by residual gases or during tokamak maintenance. Lithium PFCs will experience elevated temperatures due to plasma heat flux. This work presents measurements of lithium reactions at elevated temperatures (298-373 K) when exposed to natural air. Cylindrical TZM wells 300 microns deep with 1 cm2 surface area were filled with metallic lithium in a glovebox containing argon with less than 1.6 ppm H20, O2, and N2. The wells were transferred to a hot plate in air, and then removed periodically for mass gain measurements. Changes in the surface topography were recorded with a microscope. The mass gain of the samples at elevated temperatures followed a markedly different behavior to that at room temperature. One sample at 373 K began turning red indicative of lithium nitride, while a second turned white indicative of lithium carbonate formation. Data on the mass gain vs. temperature and associated topographic changes of the surface will be presented. [Preview Abstract] |
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JP10.00055: Parametric Study of HTS Coil Quench Protection Strategies Joseph Seibert, Michael Zarnstorff, Yuhu Zhai Next generation fusion devices require high magnetic fields to adequately contain burning plasmas. Use of high temperature superconducting (HTS) coils to generate these magnetic fields would lower energy cost of operation as well as increase stability of the superconducting state compared to low temperature superconducting coils. However, use of HTS coils requires developing quench protection strategies to prevent damage to the coils. One technique involves the utilization of copper discs and other conductors mutually coupled to the HTS coil to quickly extract the current from the coil. Another technique allows conduction between HTS turns to reduce the current in the coil during quench. This project describes a parametric study of the HTS coil and resistive-conductor setup in order to determine limiting cases of the geometry in an attempt to optimize current extraction and coil protection during quench scenarios. [Preview Abstract] |
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JP10.00056: Analysis of Mechanical Stresses/Strains in Superconducting Wire Matthew Barry, Jingping Chen, Yuhu Zhai The optimization of superconducting magnet performance and development of high-field superconducting magnets will greatly impact the next generation of fusion devices. A successful magnet development, however, relies deeply on the understanding of superconducting materials. Among the numerous factors that impact a superconductor’s performance, mechanical stress is the most important because of the extreme operation temperature and large electromagnetic forces. In this study, mechanical theory is used to calculate the stresses/strains in typical superconducting strands, which consist of a stabilizer, a barrier, a matrix and superconducting filaments. Both thermal loads and mechanical loads are included in the analysis to simulate operation conditions. Because this model simulates the typical architecture of major superconducting materials, such as Nb$_3$Sn, MgB$_2$, Bi-2212 etc., it provides a good overall picture for us to understand the behavior of these superconductors in terms of thermal and mechanical loads. [Preview Abstract] |
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JP10.00057: Automated Characterization of Rotating MHD Modes and Subsequent Locking in a Tokamak Juan Riquezes, Steven Sabbagh, Jack Berkery Disruption avoidance in tokamaks is highly desired to maintain steady plasma operation, and is critical for future reactor-scale devices, such as ITER, to avoid potential damage to device components. This high priority research is being conducted at PPPL by analyzing data from NSTX and its upgrade, NSTX-U. A key cause of disruptions is the physical event chain that comprises the appearance of rotating MHD modes, their slowing by resonant field drag mechanisms, and their subsequent locking. The present research aims to define algorithms to automatically find and characterize such physical event chains in the machine database. Characteristics such as identification of a mode locking time based on a loss of torque balance and bifurcation of the mode rotation frequency are examined to determine the reliability of such events in predicting disruptions. A goal is to detect such behavior as early as possible during a plasma discharge, and to further examine potential ways to forecast it. This capability could be used to provide a warning to use active mode control as a disruption avoidance mechanism, or to trigger a controlled plasma shutdown if desired. $^{\mathrm{\ast }}$Supported by US DOE Contracts DE-FG02-99ER54524 and DE-AC02-09CH11466. [Preview Abstract] |
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JP10.00058: Detection and Analysis of X Ray Emission from the Princeton-Field-Reversed Configuration (PFRC-2) Alexandra Bosh, Charles Swanson, Peter Jandovitz, Samuel Cohen The PFRC is an odd-parity rotating-magnetic-field-driven field-reversed-configuration magnetic confinement experiment. Studying X rays produced via electron Bremsstrahlung with neutral particles is crucial to the further understanding of the energy and particle confinement of the PFRC. The data on the x rays are collected using a detector system comprised of two, spatially scannable Amptek XR-100 CR detectors and a Amptek XR-100 SDD detector that view the plasma column at two axial locations, one in the divertor and one near the axial midplane. These provide X-ray energy and arrival-time information. (Data analysis requires measurement of each detector’s efficiency, a parameter that is modified by window transmission. Detector calibrations were performed with a custom-made X-ray tube that impinged ~1-microamp 1-5 kV electron beams onto a carbon target.) From the analyzed data, the average electron energy, effective temperature, and electron density can be extracted. Spatial scans then allow the FRC’s internal energy to be measured. We present recent measurements of the Bremsstrahlung spectrum from 0.8 to 6 keV and the inferred electron temperature in the PFRC device as functions of heating power, magnetic field and fill gas pressure. [Preview Abstract] |
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JP10.00059: Hydrodynamic MagnetoRotational Instability Analog Experiment Steven Stemmley, Eric Blackman, Kyle Caspary, Erik Gilson, Derek Hung, Hantao Ji, Peter Sloboda The MagnetoRotational Instability (MRI) is thought to be responsible for angular momentum transport in accretion disks. This transport occurs when two magnetically coupled fluid elements are perturbed and radially stretch the sufficiently weak magnetic field. To mimic these astrophysical systems, a modified Taylor-Couette device was operated with water as the working fluid at varying rotation speeds to produce hydrodynamic quasi-Keplerian flows and with a pair of test masses coupled by a spring rather than a magnetic field. This scaled experiment simulates the spring-like forces between fluid elements brought on by magnetic tension. In attempts to visually observe this MRI analog, neutrally buoyant masses of varying size were coupled by means of a spring to a fixed point rotating with the fluid. Laser Doppler Velocimetry showed good agreement with ideal Taylor-Couette velocity profiles and that no significant perturbations were present when the masses were moving at the speed of the flow. Further investigations include varying the masses, springs, and shear profiles to obtain a map of the instability threshold boundary as well as determining the effect of the mass's geometry on the flow. Results from video recording measurements and analyses are presented and discussed. [Preview Abstract] |
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JP10.00060: STELLTRANS: A Transport Analysis Suite for Stellarators Joseph Mittelstaedt, Samuel Lazerson, Novimir Pablant, Gavin Weir The stellarator transport code STELLTRANS allows us to better analyze the power balance in W7-X. Although profiles of temperature and density are measured experimentally, geometrical factors are needed in conjunction with these measurements to properly analyze heat flux densities in stellarators. The STELLTRANS code interfaces with VMEC to find an equilibrium flux surface configuration and with TRAVIS to determine the RF heating and current drive in the plasma. Stationary transport equations are then considered which are solved using a boundary value differential equation solver. The equations and quantities considered are averaged over flux surfaces to reduce the system to an essentially one dimensional problem. We have applied this code to data from W-7X and were able to calculate the heat flux coefficients. We will also present extensions of the code to a predictive capacity which would utilize DKES to find neoclassical transport coefficients to update the temperature and density profiles. [Preview Abstract] |
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JP10.00061: Simulation of Scrape-Off Layer Magnetic Field in W7-X Ben Israeli, Samuel Lazerson, Stuart Hudson, Tamara Andreeva, Sergey Bozhenkov The impact of error fields on limiter and divertor operation in W7-X is studied with the field line tracing code FIELDLINES. Recent data have confirmed coil misalignment as a source of error fields in W7-X. Such fields may contribute to uneven heat loads on the limiters currently in place and on the planned divertor system. In this work, field line tracing and diffusion algorithms are applied to investigate the effect of error fields on scrape-off layer topology and the resulting limiter or divertor load distribution. Particle flux distribution is a predicted application of a diffusion model. This model considers a test particle with constant velocity parallel to the field executing Brownian motion perpendicular to the field. Behavior of this model is derived and benchmarked. A comparison is made between results with ideal W7-X coil geometry and with the measured error fields, indicating the degree of load deviation for both limiter and divertor configurations. [Preview Abstract] |
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JP10.00062: Deuterium Neutral Beam Orbits In NSTX-U Nonaxisymmetric Vacuum Magnetic Fields Jonah Philion, Douglass Darrow Axisymmetry of the tokamak magnetic field provides good fast ion radial confinement. Perturbations from this symmetry could induce fast ion radial diffusion and loss. A nonaxisymmetric perturbation was chosen to model the effect of this symmetry loss on NSTX-U deuterium neutral beam ions. Passing and banana orbits in the perturbed field were simulated by integrating the Lorentz force over a duration shorter than the collision time of ions. Upon comparison with analogous orbits in the unperturbed field, the perturbation is shown to have a dispersive effect on the magnetic moment of particle orbit guiding centers. In particular, banana orbits acquire oscillating magnetic moments when subject to the nonaxisymmetric field. The behavior is modeled as a diffusion coefficient which varies with the magnetic moment and canonical angular momentum of the orbit. [Preview Abstract] |
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JP10.00063: Design of an Fiber-Coupled Laser Heterodyne Interferometer for the FLARE Samuel Frank, Jongsoo Yoo, Hantao Ji, Jon Jara-Almonte The FLARE (Facility for Laboratory Reconnection Experiments), which is currently under construction at PPPL, requires a complete set of laboratory plasma diagnostics. The Langmuir probes that will be used in the device to gather local density data require a reliable interferometer system to serve as baseline for density measurement calibration. A fully fiber-coupled infrared laser heterodyne interferometer has been designed in order to serve as the primary line-integrated electron density diagnostic. Thanks to advances in the communications industry many fiber optic devices and phase detection methods have advanced significantly becoming increasingly reliable and inexpensive. Fully fiber coupling a plasma interferometer greatly simplifies alignment procedures needed since the only free space laser path needing alignment is through the plasma itself. Fiber-coupling also provides significant resistance to vibrational noise, a common problem in plasma interferometry systems. This device also uses a greatly simplified phase detection scheme in which chips, originally developed for the communications industry, capable of directly detecting the phase shift of a signal with high time resolution. The design and initial performance of the system will be discussed. [Preview Abstract] |
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JP10.00064: Magnetic Field Generation by a Laser-Driven Capacitor-Coil Target Jessica Cheng, Lan Gao Magnetic fields generated by currents flowing through a capacitor-coil target were characterized using ultrafast proton radiography at the OMEGA EP Laser System [1]. Two \textasciitilde 1.25 kJ, 1-ns laser pulses propagated through the laser entrance holes in one foil of the capacitor, and were focused to the other with an intensity of \textasciitilde 3 \texttimes 10$^{\mathrm{16}}$ W/cm$^{\mathrm{2}}$. The intense laser-solid interaction induced a high voltage between the foils and generated a large current in the connecting coil. The proton data show tens of kA current producing tens of Tesla magnetic fields at the center of the coil. Theoretical lumped circuit models based on the experimental parameters were developed to simulate the target behavior and calculate the time evolution of the current in the coil. The models take into account important elements such as plasmas conditions for building up the voltage, the capacitance between the gap, the resistive heating and skin effect to gain insights on the field generation mechanism. Applications to other coil geometries and magnetic field configurations will also be described. [1] L. Gao et al, Phys. Plasma 23, 043106 (2016) [Preview Abstract] |
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JP10.00065: Use of Gaussian Beam Tracing in the Design of Millimeter-Wave Diagnostics on ITER HeeSeok Joo, Manfred Bitter, Ben Tobias, Hyeon Park, Ali Zolfaghari When the wavelength of the radiation being studied is comparable to the size optical components, the diffraction effect cannot be ignored. Gaussian beam tracing (GBT) can be used by treating the propagation of the light as a beam with certain size rather than a ray used in geometrical optics when analyzing the optics of millimeter-wave diagnostics. Gaussian optics is an effective way to represent diffraction effect because of its ability to show the beam size and the intensity that could be altered from diffraction. GBT has been used in two millimeter-wave diagnostics suited to ITER geometry. The first is in a design of a Gaussian telescope for correction of transmission line misalignment in the ITER LFS reflectometer due to motion of the vessel during heating to operating temperature from room temperature. The second is a new concept of using spherical mirrors for electron cyclotron emission imaging (ECEI) and assessing its promise of a more realistic method of ECEI in ITER than previous idea of using a cylindrical mirror that requires large access ports that can be exposed to intense neutron radiation. The spherical mirror promises a smaller aperture on the first wall of ITER. The simulation of GBT of the two applications are analyzed and discussed. [Preview Abstract] |
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JP10.00066: Computer Simulations of the Magnetorotational Instability (MRI) using the Spectral Finite-Element Maxwell and Navier-Stokes (SFEMaNS) code. Tahiri Nunez, Erik Gilson, Kyle Caspary, Fatima Ebrahimi, Jeremy Goodman, Hantao Ji, Xing Wei Magnetorotational Instability (MRI) is primarily responsible for the transport of angular momentum in accretion disks. We ran simulations using the Spectral Finite-Element Maxwell and Navier-Stokes (SFEMaNS) code (J.-L. Guermond, et al. Nonlinear magnetohydrodynamics in axisymmetric heterogeneous domains using a Fourier/nite element technique and an interior penalty method. J. Comp. Phys., 228:2739-2757, 2009.) to create synthetic diagnostics that help us understand and compare results with what has been measured in laboratory experiments at Princeton. Simulations results are shown to help to understand the behavior of the radial and axial velocity of the flow and magnetic field induced in the MRI experiment; always taking in consideration that the device used in experiments does not completely resemble an accretion disk: the geometry of the container holding the liquid Gallium creates the possibility of other instabilities occurring that we have to sort out in order to recognize MRI. We analyze data for several time-steps, changing different parameters such as rotation speed, and induced magnetic field, in order to determine whether a steady state is reached, or whether there are fluctuations that can be measured. [Preview Abstract] |
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JP10.00067: Mechanical Design, Simulation, and Testing of Self-Aligning Gaussian Telescope and Stand for ITER LFS Reflectometer Diagnostic Rachel Broughton, Michael Gomez, Ali Zolfaghari, Lewis Morris A self-aligning Gaussian telescope has been designed to compensate for the effect of movement in the ITER vacuum vessel on the transmission line. The purpose of the setup is to couple microwaves into and out of the vessel across the vacuum windows while allowing for both slow movements of the vessel, due to thermal growth, and rapid movements, due to vibrations and disruptions. Additionally, a test stand has been designed specifically to hold this telescope in order to imitate these movements. Consequently, this will allow for the assessment of the efficacy in applying the self-aligning Gaussian telescope approach. The motions of the test stand, as well as the stress on the telescope mechanism, have been virtually simulated using ANSYS workbench. A prototype of this test stand and self-aligning telescope will be built using a combination of custom machined parts and ordered parts. The completed mechanism will be tested at the lab in four different ways: slow single- and multi-direction movements, rapid multi-direction movement, functional laser alignment and self-aligning tests, and natural frequency tests. Once the prototype successfully passes all requirements, it will be tested with microwaves in the LFSR transmission line test stand at General Atomics. [Preview Abstract] |
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JP10.00068: Development of an Internet-Enabled Tool for NSTX-U Thomson Diagnostic Data William Wallace, Ahmed Diallo MultiPoint Thomson Scattering (MPTS) is an established, accurate method of finding the temperature, density, and pressure of a magnetically confined plasma. Two Nd:YAG (1064 nm) lasers are fired into the plasma with a effective frequency of 60 Hz, and the light is Doppler shifted by Thomson scattering. Polychromators on the NSTX-U midplane collect the scattered photons at various radii/scattering angles, and the avalanche photodiode voltages are saved to an MDSplus tree for later analysis. IDL code is then used to determine plasma temperature, pressure, and density from the captured polychromator measurements via Selden formulas.[1] OMFIT, from the General Atomics Fusion Theory Team, is a rich data workflow package used on DIII-D, NSTX-U, and other experiments to rapidly investigate and draw conclusions from collated data sets and simulations. OMFIT can also be used as a data access source into other toolkits and fusion analysis software. This project, written in Python and taking advantage of late-generation Internet software technologies, uses OMFIT to rapidly find and visualize Thomson diagnostic plasma characteristics enabling scientists to gain a quick understanding of shot behavior and timeframes. [Preview Abstract] |
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JP10.00069: Measuring glow discharge polymerization coating rates with a quartz crystal monitor E.T. Ostrowski, M. Schoff, A. Greenwood, E. Castillo, N. Ravelo Glow discharge polymerization (GDP) is a well-established method for fabricating the thin-walled polymer shells of targets used in laser-driven inertial confinement fusion. The GDP coating rate is slow, maxing out at approximately 0.5 $\mu$m/hr, and varies in time and with changes in system parameters. A quartz crystal monitor (QCM) was installed into a GDP coating apparatus in order to measure the coating rate and thickness in situ by relating shifts in quartz oscillation frequency to changes in mass on the quartz crystal’s surface, namely the GDP coating. Further investigation of the quartz crystal surface, post-GDP treatment, revealed that coating thickness was also radially dependent. Subsequent modelling of the thickness and coating rate was performed. The QCM was able to measure and quantify the effects of various system parameters on the GDP coating rate such that optimal coating conditions could be suggested to minimize coating times. [Preview Abstract] |
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JP10.00070: Plasma disruption prediction using machine learning methods: DIII-D L. Lupin-Jimenez, E. Kolemen, D. Eldon, N. Eidietis Plasma disruption prediction is becoming more important with the development of larger tokamaks, due to the larger amount of thermal and magnetic energy that can be stored. By accurately predicting an impending disruption, the disruption’s impact can be mitigated or, better, prevented. Recent approaches to disruption prediction have been through implementation of machine learning methods, which characterize raw and processed diagnostic data to develop accurate prediction models. Using disruption trials from the DIII-D database, the effectiveness of different machine learning methods are characterized. Developed real time disruption prediction approaches are focused on tearing and locking modes. Machine learning methods used include random forests, multilayer perceptrons, and traditional regression analysis. The algorithms are trained with data within short time frames, and whether or not a disruption occurs within the time window after the end of the frame. Initial results from the machine learning algorithms will be presented. [Preview Abstract] |
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JP10.00071: Clustering Analysis of Fast-ion Driven Instabilities J. Gresl, W.W. Heidbrink, S. Haskey, B.D. Blackwell Beam ions often drive Alfv\'en eigenmodes and other instabilities unstable in DIII-D. Many of these modes have been unambigously identified but some frequently occurring features have been neglected. In this work, datamining analysis techniques [1] that successfully analyzed magnetics data from the H-1NF heliac are applied to arrays of magnetic and electron cyclotron emission (ECE) data from DIII-D. The techniques group instabilities with similar magnetic or ECE features into clusters. Once the clusters are found, a database of plasma parameters will facilitate mode identification.\par \vskip6pt \noindent [1] S.R. Haskey et al. , Comp. Phys. Comm. 185 (2014) 1169; B.D. Blackwell et al. J. Pl. Phys. Fus. Res. (2016) submitted. [Preview Abstract] |
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JP10.00072: Understanding distortions in the DIII-D tokamak magnetic field trim coils R.T. Paulsen, C. Paz-Soldan, E.J. Strait Trim coils were originally incorporated onto the DIII-D tokamak to reduce the error fields that arise from distortions in the preexisting coils that confine the plasma. However, as a result of numerous obstacles crowding DIII-D prior to their installation, the effective geometries of the trim coils were forced to stray from a nominal rectangular shape, causing the trim coils to induce error fields of their own apart from the ones they serve to combat. Since these secondary error fields have the potential to hamper plasma operation, it is imperative to discover to what extent the trim coil geometry is understood. This work seeks to investigate the observed magnetic field measurements for the energized trim coils in the absence of plasma, assess the distortions, and compare these calculations to the same quantities estimated for schematics of the as-built trim coil configurations. Furthermore, measurements taken with plasma with and without trim coils are analyzed by tools for extracting the optimal current for error field correction and compared to the predictions for the as-built system. [Preview Abstract] |
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JP10.00073: Enabling High Fidelity Measurements of Energy and Pitch Angle for Escaping Energetic Ions with a Fast Ion Loss Detector R. Chaban, D.C. Pace, G.R. Marcy, D. Taussig Energetic ion losses must be minimized in burning plasmas to maintain fusion power, and existing tokamaks provide access to energetic ion parameter regimes that are relevant to burning machines. A new Fast Ion Loss Detector (FILD) probe on the DIII-D tokamak has been optimized to resolve beam ion losses across a range of 30 - 90 keV in energy and $40^{\circ}$ to $80^{\circ}$ in pitch angle, thereby providing valuable measurements during many different experiments. The FILD is a magnetic spectrometer; once inserted into the tokamak, the magnetic field allows energetic ions to pass through a collimating aperture and strike a scintillator plate that is imaged by a wide view camera and narrow view photomultiplier tubes (PMTs). The design involves calculating scintillator strike patterns while varying probe geometry. Calculated scintillator patterns are then used to design an optical system that allows adjustment of the focus regions for the 1 MS/s resolved PMTs. A synthetic diagnostic will be used to determine the energy and pitch angle resolution that can be attained in DIII-D experiments. [Preview Abstract] |
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JP10.00074: Testing of a diamond Brewster angle waveguide window at DIII-D A. LeViness, J. Lohr, J. Anderson, M. Cengher, Y.A. Gorelov, C. Moeller, D. Ponce, A. Torrezan, L. Ives, M. Read To avoid reflections, gyrotrons operate with output windows having thickness of ${n\lambda/2}$, where $\lambda$ is the wavelength of the rf wave in the window and n is an integer. This limits the gyrotron output frequency to discrete values. Transmission of rf through a window at the Brewster angle, ${\sim67.2^{\circ}}$ in diamond, is insensitive to wavelength for rf waves polarized with the electric field out of the window plane. Use of a Brewster angle window therefore allows operation of a gyrotron at a near-continuum of frequencies, an advantage despite the cost of such a large window. Tests of a Brewster angle window were performed for waveguide with 31.75 mm diameter, designed for a frequency of 110 GHz, but with wide bandwidth. The tests included measurement of the rf loss in the window at relatively high power and the effect of the window on mode structure of an incident $HE_{1,1}$ beam. Low power tests were performed for a range of frequencies and polarizations. [Preview Abstract] |
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JP10.00075: Ray-tracing studies of fast waves in the lower hybrid range of frequencies A. Dittman, R.I. Pinsker Fast waves in the lower-hybrid range of frequencies, also referred to as 'whistlers' or 'helicons', will be used in the DIII-D tokamak for off-axis non-inductive current drive. Ray-tracing studies have shown\footnote{R. Prater, C.P. Moeller, R.I. Pinsker,\textit{et al.}, Nucl.~Fusion \textbf{54} (2014) 083024.} that the required off-axis deposition can be achieved in target plasmas that have been recently studied in DIII-D. We wish to characterize the sensitivity of the rf power deposition profile to details of the equilibrium, and are thereby motivated to re-examine the fundamentals of ray-tracing in this regime. We have studied ray-tracing in the vicinity of regular turning points (cut-offs) and mode-coupling points in simple geometries (slab, cylinder). Later phases of the work will use the GENRAY code to study the effect of strong magnetic shear in the outer region of the plasma on the shape of the ray trajectory in that region, and on wave accessibility to the core. The usual estimate of the accessibility limit on the parallel index of refraction of the wave ($n_\parallel$), based on a slab model, is inaccurate under these conditions, which could lead to improved antenna/wave coupling by utilizing a lower $n_\parallel$. [Preview Abstract] |
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JP10.00076: Particle Dynamics in the Magnet Region of the DIII-D Neutral Beam System C.A. Blackford, B.J. Crowley, J.M. Rauch, J.T. Scoville The Neutral Beam system on the DIII-D tokamak consists of eight ion sources on four beam lines using the Common Long Pulse Source (CLPS) developed at Berkeley in the 1980s. This poster presents the results of modeling efforts aimed to understand the anomalous power deposition in the bending magnet region of the neutral beam system at DIII-D. The code tracks individual particles in 3D electric and magnetic fields. In these fields, the particles intercept solid boundaries and deposit power on the magnet pole shields as well as various collimators, the ion dump, and the beam dump calorimeter. This code allows investigation of phenomena including the non-uniformity of the magnetic field, the space charge effects on the neutral beam, and deviant ion trajectories within the system. These phenomena are expected to contribute largely to the power deposition within the bending magnet region. Results of the analysis may lead to adjustments that could increase the efficiency of the neutral beam system at the DIII-D facility. [Preview Abstract] |
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JP10.00077: Seeding the m $=$ 0 instability in dense plasma focus (DPF) Z-pinches with a hollow anode Jason Liu, Jason Sears, Matt McMahon, Drew Higginson, Anthony Link, Andrea Schmidt The dense plasma focus (DPF) is a classic Z-pinch plasma device that has been long studied as a copious source of various types of radiation. The formation of the m $=$ 0 plasma instability during the compression phase is linked to the generation of high-energy charged particle beams, which, when operated in deuterium, lead to beam-target fusion reactions and the generation of neutron yield. Here we present a novel technique of seeding the m $=$ 0 instability by varying the anode's hollow inner diameter. As the plasma sheath moves along this hollow anode structure, a low density perturbation is formed and this seeds the instability. Dynamics of the low density perturbation and seeding of the m $=$ 0 instability are studied in detail with fully kinetic plasma simulations performed in the LSP particle-in-cell code on a 60 kA device. It is discovered in the simulations that the neutron yield of the DPF may be significantly improved and made more consistent by employing an anode geometry with an appropriate inner hollow diameter. [Preview Abstract] |
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JP10.00078: Investigation of Spheromak Plasma Cooling through Metallic Liner Spallation during Compression Keeton Ross, Alex Mossman, William Young, Russ Ivanov, Peter O'Shea, Stephen Howard Various magnetic-target fusion (MTF) reactor concepts involve a preliminary magnetic confinement stage, followed by a metallic liner implosion that compresses the plasma to fusion conditions. The process is repeated to produce a pulsed, net-gain energy system. General Fusion, Inc. is pursuing one scheme that involves the compression of spheromak plasmas inside a liner formed by a collapsing vortex of liquid Pb-Li. The compression is driven by focused acoustic waves launched by gas-driven piston impacts. Here we describe a project to exploring the effects of possible liner spallation during compression on the spheromaks temperature, lifetime, and stability. We employ a 1 J, 10 ns pulsed YAG laser at 532nm focused onto a thin film of Li or Al to inject a known quantity of metallic impurities into a spheromak plasma and then measure the response. Diagnostics including visible and ultraviolet spectrometers, ion Doppler, B-probes, and Thomson scattering are used for plasma characterization. We then plan to apply the trends measured under these controlled conditions to evaluate the role of wall impurities during `field shots', where spheromaks are compressed through a chemically driven implosion of an aluminum flux conserver. The hope is that with further study we could more accurately include the effect of wall impurities on the fusion yield of a reactor-scale MTF system. Experimental procedures and results are presented, along with their relation to other liner-driven, MTF schemes. -/a [Preview Abstract] |
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JP10.00079: Improving Robotic Assembly of Planar High Energy Density Targets D. Dudt, L. Carlson, N. Alexander, K. Boehm Increased quantities of planar assemblies for high energy density targets are needed with higher shot rates being implemented at facilities such as the National Ignition Facility and the Matter in Extreme Conditions station of the Linac Coherent Light Source. To meet this growing demand, robotics are used to reduce assembly time. This project studies how machine vision and force feedback systems can be used to improve the quantity and quality of planar target assemblies. Vision-guided robotics can identify and locate parts, reducing laborious manual loading of parts into precision pallets and associated teaching of locations. On-board automated inspection can measure part pickup offsets to correct part drop-off placement into target assemblies. Force feedback systems can detect pickup locations and apply consistent force to produce more uniform glue bond thickness, thus improving the performance of the targets. System designs and performance evaluations will be presented. [Preview Abstract] |
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JP10.00080: Hybrid particle-in-cell simulations of weakly collisional shock formation. Jacob Spisak, Julio Valenzuela, Joohwan Kim, Farhat Beg Recently, we studied shock formation by the head on collision of supersonic plasma jets using a wire configuration on the compact current driver GenASIS (200 kA in 150 ns). We used two wire materials: aluminum, where radiative cooling is not significant, and copper, where radiation is important to shock dynamics. In both cases, when the jets collide a conical structure develops in time and moves towards the cathode at a speed of 20km/s. Radiation effects are apparent in the copper case, as the shock is thinner than in the Aluminum case and when it starts moving a prominent bow shock develops. Furthermore, the estimated inter jet ion mean free path is larger than the shock width, indicating a magnetic field may help mediate the shock. To investigate the physics of weakly collisional shock formation, we perform two dimensional simulations of two merging, counterpropagating jets using the initial conditions from the experiment. Electrons are treated as a fluid and ions are treated as kinetic particles using the hybrid particle in cell code LSP. We explore how shock formation is affected by radiative cooling and the presence of an external magnetic field. We also carried out simulations where both ions and electrons were treated as fluids. [Preview Abstract] |
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JP10.00081: Enhancing the predictive capability of the modified Paschen law using Bayesian calibration Rennan Silva da Costa, Venkattraman Ayyaswamy Microscale gas breakdown is an important failure mechanism that needs to be mitigated for the successful long-term operation of microelectromechanical systems operating at low to moderate voltages. While the Paschen law governs traditional breakdown in macroscale gaps, several independent datasets have observed unusual breakdown at gap sizes less than 10 μm. It is now well-established that the driving mechanism for this deviation is field-induced electron emission thereby leading to what is referred to as the modified Paschen law. In spite of the existence of several models to predict breakdown in microgaps, the significant uncertainty in the field enhancement factor of a given electrode surface limits the predictive capability of these models. More recently, it has been hypothesized that there is a strong inverse correlation between the field enhancement factor and the electric field. In this context, the current work quantifies this correlation using a modified Paschen law in conjunction with several experimental datasets by performing a rigorous calibration exercise using sophisticated statistical methods. Specifically, a Bayesian approach was used, and the outcomes of this effort are anticipated to significantly add to the predictive capability of the modified Paschen law. [Preview Abstract] |
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JP10.00082: Measurement of the 6He Decay Produced by the 9Be(n,$\alpha )$6He Reaction Katelyn Cook, Micah Coats, Mark Yuly, Stephen Padalino, Craig Sangster, Sean Regan The OMEGA laser at LLE is routinely used to implode gas-filled capsules to study light ion fusion reaction rates of interest to stellar nucleosynthesis. As a first step toward a possible measurement of the $^{\mathrm{3}}$H(t,$\gamma )^{\mathrm{6}}$He radiative capture reaction, a detector system capable of measuring the 801 ms half-life of $^{\mathrm{6}}$He has been developed and is being tested using $^{\mathrm{6}}$He nuclei produced via the $^{\mathrm{9}}$Be(n,$\alpha )^{\mathrm{6}}$He reaction. Deuterons from the SUNY Geneseo tandem Pelletron produce neutrons in a thick deuterated polyethylene target via the $^{\mathrm{2}}$H(d,n)$^{\mathrm{3}}$He reaction. These neutrons are allowed to strike a beryllium target placed in front of a silicon $\Delta $E-E detector telescope, which is used to identify the $\beta $ particles from $^{\mathrm{6}}$He decay. Following an approximately five second long activation period, the beryllium sample is immediately counted for about five seconds. The pulse heights for each detector and the timestamp are recorded using a specially configured femtoDAQ acquision system and used to measure the decay curve. Funded in part by a grant from the DOE through the Laboratory for Laser Energetics. [Preview Abstract] |
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JP10.00083: Calculation of the safety factor and homoclinic tangles of the separatrix for the Symmetric Quartic Map Danielle Baldwin, Bria Andrews, Halima Ali, Alkesh Punjabi The equilibrium generating function for the Symmetric Quartic Map (SQM) in natural canonical coordinates is constructed [M. Jones et al, Phys. Plasmas 16, 042511 (2009), A. Punjabi, Nucl. Fus. 49, 115020 (2009)]. The coefficients in the generating function are chosen to control the safety factor profile and to set the height and width of the equilibrium separatrix to be same as in the Simple Map [A. Punjabi, A. Verma, and A. Boozer, Phys. Rev. Lett. 69, 3322 (1992)]. The equilibrium separatrix of the SQM is advanced forward and backward in canonical time using the SQM [4]. When the forward and backward advanced separatrix manifolds meet in a fixed poloidal plane, they intersect and form homoclinic tangles to preserve the symplectic invariant [A. Punjabi and A. Boozer, Phys. Lett. A 378, 2410 (2014)]. The map parameter of the SQM is used to include the effects of magnetic asymmetries. The safety factor profile and the homoclinic tangles of the separatrix of the SQM for different values of the map parameter will be presented. The separatrix of the simple map is open and unbounded; while the separatrix of the SQM is closed and compact. The purpose is to study what role the topology of the separatrix plays in the homoclinic tangle in single-null divertor tokamaks. This work is supported by grants DE-FG02-01ER54624, DE-FG02-04ER54793, and DE-FG02-07ER54937. [Preview Abstract] |
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JP10.00084: SPACE PLASMAS |
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JP10.00085: Using Field-Particle Correlations to Diagnose the Collisionless Damping of Plasma Turbulence Gregory Howes, Kristropher Klein Plasma turbulence occurs ubiquitously throughout the heliosphere, yet our understanding of how turbulence governs energy transport and plasma heating remains incomplete, constituting a grand challenge problem in heliophysics. In weakly collisional heliospheric plasmas, such as the solar corona and solar wind, damping of the turbulent fluctuations occurs due to collisionless interactions between the electromagnetic fields and the individual plasma particles. A particular challenge in diagnosing this energy transfer is that spacecraft measurements are typically limited to a single point in space. Here we present an innovative field-particle correlation technique that can be used with single-point measurements to estimate the energization of the plasma particles due to the damping of the electromagnetic fields, providing vital new information about this how energy transfer is distributed as a function of particle velocity. This technique has the promise to transform our ability to diagnose the kinetic plasma physical mechanisms responsible for not only the damping of turbulence, but also the energy conversion in both collisionless magnetic reconnection and particle acceleration. [Preview Abstract] |
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JP10.00086: High-resolution 2D3V simulations of forced hybrid-kinetic turbulence Silvio Sergio Cerri, Francesco Califano, Francois Rincon, Daniel Told, Frank Jenko, Francesco Pegoraro The understanding of the kinetic processes at play in plasma turbulence is a frontier problem in plasma physics and among the topics currently of most interest in space plasma research. Here we investigate the properties of turbulence from the end of the magnetohydrodynamic (MHD) cascade to scales well below the ion gyroradius (i.e., the so-called ``dissipation'' or ``dispersion'' range) by means of unprecedented high-resolution simulations of forced hybrid-kinetic turbulence in a 2D3V phase-space (two real-space and three velocity-space dimensions). Different values of the plasma beta parameter typical of the solar wind (SW) are investigated. Several aspects of turbulence at small-scales emerging from the simulations are presented and discussed. Even within the limitations of the hybrid approach in 2D3V, a reasonable agreement with SW observations and with theory is found. Finally, we identify possible implications and questions related to SW turbulence which arise from this study. [Preview Abstract] |
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JP10.00087: Simulations and Transport Models for Imbalanced Magnetohydrodynamic Turbulence Chung-Sang Ng, T. Dennis We present results from a series of three-dimensional simulations of magnetohydrodynamic (MHD) turbulence based on reduced MHD equations. Alfven waves are launched from both ends of a long tube along the background uniform magnetic field so that turbulence develops due to collision between counter propagating Alfven waves in the interior region. Waves are launched randomly with specified correlation time $T_c$ such that the length of the tube, L, is greater than (but of the same order of) $V_A*T_c$ such that turbulence can fill most of the tube. While waves at both ends are launched with equal power, turbulence generated is imbalanced in general, with normalized cross-helicity gets close to -1 at one end and 1 at the other end. This simulation setup allows easier comparison of turbulence properties with one-dimensional turbulence transport models, which have been applied rather successfully in modeling solar wind turbulence. However, direct comparison of such models with full simulations of solar wind turbulence is difficult due to much higher level of complexity involved. We will present our latest simulations at different resolutions with decreasing dissipation (resistivity and viscosity) levels and compare with model outputs from turbulence transport models. [Preview Abstract] |
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JP10.00088: An Equilibrium MHD Model of Solar Rotation, Flow, and Magnetism: The Tachocline as a Trans-Alfvénic Feature Lee Gunderson, Amitava Bhattacharjee While helioseismology has revealed the internal density and rotation profile of the sun, knowledge of the magnetic fields and meridional circulation is confined much closer to the surface. We propose analyzing equilibrium profiles of axisymmetric ideal MHD flows as a way to extrapolate inward from this surface data. We present analytic and numerical solutions of the generalized Grad-Shafranov equation in the solar regime. In particular, we analyze behavior near the Alfv\'enic surface ($\rho v_p^2/B_p^2 = 1$), and propose that its proximity to the tachocline is not coincidental. In addition, profiles with different surface magnetic fields can offer insight about effects of the solar cycle, such as torsional oscillations and active latitudes. Future work includes: analyzing stability of the solutions, including transport to obtain a Grad-Hogan simulation of the solar cycle, and applying to other stars or planetary cores. [Preview Abstract] |
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JP10.00089: A Network of Small Spacecraft for Multipoint Measurement of Auroral Plasma T. Maximillian Roberts, Kristina Lynch, Robert Clayton, Donald Hampton Measurement of ionospheric plasma is often performed by a single in-situ device, or remotely using cameras and radar. This constrains determination of small scale variation in plasma structure to somewhat restrictive assumptions. We have developed and tested a local, multipoint measurement system composed of a network of small spacecraft which are ejected from a main payload carried by sounding rocket. The low-resource, spin-stabilized projectiles radio measurements to the main payload for transmission to ground. Measurements from an onboard LED array and IMU are used to determine the separation of the devices from the main payload and orientation relative to the geomagnetic field. The primary measurements are made by two orthogonal retarding potential analyzers on each spacecraft, allowing for determination of local ion parameters. A test flight in October 2015 demonstrated the successful application of this system, as well as revealing several important design issues. This work is in preparation for the February 2017 ISINGLASS sounding rocket mission to study the gradient scale lengths in auroral plasma, involving the deployment of two of these spacecraft networks. [Preview Abstract] |
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JP10.00090: The Colorado Solar Wind Experiment Tobin Munsat, Jia Han, Mihaly Horanyi, Zach Ulibarri, Xu Wang, LiHsia Yeo The Colorado Solar Wind Experiment (CSWE) is a new device developed at the Institute for Modeling Plasma, Atmospheres, and Cosmic Dust (IMPACT) at the University of Colorado. This large ion source is for studies of the interaction of solar wind plasma with planetary surfaces and cosmic dust, and for the investigation of plasma wake physics. With a plasma beam diameter of 12 cm at the source, ion energies of up to 1 keV, and ion flows of up to 1 mA/cm2, a large cross-section Kaufman Ion Source is used to create steady state plasma flow to model the solar wind in an experimental vacuum chamber. Chamber pressure can be reduced to 3e-5 Torr under operating conditions to suppress ion-neutral collisions and create a uniform ion velocity distribution. Diagnostic instruments such as a double Langmuir probe and an ion energy analyzer are mounted on a two-dimensional translation stage that allow the beam to be characterized throughout the chamber. Early experiments include the measurement of dust grain charging from the interaction with flowing plasma, and measurements of the plasma sheath created by the interaction of the flowing plasma impinging on a surface with a dipole magnetic field. This poster will describe the facility and the scientific results obtained to date. [Preview Abstract] |
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JP10.00091: Progress Towards a Laboratory Test of Alfv\'enic Electron Acceleration J. W. R. Schroeder, F. Skiff, G. G. Howes, C. A. Kletzing, T. A. Carter, S. Vincena, S. Dorfman Alfv\'en waves are thought to be a key mechanism for accelerating auroral electrons. Due to inherent limitations of single point measurements, \emph{in situ} data has been unable to demonstrate a causal relationship between Alfv\'en waves and accelerated electrons. Electron acceleration occurs in the inner magnetosphere where the Alfv\'en speed is greater than the electron thermal speed. In these conditions, Alfv\'en waves can have an electric field aligned with the background magnetic field $\mathbf{B_0}$ if the scale of wave structure across $\mathbf{B_0}$ is comparable to the electron skin depth. In the Large Plasma Device (LaPD), Alfv\'en waves are launched in conditions relevant to the inner magnetosphere. The reduced parallel electron distribution function is measured using a whistler-mode wave absorption diagnostic. The linear electron response has been measured as oscillations of the electron distribution function at the Alfv\'en wave frequency. These measurements agree with linear theory. Current efforts focus on measuring the nonlinear acceleration of electrons that is relevant to auroral generation. We report on recent progress including experiments with a new higher-power Alfv\'en wave antenna with the goal of measuring nonlinear electron acceleration. [Preview Abstract] |
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JP10.00092: Explaining Signatures of Auroral Arcs based on the Stationary Inertial Alfven Wave SH Nogami, ME Koepke, DJ Knudsen, DM Gillies, E Donovan, S Vincena Optical emission data from the THEMIS array of All Sky Imagers are analyzed to determine the lifetime of an auroral arc (i.e., the elapsed time during which an arc is visible). Lifetime is an important temporal signature related to the arc generation mechanism, by which arcs can be distinguished. An arc with a lifetime greater than ten minutes is consistent with arc generation by Stationary Inertial Alfven Wave (StIAW) which supports a steady-state wave electric field component parallel to a background magnetic field. An StIAW is a non-fluctuating, non-travelling, spatially periodic pattern of perturbed ion density that is static in the laboratory frame. StIAWs are the predicted result of the interaction between a magnetic-field-aligned electron current and plasma convection perpendicular to a background magnetic field [1,2]. Electrostatic probes measure the fixed pattern of perturbed ion density in LAPD-U. Electron acceleration due to StIAWs is being investigated as a mechanism for the formation and support of long-lived auroral arcs. Preliminary evidence of electron acceleration from laboratory experiment is reported. [1] \textit{J. Geophys. Res.}, 101, 10761 (1996). [2] \textit{Nonlin. Proc. Geophys.}, 15, 957 (2008). [Preview Abstract] |
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JP10.00093: New Kind of Magnetic Reconnection in Neutral Sheet Configurations Alex Fletcher, Bruno Coppi Neutral Sheet configurations are relatively simple models of the plasma and field configuration found in space physics that lend themselves to investigate the onset of relevant reconnection processes. In weakly collisional regimes these are shown to be intrinsically different from those occurring in plasma current sheets where the magnetic field is sheared but does not vanish. Considering an inhomogenous electron temperature profile with finite curvature at the center of the sheet, and anisotropic thermal conductivities one of the two kinds of mode that can produce magnetic reconnection is localized over a layer that remains significant when the macroscopic scale distances involved are very large as is the case in space and astrophysics. This mode lends itself to produce high-energy particle populations through a realistic combination of mode-particle resonances. [Preview Abstract] |
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JP10.00094: The role of Kelvin-Helmholtz instability in losses of magnetospheric energetic particles through the magnetopause: High-resolution MHD-test-particle simulations. Aleksandr Ukhorskiy, Kareem Sorathia, Viacheslav Merkin The Earth's magnetopause is a sharp boundary separating the geomagnetic field from interplanetary field and plasma. During increased solar wind driving and geomagnetic activity, energetic particles produced inside the magnetosphere can gain access to the magnetopause and be permanently lost from the system by crossing the boundary into the region of open interplanetary magnetic field lines. The efficiency of the loss process is controlled by the details of particle interaction with the magnetopause boundary. Characterizing this interaction is important for understanding storm-time variability of magnetospheric energetic particle populations including ring current and radiation belts. The magnetopause structure can be very dynamic due, in particular, to the Kelvin-Helmholtz instability (KHI) produced by the velocity shear at the magnetospheric boundary. The goal of this study is to investigate the role of KHI in energetic particle loss through the magnetopause. For the analysis we use large-scale test-particle simulations in the electromagnetic fields computed with a global magnetospheric MHD model with resolution sufficiently high to resolve KHI. We compute the spatial distributions and rates of the magnetopause losses of energetic electrons, hydrogen and oxygen ions, and discuss our results in the context of recent measurements of magnetopause losses from the Magnetospheric Multiscale (MMS) mission. [Preview Abstract] |
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JP10.00095: The observed and simulated saturation characteristics of whistler-mode chorus waves Xin An, Chao Yue, Jacob Bortnik, Viktor Decyk, Wen Li, Richard Thorne The evolution of the whistler anisotropy instability relevant to whistler-mode chorus waves in the Earth's inner magnetosphere is studied using kinetic simulations and is compared with satellite observations. The electron distribution is constrained by the whistler anisotropy instability to a marginal stability state and presents an upper bound of electron anisotropy, which agrees remarkably well with satellite observations. The electron beta $\beta_{\parallel e}$ separates whistler waves into two groups: (i) quasi-parallel whistler waves for $\beta_{\parallel e} \gtrsim 0.02$ and (ii) oblique whistler waves close to the resonance cone for $\beta_{\parallel e} \lesssim 0.02$. Landau damping is important in the saturation and relaxation stage of the oblique whistler wave growth. The magnetic amplitude of whistler waves roughly scales with the electron beta $\beta_{\parallel e}$, shown in both simulations and satellite observations. These results suggest the critical role of electron beta $\beta_{\parallel e}$ in determining the whistler wave properties in the inner magnetosphere. [Preview Abstract] |
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JP10.00096: Customized finite difference Maxwell solver for elimination of numerical Cherenkov instability in EM-PIC code Peicheng Yu, Fei Li, Thamine Dalichaouch, Frederico Fiuza, Viktor Decyk, Asher Davidson, Adam Tableman, Weiming An, Frank Tsung, Ricardo Fonseca, Wei Lu, Jorge Vieira, Luis Silva, Warren Mori we present a finite-difference-time-domain (FDTD) Maxwell solver for the particle-in-cell (PIC) algorithm, which is customized to effectively eliminate the numerical Cerenkov instability (NCI) which arises when a plasma (neutral or non-neutral) relativistically drifts on a grid when using the PIC algorithm. We control the EM dispersion curve in the direction of the plasma drift of a FDTD Maxwell solver by using a customized higher order finite difference operator for the spatial derivative along the direction of the drift ($\hat 1$ direction). We show that this eliminates the main NCI modes with moderate $\vert k_1 \vert,$ while keeps additional main NCI modes well outside the range of physical interest with higher $\vert k_1 \vert.$ These main NCI modes can be easily filtered out along with first spatial aliasing NCI modes which are also at the edge of the fundamental Brillouin zone. The customized solver has the possible advantage of improved parallel scalability because it can be easily partitioned along $\hat 1$ which typically has many more cells than other directions for the problems of interest. [Preview Abstract] |
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JP10.00097: Performance of VPIC on Trinity W. D. Nystrom, B. Bergen, R. F. Bird, K. J. Bowers, W. S. Daughton, F. Guo, H. Li, H. A. Nam, X. Pang, W. N. Rust III, J. Wohlbier, L. Yin, B. J. Albright Trinity is a new major DOE computing resource which is going through final acceptance testing at Los Alamos National Laboratory. Trinity has several new and unique architectural features including two compute partitions, one with dual socket Intel Haswell Xeon compute nodes and one with Intel Knights Landing (KNL) Xeon Phi compute nodes. Additional unique features include use of on package high bandwidth memory (HBM) for the KNL nodes, the ability to configure the KNL nodes with respect to HBM model and on die network topology in a variety of operational modes at run time, and use of solid state storage via burst buffer technology to reduce time required to perform I/O. An effort is in progress to port and optimize VPIC to Trinity and evaluate its performance. Because VPIC was recently released as Open Source, it is being used as part of acceptance testing for Trinity and is participating in the Trinity Open Science Program which has resulted in excellent collaboration activities with both Cray and Intel. Results of this work will be presented on performance of VPIC on both Haswell and KNL partitions for both single node runs and runs at scale. [Preview Abstract] |
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JP10.00098: MFE: DIII-D TOKAMAK |
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JP10.00099: A Fully Noninductive, ELM-Suppressed Scenario for ITER C.C. Petty, T.W. Petrie, R. Nazikian, F. Turco, C. Lasnier An attractive regime with beta, collisionality and plasma shape relevant to the ITER steady-state mission has been attained in DIII-D using the hybrid scenario, including complete ELM suppression using resonant magnetic perturbation (RMP) coils. Fully noninductive hybrids with simultaneous high beta ($\beta_N\leq3.1)$ and high confinement ($H_{98y2}\leq1.4)$ have achieved zero surface loop voltage for up to two current relaxation times using efficient central current drive from ECCD and NBCD. This steady-state regime has been successfully integrated with ELM suppression by applying an odd parity n=3 RMP, which has only a minor impact on the pedestal pressure $(\sim{{15}\%})$ and $H_{98y2}$ $(\sim{{10}\%})$ In radiating divertor experiments in hybrids, the combination of Argon seeding and strong Deuterium puffing more than doubles the plasma radiative power, up to 55$\%$ of the input power, with less than 10$\%$ increase in $Z_{eff}$. IR camera measurements find that the peak heat flux in the upper, outer divertor falls by a factor of 2 (from 4.6 to 2.3 $MW/m^2$). [Preview Abstract] |
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JP10.00100: Active MHD Spectroscopy measurements in the low torque ITER Baseline Scenario in DIII-D* F. Turco, J.M. Hanson, G.A. Navratil, C. Paz-Soldan, A. Turnbull, W. Solomon The first measurements of active MHD spectroscopy in ITER Baseline Scenario plasmas $({q95=3, betaN=1.9, T=0-1 nm)}$ in DIII-D show the approach to an instability at low torque, where most of the discharges are terminated by a disrupting ${m=2/n=1}$ tearing instability. The amplitude of the response increases rapidly as rotation slows, and the phase measurements show an abrupt change by ${20-25}^{\circ}$ in the same rotation range, which has been shown to be typical of crossing an ideal stability limit [1]. This technique could represent a potential warning system for impending disruptions. Modelling with the MARS-K code [2] shows that the inclusion of drift kinetic effects and collisionality is crucial to obtain quantitative agreement in the amplitude results at moderate to high rotation, while resistivity is necessary to observe a partial increase in the plasma response at low rotation. However the code does not quantitatively predict the rise in amplitude and change in phase at lowest rotation – investigation of the potential causes of this discrepancy will be described.\\ \\ $[1]$ M.J. Lanctot, Phys. Plasmas 17, 0307001 (2010); [2] Y. Liu, Phys. Plasmas 15, 092505 (2008) [Preview Abstract] |
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JP10.00101: The Effect of Electron Cyclotron Heating on Multi-Scale Fluctuations in ITER Baseline Scenario Discharges on DIII-D A. Maronini, J.C. Rost, M. Porkolab, E.M. Davis, R.I. Pinsker, K.H. Burrell, G.M. Staebler, B.A. Grierson Experiments on DIII-D simulating the ITER Baseline Scenario show that torque-free pure electron heating (ECH) modifies profiles and affects density fluctuations at electron and at ion scales in different ways. The Phase Contrast Imaging diagnostic is used to measure the time evolution of density fluctuations going from mixed beam/ECH to pure beam heating at fixed $\beta_N$. The intensity of fluctuations at scales between 2 and 5 cm$^{-1}$ increases promptly after turning off ECH; at larger scales, in contrast, it decreases only after other equilibrium quantities have evolved to a new stationary state. Non-linear gyro-kinetic simulations suggest that the former response is due to ETG modes that also generate a prompt inward particle pinch; the latter is consistent with the dominant ITG modes being weakened by the increased flow shear in the new state. Such fluctuations in ITER might affect fusion performance via modifications to steady-state profiles. [Preview Abstract] |
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JP10.00102: Parameter Space for Self-Consistent High $\beta_N$, High $\ell_i$ Discharges in Steady-State J.R. Ferron, T.C. Luce, C.T. Holcomb, J.M. Park A tokamak scenario with a peaked current profile ($\ell_i$>0.9), is a promising candidate for a high $\beta_N$ and Q power plant because of the increased stability limits and confinement. Model equilibria have been used to show that the present DIII-D experiments in this range of $\ell_i$, with $\beta_N$=5 and evolving current density (J) profile, can be extended to 100$\%$ noninductively driven current with stationary, self-consistent J and pressure (P) profiles. $\beta_N$=4, $q_{95}$<6.5, bootstrap current fraction $f_{BS}$<0.46 is predicted stable to ideal low-n modes without requirement for a conducting wall, while $\beta_N$=5, $f_{BS}$<0.6 is predicted stable when the effect of the vacuum vessel is included. These results reflect the trade-off between high $f_{BS}$ and high $\beta_N$ that is required because, as $\beta_N$ is increased, bootstrap current in the plasma outer half, from the H-mode pedestal and the broad pressure profile, reduces $\ell_i$ and the ideal stability limit. Full simulations using the TGLF transport model and the DIII-D current drive/heating sources yield similar parameters. [Preview Abstract] |
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JP10.00103: Stability of Elevated-$q_{min}$ Steady-State Scenarios on DIII-D C.T. Holcomb, B. Victor, J.R. Ferron, T.C. Luce, E. Schuster Limits to high performance steady-state operation with $q_{min}$$>$1.4 and ${\beta_N\leq3.5}$ are identified and explained. Various $\beta_N$ and q-profile histories were produced while testing feedback control of these profiles. Ten pulses had no core MHD at $\beta_N$=3.4-3.5, with $q_{min}$=1.4-1.8, and $q_{95}$=5-5.8. These have predicted ideal-wall kink $\beta_N$ limits between 4 and 5. One pulse had an n=1 tearing mode (TM) at $\beta_N$=3.5 with no clear trigger. Five pulses developed n=1 TMs when $\beta_N$=2, $q_{min}$=2, and $q_{95}$=4.7. Stability calculations for these latter cases will be shown. In seven other shots, additional NBI power from sources with more normal injection was used, and these had off-axis fishbone (OAFB) modes at $\beta_N$=3.5. These sources produce more large-radius trapped ions whose precession can drive OAFB. Preliminary analysis suggests a threshold power or voltage exists. In some cases OAFB appear to trigger n=1 TMs. These studies seek to clarify the operational limits of a steady-state scenario for next step devices. [Preview Abstract] |
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JP10.00104: Non-inductive Hybrid Scenario—Transport and Turbulence at Reduced Plasma Torque K.E. Thome, C.C. Petty, D.C. Pace, F. Turco, T.L. Rhodes As the neutral beam injection (NBI) torque is lowered in steady-state hybrid plasmas via counter-beam injection, increased turbulence and thermal transport is observed, particularly in the ion channel. These discharges require $\textit{P}_{co-NBI}{=11}$ MW and $\textit{P}_{ECH}{=3}$ MW to achieve zero surface loop voltage. As the beam torque is reduced from ${\sim}{8.5}$ N-m to ${\sim}{4}$ N-m with $\beta_{N}\sim3$ and $\textit{q}_{95}\sim6$, the global confinement decreases from $\textit{H}_{98y,2}$ of ${\sim1.5}$ to ${\sim1.2}$. Local transport analysis using TRANSP shows that the lower torque discharges have increased ion thermal diffusivity across the whole profile and increased electron thermal diffusivity localized to the $\rho{=0.7}$ region. Similarly, Doppler Backscattering shows increased density fluctuations at intermediate wavenumbers at the lower torque. However, fast-ion transport caused by off-axis fishbones favorably decreases from $\sim0.7{m^2{/s}}$ to ${\sim}0.1{m^2{/s}}$ as the torque is lowered, partially offsetting the thermal transport reduction. These measured changes in turbulence and transport are being compared to plasma simulations using TGLF/GYRO to better predict the confinement of future steady-state hybrids that will be primarily RF-heated. [Preview Abstract] |
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JP10.00105: Dependency of Tearing Mode Stability on Current and Pressure Profiles in DIII-D Hybrid Discharges K. Kim, J.M. Park, M. Murakami, R.J. La Haye, Y-S. Na Understanding the physics of the onset and evolution of tearing modes (TMs) in tokamak plasmas is important for high-$\beta$ steady-state operation. Based on DIII-D steady-state hybrid experiments with accurate equilibrium reconstruction and well-measured plasma profiles, the 2/1 tearing mode can be more stable with increasing local current and pressure gradient at rational surface and with lower pressure peaking and plasma inductance. The tearing stability index $\Delta$', estimated by the Rutherford equation with experimental mode growth rate was validated against $\Delta$' calculated by linear eigenvalue solver (PEST3); preliminary comprehensive MHD modeling by NIMROD reproduced the TM onset reasonably well. We present a novel integrated modeling for the purpose of predicting TM onset in experiment by combining a model equilibrium reconstruction using IPS/FASTRAN, linear stability $\Delta$' calculation using PEST3, and fitting formula for critical $\Delta$' from NIMROD. [Preview Abstract] |
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JP10.00106: Development of high poloidal beta, steady-state scenario with ITER-like W divertor on EAST A.M. Garofalo, M. Lanctot, X.Z. Gong, S. Ding, G. Li, H. Liu, B. Lyu, J. Qian, P.T. Bonoli, S. Shiraiwa, C. Holcomb, J. McClenaghan Experiments on EAST have started to adapt the fully-noninductive high poloidal beta scenario developed on DIII-D, in order to demonstrate steady state tokamak operation at high performance on metal walls. Unlike on DIII-D, where the creation of a broad current profile requires early heating at low density, on EAST a broad current profile can be obtained simply by increasing the electron density, when most of the current drive is provided by lower hybrid wave. Systematic scans yield lower internal inductance with higher density. The hypothesis is that the LHCD profile becomes more off-axis with higher density. With the newly commissioned POINT (polarimeter-interferometer) diagnostic for q-profile measurements, these experiments enable strict tests of LHCD deposition models. [Preview Abstract] |
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JP10.00107: Validation of coupled core-edge pedestal-SOL modeling against DIII-D high beta discharges J.M. Park, D. Green, D. Batchelor, W. Elwasif, P.B. Snyder, O. Meneghini, J. Candy, K. Kim A new core-edge pedestal-SOL modeling has been validated against the DIII-D experiments by integrating three independent, compound workflows of FASTRAN (1D core), EPED (edge pedestal), and C2 (2D SOL) within the Integrated Plasma Simulator (IPS) framework. The FASTRAN workflow computes all transport channels including the density, temperature, rotation, and plasma current, self-consistently with an EPED1 edge pedestal, MHD equilibrium, external heating and current drives. The particle and energy fluxes are matched at the separatrix between the FASTRAN-EPED and C2 workflows in an iterative steady-state solution procedure to determine the density and temperature at the separatrix, which is used to provide improved EPED1 input and to efficiently close the strong dependency loop among the regions. The result reproduces the experimental profiles from the magnetic axis to divertor/wall for the DIII-D high $\beta$ discharges, guiding an optimum core-edge solution for the $\beta_N>4$ steady-state operation. [Preview Abstract] |
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JP10.00108: AE activity during transient beta drops in high poloidal beta discharges J. Huang, X.Z. Gong, Q.L. Ren, S.Y. Ding, J.P. Qian, C.K. Pan, G.Q. Li, W.W. Heidbrink, A.M. Garofalo, J. McClenaghan Enhanced AE activity has been observed during transient beta drops in high poloidal beta DIII-D discharges with internal transport barriers (ITBs). These drops in beta are believed to be caused by n=1 external kink modes. In some discharges, beta recovers within $\sim$200 ms but, in others, beta stays suppressed. A typical discharge has $\beta_P$ $\sim$3, $q_{min}\sim$ 3, and $q_{95}$ $\sim$ 12. The drop in beta affects both fast ions and thermal particles, and a drop is also observed in the density and rotation. The enhanced AE activity follows the instability that causes the beta drop, is largest at the lowest beta, and subsides as beta recovers. MHD stability analysis is planned. A database study of the plasma conditions associated with the collapse will be also presented. [Preview Abstract] |
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JP10.00109: Turbulence and sheared flow structure behind the isotopic and q95 dependencies of the L-H power threshold on DIII-D Z. Yan, G.R. McKee, P. Gohil, C. Petty, B. Grierson, D. Eldon, L. Schmitz, T. Rhodes Measurements of long wavelength density fluctuation characteristics in the edge of both Deuterium (D) and Hydrogen (H) plasmas across the L-H transition on DIII-D demonstrate the existence of dual frequency counter-propagating modes, which are strongly correlated with a reduced L-H power threshold ($P_{LH})$. E$\times$B shear near r/a$\sim$0.95-1.0 is larger in D than in H plasmas at low density, and the dual mode is only observed in D plasmas. Such a dual mode is also observed in a q95 scan of the L-H transition in D plasmas when the $P_{LH}$ is lower, where $P_{LH}$ is found to increase with plasma current but with complex density dependence: the largest increase of $P_{LH}$ is seen at $n_e\sim3.2e19$ $m^{-3}$. The complex behaviors of the turbulence characteristics (amplitude, decorrelation rate, etc.) and dual frequency modes interactions all together will impact the flow shear generation, the transition process and the power threshold scaling. [Preview Abstract] |
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JP10.00110: Towards a Physics-Based L-H Transition Model L. Schmitz, T.L. Rhodes, T. Neiser, L. Bardoczi, F. Jenko, L. Zeng, P. Gohil, C. Chrystal, B.A. Grierson, D. Eldon, Z. Yan, G.R. McKee, J. Boedo L-mode turbulence properties, collisionality, and ion transport fluxes across the separatrix are shown to determine the pre-transition ion poloidal and diamagnetic L-mode edge flow and the shear flow amplification triggering the L-H transition. L-mode ion thermal fluxes increase with density above the power threshold minimum, and are higher in hydrogen than in deuterium plasmas. The long-range toroidal ExB flow correlation at the L-H transition trigger time is observed to peak at intermediate plasma density around the L-H power threshold minimum, and is higher in D-plasmas in comparison to H-plasmas, indicating a possible link between trigger physics and power threshold. The turbulence-driven poloidal ion flow is found decisive for initial turbulence suppression, with a Reynolds stress gradient sufficiently large to account for the measured poloidal flow acceleration in the plateau collisionality. [Preview Abstract] |
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JP10.00111: Dynamic Turbulence Evolution during current ramp in ITER-like plasmas on DIII-D G.R. McKee, Z. Yan, C. Holland, R. Bravenec, T. Luce Low-wavenumber density fluctuations exhibit rapidly changing characteristics during the current ramp-up of ITER-like discharges that reflect a complex interaction between electron transport, safety factor (q), and n$_e$ and T$_e$ profiles. These measurements and analysis may help explain discrepancies between transport models and measurements during ramp-up. Measurements of the 2D fluctuation properties are obtained across the outer half-radius with Beam Emission Spectroscopy. Density fluctuations at rho=0.55 exhibit fluctuations that decrease in amplitude with time. Transient windows of suppressed fluctuations are observed during ramp-up, which correspond to low-order-rational q-surfaces that are associated with localized improved transport. At rho=0.82, a large amplitude burst of low-frequency turbulence occurs early in the current ramp. The amplitude profile of low-k fluctuations exhibits a strong reduction in turbulence with reduced q$_{95}$; thermal energy confinement likewise increases with decreasing q$_{95}$. [Preview Abstract] |
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JP10.00112: First experiments with negative triangularity shape in DIII-D[1] M.E. Austin, A. Marinoni, M.L. Walker, M.W. Brookman, J.S. deGrassie, A.W. Hyatt, C.C. Petty, T.L. Rhodes, C. Sung For the first time on DIII‑D, discharges with a negative triangularity shape ${(\delta = -0.4)}$ were created to investigate the effects of this shape on transport and turbulence. Significant shape control development was required with unconventional patch panel configurations and a new startup scenario to successfully establish the discharge. These ‘reverse D’ discharges were ${L-mode}$, inner-wall limited with 1 MA current, 3.8 MW NBI, and 2.7 MW ECH. $H_{98,y2}$ factors up to 0.85 and $\beta_N$ values up to 1.7 were attained in ELM-free stationary discharges. The confinement behavior mimics Alcator scaling[2], with confinement increasing with density. Other interesting features of the experiment were a higher than typical intrinsic $co-\textit{I}_p$ edge rotation and an increase in density with ECH power. This behavior contrasts with the ECH-induced drop in rotation and density pump-out effects observed in standard ${\delta\hspace{1.5 mm}\textgreater\hspace{1.5 mm}0}$ ECH-dominated DIII-D discharges. A full set of turbulence data was obtained over low, intermediate, and high $\textit{k}$ ranges. $^1$Work supported by USDOE - DE-FG02-97ER54415 and DE-FC02-04ER54698. $^2$ Gondhalekar, A. et al, Proc. 7th IAEA Int’l Conf, Innsbruck, 1978, Vol 1, 199. IAEA, Vienna (1979). [Preview Abstract] |
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JP10.00113: ABSTRACT WITHDRAWN |
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JP10.00114: Improvements, upgrades, and plans for Thomson scattering on DIII-D T.N. Carlstrom, D. Du, F. Glass, C. Liu, M. Watkins, A.G. McLean The Thomson scattering diagnostic on DIII-D consists of 3 beam lines that probe vertically, horizontally, and in the divertor region of the tokamak, with 54 spatial locations, edge spatial resolution down to 5 mm, and 10 Nd:YAG lasers. In its 25-year history, the collection lens optics and interference filters degraded and have been replaced, restoring previous performance. In addition, improved calibrations and detector temperature control (+/- 0.1 C) have reduced systematic errors. Cross calibration with the CO2 interferometer and ECE cut-off have improved the density calibration. Improvements to the beam line and lasers have increased the laser energy delivered to the scattering volume in the plasma. Future plans include moving the divertor system to measure regions of high triangularity using in-vessel mirrors to redirect the laser beam; adding a wide angle lens to the horizontal system to view the entire plasma radius near the plasma mid plane; and reversing the direction of the laser beam on the horizontal system to reduce the scattering angle and compressing the spectrum in wavelength space so that higher central Te measurements ($\textless$5\hspace{1.75 mm}KeV) can be made with improved accuracy. [Preview Abstract] |
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JP10.00115: First results of Faraday-effect polarimeter measurements of internal magnetic fluctuation in DIII-D J. Chen, W.X. Ding, D.L. Brower Motivated by the need to measure fast equilibrium temporal dynamics, non-axisymmetric structures and core magnetic fluctuations (coherent and broadband), a 694 GHz Faraday-effect polarimeter has recently been installed on the DIII-D tokamak. A novel detection scheme is utilized, which results in simultaneous integral density measurement, to isolate the magnetic component, along with fast time response (up to 3MHz) and high phase resolution (1$\times$10$^{-4}$ degree$^2$/kHz, equivalent to ${\textless1}$ Gauss at medium to high electron density conditions). Spatial resolution is provided by three radial chords located at ${z=0}$ cm and ${z=}$\pm${13.5} cm (${z=0}$ cm is machine center). Simultaneous Faraday rotation and integral density measurements have been demonstrated in the experimental campaign of 2016, with good agreement with MSE-constrained EFIT. The change of Faraday rotation during sawteeth indicates periodic evolution of current density in the core plasma. Coherent and broadband fluctuations associated with plasma instabilities and turbulence, up to 500 kHz, have been observed on both Faraday rotation and integral density data. [Preview Abstract] |
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JP10.00116: Study of ELM Density Turbulence using the Upgraded Phase Contrast Imaging on DIII-D J.C. Rost, E.M. Davis, A. Marinoni, M. Porkolab, K.H. Burrell Recent studies of the turbulent density fluctuations accompanying ELMs in mixed ELM-type discharges have exploited the expanded wavenumber range of the upgraded Phase Contrast Imaging (PCI) diagnostic. The PCI data demonstrate the difference between the fluctuations generated by Type I ELMs, which are broadband in frequency and wavelength, and those generated by Type III ELMs, which are similar in amplitude but restricted to long wavelengths, suggesting that turbulence may play a significant role in Type I ELM transport. The high frequency response of PCI makes it ideal for studying the ELM-associated density fluctuations, which are observed at frequencies up to several MHz, evolve on time scales of 10s of $\mu$s, and persist after the magnetic component of the ELM has decayed away. The upgraded PCI, with independent systems for long and short wavelength detection ($k$ $<$ 5 cm$^{-1}$ and 1 $<$ $k$ $<$ 30 cm$^{-1}$ respectively), demonstrated coverage of the full wavenumber range of interest. [Preview Abstract] |
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JP10.00117: A combined phase contrast imaging-interferometer system for the detection of multiscale density fluctuations on DIII-D E.M. Davis, J.C. Rost, M. Porkolab, A. Marinoni, M.A. Van Zeeland A heterodyne interferometer channel has been added to the DIII-D phase contrast imaging (PCI) system. Both measurements share a single 10.6 $\mu$m probe beam. Whereas the PCI excels at detecting medium- to high-$k$ fluctuations (1.5 cm$^{-1}$ $\le$ $k$ $\le$ 20 cm$^{-1}$), the interferometer extends the system sensitivity to low-$k$ fluctuations ($k$ $\le$ 5 cm$^{-1}$), allowing simultaneous measurement of electron- and ion-scale instabilities with sub-microsecond resolution. Further, correlating measurements from the interferometer channel with those from DIII-D’s pre-existing, toroidally separated interferometer ($\Delta\emptyset$ = 45$^{\circ}$) allows identification of low-$n$ modes. This new capability has been corroborated against magnetic measurements and may allow novel investigations of $core-localized$ MHD that is otherwise inaccessible via external magnetic measurements, with potential applications to fast particle transport and disruptions. [Preview Abstract] |
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JP10.00118: Role of zonal flows and electromagnetic effects in ITER turbulence simulations near threshold J. Candy, G. Staebler, P. Snyder, C. Holland Design of accurate transport models requires a database of nonlinear gyrokinetic simulations -- a computationally challenging undertaking. As early as 2008, GYRO simulations of TGLF-computed ITER operating scenarios were observed to produce levels of nonlinear zonal-flow (ZF) activity large enough to quench turbulence inside the plasma core, implying that fusion power predictions in ITER were pessimistic because turbulence was overestimated. This was in contrast to GYRO-TGLF comparisons for modern-day tokamaks, where GYRO and TGLF are in good agreement. It was speculated that closeness to threshold, ZF activity, and electromagnetic effects, could all play a key role in this discrepancy. It became clear that TGLF must be improved to include ZF stabilization for more accurate ITER simulations. The workflow for inclusion of ZF effects in TGLF is challenging because of intermittency in near-threshold GYRO simulations. GYRO simulation and subsequent TGLF improvement efforts are summarized, representing a significant undertaking carried out over a period of years. [Preview Abstract] |
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JP10.00119: Collisional Ion and Electron Scale Gyrokinetic Simulations in the Tokamak Pedestal E.A. Belli, J. Candy, P.B. Snyder A new gyrokinetic solver, CGYRO, has been developed for precise studies of high collisionality regimes, such as the H-mode pedestal and L-mode edge. Building on GYRO and NEO, CGYRO uses the same velocity-space coordinates as NEO to optimize the accuracy of the collision dynamics and allow for advanced operators beyond the standard Lorentz pitch-angle scattering model. These advanced operators include energy diffusion and finite-FLR collisional effects. The code is optimized for multiscale (coupled electron and ion turbulence scales) simulations, employing a new spatial discretization and array distribution scheme that targets scalability on next-generation (exascale) HPC systems. In this work, CGYRO is used to study the complex spectrum of modes in the pedestal region. The onset of the linear KBM with full collisional effects is assessed to develop an improved KBM/RBM model for EPED. The analysis is extended to high k to explore the role of electron-scale (ETG-range) physics. Comparisons with new analytic collisional theories are made. Inclusion of sonic toroidal rotation (including full centrifugal effects) for studies including heavy wall impurities is also reported. [Preview Abstract] |
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JP10.00120: Gyrokinetic Analysis of the Current Ramp Phase of an ITER-like DIII-D Discharge B. Bravenec, C. Holland, G.R. McKee, J. Candy, T. Görler Being able to predict transport, especially electron, during the current ramp-up phase of a discharge is of great interest, especially for ITER. Here we present results, both linear and nonlinear, from the gyrokinetic codes GYRO, CGYRO, GS2, and GENE (a benchmarking effort) for a DIII-D discharge run with the ITER shape and normalized current, field and ramp rate. Preliminary results at the mid-radius ($\it{r/a}$ = 0.6) and at the end of the current ramp from GENE are insignificant fluxes while CGYRO predicts only a finite electron energy flux. However, this flux is from fluctuations at the highest poloidal wave numbers of the simulations, implying that valid simulations may need to resolve the electron scales. These results plus linear analysis and nonlinear simulations at other times during the ramp and at other locations in the plasma will be presented. [Preview Abstract] |
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JP10.00121: Neural-network accelerated fusion simulation with self-consistent core-pedestal coupling O. Meneghini, J. Candy, P.B. Snyder, G. Staebler, E. Belli Practical fusion Whole Device Modeling (WDM) simulations require the ability to perform predictions that are fast, but yet account for the sensitivity of the fusion performance to the boundary constraint that is imposed by the pedestal structure of H-mode plasmas due to the stiff core transport models. This poster presents the development of a set of neural-network (NN) models for the pedestal structure (as predicted by the EPED model), and the neoclassical and turbulent transport fluxes (as predicted by the NEO and TGLF codes, respectively), and their self-consistent coupling within the TGYRO transport code. The results are benchmarked with the ones obtained via the coupling scheme described in [Meneghini PoP 2016]. By substituting the most demanding codes with their NN-accelerated versions, the solution can be found at a fraction of the computation cost of the original coupling scheme, thereby combining the accuracy of a high-fidelity model with the fast turnaround time of a reduced model. [Preview Abstract] |
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JP10.00122: Measurement of Runaway Electron Plateau Final Loss Energy Deposition into Wall of DIII-D E.M. Hollmann, I. Bykov, R.A. Moyer, D.L. Rudakov, N. Commaux, D. Shiraki, C. Lasnier, R. Martin-Solis, C. Cooper, N. Eidietis, P. Parks, C. Paz-Soldan Intentional runaway electron (RE) plateau-wall strikes with different initial impurity levels are used to study the effect of background plasma relativistic electron Z (as well as plasma resistivity for slow electrons) on RE-wall loss dynamics. RE wall loss time is found to be close to the avalanche time ($m_e$C/eE_{||}$)1n\lambda\sqrt{3(Z+5)/\pi}$, consistent with REs being lost by a series of MHD reconnection events, with timescale limited by current profile filling via avalanche. Local kinetic energy deposition is estimated with both hard x-ray emission and with infra-red imaging. At higher plasma impurity levels Z$\sim10$, energy deposition appears to be consistent with power balance estimates, as long as collisional dissipation during the final loss event is included. At low impurity levels Z$\sim1$, however, local energy deposition appears around 10× less than expected, indicating that the energy dissipation at low Z is still poorly understood. [Preview Abstract] |
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JP10.00123: Dissipation of post-disruption runaway electron plateaus by shattered pellet injection in DIII-D D. Shiraki, N. Commaux, L.R. Baylor, C.M. Cooper, N.W. Eidietis, C. Paz-Soldan, E.M. Hollmann, R.A. Moyer Effective runaway electron (RE) mitigation strategies are essential for protecting ITER from the potential damage of a first wall strike. In DIII-D, shattered pellet injection (SPI) with large Ne pellets demonstrates the dissipation of post-disruption RE plateaus by collisions with high-Z impurities, while equivalently sized $D_2$ pellets lead to a reduction of the impurity content of the background plasma, reducing RE dissipation. Varying the relative quantities of $Ne/D_2$ in mixed species pellets shows that the effect of $D_2$ may be dominant in determining the RE/pellet interaction. Compared with injection of the same quantity of Ne by massive gas injection, SPI achieves a similar initial RE current decay rate, but residual RE current remains after SPI. This may be due to the effects of a small quantity of $D_2$ (used as a “shell” for firing of the Ne pellets) displacing high-Z impurities. These results will help guide the optimization of injection schemes and pellet compositions for the RE mitigation system in ITER. [Preview Abstract] |
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JP10.00124: Design upgrades to the DIII-D gamma ray imager A. Lvovskiy, C.M. Cooper, N.W. Eidietis, D. Pace, C. Paz-Soldan Generation of runaway electrons (RE) in tokamak disruptions can cause damage of plasma facing components. RE studies are necessary in order to provide a reliable mechanism of RE mitigation. For that task a gamma ray imager (GRI) has been developed for DIII-D. It measures the bremsstrahlung emission by RE providing information on RE energy spectrum and RE distribution across a poloidal cross-section. The GRI consists of a lead pinhole camera illuminating a 2D array of 30 BGO detectors placed in the DIII-D mid-plane. First results showed the successful measurements of RE energy spectra in the range 1 - 60 MeV with time resolution 100 $\mu$s. They have been obtained in the low-flux quiescent RE regime via pulse-high analysis. The measurements in the high gamma flux post-disruption RE regime showed strong signal saturation. Here we present GRI design upgrades towards signal attenuation and better detector shielding including Monte-Carlo Neutral Particle modeling of GRI irradiation, as well as improved calibration techniques and options to improve electronic noise rejection. [Preview Abstract] |
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JP10.00125: Critical Gradient Behavior of Alfv\'en Eigenmode Induced Fast-Ion Transport in Phase Space C.S. Collins, D.C. Pace, M.A. Van Zeeland, W.W. Heidbrink, L. Stagner, Y.B. Zhu, G.J. Kramer, M. Podesta, R.B. White Experiments on DIII-D have shown that energetic particle (EP) transport suddenly increases when multiple Alfv\'en eigenmodes (AEs) cause particle orbits to become stochastic. Several key features have been observed; (1) the transport threshold is phase-space dependent and occurs above the AE linear stability threshold, (2) EP losses become intermittent above threshold and appear to depend on the types of AEs present, and (3) stiff transport causes the EP density profile to remain unchanged even if the source increases. Theoretical analysis using the NOVA and ORBIT codes shows that the threshold corresponds to when particle orbits become stochastic due to wave-particle resonances with AEs in the region of phase space measured by the diagnostics. The kick model in NUBEAM (TRANSP) is used to evolve the EP distribution function to study which modes cause the most transport and further characterize intermittent bursts of EP losses, which are associated with large scale redistribution through the domino effect. [Preview Abstract] |
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JP10.00126: Suppressing Alfven eigenmodes by q-profile engineering to improve fast-ion confinement G.J. Kramer, B.J. Tobias, R. Nazikian, C. Holcomb, C. Collins, M.A. van Zeeland, W.W. Heidbrink, Y. Zhu High levels of Alfven eigenmode (AE) activity often limit the plasma performance of steady-state target plasmas. Experiments were performed on DIII-D to suppress harmful AEs by q profile engineering. Current ramp rates of 0.6 MA/s are typically used in L-mode discharges to create $q_{min}$ near r/a = 0.3 where the fast-ion pressure gradient is strong, leading to strong AEs and enhanced fast-ion transport. In a new experiment a current ramp-rate of 7 MA/s was used together with ECCD at mid-radius. This resulted in a $q_{min}$ radius larger than 0.5 which is outside the fast-ion pressure gradient region. This resulted in a complete suppression of TAEs in the core and a highly reduced RSAE activity near $q_{min}$ giving rise to classical fast-ion transport as deduced from neutron measurements. Although $q_{min}$ was not sustained at large radii, these experiments show that AEs can be suppressed by q profile engineering. For sustaining $q_{min}$ at large radii a stronger off-axis current drive source is planned with neutral beam upgrades in 2017. [Preview Abstract] |
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JP10.00127: Feasibility of inferring the full fast-ion distribution function via Orbit Tomography at the DIII-D Tokamak L. Stagner, W.W. Heidbrink The sensitivity of fast-ion diagnostics to different regions of the fast-ion distribution (FID) phase space can be calculated. These phase space sensitivities when convolved with a local FID gives the expected experimental measurement. This process can be reversed to reconstruct the local FID from many experimental measurements in a method known as Velocity-space Tomography (VST). However, VST requires many radially overlapping measurement volumes which limits its applicability since most existing diagnostics are setup as radially separated arrays. Orbit Tomography (OT), an extension of VST that allows for the inference of the full FID, has been proposed as a solution to this problem. Unlike VST which reconstructs the fast-ion density on a 2D energy-pitch grid, OT infers the number of fast-ions on a particular orbit. This naturally correlates different radial locations allowing for any viewing chord to be used in the analysis. In the present work we will give an overview of OT and demonstrate its feasibility with the current diagnostic capability of the DIII-D tokamak. [Preview Abstract] |
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JP10.00128: Tokamak Equilibrium Reconstruction with MSE-LS Data in DIII-D L. Lao, B. Grierson, K.H. Burrell Equilibrium analysis of plasmas in DIII-D using EFIT was upgraded to include the internal magnetic field determined from spectroscopic measurements of motional-Stark-effect line-splitting (MSE-LS). MSE-LS provides measurements of the magnitude of the internal magnetic field, rather than the pitch angle as provided by MSE line-polarization (MSE-LP) used in most tokamaks to date. EFIT MSE-LS reconstruction algorithms and verifications are described. The capability of MSE-LS to provide significant constraints on the equilibrium analysis is evaluated. Reconstruction results with both synthetic and experimental MSE-LS data from 10 DIII-D discharges run over a range of conditions show that MSE-LS measurements can contribute to the equilibrium reconstruction of pressure and safety factor profiles. Adequate MSE-LS measurement accuracy and number of spatial locations are necessary. The 7 available experimental measurements provide useful additional constraints when used with other internal measurements. Using MSE-LS as the only internal measurement yields less current profile information. [Preview Abstract] |
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JP10.00129: Real Time Computation of Kinetic Constraints to Support Equilibrium Reconstruction W.J. Eggert, E. Kolemen, D. Eldon A new method for quickly and automatically applying kinetic constraints to EFIT equilibrium reconstructions using readily available data is presented. The ultimate goal is to produce kinetic equilibrium reconstructions in real time and use them to constrain the DCON stability code as part of a disruption avoidance scheme. A first effort presented here replaces CPU-time expensive modules, such as the fast ion pressure profile calculation, with a simplified model. We show with a DIII-D database analysis that we can achieve reasonable predictions for selected applications by modeling the fast ion pressure profile and determining the fit parameters as functions of easily measured quantities including neutron rate and electron temperature on axis. Secondly, we present a strategy for treating Thomson scattering and Charge Exchange Recombination data to automatically form constraints for a kinetic equilibrium reconstruction, a process that historically was performed by hand. [Preview Abstract] |
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JP10.00130: Equilibrium reconstructions using imaging MSE on the DIII-D tokamak B.S. Victor, C.T. Holcomb, S.L. Allen, A. Thorman, J. Howard For the first time, an imaging motional Stark effect (IMSE) diagnostic has been successfully implemented on DIII-D. This poster presents initial results on incorporating these measurements into EFIT equilibrium reconstructions. IMSE provides a 2D image of the polarization angle as a function of major radius and vertical position. The single, wider bandpass filter used with IMSE allows for polarization angle measurements across multiple neutral beams and with variable beam voltage. The traditional MSE systems on DIII-D only work with one beam at a constant voltage. In addition to 2D data with improved spatial resolution, IMSE has provided the lowest major radius internal plasma magnetic measurements on DIII-D, producing new equilibrium constraints. Advanced tokamak scenarios with $q_{min}>1.5$ are studied in detail with the new constraints provided by the IMSE system. The additional constraints are being used to assess ideal, resistive, and energetic particle stability in these scenarios. [Preview Abstract] |
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JP10.00131: Reconstruction of 3D VMEC equilibria with helical cores in DIII-D A. Wingen, R.S. Wilcox, M.R. Cianciosa, S.K. Seal, E.A. Unterberg, S.P. Hirshman, P. Piovesan, F. Turco A helical core is a feature accessible by high performance hybrid discharges. It becomes dominant, if the 3/2 tearing mode, typically dominating hybrid discharges, is suppressed. It has been experimentally verified in ASDEX-U, and recently in DIII-D. The VMEC/V3FIT codes allow for 3D reconstruction, which is shown here for the first time in a tokamak. The reconstructed helical core equilibrium can be used to numerically study the properties of an experimentally observed helical core. The helical core is a saturated internal kink, excited by 3D perturbation fields and driven primarily by the pressure gradient near q = 1. It is bifurcated from an axisymmetric state by 3D fields. It flattens the q-profile in the core, potentially stabilizing sawteeth. It contributes to flux pumping, which broadens the current density profile. This analysis will help to determine possible benefits or disadvantages for the high beta hybrid scenario. [Preview Abstract] |
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JP10.00132: Gyrokinetic Simulations of RMP Effects on DIII-D Edge Turbulence Sam Taimourzadeh, Ihor Holod, Zhihong Lin, Raffi Nazikian, Andreas Wingen It has been demonstrated that edge localized modes (ELMs) can be fully suppressed in DIII-D H-mode plasmas with the application of resonant magnetic perturbations (RMPs), and that there is a corresponding reduction of pedestal gradients, changes in rotation, and changes in the radial electric field (Er) profile [Nucl. Fusion 55, 023002 (2015)]. However, with the application of RMPs there is also an increase in long wavelength, electrostatic turbulence on top of the pedestal, as observed with BES, DBS, and other fluctuation diagnostics. Using the Gyrokinetic Toroidal Code (GTC), DIII-D shots 158103, at times 3750 ms (ELMing w/ RMP) and 3050 ms (ELM suppressed w/ RMP), and shot 158104.1350 (ELMing) are investigated, and a link between increased pedestal top turbulence, during the ELM suppressed phase, and a shift in the Er profile is demonstrated. [Preview Abstract] |
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JP10.00133: Probing of the m/n=2/1 tearing mode by applied rotating magnetic field in DIII-D R.J. LaHaye, E.J. Strait, M. Lanctot, C. Paz-Soldan, J. Hanson DIII-D experiments are studying the active probing of tearing stability. Of particular interest is the m/n=2/1 tearing mode in the low torque ITER baseline scenario. A rotating n=1 magnetic field was applied with frequency swept in steps across the anticipated 2/1 natural mode frequency to stimulate a plasma response measured with the Mirnov magnetic probe array. Differential rotation of the applied n=1 field from the natural rotation should result in induced helical currents at q=2 that inhibit the reconnection; the detected n=1 field should thus exhibit a 180 deg. change in phase in sweeping across the resonant frequency [1]. When matching the resonant frequency, the magnetic response should become singular as the tearing mode approaches marginality. In practice, peaks in the response are indeed observed but with less than 180 degree shifts (suggesting an n=1 kink response too) and not well resolved with the frequency steps used. Results and plans for a follow-up will be presented.\par \vskip6pt \noindent [1] R. Fitzpatrick, Physics of Plasmas 5, 3325 (1998) [Preview Abstract] |
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JP10.00134: Impact of local turbulence on Neoclassical Tearing Mode stability in the DIII-D Tokamak L. Bardoczi, T.L. Rhodes, T.A. Carter, W.A. Peebles, N.A. Crocker, G. McKee We report the first experimental observation of local, Ion Temperature Gradient (ITG) scale turbulence accelerating the growth of large Neoclassical Tearing Mode (NTM) islands. Saturated islands respond with the peaking of the O-point electron temperature $T_e$ to Edge Localized Modes (ELM). In sync the island width $w$ shrinks by as much as 30$\%$ suggesting a key role of the $T_e$ peak in NTM stability (via a modified bootstrap current). The $T_e$ peak then relaxes via anomalous transport and $w$ recovers. ITG-scale turbulence $\tilde{n}$ is reduced at the O-point of flat islands [1] but $\tilde{n}$ is restored when $T_e$ is peaked offering an explanation for the anomalous transport. Therefore, these measurements indicate that $\tilde{n}$ accelerates NTM recovery after an ELM crash via relaxing $T_e$ at the O-point. The key physics of the relationship between the $T_e$ peak and NTM stability has potentially far-reaching consequences, such as NTM control via pellet injection in large fusion devices, for example in ITER. [Preview Abstract] |
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JP10.00135: Neoclassical Tearing Mode Locking Avoidance by 3D Fields and Recovery of High Confinement M Okabayashi, B Budny, D Brennan, N Ferraro, B Grierson, S Jardin, N Logan, R Nazikian, B Tobias, Z Wang, E Strait, J de Grassie, R La Haye, C Paz-Soldan, Z Taylor, D Shiraki, J Hanson, C Holcomb, Y Liu A slowly rotating n=1 helical magnetic field has been applied for Neoclassical Tearing Mode (NTM) locking avoidance in the DIII-D tokamak. This 3D field applied through feedback recovered a high performance configuration by rebuilding a H-mode edge and high ion temperature internal transport barrier in the plasma core, although, at present, the $\beta_n$ was reduced by 30$\%$. The m/n=2/1 component of 3D field served to avoid NTM locking, while the m/n=1 and the m/n=(4-5)/1 components recover core confinement and H-mode edge. Preliminary analysis shows a quasi-steady helical plasma flow was built up around the core, mostly parallel to the equilibrium magnetic field. The optimization of m-components with n=1 is a promising approach for integrating optimizations of MHD stability from core to edge. [Preview Abstract] |
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JP10.00136: Effects of ELM and Sawtooth Crashes on RWM Control Performance A. Battey, J.M. Hanson, F. Turco, G.A. Navratil The impact of ELM crashes on DIII-D RWM feedback performance was evaluated in order to improve control robustness. The advanced RWM control algorithm recently implemented for DIII-D incorporates a Kalman filter observer that assumes white, Gaussian measurement noise. Contrary to this assumption some sources of plasma-generated noise such as ELM and sawtooth crashes are better described as discrete, delta function-like events. These events can propagate through the feedback algorithm, leading to large transient and possibly deleterious control commands. However, RWM control has previously been observed to suppress the transient plasma response following ELM crashes. Thus, maintaining some level of RWM feedback response during the ELM transient may be optimal. We will present simulations from an improved control algorithm, which aims to differentiate between quick ELM-like events and unstable RWMs. This approach can potentially improve feedback robustness and reduce the amount of power needed to maintain feedback control, improving the viability of a feedback controlled fusion device. [Preview Abstract] |
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JP10.00137: Validation of conducting wall models using magnetic measurements J.M. Hanson, J. Bialek, F. Turco, G.A. Navratil, J. King, E.J. Strait, A.D. Turnbull Comparisons between magnetic measurements of the DIII D wall eddy current response to applied ac, non-axisymmetric fields and MHD stability code predictions favor a fully 3D treatment of the conducting elements in the system. We describe validation studies of the wall models in the MARS-F and VALEN stability codes, using coil–sensor vacuum coupling measurements. The measurements are sensitive to induced wall currents, owing to the close proximities of the sensors and coils to the wall. VALEN treats conducting structures with arbitrary 3D geometries, while MARS-F uses an axisymmetric wall model and spectral decomposition of the problem geometry. Straightforward improvements to the VALEN model, such as refining the wall mesh and sensor geometry, lead to good agreement with single-channel measurements. Comparisons of couplings to multi-coil toroidal mode perturbations to both codes favor the 3D simulation approach, likely because it naturally treats sidebands generated by the coils and wall currents. [Preview Abstract] |
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JP10.00138: Correlated enhancement of momentum and stochastic energetic ion transport due to multi-helicity tearing modes on DIII-D B. Tobias, N. Ferraro, S. Jardin, G. Kramer, T. Evans, C.W. Domier, N.C. Luhmann, Jr. The onset of energetic particle stochasticity has been correlated with the transition to a hollow rotation profile by scaling linear tearing modes from M3D-C1 to ECEI data and following energetic particles in the SPIRAL code. The superposition of two tearing modes of different n-number increases magnetic field line stochasticity by generating tertiary magnetic islands, even when the flux perturbation is composed of only two linearly independent solutions. Furthermore, particle orbit stochasticity increases with particle energy—a mechanism for non-ambipolar transport that modifies fluid rotation in a regime relevant to the saturated island widths, neutral beam injection energies, and physical dimensions of DIII-D. This demonstrates that energy-dependent stochastic effects operate alongside nonlinear MHD coupling and neoclassical toroidal viscosity to determine the dynamics of non-axisymmetric and tearing-unstable systems, including disruptive tokamak discharges. [Preview Abstract] |
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JP10.00139: Simulations and control feedback based on the VALEN RWM model M. Clement, G. Navratil, J. Hanson, J. Bialek The VALEN Resistive Wall Mode (RWM) model [1] has been used to gauge the effectiveness of RWM control algorithms in tokamaks. VALEN models the perturbed magnetic field from a single MHD instability and its interaction with surrounding conducting structures as a series of coupled circuit equations. Results of experiments to develop control of a rotating $n$ =1 perturbation using external coils will be presented. Results from high $\beta_N$ experiments also suggest that advanced feedback techniques using external control coils may be as effective as internal control coil feedback using classical control techniques. Simulations used to inform the design of feedback control algorithms based on VALEN will also be presented.\par \vskip6pt \noindent [1] Bialek, James. 2001, Physics of Plasmas, Vol. 8.\par [Preview Abstract] |
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JP10.00140: Identification of multi-mode plasma response and extraction of plasma transfer function in tokamaks[1] Z.R. Wang, Y.Q. Liu, J.K. Park, M.J. Lanctot, Y.W. Sun, C. Paz-Soldan, N. Logan, J. Menard, R. Nazikian Plasma response, is key to ELM control using magnetic coils and has been extensively measured in tokamak experiments. In this work, a modified Nyquist analysis, including both coil phase and frequency scan, is developed to analyze the plasma response for directly identifying the multiple modes responses with the stable plasmas. The method, combined with the Pade approximation, can extract the plasma transfer functions through the magnetic response measurements, providing in-depth physics understanding. The eigenvalue in the transfer function can quantitatively infer the plasma stability. The transfer function can be applied to optimize the coil configuration to amplify the preferred eigenmode for potential ELM suppression. The drift-kinetic effects modifying the plasma response [2] can be further validated. In this work, these aspects are studied with the simulated response based on various experiments including NSTX, DIII-D and EAST. The preliminary application of this modified Nyquist analysis on existing DIII-D experiments [3] indicates the feasibility of applying the method in experiments. [1] Work under DE-FC02-04ER54698 and DE-AC02-09CH11466; [2] Z.R. Wang et al, Phys, Rev. Lett. 114, 145005 (2015); [3] C. Paz-Soldan et al, Phys, Rev. Lett. 114, 105001(2015) [Preview Abstract] |
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JP10.00141: LOW TEMPERATURE PLASMA SCIENCE, ENGINEERING AND TECHNOLOGY |
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JP10.00142: Plasma driven by helical electrodes Cihan Akcay, John Finn, Richard Nebel, Daniel Barnes A novel plasma state, obtained by applying a helical voltage at the wall with a uniform axial magnetic field, is studied by means of zero-pressure resistive MHD simulations in a periodic cylinder. The radial magnetic field at the wall is taken to be zero. For a small helical electrode voltage, the helical perturbation in the plasma is small and localized to the edge. Beyond a critical electrode voltage, there is a bifurcation to the newly discovered state, which is a single-helicity Ohmic equilibrium with the same helicity as the electrodes, \textit{i.e.}, the fields depend only on radius and $m\theta-n\varphi$, where $\theta$ and $\varphi=z/R$ are the poloidal and toroidal angles. For electrostatic driving with $m=1$, the mean magnetic field ($m=n=0$) has field line safety factor $q(r)$ equal to the pitch of the electrodes $m/n=1/n$ except near the edge, where it monotonically increases an amount of order unity. The plasma is force-free in the interior. Near the edge, however, the current crosses the field lines to enter and exit through the helical electrodes. A large helical plasma flow related Pfirsch-Schl\"{u}ter-like currents exist in this edge vicinity. Applications to current drive in tokamaks, as well as to straight plasmas with endcap electrodes are discussed. [Preview Abstract] |
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JP10.00143: First experimental results from DC/DC and AC/DC plasma-based power transformers Aaron McEvoy, William Gibson, Richard Nebel A plasma-based power transformer has been built and operated in both DC/DC and AC/DC mode. The proprietary Tibbar Plasma Technologies, Inc. transformer design consists of two cylindrically symmetric helical primary electrodes surrounding a low temperature plasma within which a secondary axial current is generated. Initial experimental results have compared well with simulations and moderate conversion efficiencies have been observed. A new proprietary device is currently being constructed that will utilize 3-phase 480 VAC input to achieve higher conversion efficiency and output power. A description of the apparatus and several potential applications will be presented along with preliminary experimental data demonstrating the DC/DC and AC/DC conversion processes. [Preview Abstract] |
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JP10.00144: CO$_{\mathrm{2}}$ remediation using high power electron beams. Tzvetelina Petrova, George Petrov, John Apruzese, Matthew Wolford To mitigate increasing CO$_{\mathrm{2}}$ concentrations in the atmosphere and alleviate global warming, we investigated a method of CO$_{\mathrm{2}}$ reduction using high-power electron beams. A series of experiments were conducted in which the reduction of CO$_{\mathrm{2}}$ is measured for different gas compositions and power deposition rates [1]. Electron beam irradiation of gas containing 90{\%} CO$_{\mathrm{2}}$ and 10{\%} CH$_{\mathrm{4}}$ at beam energy density deposition of 4.2 J/cm$^{\mathrm{3}}$, reduced the CO$_{\mathrm{2}}$ concentration to 78{\%}. Analogous experiments with a gas mixture containing 11.5{\%} CO$_{\mathrm{2}}$, 11.5{\%} CH$_{\mathrm{4}}$ and balance of Ar, reduced the CO$_{\mathrm{2}}$ concentration to below 11{\%} with energy deposition 0.71 J/cm$^{\mathrm{3}}$. An electron beam deposition model computed the energy cost for breaking a CO$_{\mathrm{2}}$ molecule in flue gas (82{\%} N$_{\mathrm{2}}$, 6{\%} O$_{\mathrm{2}}$ and 12{\%} CO$_{\mathrm{2}})$ to be 85 eV per molecule [1]. Other techniques to enhance the removal of CO$_{\mathrm{2}}$ with pulsed electron beams are also explored, yielding new possible avenues of research. [1] G. M. Petrov, J. P. Apruzese, Tz. B. Petrova, and M. F. Wolford, J. Appl. Phys. \textbf{119}, 103303 (2016). [Preview Abstract] |
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JP10.00145: Abatement of Perfluorinated Compounds Using Cylindrical Microwave Plasma Source at Low Pressure Seong Bong Kim, S. Park, Y. Park, S. Youn, S.J. Yoo Microwave plasma source with a cylindrical cavity has been proposed to abate the perfluorinated compounds (PFCs). This plasma source was designed to generate microwave plasma with the cylindrical shape and to be easily installed in existing exhaust line. The microwave frequency is 2.45 GHz and the operating pressure range is 0.1 Torr to 0.3 Torr. The plasma characteristic of the cylindrical microwave plasma source was measured using the optical spectrometer, and tunable diode laser absorption spectroscopy (TDLAS). The destruction and removal efficiency (DRE) of CF4 and CHF3 were measured by a quadrupole mass spectroscopy (QMS) with the various operation conditions. The effect of the addition of the oxygen gas were tested and also the correlation between the plasma parameters and the DRE are presented in this study. [Preview Abstract] |
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JP10.00146: Characteristics of Cylindrical Microwave Plasma Source at Low Pressure Seungil Park, S. Youn, S.B. Kim, S.J. Yoo A microwave plasma source with a cylindrical resonance cavity has been proposed to generate the plasma at low pressure. This plasma source consists of magnetron, waveguide, antenna, and cavity. The microwave generating device is a commercial magnetron with 1 kW output power at the frequency of 2.45 GHz. The microwave is transmitted through the rectangular waveguide with the whistle shape, and coupled to the cavity by the slot antenna. The resonant mode of the cylindrical cavity is the TE111 mode. The operating pressure is between 0.1 Torr and 0.3 Torr with the Argon and nitrogen gas. The electron temperature and electron number density of argon plasma were measured with the optical emission spectroscopy measurement. And Ar1s5 metastable density was measured using tunable diode laser absorption spectroscopy (TDLAS). The plasma diagnostic results of a cylindrical microwave plasma source would be described in this study. [Preview Abstract] |
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JP10.00147: Electron Temperature of the Arc Discharge for Nanomaterial Synthesis Matthew Feurer, Vladislav Vekselman, Brentley Startton, Yevgeny Raitses Since the discovery of different allotropes of carbon in the twentieth century many uses have been found for carbon based nanomaterials such as buckyballs, nanotubes (CNTs), and graphene. An atmospheric pressure arc discharge with graphite electrodes is a promising technique for producing large volumes of these carbon nanostructures. Plasma drives the synthesis providing carbon feedstock by anode ablation and sustaining required composition and temperature of nanomaterial species, as such it is important to characterize the plasma used in this process in order to control the quality and attributes of the resulting carbon nanostructures. In work we present detailed in-situ measurements of spatial distribution of arc plasma parameters obtained with optical emission spectroscopy (OES) diagnostics. The plasma temperature has been determined using Boltzmann diagram method with collisional radiative modeling due to plasma deviation from complete local thermodynamic equilibrium (LTE). Results of these measurements demonstrate a strong correlation between arc plasma and synthesis processes. [Preview Abstract] |
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JP10.00148: Validation and Verification of Two Particle-In-Cells Codes for a Glow Discharge Johan Carlsson, Alexander V. Khrabrov, Igor D. Kaganovich, Timothy Sommerer The two particle-in-cell codes EDIPIC and LSP were benchmarked and validated for a parallel-plate glow discharge in helium, in which the axial electric field had been carefully measured [1]. Both particle-in-cell codes reproduce very well cathode fall and negative glow regions of the discharge, including formation of high density plasma with very low-energy electrons in negative glow. A detailed code comparison was performed for several synthetic cases of electron-beam injection into helium gas and showed that the codes are in excellent agreement for ionization rate, as well as for elastic and excitation collisions with isotropic scattering pattern. However, electron velocity distribution is anisotropic in the cathode fall, and therefore, a more accurate model of anisotropic scattering in elastic and ionization cross sections needs to be taken into account. In the process of validation several issues with both codes were fixed, including necessity to use modern random generators in both codes, and choose efficient numerical model from EDIPIC for secondary electron emission and circuit model in LSP. [1] E A den Hartog, D A Doughty and J E Lawler, Physical Review A \textbf{38}, 2471 (1988). [Preview Abstract] |
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JP10.00149: The role of collisions and scattering in differential confinement Ian Ochs, Nathaniel Fisch, Renaud Gueroult, Stewart Zweben Much of plasma physics is concerned with the overall confinement of all species present. However, in certain applications, it is desirable to confine some species while allowing others to escape, or to have different species escape to different regions. In this study, we examine one class of differential confinement system, the plasma mass filter, and evaluate the regimes of feasible operation given realistic confounding effects such as collisions with neutrals and ions, turbulence, and radiative losses. In schemes that rely on Larmor motion, we find that the low-temperature requirement imposed by line radiation necessitates a large ($\sim$1 T) magnetic field at the densities required for high throughput, since the Coulomb collision frequency scales as $T^{-3/2}$. There are, however, a variety of ways that may be contemplated to achieve separation effects. [Preview Abstract] |
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JP10.00150: Physical investigation of a quad confinement plasma source Aaron Knoll, Andrea Lucca Fabris, Christopher Young, Mark Cappelli Quad magnetic confinement plasma sources are novel magnetized DC discharges suitable for applications in a broad range of fields, particularly space propulsion, plasma etching and deposition. These sources contain a square discharge channel with magnetic cusps at the four lateral walls, enhancing plasma confinement and electron residence time inside the device. The magnetic field topology is manipulated using four independent electromagnets on each edge of the channel, tuning the properties of the generated plasma. We characterize the plasma ejected from the quad confinement sources using a combination of traditional electrostatic probes and non-intrusive laser-based diagnostics. Measurements show a strong ion acceleration layer located 8 cm downstream of the exit plane, beyond the extent of the magnetic field. The ion velocity field is investigated with different magnetic configurations, demonstrating how ion trajectories may be manipulated. [Preview Abstract] |
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JP10.00151: Electronegative Plasma Instabilities in Industrial Pulsed Plasmas Patrick Pribyl, Anders Hansen, Walter Gekelman Electronegative gases that are important for industrial etch processes have a series of instabilities that occur at process relevant conditions. These have been studied since the 1990s, but are becoming a much more important today as plasma reactors are being pushed to produce ever finer features, and tight control of the etch process is becoming crucial. The experiments are being done in a plasma etch tool that closely simulates a working industrial device. ICP coils in different configurations are driven by a pulsed RF generators operating at 2-5 MHz. A computer controlled automated probe drive can access a volume above the substrate. The probe can be a Langmuir probe, a ``Bdot'' probe, or an emissive probe the latter used for more accurate determination of plasma potential. A microwave interferometer is available to measure line-averaged electron density. The negative ion instability is triggered depending upon the gas mix (Ar,SF$_{\mathrm{6}})$, pressure and RF power. The instability can be ``burned through'' by rapidly pulsing the RF power. In this study we present measurements of plasma current and density distribution over the wafer before, after and during the rapid onset of the instability. [Preview Abstract] |
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JP10.00152: Characterization of a plasma photonic crystal using the multi-fluid plasma model Whitney Thomas, Uri Shumlak, Sean Miller Plasma photonic crystals have great potential to expand the capabilities of current microwave filtering and switching technologies by providing high speed control of energy band-gap/pass characteristics. While there has been considerable research into dielectric, semiconductor, metallic, and even liquid crystal based radiation manipulation, using plasmas is a relatively new field. Concurrently, processing power has reached levels where realistic, computationally expensive, multi-fluid plasma simulations are now possible. Unlike single-fluid magnetohydrodynamic (MHD) models, multi-fluid plasma models capture the electron fluid response to electromagnetic waves, a key process responsible for reflecting radiation. In this study, a 5-moment multi-fluid plasma model is implemented in University of Washington's WARPXM computational plasma physics code to examine the energy band-gap characteristics of an array of plasma-filled rods. This configuration permits the thorough analysis of the effect that plasma temperature, density, and array configuration have on energy transmission, absorption, and reflection. Furthermore, high-resolution simulations of the plasma columns gives a detailed window into plasma-radiation interactions. [Preview Abstract] |
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JP10.00153: Dynamic Fractal TRIDYN: Modeling Surface Morphology and Composition Evolution under Ion Bombardment Jon Drobny, Alyssa Hayes, David Ruzic Fractal TRIDYN (FTRIDYN) is an upgraded version of the Monte-Carlo, Binary Collision Approximation (BCA) code TRIDYN that includes an explicit, dynamically evolving fractal model of surface roughness in addition to the dynamic composition model included in standard TRIDYN. The complete effect of surface roughness on plasma-material interactions, especially the time-resolved dynamics of surfaces under ion bombardment, is not fully understood. Presented is a version of FTRIDYN that includes new algorithms for handling the evolution of fractal surfaces. Fractals provide a consistent and physically realistic method to model rough surfaces using fractal dimension as a single input parameter that correlates with roughness. Particularly, a new algorithm for measuring the fractal dimension of noisy surfaces and capturing complicated surface morphology has been designed and utilized for this purpose. This allows for the simulation of a surface that evolves simultaneously in both surface composition and morphology, opening up the possibility of exploring these phenomena together. Simulations for proposed Plasma-Facing Components (PFCs) for fusion reactors, Beryllium and Tungsten, as well as for Argon incident on Silicon, are presented in this study. [Preview Abstract] |
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JP10.00154: AC-driven plasma modification of spoof plasmon propagation along metamaterial-dielectric interfaces Ricky Lee, Benjamin Wang, Mark Cappelli There is a growing interest in the use of surface plasmons to guide electromagnetic waves and a concomitant increase in the need for control of their propagation. Surface plasmons are bound electromagnetic waves that propagate along metal-dielectric interfaces, typically with optical to near- infrared frequencies. We study the control of spoof plasmon (plasmons of lower frequency) propagation through periodic metal-dielectric structures by generating alternating-current (AC) barrier discharge plasmas to modify both resonator unit cell capacitance and the air-side dielectric constant. A simple theory is presented that describes the increase in spoof plasmon resonance frequency through the introduction of air-side plasma, thereby shrinking the spoof plasmon dispersion bandgap. Plasma is produced using a dielectric barrier discharge on top of a flat copper plated PCB board etched with a comb configuration of 5 mm periodicity. When driving the comb at microwave frequency within the plasmon dispersion bandgap ($\sim$10 GHz), we demonstrate, both computationally and by experiments, that the modulation of the air-side plasma has a significant effect on the surface propagation of the interfacial fields. [Preview Abstract] |
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JP10.00155: Ab initio approach to the ion stopping power at the plasma-solid interface Michael Bonitz, Niclas Schl\"unzen, Lasse Wulff, Jan-Philip Joost, Karsten Balzer The energy loss of ions in solids is of key relevance for many applications of plasmas, ranging from plasma technology to fusion. Standard approaches are based on density functional theory or SRIM simulations, however, the applicability range and accuracy of these results are difficult to assess, in particular, for low energies. Here we present an independent approach that is based on ab initio nonequilibrium Green functions theory, e.g. [1,2] that allows to incorporate electronic correlations effects of the solid. We present the first application of this method to low-temperature plasmas, concentrating on proton and alpha-particle stopping in a graphene layer. In addition to the stopping power we present time-dependent results for the local electron density, the spectral function and the photoemission spectrum [3] that is directly accessible in optical, UV or x-ray diagnostics.\\ $[$1$]$ M. Bonitz, “Quantum Kinetic Theory”, Teubner 1998, 2nd ed. Springer 2016\\ $[$2$]$ K. Balzer and M. Bonitz, Lect. Notes Phys. Vol. 867 (2013).\\ $[$3$]$ M. Eckstein and M. Kollar, Phys. Rev. B 78, 245113 (2008). [Preview Abstract] |
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JP10.00156: Particle-in-Cell and molecular dynamics simulation of plasma-surface interaction Hanno Kaehlert, Alexei Filinov, Michael Bonitz Depending on their energy, particles from a plasma can initiate various processes on the surface of a solid. This includes, i.a., sputtering, adsorption of the particle on the surface, or the emission of secondary electrons back into the plasma. Particle-in-Cell simulations with Monte Carlo Collisions (PIC-MCC) have been used to investigate the influence of surface processes on the physical conditions in an rf discharge~[1]. Here, we perform PIC-MCC simulations and focus on the physical parameters in the sheath region as the plasma-surface boundary layer from which energetic plasma particles reach the surface and into which particles from the solid are emitted. Molecular dynamics simulations are used to gain a better understanding of the microscopic processes on the surface.\\ $[1]$ A. Derzsi \textit{et al.}, Plasma Sources Sci. Technol. \textbf{24}, 034002 (2015). [Preview Abstract] |
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JP10.00157: Reduction of collisional-radiative models for laser-produced argon plasmas Richard June Abrantes, Ann Karagozian, Hai Le The formation of a laser-induced plasma involves a variety of physical phenomena stemming from the laser-plasma interaction. A thorough understanding of these processes encourages improvement and innovation for many applications. In this work, we aim to computationally reduce a previously-developed collisional-radiative (CR) model constructed from the LANL database\footnote{Argon Atomic Data Sets. https://www-amdis.iaea.org/LANL/argon/}, which includes all of the relevant collisional and radiative processes for all the ionic stages of argon. The laser is coupled to the plasma via multiphoton ionization and inverse Bremsstrahlung, processes important for electron production and heating. The use of the CR model allows us to identify dominant mechanisms responsible for initial breakdown of the gas and thermal equilibriation processes. The results are compared with experimental data from laser-induced breakdown experiments\footnote{Sircar et al. \textit{Appl. Phys. B} 63, 623-627 (1996).}. [Preview Abstract] |
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JP10.00158: Plasma-enhanced preparation of graphene composites with polyaniline and polypyrrole Aysegul Uygun Oksuz, Sadik Cogal, Gamze Celik Cogal, Emre Uygun, Lutfi Oksuz This study presents the preparation of graphene (GR) nanocomposites with polyaniline (PANI) and polypyrrole (PPy) through the fast, versatile and environmentally friendly process of radiofrequency (RF) -plasma polymerization. Morphological characterization of nanocomposites was performed using scanning electron microscopy (SEM) and showed that the PANI and PPy conducting polymers coated the GR surface. The surface properties of the GR nanocomposites were determined using Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) analysis. [1] G. Gustafsson, Y. Cao, G. M. Treacy, F. Klavetter, N. Colaneri, and A. J. Heeger, ``Flexible light-emitting diodes made from soluble conducting polymers'', \textit{Nature}, 357 (6378) (1992) 477--479. [2] A. J. Heeger, ``Semiconducting and Metallic Polymers:~ The Fourth Generation of Polymeric Materials'', \textit{J. Phys. Chem. B}, 105 (36) (2001) 8475--8491. [3] A. K. Geim, ``Graphene: status and prospects'', \textit{Science}, 324 (5934), (2009) 1530--1534. [Preview Abstract] |
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JP10.00159: Results from a Pre-Ionization Study of a 30 kW RMF-FRC Experiment for Space Propulsion Carrie Hill, Nolan Uchizono, Michael Holmes Field-Reversed-Configuration (FRC) plasma thrusters are an attractive concept for in-space propulsion. These thrusters operate in a quasi-steady manner by expelling successive bursts of FRC plasmoids on the order of the neutral-gas refill rate. Pre-ionization (PI) of the seed gas is a challenge for these repetitive systems as the starting mix is a combination of the hot remnants from the recently-departed FRC and the cold refill gas. Pre-ionization of this mixture is critical to the RMF current drive and energy coupling of the system and therefore must be optimized to maximize performance. An empirical PI study was conducted on a 30-kW RMF-FRC benchtop experiment to examine how coil geometry and initial plasma distribution affects the plasmoid formation and acceleration processes. Three different inductively-coupled PI coil geometries were investigated. Their effectiveness was monitored by recording the downstream plasma velocity distribution, density, and energy coupling to the RMF antennas. The initial seed plasma created by these sources was also mapped in limited regions to compare the starting conditions for the FRC plasmoid in each case. [Preview Abstract] |
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JP10.00160: Rotating Magnetic Field FRC Formation Studies using the Multi-Fluid Plasma Model Eder Sousa The multi-fluid plasma model equations are derived by taking velocity moments of the Boltzmann equation for each of the components in a plasma, and each species mass density, momentum density and total energy are evolved in time. This model is used to study field-reversed configuration (FRC) formation dynamics using a Rotating Magnetic Field (RMF) as an electron current drive. Particular interest is placed on the coupling of the RMF to the plasma and collisional effects between the electron, ion and neutral fluids, and some consideration to ionization effects. The simulations are designed such that they can be compared to experimental results using collisional-radiative (CR) models developed at the Air Force Research Laboratory. Distribution A: Approved for public release; distribution unlimited AFTC/PA clearance No. 15399. [Preview Abstract] |
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JP10.00161: High-current plasmas switching devices. Aleksandr Mustafaev, Artiom Grabovskiy, Oscar Murillo, Vladimir Soukhomlinov Nowadays, the level of development of spatial and earthly nuclear energetic lays down big requirements: total control possibility of current density with a stable work of the instrument in extreme conditions with a big radiation level and temperatures of 1000 K. Among the ways of solving this problem the application of key elements with binary cesium-barium plasmas are available. The results of the investigation on electro-kinetic parameters of plasma Knudsen Cs-Ba key element with big current densities are presented in this work: \newline \textgreater The phenomenon of spontaneous current breakage, which has a big influence on the efficiency of the grid extinction, was investigated; \textgreater Unique regimes of effective grid extinction, in which the rise of modulated power is realized with a declining of the energetic cost of controlling the current of the key element, were found; \textgreater Record energetic parameters for the binary key element were obtained: at an anode potential of 50 V, stable frequencies modulation at 1-10 kHz, the electric power density of 5 kW/cm$^{\mathrm{2\thinspace }}$and the efficiency more than 95{\%}. [Preview Abstract] |
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JP10.00162: Electrodeless RF Plasma Propulsion by Rotating Magnetic Field Method Takerku Furukawa, Kohei Takizawa, Daisuke Kuwahara, Shunjiro Shinohara Electric propulsion scheme is promising in the field of the space propulsion because of high fuel efficiency and long operating time. However, this time is limited due to the loss of electrodes contacting with plasmas directly. In order to solve this problem, we have proposed electrodeless acceleration schemes [1], e.g., a rotating magnetic field (RMF [2]) scheme [1,3]. In this RMF scheme, we use two pairs of 5 turns RMF coils with AC currents, which have a 90 deg. phase difference. The rotating magnetic field induces azimuthal current $ j$ by a nonlinear effect. Then, plasma is accelerated by the axial Lorentz force using the product of $j$ and the radial component of external magnetic field. We have investigated the effect of the RMF current frequency $f$, and 24 {\%} increase of ion velocity in the case of $f=$ 3 MHz. We will present the experimental results, using lower $f$ and gas pressure, and also discuss the penetration of RMF into the plasma. [1] S. Shinohara \textit{et al}., \textit{IEEE} \textit{Trans. on Plasma Sci.} \textbf{42} (2014) 1245. [2] I. R. Jones, \textit{Phys}. \textit{Plasmas} \textbf{6} (1990) 1950. [3] S. Otsuka \textit{et al}., Plasma Fusion Res. \textbf{10} (2015) 3401026. [Preview Abstract] |
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JP10.00163: Electrodeless RF Plasma Thruster Using $m=$ 0 Coil Shuichi Nishimura, Daisuke Arai, Daisuke Kuwahara, Shunjiro Shinohara In order to realize a deep space exploration in the future, we have been developing a next generation electrodeless electric propulsion system by electromagnetic acceleration of high-density helicon plasma [1]. A new proposed method by $m=$ 0 coil plasma acceleration [1,2] ($m$ is an azimuthal mode number) is based on the Lorentz force: a product of the induced azimuthal current by supplying an AC current to the $m=$ 0 coil and the radial component of the externally applied magnetic field (divergent field configuration). Here, we have investigated the dependences of an ion velocity and an electron density on the external parameters, leading to optimized conditions, using the SHD device [3]. By increasing AC current on the order of 100 A, we could see the increase of ion velocity and electron density by a factor of 2.5 and 3, respectively. [1] S. Shinohara \textit{et al.}, IEEE Trans. Plasma Sci. \textbf{42} (2014) 1245. [2] T. Ishii \textit{et al.}, JPS Conf. Proc. \textbf{1} (2014) 015047. [3] D. Kuwahara \textit{et al}., Rev. Sci. Instrum. \textbf{84} (2013) 103502. [Preview Abstract] |
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JP10.00164: Continuum-kinetic approach to sheath simulations Petr Cagas, Ammar Hakim, Bhuvana Srinivasan Simulations of sheaths are performed using a novel continuum-kinetic model with collisions including ionization/recombination. A discontinuous Galerkin method is used to directly solve the Boltzmann-Poisson system to obtain a particle distribution function. Direct discretization of the distribution function has advantages of being noise-free compared to particle-in-cell methods. The distribution function, which is available at each node of the configuration space, can be readily used to calculate the collision integrals in order to get ionization and recombination operators. Analytical models are used to obtain the cross-sections as a function of energy. Results will be presented incorporating surface physics with a classical sheath in Hall thruster-relevant geometry. [Preview Abstract] |
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JP10.00165: Laser characterization of the unsteady 2-D ion flow field in a Hall thruster with breathing mode oscillations Andrea Lucca Fabris, Christopher Young, Natalia MacDonald-Tenenbaum, William Hargus Jr., Mark Cappelli Hall thrusters are a mature form of electric propulsion for spacecraft. One commonly observed low frequency (10--50 kHz) discharge current oscillation in these $E \times B$ devices is the breathing mode, linked to a propagating ionization front traversing the channel. The complex time histories of ion production and acceleration in the discharge channel and near-field plume lead to interesting dynamics and interactions in the central plasma jet and downstream plume regions. A time-resolved laser-induced fluorescence (LIF) diagnostic non-intrusively measures 2-D ion velocity and relative ion density throughout the plume of a commercial BHT-600 Hall thruster manufactured by Busek Co. Low velocity classes of ions observed in addition to the main accelerated population are linked to propellant ionization outside of the device. Effects of breathing mode dynamics are shown to persist far downstream where modulations in ion velocity and LIF intensity are correlated with discharge current oscillations. [Preview Abstract] |
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JP10.00166: Laser-Bioplasma Interaction: The Epilepsy-Topion-Bioplasma, (the Seizure Onset Area) Upon the Action of the Optical-Fiber-Guided Multi-Ultraviolet-Photon Beams V. Alexander Stefan The ultraviolet photons may control the imbalance of sodium and potassium ions in the brain bioplasma and, consequently, may prove to be efficient in the prevention of epileptic seizures.\footnote{V. Alexander Stefan, APS-March-2016, Abstract \textbf{{\#}}M1.00310;APS-DPP-November-2015, Abstract {\#}JP12.00155.} A novel method is based on the multi-ultraviolet-photon beam interaction\footnote{V. Stefan, B. I. Cohen, C. Joshi, \textit{Science}, 243, 4890, (Jan.27, 1989); Stefan et al., Bull. APS 32, No.9, 1713, (1987); Stefan, APS-March-2015, Abstract {\#} P1.00099;\textbf{~}V. Alexander Stefan, Neurophysics\textit{, Stem Cell Physics, and Genomic Physics: Beat-Wave-Driven-Free Electron Laser Beam Interactions with the Living Matter}, (S-U-Press, La Jolla, Calif, 2012).} with the epilepsy-topion-bioplasma, (nonlinear coupling of an ultra high frequency mode to the brain beta phonons). It is hypothesized that epilepsy is a chaotic-dynamics phenomenon: small electrical changes in the epilepsy-topion-bioplasma lead, (within the 10s of milliseconds), to the onset of chaos, (seizure---excessive electrical discharge), and subsequent cascading into adjacent areas.\footnote{H.P. Zaveri et al., Localization-related epilepsy exhibits significant connectivity away from the seizure-onset area, Neuroreport, 20(9), 891-5, Jun17, 2009.\par } [Preview Abstract] |
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JP10.00167: Development of a compact neutron source by a high voltage ring electrode discharge Masayuki Watanabe Neutron is one of the particles in atomic nucleus. Neutron beam has many physical characteristics as follows; (a) the transmittance in a matter is high and (b) the interaction with atomic nuclei is dominant. For these reasons, the development of the neutron beam source is expected in many engineering and medical applications. However, it is still under development, because there is no compact neutron beam source. The purpose of this research is to develop the compact neutron beam source. The neutron is generated by using the inertial electrostatic confinement fusion. In this experiment, a ring-shaped electrode (cathode) is used for the convergence of the deuterium nucleus. To product the neutron by a D-D nuclear reaction, it is necessary to apply a high voltage into the glow discharge plasma. The neutron production rate is approximately 10\textasciicircum 5 n/s under the condition that the cathode voltage is -15kV and discharge current is 10 mA. The neutron production rate increases with increasing the ring cathode voltage or discharge current. It will be possible to increase the number of neutrons by the stabilizing of the high voltage and high current discharge. [Preview Abstract] |
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JP10.00168: Generation of anomalously energetic suprathermal electrons by an electron beam interacting with a nonuniform plasma Dmytro Sydorenko, Igor D. Kaganovich, Peter L.G. Ventzek Electrons emitted from electrodes are accelerated by the sheath electric field and become the electron beams penetrating the plasma. The electron beam can interact with the plasma in collisionless manner via two-stream instability and produce suprathermal electrons. In order to understand the mechanism of suprathermal electrons acceleration, a beam-plasma system was simulated using a 1D3V particle-in-cell code EDIPIC. These simulation results show that the acceleration may be caused by the effects related to the plasma nonuniformity. The electron beam excites plasma waves whose wavelength and phase speed gradually decrease towards anode. The short waves near the anode accelerate plasma bulk electrons to suprathermal energies. Rich complexity of beam- plasma interaction phenomena was also observed: intermittency and multiple regimes of two-stream instability in a dc discharge, band structure of the growth rate of the two-stream instability of an electron beam propagating in a bounded plasma, multi-stage acceleration of electrons in a finite system. [Preview Abstract] |
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JP10.00169: Dissociation of carbon-dioxide at high-pressure using nanosecond-pulsed dielectric barrier discharges Taemin Yong, Mark Cappelli This study investigates the efficiency of the conversion of CO$_{2}$ into CO and O$_{2}$ using nanosecond repetitively pulsed discharges in a high pressure reactor capable of exceeding the supercritical point. The electrode configuration consists of a pin-to-plane geometry with the plane electrode covered by dielectric material (SiO$_{2})$. The products of CO$_{2}$ splitting are measured using mass spectrometry. The energy efficiency is determined for a range of residence times, pulse frequency and energy, and reactor pressures. The extent of CO$_{2}$ conversion is found to be dependent on the duration of the processing time, reaching an equilibrium level that is linearly-dependent on the discharge pulse energy. The results are compared with our previous experiment conducted in the absence of the dielectric layer. [Preview Abstract] |
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JP10.00170: Schlieren High Speed Imaging on Fluid Flow in Liquid Induced by Plasma-driven Interfacial Forces Janis Lai, John Foster Effective plasma-based water purification depends heavily on the transport of plasma-derived reactive species from the plasma into the liquid. Plasma interactions at the liquid-gas boundary are known to drive circulation in the bulk liquid. This forced circulation is not well understood. A 2-D plasma- in-liquid water apparatus is currently being investigated as a means to study the plasma-liquid interface to understand not only reactive species flows but to also understand plasma- driven fluid dynamic effects in the bulk fluid. Using Schlieren high speed imaging, plasma-induced density gradients near the interfacial region and into the bulk solution are measured to investigate the nature of these interfacial forces. Plasma-induced flow was also measured using particle imaging velocimetry. [Preview Abstract] |
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JP10.00171: High Throughput Plasma Water Treatment Selman Mujovic, John Foster The troublesome emergence of new classes of micro-pollutants, such as pharmaceuticals and endocrine disruptors, poses challenges for conventional water treatment systems. In an effort to address these contaminants and to support water reuse in drought stricken regions, new technologies must be introduced. The interaction of water with plasma rapidly mineralizes organics by inducing advanced oxidation in addition to other chemical, physical and radiative processes. The primary barrier to the implementation of plasma-based water treatment is process volume scale up. In this work, we investigate a potentially scalable, high throughput plasma water reactor that utilizes a packed bed dielectric barrier-like geometry to maximize the plasma-water interface. Here, the water serves as the dielectric medium. High-speed imaging and emission spectroscopy are used to characterize the reactor discharges. Changes in methylene blue concentration and basic water parameters are mapped as a function of plasma treatment time. Experimental results are compared to electrostatic and plasma chemistry computations, which will provide insight into the reactor's operation so that efficiency can be assessed. [Preview Abstract] |
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JP10.00172: Investigating the Neutral-Gas Manometers in the Wendelstein 7-X Experimental Fusion Reactor Jeannette Maisano-Brown, Uwe Wenzel, Thomas Sunn-Pederson The neutral-gas manometer is a powerful diagnostic tool used in the Wendelstein 7-X stellarator, a magnetized fusion experiment located in Germany. The Wendelstein, produced at a cost of 1.2 billion euros, and 20 years in the making, had its first experimental results in Winter 2016. Initial findings exceeded expectations but further study is still necessary. The particular instrument we examined was a hot-cathode ionization gauge, critical for attaining a quality invessel environment and a stable plasma. However, after the winter operation of Wendelstein, we found that some of the gauges had failed the six-second (maximum) plasma runs. Wendelstein is on track for 30-minute operations within three years, so it has become of upmost importance to scrutinize gauge design claims. We therefore subjected the devices to high magnetic field, input current, and temperature, as well as to long operational periods. Our results confirmed that the manometer cannot survive a 30-minute run. Though our findings did motivate promising recommendations for design improvement and for further experimentation so that the gauge can be ready for upcoming operations in Summer 2017 and eventual installment in ITER, the International Thermonuclear Experimental Reactor, currently under construction. [Preview Abstract] |
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