Bulletin of the American Physical Society
53rd Annual Meeting of the APS Division of Plasma Physics
Volume 56, Number 16
Monday–Friday, November 14–18, 2011; Salt Lake City, Utah
Session JP9: Poster Session VI: Education/Outreach; Undergrad/High School Research; Solar, Interplanetary, and Magnetospheric Plasma Physics; Divertors, Edge Physics/Fueling, Simulation/Modeling of Magnetic Conf.; Mini-Conf. on Understanding Astrophysical Dynamos I |
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Room: Hall A |
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JP9.00001: EDUCATION AND OUTREACH |
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JP9.00002: The IPA appointment as a professional-development learning platform Mark Koepke Federal agencies make most of their Intergovernmental Personnel Act (IPA) mobility assignments with academia in order to bring personnel with specialized experience into the federal government. Federal detailing and non-federal contracting are also used as programmatic needs arise. In this poster, an IPA mobility assignment in the DOE Office of Fusion Energy Sciences (FES) is described that took place from August 2009 to August 2011. The title of the assignment was Senior Scientific Coordinator and the range of responsibility was extensive. The timing of the assignment coincided with significant personnel changes at the senior management level within DOE and this worked to the benefit of the strategic planning nature of the assignment. The implementation of the recommendations of the Physics 2010: Plasma Science NRC report will be outlined. The positive outcomes from the IPA experience will be put into the context of suggesting that university professors could find intellectual stimulation and professional reward, while serving the plasma physics community, by participating in an IPA. [Preview Abstract] |
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JP9.00003: The PPPL Science Education Pipeline - Where Does it Lead? Andrew Zwicker, S.A. Wissel, Aliya Merali, Deedee Ortiz, John DeLooper PPPL's Science Education Program includes programs for students of all ages. Opportunities for the general public include a lecture series and exhibits in science museums on plasmas and fusion energy. K-12 students perform summer research, participate in quiz competitions, and enrichment workshops. K-12 teachers go to Plasma Camp, ``Energy in the 21st Century'' workshops, and perform research. Undergraduates, including community college students, perform research throughout the year. To measure the quality and effectiveness of each program, we study the short term impact through pre- and post-surveys, and the long-term outcome through longitudinal studies. For example, from 2000-2009, 72{\%} of the undergraduate interns entered graduate school in physics or engineering and 45{\%} studied plasma physics. However, data shows a significant gender difference in graduate school enrollment and points to an overall issue with recruitment in all of our programs. Thus, we have recently added new programs that target at-risk students and their teachers as well as young women in middle and high school. [Preview Abstract] |
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JP9.00004: Making a Splash in Microgravity with Teachers Stephanie Wissel, Andrew Zwicker, Aliya Merali, Katherine Litman, Bruce Williams, David West, Jonathan Grom, Haazim Muneer, Bocary Bandeh, Mary Courtney, Maureen Quinn PPPL recently entered into a three-year Space Act Agreement with NASA to create a new K-12 research experience for teachers where they y an experiment on the ``Weightless Wonder''. One team comprises six teachers from the Trenton Public School District, ranging in focus from K-2 special education to 9-12 teachers, who were selected for their enthusiasm for science and desire to incorporate a research project into their curriculum. They conducted an experiment that observed the splashes resulting from the water entry of both hydrophobic and hydrophilic steel balls where the change in gravity affects the resulting splash dynamics. The program also requires concurrent curriculum development incorporating the project into their classes. The teachers and students from the same district will analyze the data and use inform the experiment to be own in 2012. We report on the results of the experiment, the subsequent implementation of the curricula, and the initial impact on the students. [Preview Abstract] |
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JP9.00005: Sparking Women's Interest in Physics through Science Education Aliya Merali, S.A. Wissel, M. Ortiz, J.T. Morgan, A. Zwicker As of 2010, less than 10{\%} of the members of the APS division of plasma physics are female. Data from a 2005 AIP publication indicate that a lack of female presence in physics exists as early as high school and is perpetuated throughout the educational careers of women. Of the undergraduate programs run by PPPL, 16{\%} of participants are female, and only 11{\%} of participants that continue on to graduate school are female. In an effort to increase the exposure of young women to physics, we have expanded existing programs and initiated new programs such as a mentorship program and an energy focused essay contest. The goal of these programs is to bridge the gap between young and established women in science in order to increase young women's interest in the field of physics and thus increase the likelihood that they will continue on to study higher-level physics. Using data collected from participant surveys we have assessed the short-term effectiveness of PPPL programs in influencing young women to pursue careers in science and plasma physics. \textit{Ivie and Ray. AIP Publication Number R-430.02 (February 2005)} [Preview Abstract] |
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JP9.00006: UNDERGRADUATE AND HIGH SCHOOL RESEARCH |
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JP9.00007: Using Raman Spectroscopy to Study Diamond Thin Films Yi-Hsuan Lin, Andrew Zwicker Diamond thin films (DTF), due to their extreme hardness, low electrical conductivity and chemical inertness, have various applications in semiconductor and machining industry. DTF strengthen machining and cutting tools that demand more precision and resist chemical corrosions as electrodes. The DTF created in this investigation were produced using a hybrid physical-chemical vapor deposition process in an electron cyclotron resonance sputter source. The samples formed can be amorphous carbon, graphite, or diamond. A method to test whether the sputter source successfully created diamond is Raman spectroscopy, a non-invasive technique that utilizes photo excitation and Raman scattering of monochromatic light. A sharp peak at 1332 inverse cm indicates the signature Raman shift of the sp3 C-C bond of pure diamond in these spectra. Graphite and amorphous carbon have their signature peaks near 1580 inverse cm and 1343 inverse cm. The technique is used to study wafer quality as a function of plasma parameters. Results will ultimately be benchmarked against Raman spectroscopy system at The College of New Jersey, and more samples will be produced to ensure the uniformity of the sputter source. [Preview Abstract] |
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JP9.00008: Effect of Plasma Modulation on the Corona of a Tesla Coil Robert Clayton, Hans Schneider, Andrew Zwicker Modulating an audio signal into a Tesla coil, one can create a plasma speaker.~~Documented use of plasma speakers dates back to 1900 with William Duddell's singing arc.~~In order to understand the mechanisms present in plasma speaker, and further the research that has been done by Nicholas Braithwaite, et al. in observing audio modulation in plasma (Visualizing Gas Heating from an RF Plasma Loudspeaker; 2008);~a plasma speaker was constructed with a 4 MHz plasma frequency providing $\sim $10,000 volts in the secondary coil, which generates a 1-inch corona emitted from the electrode.~~The 4 MHz signal is outside of the audio range, therefore any audio signal can be modulated on top of the plasma without approaching the frequency of the plasma.~~A high speed video camera is used to look at plasma dynamics as a function of electrode shape and input power. ~Providing pure tones to modulate the speaker, the emitted corona will be analyzed at a frame rate at or above the frequency of the test signal to determine the effects of the modulation on the plasma.~~Audio quality will be studied with a frequency analyzer and correlated to plasma parameters. [Preview Abstract] |
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JP9.00009: Development of a Dust Dropper for Dusty Plasma Experimentation Chioma Udemgba, Dennis Mansfield, Aliya Merali, Stephanie Wissel, Andrew Zwicker Dusty plasma research has applications in many scientific disciplines, from space physics to fusion engineering. Experimentally creating these complex systems requires the addition of fine dust particles to low temperature plasmas in a controlled way. This project focuses on engineering a dust particle dropper to insert 104-106 spherical SiO2 beads (40$\mu$m diameter) into argon plasma at 10-3-10-4 Torr at a steady rate. Dust particles are deposited at as low as 0.04 mg/s and as high as 3 mg/s into the plasma with the use of an adapted particle dropper (Mansfield, 2010) consisting of a piezoelectric disk that confines particles to a central 2.54 cm circle when it is driven with a 2.0 kHz signal. The device regulates the motion of the dust particles using both acoustical and mechanical constraints in order to provide linearity and strict control of particle deposition through a central 0.08 cm aperture. The use of this device will allow for a reproducible addition of dust particles into plasma and enable the production of stable dusty plasma which aids in investigating the charge accumulation of dust clouds, as well as the study of the formation and characterization of dusty plasmas. (See J. Blumenkopf's abstract for information on simulation of dusty plasmas in a DC field.) [Preview Abstract] |
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JP9.00010: DC Dusty Plasma Simulation Joshua Blumenkopf, Stephanie Wissel, Andrew Zwicker We describe the development of simulations of a complex plasma-composed of a low-temperature plasma and dust grains-to be used in comparing the electron, dust and ion interactions in the simulations to the Dusty Plasma eXperiments (DPX) being conducted at the Princeton Plasma Physics Laboratory (PPPL). There are two DPX experiments: a ground-based experiment used to investigate the spontaneous formation of dust acoustic waves and the flight-based experiment that has gone on three flights on NASA's ``Weightless Wonder.'' The latter experiment has recently been outfitted with a thermal heater used to generate a thermal gradient in the device. This thermal gradient produces a thermophoretic force on the charged dust grains that counteracts gravity, thereby simulating the flights on the ``Weightless Wonder.'' We have modified the XOOPIC code (J.P. Verboncoeur et al., Comp. Phys. Comm., 87, May 11, 1995, pp. 199-211) to simulate the DPX apparatuses by adding a new dielectric particle species and creating additional modules to handle dust by allowing variable charge and deposition currents during the collision phase of the code. Using these simulations, plasma dynamics and dust cloud characteristics are compared with experimental results (C. Udemgba, these proceedings). [Preview Abstract] |
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JP9.00011: A graphical interface for the Plasma Apprentice: Easier access to plasma physics knowledge B. Weinstein, J. Liu, H. Mynick, E. Feibush Obtaining and evaluating relevant formulae for a given plasma physics problem is often tedious. PAP, the Plasma Apprentice, was developed [1] to automate this process. To provide easier access to the PAP ``kernel,'' written in Mathematica, we have designed a graphical user interface in Java. To link Mathematica and Java, we used Mathematica's Java-Link (JLink) library and the Java Universal Network/Graph Framework (JUNG) to provide additional functionality. The Java client allows one to select and evaluate predefined quantities symbolically and numerically. To aid numerical computation, scientists can use parameter presets from existing machines (e.g. stellerators) when evaluating quantities. A command-line interface allows users direct access to the PAP kernel. PAP can easily be extended and offers templates to help users define new quantities. Presently, users can save their changes to the program locally. Future functionality may allow users to publish their changes to a ``PAP Repository.'' Ultimately, the authors hope that PAP will gain widespread use and will be enhanced by others. \\[4pt] [1] H.E. Mynick, Physica Scripta $<$T16$>$, 133-142 (1987). [Preview Abstract] |
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JP9.00012: Modeling Xenon Purification Systems in a Laser Inertial Fusion Engine Ann Hopkins, Charles Gentile A Laser Inertial Fusion Engine (LIFE) is a proposed method to employ fusion energy to produce electricity for consumers. However, before it can be built and used as such, each aspect of a LIFE power plant must first be meticulously planned. We are in the process of developing and perfecting models for an exhaust processing and fuel recovery system. Such a system is especially essential because it must be able to recapture and purify expensive materials involved in the reaction so they may be reused. One such material is xenon, which is to be used as an intervention gas in the target chamber. Using Aspen HYSYS, we have modeled several subsystems for exhaust processing, including a subsystem for xenon recovery and purification. After removing hydrogen isotopes using lithium bubblers, we propose to use cryogenic distillation to purify the xenon from remaining contaminants. Aspen HYSYS allows us to analyze predicted flow rates, temperatures, pressures, and compositions within almost all areas of the xenon purification system. Through use of Aspen models, we hope to establish that we can use xenon in LIFE efficiently and in a practical manner. [Preview Abstract] |
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JP9.00013: Modeling the Removal of Xenon from Lithium Hydrate with Aspen HYSYS Phillip Efthimion, Charles Gentile The Laser Inertial Fusion Engine (LIFE) project mission is to provide a long-term, carbon-free source of sustainable energy, in the form of electricity. A conceptual xenon removal system has been modeled with the aid of Aspen HYSYS, a chemical process simulator. Aspen HYSYS provides excellent capability to model chemical flow processes, which generates outputs which includes specific variables such as temperature, pressure, and molar flow. The system is designed to strip out hydrogen isotopes deuterium and tritium. The base design bubbles plasma exhaust laden with x filled with liquid helium. The system separates the xenon from the hydrogen, deuterium, and tritium with a lithium hydrate and a lithium bubbler. After the removal of the hydrogen and its isotopes, the xenon is then purified by way of the process of cryogenic distillation. The pure hydrogen, deuterium, and tritium are then sent to the isotope separation system (ISS). The removal of xenon is an integral part of the laser inertial fusion engine and Aspen HYSYS is an excellent tool to calculate how to create pure xenon. [Preview Abstract] |
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JP9.00014: Simulation and Analysis of Isotope Separation System for Fusion Fuel Recovery System Bathiya Senevirathna, Charles Gentile This paper presents results of a simulation of the Fuel Recovery System (FRS) for the Laser Inertial Fusion Engine (LIFE) reactor. The LIFE reaction will produce exhaust gases that will need to be recycled in the FRS along with xenon, the chamber's intervention gas. Solids and liquids will first be removed and then vapor traps are used to remove large gas molecules such as lead. The gas will be reacted with lithium at high temperatures to extract the hydrogen isotopes, protium, deuterium, and tritium in hydride form. The hydrogen isotopes will be recovered using a lithium blanket processing system already in place and this product will be sent to the Isotope Separation System (ISS). The ISS will be modeled in software to analyze its effectiveness. Aspen HYSYS was chosen for this purpose for its widespread use industrial gas processing systems. Reactants and corresponding chemical reactions had to be initialized in the software. The ISS primarily consists of four cryogenic distillation columns and these were modeled in HYSYS based on design requirements. Fractional compositions of the distillate and liquid products were analyzed and used to optimize the overall system. [Preview Abstract] |
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JP9.00015: A conceptual plasma exhaust system for the Laser Inertial Fusion Engine (LIFE) Alexander Iriza, Charles Gentile, William Blanchard, Thomas Kozub The Laser Inertial Fusion Engine (LIFE) project proposes the construction of an indirect-drive inertial fusion reactor for the generation of electrical energy. LIFE will use hohlraum targets containing a deuterium-tritium fuel mixture which will be ignited by lasers at a rate of 16 times per second. In order to shield the first wall from high-energy x-rays and ions, the reactor vessel will be filled with an intervention gas of xenon. The average xenon density from the center to the first wall must be at least 8 $\frac{g}{m^3}$ to ensure sufficient stopping power, while, because of nuclear exposure concerns, the amount of tritium in the vessel must not exceed 10 g. A conceptual design of the LIFE exhaust-processing system is undertaken with a focus on assessing its efficacy in meeting these two requirements simultaneously. A model of the density profile within the vessel indicates that an exhaust rate at the first wall of at least 26 $\frac{m^3}{s}$ is necessary to keep the tritium inventory below 10 g. At this rate, in order to maintain the required xenon density, approximately 40 tons of xenon will need to be exhausted, processed, and recirculated each day. This paper will discuss the operating parameters of this progenitor system for this and future IFE fusion reactors. [Preview Abstract] |
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JP9.00016: Plasma in the Synthesis of Nanoparticles Taylor Laub, Charles Gentile, Yevgeny Raitses Development of nanotechnology, specifically the production of carbon nanotubes, may be integral to innovation in an array of fields, from textiles to electronics. The structure of carbon nanotubes affords for the creation of materials with exceptional strength and conductivity. At present, scientists rely on ``cut-and-try'' methods to perfect the plasma synthesis, leaving an interface gap between plasma and material sciences. As a result, methods of producing carbon nanotubes are expensive and length is difficult to standardize. Therefore, the development of a method to produce carbon nanotubes efficiently and in uniform sizes is of great interest. To elucidate the role of plasma in the synthesis of nanoparticles, Princeton Plasma Physics Lab is developing a Plasma-Based Nano Laboratory (PBNL). The PBNL houses an Electron Diffusion Gauge Experiment (EDGE) as well as a Nanotube Arc Discharge Experiment (NADE) with the purpose of investigating plasma-nanoparticle interaction. The NADE studies the ability to control the diameter and length of nanotube formation through a set of experimental parameters. In addition, the potential to increase nanotube length will be studied. PPPL's expertise on plasma science could be critically valuable to the successful development of highly efficient and low cost plasma-based techniques, which have the potential to increase accessibility of nanotubes, and propel further innovation rooted in nanotechnology. [Preview Abstract] |
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JP9.00017: Study of Sheath Potential and Plasma Density Profiles in the Presence of Strong Secondary Electron Emission from Walls Huy-Sinh Trung, Igor Kaganovich, Alexander Khrabrov We study the behavior of plasmas confined within walls, which emit secondary electrons. A set of fluid equations for ions, the Vlasov equation for electrons, and Poisson's equation are solved together numerically to obtain potential and density distributions. We explore the transition to the space charge limited regime in the sheath. The potential and density profiles are monotonic if the emission coefficient is set below the critical emission coefficient. Above the critical emission coefficient, the profiles become non monotonic. We recover the results obtained by Hobbs \& Wesson [1] and compare them to the full-scale simulation results of a particle-in-cell code, EDIPIC.\\[4pt] [1] G. D. Hobbs and J. A. Wesson, $Plasma$ $Phys.$, 9:85--87, 1967. [Preview Abstract] |
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JP9.00018: Langmuir probe measurements on the Lithium Tokamak eXperiment (LTX) Albert Ryou, Michael Jaworski, Richard Majeski LTX aims to enhance plasma energy confinement time by coating the plasma-facing surfaces of the tokamak with liquid lithium, which reduces the recycling of hot plasma particles into cold gas at the edge of the tokamak. A diagnostic single-tip Langmuir probe, along with the electronic circuit for signal analysis, was designed and constructed to determine the IV characteristic, from which the edge parameters, namely, the electron density, temperature, and the saturation currents will be calculated. A 1 mm diameter cylindrical tungsten electrode with two independent coaxial ground shields of stainless steel, separated by alumina tubing, will be inserted into the LTX plasma. A bellows-sealed linear motion feedthrough, mounted at the outer midplane of the device, is used to position the probe. The probe tip will be inserted into the scrape-off layer plasma beyond the last closed flux surface. A model based on the conventional Langmuir probe theory was developed to find the parameters, and the results will be compared to those determined from other diagnostic techniques such as Thomson scattering. [Preview Abstract] |
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JP9.00019: Convective Stirring in Liquid Lithium (LTX) Margaret Cassin, Eugene Kearns, Richard Majeski LTX is a spherical tokamak with R=0.4 m, a=0.26 m, and elongation=1.5. LTX has a heated (300 -- 400 C) liner, designed to be coated with lithium. During experiments in 2010, oxidation of the lithium surface was observed when the liner was heated to 300 C, above the melting point of lithium (182 C). A pumping system is being installed to absorb and pump background gasses which react with lithium, similar to a getter pump, using liquid and solid lithium. Lithium will be loaded into a yttria crucible heated from below by a small, HeatWave model TB175 300W cartridge heater to produce convective currents in order to maintain a clean lithium surface and decrease the time for oxide formation. This system was tested in an argon glove box using a copper heat concentrator -- instead of the HeatWave vacuum-compatible unit. Infrared thermometry and thermocouples were used to monitor the surface temperature of the molten lithium, and convective flow patterns. A 200 FPS high speed camera was also employed to monitor flows, using the motion of residual oxide patches. Results from the measurements will be presented. [Preview Abstract] |
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JP9.00020: Breaking the Four-Fold Symmetry in the Paul Trap Simulator Experiment S. Koppell, H. Wang, R.C. Davidson, E.P. Gilson, P.C. Efthimion, R. Majeski, E.A. Startsev The Paul Trap Simulator Experiment (PTSX) is a cylindrical Paul trap used to study transverse beam dynamics for propagation over many lattice periods. Previous experiments have studied the effect of various symmetric perturbations on beam properties. An additional arbitrary function generator was added to the system to generate asymmetric fields. Dipole field components were used to excite and identify collective modes of excitation in the beam. In agreement with expectations, mode excitation by a dipole field was found to efficiently excite a different set of modes than those excited by perturbations with quadrupolar spatial symmetry. Asymmetric fields were also used to study beam response to lattice errors. It is demonstrated that lattice errors due to finite mechanical tolerance in a series of quadrupole magnets will manifest itself primarily as the superposition of an oscillating constant voltage offset, and a dipole field. It has been shown that the presence of an oscillating voltage offset in the trap does not affect the dynamics of the plasma. The magnitude of dipole noise is related to the rate of emittance growth and particle loss. [Preview Abstract] |
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JP9.00021: Effects of External Driving on Magnetic Reconnection in MRX N. Kosar, S. Dorfman, E. Lawrence, H. Ji, M. Yamada, J. Yoo, C. Myers, T. Tharp In the Magnetic Reconnection Experiment (MRX), two sets of windings, known as flux cores are used to create plasma and force reconnection. One active topic of research is the relationship between the external forcing and the local physics at the reconnection point. The rate at which the flux core current changes is defined as the ``drive time'' of the experiment. In 2-D simulations of MRX [1] and in previous MRX experiments, it was found that the electric field at the reconnection point scales linearly with the external forcing up to a point, but when the drive is too fast, the scaling saturates. While this scaling may be expressed in dimensionless parameters for the simulation, producing a comparable normalization for the experiment has proved difficult, possibly due to the effect of initial conditions. A new experimental scheme has been designed to produce a range of drives by changing the slope of the current waveform at a single breakpoint, resulting in uniform initial conditions. Results from the new setup will be presented. This work was supported by DOE, NASA, and NSF.\\[4pt] [1] Dorfman, et al, Phys. Plasmas 15, 102107 (2008). [Preview Abstract] |
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JP9.00022: Measurement of ion velocity profiles in a magnetic reconnection layer via current sheet jogging G. Stein, J. Yoo, M. Yamada, H. Ji, S. Dorfman, E. Lawrence, C. Myers, T. Tharp In many laboratory plasmas, constructing stationary Langmuir and Mach probe arrays with resolution on the order of electron skin depth is technically difficult, and can introduce significant plasma perturbations. However, complete two- dimensional profiles of plasma density, electron temperature, and ion flow are important for studying the transfer of energy from magnetic fields to particles during magnetic reconnection. Through the use of extra ``Shaping Field'' coils in the Magnetic Reconnection Experiment (MRX) at the Princeton Plasma Physics Laboratory, the inward motion of the current sheet in the reconnection layer can be accelerated, or ``jogged,'' allowing the measurement of different points across the sheet with stationary probes. By acquiring data from Langmuir probes and Mach probes at different locations in the MRX with respect to the current sheet center, profiles of electron density and temperature and a vector plot of two-dimensional ion velocity in the plane of reconnection are created. Results from probe measurements will be presented and compared to profiles generated from computer simulation. [Preview Abstract] |
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JP9.00023: Analysis of emissive probe techniques for measurements of plasma potential Daniel Edward Ruiz, Martin Griswold, Yevgeny Raitses We compare the accuracy of several emissive probe techniques for measurements of the plasma potential, including various inflection point methods, saturated floating potential, and separation point. Uncertainties due to voltage drop across the hot filament wire, space-charge effects, secondary electron emission (SEE) and orbital motion effects are studied both theoretically and experimentally. In particular, it is shown that the probe dc heating can cause a non-uniform electron emission and collection across the filament wire. This can reduce the accuracy of probe measurements. [Preview Abstract] |
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JP9.00024: Studying Angular Momentum Transport in Discs Using a Rotating Gas Experiment Kyle Kremer, Hantao Ji The physics of the accretion process in astrophysical discs surrounding bodies such as black holes and protostars is not well-understoood. Specifically, the cause of the turbulent outflux of angular momentum necessary for accretion to occur remains a mystery. It is suspected magnetohydrodynamic (MHD) instabilities may be responsible for the turbulence in magnetized discs. The magnetorotational instability (MRI), in particular, has received acceptance as a viable accretion mechanism, but direct evidence of the MRI has yet to be realized observationally or experimentally. Experimentalists have recently used rotating liquid metals, which can be described using resistive MHD, to study the MRI. However, this approximation is limited because effects beyond resistive MHD are likely important in real astrophysical discs. Namely, kinetic effects and the Hall effect are not accounted for by liquid metal experiments. In order to achieve a better representation of a realistic accretion disc, we propose an experiment using rotating gas. The experimental set-up is explained and preliminary rotational profile results are presented. This experiment will help shed light on how the MRI behaves under departures from MHD which are present in a rotating gaseous disc. [Preview Abstract] |
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JP9.00025: Characterization of large-scale velocity fluctuations in the Princeton MRI experiment W. Love, A. Roach, E. Spence, H. Ji The Princeton MRI Experiment is a modified Taylor-Couette device that uses GaInSn as its working fluid. An Ultrasonic Doppler Velocimetry (UDV) system allows the measurement of internal fluid velocities. Starting from both hydrodynamically stable and unstable background flow states, prior work has demonstrated the existence of large-scale, large-amplitude, coherent, nonaxisymmetric velocity fluctuations when a sufficiently strong magnetic field is applied. Characterizations of these oscillations are made by looking at the dominant fluctuations in the azimuthal and radial velocity field components and matching these features to different model velocity profiles. These profiles are calculated by starting with a model azimuthal flow and calculating the resultant radial flow, assuming no vertical dependence. The relative magnitudes of the calculated azimuthal and radial flows are compared to experimental UDV data to determine the validity of the vertical symmetry assumption. Additional calculated properties such as the Reynolds stress, current distributions, and final velocity profiles will be presented. [Preview Abstract] |
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JP9.00026: ABSTRACT WITHDRAWN |
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JP9.00027: Compact Spectrometer Array Spectra Analysis and Data Storage for the National Spherical Torus Experiment Rose Soskind, Adam McLean The Compact Spectrometer Array (CSA) is a set of several high-speed Ocean Optics HR2000+ spectrometers which has recently been installed in the National Spherical Torus Experiment (NSTX) at the Princeton Plasma Physics Laboratory (PPPL). Spectral data from each instrument spans the 380 -- 590 nm region with 0.1 nm pixel resolution and 0.4 nm optical resolution. Three available chords exist in the machine view: a) an ATJ graphite tile in the inner divertor, b) a Molybdenum tile in the inner divertor, and c) the inside portion of a Liquid Lithium Divertor (LLD) plate in the outer divertor, each with a 2.5 cm diameter spot size. All views include absolute intensity calibration for measurement of spectral radiance. Data from the CSA were stored in the MDSplus database system via a C++-based interface. Spectra from the CSA have been captured so far through the 2011/2012 NSTX campaign to reveal trends in integrated emissions and emission ratios with increasing surface exposure in the divertor and incremental use of lithium for wall conditioning. [Preview Abstract] |
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JP9.00028: Magnetohydrodynamic Vortex Behavior in Free-Surface Channel Flow J. Kubricht, J. Rhoads, E. Spence, H. Ji Flowing liquid plasma-facing systems have been proposed for fusion devices due to their structural consistency and capability to withstand enormous heat fluxes. In support of these designs, the effects of magnetic field on the thermal mixing of conductive fluids need to be studied and understood. The Princeton Liquid Metal Experiment (LMX) consists of a free-surface, externally driven channel flow subjected to a strong vertical magnetic field. LMX uses an infrared camera and non-intrusive heat signatures to visually study the vortex street of a vertical cylinder while an array of potential probes has been installed to map the velocity profile for varying magnetic field strengths. Our studies show a decrease in surface activity with increasing field strength as well as distinct changes in vortex behavior. Velocity distributions across the channel are compared with infrared observations and the relationship between Strouhal number and magnetic field strength is examined. [Preview Abstract] |
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JP9.00029: Particle-In-Cell Simulation of Ion Beam Neutralization by a Tenuous Background Plasma William Berdanier, Gennady Shvets, Igor Kaganovich The neutralization and focusing of intense charged particle beam pulses by electrons forms the basis for a wide range of applications for accelerators, heavy ion fusion, and astrophysics. For intense ion beam pulses, a background plasma can be used to effectively neutralize the beam charge and current, thereby neutralizing the self-fields. We show that even a tenuous background plasma with a small relative density can achieve high neutralization. Using the Large Scale Plasma (LSP) particle-in-cell code, the interaction of an intense ion beam with an underdense plasma was simulated. It was shown that if the total plasma electron charge is comparable to the beam charge, electron emitters are necessary for effective neutralization. These are not needed if the plasma volume is large. A variety of plasma densities was investigated, including the case of emitters without plasma, which did not effectively neutralize the beam. Over 95{\%} neutralization was found for even very tenuous background plasma, in agreement with earlier analytical studies. [Preview Abstract] |
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JP9.00030: Diagnostic System for Identifying High Energy Prompt Gamma Rays in a Fusion Device Aaron Fancher, Charles Gentile A diagnostic system is being developed for the capture and identification of high energy prompt gamma ray spectra in a fusion device. Gamma ray spectrometry for a pulsed device enables the observation of many gamma producing phenomena that occur during fusion shots with the potential to observe prompt gamma profiles, reaction rates, or particle interactions to name a few. A preliminary design was created for the National Spherical Torus Experiment, NSTX, consisting of scintillation type detectors placed near the neutral beam injector, NBI, port and linked to a data acquisition system. This diagnostic was used to collect and analyze prompt emission spectra originating from a deuterium plasma during a series of fusion shots. Focus was placed on the monitoring and identification of prompt gamma spectra near the NBI region which previously had been unobserved. Results will be presented. [Preview Abstract] |
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JP9.00031: GPU-Accelerated Full-Wave Calculations for Microwave and Millimeter-Wave Diagnostics on NSTX T.A. Bechtel, S. Kubota, W.A. Peebles, W. Guttenfelder GPGPU (General-Purpose computing on Graphics Processing Units) has been gaining popularity in many engineering and science fields as an inexpensive platform for accelerating compute- intensive codes. Similar applications have seen order-of- magnitude increases in speed through GPGPU. Here we report on a 1-D finite-difference time-domain Maxwell code ported to utilize the massively parallel processing capabilities of the NVIDIA C1060 GPU. The C for CUDA (Compute Unified Device Architecture) extension of the C programming language was used. Detailed benchmarking between the GPU code and a version running on traditional multicore processors will be presented. The code will be utilized as a synthetic diagnostic for Frequency-Modulated Continuous-Wave reflectometry and backscattering, as well as radial polarimetry on NSTX (National Spherical Torus eXperiment). The response of these diagnostics to turbulence from gyrokinetic simulations will be explored. [Preview Abstract] |
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JP9.00032: A post-processor for analyzing and visualizing results from the SPIRAL code Parag Srivastava, Eliot Feibush, Gerrit Kramer The full-orbit following code SPIRAL can calculate the effects of magnetic ripple fields, MHD activity, and ICRF fields on the confinement of fast ions in Tokamaks. The confinement of fast ions is very important for fusion plasmas because they heat the plasma when they slow down. With the SPIRAL code sets of data are generated for a large number of test particles. In order to extract useful information on the behavior of ensembles of those test particles a user-friendly graphical user interface (GUI) was developed. With this GUI the data can be visualized in different spaces, and changes in the particle populations due to MHD activity, ICRF waves, and ripple fields can be studied effectively. In this presentation simulations from the National Spherical Torus Experiment (NSTX) where finite Lamor radius effects are significant because of its low toroidal field, are presented to illustrate the capabilities of the GUI. The interface is based on the Java Native Interface (JNI) and is interfaced with a number of C routines for reading and processing the data that is generated by the SPIRAL code. [Preview Abstract] |
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JP9.00033: Development of Polarization Rotator for the Motional Stark Effect with Laser-Induced Fluorescence Diagnostic J.E. Zelenty, E.L. Foley The motional Stark effect with laser-induced florescence (MSE-LIF) diagnostic is currently being installed on NSTX at PPPL. The MSE-LIF diagnostic will be responsible for measuring the magnetic field magnitude and pitch angle in the low magnetic field regime of NSTX. The method used for MSE-LIF is based on the observation of the laser-induced florescence of the Balmer-alpha transitions in hydrogen from a diagnostic neutral beam. As the neutral beam passes through the magnetic field, B, with a high velocity, v, the hydrogen atoms experience an electric field in their rest frame, E = v x B. This electric field causes a splitting and polarization of the H-alpha emission. Using the polarization orientation of this emission, the magnetic field pitch angle can be determined. This orientation can be resolved by polarizing the laser light responsible for exciting the hydrogen atoms via a polarization rotator. In this investigation, a polarization rotator for the MSE-LIF laser is designed, built, and tested. The results will be presented and discussed. [Preview Abstract] |
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JP9.00034: The dependence of the H-mode pedestal height and width on plasma current Mordecai Segall, R. Maingi, T.K. Gray, T. Osborne The H-mode pedestal in divertor tokamaks is subject to periodic peeling and ballooning instabilities (Edge-Localized Modes, or ELMs) which discharge up to 20\% of the total plasma energy into the scrape off layer and the divertor in a matter of milliseconds. Controlling the density, temperature, and pressure profiles in the pedestal is essential to preventing these potentially disastrous ELMs in tokamaks such as ITER. It is already known that some pedestal profiles are stable to ELMs while some are not. We use a kinetic equilibrium fitting algorithm to map multiple pedestal profiles from Thomson scattering and charge exchange and recombination spectroscopy (CHERS) data and create a set of composite profiles for NSTX. We fit these edge profiles to a (standard) modified hyperbolic tangent functional form. We plot the resulting pedestal fit parameters against plasma current, which is known to affect global discharge characteristics and pedestal profiles. We compare the dependencies of the pedestal height and also the global stored energy on plasma current [Preview Abstract] |
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JP9.00035: Measurement of kHz scale oscillations of the magnetic field inside Tokamak plasmas using the Motional Stark Effect diagnostic L.W. Clark, E.L. Foley The Motional Stark Effect (MSE) diagnostic has become the standard for making internally resolved measurements of the magnetic field pitch angle profile in plasmas. However, ordinary MSE analysis cannot incorporate many important phenomena, including some Magnetohydrodynamic instabilities and turbulence, which can cause oscillations in the pitch angle with frequencies in the range of 1 to 100 kHz. In order to measure such fluctuations using MSE, one must isolate the light intensity signals at the frequencies of beats between the magnetic field fluctuations and the photoelastic modulators used during signal collection. We are writing and optimizing a software package to obtain those signals from MSE measurements. We will apply the complete analysis package to data collected at the National Spherical Torus Experiment. Results will be presented. [Preview Abstract] |
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JP9.00036: Reducing the Spikes of Avalanche Photodiode Measurements at the National Spherical Torus Experiment Z.E. Brubaker, E.L. Foley Avalanche Photodiodes (APD) used at the National Spherical Torus Experiment (NSTX) make important measurements for the Motional Stark Effect (MSE) diagnostic. However, they are very sensitive, and if radiation consistently reaches these detectors they are damaged over time. Furthermore, they also display spikes in their readings, which greatly complicates the data analysis for MSE. Due to our Collisionally-Induced Fluorescence Motional Stark Effect diagnostic observing significant radiation despite being shielded by a 3 foot concrete wall, we must devise a plan for shielding our new Laser-Induced Fluorescence Motional Stark Effect diagnostic, as well as determining the best possible location for them. In order to reduce the amount of spikes seen in our readings and to preserve our detectors, I investigated the type of radiation responsible, the locations most affected, and tested various materials for shielding. Results will be presented. [Preview Abstract] |
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JP9.00037: Emission Spectroscopy of RF Helicon Heated Plasmas T.R. Younkin, T.M. Biewer, R.H. Goulding, D.L. Hillis, R. Isler In order to study plasma-material interfaces under high power and particle flux, large linear machines are being constructed that can effectively simulate conditions that will be found in fusion-grade toroidal devices such as ITER and DEMO. A 15 cm diameter, 1.5 m long linear machine has been built at ORNL using a new helicon antenna designed for input powers up to 100 kW, producing a plasma that will be used to bombard material targets. Visible spectroscopy has been used to measure emission line spectra of the helicon heated plasma from 200 nm to 1100 nm at low resolution. The spectrometer is thoroughly calibrated for wavelength and intensity in order to determine electron density and temperature using the ratios of spectral line intensities. A variety of gas species have been heated, including hydrogen, deuterium and helium. Residual amounts of foreign materials can be monitored near the plasma-wall interface. Results on how magnetic field scans, probe scans, and power scans affect the plasma will be analyzed and presented. [Preview Abstract] |
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JP9.00038: Simulation of Shear Alfv\'{e}n Waves in LAPD using the BOUT++ code Di Wei, B. Friedman, T.A. Carter, M.V. Umansky The linear and nonlinear physics of shear Alfv\'{e}n waves is investigated using the 3D Braginskii fluid code BOUT++. The code has been verified against analytical calculations for the dispersion of kinetic and inertial Alfv\'{e}n waves. Various mechanisms for forcing Alfv\'{e}n waves in the code are explored, including introducing localized current sources similar to physical antennas used in experiments. Using this foundation, the code is used to model nonlinear interactions among shear Alfv\'{e}n waves in a cylindrical magnetized plasma, such as that found in the Large Plasma Device (LAPD) at UCLA. In the future this investigation will allow for examination of the nonlinear interactions between shear Alfv\'{e}n waves in both laboratory and space plasmas in order to compare to predictions of MHD turbulence. [Preview Abstract] |
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JP9.00039: Studies of Turbulence and Flow in Magnetized Plasma Using Visible Light Imaging Daniel Guice, David Schaffner, Troy Carter, Giovanni Rossi, Steve Vincena Studies of phenomena like turbulence and flow have traditionally been performed by probes in the Large Plasma Device (LAPD) at UCLA. In this work a fast framing camera was used to image the fluctuations in visible light emissions. The camera was placed at one end of the LAPD and aimed through a window at a Langmuir probe in the plasma. The signals from a single pixel and the Langmuir probe were compared showing high correlation. While a probe can only study one spatial location at a time, the camera is able to capture two-dimensional information in a single time series giving a wealth of information and enabling a noninvasive study of the plasma. The camera data has been used to measure flow using time delay estimation and to calculate k-spectra of turbulent fluctuations. [Preview Abstract] |
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JP9.00040: Ramifications of driven spontaneous flow and turbulent transport on cross-correlation functions in the Large Plasma Device Giovanni Rossi, David Schaffner, Troy Carter, Danny Guice Spontaneous edge transport barriers that reduce cross-field turbulent transport are observed in the Large Plasma Device (LAPD) at UCLA. In this experiment, recently installed limiter plates form a collimating circle, which when biased relative to the plasma source cathode, drive azimuthal flow at the edge of these limiters and the plasma. These azimuthally symmetric E$\times$B shear flows, thought to be zonal flows, have an associated shear decorrelation mechanism and localized, nonuniform radial electric field, giving them the potential to improve confinement. With increasing bias', the radial electric field is able to penetrate further until there is a sudden steepening of the the density profile, lending forth to an increase in radial particle confinement similar to that of an L-H mode transition found in toroidal fusion devices. Through varying bias' and plasma parameters, we are able to observe the effects of turbulent transport and spontaneous driven flows on two-dimensional cross-correlation measurements. Using these investigations we compare the results from cross-correlation planes against traditional flow generation theories to determine the meaning of energy transfer for reducing turbulent transport, such as via elongation and tilting of embedded eddies due to zonal-flow vorticity. [Preview Abstract] |
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JP9.00041: CRDS Measurements of Velocity Distributions in a Helicon Plasma Source Robert VanDervort, Dustin McCarren, Jerry Carr Jr., Saikat Chakraborty Thakur, Matthew Galante, Amy Keesee, Greg Lusk, Richard Magee, Earl Scime, Eric Reynolds, Stephanie Sears Laser induced fluorescence (LIF) is routinely used to measure velocity distribution functions (VDFs) of argon ions, argon neutrals, helium neutrals and xenon ions. However, for some target species and plasma conditions, LIF lacks sufficient sensitivity. Cavity ring down spectroscopy (CRDS) is an ultra-sensitive, cavity enhanced, absorption spectroscopy technique. Combined with a tunable, continuous wave (CW), narrow line width, diode laser, CW-CRDS becomes an alternative technique to measure VDFs. Recently, we demonstrated the first CW-CRDS measurements of the VDF of argon ions in a helicon plasma source. Here we present CW-CRDS measurements of the VDFs of argon ions and argon neutrals using an upgraded version of the CW-CRDS diagnostic. The new apparatus includes a high-speed, 16-bit digitizer, improved electronics, and gas curtains for protection of the high-reflectivity mirrors. Here we present our VDF measurements in the completely rebuilt CHEWIE helicon plasma source as a function of source parameters as well as the details of the electronics design and testing. [Preview Abstract] |
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JP9.00042: Measurement of Neutrons Produced by Beam-Target Interactions via a Coaxial Plasma Accelerator Scott Cauble, Flavio Poehlmann, Gregory Rieker, Mark Cappelli This poster presents a method to measure neutron yield from a coaxial plasma accelerator. Stored electrical energies between 1 and 19 kJ are discharged within a few microseconds across the electrodes of the coaxial gun, accelerating deuterium gas samples to plasma beam energies well beyond the keV energy range. The focus of this study is to examine the interaction of the plasma beam with a deuterated target by designing and fabricating a detector to measure neutron yield. Given the strong electromagnetic pulse associated with our accelerator, indirect measurement of neutrons via threshold-dependent nuclear activation serves as both a reliable and definitive indicator of high-energy particles for our application. Upon bombardment with neutrons, discs or stacks of metal foils placed near the deuterated target undergo nuclear activation reactions, yielding gamma-emitting isotopes whose decay is measured by a scintillation detector system. By collecting gamma ray spectra over time and considering nuclear cross sections, the magnitude of the original neutron pulse is inferred. [Preview Abstract] |
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JP9.00043: Magnetic Field Structure in the Madison Dynamo Experiment A.M. Rasmus, M. Clark, E.J. Kaplan, M.D. Nornberg, K. Rahbarnia, N.Z. Taylor, C.B. Forest The Madison Dynamo Experiment(MDE) is expected to spontaneously self-generate a magnetic field in a two vortex flow geometry driven by counter rotating impellers in a $1 m$ diameter sphere filled with liquid sodium. Prevoiusly an equatorial baffle was installed and has been demonstrated to reduce the largest scale turbulent-eddies. An additonal set of six rotatable baffles have been installed to optimize the helicity of the flow, lowering the critical magnetic Reynolds number. This poster will focus on the spatial structure of the magnetic field associated with the dynamo eigenmodes and the turbulent fluctuations. Singular value decomposition(SVD) and cross correlation analysis between the surface harmonics and internal probes will be used to determine the internal structure associated with each spherical harmonic. Spherical harmonic decomposition is of limited utility when analysing the equatorial array of internal probes as there is a limited angular spread (only one theta value and two phi values), whereas cross correlation and SVD allow the use of time domain data to infer internal modes excited via three-wave couplings. This work is supported by the NSF/DOE partnership in plasma physics. [Preview Abstract] |
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JP9.00044: Plasma Behavior in a Plasma Gun Jet Daniel Pulliam, Thomas Intrator, Colin Adams, Jason Sears, Thomas Weber Plasma guns will provide initial pre-ionized plasma for a field reversed configuration experiment (FRX-L). The development and testing of these guns is being carried out on the Reconnection Scaling experiment (RSX). Successful gun operation requires the ionized plasma leaving the guns to be maximized and the neutral gas particles surrounding each gun jet to be minimized. A fast ionization gauge (FIG) produced by Applied Pulsed Power, Inc. with a response time of $>$20 mTorr/$\mu$s will be used to measure the density of hydrogen plasma in the RSX in order to determine the shape of the plasma pulse and the speed of the particles. Additionally, the FIG will provide data to calculate the quantity of gas particles preceding the plasma jet and a Mach number of the plasma leaving the gun. An equation of state fluid model will be used for the system and to compare calculations with experimental data. [Preview Abstract] |
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JP9.00045: Measuring the Effect of a Transmission Photocathode on Microchannel Plate Quantum Efficiency Britney Blankenship, Donna Marion, Mariano Lowenstern, Eliseo Gamboa, Eric Harding, Carolyn Kuranz, R.P. Drake Microchannel plates (MCPs) are a vital component in imaging for a variety of high-energy-density experiments. To ensure the highest quality images, particularly in low-photon environments, it is desirable to maximize the quantum efficiency (QE) of the MCP. When secondary electrons are released from the MCP as a result of photons colliding with the inter-pore regions, these electrons do not contribute to the signal. One way to increase the QE is by redirecting these secondary electrons back toward the MCP. By applying a voltage to a 50nm titanium transmission photocathode (TPC) in front of the MCP, theoretically we will create an electric field that will accelerate the electrons back toward the MCP. This is a continuation of similar work done with a nickel mesh grid in place of a TPC. The results presented are the effect of the Ti TPC on the QE of the microchannel plate. [Preview Abstract] |
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JP9.00046: Comparison of radial measurements of ion velocity using Mach Probes, TDE and LIF in the linear magnetized device CSDX Ty Lee, Saikat Chakraborty Thakur, Min Xu, Peter Manz, Nicolas Fedorczak, Jonathan Yu, George Tynan, Dustin McCarren, Earl Scime Previous experimental studies carried out in the Controlled Shear Decorrelation Experiment (CSDX) plasma device demonstrated the existence of an azimuthally symmetric radially sheared plasma fluid flow (i.e., a zonal flow). These measurements were based on time delay estimation (TDE) between two spatially separated Langmuir probes and Mach probes. While TDE measurements cannot distinguish between ion fluid velocities and phase velocities, Mach probes are perturbative. Laser induced florescence (LIF) is a non-perturbative, spatially resolved diagnostic technique that, in CSDX, provides direct measurement of the velocity distribution function (VDFs) of argon ions. The bulk ion velocity and ion temperature are determined from fits to the measured VDFs. For the LIF measurements in these experiments, we used an amplified tunable diode laser at 668.6139 nm (vacuum wavelength), the wavelength required for a three-level LIF scheme in Ar II that begins with a metastable ion state. Here we report detailed comparisons of the radial profiles of azimuthal ion velocity in CSDX using all the three diagnostics. [Preview Abstract] |
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JP9.00047: Identifying and Correcting Potential Sources of Experimental Error in HBT-EP Diagnostic Equipment Daniel Woodman, LCDR Royce James, Michael Mauel, David Mauer, Jeffrey Levesque, Gerald Navratil, Nicholas Rivera Successful modeling and implementation of diagnostic and support equipment must be carefully considered in order to minimize external interferences and experimental error. Several approaches to minimize diagnostic errors have been implemented at the High Beta Tokamak-Extended Pulse (HBT-EP) including re-cabling diagnostics to reduce electromagnetic interference (EMI), updating the HBT-EP ignitron Spice model to ensure accurate pulsed-power simulations, and determining non-ideal parameters of a transformer component in a proposed bias-probe experiment. Progress on recabling using twisted-pair wire for sensors adjacent to the chamber to reduce EMI; the design of the new Spice ignitron to replace the 1990 legacy model; plus results of a quantitative frequency-dependence analysis of a three-phase, step-down transformer recapitalized as a one-phase, step-up transformer consisting of a series of cascaded windings; are among the efforts to reduce systematic error during HBT-EP operations, that will be reported. [Preview Abstract] |
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JP9.00048: Magnetic Structures in WIRX M. McMillan, C. Adams, M. Cartolano, D. Craig We have developed a set of magnetic field probes to track structural changes in the magnetic field in the Wheaton Impulsive Reconnection Experiment (WIRX) and to look for candidate magnetic reconnection sites. These probes complement several existing fast imaging diagnostics. It is found that the light emitted by the plasma correlates well with the spatial position of the current as deduced from the magnetic field measurements. Both emission and magnetic profiles vary with plasma current and vacuum coil field. In some plasma, we observe bursty, fast time scale events in both photodiode camera data and magnetic data. The propagation of these magnetic disturbances throughout the plasma has been studied using correlation techniques. Work is ongoing to assess whether these fast events may involve magnetic reconnection. Work supported by U.S.D.O.E. grant DE-FG02-08ER55002. [Preview Abstract] |
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JP9.00049: Emulating microwave-induced breakdown in air with trigatron spark gap B. Lenardo, C.A. Romero-Talamas, V.L. Granatstein, G.S. Nusinovich A spark gap and power supply have been constructed to emulate the duration and energy dissipation of air breakdown induced by a 670GHz gyrotron beam, a source that our group plans to use to explore remote detection of concealed radioactive materials. The spark gap is being used in calibration and testing of diagnostics, including atomic line spectroscopy, mass spectrometry, and microwave scattering. The power supply accepts a variable high voltage input up to 5 kV, stores energy in a 1.8 microfarad capacitor, and arcs across a gap of 1.34 mm. The gap is triggered by a AA-battery powered piezoelectric igniter available commercially (used in common gas grills). Preliminary results show that for a charging voltage of 3 kV, we are able to trigger a spark with energy 1.78 $\pm $ 0.23 Joules lasting approximately 2 microseconds, values which can be tuned by varying resistance and charging voltage of the discharge circuit. Our goal is to dissipate 3 Joules in 10 microseconds, which we expect to see in the gyrotron beam breakdown. [Preview Abstract] |
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JP9.00050: Comparison of Diagnostic Measurements on a Small Plasma Test Source Dakota Starkey, David Hwang, Robert Horton, Russ Evans, Ruth Klauser A simple pulsed plasma test source has been constructed to test different diagnostic methods, specifically laser deflection and spectroscopic measurements to assess plasma density. Previous laser deflection measurements have shown densities between 10$^{13-14}$ cm$^{-3}$. Optical fibers were also installed to view plasma light emission and were coupled with a spectrometer and a photomultiplier tube for increased sensitivity to small signals. The spectrometer was used as a monochromator to view time dependent aspects of a selected wavelength determined from previous spectroscopic data viewing the plasma across multiple wavelengths at a single time. This setup has the advantage of allowing deflection and spectroscopic data to be taken simultaneously at each plasma location. Comparison of the two types of time dependent measurements will be discussed. Furthermore, possible relations between the two density profiles will be explored. [Preview Abstract] |
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JP9.00051: Wave propagation in a strongly coupled magnetized plasma Alexi Reynolds, Hanno K\"ahlert, Michael Bonitz Strongly coupled plasmas play a growing role in many fields of physics---from dusty plasmas to compact stars and the quark-gluon plasma, e.g.~[1]. In many cases these plasmas are subject to a strong magnetic field. The one-component plasma (OCP) model is often used to theoretically analyze strong plasma correlations. Here the wave propagation in a strongly coupled OCP subject to an external magnetic field is investigated by means of the quasi- localized charge approximation~[2]. The dispersion relation and the wave polarization are studied for wave propagation across and along the magnetic field as well as for arbitrary directions of the wave vector. \\[1ex] [1] M. Bonitz, C. Henning and D. Block, Rep. Prog. Phys. \textbf {73}, 066501 (2010)\\[0ex] [2] G. Kalman and K. I. Golden, Phys. Rev. A \textbf{41}, 5516 (1990) [Preview Abstract] |
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JP9.00052: Particle-in-cell simulation of field-reversed configuration plasmas with odd-parity rotating magnetic fields Jeffrey Kollasch, Dale Welch, Samuel Cohen, Stephane Ethier Three-dimensional particle-in-cell (PIC) simulations using the Lsp code are being carried out in support of the Princeton Field-reversed Configuration (PFRC) experiment. This poster presents preliminary results using a new particle advancing algorithm currently under development at Voss Scientific, LLC called magnetic implicit (MI). Algorithm performance is compared with prior implicit and explicit particle pushers implemented in Lsp for both the PFRC and simpler test cases. Simulation results and their relevance to current and future FRC fusion research will be discussed. [Preview Abstract] |
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JP9.00053: Ray Splitting Model of O-X Mode Conversion Joshua Achiam, Andrew Richardson, Francesco Volpe Mode conversions (MCs) allow waves to be transmitted through evanescent layers and power to be deposited in (and diagnostic information to be extracted from) otherwise inaccessible regions in magnetized fusion plasmas. MCs can only be modeled by conventional ray tracing techniques if the incident ray is fully converted into an outgoing, transmitted ray and if the WKB approximation is fulfilled everywhere. However, in most experiments the conversion is partial; only some of the incident power is mode-converted. The WKB approximation also fails in the cases of resonances and cutoffs. An algorithm was recently developed which models the MC as the splitting of a single ray into a transmitted and reflected part. Continued testing of this algorithm was carried out by developing a module for the ART ray tracing code and simulating the O-X mode conversion, where an incoming ordinary mode ray splits into a reflected ordinary mode ray and a transmitted extraordinary mode ray. Computed conversion efficiencies were compared with analytical predictions. [Preview Abstract] |
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JP9.00054: Verification Studies for Multi-Fluid Plasma Algorithms with Applications to Fast MHD Physics Joe Becker, Ammar Hakim, John Loverich, Peter Stoltz In this paper we present a series of verification studies for finite volume algorithms in Nautilus, a numerical solver for fluid plasmas. Results include a set of typical Euler, Maxwell, MHD and Two-fluid benchmarks. In addition results and algorithms for a set of hyperbolic gauge cleaning schemes that can be applied to the MHD and Two-fluid systems using finite volume type methods will be presented. Finally we move onto applications in field reversed configuration (FRC) plasmas. [Preview Abstract] |
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JP9.00055: Fluctuation and turbulence studies in the SSX plasma wind tunnel K. Flanagan, T. Gray, M.R. Brown Fluctuations and turbulence in the SSX plasma wind tunnel are examined by means of two high resolution (16 positions at $0.46~cm$ spacing) radial magnetic probes and one lower resolution (19 positions at $4.8~cm$ spacing) axial probe. The SSX wind tunnel is a copper 10:1 flux conserver with dimensions $L\cong 1~m$ and $R=0.08~m$. Plasmas in this wind tunnel typically have densities on the order of $1-5 \times 10^{15}~cm^{-3}$ and flow speeds of $50~km/s$. Auto- and cross-correlation analysis of the axial probe data showed a spatial periodicity of $0.2~m$. Initial results from one of the radial probes shows a temporal periodicity in the spatial auto- correlation that is suspected to be indicative of azimuthal rotation. Comparisons between the two radial probes at different azimuthal locations are underway to explore the effect of this rotation on radial correlation measurements. In addition to magnetic turbulence studies, high frequency fluctuations are measured with a He-Ne interferometer and a four-filter soft x-ray detector which both have sampling rates of $100~MHz$. Preliminary results show fluctuations in the line averaged density at $1.5$, $15$, and $35~MHz$. [Preview Abstract] |
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JP9.00056: Radial Density Profile in the SSX Plasma Wind Tunnel using a Double Langmuir Probe D.L. Weinhold, K. Flanagan, T. Gray, M.R. Brown We present preliminary results from a moveable double Langmuir probe in the present plasma wind tunnel configuration of SSX. The probe is designed to measure radial profiles of electron density ($n_e$) and electron temperature ($T_e$) across the midplane with a $1~cm$ resolution. Line-averaged densities from He-Ne interferometry show densities of $1-5 \times 10^{15}~cm^{-3}$. In addition to mean values, we will also present electrostatic fluctuations and correlations with magnetic field measurements. The double Langmuir probe also measures local $T_e$. Line-averaged measurements from VUV spectroscopy indicate $T_e \sim 10~eV$. The Langmuir probe stalk diameter measures $6.5~mm$ and tip spacing is $1.1~mm$. The SSX plasma wind tunnel has dimensions $L\cong 1~m$ and $R=0.08~m$. Plasma flow speeds are $v\ge 50~km/s$. The cylindrical copper boundary and probe surfaces are baked and cleaned in a $He$ glow discharge to maintain excellent vacuum and surface conditions. Electrostatic measurements during merging will be presented if available. [Preview Abstract] |
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JP9.00057: Collision Models for Particle Orbit Code on SSX M.W. Fisher, D. Dandurand, T. Gray, M.R. Brown, V.S. Lukin Coulomb collision models are being developed and incorporated into the Hamiltonian particle pushing code (PPC) for applications to the Swarthmore Spheromak eXperiment (SSX). A Monte Carlo model based on that of Takizuka and Abe [JCP {\bf 25}, 205 (1977)] performs binary collisions between test particles and thermal plasma field particles randomly drawn from a stationary Maxwellian distribution. A field-based electrostatic fluctuation model scatters particles from a spatially uniform random distribution of positive and negative spherical potentials generated throughout the plasma volume. The number, radii, and amplitude of these potentials are chosen to mimic the correct particle diffusion statistics without the use of random particle draws or collision frequencies. An electromagnetic fluctuating field model will be presented, if available. These numerical collision models will be benchmarked against known analytical solutions, including beam diffusion rates and Spitzer resistivity, as well as each other. The resulting collisional particle orbit models will be used to simulate particle collection with electrostatic probes in the SSX wind tunnel, as well as particle confinement in typical SSX fields. [Preview Abstract] |
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JP9.00058: Tuning and testing a one-dimensional transport model L. Jones, A.S. Ware, D. Brugger, M. Gilmore, E. Schuster Modeling of transport and flow generation in a linear plasma device using a 1-D transport code is presented. Drift wave turbulence models have been analyzed to derive models for the growth rate and nonlinear saturation mechanism used in the transport model. The model has also been modified to include a cold-ion option and to explore different Reynolds stress parameterizations. We present comparisons with density and density fluctuation profiles from HELCAT experiments. The use of biased concentric rings as control elements for the radial electric field profile in HELCAT is also modeled in the transport code. By varying the bias voltages, the local {\bf E}$\times${\bf B} flow can be modified. By varying the momentum sources a sheared radial electric field can be generated that suppress turbulent particle and heat transport. The impact of biasing, axial flow and plasma boundary conditions are investigated. [Preview Abstract] |
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JP9.00059: Quasi-symmetry in a torsatron device F. Bunt, A.S. Ware Initial exploration of an optimization of quasi-symmetric magnetic configurations using torsatron coils is presented. Quasi-symmetry of the magnetic field strength in flux coordinates can result in three- dimensional magnetic confinement devices achieving confinement comparable to axisymmetric configurations. Previous optimization of quasi-symmetric configurations have been done using modular coils, including the designs of the currently operating HSX stellarator and the W7-X stellarator which is under construction. In this work, different classes of quasi-symmetric configurations are examined using parameterized torsatron coils as the basis of the optimization. This is a numerical investigation in which equilibria are optimized for different quasi-symmetries, number of helical coils, and number of field periods, but with other parameters such as average field strength, major radius, and aspect ratio, equivalent across the configurations. Equilibrium and stability characteristics will be compared across the configurations. [Preview Abstract] |
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JP9.00060: Transforming between Boozer and VMEC coordinates K. Lennard, A.S. Ware, S.P. Hirshman A method of transforming between straight-field line Boozer coordinates and Fourier- optimized VMEC coordinates is discussed. A number of numerical codes exist that transform from VMEC (or cylindrical) coordinates to Boozer coordinates. Optimizations of stellarator configurations often target properties of the configuration in Boozer coordinates but the optimization are performed in VMEC coordinates. Each configuration must be transformed to Boozer coordinates to calculate the target quantities (e.g., quasi-symmetry). In this work we provide one such transformation method and develop an inverse method to transform from Boozer coordinates back to VMEC coordinates. This technique would allow possible future optimizations to be performed directly in Boozer coordinates with a transformation back to VMEC coordinates only after the optimization is complete. [Preview Abstract] |
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JP9.00061: Experimentally validating numerical codes describing non-neutral plasmas Jordan K. Davis, Grant W. Hart, Bryan G. Peterson There are several numerical codes commonly used to describe non-neutral plasmas. These include an equilibrium code, EQUILSOR, and a 2D PIC code, RATTLE. As with all computations, they have assumptions about the relevant physics to include. We are attempting to determine the region of validity of these codes by carefully comparing their output with experimentally measured quantities. We will be measuring the density profile, temperature profile, and Trivelpiece-Gould modes of oscillation, along with the diocotron frequency and compare the spectra produced by the codes to those measured experimentally. [Preview Abstract] |
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JP9.00062: Azimuthally Symmetric Radial Resonance near the Cyclotron Frequency in a Non-Neutral Ion Plasma William Hall, Bryan Peterson An experiment designed to measure radial m=0 plasma resonances near the cyclotron frequency in a boron ion plasma will be described. Plasmas are captured in a Malmberg-Penning trap with an axially symmetric magnetic field of nominally .22 Tesla. Captured plasmas generally measure 6-8 centimeters along the axis with 2 centimeter radii. Modes are exited through small AC perturbations on the confinement rings. Due to the short length of the plasma, the modes can be measured utilizing finite length effects of short cylindrical plasmas. The current status of the experiment will be discussed. [Preview Abstract] |
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JP9.00063: IViPP: A Tool for Visualization in Particle Physics Hieu Tran, Elizabeth Skiba, Doug Baldwin Experiments and simulations in physics generate a lot of data; visualization is helpful to prepare that data for analysis. IViPP (Interactive Visualizations in Particle Physics) is an interactive computer program that visualizes results of particle physics simulations or experiments. IViPP can handle data from different simulators, such as SRIM or MCNP. It can display relevant geometry and measured scalar data; it can do simple selection from the visualized data. In order to be an effective visualization tool, IViPP must have a software architecture that can flexibly adapt to new data sources and display styles. It must be able to display complicated geometry and measured data with a high dynamic range. We therefore organize it in a highly modular structure, we develop libraries to describe geometry algorithmically, use rendering algorithms running on the powerful GPU to display 3-D geometry at interactive rates, and we represent scalar values in a visual form of scientific notation that shows both mantissa and exponent. [Preview Abstract] |
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JP9.00064: Performance Characterization of RaPToRS Systems K. Shibata, M. Krieger, J. Fallica, R. Henchen, E. Pogozelski, S. Padalino The Rapid Pneumatic Transport of Radioactive Samples (RaPToRS) system can quickly and efficiently move radioactive materials from their activation site to a counting station. Facilities such as the NIF and LLE are considering these systems while NRL is currently using one. The system is essentially a 10 cm diameter pneumatic tube with a cylindrical sample carrier. The performance of the system depends on many factors, including the mass of the carrier, length of the tube, angle and difference in height of the tube's endpoints, the carrier's physical design, and the number, type, and distribution of blowers attached to the tube. These factors have been systematically examined to develop the fastest and most reliable system. The most significant factors are the mass and the vertical travel of the carrier. When the carrier mass is low, moving air supports the carrier in the tube, resulting in low friction. The terminal velocity ranges from 13.5 to 2.5 m/s for masses varying from 1 kg to 3 kg. Using a single 1100 W blower, the initial force exerted on the carrier was 11.3 N. [Preview Abstract] |
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JP9.00065: A Retrieval System for Radioactive Target Materials at the NIF M. Krieger, K. Shibata, J. Fallica, R. Henchen, E. Pogozelski, S. Padalino, T.C. Sangster Currently, solid radioactive material collection from the NIF target chamber is performed via the DIM. The retrieval process takes several hours to complete. To decrease this time for short lived radioisotopes, the Target Materials Retrieval System (TMRS) is being designed to move a radioactive sample from the target chamber to the counting station in less than 50 seconds, using a closed-loop helium filled RaPToRS system. The TMRS consists of three components: the retrieval apparatus, RaPToRS and the counting station. Starting at 0.5 meters from TCC, the sample will move from the vacuum chamber, travel through 60 meters of 10 centimeter diameter RaPToRS tubes, reaching speeds of 10 m/s. The sample will then arrive at the counting station, where it be robotically placed in front of a gamma ray detector. The use of helium will decrease background gamma radiation produced by activated N2 normally found in a pressurized air system. [Preview Abstract] |
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JP9.00066: Upgrades to a Table-top System for Characterizing ICF Charged Particle Detectors Hannah Miller, Kristina Punzi, John Dermigny, Kurt Fletcher, Stephen Padalino, T. Craig Sangster A simple, high-current system has been assembled to test and calibrate charged particle detectors for ICF. A duoplasmatron ion source system produces 0-30 keV deuterons that are focused by an einzel lens and strike a deuterated polyethylene target, initiating the $^{2}$H(d,p)$^{3}$H and $^{2}$H(d,n)$^{3}$He reactions. An upgrade of the system is underway to increase the count rate for the fusion products. The main challenge is the stability of the polymer target, which melts and disintegrates under bombardment by the intense (1 mA) beam. Using a thermocouple system to monitor the target temperature, modifications to the water-cooled target mount and different target designs have been studied. In addition, a Wien filter has been installed downstream of the einzel lens to ensure that the ion beam is well characterized. The deflection of the individual electric and magnetic fields of the Wien filter have been measured and compared to calculated values. [Preview Abstract] |
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JP9.00067: Calibration of the response of radiochromic film to monoenergetic ion beams from a 1.7 MV Pelletron accelerator C.R. Stillman, K.R. Crompton, M.J. Schepis, C.G. Freeman, S.J. Padalino, T.C. Sangster Radiochromic film (RCF) is used to study protons and other ions that are accelerated from the rear side of targets illuminated with ultra-intense laser light. An experiment is underway to characterize the response of RCF to protons, deuterons, and alpha particles of various energies using the 1.7 MV tandem Pelletron accelerator at SUNY Geneseo. A monoenergetic ion beam from the accelerator is incident on a thin ($\sim$0.1 $\mu$m) gold foil placed in the center of a 28-inch diameter scattering chamber. A strip of RCF is positioned in a circular arc that is centered on the gold foil. The ion beam strikes the gold foil, causing the RCF to be exposed to elastically backscattered ions. The scattered ion fluence on the RCF strip varies as a function of the scattering angle. After removal from the chamber, the RCF is scanned in transmission mode using an Epson 10000 XL flatbed scanner. The red channel of the resulting scan is used to determine the optical density of the film. The output from the flatbed scanner is cross calibrated with a precision microdensitometer (PDS). [Preview Abstract] |
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JP9.00068: 3D Magnetic Reconnection and Turbulence Study on Natural and Laboratory Plasmas at RSX D.T. Liu, T.P. Intrator, T.E. Weber, J.A. Sears, C.S. Adams In natural and laboratory plasmas, magnetic reconnection and turbulence are difficult 3-dimensional problems and data from the Reconnection Scaling Experiment (RSX) can help address these questions. The data from RSX are fully 3D (no symmetries)and capture the unsteady, dynamic plasma physics of colliding flux ropes that reconnect and form turbulent modes. Data obtained from RSX via B-dot and triple Langmuir probes will be used to determine the time-integrated magnetic field, plasma density, floating potential, and electrostatic field. Additionally, there exist related reconnection and turbulence data from spacecraft that must be downloaded and distilled from large, cumbersome datasets, a process hampered by low telemetry rates. Simulated spacecraft trajectories through the RSX datasets provide insight for data acquisition, analysis, and download aboard spacecraft missions. [Preview Abstract] |
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JP9.00069: An Intensified Photodiode Array for Characterizing Argon Plasma Jets on the Plasma Liner Experiment J.S. Davis, T.J. Awe, S.C. Hsu, A. Case The Plasma Liner Experiment (PLX) will merge 30 high Mach number plasma jets to form an imploding spherical plasma liner for high energy density physics and magneto-inertial fusion studies. The peak stagnation pressures achieved will be highly dependent on the implosion velocity of the liner, which is in turn dependent on the velocities of the merging plasma jets. For initial experiments characterizing single jet propagation, an array of three intensified photodiode (gain of roughly 25 dB and a spectral range of 350--1100 nm) will be used to measure the jet's velocity (up to 50 km/s) and acceleration (if any) as it travels from the chamber wall toward the center of a 9 ft.\ diameter spherical vacuum chamber. By adding filters to the photodiodes, it will be possible to correlate stages of jet evolution to specific argon emission lines, thus providing information on the state of the argon plasma as it propagates. Alignment and light collection are achieved via an aperture, lens, and fiber optic chain with the photodiodes themselves situated in an electromagnetically shielded ``screen cage.'' This poster will discuss the detailed design, setup, alignment, and initial experimental data of the photodiode array. [Preview Abstract] |
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JP9.00070: Visible Spectroscopy on the Plasma Liner Experiment (PLX) J.A. Schwartz, T.J. Awe, S.C. Hsu, E.C. Merritt, A.G. Lynn, M.A. Gilmore, S. Fuelling The Plasma Liner Experiment (PLX) will study the merging of thirty high Mach number jets of argon plasma in a spherically convergent configuration. Initial experiments will study single jet propagation, where it is important to measure the jet density, velocity, and temperature to evaluate jet evolution during its transit from the chamber wall toward the center. We have constructed a broad band visible light survey spectrometer to observe light emitted from the plasma jet in order to identify the best specific argon emission lines on which to perform Doppler and Stark broadening analysis. Special attention has been paid to maximize throughput because of low expected light levels. Light is collected by a lens coupled to a hexagonal bundle of seven 1 mm core diameter fibers. The fibers fan out to couple to the slit of a 14 cm focal length spectrometer which is observed by an intensified CCD camera. We discuss the design and assembly of this spectrometer system and (time permitting) initial data from single jet experiments. This work will inform the design of a high resolution spectroscopy system for future PLX experiments. [Preview Abstract] |
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JP9.00071: Oscillation Modes of a Relativistic Drifting Cold Plasma Michael Meyers, Chengkun Huang, B.J. Albright Examining the behavior of a drifting plasma could shed light on proposed computational gains of boosted frame simulations [1] and allow insight to electron-ion acceleration processes associated with ultra intense short pulse lasers [2]. The cold fluid approximation is a simple way to model such a drifting plasma, assuming zero thermal distribution. Electrostatic and electromagnetic dispersion relations have been obtained for the case of cold unmagnetized plasma and are checked for agreement with particle in cell (PIC) simulations. The roots obtained from the dispersion relations will be discussed and compared with the results found via a kinetic treatment. \\[4pt] [1] J.-L. Vay, Physical Review Letters 98, 130405 (2007). \\[0pt] [2] L. Yin et al., Physics Of Plasmas 14, 056706 (2007). [Preview Abstract] |
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JP9.00072: Portable rotating discharge plasma device B.L. Dwyer, N.H. Brooks, R.L. Lee We constructed two devices for the purpose of educational demonstration: a rotating tube containing media of two densities to demonstrate axial confinement and a similar device that uses pressure variation to convert a long plasma glow discharge into a long straight arc [1]. In the first device, the buoyant force is countered by the centripetal force, which confines less dense materials to the center of the column. Similarly, a plasma arc heats the gas through which it passes, creating a hot gaseous bubble that is less dense than the surrounding medium. Rotating its containment envelope stabilizes this gas bubble in an analogous manner to an air bubble in a rotating tube of water. In addition to stabilization, the rotating discharge also exhibits a decrease in buoyancy-driven convection currents. This limits the power loss to the walls, which decreases the field strength requirement for maintaining the arc. These devices demonstrate principles of electrodynamics, plasma physics, and fluid mechanics. They are portable and safe for classroom use. \vskip6pt \noindent [1] N.H. Brooks, et al., J. Appl. Phys. {\bf 94}, 1402 (2003). [Preview Abstract] |
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JP9.00073: Optimizing target surfaces for inertial confinement fusion experiments using micro-electrical discharge machining C. Waltz, J.J. Jaquez Cone guided fast-ignition laser fusion uses a re-entrant cone target to allow laser access through the plasma overlying the compressed core. Current experiments emulate that situation with a conical hole in an aluminum foil. It is critical that the 10 $\mu$m diameter laser spot be centered on the 30 $\mu$m diameter flat cone tip. Alignment is achieved by retro-imaging a low power beam from the cone tip. Micron scale roughness on the cone tip limits reflected light intensity making alignment difficult; an improved surface finish is required. The buried cone targets are fabricated by micro-electrical discharge machining (EDM). Various parameters are investigated to decrease the roughness and to improve the uniformity of the EDM cone tip surface: EDM wire material and shape, electrode voltage, machine capacitance, and machining speed. Results of surface roughness, uniformity, and material removal rate will be presented. [Preview Abstract] |
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JP9.00074: Development of unified plotting tools for GA transport analysis M. Buuck, J. Candy A collection of python classes for the TGYRO suite of codes (NEO, GYRO, TGYRO, TGLF) has been developed that provide both the expert user with conceptually simple access to all code output data, and the casual end user with simple command-line control of plotting. The user base for these transport analysis codes continues to grow, raising the urgency of modernizing and unifying the plotting tools used for post-simulation analysis. Simultaneously, there is a push toward larger-scale fusion modeling underscoring the need for a revised, modernized approach to data management and analysis. The TGYRO suite is currently in use at all major fusion laboratories worldwide, and allows the user to make steady-state profile predictions for existing devices and future reactors, and simultaneously to carry out fundamental research on plasma transport (both collisional and turbulent). [Preview Abstract] |
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JP9.00075: Improved timing sequence generator on the DIII-D tokamak R.A. Colio, D.F. Finkenthal, T.M. Deterly The DIII-D tokamak uses a central clock source and trigger system to synchronize plant operations and diagnostics. The system uses a bi-phase encoding technique to send both clock and trigger signals to remote receivers, and supports both pre-programmed sequences of triggers as well as event-driven triggers. A 1 MHz timebase is used and triggers are encoded as eight-bit hexadecimal words. Currently, the system relies on a cascaded series of CAMAC-based delay generators to produce the trigger sequence. We present a modern and more versatile implementation based on a single FPGA (field programmable gate array) capable of providing clock rates upward of 100 MHz while maintaining compatibility with existing equipment. A proposal for system clock synchronization with GPS for improved precision is also presented. [Preview Abstract] |
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JP9.00076: Effect of clock jitter on plasma density measurements relying on direct digital demodulation techniques B.W. Hamming, R.A. Colio, D.F. Finkenthal, M.A. Van Zeeland, T.M. Deterly Real-time measurement of plasma density is essential to effective closed-loop plasma control systems in fusion-type reactors. The DIII-D tokamak currently employs a Michelson-type interferometer in combination with heterodyned lasers to make real-time density measurements utilizing embedded digital signal processing (DSP) techniques. This technique relies on high-speed analog-to-digital converters clocking at four times the 40 MHz reference frequency, and clock jitter becomes a critical source of noise in the measurement indistinguishable from phase noise of the interferometer signals. We present a study of the effect of clock jitter on system noise and recommendations for improvement. [Preview Abstract] |
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JP9.00077: Mode content and transmission measurements on components of the ECH transmission lines on DIII-D A. Richenderfer, M. Cengher, J. Lohr, C.P. Moeller On the DIII-D ECH system about 25\% of the generated rf power is lost in the 90 m long transmission lines, including, typically, 4\% at the coupling mirror and 2\% intrinsic loss in the straight waveguide sections. The main sources of loss are the $\sim$10 miter bends per line, where Ohmic loss contributes about 0.3\% per miter and over 1\% additional loss per miter comes from mode conversion due to diffraction. The footprint of the rf beam at the miter mirror, hence the diffraction, can be reduced by combining waveguide modes with power ratios and phase differences such that the resultant wall electric field is close to zero. Such modes can be generated in a tapered input arm. The taper design assumes a perfect HE$_{11}$ mode propagating into the miter, but in high power tests, the miter losses actually increased, leading to the hypothesis that the high power beam contained other than a pure HE$_{11}$ mode. Tests of these miters and of their sensitivity to unwanted modes will be presented. [Preview Abstract] |
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JP9.00078: Studies of prompt losses from neutral beam injection into DIII-D D.A. Sutherland, R.K. Fisher, D.C. Pace, W.W. Heidbrink, X. Chen A study of the prompt losses of injected neutral beam ions was conducted on the DIII-D tokamak using the scintillator-based fast-ion loss detector (FILD) diagnostics and a reverse-orbit calculation code. Prompt losses, also called first orbit losses, result from injected neutrals that are ionized and born on orbits that intersect the outer wall. Measurements of the pitch angle and gyro-radius of the lost ions provide the input to a reverse-orbit calculation used to follow the detected ions back to their birth at the intersection of the reverse orbit with the incident neutral beam footprint. The MHz response time of the FILD scintillator allows us to compare the measured time delay between the onset of the neutral beam injection and the measured FILD loss signals, and compared this to the calculated transit time based on the path length of the reverse orbit. The effects of off-axis beam injection on the measured prompt losses will also be investigated. [Preview Abstract] |
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JP9.00079: The transition from compressional Alfv\'en waves to whistler-like propagation in tokamaks T.E. Whittle, R.I. Pinsker, R. Prater In a cold magnetized plasma, the compressional Alfv\'en wave ($\omega\ll \Omega_i$) smoothly transitions to the fast wave at frequencies above $\omega = \Omega_i$ and connects to the whistler wave at higher frequencies. The accompanying changes in wave dispersion have important consequences for the propagation and damping of these modes in tokamak equilibria [1]. A theoretical model for this transition is being developed based on the full cold plasma dispersion relation. We study the effect of whistler-wave-like propagation in DIII-D equilibria with analytic models as well as the GENRAY ray tracing code. As the whistler-like regime is approached, the $n_{\parallel}$ upshift effect can have a decisive effect on the first-pass absorption in DIII-D cases, significantly enhancing damping on electrons beyond the level expected from simple theory. \vskip6pt \noindent [1] R.I. Pinsker, et al., Nucl. Fusion {\bf 46}, S416 (2006). [Preview Abstract] |
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JP9.00080: Single particle model of Alfv\'en wave heating at plasma edge C.A. Schuch, T.E. Evans, D.M. Orlov Alfv\'en wave heating is an active area of research due to its importance in toroidal magnetic confinement devices and space physics. A theoretical model describing the motion of charged particles under the influence of Alfv\'en waves is developed for linear and circularly polarized plane waves, largely following the approach laid out by R. White [1]. A simplified slab geometry with a uniform background magnetic field is used in order to facilitate the calculations. The resulting system of differential equations is used to study conditions necessary for resonant heating to occur. The influence of the Alfv\'en wave amplitude, frequency, and propagation direction on the efficiency of heating is investigated. It is shown that frequencies significantly below the cyclotron frequency may give rise to resonant behavior, resulting in heating of the plasma. The analysis is focused on the parameters typical for the edge plasma region in the DIII-D tokamak. \vskip6pt \noindent [1] R. White, L. Chen, and Z. Lin, Phys. Plasmas {\bf 9}, 1890 (2002). [Preview Abstract] |
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JP9.00081: Fractional Resonances in Ion Bernstein Wave Heating in a Helicon Plasma Discharge Julian Kates-Harbeck This work concerns a novel magneto-plasmonic propulsion system. It generates thrust by ejecting magnetically confined, RF heated ions through a magnetic nozzle. Ions are heated through Ion Bernstein Wave Heating (IBWH). We studied IBW heating properties by developing two computational models: firstly, a 3D particle mover, which, with reasonable computational effort, can simulate the behavior of $\sim $10$^{4}$ particles in a field configuration consisting of a uniform background magnetic field and the electrostatic IBW; secondly, a 2D particle-in-cell (PIC) simulation, capable of modeling $\sim $10$^{6}$ particles including their electrostatic and magnetostatic interactions in the corresponding 2D field configuration. While the 3D particle mover predicts heating resonances at all harmonics of the ion cyclotron frequency $\omega _{ci}$, the PIC simulation shows damping and distortion of the full harmonics of $\omega _{ci}$, rendering them impractical for ion heating. The particle mover also predicts heating at 4/3 and 3/2 of $\omega _{ci}$, as anticipated theoretically and reported experimentally. The simulations thus reveal these fractional harmonic resonances as potential candidates for IBWH. [Preview Abstract] |
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JP9.00082: Electrostatic Focusing Lens Eric Thomas, Demitri Hopkins We developed an electrostatic focusing lens capable of generating DD reactions, by focusing deuterium ions generated from a pointed emitter at a frozen heavy water target. Due to difficulty with the pointed emitter, we later switched to a hollow cathode design. To model the lenses, chamber, and calculate the dimensions for the design that would maximize ion energy and density, the program SIMION was used. During stable operation, vacuum was hand adjusted around 10-13 mTorr. To keep stable beam, DC voltage generator was varied between 15-25kV. Hand adjusting was necessary, because at points in the operation the frozen heavy water would release vapor at an increased rate. This caused the pressure to rise and the beam current to spike, creating instabilities and an arc to the lens. Three methods were used to determine successful DD production. (1) Two differently shielded Geiger counters (unshielded and UHMW-PE insulated tube), (2) Spectrophotometer comparing control peaks with heavy water tests, and (3) a calibrated bubble dosimeter specific to neutrons. Analysis of the results suggest the neutrons flux varied from 532 to 1.4x10$^6$ neutrons/ sec, and require further tests to plot and narrow results. [Preview Abstract] |
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JP9.00083: Production of Medical isotope Technecium-99 from DT Fusion neutrons John Boguski, Charles Gentile, George Ascione High energy neutrons produced in DT fusion reactors have a secondary application for use in the synthesis of valuable man- made isotopes utilized in industry today. One such isotope is metastable Technecium-99 (Tc99m), a low energy gamma emitter used in $\sim$ 85\% of all medical imaging diagnostics. Tc99m is created through beta decay of Molybdenum-99 (Mo99), which itself has only a 66 hour half-life and must be created from a neutron capture by the widely available and stable isotope Molydenum-98. Current worldwide production of Tc99m occurs in just five locations and relies on obtaining the fission byproduct Mo99 from highly enriched Uranium reactors. A Tc99m generator using DT fusion neutrons, however, could potentially be operated at individual hospitals and medical facilities without the use of any fissile material. The neutron interaction of the DT neutrons with Molybdenum in a potential device geometry was modeled using Monte Carlo neutron transport code MCNP. Trial experiments were also performed to test the viability of using DT neutrons to create ample quantities of Tc99m. Modeling and test results will follow. [Preview Abstract] |
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JP9.00084: DIVERTORS, EDGE PHYSICS AND FUELING, SIMULATION AND MODELING OF MAGNETIC CONFINEMENT |
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JP9.00085: Time-dependent 2-D modeling of edge plasma transport with high intermittency due to blobs A.Yu. Pigarov, S.I. Krasheninnikov, T.D. Rognlien Edge plasma transport is well known to be highly intermittent and non-diffusive via coherent structures (so-called blobs and ELM filaments) moving ballistically to walls. This intermittent transport has strong impact on both edge plasma parameters and plasma-wall interactions. The ``macro-blob'' approach to simulate simultaneously the edge plasma transport, statistical turbulent properties, impurities, and wall dynamics within the framework of 2-D edge-plasma fluid transport code has been developed and implemented into UEDGE. The results of time-dependent modeling of bursty plasma and wall responses with the improved UEDGE will be presented. The effect of a sequence of macro-blobs on background plasma profiles, on hydrogen radiation and recycling, and on particle and energy fluxes will be discussed. Impurity dynamics with macro-blobs is also presented showing the enhancement of sputtering rates, alteration of charge state profiles (caused by enhanced outward transport of high states and simultaneous advancement of low states toward the core), and change in erosion/deposition patterns. Work supported by DOE grant DE-FG02-04ER54739 at UCSD and DE-AC52-07NA27344 at LLNL. [Preview Abstract] |
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JP9.00086: Analysis of hydrogen retention with nonlinear reaction-diffusion equations J. Guterl, R.D. Smirnov, S.I. Krasheninnikov The nonlinear reaction-diffusion equations are rather widely used for the assessment of hydrogen trapping in plasma facing components of magnetic fusion devices. Depending on the sophistication of the model different species (e.g. free and trapped hydrogen, interstitials, clusters, etc.) are considered. However, so far no attempt to study general properties of the solutions of these equations was made. Here we present the results of the analysis of general time-dependent solutions of the nonlinear reaction-diffusion equations for the simple case of evolution of basic species (free and trapped hydrogen and mobile trapping sites) in the bulk wall material. The hydrogen implantation, desorption, wall erosion and co-deposition processes are included in the consideration. We compare our results with available experimental data on the dependences of hydrogen retention in beryllium on the depth and the sample's temperature. [Preview Abstract] |
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JP9.00087: Dynamics, transport and impact of dust in fusion plasmas R.D. Smirnov, S.I. Krasheninnikov, A.Yu. Pigarov, D.A. Mendis, T.D. Rognlien It has been well established now that dust is commonly present in magnetic fusion devices. It is expected that dust formation will increase significantly due to increased power and prolonged plasma operation in ITER and future fusion reactors. In this work we investigate dynamics, transport and effects of dust in tokamak plasmas. Recent advancements in development of theoretical models and simulations with the DUSTT/UEDGE code of dust-plasma interactions in tokamaks are reported. These include studies of dynamics of non-spherical dust, effects of dust ablation cloud, and possible impact of dust and dust originated impurities on fusion plasmas. It is shown that naturally formed or deliberately injected dust can be a significant source of impurities in the plasmas that can have drastic impact on plasma profiles, instabilities, and radiation power losses. Using DUSTT/UEDGE code we assess dust effects on the plasmas, simulating controlled dust injection with different sizes and injection speeds in modern tokamaks and ITER. Possible applications of dust injection for power dissipation in SOL/divertor and during plasma quench are discussed. [Preview Abstract] |
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JP9.00088: Consistent Recycling in a Coupled Kinetic Plasma - Neutral Transport Code D.P. Stotler, C.S. Chang, G. Park The role of neutral fueling in the buildup of the H-mode pedestal is a topic of interest for the FY2011 Joint Research Target on Pedestal Structure. The particular effects of kinetic neutral and plasma phenomena in the pedestal buildup are being examined via the coupled DEGAS~2 Monte Carlo neutral and XGC neoclassical particle transport codes, developed as part of the Center for Plasma Edge Simulation. The coupled codes have recently been used to quantify the particle pinch associated with cold ions resulting from recycling at the plasma edge\footnote{W. Wan et al., Phys. Plasmas {\bf 18}, 056116 (2011)}. The next step in the code development is to use the flux of ions striking material surfaces in XGC as the source of recycled neutral atoms and molecules in DEGAS 2. In this way, the poloidal distribution of the neutral source will evolve consistently with the plasma as the pedestal builds up. XGC will also provide the energy of the ions hitting the surface, allowing the application of detailed plasma material interaction models to determine the relative fractions of atoms and molecules generated by recycling. The atom / molecule ratio in turn impacts the velocity distribution of the neutral species and, thus, their penetration into the core plasma. [Preview Abstract] |
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JP9.00089: Heat Transmission through Weakly Collisional Plasma Sheath Alexander V. Khrabrov, Igor D. Kaganovich Under the condition of weak collisions, the distribution of plasma electrons in a sheath near the wall becomes anisotropic and non-Maxwellian due to the ``loss cone'' effect. As a result, the structure and the transport properties of the sheath are strongly modified relative to the collisional case. This non-local kinetics may be important for analyzing edge plasmas in magnetic confinement devices, such as the divertor scrape-off layer. For example, with a velocity distribution strongly depleted in the direction normal to the wall, when most of the electron energy is in the perpendicular motion, the heat transmission factor of the sheath can reach a low value of about 2, compared to the conventional theoretical value of 7. We present the results of numerical simulations with a particle-in-cell code, in which both the sheath and the quasi-neutral plasma are modeled self-consistently (not requiring approximated boundary conditions at the sheath edge). The simulation takes into account both electron-neutral and ion-neutral collisions, as well as Coulomb collisions between the electrons. [Preview Abstract] |
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JP9.00090: Parallel Transport on Open Magnetic Field Lines Zehua Guo, Xianzhu Tang The plasma parallel transport on open magnetic fields can become dominant, and its theory becomes especially challenging when the mean-free-path({\it{mfp}}) of the plasma is comparable to or greater than the field line length scale of B modulation. Here we present a fluid theory based on the lowest order expansion of Vlasov equation in $\rho/L$. The different roles of $\|B\|$ modulation and the two components of the parallel heat flux ($q_n$ and $q_s$, associated with the parallel and perpendicular thermal energies respectively), in determining the plasma profiles ($n$, $T_\parallel$, $T_\perp$, $\phi$, and $u_\parallel$), are elucidated by general analytical expressions and confirmed by first-principle kinetic simulations of a flux expander into absorbing walls. The parallel heat flux, calculated from kinetic theory in the long {\it{mfp}} regime, is shown to have surprising behaviors along an open field line. For example, $q_n$ can run against the parallel temperature gradient when there is significant flux expansion toward the wall. A scan from low to high collisionality is then performed to clarify the dramatic difference in plamsa profiles. This work was supported by the DOE OFES. [Preview Abstract] |
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JP9.00091: Overview of the ArbiTER edge plasma eigenvalue code Derek Baver, James Myra, Maxim Umansky The Arbitrary Topology Equation Reader, or ArbiTER, is a flexible eigenvalue solver that is currently under development for plasma physics applications. The ArbiTER code builds on the equation parser framework of the existing 2DX code, extending it to include a topology parser. This will give the code the capability to model problems with complicated geometries (such as multiple X-points and scrape-off layers) or model equations with arbitrary numbers of dimensions (e.g. for kinetic analysis). In the equation parser framework, model equations are not included in the program's source code. Instead, an input file contains instructions for building a matrix from profile functions and elementary differential operators. The program then executes these instructions in a sequential manner. These instructions may also be translated into analytic form, thus giving the code transparency as well as flexibility. We will present an overview of how the ArbiTER code is to work, as well as preliminary results from early versions of this code. Work supported by the U.S. DOE. [Preview Abstract] |
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JP9.00092: Stabilizing Effects of Edge Current Density on Peeling-Ballooning Instability P. Zhu, C.C. Hegna, C.R. Sovinec Resistive MHD computations using the NIMROD code find a strong dependence of low-$n$ edge instabilities on the edge parallel current density distribution. Here $n$ is the toroidal mode number. The low-$n$ edge-localized-modes can be driven unstable by increasing the edge current density across the peeling-ballooning stability boundary. When edge peak current density is sufficiently large, the corresponding safety factor $q$ profile obtains an edge region with zero or reversed magnetic shear, and the low-$n$ edge instabilities are partially or fully stabilized. These results are consistent with previous analytic theory on peeling modes which indicates that zero or reversed magnetic shear can be stabilizing. Nonlinear simulations indicate that the stabilizing effects of edge current density on the low-$n$ peeling-dominant modes through zero and reversed shear can persist throughout the nonlinear exponential growth phase. Near the end of this nonlinear phase, the radial extent of the filament exceeds the pedestal width, and disconnected blob-like substructures start to develop within the filaments. Relative pedestal energy loss from these radially extending filaments can reach $20-30\%$. Both filament size and pedestal energy loss from the nonlinear low-$n$ peeling-dominant instabilities can be reduced and regulated by the equilibrium edge current density distribution. [Preview Abstract] |
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JP9.00093: Rotation effects on peeling-ballooning and infernal modes at H-mode pedestal Linjin Zheng, M.T. Kotschenreuther, P. Valanju, S. Mahajan Due to unbalanced ion and electron transports at plasma edge, rotation and rotation shear are always connected to the tokamak pedestal. Since the bootstrap current at pedestal may reduce or even reverse the magnetic shear at plasma edge, and rotation effect can be enhanced by a small magnetic shear, investigation of rotation effects on MHD modes at H-mode pedestal becomes interesting. In this investigation, we use VMEC code to construct tokamak equilibrium (with bootstrap current taken into account) and use AEGIS code to investigate MHD stability. Both peeling-ballooning and infernal modes at H-mode pedestal are studied. The relation of the modes with ELM excitation and edge hormonic oscillation (EHO) will be discussed. [Preview Abstract] |
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JP9.00094: Edge instabilities and stability in free and fixed boundary plasmas Linda Sugiyama, Henry Strauss Magnetically confined fusion plasmas can achieve good confinement by operating in H-mode, using a D-shaped plasma cross-section with a magnetic X-point(s). The steep edge pressure gradient can destabilize electromagnetic instabilities, from large periodic edge crashes (ELMs) to small continuous oscillations, to stability. Applied nonaxisymmetric magnetic fields can pump out plasma density, altering edge pressure and stability. Nonlinearly, if the plasma magnetic boundary is free to move, edge instabilities can drive a tangle-like magnetic field structure [1]. Despite being a small perturbation phenomenon in Hamiltonian systems, the tangle does not appear in standard linearized plasma theory. Its largest deviation, near the X-point(s), is remote from the driving region and cannot grow on the same exponential time scale due to propagation delay. We clarify the nonlinear nature of the tangle and, using the M3D code, investigate differences in linear and nonlinear stability of edge instabilities, for fixed and free plasma boundaries.\\[4pt] [1] L. Sugiyama, et al., \emph{Phys. Plasmas} \textbf{17} 062505 (2010). [Preview Abstract] |
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JP9.00095: Net electromagnetic torque induced by multiple neighboring resonant magnetic perturbations A.J. Cole, C.C. Hegna, J.D. Callen In this work, previous calculations [1,2] of the electromagnetic torque exerted by coupled resonant magnetic perturbations on a toroidal plasma are expanded to include many resonant surfaces in close proximity. We are interested in the possibility of a simplified torque expression in the limit that the distance between resonant surfaces collapses, i.e. as in the edge region where the $q$-profile is steep and their singular layers might overlap. Such a case is relevant to the ELM control community when resonant magnetic perturbation (RMP) fields are applied. Present analytic estimates of the shielding or penetration of an applied RMP field are done using single surface models, while in practice multiple neighboring resonances exist. \\[4pt] [1] J.W. Connor, S.C. Cowley, R.J. Hastie, et al., Phys.\ Fluids {\bf 31}, 577 (1988).\\[0pt] [2] R. Fitzpatrick, Phys.\ Plasmas {\bf 16}, 032502 (2009). [Preview Abstract] |
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JP9.00096: Global simulation of edge pedestal micro-instabilities Weigang Wan, Scott Parker, Yang Chen We study micro turbulence of the tokamak edge pedestal with global gyrokinetic particle simulations. The simulation code GEM is an electromagnetic $\delta\!f$ code. Two sets of DIII-D experimental profiles, shot \#131997 and shot \#136051 are used. The dominant instabilities appear to be two kinds of modes both propagating in the electron diamagnetic direction, with comparable linear growth rates. The low n mode is at the Alfven frequency range and driven by density and ion temperature gradients. The high n mode is driven by electron temperature gradient and has a low real frequency. A $\beta$ scan shows that the low n mode is electromagnetic. Frequency analysis shows that the high n mode is sometimes mixed with an ion instability. Experimental radial electric field is applied and its effects studied. We will also show some preliminary nonlinear results. [Preview Abstract] |
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JP9.00097: Tightly Coupled Kinetic-MHD Simulations of ELM Effects on Divertor Heat Loads Julian Cummings, C.S. Chang, Gunyoung Park, Linda Sugiyama The behavior of divertor heat load profiles during discharges with Type I ELMs is under investigation in present-day tokamak experiments such as DIII-D and NSTX. We present here simulations of ELM activity and associated divertor heat loads in which we couple the discrete guiding-center neoclassical transport code XGC0 with the nonlinear extended MHD code M3D. XGC0 starts from the equilibrium reconstruction of a specific discharge, just before the onset of a Type I ELM. M3D models the fast ELM event and sends updates of the electrostatic potential and magnetic field perturbations on the Alfv\'{e}n time scale to XGC0. The XGC0 code tracks ion and electron dynamics within these perturbed fields and collects divertor particle and energy flux statistics over several time intervals before and during the nonlinear ELM. In addition, XGC0 computes kinetic plasma response in the form of the anisotropic CGL pressure tensor and sends this data back to M3D as the ELM simulation proceeds. Building upon our previously reported coupled kinetic-MHD simulations, we now demonstrate a two-way coupling capability and discuss results for a selection of discharges from the 2010 JRT studies. [Preview Abstract] |
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JP9.00098: The Effect of Anomalous Electron Viscosity on Magnetic Reconnection During ELMs Joshua Sauppe, Carl Sovinec, Xueqiao Xu, Maxim Umansky Edge-localized modes (ELMs) allow rapid releases of particles and energy in a magnetically confined plasma. The initial linear evolution of an ELM is dominated by the ideal peeling-ballooning instability, after which non-ideal effects come into play [Snyder et. al., POP 12, 056115 (2005)]. Numerical simulations using the BOUT++ plasma edge code demonstrate that by including several non-ideal effects the simulated ELM size is consistent with experimental observations [Xu et. al., PRL 105, 175005 (2010)]. Anomalous electron viscosity limits the high radial wavenumbers k$_{r}$ normal to the flux surfaces to facilitate magnetic reconnection; diamagnetic drifts limit the high toroidal modes n in the bi-normal direction. Using the BOUT++ code, we investigate the role that anomalous electron viscosity plays in the magnetic reconnection event and pedestal collapse by varying both the Lundquist number S and the dimensionless hyper-Lundquist parameter $\alpha _{H}=\eta _{H}$/R$^{2}\eta $ where $\eta _{H}$ is the anomalous viscosity. Comparisons to ELM simulations using the NIMROD plasma code with two-fluid effects are discussed. [Preview Abstract] |
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JP9.00099: Algorithmic Issues and Applications of BOUT++ to Simulation of Realistic Tokamak Configurations Bruce Cohen, Maxim Umansky, Michael Makowski Progress is reported on simulations of electrostatic resistive ballooning instabilities in realistic tokamak geometries using the BOUT++ three-dimensional fluid code [1]. ~The simulations extend to include the open flux region and a single divertor with X-point, using the actual magnetic geometry of the DIII-D tokamak. Comparisons of the growth rates for linear instabilities are made to those from the 2DX linear code [2]. It is found that unphysical grid oscillations tend to emerge in the parallel coordinate at the shortest wavelength, and two methods are used to control it - inclusion of an artificial spatial diffusion operator or use of a staggered grid. Simulations of a nonlinear saturated state are presented along with initial comparison to experimental data from DIII-D. \\[4pt] [1] B. D. Dudson, et al., Computer Phys. Comm. \textbf{180}, 1467 (2009). \\[0pt] [2] D. A. Baver, J. R. Myra and M.V. Umansky, Computer Phys. Comm. \textbf{182}, 1610 (2011). [Preview Abstract] |
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JP9.00100: Modeling of local edge plasma perturbations induced by a biased probe M.V. Umansky, D. Brunner, B. LaBombard, T.D. Rognlien In tokamak edge plasma experiments, a so-called ``death-ray'' regime is found where the downstream electron pressure measured by Langmuir probes at the divertor plate exceeds the upstream values by a factor of $\sim$2 over a narrow radial region at the strike point [1,2]. However, recent studies on Alcator C-Mod indicate that the death-ray over-pressure may be a result of local plasma perturbations by the probe [3]. We investigate the effects of probe plasma perturbation using the tokamak edge fluid code UEDGE. The code models a 2D slab-like configuration roughly matching the basic dimensions and characteristics of edge plasma in Alcator C-Mod near detachment, where the death-ray is often observed. It is observed in the numerical solutions that at sufficiently negative bias voltage, the probe substantially modifies the local plasma parameters. Several characteristics appear to be similar to experimental observations of the death-ray regime, pointing to the interplay of perpendicular plasma viscosity, ion-neutral interaction, and the electron sheath heat flux.\\[0pt][1] LaBombard et al., J. Nucl. Mater., 241-243, p. 149 (1997); [2] Loarte et al., Nucl. Fusion 38 (1998) 331; [3] Brunner et al., APS DPP 2010, poster TP9.00069. [Preview Abstract] |
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JP9.00101: H-mode pedestal turbulence in DIII-D and NSTX using BOUT++ X.Q. Xu, B.D. Dudson, I. Joseph, R.J. Groebner, R. Maingi In this work, we will report BOUT++ simulations for H-mode pedestal instabilities and turbulent transport. For DIII-D H-mode discharges, the BOUT++ peeling-ballooning ELM model including electron inertia was used to analyze the ideal linear stability and ELM dynamics. The beta scan is carried out from a series of self-consistent MHD equilibria generated from EFIT by varying pressure and/or current. For typical tokamak pedestal plasmas with high temperature and low collisionality, we found that the collisionless ballooning modes driven by electron inertia are unstable in the H-mode pedestal and have a lower beta threshold than ideal peeling-ballooning modes, which are the triggers for Edge Localized Modes. The growth rate of electron inertia ballooning modes is found to increase with the magnitude of the electron skin depth d$_{e}$=c/$\omega _{pe}$. Thus, collisionless (electron inertia) ballooning modes might be responsible for H-mode turbulence transport when the pedestal is stable to peeling-ballooning modes. BOUT++ calculations also show that NSTX Elm stability boundaries are sensitive to flow shear profile. Attempts are underway to calculate nonlinear turbulence and transport in H-mode discharges due to the non-ideal effects. [Preview Abstract] |
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JP9.00102: Five-field peeling-ballooning modes simulation with BOUT++ code T.Y. Xia, X.Q. Xu, J.G. Li The fast-reconnection simulation of ELMs in high-confinement mode tokamak discharges has been reported by Xu, et al with a minimum set of three-field two-fluid equations (Xu, et al., PRL, V.105, 175005 (2011)). Here we improve the simulation by separating the pressure into ion density, ion and electron temperature equations, to describe the pedestal collapse with the BOUT++ code. For the same equilibrium pressure profiles and different constant equilibrium density n$_{0}$, the normalized growth rate of peeling-ballooning modes is independent of n$_{0}$, the same as the previous three-field results. For constant temperature, when the inhomogeneous equilibrium density effects are considered, the linear growth rate becomes larger than the constant n$_{0}$ cases, increased around 6.2{\%}. The growth rate is also decreased by the diamagnetic effects, especially for high toroidal mode number. This is also the same as the previous results. The stabilizing effects are more effective for smaller n$_{0}$. The nonlinear simulation, the effects of thermal conductivities, and simulations for new EAST superconducting tokamak ELM experiments will be reported. [Preview Abstract] |
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JP9.00103: Influence of Equilibrium Perpendicular Shear Flow on Peeling-ballooning Instabilities P.W. Xi, X.Q. Xu The influence of perpendicular ExB shear flow on peeling-ballooning instabilities is investigated with BOUT++ code. In our simulation, a set of reduced MHD equations are solved for a very unstable equilibrium and a marginal unstable equilibrium in shifted-circular tokamak geometry. For ideal MHD cases without diamagnetic terms and resistivity, we find that flow shear shows dramatic stabilizing effect on peeling-ballooning modes and the stabilizing degree increases with mode number. When the flow shear is large enough, we find the curvature of growth rate verse mode number has the same shape like that for the case with only diamagnetic term, and this implies that diamagnetic term and the shear flow have the same mechanism acting on peeling-ballooning instabilities. The role of Kelvin-Helmholtz term is also investigated and we find it is destabilizing and the effect depends on both flow shear and mode number. For cases with both diamagnetic term and the applied shear flow, modes with intermediate mode number are strongest stabilized while high n and low n mode keep unstable. Based on these results, an ELM trigger sketch is proposed. [Preview Abstract] |
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JP9.00104: A snowflake divertor: reduction of the ELM heat load due to plasma convection D.D. Ryutov, R.H. Cohen, T.D. Rognlien, M.V. Umansky A snowflake magnetic configuration is created when the poloidal magnetic field and its spatial derivatives turn zero at a certain point. The separatrix then acquires a characteristic hexagonal shape reminiscent of a snowflake and the number of divertor plate strike points increases from two to four. We point out that the snowflake divertor could solve the ELM heat load problem by spreading the heat over a large area and engaging all four strike points. The mechanism is related to a fast increase of the plasma beta in the divertor region during ELM. Due to very low values of the poloidal magnetic field over a large area of a snowflake divertor, plasma convection sets in that leads to the desired effect. Conditions for the onset of a convective instability and/or the loss of equilibrium are formulated, and estimates of the size of the zone involved in convective motion are presented. Work performed for U.S. DoE by LLNL under Contract DE-AC52-07NA27344. [Preview Abstract] |
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JP9.00105: Reduced ELM heat loads from increased magnetic field-line length in snowflake configurations T.D. Rognlien, D.D. Ryutov, M.V. Umansky A major concern for fusion devices is the temperature rise of bounding material surfaces from plasma energy exhaust. For short bursts of energy deposition, as from edge-localized modes (ELMs), the temperature rise scales as the total energy deposited divided by the square root of the burst duration, T$_{b}$. The time T$_{b}$ is known to depend on electron and ion convective and conductive transport along the field line, electron and ion collisional equilibration, and radiative losses. The conduction time scales as the field-line length, L, whereas the conduction time scales as L$^{2}$. The snowflake configuration naturally has a much larger L than the conventional X-point divertor, thus yielding larger T$_{b}$, and reduced surface temperature rise. The quantitative impact for the snowflake is presented through the comparison of 3 models: 2-point analytic scaling, 1D along a field line, and 2D including full snowflake tokamak geometry. [Preview Abstract] |
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JP9.00106: Simulation of neoclassical transport with the continuum gyrokinetic code COGENT M. Dorf, R.H. Cohen, J.C. Compton, M. Dorr, T.D. Rognlien, J. Angus, S. Krasheninnikov, P. Colella, D. Martin, P. Mccorquodale COGENT is a continuum gyrokinetic code for edge plasmas being developed by the Edge Simulation Laboratory collaboration. The code is distinguished by 4th order conservative discretization and mapped multiblock grid technology to handle the geometric complexity of the tokamak edge. It is written in v$_{\vert \vert }$, $\mu $ velocity coordinates, and the gyro-Poisson equation is implemented for calculation of the self-consistent electric potential. We report on a verification campaign involving neoclassical simulation of tokamak transport. The results include recovery of neoclassical fluxes, and verification tests of the self-consistent potential model. Work in progress includes investigation of the large radial electric field effects on the neoclassical transport coefficients and flow velocities. There has also been substantial progress in applying the mapped-multiblock capability to divertor geometry; we anticipate presenting initial results. We also report on studies incorporating a model diffusion oerator to model the effects of anomalous transport. [Preview Abstract] |
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JP9.00107: Flux tube gyrokinetic simulations of the edge pedestal Scott Parker, Weigang Wan, Yang Chen The linear instabilities of DIII-D H-mode pedestal are studied with gyrokinetic micro-turbulence simulations. The simulation code GEM is an electromagnetic $\delta\!f$ code with global tokamak geometry in the form of Miller equilibrium. Local flux tube simulations are carried out for multiple positions of two DIII-D profiles: shot \#98889 and shot \#131997. Near the top of the pedestal, the instability is clearly ITG. The dominant instability of the pedestal appears at the steep gradient region, and it is identified as a low frequency mode mostly driven by electron temperature gradient. The mode propagates along the electron diamagnetic direction for low n and may propagate along the ion direction for high n. At some positions near the steep gradient region, an ion instability is found which shows some characteristics of kinetic ballooning mode (KBM). These results will be compared to the results of E. Wang et al. and D. Fulton et al. in the same session. [Preview Abstract] |
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JP9.00108: Gyrokinetic analysis of linear instabilities within the pedestal of experimental discharges Eric Wang, Xueqiao Xu, Jeff Candy, Rich Groebner, Phil Snyder A pedestal pressure scan based on DIII-D discharge 131997 is being studied with GYRO in the numerically challenging edge pedestal regime to explore the physics of relevant microinstabilities. Initial studies seek to characterize electron drift instabilities in the edge barrier as well as study the onset of the KBM. In GYRO, both an initial value and an eigenvalue solver are employed to study both dominant and sub-dominant instabilities. A strong sensitivity of the growth rate and real frequency to small changes in the equilibrium profile is observed. To simplify the underlying physics, the Miller formulation for the flux surface geometry will be used in attempts to clearly identify the KBM. Beyond the Miller geometry, the exact flux-surface shape, including up- down asymmetry, is required to get accurate results, as the symmetry-breaking mechanism may generate significant momentum transport in the edge. [Preview Abstract] |
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JP9.00109: Gyrokinetic analysis of kinetic ballooning instability using real magnetic geometry Daniel Fulton, Yong Xiao, Zhihong Lin Understanding the physics of the pedestal region of toroidal plasmas is critical to obtaining confinement with high core temperatures. The pedestal region is characterized by large gradients in pressure, temperature, and density profiles, which provide a source of free energy to drive a number of instabilities. Studying these instabilities can provide information on maximal allowable gradients in the pedestal. One of the most dangerous instabilties is the kinetic ballooning mode (KBM), driven by the pressure gradient. In this study, we do a pressure scan to explore the threshold of the KBM mode, using gyrokinetic simulation code GTC and equilibriums based on DIII-D discharge 131997. The nonlocal aspects of GTC allow us to evaluate the effects of real magnetic geometry on the KBM. Comparisons between codes GTC, GYRO, GEM, and BOUT++ are underway to benchmark all simulations. [Preview Abstract] |
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JP9.00110: Transport studies in the snowflake divertor in TCV H. Reimerdes, G.P. Canal, S. Coda, B.P. Duval, B. Labit, F. Piras, W. Vijvers, G. de Temmerman, J. Zielinski, B. Tal, S.Y. Medvedev, T.D. Rognlien, D.D. Ryutov, M.V. Umansky The transport of heat and particles in a tokamak plasma with a snowflake divertor has been studied in recent TCV experiments. Estimates of the power flux onto the divertor plates are obtained from measurements with multiple infrared cameras and Langmuir probes. The studies include L- and ELMy H-mode plasmas and confirm some of the advantageous properties of the snowflake configuration, such as the distribution of the exhaust power on more strike points than the two that characterize conventional divertor configurations. Modifications of the divertor configuration from single null towards a perfect snowflake (second-order null) show that already near-snowflake configurations lead to an appreciable power flux across the region of weak poloidal magnetic field. [Preview Abstract] |
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JP9.00111: SOLPS Modeling of Transport of the Super-X Divertor for the CFNS/Fusion-Fission Hybrid Brent Covele, Mike Kotschenreuther, Swadesh Mahajan, Prashant Valanju Recent transport results from the B2-Eirene fluid/Monte-Carlo code will be presented for the Super-X Divertor in the Compact Fusion Neutron Source, a high-power-density, low-aspect-ratio double-null tokamak design. The Super-X Divertor, a novel magnetic geometry, greatly reduces heat fluxes and plasma temperatures at the outer target plates (with an outer:inner total power ratio of 10:1) while maintaining excellent core plasma shape characteristics. [Preview Abstract] |
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JP9.00112: Dynamic Divertor Concept by Plasmoid Ejection in TS-4 Spherical Tokamak Experiment Yasushi Ono, Shizuo Inoue, Takenori Watanabe, Shingo Ito, Toru Ii, Syuji Kamio, Takuma Yamada, Michiaki Inomoto We proposed a new type of dynamic divertor by use of intermittent plasmoid ejection from the main plasma to divertor coil. Our 2-D MHD simulation demonstrated for the first time how the plasmas and coil conditions can control plasmoid dynamics for this divertor action. This dynamic divertor has four essential steps. First, current drive and heating cause the main detached plasma to expand to the divertor region, causing a plasmoid formation. Second, the expanding core plasma finally pinches off the small plasmoid. Next, the plasmoid isolated from the main plasma is cooled down by Argon gas puffing and finally is connected with the divertor plate. The series of divertor actions are expected to reduce the heat road to divertor plate significantly, suggesting a new type divertor useful for heavy heat road from type I Edge-Localized Mode(ELM). We will present its simulation result and the corresponding experiments of plasmoid ejection in TS-2 and TS-4 merging experiments. [Preview Abstract] |
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JP9.00113: Wide-angle Tangential Viewing System for DIII-D C.J. Lasnier, S.L. Allen, M.E. Fenstermacher, D.N. Hill, T.R. Weber We are designing a wide-angle tangential viewing system for DIII-D, with co-registered views in the visible and IR. We will examine toroidal and poloidal asymmetries of wall heating and particle flux during ELMs, magnetic perturbations, and disruptions; toroidal and poloidal mode structure of ELMs; poloidal distribution of particle flow velocities, and others. The system will simultaneously view the inner wall, outer wall, and upper and lower divertors, and will have an independent 3X optical zoom capability in visible and IR. Various parts of the image may be viewed at 3X magnification by translating the camera(s) vertically and laterally in the image plane. For IR we have a FLIR SC6000HS 3-5~$\mu$m camera, and for visible a Phantom V7.3. Both have high frame rate capability. Visible wavelength and neutral density filters may be selected, or interferometric flow measurement optics may be substituted for the filter system. This system was inspired by a design by CEA Cadarache for JET, and is similar to a system designed by LLNL for ITER upper ports. [Preview Abstract] |
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JP9.00114: Impurity transport measurements in the PISCES-A linear plasma device B.F. Hudson, R.P. Doerner, E.M. Hollmann, D. Nishijima The parallel transport, in terms of diffusion and advection by entrainment in parallel plasma flow, of impurities relevant to proposed ITER divertor materials (W, C) are studied in a linear He plasma. Introduction of the impurities in controlled amounts is accomplished by blow-off of thin films using a (1064nm, 75 mJ) pulsed Nd:Yag laser. Neutral and ion excited state emission are measured with an optically filtered PMT array. Emission profiles are compared to a 1.5 D advection plus diffusion numerical model to obtain a parallel flow speed and parallel and perpendicular diffusion coefficients. This work also expands on earlier results [1] by including multiple downstream measurement locations to quantify impurity acceleration and the controlled spot size of impurity blow-off. \\[4pt] [1] E. M. Hollmann et. al., J. Nucl. Mater (2010) in press [Preview Abstract] |
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JP9.00115: Low temperature tungsten spectroscopy on a Penning Ionization Discharge Deepak Kumar, Alexander Englesbe, Dan Stutman, Michael Finkenthal Complete Tungsten divertor operation is being planned on many tokamaks including Tore Supra and ITER. Thus, low temperature tungsten spectroscopy is important for aiding the divertor diagnostics on larger machines. A Penning Ionization Discharge (PID) at the Johns Hopkins University produces steady state plasmas with $T_e \sim 2$ eV, $n_e \sim 10^{13}$ cm$^{-3}$ and a fast electron fraction at $\sim 10$s eV. Similar bi-Maxwellian distributions, but with slightly higher electron temperatures, are found in the divertor plasmas of tokamaks. The two significant populating mechanisms for higher charge states in the PID are: (a) collisional excitation from bulk electrons, and (b) inner shell ionization from the fast electrons. The PID is diagnosed in a wide wavelength range - XUV, VUV and visible, to differentiate the two populating mechanisms. W is introduced in the PID by the sputtering of cathodes made of CuW alloy. Spectral emission from significantly higher charge states of W (up to W IV) has been observed in the experiment. This poster will describe results indicating the populating mechanism of W ions and also describe plans on upgrading the experiment to achieve higher temperatures which are closer to the divertor conditions. [Preview Abstract] |
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JP9.00116: New Results with the Ignitor Pellet Injector A. Frattolillo, S. Migliori, S. Podda, F. Bombarda, L.R. Baylor, S.K. Combs, C.R. Foust, S. Meitner, D. Fehling, G. Roveta The Ignitor Pellet Injector (IPI) has been developed in collaboration between ENEA and ORNL to provide greater control over the density time evolution and the density peaking in plasmas produced by the Ignitor device. The four barrel, two stage injector has been designed to reach speeds up to 4 km/s, for effective low field side injection into ignited plasmas ($T_e\cong T_i\cong 11$ keV). The present arrangement accomodates both a two-stage gun and a standard propellant valve on each barrel, allowing seamless switching between standard and high speed operation on any or all gun barrels. The cryostat is actively cooled by a pulse tube refrigerator, equipped with supplemental cooling from a liquid He dewar. The injector has shown very good repeatability; however, intact pellets were not observed over 2 km/s, possibly due to a spinning effect on the pellets at higher speed. The cross sections of the guiding tubes have been increased and other design improvements have been implemented, aimed in particular at reducing leak rates and reducing the dispersion of the pellet trajectories, in preparation of the experimental campaign reported here. [Preview Abstract] |
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JP9.00117: Electric potential and magnetic topology in RFX-mod boundary P. Scarin, M. Agostini, G. Spizzo, M. Spolaore, N. Vianello The boundary in the Reversed Field Pinch experiment RFX-mod ($R=2$~m, $a=0.46$~m) is dominated in the high current regime by the helical deformation induced by the dominant toroidal mode $m=1, n=-7$. The outward deformation causes a local enhancement of the Plasma Wall Interaction with an electron pressure increase, a more negative floating potential and a higher particle influx. An analysis of the edge electric field, helical flow and coherent structures growing in the boundary, will be presented. The radial component of the electric field (fundamental in the plasma boundary), is obtained through the edge toroidal flow evaluation as results from the cross-correlation method applied to measurements of optical fluctuations and of floating potential. Our analysis is that a weakly chaotic edge magnetic topology produces a modification of the electron to ion relative diffusion ($D_e/D_i$), due to a larger electron transit time in correspondence to island X-points. The resulting ambipolar electric potential, which guarantees quasi-neutrality in a sheath next to the wall, exhibits a periodicity linked to the dominant island symmetry. [Preview Abstract] |
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JP9.00118: Status of the PIES 3D Equilibrium Code A. Reiman, D. Monticello, D. Raburn, S. Lazerson PIES is a 3D, free-boundary, equilibrium code that can handle islands and stochastic regions. We discuss the present status of the code, focusing particularly on improvements that have been made over the last few years. The code has been modified to provide two additional options for convergence algorithms: 1) a Jacobian-Free Newton-Krylov (JFNK) algorithm, with an adaptive preconditioner, globalized by a subspace restricted backtracking scheme [1]; 2) a full Newton algorithm, appropriate for massively parallel computation. An adaptive grid for calculating the current has also been implemented in recent years, providing a more accurate treatment of the physically important currents near the island separatrices, and of neoclassical effects on tearing modes. In addition, a theory of equilibria in stochastic regions has been developed, and a version of the corresponding algorithm has been implemented in the PIES code [2]. This has been motivated by indications in contemporary stellarator experiments that there are large stochastic regions with significant nonzero pressure gradients.\\[4pt] [1] D. Raburn, Ph.D. Thesis, Princeton University, 2011.\\[0pt] [2] A. Reiman, M. Zarnstorff, D. Monticello, et al, Nucl. Fusion 47, 572-578 (2007); J. A. Krommes and A. H. Reiman, Phys. Plasmas, 16, 072308(2009). [Preview Abstract] |
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JP9.00119: Relaxed Perturbed Equilibria in Tokamaks Jong-Kyu Park, Alan Glasser, Allen Boozer, Jonathan Menard Perturbed equilibria can efficiently model tokamak plasma responses to small 3D magnetic fields. Ideal Perturbed Equilibrium Code (IPEC) and its applications have shown its validness in a wide range of plasma conditions. However, it is also important to understand plasma responses when 3D magnetic fields open magnetic islands in a localized region nearby the rational surfaces, while most of regions remain ideal. In these relaxed perturbed equilibria, the same Euler-Lagrange equations for $\delta $W can be used to solve the ideal force balance, but non-ideal part of solutions should be maintained to control shielding currents and thus to allow magnetic islands at the rational surfaces. DCON and IPEC codes have been modified for this purpose. Initial tests have shown that a relaxed perturbed equilibrium can be unstable even when an ideal perturbed equilibrium is highly stable, which implies in this case that an island cannot be stably relaxed nor maintained. Physics in relaxed perturbed equilibria is more complex than in ideal perturbed equilibria, as will be discussed in details. This work was supported by the US DOE Contract {\#}DE-AC02-09CH11466. [Preview Abstract] |
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JP9.00120: The effects of applied 3-D magnetic fields and resistive wall boundary conditions on nonlinear MHD simulations A.L. Montgomery, C.C. Hegna, C.R. Sovinec, A.J. Cole, S.E. Kruger Two applications of a resistive wall boundary condition are implemented in \textsc{nimrod}: the periodic cylinder with external resonant magnetic fields, and a toroidal resistive wall condition. The resonant 3-D magnetic fields are used to study the shielding of error-fields by axial flow and error-field penetration leading to locked magnetic islands. These studies employ stable, zero-$\beta $ equilibria, and the effects of the degree of stability (measured by the parameter $\Delta $') are investigated. A toroidal resistive wall boundary condition is also developed for \textsc{nimrod} by matching the magnetic fields inside the domain with the external fields found using a vacuum-field solver. The toroidal boundary condition is tested in the large aspect ratio, circular cross-section limit, and compared to the results from the periodic cylinder boundary condition. [Preview Abstract] |
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JP9.00121: Non-linear dynamics of the wall touching kink mode and Hiro current simulation with DSC S.A. Galkin, V.A. Svidzinski, E.G. Evstatiev, L.E. Zakharov The Disruption Simulation Code (DSC) was initially implemented in 2D (single helicity) with all basic MHD components of the full 3D version. It performs adaptive, meshless free-boundary ideal one-fluid MHD simulations of plasma separated from conducting in-vessel structures by a vacuum region. Vacuum fields, the plasma surface and wall currents are calculated using both Green's functions and Poisson equation methods. Two non-linear regimes of the wall touching kink mode were simulated for the first time: (a) a fast ideal MHD regime till the saturation due to excitation of the Hiro currents in a tile covered plasma facing surface, and (b) a slower regime of the current quench due to resistive decay of the Hiro currents. Corresponding sideways forces applied to the plasma facing components and to the vacuum vessel were calculated. Progress on the 3D DSC extension of ideal one fluid MHD is presented. Implementation of the full 3D resistive MHD will be outlined. Together with realistic wall model this will enable DSC to address the MHD issues of the entire disruption problem and to move forward for understanding opportunities for mitigation and prediction of disruptions in ITER. [Preview Abstract] |
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JP9.00122: Concept for Numerical Calculation of 3D MHD Equilibria with Flow and FLR Effects Daniel Raburn, Atsushi Fukuyama Equilibrium flows and 3D effects can significantly impact plasma stability and energy confinement. Further, in equilibria with flow, FLR effects can play an important role. Presently, there exist a number of codes which can calculate MHD equilibria with a subset of the above effects, such as: the FLOW code,[1] the PIES code [2], and a recently developed code for calculating axisymmetric equilibria with flow and hot ions in the large aspect-ratio limit [3]. Using insights gained from these codes, the concept for a new code for calculation of 3D MHD equilibria with flow and FLR effects is being developed; the code is called the Kyoto ITerative Equilibrium Solver (KITES). \\[4pt] [1] L. Guazzotto, R. Betti, J. Manickam, and S. Kaye, Phys. Plasmas 11, 604 (2004).\\[0pt] [2] H. S. Greenside, A. H. Reiman and A. Salas, J. Comput. Phys., 81(1): 102-136, (1989).\\[0pt] [3] D. Raburn and A. Fukuyama, Phys. Plasmas 17, 122504 (2010). [Preview Abstract] |
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JP9.00123: Two-dimensional magnetohydrodynamic simulations of poloidal flows and pedestal formation by transonic effects Luca Guazzotto, Riccardo Betti Highly sheared poloidal flows are present across the H-mode pedestal. Transonic equilibria produce a radial jump (tangential discontinuity in ideal MHD) in density and poloidal velocity. The tangential discontinuity, required by equilibrium force balance and mass and energy conservation, is not a shock, and there is no flow across the discontinuity. In transonic equilibria edge poloidal velocity exceeds the poloidal sound speed $C_{sp} \equiv C_s B_p/B\sim$ 10s km/s. In the present work, we simulate the time evolution of tokamak plasmas in the presence of a smooth source of poloidal velocity with the 2D resistive-MHD code SIM2D. Simulations include a cold halo region (resistive plasma) outside the plasma, and realistic magnetic configurations, including X-points. Simulations show the formation of a discontinuous profile for velocity and density. Plasma core and magnetic field are not modified by the transient. Remarkably, and differently from equilibrium theory, time-dependent simulations show the formation of a pedestal at all angular locations, due to mass redistribution during the transient. [Preview Abstract] |
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JP9.00124: Development of a Fast Scalable Parallel Solver for the HiFi 3D Extended MHD Code A.H. Glasser, V.S. Lukin We report on the development of a fast parallel solver for the HiFi 3D extended MHD code, porting and testing methods previously developed for the 2D version of this code. Physics-based preconditioning is used to reduce the order and condition number and increase the diagonal dominance of matrices. Static condensation is used to eliminate higher-order spectral element amplitudes by local application of SuperLU, automatically exploiting substantial sparsity among the physical dependent variables. A flexible interface to the PETSc library runtime options and profiling capabilities has been developed to test a variety of solvers and preconditioners on the resulting reduced linear systems, and identify bottlenecks amenable to optimization. Matrix assembly has been accelerated by collapsing 3D indices to one in much of the coding. Weak scaling tests up to 4096 cores of the NERSC Hopper Cray XE6 will be presented for a range of 3D test problems, including sound waves, ideal MHD waves, and merging spheromaks. [Preview Abstract] |
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JP9.00125: Improved Parallelization of the SIESTA Magnetohydrodynamic Equilibrium Code Using Cyclic Reduction S. Seal, K. Perumalla, S. Hirshman, C. Cook, R. Sanchez SIESTA is a scalable iterative 3D MHD solver used to find ideal equilibria including islands and stochastic regimes. Its original design used SCALAPACK to parallelize the time-intensive calculation of the physics-based preconditioner involving the inverse of a large block-tridiagonal matrix. The algorithm was based on the Thomas algorithm. Scalability at small to moderate problem sizes was limited due to the sequential nature of the Thomas algorithm. Improved performance has been achieved by incorporating the BCYCLIC code, which uses cyclic reduction in addition to SCALAPACK, to attain 3D scalability with both the 2D block size and the 1D radial dimension. Runtime profile information and model semantics were used to identify scale-dependent bottlenecks of the code, resulting in a cumulative increase of speed over 10X and scalability utilizing a few thousand cores. [Preview Abstract] |
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JP9.00126: The design and implementation of Los Alamos PLasma Simulation (LAPS) code Xianzhu Tang, Alessandro Corbetta, Maria Missanelli, Cecilia Pagliantini, Laura Scarabosio, Gian Luca Delzanno, Zehua Guo, Bhuvana Srinivasan Los Alamos Plasma Simulation (LAPS) is an integrated modeling code based on a common-data framework for multiphysics simulation of both magnetic and inertial confinment fusion (ICF) plasmas. Its principal design goal is to provide a common data structure on computational grids and plasma states for different components of the multiphysics integration. LAPS provides an optimal mesh generation for one to three dimensional configuration space discretization and an adaptive mesh scheme that equi-distributes application-specified error. The plasma state is defined on this mesh. LAPS supports the solution of moment and kinetic equations using grids, particle-in-cell, Monte-Carlo, and molecular dynamics. The parallel data structure and (non)linear solvers for PDEs are based on PETSc, while the parallel data structure and communication for particle and Monte-Carlo method are native to LAPS. LAPS separates the numerical discretization from application PDEs. The initial focus is on spectral method, including the spectral element/volume and discontinuous Garlekin scheme for conservative PDEs. The initial set of applications for LAPS development include PIC modeling of plasma transport and rotation in field reversed configuration, fluid-moment and kinetic model of tokamak scrape-off layer; a two-fluids plasma model of spherical implosion for ICF. [Preview Abstract] |
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JP9.00127: LAPS Grid generation and adaptation Cecilia Pagliantini, Gia Luca Delzanno, Zehua Guo, Bhuvana Srinivasan, Xianzhu Tang, Luis Chacon LAPS uses a common-data framework in which a general purpose grid generation and adaptation package in toroidal and simply connected domains is implemented. The initial focus is on implementing the Winslow/Laplace-Beltrami method for generating non-overlapping block structured grids. This is to be followed by a grid adaptation scheme based on Monge-Kantorovich optimal transport method [Delzanno et al., J. Comput. Phys,227 (2008), 9841-9864], that equidistributes application-specified error. As an initial set of applications, we will lay out grids for an axisymmetric mirror, a field reversed configuration, and an entire poloidal cross section of a tokamak plasma reconstructed from a CMOD experimental shot. These grids will then be used for computing the plasma equilibrium and transport in accompanying presentations. A key issue for Monge-Kantorovich grid optimization is the choice of error or monitor function for equi-distribution. We will compare the Operator Recovery Error Source Detector (ORESD) [Lapenta, Int. J. Num. Meth. Eng,59 (2004) 2065-2087], the Tau method and a strategy based on the grid coarsening [Zhang et al., AIAA J,39 (2001) 1706-1715] to find an ``optimal'' grid. [Preview Abstract] |
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JP9.00128: LAPS parallel data and communication for particle and Monte Carlo methods Alessandro Corbetta, Gia Luca Delzanno, Zehua Guo, Bhuvana Srinivasan, Xianzhu Tang LAPS provides parallel data structure and communication infrastructure for plasma simulation using particle and Monte-Carlo methods. This supplements the parallel data and communication provided by PETSc for grid-based PDE solvers. They nevertheless share non-overlapping block structured grids with three dimensional domain decomposition, that are generated by LAPS griding package using Winslow/Monge-Kantorovich methods. The connectivity matrix of the 3D domain decomposition sets the nearest-neighbor communication pattern. The communication buffers stores the boundary-crossing markers (particles) states using linked lists. Standard MPI send/recv exchanges the transpassing marker information in these dynamically assembled lists. As an initial application, we will implement a parallel electrostatic particle-in-cell solver to compute the plasma transport in a Field Reversed Configuration (FRC) and a tokamak scrape-off-layer (SOL). Full particle is integrated for FRC, while drift-kinetic equation is solved for the tokamak SOL. Particular attention will be devoted to the ambipolar potential due to non-integrable ion orbits in FRC and drift orbits crossing the magnetic separatrix in a tokamak. [Preview Abstract] |
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JP9.00129: LAPS discretization and solution of plasma equilibrium Maria Missanelli, Gian Luca Delzanno, Zehua Guo, Bhuvana Srinivasan, Xianzhu Tang LAPS provides spectral element discretization for solving steady state plasma profiles. Our initial focus is on its implementation for two dimensional open magnetic field equilibria in linear and toroidal geometries. The linear geometry is an axisymmetric magnetic mirror with anisotropic pressure. The toroidal case is a tokamak scrape-off layer plasma. Structured grids are produced by the grid generation package in LAPS. The spectral element discretization uses modal bases over quadrilateral elements. A Newton-Krylov solver implemented with the Portable, Extensible Toolkits for Scientific Computing PETSc is applied to iteratively converge the solution. Care has been taken in the code design to separate the grid generation, spectral element discretization, and (non)linear solver from the user-specified equilibrium equations, so the LAPS infrastructure can be easily used for different applications. [Preview Abstract] |
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JP9.00130: LAPS discretization and solution of plasma dynamics Laura Scarabosio, Gian Luca Delzanno, Zehua Guo, Bhuvana Srinivasan, Xianzhu Tang LAPS provides spectral volume discretization for evolving plasma dynamics described by conservative partial differential equations. Our initial focus is on its implementation for one dimensional spherical and two dimensional cylindrical plasma implosion for inertial confinement fusion (ICF) applications. LAPS primarily targets spectral methods which include spectral volume/element/difference. The spectral volume formulation is particularly attractive for ICF for its explicit local conservation properties and the spectral convergence of the solution. It is also advantageous for plasma transport in magnetic fusion in which cell-wise conservation improves the physics fidelity. Care has been taken to separate the grid generation, spectral volume discretization, and time stepping scheme for the time-dependent two-fluids plasma equations, so the LAPS infrastructure can be easily used for different applications such as tokamak scrape-off layer modeling. [Preview Abstract] |
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JP9.00131: Simulations of ICC Experiments by the PSI-Center Brian Nelson, A.H. Glasser, T.R. Jarboe, C.C. Kim, G.J. Marklin, W. Lowrie, E.T. Meier, R.D. Milroy, U. Shumlak, C.R. Sovinec, J.B. O'Bryan, E. Held, J.-Y. Ji, V.S. Lukin The Plasma Science and Innovation Center (PSI-Center - http://www.psicenter.org) assists collaborating innovative confinement concept (ICC) experiments with extended MHD simulations. Collaborators include the Bellan Plasma Group (Caltech), CTH (Auburn U), FRX-L (Los Alamos National Laboratory), HIT-SI (U Wash - UW), LDX (M.I.T.), MST \& Pegasus (U Wisc-Madison), PHD (UW), PFRC (PPPL), SSX (Swarthmore College), TCS (UW), and ZaP (UW). Modifications have been made to the NIMROD, HiFi, and PSI-Tet codes to specifically model these ICC experiments, including mesh generation/refinement, appropriate boundary conditions (external fields, insulating BCs, etc.), and kinetic and neutral particle interactions. Interfaces of these codes to the powerful 3-D visualization program, VisIt (http://www.llnl.gov/visit) have been developed and implemented. Results from these simulations, as well as an overview of the Interfacing Group status will be presented. [Preview Abstract] |
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JP9.00132: A comparison of NIMROD simulations of RMF current drive with 3-axis probe data from the TCSU experiment Richard Milroy, Katherine Velas The NIMROD code has been adapted to simulate the formation and sustainment of FRCs using Rotating Magnetic Fields (RMF) [R.D. Milroy, C.C. Kim and C.R. Sovinec, Phys. Plasmas, {\bf17}, 062502 (2010)]. Calculations have been performed with the magnetic boundary conditions adjusted to match those of recent experimental measurements as closely as possible. First the n=0 flux on the radial wall is set to match that measured in the experiment, and secondly the n=1 fields imposed are made to approximate the boundary fields measured by the recently installed 3-axis probe. The experimental measurements were made with a new 3-axis probe that was installed on TCSU shortly before its final shut-down. This probe has 90 windings that can simultaneously measure B$_{r}$, B$_{\theta}$, and B$_{z}$ at 30 radial positions. Calculations and experiments were performed with both even-parity and odd-parity antenna sets. For both cases, a comparison of the steady n=0 component of the calculated field shows a very similar structure to that obtained with experimental measurements. [Preview Abstract] |
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JP9.00133: MHD Simulations of Spheromaks and HIT-SI George Marklin, Chris Hansen, Tom Jarboe The PSI Center's tetrahedral mesh MHD equilibrium code, PSI-TET, has been upgraded to solve the time-dependent ideal and resistive MHD equations with either bare conductor or insulated conductor boundary conditions. This poster will describe the numerical methods for solving both the linear and non-linear MHD equations and the numerical technique for implementing the insulated conductor boundary condition. Solutions will be presented for: (1.) Ideal and resistive MHD simulations of a cylindrical spheromak tilting mode with both bare conductor and insulated conductor boundary conditions, which are compared to highlight the effect of an insulated conducting wall and: (2.) Resistive MHD simulations of an inductively formed and sustained spheromak in the HIT-SI experiment with insulated conducting walls and specified time varying injector fluxes and currents. [Preview Abstract] |
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JP9.00134: Open boundary conditions for dissipative MHD Eric Meier, Alan Glasser, Vyacheslav Lukin, Uri Shumlak In modeling magnetic confinement, astrophysics, and plasma propulsion, representing the entire physical domain is often difficult or impossible, and artificial, or ``open'' boundaries are appropriate. A novel open boundary condition (BC) for dissipative MHD, called Lacuna-based open BC (LOBC), is presented. LOBC, based on the idea of lacuna-based truncation originally presented by V.S. Ryaben'kii and S.V. Tsynkov [1], provide truncation with low numerical noise and minimal reflections. For hyperbolic systems, characteristic-based BC (CBC) exist for separating the solution into outgoing and incoming parts. In the hyperbolic-parabolic dissipative MHD system, such separation is not possible, and CBC are numerically unstable. LOBC are applied in dissipative MHD test problems including a translating FRC, and coaxial-electrode plasma acceleration. Solution quality is compared to solutions using CBC and zero-normal derivative BC. LOBC are a promising new open BC option for dissipative MHD. \\[4pt] [1] V.S. Ryabenkii et al., J. Comput. Phys., 174 (2001) 712 [Preview Abstract] |
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JP9.00135: Multi-Block Development and Application to a Shear Flow Z-Pinch Kink Mode Stabilization W. Lowrie, U. Shumlak, A.H. Glasser, V.S. Lukin Recent improvements to the 3D high-order finite (spectral) element HiFi code allow for combining multiple domain blocks into a single computational domain. The blocks themselves must be structured, but the collection of blocks can be unstructured, forming a semi-structured high-order finite element hexahedral mesh. This new feature allows for much more complex and realistic domains to be modeled, including body-fitted and non-simply connected 3D geometries. Additionally an a priori mesh quality analysis is applied to the new meshes to better understand the error associated with deformed mesh elements that result from the more complex geometric domains. Using this new capability of the HiFi code, a verification study of Z-Pinch stability against external kink is performed on a semi-structured cylindrical grid. Applications of a shear flow stabilized Z-Pinch with non-axisymmetric geometry are also presented. The non-axisymmetric geometry aims to model changes in the ZaP Z-Pinch experiment design at the University of Washington, and will provide predictive modeling feedback to the experiment. [Preview Abstract] |
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JP9.00136: MHD-based Modeling of Coaxial Helicity Injection (CHI) in HIT-II C.R. Sovinec, E.C. Howell, A.J. Redd Results from the Helicity Injected Torus-II experiment at the Univ. of Washington distinguish CHI operational regimes for STs with weak and strong levels of magnetic relaxation [Redd, et al., PoP 14, 112511 (2007) and PoP 15, 22506 (2008)]. Numerical time-dependent computation with a simplified zero-$\beta$ resistive-MHD model reproduce the scalings associated with sheet-current equilibria [Bayliss, et al., PoP submitted] in weakly relaxing conditions. The comparisons of laboratory and numerical results from this study are reviewed here, together with a dimensional analysis for ST CHI based on the Grad-Shafranov equation. New computational results for conditions with larger ratios of injected and toroidal-field current are also presented. Symmetry-breaking MHD instabilities relax the current profile and amplify the poloidal flux relative to the vacuum injector flux. The influence of temperature evolution and temperature-dependent transport coefficients is described. [Preview Abstract] |
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JP9.00137: Asynchronous Multi-Dimensional Hybrid Simulations of Magnetized Plasmas Y.A. Omelchenko, H. Karimabadi, M. Brown, U.V. Catalyurek, E. Saule Hybrid simulations provide important insight into the physics of magnetized plasmas with energetic ion components. Ion-driven processes are crucial for understanding the behavior of complex plasma systems such as the Earth magnetosphere and the Field-Reversed Configuration (FRC). Largely varying time and length scales often prevent simulating these systems with adequate resolution. To resolve this issue we developed an asynchronous, uni-dimensional hybrid code, HYPERS. Instead of stepping all simulation variables uniformly in time, HYPERS tracks meaningful changes to individual particles and cell-based electromagnetic fields via discrete events. HYPERS has recently been parallelized with the Preemptive Event Processing (PEP) technique. The parallel algorithm enables arbitrary domain decompositions and processor configurations on restarts. This is a critical prerequisite for implementing a full load balancing functionality. We validate HYPERS by simulating the interaction of streaming plasmas with dipole magnetospheres and show that our approach results in superior numerical metrics (stability, accuracy and speed) compared to conventional techniques. As the first step towards simulating the FRC, we apply HYPERS to study magnetically-driven plasma compression in two dimensions. [Preview Abstract] |
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JP9.00138: Status of TRANSP/PTRANSP Douglas McCune, Rob Andre, Eliot Feibush, Marina Gorelenkova, Christiane Ludescher-Furth, Xingqiu Yuan This poster summarizes the status of TRANSP/PTRANSP code development and run production operations. Production system utilization rates, particularly for MPI jobs, continue to climb. The poster will show production system utilization history and describe status and plans for production facilities and supporting software, as well as the major areas of physics code development. The major physics areas are: simulation using free boundary MHD equilibrium (ISOLVER); neutral beam and fusion product fast ion heating and current drive (NUBEAM); RF heating and current drive (TORIC, GENRAY, and other codes); and predictive transport modeling (PTRANSP and associated modular solvers). In addition, there have been promising advances in capabilities for post-processing and analysis of TRANSP results, based on the SWIM Plasma State software; these too will be described. [Preview Abstract] |
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JP9.00139: A modular, parallel, multi-region predictive transport equation solver, installed and available in PTRANSP Xingqiu Yuan, Douglas McCune, Greg Hammett In this presentation, we introduce a modular, parallel, multi-regional, implicit transport equation solver built over the Plasma State and other publicly available (NTCC) libraries. The solver has been installed, tested, and is available for use in predictive TRANSP (PTRANSP), but, the solver itself does not depend on PTRANSP internals and will itself be made publicly available through the NTCC website. In PTRANSP, the solver is used to integrate the highly nonlinear time-dependent equations for ion, and electron temperatures and densities, and angular momentum with implicit Newton iteration methods. The user controls choice of transport models attached to the solver, with a wide range of neoclassical and/or turbulent, or semi-empirical or data driven choices available. Available turbulent transport models include: MMM series, GLF23, and TGLF. For the more expensive transport coefficient models such as TGLF, a multi-level, communicator splitting method is used to parallelize the computation of transport coefficients using MPI, which allows the code to run on parallel supercomputers. In order to test and benchmark the code, PTRANSP code predicted temperature profiles have been compared to the experimental data, and good agreements have been achieved. [Preview Abstract] |
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JP9.00140: Implementation and Verification of Multi-Mode Transport Model v7.1 in the SWIM/IPS Framework L. Luo, T. Rafiq, A.H. Kritz, G. Bateman The Multi-Mode anomalous transport model, version 7.1 (MMM v7.1) [1], is implemented as a component of the SWIM Integrated Plasma Simulator (IPS). MMM v7.1 is an anomalous theory-based transport model that includes an improved Weiland model for the ITG, TEM and ideal MHD modes together with a quasilinear model for ETG modes and a new model for the drift resistive inertial ballooning modes. Simulations of ITER scenarios are carried out using IPS with MMM v7.1, and the simulation results are verified with those obtained in comparable PTRANSP simulations. In particular, the temperature profiles predicted in the SWIM simulations are compared with those obtained in the PTRANSP simulations. The IPS provides a flexible, extensible computational framework capable of coupling state-of-the-art models for energy and particle sources, transport, and stability for tokamak core plasma. In the ITER simulations, the parallel versions of the NUBEAM and TORIC components are used for auxiliary heating, while feedback loops in the TSC component are used to control the plasma position and shape. \\[4pt] [1] T Rafiq \textit{et al,} poster at this APS meeting. [Preview Abstract] |
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JP9.00141: Physics Basis of Multi-Mode Module v7.1 T. Rafiq, A.H. Kritz, G. Bateman, L. Luo In this study, a description and derivation of the theory based Multi-Mode module, MMM v7.1, is presented together with a few examples of simulations of DIII-D tokamak discharges. The module consists of a combination of theory-based transport models that is used to predict the evolution of temperature, density and toroidal rotation profiles in tokamak plasmas. The MMM v7.1 is a multi-fluid model that includes ion and electron temperature gradient modes (ITG and ETG), trapped electron modes (TEM), ideal MHD and drift resistive inertial ballooning modes (DRIBM). The combination of models is necessary in order to include the different physical phenomena that provide contributions to transport in different radial regions of the plasma discharge. For example, the ITG and TEM modes contribute to transport mostly in the plasma core, whereas, DRIBM transport contributes at the plasma edge. Simulated temperature and current density profiles using MMM v7.1 in PTRANSP are compared with data from DIII-D tokamak discharges. The comparison includes the entire profiles from the magnetic axis to the plasma edge. [Preview Abstract] |
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JP9.00142: Variational Symplectic Orbit Code in 3-D Tokamak Geometry Charles Ellison, Hong Qin, William M. Tang Since advanced tokamak experiments -- including ITER -- are long-pulse systems, it is important to develop accurate numerical methods to track plasma dynamics over an extended temporal period. When attempting to model the motion of individual particles, standard integrators (e.g. 4th order Runge-Kutta) discretize the differential equations of motion -- but do not possess desired properties such as energy conservation. The variational symplectic integrator adopts instead a different approach via minimizing the action of the guiding center motion to determine iteration rules. Consequently, the Lagrangian symplectic structure is conserved, and the numerical energy error is bounded by a small number for all time-steps. In previous work [1], the theoretical basis for this method was introduced, but the implementation was for 2-D geometry. To address realistic experimental scenarios, the variational symplectic integrator has been implemented for 3-D tokamak geometry for the first time. Sample results will be presented and compared with those from standard Runge-Kutta-based 3-D tokamak orbit codes. \\[4pt] [1] H. Qin, X. Guan, and W. M. Tang, PHYSICS OF PLASMAS 16, 042510 2009. [Preview Abstract] |
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JP9.00143: Quasilinear Line Broadened Model for Energetic Particle Transport Katy Ghantous, Nikolai Gorelenkov, Herbert Berk We present a self-consistent quasi-linear model that describes wave-particle interaction in toroidal geometry and computes fast ion transport during TAE mode evolution. The model bridges the gap between single mode resonances, where it predicts the analytically expected saturation levels, and the case of multiple modes overlapping, where particles diffuse across phase space. Results are presented in the large aspect ratio limit where analytic expressions are used for Fourier harmonics of the power exchange between waves and particles, $< e v_d \cdot \delta E >$. Implemention of a more realistic mode structure calculated by NOVAK code are also presented. [Preview Abstract] |
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JP9.00144: Implementation of and first results from FACETS embedded core turbulence transport solver Johan Carlsson, Ammar Hakim, Tom Epperly We present progress in implementation of a core-transport solver with fluxes computed from gyrofluid/gyrokinetic calculations. The gyrofluid fluxes are computed using the theory-based Trapped Gyro-Landau Fluid (TGLF) flux model while the gyrokinetic fluxes are computed from the continuum code GYRO. The solver itself is implemented in the FACETS whole-device modeling framework. Our solver uses a matrix-free Newton solver from the PETSc library, a hypersecant Jacobian evaluation and a novel grid sequencing strategy to accelerate the convergence of the non-linear iterations, minimizingg the flux evaluations. In addition, we have implemented a load balancing scheme using mixed integer linear programming techniques allowing us to achieve near-optimal parallel scaling while using GYRO. We present results of evolving temperature profiles of electrons and ions from DIII-D shot 118897. Time dependent boundary conditions are applied at the core-edge boundary and are taken from experimental measurements. Core heating profiles are held fixed during the evolution and are taken from an interpretive ONETWO simulation. Neoclassical fluxes are computed using a Chang-Hinton model. We compare the evolution with embedded turbulence fluxes to that obtained from the GLF23 model and discuss plans to validate the solver with experimental data. [Preview Abstract] |
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JP9.00145: Improved Numerical Methods for the Plasma Transport Problem G.W. Hammett, J.L. Peterson, J. Candy Direct calculation of the evolution of a magnetic fusion plasma due to small scale turbulence is very challenging because of the wide range of time and space scales. TGYRO [1] and TRINITY [2] solve this problem by a multiscale expansion, using implicit methods to couple the long-time transport equations to gyrokinetic turbulence calculations. TGYRO solves the steady-state problem using a Newton solver to iterate to a global solution. However, with a complex residual terrain, this problem is difficult for a traditional Newton algorithm. Using intuition gained by a simple test problem, we develop improved algorithms that improve the efficiency and reliability of the root-finder. These include a Levenberg-Marquardt algorithm and line backtracking. As a test, we compare these methods on discharges from DIII-D and NSTX using the TGLF transport model [3]. Finally, we predict results for an upcoming experiment on NSTX and explore how impurities can improve electron confinement.\\[4pt] [1] J. Candy et al., Phys. Plasmas 16, 060704 (2009)\\[0pt] [2] M. Barnes et al., Phys. Plasmas 17, 056109 (2010)\\[0pt] [3] G. M. Staebler and J. E. Kinsey, Phys. Plasmas 17, 122309 (2010) [Preview Abstract] |
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JP9.00146: Numerical calculation of the neoclassical electron distribution function in an axisymmetric torus B.C. Lyons, S.C. Jardin, J.J. Ramos We solve for a stationary, axisymmetric electron distribution function ($f_e$) in a torus using a drift-kinetic equation (DKE) with complete Landau collision operator. All terms are kept to gyroradius and collisionality orders relevant to high- temperature tokamaks (i.e., the neoclassical banana regime for electrons). A solubility condition on the DKE determines the non-Maxwellian pieces of $f_e$ (called $f_{NMe}$) to all relevant orders. We work in a 4D phase space $(\psi, \theta, v, \lambda)$, where $\psi$ defines a flux surface, $\theta$ is the poloidal angle, $v$ is the total velocity, and $\lambda$ is the pitch angle parameter. We expand $f_{NMe}$ in finite elements in both $v$ and $\lambda$. The Rosenbluth potentials, $\Phi$ and $\Psi$, which define the collision operator, are expanded in Legendre series in $\cos \chi$, where $\chi$ is the pitch angle, Fourier series in $\cos \theta$, and finite elements in $v$. At each $\psi$, we solve a block tridiagonal system for $f_{NMe}$, $\Phi$, and $\Psi$ simultaneously, resulting in a neoclassical $f_e$ for the entire torus. Our goal is to demonstrate that such a formulation can be accurately and efficiently solved numerically. Results will be compared to other codes (e.g., NCLASS, NEO) and could be used as a kinetic closure for an MHD code (e.g., M3D-C1). [Preview Abstract] |
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JP9.00147: Gyrokinetic Particle Simulation of Alfven Eigenmodes with Zonal Fields Zhixuan Wang, Zhihong Lin Effects of collective Shear Alfven wave instabilities on the energetic particle confinement in Tokamak depend ultimately on the nonlinear evolution of the turbulence with spontaneously generated zonal fields (zonal flows and zonal currents). In this work, we study nonlinear interaction of Alfven eigenmodes with zonal fields using global gyrokinetic toroidal code GTC. At first, we verified GTC for linear electrostatic simulation in cylindrical geometry with the E x B flow shear. Ion temperature gradient instability is observed to be suppressed when E x B flow shear is strong enough. Recently, we have extended our study into electromagnetic simulation. We benchmarked our simulation result against both gyrokinetic theory and experimental data from LArge Plasma Device. In the next step, we will gradually include nonlinear, toroidal effects to study the interaction between zonal fields and Alfven Eigenmodes in tokamaks. Work supported by DOE SciDAC GSEP Center and Plasma Science Center. [Preview Abstract] |
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JP9.00148: Phase Space Analysis of Hybrid Kinetic-MHD Simulations Charlson Kim, Dylan Brennan We present new phase space analysis of energetic particle simulations using the hybrid kinetic-MHD option\footnote{C.~C.~Kim, \textit{PoP}, \textbf{15} 072507 (2008)} in the NIMROD code.\footnote{C.~R.~Sovinec et al., \textit{JCP}, \textbf{195} 355 (2004)} The intent of these new $\delta\!f$ PIC\footnote{S.~E.~Parker and W.~W.~Lee, \textit{PFB}, \textbf{5} 77 (1993)} phase space diagnostics is to help elucidate the physics of energetic particle interactions with MHD modes. In particular we will examine the evolution of $\delta\!f$ in $(v_\parallel,v_\perp)$ space and convolution of the terms in the $\delta\!f$ evolution equation. The contributions from passing and trapped subpopulations are also examined and both are shown to contribute significantly to energetic particle-MHD mode evolution. This phase space analysis reveals that the region near the trapped/passing boundary is a key region of activity. The analysis is in its developmental stage and primarily phenomenological, but continued development and refinement will mature these tools to quantitative and potentially predictive measurements. [Preview Abstract] |
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JP9.00149: Gyrokinetic Simulation of Reverse Shear Alfven Eigenmodes in DIII-D Plasmas Yang Chen, Scott Parker, Jianying Lang, Guo-Yong Fu We present simulation results of the beam driven Reverse Shear Alfven Eigenmodes (RSAE) observed in DIII-D discharge 142111 using the GEM code. Bulk ions and energetic particles are gyrokinetic, but electrons are described by a mass-less fluid model. We observed modes with frequencies sensitive to qmin, and the mode structure dominated by a single poloidal harmonics, suggesting RSAE. The frequency chirping range in the simulation is in agreement with experimental observations. The mode is sensitive to the beam distribution, and for some beam distribution, as qmin is decreased a transition in the most unstable mode is seen. The new mode has a higher frequency that continues to chirp up in time. The beam particles distribution is currently assumed to be slowing-down and isotropic in pitch-angle, but more realistic distributions will be used. Nonlinear simulations will be carried out to determine the saturation amplitude of RSAE with the beam particle collisional effects. We also report code verification results between GEM and M3D-K. [Preview Abstract] |
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JP9.00150: ABSTRACT WITHDRAWN |
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JP9.00151: TAEs excited by ICRH beatwaves in the ASDEX Upgrade Tokamak K. Sassenberg, P.J. McCarthy, M. Maraschek, W. Bobkov, M. Garc\'{I}a-Mu\~{n}oz, V. Igochine, P. Lauber, S. G\"{u}nter, N. Hicks Loss of fast ions caused by Toroidicity induced Alfv\'{e}n Eigenmodes (TAEs) reduces plasma heating and can cause damage to plasma facing components in the vacuum vessel. TAEs are typically excited through auxilliary heating schemes, such as Ion Cyclotron Resonance Heating (ICRH) with limited control. Here an ICRH beatwave can provide that control. The radial structure of a beatwave excited TAE reconstructed from Soft X-Ray measurements is shown to agree with simulations from the gyro- kinetic code LIGKA, and its amplitude is sufficiently small so as not to perturb the plasma state. Since each excited TAE also provides a point of q-profile information to constrain the equilibrium reconstruction, a passive diagnosis of the plasma's safety factor profile can be made. Furthermore, an ICRH beatwave can increase the amplitude of existing TAEs thereby providing the opportunity to study their effect on the fast ion population. [Preview Abstract] |
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JP9.00152: Modification of particle distributions by MHD instabilities Roscoe White The modification of particle distributions by magnetohydrodynamic modes is an important topic for magnetically confined plasmas. Low amplitude modes are known to be capable of producing significant modification of injected neutral beam profiles, and the same can be expected in burning plasmas for the alpha particle distributions. Flattening of a distribution due to phase mixing in an island or due to portions of phase space becoming stochastic is a process extremely rapid on the time scale of an experiment but still very long compared to the time scale of guiding center simulations. In this work we introduce a new method of determining domains of phase space in which good KAM surfaces do not exist, giving exact resonance locations and island widths [1,2]. We use this method for quickly finding the evolution of the particle distribution without carrying out a full guiding center simulation. As examples, profile flattening due to particle avalanche caused by island overlap and large scale flattening of a beam distribution in DIII-D [3,4] due to a large spectrum of low amplitude TAE modes are considered. [1] R. B. White, \textit{Comm. in Nonlinear Science and Numerical Simulations}, CNSNS1906 (2011) [2] R. B. White, \textit{Plasma Physics and Controlled Nuclear Fusion} (2011) [3] R. B. White, N. N. Gorelenkov, W. W. Heidbrink, M. A. Van Zeeland, \textit{Phys. of Plasmas} {\bf 17} 056107 (2010) [4] R. B. White, N. N. Gorelenkov, W. W. Heidbrink, M. A. Van Zeeland, \textit{Plasmas Physics Controlled Fusion} {\bf 52} 045012 (2010) [Preview Abstract] |
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JP9.00153: Nonlinear Theory and Simulation of Energetic Particle-induced Geodesic Acoustic Mode Guoyong Fu Intense axisymmetric density fluctuations were recently observed in DIII-D neutral beam-heated reversed shear plasmas [1]. The instability was identified by analytic theory as the energetic particle-driven GAM or EGAM [2]. The DIII-D experiment also revealed several important nonlinear features of EGAM including a significant second harmonic of the density fluctuation and a clear radial propagation of the mode [3]. In this work, the nonlinear self-interaction of energetic particle-driven geodesic acoustic mode is studied analytically [4] and numerically via hybrid simulation. It is shown that a second harmonic of plasma density perturbation is generated mainly by the convective nonlinearity of both thermal plasma and energetic particles. Near the mid-plane of a tokamak, the second-order plasma density perturbation is negative on the low field side with its size comparable to the main harmonic at low fluctuation level. These analytic results have been confirmed by nonlinear hybrid simulation of EGAM using the parameters and profiles of the DIII-D experiments. The analytic and numerical results are consistent with the experimental observation in DIII-D [3].\\[0pt] [1] R. Nazikian et al., Phys. Rev. Letts. 101, 185001 (2008). [2] G. Y. Fu, Phys. Rev. Letts. 101, 185001 (2008). [3] R. Nazikain et al., Transport Taskforce Workshop, San Diego, April 6-9, 201. [4] G.Y. Fu, J. Plasma Physics, DOI:10.1017/S0022377810000619, (2010) [Preview Abstract] |
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JP9.00154: M3D-K Simulation of Beam-Driven Alfven Modes in DIII-D J. Lang, G.-Y. Fu, Y. Chen, J. Breslau, J. Chen, G. Kramer, M. Van Zeeland M3D-K hybrid simulations [1] are carried to study the beam-driven AEs and compare with the experimental results observed in the DIII-D [2]. We have carried out code benchmark studies for the DIII-D discharge shot {\#}142111. In ideal MHD limit, the M3D-K results agree with that of NOVA in terms of mode structure and mode frequency. However, with energetic beam ions (using the beam pressure profile from TRANSP), RSAEs are not excited in the M3D-K simulations for the DIII-D discharge. The excited mode frequency is not sensitive to q$_{min}$ and the calculated mode structure is also different from the RSAEs obtained in MHD limit of M3D-K simulations. The mode peak is shifted outward with a larger width as compared to that of the RSAE's. Variation in beam profile has little effect on the mode frequency or mode structure. The initial nonlinear simulation showed that the mode structure and mode frequency both change during saturation. Detailed code benchmark with the gyrokinetic electromagnetic code GEM [3] and further comparisons with experiments will be carried out. [1] G.-Y. Fu et al., Phys. Plasmas \textbf{13}, 052517 (2006); [2] B. J. Tobias \textit{et al.}, Phys. Rev. Lett. \textbf{106}, 075003 (2011); [3] Y. Chen and S. E. Parker, J. Comput. Phys. \textbf{220}, 839 (2007). [Preview Abstract] |
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JP9.00155: Fishbone instability and kink mode stabilization in nonperturbative simulations Nikolai Gorelenkov Two phenomena relying on the nonperturbative treatment of the fast ion terms are the fishbone instability and ideal kink mode stabilization. We employ the global NOVA-KN hybrid kinetic-MHD code to study the stability properties of these low-n solutions, such as the resonant (fishbone) and non-resonant (ideal) branches. The nonperturbative approach treats fast ions with their realistic drift orbits numerically by computing the moments of their perturbed pressure tensors in order to include them into the eigenmode equation. We introduce this technique together with the new conforming velocity space grid to efficiently evaluate the wave-particle interaction matrix. The used method results in both resonant and modified non-resonant branches, which are further studied to understand their stability properties in the presence of energetic ions [C.Z. Cheng, Phys. Reports, v.211,p.1 (1992)]. We include the destabilizing effects from energetic beam ions and alpha particles, which seem to be important for the studied instabilities. A model used for beam ion distribution is also presented. We study the properties of those branches in details. The applications to the modified burning ITER plasma are discussed to understand how far the stability region is in the operating space from its nominal values. [Preview Abstract] |
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JP9.00156: Numerical and analytic models of spontaneous frequency sweeping for energetic particle-driven Alfven eigenmodes Ge Wang, H.L. Berk The frequency chirping signal arising from spontaneous a toroidial Alfven eigenmode (TAE) excited by energetic particles is studied for both numerical and analytic models. The time-dependent numerical model is based on the 1D Vlasov equation. We use a sophisticated tracking method to lock onto the resonant structure to enable the chirping frequency to be nearly constant in the calculation frame. The accuracy of the adiabatic approximation is tested during the simulation which justifies the appropriateness of our analytic model. The analytic model uses the adiabatic approximation which allows us to solve the wave evolution equation in frequency space. Then, the resonant interactions between energetic particles and TAE yield predictions for the chirping rate, wave frequency and amplitudes vs. time. Here, an adiabatic invariant J is defined on the separatrix of a chirping mode to determine the region of confinement of the wave trapped distribution function. We examine the asymptotic behavior of the chirping signal for its long time evolution and find agreement in essential features with the results of the simulation. [Preview Abstract] |
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JP9.00157: Nonlinear Frequency Chirping of beta-induced Aflven eigenmode Huasen Zhang The $\beta$-induced Alfv\'en eigenmode (BAE) is studied using global gyrokinetic toroidal code GTC. Linear simulations show that kinetic effects modify BAE mode structure and reduce the frequency relative to the MHD theory. Both passing and trapped energetic particles contribute to BAE excitation through transit and bounce- precessional resonance, respectively. Nonlinear simulations show that the unstable BAE saturates due to nonlinear wave-particle interaction with both thermal and energetic particles. The saturated amplitude exhibits a coherent oscillation with an asymmetric growing and damping phase. Wavelet analysis shows that the mode frequency has a strong chirping associated with the oscillation of the mode amplitude. Analysis of nonlinear wave-particle interaction shows that the frequency chirping is induced by the nonlinear evolution of coherent structures in the energetic particle phase space of toroidal angle and precessional frequency. Controlled simulations further find that thermal particle nonlinearity plays a key role in controlling the saturation amplitude. We will also report self-consistent energetic particle transport from turbulence simulation with wave-particle and wave-wave nonlinearity treated on the same footing for the first time. Work in collaboration with W. Deng, I. Holod, Z. Lin, Y. Xiao and supported by DOE SciDAC GSEP Center and INCITE Program. [Preview Abstract] |
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JP9.00158: Excess-density-driven snakes in tokamaks A.Y. Aydemir, K.C. Shaing, F.L. Waelbroeck ``Snakes'' refer to sinusoidal patterns observed on space-time plots of soft-X-ray signals in tokamak plasmas. They are generally attributed to persistent and localized density perturbations that form at a rational surface after pellet injection (Weller, JET 1987), and Parker, Alcator-C 1987), or impurity accumulation (Naujoks, ASDEX 1996, Delgado-Aparicio, C-Mod 2011). It is not clear whether all snake observations have a unique origin. A likely explanation is that material trapped inside an island driven by a temperature hole leads to the observed soft-X-ray signals (Wesson 1995). More recently, it has been suggested that they could be the result of saturated nonlinear internal kinks in low, or reversed-shear geometries (Cooper 2011). We have started an examination of some of these issues using ideas from neoclassical transport theory (Shaing 2007) in conjunction with various magnetohydrodynamic models. In a RMHD model, we demonstrated that excess-density-driven bootstrap current can stabilize a resistive $m=1$ island at a small amplitude, leaving a radially and poloidally localized snake-like structure. Extension of this work to more sophisticated models that include diamagnetic effects, and possibly more realistic geometries, will be presented. [Preview Abstract] |
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JP9.00159: Dual Hot Flux Ropes in the Tokamak Core G.S. Yun, H.K. Park, W. Lee, M.J. Choi, S.W. Yoon, Y.M. Jeon, J.H. Lee, C.W. Domier, N.C. Luhmann, Jr., B. Tobias, A.J.H. Donn\'e Dual hot flux ropes interacting in the core of the KSTAR plasmas heated by electron cyclotron resonant waves have been observed by a 2-D ECE imaging diagnostic [1]. The hot flux ropes formed along the m/n=1/1 helical magnetic fields evolve in four distinctive phases: (1) slow growth of a flux rope in the core, (2) sudden emergence of another smaller flux rope co-rotating with the first one, (3) merging of the two, and (4) fast localized crash similar to the sawtooth crash [2]. The observed merging process is consistent with a simple model of two current-carrying wires confined on a flux surface. Implications to the sawtooth control and relevance to the dynamics of solar coronal loops are discussed.\\[4pt] [1] G.S. Yun et al., Rev. Sci. Instr. 81 (2010)\\[0pt] [2] H.K. Park et al., this conference. [Preview Abstract] |
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JP9.00160: The effect of poloidal asymmetries on impurity transport driven by electrostatic microinstabilities A. Moll\'en, S. Moradi, T. F\"ul\"op, I. Pusztai Poloidal asymmetries of impurities in tokamaks can arise due to toroidal rotation, neoclassical effects, asymmetry in impurity source location or the presence of radio frequency (RF) heating. If the density of the impurity ions is poloidally asymmetric then the zero-flux impurity density gradient (the peaking factor) can be reduced. The convective impurity flux can even change sign if the asymmetry is sufficiently large. This effect is most effective in low-shear plasmas with the impurity density peaking on the inboard side and may be a contributing factor to the observed outward convection of impurities in the presence of radio frequency heating. [Preview Abstract] |
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JP9.00161: Observation of Multiple Reconnections during Self-organization Process of High Temperature Fusion Plasma H.K. Park, B. Tobias, M.J. Choi, G.S. Yun, C.W. Domier, N.C. Luhmann, Jr., T. Munsat, A.J.H. Donn\'e, G.W. Spakman Images of a high resolution 2-D Electron Cyclotron Emission Imaging (ECEI) diagnostic shows evidence of multiple magnetic reconnection processes during the internal disruption of a high temperature tokamak plasmas. The disruption induces magnetic self-organization of the toroidal plasma being accompanied by successive or simultaneous multiple layer reconnection. The degree of asymmetric deformation of the internal magnetic structure (m/n=1/1 mode) prior to temperature crash influences the outcome of the disruptive behavior. The observation is critical for the building block of first principle theoretical modeling of the sawtooth oscillation in current driven toroidal plasmas and the understandings can be applied to the impulsive disruptive behavior in flares of the solar, accretion disk and stellar coronae, Earth magnetospheric storms, and controlled fusion. [Preview Abstract] |
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JP9.00162: ABSTRACT WITHDRAWN |
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