Bulletin of the American Physical Society
55th Annual Meeting of the APS Division of Plasma Physics
Volume 58, Number 16
Monday–Friday, November 11–15, 2013; Denver, Colorado
Session JP8: Poster Session IV: Education and Outreach, MHD, Alpha Heating & Computational Methods |
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Room: Plaza ABC |
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JP8.00001: EDUCATION AND OUTREACH |
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JP8.00002: Scientists in the Classroom Activities at LLNL Donald Correll, Joanna Albala, Richard Farnsworth, William Meyer LLNL fusion and plasma education activities are broadening into the ``Scientists in the Classroom'' collaboration between LLNL's Science Education Program (http://education.llnl.gov) and California's San Joaquin County Office of Education (SJCOE). Initial activities involved Grades 6 - 12 teachers attending the SCJOE 2013 summer workshop addressing the physical sciences content within the Next Generation Science Standards (NGSS) as described at http://www.nextgenscience.org/. The NGSS Science and Engineering Practices in Physics workshop (June 22-26, 2013) that took place at the University of the Pacific included participation by the first author using video conferencing facilities recently added to the Edward Teller Education Center adjacent to LLNL. ETEC (http://etec.llnl.gov/) is a partnership between LLNL and the UC Davis School of Education to provide professional development for STEM teachers. Current and future activities using fusion science and plasma physics to enhance science education associated with ``Scientists in the Classroom'' and NGSS will be presented. [Preview Abstract] |
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JP8.00003: The CASPER Virtual Physics Circus Jorge Carmona-Reyes, Brandon Harris, Mudi Chen, Lorin Matthews, Truell Hyde CASPER's Virtual Physics Circus (VPC) is based on the long-running CASPER Physics Circus and is the most recent component in CASPER's ``Seamless Pathway'' educational outreach initiative. The VPC was developed by an interdisciplinary group of physicists, web-designers and educators and employs both web and video game environments to provide students and teachers with engaging, fast-paced educational activities. Access to an integrated curriculum and video library, aligned to both the TEKS (Texas Essentials Knowledge and Skill) and the National Science and Mathematics Standards, is also part of the VPC package. In this talk an initial beta-test of the VPC, conducted for a central Texas independent school district, will be discussed. Future plans for both expansion and translation into Spanish will also be discussed. [Preview Abstract] |
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JP8.00004: Recent Science Education Initiatives at the Princeton Plasma Physics Laboratory Andrew Zwicker, Arturo Dominguez, Sophia Gershman, Nick Guilbert, Aliya Merali, Deedee Ortiz An integrated approach to program development and implementation has significantly enhanced a variety of Science Education initiatives for students and teachers.~This approach involves combining the efforts of PPPL scientists, educators, research and education fellows, and collaborating non-profit organizations to provide meaningful educational experiences for students and teachers. Our undergraduate internship program continues to have outstanding success, with 72{\%} of our participants going to graduate school and 45{\%} concentrating in plasma physics. New partnerships have allowed us to increase the number of underrepresented students participating in mentored research opportunities. The number of participants in our Young Women's Conference increases significantly each year. Our Plasma Camp workshop, now in its 15$^{\mathrm{th}}$ year, recruits outstanding teachers from around the country to create new plasma-centered curricula. Student research in the Science Education Laboratory concentrates on the development of a high-fidelity plasma speaker, a particle dropper for a dusty plasma experiment, microplasmas along liquid surfaces for a variety of applications, an Internet-controlled DC glow discharge source for students, and a Planeterrella for demonstrating the aurora and other space weather phenomenon for the general public. [Preview Abstract] |
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JP8.00005: Infusing Plasma into the High School Curriculum through Teacher Professional Development Aliya Merali, Nicholas Guilbert, Myrna Ortiz, Andrew Zwicker A 2004 report submitted by the Fusion Energy Sciences Advisory Committee noted a critical need for action to prevent a shortage of fusion researchers, specifically highlighting the need for more students to enter the field. In an effort to expose students to plasma physics early on, PPPL created a professional development program for teachers, which provides the resources for infusing plasma into high school curricula. Over the last 15 years, teachers from across the country have participated in a one-week Plasma Camp course including lectures, labs, tours, curriculum planning, and classroom equipment funding opportunities. A 2005 survey indicated that at least 75{\%} of program alumni used material from the workshop annually, primarily in the form of demonstrations.\footnote{D. Nuzzolese, et al. \textit{A Decade of Plasma Camp.} APS DPP 2008.} In a 2013 survey, participants were asked to detail how they use the workshop information in their classrooms, how the program has altered their teaching methods, and what factors, if any, have hindered the implementation of a plasma curriculum. Results of the 2013 survey will be presented. [Preview Abstract] |
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JP8.00006: Remote control of a DC discharge experiment Arturo Dominguez, A. Zwicker, S.A. Wissel, J. Ross Glow discharges are an excellent tool to introduce plasmas to the general public, in part, because of their visual nature [1]. In this poster, we present recent developments of the Remote DC Discharge Experiment. This experiment consists of a 36'' long x 3.5'' radius glass tube containing air held at pressures of approximately 30-200mTorr with a variable voltage between the ends which can be set between 0-2000V to create a glow discharge. Surrounding the tube, a set of Helmholtz coils can be controlled to demonstrate the effects of axial magnetic fields on the plasma. While the experiment is located at PPPL, a webcam displays the experiment online. The parameters (voltage, magnetic field and pressure) can be controlled remotely in real-time by opening a URL which shows the streaming video, as well as a set of Labview controls. The interface has been designed to attract users with a wide range of academic backgrounds by presenting different levels of interactivity, including the most advanced level which gives the user the possibility of empirically finding the breakdown voltage as a function of pressure and electrode separation.\\[4pt] [1] S. A. Wissel, A. Zwicker, J. Ross, S. Gershman, ``The Use of DC Glow Discharges as Undergraduate Educational Tools'' AJP in press 2013 [Preview Abstract] |
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JP8.00007: UNDERGRADUATE AND HIGH SCHOOL RESEARCH |
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JP8.00008: Aurora Borealis Experiment (ABX): A Planeterrella for Education and Outreach Michael McNulty, Andy Carpe, Andrew Zwicker The Planeterrella is an experiment invented by Jean Lilensten of the Laboratoire de Planetologie de Grenoble in France designed to simulate aurorae of various planets. It is done by placing two differently sized aluminum spheres in a bell jar with a pressure of approximately 75 mTorr. Each sphere has magnets inside and is electrically biased. An electrode with the opposite electrical bias is inserted into the bell jar so that the voltage between them is on the order of 300 V. A plasma is then created and an aurora is formed around the magnetic poles of the spheres or near the edge of the electrode. We have made a modified version of the planeterrella, called the Aurora Borealis Experiment (ABX), based upon Lilensten's plans. We will present the technical details of the experiment and preliminary results of its use with a variety of different audiences. [Preview Abstract] |
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JP8.00009: Design and construction of Faraday cup ion detectors using thin film deposition Gregory Szalkowski, Douglass Darrow, Ed Cecil Thin film Faraday cup detectors can provide measurements of fast ion loss from magnetically confined fusion plasmas. These multilayer detectors resolve the energy distribution of the lost ions in addition to giving the total loss rate. Past detectors were assembled by stacking discrete foils and insulating sheets. Outlined here is a design and fabrication methodology for those detectors using thin film deposition. The intention is to use detectors fabricated by this method on JET and NSTX-U. The detectors will consist of alternating layers of aluminum and silicon dioxide. The thicknesses of the films have been designed to isolate energies of interest. Thin film deposition offers the advantage of relatively simple and more mechanically robust construction compared to other methods, as well as precise control of film thickness. Furthermore, this depositional fabrication technique places the layers in intimate thermal contact, providing for 3D conduction and dissipation of the ion-produced heating in the layers rather than the essentially 2D heat conduction in the discrete foil stack implementation. [Preview Abstract] |
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JP8.00010: Experimental study of electric discharge propagation in gas bubbles in liquid Jessica Faust, Sophia Gershman The studies of pulsed electrical discharges in gas bubbles in liquids continue to generate interest by their practical applications to the water treatment as well their theoretical significance for the understanding of the discharge propagation along liquid surfaces. Computational models suggest that the discharge path depends on the ratio of the dielectric constant of the liquid and the gas [1]. This study investigates the formation and propagation of the discharge inside a gas bubble in water and glycerin (dielectric constants of approximately 80 and 41, respectively, at 20 C). The discharge is generated by a 1 $\mu $s pulse of 10 - 15 kV applied between a needle electrode piercing the bubble wall and a disk electrode submerged in the liquid. Time-resolved 5 - 10 ns exposure ICCD images are used to compare the discharge path in Ar, O$_{\mathrm{2}}$, and air bubbles in the two liquid dielectrics. 10 nm bandpass filters are used to image the behavior of various excited species, ex. Ar$+$, OH. Experimental results are compared to the previous modeling results [1]. \\[4pt] [1] N. Yu Babaeva, M. Kushner, J. Phys. D 42, 132003 (2009) [Preview Abstract] |
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JP8.00011: Scaling of a miniaturized cylindrical Hall thruster Daniel Kennedy, Yevgeny Raitses Electric propulsion provides a significantly higher specific impulse that allows mass reduction for spacecraft when used in lieu of chemical propulsion. For micro and nano satellite applications, plasma thrusters should not only be miniaturized in mass and geometry, but also capable of operating efficiently at very low power levels of a few watts or less. Research was conducted to determine theoretical limits and practical restrictions on materials and electrodes for miniaturization of cylindrical Hall thrusters [1,2]. Analysis of the scaling relationships for plasma properties and thruster performance were derived and the thruster design, including the magnetic circuit, will be presented. \\[4pt] [1] Y. Raitses and N. J. Fisch, Phys. Plasmas 8, 2579 (2001).\\[0pt] [2] A. Smirnov, Y. Raitses, and N.J. Fisch, Phys. Plasmas 14, 057106 (2007). [Preview Abstract] |
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JP8.00012: Evolution of Boundary Driven Velocity Fluctuations on the Princeton MRI Experiment Tom Zick, Ethan Schartman, Hantao Ji, Austin Roach, Jeremy Goodman, Eric Edlund, Erik P. Gilson, Peter Slodoba The Princeton MRI Experiment is a modified Taylor-Couette device consisting of two coaxial differentially rotating cylinders with split endcaps capable of producing quasi-Keplarian (qK) flows in a working fluid of GaInSn. The ultimate goal of this experiment is to excite and study the Magneto-Rotational Instability (MRI), thought to regulate the transport of angular momentum in accretion disks through the application of an axial magnetic field. As the MRI has been predicted to alter the flow velocity profile by only a few percent, it is imperative to fully characterize the magnetized boundary layers of the flow to allow unambiguous detection of the MRI. Spatial and temporal evolutions of the flow are observed with a set of Ultrasound Doppler Velocimetry diagnostics, optimized to measure both azimuthal and radial velocities. We report on experiments investigating the evolution of endcap driven fluctuations in qK flows under the effect of an applied axial magnetic field. The fluctuation spectra and radial profiles of velocity are presented with respect to the coupling of flow to the vertical boundaries. [Preview Abstract] |
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JP8.00013: Characterizing the Velocity Profile of a Swirling Gas Experiment by Particle Imaging Velocimetry to Study Angular Momentum Transport in Accretion Disks Samuel Greess, Hantao Ji, Enrique Merino, William Berrios The method by which angular momentum transfers between different sections of accretion disks is a matter of ongoing debate. One suggested answer is Magnetorotational instability (MRI), which would facilitate this transfer through the magnetic interactions between particles at different distances from the center of the disk. While ongoing experiments with MRI have focused on the use of liquid metals to test the effects of magnetic fields, we are developing a swirling gas experiment to study effects beyond incompressible hydrodynamics, including compressible gas dynamics and plasma effects when gas is ionized. A second-generation prototype swirling gas experiment has been built to test the principle and to establish favorable rotation profiles using a chamber of swirling fog to simulate the formation and movement of accretion disks about some gravitational center. The paths of the visible fog particles can then be analyzed with Particle Imaging Velocimetry (PIV) techniques; these velocity measurements can then be organized by a Python program. Anticipated results include a radial profile of velocities at different times during the gas injection process, as well as further refinement of the fog chamber design to improve the accuracy in controlling the profile. [Preview Abstract] |
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JP8.00014: Using High Speed Rotating Gas to Study Angular Momentum in Accretion Disks William Berrios, Samuel Greess, Enrique Merino, Hantao Ji Accretion disks are a sheet of gas and dust which surrounds black holes and quasars. The angular momentum in accretion disks is one of the biggest mysteries in astrophysics. A machine was recently built to create accretion disks in a closed chamber. In order to study this, there are several important instruments that are used: a fog machine to see the accretion disks form within the chamber, a high speed camera to observe and record the formation of the accretion disks, and Particle Image Velocimetry (PIV) to analyze velocity profile of the rotating gas and better understand this phenomenon. By collecting relevant data and subsequent computational analysis, results from a previous experiment are reproduced, expanded and the new properties observed with this experiment are characterized. A discussion of any modifications done to the machine, technical challenges and preliminary results will be presented. [Preview Abstract] |
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JP8.00015: An Alternative Optical System for the Motional Stark Effect Diagnostic T. Milbourne, J. Liu, M. Bitter, A. Diallo, P.C. Efthimion, R. Mumgaard, F. Levinton, K.W. Hill, N. Pablant, S. Scott The presently used systems for Motional Stark Effect (MSE) diagnostics are complex and include many optical components which can degrade the signal intensity and polarization. We propose a new optical system for MSE measurements which uses only one spherical mirror to image the spectral lines. This alternative system offers the following advantages: (1) it consists of only one optical component; (2) by exploiting the astigmatism of a spherical mirror, it focuses the radiation emitted from an entire line segment, perpendicular to the direction of the neutral beam, onto a point on the detector and provides spatial resolution along the beam direction; (3) due to the symmetry of the system, the polarization of the spectral lines is essentially conserved; (4) only a thin slit at the meridional focus is required as a viewing port to the plasma, which will protect the detector from intense neutron and gamma radiation. Test results verifying the polarization-conserving properties for various angles of incidence will be presented. [Preview Abstract] |
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JP8.00016: Ion Flux Characterization of H$_{2}$ and D$_{2}$ Plasmas Produced by an ECR Plasma Source Eric Kaiser, Angela Capece, John Roszell, Charles Skinner, Bruce Koel The use of lithium-conditioned plasma facing components in tokamaks has been shown to improve plasma confinement through a reduction in hydrogen recycling. Surface science techniques are being applied to probe the interactions between lithiated PFC's and H/D plasmas. A Tectra$^{TM}$ Gen 2 plasma source has been commissioned that utilizes electron cyclotron resonance to produce a plasma discharge inside a vacuum test chamber and can produce ion fluxes similar to those typically seen in tokamaks. This source will be utilized to study H/D uptake by lithium films on Mo substrates as a precursor to NSTX-U experiments. In this work we report on the characterization of this source as a first step in its use in surface analysis studies. The source is operated in H$_{2}$ and D$_{2}$ gases and the subsequent ion flux of the plasma is measured by a Faraday Cup. Ion flux measurements are presented in a range of gas pressures and grid voltages up to 2kV. [Preview Abstract] |
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JP8.00017: Neutral-beam-injection fueling for a small, D-3He burning, field-reversed-configuration reactor Michael Buttolph, Daren Stotler, Samuel Cohen Rocket propulsion powered by the D-$^3$He fusion reaction in a Field Reversed Configuration (FRC) has been proposed for a variety of solar-system missions. Two key unique features of this concept are a relatively small, 25-cm-radius, plasma core and a relatively thick (10 cm), dense (1e14 cm$^3$), and cool (100 eV electron temperature) scrape-off layer (SOL). The SOL contains the heated propellant -- likely hydrogen, deuterium or helium -- and also fusion reaction products at a lower density (ca. 1e12 cm$^{-3}$). A critical design question is the refueling of the fusion reactants. A moderate energy neutral-beam method is considered. It must be able to penetrate the SOL without significant losses but must be stopped in the core. DEGAS 2, a Monte-Carlo code designed to model neutral transport, was implemented to simulate beam-plasma interactions including ionization and charge exchange of the neutral beam's helium-3 and deuterium atoms by impact in the SOL and core plasma with thermal plasma constituents and fusion reaction products. Operational methods to alleviate the effects deleterious reactions such as deuterium charge-exchange in the SOL are described. [Preview Abstract] |
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JP8.00018: Modular Python-based Code for Thomson Scattering System on NSTX-U Benjamin Horowitz, Ahmed Diallo, Eliot Feibush, Benoit LeBlanc Fast accurate and reliable measurements of electron temperature and density profiles within magnetically confined plasmas are essential for full operation of fusion devices. We detail the design and implementation of a modular Pythonbased code for the Thomson Scattering diagnostic system of NSTX-U which offers improvements in speed by making full use of the Python's architecture, open-source module packages, and ability to be parallelized across many processors. SciPy's weave package allows the implementation of C/C++ code within our program to clear up bottlenecks in data fitting while not loosing the flexibility and clarity of Python, while Numpy and MatplotLib allow calculations and plotting of the processed data. Using the standard MDSplus input, we create a flexible and expandable algorithm structure which can be implemented on any fusion device utilizing polychromator-based Thomson scattering diagnostic system. [Preview Abstract] |
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JP8.00019: Construction and implementation of a novel dust dropper for the PPPL Dusty Plasma Experiment Roy Tinguely, Arturo Dominguez, Andrew Carpe, Andrew Zwicker The applications of dusty plasma research are far-reaching, from understanding astrophysical systems to studying plasma-wall interactions in magnetically confined plasma experiments. Unfortunately, dusty plasma environments can be difficult to control and replicate in laboratory settings. This poster details the construction, vacuum operation, and initial results of a multifaceted dust dropper, which is being implemented in the PPPL Dusty Plasma Experiment and is expected to improve the reproducibility and characterization of dust cloud formation. The cylindrical plastic shaker comprises four pairings of electromagnets and neodymium magnets, with eight stabilizing springs. The amplitude and frequency of a pulsed current determine the dust dispersal rate, while a biased metallic mesh regulates the area of dispersion and size and charge of dropped particles. Preliminary testing shows that, for 44 micron silica dust, steady dispersal rates as fast as 0.2 mg/s (approximately 1700 particles/s) can be achieved. [Preview Abstract] |
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JP8.00020: Analysis of dust detector response to stainless steel particles P. Landy, C.H. Skinner, H. Schneider Dust accumulation inside next step fusion devices poses a significant safety concern and dust diagnostics will be needed to assure safe operations. A recently developed electrostatic dust detection device has been successfully demonstrated in the NSTX and Tore Supra tokamaks [1,2] and dust detection in the Large Helical Device (LHD) is planned. Both carbon and stainless steel dust particles have been observed in LHD. The detector's response to carbon particles is well understood from laboratory experiments [3], but to date no data exists on its response to stainless steel particles. This work intends to characterize the response of the electrostatic dust detector to 4 to 8 micron diameter stainless steel particles of size comparable to that found in LHD and compare the sensitivity and waveforms generated by stainless steel dust to carbon dust. Results will be used to guide future experiments in LHD.\\[4pt] [1] C.H. Skinner et al., Rev. Sci Instrum. 81, 10E102 (2010).\\[0pt] [2] H. Roche et al., Phys. Scr., T 145 (2011).\\[0pt] [3] D.P. Boyle et al., J. Nucl. Mater. 390-391,1086 (2009). [Preview Abstract] |
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JP8.00021: Development of a GPU-Accelerated 3-D Full-Wave Code for Reflectometry Simulations K.S. Reuther, S. Kubota, E. Feibush, I. Johnson 1-D and 2-D full-wave codes used as synthetic diagnostics in microwave reflectometry are standard tools for understanding electron density fluctuations in fusion plasmas. The accuracy of the code depends on how well the wave properties along the ignored dimensions can be pre-specified or neglected. In a toroidal magnetic geometry, such assumptions are never strictly correct and ray tracing has shown that beam propagation is inherently a 3-D problem. Previously, we reported on the application of GPGPU's (General-Purpose computing on Graphics Processing Units) to a 2-D FDTD (Finite-Difference Time-Domain) code ported to utilize the parallel processing capabilities of the NVIDIA C870 and C1060 [1]. Here, we report on the development of a FDTD code for 3-D problems. Initial tests will use NVIDIA's M2070 GPU and concentrate on the launching and propagation of Gaussian beams in free space. If available, results using a plasma target will also be presented. Performance will be compared with previous generations of GPGPU cards as well as with NVIDIA's newest K20C GPU. Finally, the possibility of utilizing multiple GPGPU cards in a cluster environment or in a single node will also be discussed. \\[4pt] [1] B.C. Rose et al., Poster JP8.00017, APS DPP09 Meeting, Nov. 2-6, 2009, Atlanta, GA [Preview Abstract] |
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JP8.00022: Benchmarking a Discontinuous Galerkin Vlasov-Poisson solver in Gkeyll James Juno, Ammar Hakim, Greg Hammett Gkeyll is a discontinuous Galerkin (DG) code under development to solve a variety of kinetic equations in plasmas, with the aim of solving 5D gyrokinetic equations for edge turbulence. For bench-marking the code, we solved the Vlasov-Poisson system of equations, modeling the two-stream instability, as well as current research in nonlinear wave modes of plasmas, such as Bernstein, Green, and Kruskal (BGK) and kinetic electrostatic electron nonlinear (KEEN) wave modes. Results from Gkeyll compared well with linear and nonlinear analysis of the two-stream instability, and matched results of other computational techniques being used to examine BGK and KEEN wave modes. On bounded domains, we explored sheath plasma physics, and modeled the Pierce Diode connected to an external circuit. These sheath studies will contribute to an understanding of boundary conditions for gyrokinetic equations in the edge of tokamaks. [Preview Abstract] |
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JP8.00023: Characterization of muon and gamma radiations at the PTOLEMY site Susannah Betts, Charles Gentile, Chris Tully, Sandra Zapata PTOLEMY is an experimental project at Princeton Plasma Physics Laboratory designed to determine the present day number density of relic neutrinos through measurement of electrons produced from neutrino capture on tritium. The weak interaction cross section for relic neutrino interactions necessitates high sensitivity measurements that could be influenced by high energy particles, like muons and gamma ray photons, which induce nuclear transitions and secondary electrons. Muons produced from the collision of cosmic rays with atmospheric nuclei are a significant source of background radiation at and below Earth's surface. The muon flux is measured by the coincidence of minimum ionization radiation loss in two plastic scintillator paddles. The spectrum of gamma ray photons is measured using sodium iodide based scintillators. These measurements will provide a characterization of the background and rates at the PTOLEMY site. [Preview Abstract] |
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JP8.00024: High-Field Superconducting Magnets Supporting PTOLEMY Ann Hopkins, Audrey Luo, Benjamin Osherson, Charles Gentile, Chris Tully, Adam Cohen The Princeton Tritium Observatory for Light, Early Universe, Massive Neutrino Yield (PTOLEMY) is an experiment planned to collect data on Big Bang relic neutrinos, which are predicted to be amongst the oldest and smallest particles in the universe. Currently, a proof-of-principle prototype is being developed at Princeton Plasma Physics Laboratory to test key technologies associated with the experiment. A prominent technology in the experiment is the Magnetic Adiabatic Collimation with an Electrostatic Filter (MAC-E filter), which guides tritium betas along magnetic field lines generated by superconducting magnets while deflecting those of lower energies. B field mapping is performed to ensure the magnets produce a minimum field at the midpoint of the configuration of the magnets and to verify accuracy of existing models. Preliminary tests indicate the required rapid decrease in B field strength from the bore of the more powerful 3.35 T magnet, with the field dropping to 0.18 T approximately 0.5 feet from the outermost surface of the magnet. [Preview Abstract] |
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JP8.00025: Multi-threaded acceleration of ORBIT code on CPU and GPU with minimal modifications Ante Qu, Stephane Ethier, Eliot Feibush, Roscoe White The guiding center code ORBIT [1] was originally developed 30 years ago to study the drift orbit effects of charged particles in the strong equilibrium magnetic fields of tokamaks. Today, ORBIT remains a very active tool in magnetic confinement fusion research and continues to adapt to the latest toroidal devices, such as the NSTX-Upgrade, for which it plays a very important role in the study of energetic particle effects. Although the capabilities of ORBIT have improved throughout the years, the code still remains a serial application, which has now become an impediment to the lengthy simulations required for the NSTX-U project. In this work, multi-threaded parallelism is introduced in the core of the code with the goal of achieving the largest performance improvement while minimizing changes made to the source code. To that end, we introduce preprocessor directives in the most compute-intensive parts of the code, which constitute the stable core that seldom changes. Standard OpenMP directives are used for shared-memory CPU multi-threading while newly developed OpenACC (www.openacc.org) directives are used for GPU (Graphical Processing Unit) multi-threading. Implementation details and performance results are presented.\\[4pt] [1] R.B. White and M.S. Chance, Phys. Fluids 27, 2455 (1984) [Preview Abstract] |
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JP8.00026: 3D printed electrodes for a dielectric barrier discharge Robert Albertson, Sophia Gershman, Andrew Zwicker The affordability and advancements in 3D printing technology make it the method of choice for prototyping and development. We investigate how the thickness and density of 3D printed electrodes affects the formation of microdischarges inside a dielectric barrier discharge (DBD) surface modification reactor. We use a Makerbot Replicator II 3D printer to manufacture the electrodes by encasing thin pieces of copper tape in PLA plastic. The DBD setup consists of a cylindrical aluminum HV electrode which is surrounded by a layer of 5mm thick Alumina and is connected to a 15kV, 75-300 kHz, AC power supply. The printed electrodes are grounded and held 5mm beneath the Alumina, forming a discharge gap. The DBD is operated with Ar/Air and Ar/O$_{\mathrm{2}}$/Air mixtures at atmospheric pressure. A PI-MAX 3 ICCD camera is used to image the microdischarges at various stages of their development. The image analysis suggests that the printed electrodes with a thicker plastic layer and a greater infill density have more uniform discharges. Quickfield electric field simulations suggest that the field inside the discharge gap is distorted near the surface of the electrodes due to irregularities in the printed material. These results can be used to guide the future design of 3D printed electrical components. [Preview Abstract] |
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JP8.00027: Experimental results on the structure of hydronamic turbulence in accretion disks Eli Chertkov, E.M. Edlund, H. Ji The Princeton Hydrodynamic Turbulence Experiment (HTX) is a Taylor-Couette device with a variable speed rings at the axial boundaries and the ability to perturb quiescent flow regimes via a pump system. The experiment is designed to quantify purely hydrodynamic effects present in accretion disks, as well as study boundary effects, such as Ekman circulation and Stewartson layers, in Taylor-Couette systems. The results of this experiment supplement those of the Princeton MRI experiment, a Taylor-Couette device filled with a GaInSn fluid, which was designed to study the magnetorotational instability (MRI), the current explanation for observed accretion rates in accretion disks. The main diagnostic in HTX is a laser doppler velocimetry (LDV) system capable of correlating azimuthal and radial velocity measurements. We present recent experimental results on the lifetimes of turbulence forced by direct perturbations as a function of dimensionless rotational shear ($q$) as well as an autocorrelation analysis of the azimuthal velocity fluctuations in the quasi-Keplerian regime. [Preview Abstract] |
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JP8.00028: Voltage Effects on a Commercial Plasma Globe G.G. Simmons, L. Saucedo, M.J. Burin, A. Nagy, S.J. Zweben Filamentary structures have been observed in both atmospheric and industrial dielectric barrier discharges, yet various physical aspects of filament formation remain unclear. An example of filament formation can be found in commercial plasma globes. These globes typically contain Neon/Xenon at a pressure near 740 Torr, and are supplied with high voltage (5-10kV) near 25 kHz. The reason why these conditions are optimal for filamentary structures is unknown. This work analyzes the effects of voltage amplitude and frequency on a plasma globe using a programmable high voltage supply. We find that increasing voltage amplitude generally increases the drawn current and the number of filaments, but does not significantly affect filament structure. Changing the AC voltage frequency on the other hand significantly affects filament structure, with higher frequencies generally resulting in more focused (smaller average diameter) filaments. These trends are discussed along with their physics and possible applications. [Preview Abstract] |
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JP8.00029: Reynolds number measurement from correlation function analysis on the SSX MHD wind tunnel Adrian Wan, David Schaffner, Jeffrey Owusu-Boateng, Michael Brown Plasma turbulence and magnetic reconnection are studied at the Swarthmore Spheromak Experiment through high velocity counter-helicity spheromak merging and single-plume relaxation experiments (typical values $n\geq10^{20}~m^{-3}, T \geq 20~eV, B\cong 0.1~T$). Fluctuations in magnetic field, velocity field, density, and soft x-ray light are measured in the SSX MHD wind tunnel configuration ($L \cong 1~m$, $r \cong 10~cm$). Magnetic structure and fluctuations in SSX plasmas are measured with a 16 channel high-resolution probe array ($4~mm$ spatial resolution, $30~MHz$ bandwidth), inserted radially at the midplane of the flux conserver. The magnetic Reynolds number of the turbulence can be estimated directly from the radial correlation function between probe channels. The correlation function $R({\bf r}) = \langle {\bf b(x) b(x+r)} \rangle \cong 1 - r^2/2 \lambda_T^2$ yields an estimate for the Taylor microscale $\lambda_T$, the scale at which dissipation commences.\footnote{Matthaeus \textit{et al.}, PRL 2005} The correlation scale $\lambda_C$ is the size of the largest magnetic eddies. The effective magnetic Reynolds number is then $R_M = (\lambda_C/\lambda_T)^2$. Preliminary estimates of $R_M$ measured this way show $R_M \sim 10$. [Preview Abstract] |
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JP8.00030: Minimal ad-hoc screening coefficient from RMP x-point lobe-structures in MAST Isabelle Lee, Saskia Mordijck, Andrew Kirk, James Harrison Resonant Magnetic Perturbations (RMPs) have successfully been employed to mitigate ELMs by changing the pedestal pressure profile. Recently visual x-point camera data on the MAST tokamak was able to observe the creation of 3D tangle structures for various toroidal mode number applications with the RMP coils. By comparing the 2D images of the lobe structures with vacuum calculations of the tangles we can find the minimum needed plasma response to the applied RMPs. Using field line tracing to investigate whether a field line is outside or inside the experimental lobe structure, we can adjust the ``effective'' radial magnetic field perturbation on that a flux surface using a quick-sort algorithm until the field line remains inside the experimental observed lobe-structure. This allows us to quickly calculate a minimum ad-hoc screening that can be compared with actual complicated plasma response models. [Preview Abstract] |
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JP8.00031: The double-null map - equilibrium, safety factor on magnetic axis, and perturbation from map parameter Daniel Barnes, Asiha Braxton-Gravin, Jade Jenkins, Halima Ali, Alkesh Punjabi The double-null map is the simplest symplectic map that has the generic magnetic topology of double-null divertor tokamaks. The generating function of the double-null map is given by $S(x$,$y)=x^{2}$/2$+y^{2}$/2-$y^{4}$/4. The equilibrium magnetic surfaces of the double-null map are calculated from the generating function. 0\textless $S$\textless 1/4 gives closed surfaces and private flux surfaces; $S=$1/4 gives the separatrix, and $S$\textgreater 1/4 gives open surfaces. The scaling of safety factor on the magnetic axis, $q_{0}$, with map parameter $k$ is calculated. The scaling of root mean square deviation of energy on the $q_{95}$ surface with map parameter $k$ is calculated and taken as the estimate of magnetic asymmetry to represent the magnetic perturbation. The results of this work will be reported. These results are used to calculate heteroclinic tangles of the separatrix of double-null map. This work is supported by grants DE-FG02-01ER54624, DE-FG02-04ER54793, and DE-FG02-07ER54937. [Preview Abstract] |
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JP8.00032: Heteroclinic tangles of the separatrix of double-null map Asiha Braxton-Garvin, Daniel Barnes, Jade Jenkins, Alkesh Punjabi, Halima Ali The double-null map is the simplest symplectic map that has the generic magnetic topology of double-null divertor tokamaks. The generating function of the double-null map is given by $S(x$,$y)=x^{2}$/2$+y^{2}$/2-$y^{4}$/4. $S=$1/4 gives the separatrix surface. The scaling of safety factor on the magnetic axis, $q_{0}$, with map parameter $k$ is used to calculate the number of iterations of the double-null map $N_{p}$ that is equivalent to a single toroidal circuit of the tokamak. The scaling of root mean square deviation of energy on the $q_{95}$ surface with map parameter $k$ is taken as the estimate of magnetic asymmetry to represent the magnetic perturbation from map parameter $k$. These data is used in the forward and backward double-null maps to calculate the heteroclinic tangles of the ideal separatrix of generic double-null divertor tokamaks from magnetic asymmetries. This work is supported by grants DE-FG02-01ER54624, DE-FG02-04ER54793, and DE-FG02-07ER54937. [Preview Abstract] |
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JP8.00033: Experimental and Computational Studies of Rotational and Magnetic Pumping in a Toroidal Electron Plasma Alex S. Patterson, Andrew R. Doares, Matthew R. Stoneking Electron plasma is confined using a purely toroidal magnetic field ($R_0$=18 cm, B $<$ 1 kG) for times (1s) that are much longer than any of the dynamical timescales of the system. The Lawrence Non-Neutral Torus II (LNT II) can be operated as a partial torus in which plasma is confined in C-shaped set of toroidal sectors or as a fully toroidal, closed-field trap. Experimentally controlling the plasma's equilibrium position is found to increase the m=1 diocotron mode damping time from near 40ms to near 400ms. Three-dimensional equilibria are computed by enforcing a Boltzman distribution along field lines, yielding new predictions of rotational and magnetic pumping timescales for this diocotron mode. Recent magnetic field enhancements permit extension of mode damping and confinement studies to higher field (from B $<$ 500 G up to 1 kG) strengths. This work is supported by National Science Foundation Grant Award No.1202540. [Preview Abstract] |
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JP8.00034: Characterization of the Horizontal Confinement Produced by a Glass Box in a Complex Plasma Jace Bradshaw, Angela Douglass The majority of plasmas in the visible universe are complex plasmas, consisting of not only electrons, ions, and neutral particles, but also small, usually micron-sized particles called ``dust.'' Recent complex plasma experiments have placed a glass box on the lower electrode of a GEC RF reference cell in order to alter the electric confinement experienced by micrometer-sized particles in the plasma. While this has led to interesting observations, such as vertical chains and Coulomb balls, the nature of the confinement is not well understood. In this experiment, a single melamine formaldehyde dust particle was levitated in the plasma sheath and contained by a glass box. The dust particle was then struck by a laser pulse to perturb the particle from its equilibrium position. The trajectory of the particle was analyzed to determine the nature of the electric potential produced by the walls of the glass box. Trials were run with varying pressures, particle sizes, box sizes, and plasma powers to determine the effect of each parameter on the confinement. [Preview Abstract] |
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JP8.00035: Applying a Kalman Filter to Magnetic Diagnostics R. Arbacher, S. Angelini, J.P. Levesque, M.E. Mauel, G.A. Navratil, Q. Peng, D. Rhodes Accurate and efficient filtering is vital to removing noise and improving feedback, which in turn allows for longer and more effective containment of plasmas in tokamaks. Assuming random Gaussian noise, the Kalman filter is ideally suited for noise elimination, as it acts recursively using an optimized model to assess both the noise present in the system and the noise inherent to the measurement. This allows for the calculation of a locally accurate Kalman gain, which can be applied in real time. The data for this particular implementation of a Kalman filter derives from 40 sensor pairs spaced evenly around HBT-EP's ten shells, with each pair providing a radial and a poloidal component. These signals, when combined with a resistive wall mode (RWM) dispersion relation [1], yield the magnetic flux both at the wall and at the plasma's edge. This information can be used to identify the RWM and the ideal kink mode, and to apply the appropriate fields to prevent disruption and prolong the life of the plasma. Variation in the initial noise parameters can also induce signal differentiation, which can help isolate non-dominant modes whose effects would otherwise be masked. \\[4pt] [1] Mauel, M. E., \emph{et al}, (2005). Nuclear fusion, \textbf{45} (4), 285. [Preview Abstract] |
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JP8.00036: Electron Temperature Gradient Mode Driven Transport in Alcator C-Mod Plasmas Samuel Bauman, Nathan Howard, Felix Parra, Choongki Sung, Justin Ball, Martin Greenwald, Anne White A series of unique multi-scale (ITG/TEM/ETG) turbulence simulations is currently being performed to investigate the role of Electron Temperature Gradient driven electron heat transport in Alcator C-Mod plasmas where electron heat flux, but not ion heat flux, is underpredicted [Howard Phys. Plasmas 20, 032510 (2013)]. This poster will present detailed linear stability analysis, using the GYRO and GS2 codes, to investigate a hypothesis that the ratio of ETG and ITG/TEM growth rates in two k-ranges can be used to track whether or not ETG driven heat flux is experimentally relevant. Nonlinear GENE simulations [Jenko Phys. Plasmas, 7,1904 (2000)] of ion and electron-scale turbulence show that when the ratio of the growth rates in the two k-ranges is close to the square root of the mass ratio significant electron heat flux is driven by ETG turbulence. Initial investigations indicate that C-Mod plasmas exhibiting underpredictions of electron heat flux satisfy this growth rate ratio criterion. [Preview Abstract] |
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JP8.00037: A Frequency-Varied, Inductively-Coupled Plasma Source for Laboratory Use Anthony Rogers, F. Skiff Presented here is a description of an inductively-coupled plasma source with a folded geometry driven by a capacitive matching network. The inclusion of a matching network allows use of the source over a range of frequencies ($\sim$10-20MHz). The goal is to develop a source with independent control of plasma density and electron temperature by varying the neutral density, source frequency, and source power. The source described is currently in use in a 3-meter long, cylindrical, magnetically-confined Ar II plasma experiment. A survey of plasma electron temperature and density over varied frequencies, neutral densities, and source power will also be presented. [Preview Abstract] |
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JP8.00038: Measurements of the sensitivity of radiochromic film using ion beams J.A. Steidle, J.P. Shortino, D.M. Ellison, C.G. Freeman, T.C. Sangster Radiochromic film (RCF) is used in several diagnostics as a dosimeter that chromatically responds to incident particles. This response depends on the fluence, energy, and species of the incident particles. A 1.7 MV tandem Pelletron accelerator is used to create a monoenergetic ion beam which is scattered off a thin gold target onto a strip of RCF. A surface barrier detector is positioned behind a small hole in the film to measure the ion fluence on the nearby film. Once the film develops, it is scanned to examine its optical density. A response curve is acquired by fitting a three parameter formula to optical density and dose. These calibration curves can be used to help determine incident doses in a variety of situations. [Preview Abstract] |
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JP8.00039: UV Enhancement of Etch Parameters of Nuclear Tracks in CR-39 Nathan Traynor, Christopher McLauchlin, Kenneth Dodge, Graham Jensen, Dante Tufano, James G. McLean, Stephen J. Padalino, Michelle Burke, Craig Sangster The use of CR-39 plastic as a SSNTD is an effective technique for recovering data in high-energy particle experiments including inertial confinement fusion. To analyze particle track data after irradiation, CR-39 is chemically etched at elevated temperatures with NaOH, producing pits at the nuclear track sites that are measurable by an optical microscope. We have shown that CR-39 exposed to high intensity UV light after nuclear irradiation and before etching exhibits increased ratio of track etch rate to bulk etch rate, also known as sensitivity, as evidenced by increased pit diameter compared to non UV exposed CR-39. Pit enhancement has been seen at wavelengths shorter than 350 nm; wavelengths shorter than 250 nm have not been tested. The enhancement appears to be a result of an increase in the track etch rate, as the bulk etch rate exhibits no dependence on wavelength in the region of interest. Detailed analysis of how this effect depends on the intensity and duration of UV exposure is underway. Further, other factors that can arise during UV exposure, such as increased temperature and production of ozone, may also affect sensitivity and are currently being investigated and mitigated. [Preview Abstract] |
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JP8.00040: 3 by 3 Sodium Iodide Absolute Efficiency Determination Stephen Padalino, Megan Russ, Mollie Bienstock, Angela Simone, Drew Ellison, Holly DeSmitt, Craig Sangster Thallium doped sodium iodide (NaI-Tl) detectors are frequently used to measure the activity of samples exposed to ICF neutrons. The absolute detection efficiency for NaI-Tl detectors cannot be represented by a single quoted value. Detection efficiency is largely dependent on gamma ray energy, source location, activity, source and detector geometry and composition, all of which are quantities that are situational. A series of experiments were performed at the State University of New York at Geneseo to determine the absolute detection efficiency for both a single detector and two in-line coincidence detectors using 511 keV gamma rays. A low activity Na-22 gamma ray point source was placed flush against the detector faces of a pair of matched 3''x3'' cylindrical NaI-Tl detectors. The source was then moved relative to the detector face to determine geometric and off-axis effects on the detector's absolute efficiency. The manufacturers of the NaI-Tl detectors quote the absolute photo peak efficiency, at a distance of 10 cm from the detector face, to be 1.2{\%} for a low activity 511keV point source. Using this information the efficiency as a function of position was determined and compared to calculated values. Funded in part by a LLE contract through the DOE. [Preview Abstract] |
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JP8.00041: A Time-of-Flight System for Low Energy Charged Particles Micheal Giordano, Krystalyn Sadwick, Kurt Fletcher, Stephen Padalino A time-of-flight system has been developed to measure the energy of charged particles in the keV range. Positively charged ions passing through very thin carbon films mounted on grids generate secondary electrons. These electrons are accelerated by a -2000 V grid bias towards a grounded channeltron electron multiplier (CEM) which amplifies the signal. Two CEM detector assemblies are mounted 23.1 cm apart along the path of the ions. An ion generates a start signal by passing through the first CEM and a stop signal by passing through the second. The start and stop signals generate a time-of-flight spectrum via conventional electronics. Higher energy alpha particles from radioactive sources have been used to test the system. This time-of-flight system will be deployed to measure the energies of 15 to 30 keV ions produced by a duoplasmatron ion source that is used to characterize ICF detectors. [Preview Abstract] |
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JP8.00042: Investigation of Turbulence and Driven Flow in Magnetized Plasma Using Visible light Imaging Daniel Guice, David Schaffner, Troy Carter, Brett Friedman, Giovanni Rossi, Steve Vincena A fast framing camera is used to image plasma in the Large Plasma Device (LAPD) at UCLA. The use of a camera enables high spatial resolution in a single plasma discharge, without perturbing the plasma. Correlation between light fluctuations and plasma density is high, giving a physical link to what the camera records. From the light fluctuations instantaneous velocity fields are calculated using a wavelet based method that gives us the ability to estimate particle flux and Reynolds stress. These quantities are compared with results obtained with probes. Flow is continuously varied on the LAPD using bias able limiters; this allows for a detailed study of how flow and flow shear modify turbulence and transport. BOUT $++$ simulation code of the LAPD is compared against the fast camera data, and shows similar results. [Preview Abstract] |
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JP8.00043: Optical Emission Spectroscopy in an Unmagnetized Flowing Plasma Blair Seidlitz, Cami Collins, Mark Nornberg, John Boffard, Cary Forest Recently, a new technique has been developed to create a large, weakly magnetized, fast flowing, and hot plasma in the laboratory. These unique conditions make it possible to study a wide variety of phenomena in plasma astrophysics which is the goal of the Plasma Couette Experiment. Accurate measurements of plasma properties such as density and temperature have been challenging with Langmuir probes due to contamination, their perturbative nature, and the flowing plasma. To achieve a non-invasive measurement of relevant parameters, Optical Emission Spectroscopy techniques have been implemented using a low resolution ($\sim$1.5nm) fiber-coupled broad wavelength spectrograph. Argon line ratios were used to determine the metastable ArI densities through radiation trapping and electron temperature was deduced from the energy dependence of many optical emission cross sections. ~Time resolved measurements and radial profiles of temperature have been produced and have shown good agreement with triple probe results in the 2-6eV range. We are expanding these techniques to measurements of the electron density (using quenching of certain transitions), multispecies ion densities and further exploration of higher temperature regions all utilizing spectra from the above mentioned spectrograph, fully exploiting its wide wavelength range. [Preview Abstract] |
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JP8.00044: Astrophysical Jet Formation in a Laboratory Environment Aaron Stemo, Matthew Brookhart, Mike Clark, John Wallace, Cary Forest Astrophysical jets are commonly associated with accreting bodies such as active galactic nuclei (AGN), binary systems, and protostars. These plasma jets are formed due to interactions between the magnetic field of the accreting body and the conducting accretion material. Observational limitations prevent a detailed understanding of the mechanism which launches the jets. Utilizing existing equipment associated with the Line-Tied Reconnection Experiment (LTRX) we have created a new experiment to simulate astrophysical jet formation in a laboratory environment. In contrast to similar experiments, our jets are long-lived, encompass a large volume, and undergo quasi-equilibrium evolution. We have obtained initial results from a high-speed camera showing the evolution of plasma jets in our experiment under varying current levels and field strengths. Future work will include utilization of scanning probes to measure plasma characteristics such as temperature, density, and magnetic field. [Preview Abstract] |
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JP8.00045: Graphics Processing Unit Acceleration of Gyrokinetic Turbulence Simulations Benjamin Hause, Scott Parker, Yang Chen We find a substantial increase in on-node performance using Graphics Processing Unit (GPU) acceleration in gyrokinetic delta-f particle-in-cell simulation. Optimization is performed on a two-dimensional slab gyrokinetic particle simulation using the Portland Group Fortran compiler with the OpenACC compiler directives and Fortran CUDA. Mixed implementation of both Open-ACC and CUDA is demonstrated. CUDA is required for optimizing the particle deposition algorithm. We have implemented the GPU acceleration on a third generation Core I7 gaming PC with two NVIDIA GTX 680 GPUs. We find comparable, or better, acceleration relative to the NERSC DIRAC cluster with the NVIDIA Tesla C2050 computing processor. The Tesla C 2050 is about 2.6 times more expensive than the GTX 580 gaming GPU. We also see enormous speedups (10 or more) on the Titan supercomputer at Oak Ridge with Kepler K20 GPUs. Results show speed-ups comparable or better than that of OpenMP models utilizing multiple cores. The use of hybrid OpenACC, CUDA Fortran, and MPI models across many nodes will also be discussed. Optimization strategies will be presented. We will discuss progress on optimizing the comprehensive three dimensional general geometry GEM code. [Preview Abstract] |
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JP8.00046: Electron Density Fluctuations within the HIT-SI Experiment Taylor Fryett, Brian Victor, Tom Jarboe This research traces the origins of electron density fluctuations in the HIT-SI experiment. HIT-SI is a magnetic confinement experiment that uses two helicity injectors to initialize and sustain current in the confinement region. Densities of 1-10e19 m$^{-3}$ with density fluctuations related to the injector frequency are measured with an FIR interferometer. After spheromak formation, injector currents flow in the direction of toroidal current in the confinement volume. Peaks in the density fluctuations are seen when the injector current passes through the beam path of the interferometer. These observations are consistent with particle motion in the direction of injector current as expected by anti-dynamo action in this region. Furthermore, we have observed fluctuations that indicate that the injector current displaces the confined current. Calculating the toroidal current centroid from surface magnetic probe measurements as a function of time provides further testing of this model. Understanding density fluctuations allows a more complete description of the physics of current drive in HIT-SI. [Preview Abstract] |
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JP8.00047: Validation of Confocal Laser Induced Fluorescence Measurements in an Argon Plasma Robert VanDervort, Jerry Carr Jr., Matthew Galante, Richard Magee, Dustin McCarren, John McKee, Earl Scime, Stephanie Sears, Mark Soderholm To obtain a spatially localized measurement, conventional laser induced fluorescence (LIF) requires overlapping optical paths, i.e., injection and collection paths. Often the injection laser path is focused down to tens of microns at the measurement location. Alignment of the collection optics to the focal spot can be problematic. Two optical ports are often not available. Here we describe the application of confocal optics to LIF measurements in an argon plasma. In a confocal measurement, a single lens is used for both injected light focusing and fluorescence light collection, thereby eliminating the need for laborious optical alignment. The injected laser light and the fluorescent emission are separated by wavelength filtering optical elements and scanning of the measurement location is accomplished by scanning the focusing lens towards or away from the plasma. In this work, we compare ion metastable density and ion temperature profile measurements in argon plasmas obtained by high spatial resolution, conventional crossed-path LIF optics and a compact, optical fiber coupled, confocal LIF measurement system. The data indicate that the confocal system averages over no more than a few mm of the plasma, which is sufficient spatial resolution for nearly any measurement need. [Preview Abstract] |
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JP8.00048: Electron Temperature and Potential Measurements in a Helicon Plasma J. Plank, T.R. Hayes, M. Gilmore Measurements of plasma potential, floating potential, and electron temperature, Te, are notoriously difficult in RF-produced plasmas such as helicons. This work presents comparisons of potential and Te measurements made via swept and stepped compensated and uncompensated single and double Langmuir probes, emissive probes, and static triple probes. These measurements have been made in the HelCat (Helicon-Cathode) linear plasma device at the University of New Mexico using HelCat's helicon source. HelCat is a 4 m long, 0.5 m diameter device with magnetic field, B$_{\mathrm{0}}$ \textless~2.2 kG, and typical densities n $\sim$ 10$^{18}$ -- 10$^{20}$ m$^{-3}$. Comparisons between the measurements and expected theoretical differences will be presented. [Preview Abstract] |
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JP8.00049: Coupling and decoupling of the dust acoustic wave Steven La Count, Jeremiah Williams A dusty plasma consists of ions, electrons, neutral particles and charged microparticles. These charged microparticles result in new collective modes, such as the dust acoustic wave. In this work, the Hilbert Transform is applied to high speed video imaging to examine the transition between the driven and naturally-occurring dust acoustic wave mode in a weakly-coupled, argon dc glow plasma. [Preview Abstract] |
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JP8.00050: Development of time-resolved particle image velocimetry for laboratory and microgravity dusty plasma studies Taylor Hall, Uwe Konopka, Edward Thomas For over a decade, particle image velocimetry (PIV) techniques have been used to study particle transport, instabilities, and the thermal properties of the microparticle component of dusty plasmas. However, dedicated PIV systems are often limited in their temporal resolution to a few Hertz because of the requirements to synchronize the various hardware components of the system. By using a high-speed camera that can record digital video at over 100 Hz, it becomes possible to make temporally resolved measurements of particle motion in a dusty plasma. This presentation will describe the development of an imaging system that will be used for time-resolved PIV measurements of a dusty plasma. In particular, results will be presented on experiments in which different video frame rates are used to make measurements of the effects of a pulsed perturbation that is applied to a dusty plasma. These perturbation studies will be used to determine the optimum frame rate for PIV. [Preview Abstract] |
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JP8.00051: Molecular dynamics simulation of a magnetized dusty plasma using the DEMON code James Schloss, Mark Cianciosa, Edward Thomas A dusty plasma is a four-component plasma system consisting of electrons, ions, neutral atoms, and charge microparticles (i.e., ``dust''). The dynamics of a dusty plasma can often be simulated using molecular dynamics techniques to model the behavior of the charged microparticles in the background plasma. DEMON (dynamic exploration of microparticle clouds optimized numerically) is a modular, object-oriented, molecular dynamics code that has been used to simulate particle transport and waves in a dusty plasma [R. Jefferson, et al., Phys. Plasmas, 17, 113704 (2010)]. Recently, the DEMON code has been modified to include magnetic field effects on the microparticles. This presentation will report on benchmarking magnetic field effects on a dusty plasma in DEMON simulations. Use of the simulation results to aid in interpreting experimental measurements of magnetized dusty plasmas may also be discussed. [Preview Abstract] |
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JP8.00052: Implementation of a high throughput spectrograph for Thomson scattering measurements on the Compact Toriodal Hybrid Matthew Goforth, Peter Traverso, David Maurer To better understand the equilibrium and stability of Compact Toroidal Hybrid (CTH) plasmas, a multipoint Thomson scattering system is under development at Auburn University. Thomson scattering will be performed at 532nm using a frequency doubled Continuum PL DLS Nd:YAG laser [1, 2]. The Thomson scattered light will be measured using a high throughput HoloSpec $f$/1.8i imaging spectrograph with in-line interference filter for spectral discrimination of stray laser light. An image intensified charge coupled device (ICCD) camera employing a Gen III photocathode with quantum efficiency of approximately 50{\%} near the frequency doubled laser line is planned as the detection element for the scattered light. Bench and CTH impurity line emission measurements will be presented quantifying spectrometer and ICCD performance and suitability for scattering measurements over the visible spectral region near 532nm. \\[4pt] [1] D. J. Schlossberg, et al., Rev. Sci. Instr. 82, 10, 10E335\\[0pt] [2] N. L. Schonenbeck, et al., Rev. Sci. Instr. 82, 10, 10E330 [Preview Abstract] |
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JP8.00053: Two-dimensional laser interferometry analysis Leo Mehr, Ricky Concepcion, Robert Duggan, Hannah Moore, Asher Novick, Lauren Ransohoff, Pierre-Alexandre Gourdain, David Hammer, Bruce Kusse The objective of our research was to create a two-dimensional interferometer which we will use to measure plasma densities at the Cornell Research Beam Accelerator (COBRA). We built two shearing interferometers and mounted them on an optics table. They intercept the probe laser beam which travels directly through the plasma and is captured by a 16-bit CCD camera. In comparing the interferometer images before the shot and during the plasma shot, we observed both lateral and vertical shifts in the interference pattern caused by the change of the refractive index due to the plasma electrons. We developed a computer program using Matlab to map a vector field depicting the shift between the two images. This shift is proportional to the line integral of electron density through the plasma chamber. We show this method provides a reliable way to determine the plasma electron density profile. Additionally, we hope this method can improve upon the diagnostic capabilities and efficiency of data collection used with standard one-dimensional interferometry. [Preview Abstract] |
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JP8.00054: High-resolution, 3D mapping of the strapping field for the Caltech Solar Coronal Loop Experiment Patricio Arrangoiz, Bao Ha, Paul Bellan The Caltech Solar Coronal Loop experiment is designed to produce laboratory prominences whose qualitative behavior is scalable to the solar regime. The expansion instability of these plasma loops, often called the torus instability, is attributed to a background magnetic field that straps down the plasma by means of a $\mathbf{J} \times \mathbf{B}$ force. The strapping field profile in the direction of the loop radius can be described by a global power-law dependence with a characteristic exponent. This decay index $n$ must exceed a threshold for the instability to develop. A novel coil setup in the final stages of construction is expected to produce a field with these properties. Here, we present a diagnostic system designed to systematically map both the background and plasma magnetic fields. The former is mapped via custom-built 3-axis Hall sensors with adjustable $(x,y,z)$-position and the latter via a 4-channel, 3-axis B-dot probe. Efficient data visualization techniques are also being developed concurrently. These will in principle allow us to study the relationship between the field profiles and the onset of the instability, complementing recent analytical and numerical treatments. [Preview Abstract] |
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JP8.00055: Development of Linear Image Sensor to Probe Coaxial Magnetized Plasma Jet Formation Maxwell De Jong, Vernon Chaplin, Paul Bellan The Caltech coaxial magnetized plasma jet experiment involves dynamics on sub-microsecond timescales, so fast diagnostics are needed. An expensive fast framing camera is currently used to study jet evolution. To take additional images of jet evolution from different angles, we developed an inexpensive photosensitive detector built around a high performance linear image sensor, the Dynamax ELIS-1024. The linear imager has an array of 1024 pixels with a variable exposure time as small as 10 ns. We designed a circuit to trigger the ELIS-1024 and amplify the output and mounted the circuit on a printed circuit board. The final system will be capable of taking 1D photographs of the plasma or serving as a detector on a spectrometer. Emission spectroscopy identifies the species in the plasma and enables electron temperature estimation through emission line intensity ratios and ion temperature estimation through Doppler broadening. Stark broadening may also be detected. The sensitivity of the detector to these features will be reported. The sensor is also being evaluated for use with a 1D coded aperture imaging system in a separate project. [Preview Abstract] |
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JP8.00056: Particle Probe Investigations on the Helicon Plasma Experiment (HPX) Justin Sherman, R.W. James, S. Nolan, E.J. Page, B. Romano, J. Zuniga, C. Schlank, M. Lopez, J. Karama, O. Duke-Tinson, B.S. Stutzman Coast Guard Academy Plasma Lab(CGAPL) has constructed a Helicon Plasma Experiment. Plasmas will be used in high-temperature and -density diagnostic development for future lab investigations of fusion-grade plasma. Efforts to develop and enhance high temperature and density (10$^{13}$cm$^{-3}$ and up) helicon plasmas at low pressures (.01T) reported by Toki, et.al continue. HPX will integrate a 32-channel National Instruments DAQ(Data Acquisition) board, designed to digitize data from tests. With LabView as the programing language, CGAPL will take samples at 12bits of precision at 2MS/s to create a Graphical User Interface (GUI). The GUI will control experimental variables (one or several concurrent tests) and monitor systems during data collection. Data collection will be conducted with particle probes, currently under construction. Probes, used to discern the plasma mode transitions, will measure plasma particle velocity, temperature, density and floating potential at different regimes. Once independent triple and mach probes for surface point investigations are installed, a triple probe array to produce a more comprehensive density and surface view will follow. Progress on development of GUI and construction of probes will be reported. [Preview Abstract] |
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JP8.00057: Progress on the Pre-Stage Magnetic Coil to Enhance Helicon Mode Excitation on the Helicon Plasma Experiment (HPX) C. Schlank, R.W. James, J. Sherman, S. Nolan, J. Karama, O. Duke-Tinson, M. Lopez, J. Zuniga, E.J. Page, B.S. Stutzman, R.N. Paolino HPX is being developed to utilize the reputed high density (10$^{13}$ cm$^{-3}$ and higher) at low pressure (.01 Torr) [1] Helicon Mode Plasmas. HPX Plasmas are created by imparting directed energy into a Pyrex tube preloaded with Ar gas at fill pressures on the order of 10$^{4}$ mTorr utilizing an RF power supply and matching box that can deliver about 250 W of power in the 20 MHz to 100 MHz frequency range. It has been demonstrated [1] that a uniform magnetic field in lower energy level plasmas can facilitate a decrease in inertial effects, which promotes energy conservation within the plasma to provide the necessary external energy in the plasma's magnetic field required to reach the Helicon Mode. Initial Hall Effect probe testing and calibration has been successful and installation of a 400 to 1000 Gauss electromagnet is being installed to establish and measure the aforementioned uniform field. An acceleration coil, currently under construction, will be used to increase the plasma velocity to facilitate particle and optical probing within the vacuum chamber, for experimental analysis. Initial accuracy and calibration measurements of the relative magnetic fields, created by both electromagnets and measured by the external Hall Effect Probes, will be reported.\\[4pt] [1] K. Toki, et al., Thin Solid Films 506-507 (2005) [Preview Abstract] |
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JP8.00058: Status of the Thomson Scattering System Developed for Diagnostic Testing on the Helicon Plasma Experiment (HPX)* O. Duke-Tinson, R. James, S. Nolan, E. Page, R. Paolino, B. Romano, J. Zuniga, C. Schlank, M. Lopez, J. Karama, J. Sherman, B. Stutzman HPX will utilize Electromagnetic Radiation Scattering to make internal plasma temperature and density point measurements. The United States Coast Guard Academy Plasma Laboratory's (CGAPL's) Thompson Scattering single spatial point system employs a 300 W CW YAG laser. We will use the internal temperature and density measurements in conjunction with the particle and spectral probes to track the plasmas transitions through the capacitive and inductive modes to ultimately reach the helicon mode. Once achieved, the system will be invaluable in making plasma quantitative temperature and density observations that will contribute to a comprehensive plasma profile. Most of the efforts thus far have been in the alignment and repair of the laser system. As this stage nears an end, efforts have begun to shift towards installing the aligned Thomson Scattering system (TS) into its permanent location, with mounted collection optics on HPX's top port. HPX will likely employ a polychrometer similar to the ones currently in use by HBTEP at Columbia University, for the spectral analysis of the scattered light. Data collected by the TS system will then be logged in real time by CGAPL's Data Acquisition (DAQ) system currently under construction. Further additions and progress of the TS alignment, installation, and calibration on HPX will be reported. [Preview Abstract] |
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JP8.00059: D-alpha Probe Investigation on the Helicon Plasma Experiment (HPX) Jackson Karama, Royce James, Justin Sherman, Eric Page, Carter Schlank, Brook Stutzman, Omar Duke-Tenson Now that reproducible plasmas have been created on HPX at the Coast Guard Academy Plasma Laboratory (CGAPL) we are starting to set up a spectral probes to help verify plasma mode transitions to the W-mode. These optical probes will utilize movable filters, ccd cameras and diodes, to gather data at selected spectral frequency bands. Data collected will be used to investigate the plasma's structure and behavior during experiments. The spectral probes will take advantage of HPX's magnetic fields to define and measure the plasma's radiation temp as a function of time. A d-alpha filter will allow for the collection of neutral density fluctuations for different plasma behaviors. In d-alpha mode, the probe may also provide some information on the internal plasma structure and perhaps reveal some global plasma interactions. The spectral probe will add to HPX's data collection capabilities and be used in conjunction with the particle probes, and Thomson Scattering device to create a robust picture of the internal and external plasma parameters on HPX. Progress on the construction of the probe will be reported. [Preview Abstract] |
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JP8.00060: Experimental measurements and modeling of the electron spectrum and betatron x-ray beam profile in a laser-wakefield accelerator Nicholas Chaves, Bradley Pollock, Alethia Barnwell, Paul Campbell, Jessica Shaw, Ken Marsh, Chris Clayton, Arthur Pak, Joseph Ralph, David Alessi, Yu Hsin Chen, Siegfried Glenzer, Chan Joshi, Felicie Albert We have performed experiments using the 200 TW Callisto laser system at LLNL to produce GeV-class electron beams and keV Betatron x-rays. The laser was focused into various gas cells with sizes ranging from 3 to 10 mm that contained a mixture of gases (He, N, Ar). We correlated the measured electron beam to its corresponding x-ray beam profile. These experimental results are benchmarked against a code that solves the equation of motion of electrons oscillating in the plasma wake and by calculating the corresponding x-ray radiation spectrum and profile. [Preview Abstract] |
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JP8.00061: Measuring the betatron x-ray source size from a laser-wakefield accelerator Paul Campbell, Bradley Pollock, Alethia Barnwell, Nicholas Chaves, Jessica Shaw, Ken Marsh, Chris Clayton, Joseph Ralph, Arthur Pak, David Alessi, Yu Hsin Chen, Chan Joshi, Sigfried Glenzer, Felicie Albert We have performed experiments using the 200 TW Callisto laser system at LLNL to produce GeV-class electron beams and keV Betatron x-rays. The laser was focused into various gas cells with sizes ranging from 3 to 10 mm that contained a mixture of gases (He, N, Ar). We determined the betatron x-ray source size using a computer model and experimental observations of straight edge Fresnel diffraction. Experimental results are benchmarked against a code that solves the equation of motion of electrons oscillating in the plasma wake and by calculating the corresponding x-ray radiation spectrum and profile. [Preview Abstract] |
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JP8.00062: Measuring Ion Impurities using EUV Spectroscopy on LTX Grant Bodner, Dennis Boyle, Robert Kaita, Peter Beiersdorfer The Lithium Tokamak eXperiment is a small low-aspect ratio spherical tokamak that investigates the relationship of lithium (Li) wall coatings and plasma-facing components (PFCs). Plasmas produced by tokamaks such as LTX possess similar characteristics to astrophysical plasma phenomena, most notably the stellar flares of the solar corona. Impurities in LTX can emit radiation in the extreme-ultraviolet (EUV) regime with similar spectra seen in these astrophysical plasmas. The Long-Wavelength Extreme Ultraviolet Spectrometer (LoWEUS) was recently added to LTX, to identify ion emission in the 60-400 {\AA} range. LoWEUS is a flat-field grazing-incidence spectrometer that uses a grating with variable line spacing in order to diffract the incident EUV radiation into its respective spectral lines. The EUV spectra collected by LoWEUS can be used to measure both the ion impurity content in LTX as well as to calibrate atomic models used to analyze ion emission from stellar spectra. [Preview Abstract] |
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JP8.00063: Characterization of CNT Plasma Using Single-Angle Imaging Yosef Kornbluth, Francesco Volpe Neutral plasmas were generated in the Columbia Non-neutral Torus (CNT) by means of microwave heating at 2.45 GHz. Visible images of the plasma were collected by a CCD camera and processed to remove the image of the vessel, retaining only the plasma light. The images were then analyzed by two techniques to infer the 3D profile of plasma emissivity at various wavelengths, for the sake, among others, of reconstructing the last closed flux surface and estimating the content and distribution of plasma impurities. In the first technique, we collected images of the same plasma from different angles, reorganized these images in different data arrays, which we treated as a Radon transform of the plasma. In this approach, we made no assumptions about the shape of the flux surfaces. In the second approach, the shapes were calculated beforehand by taking into account the currents in the four CNT coils, but not the plasma response, supposed negligible. By assuming that the plasma emissivity is constant along each flux surface, we infer the profile of emissivity from a single image. This can be considered a 3D generalization of the Abel inversion. We also present numerical tests of the validity of the assumption of uniform emissivity on each surface and discuss the removal of this assumption. [Preview Abstract] |
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JP8.00064: Validation of X-ray Line Ratios for Electron Temperature Profiles in Tokamak Plasmas Andrew Rosen, Matthew Reinke, John Rice, Amanda Hubbard, Jerry Hughes X-ray imaging crystal spectroscopy (XICS) has been implemented on magnetic confinement fusion devices as a novel means of measuring local plasma temperature and flow profiles. At Alcator C-Mod, XICS allows for spatially-resolved, high spectral resolution measurements between 0.3 nm and 0.4 nm, enabling detailed analysis of He-like and H-like argon x-ray emission. Electron temperature profiles in the range of 0.5 keV \textless\ T$_{\mathrm{e}}$ \textless\ 5.0 keV are computed from ratios of the n $=$ 3 dielectronic satellites to the 1s$^{2}$-1s2p resonance lines in He-like argon. These data are validated against existing measurements of Te from electron cyclotron emission and Thomson scattering. Line ratio data are analyzed via a tomographic inversion procedure, overcoming the traditional issue of data being averaged over the plasma cross-section. The implications of utilizing x-ray line ratios as valid local temperature diagnostics are not limited to Alcator C-Mod; plasma properties in future experiments as well as in astrophysical phenomena can also be investigated. [Preview Abstract] |
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JP8.00065: Effect of magnetic shear on critically balanced ITG turbulence Noah Mandell, Michael Barnes, William Dorland, Felix Parra, Peter Catto Critical balance provides a relation between the parallel and perpendicular scales in turbulence [1]. By assuming critical balance and that the maximum parallel correlation length of the turbulence is limited by the magnetic geometry, it is possible to find robust scalings for the maximum perpendicular eddy size and the saturation amplitude of the turbulence with some magnetic geometry parameters [1]. Using a newly developed gyrofluid code called GryfX, along with the gyrokinetic code GS2, we study the effect of magnetic shear on critical balance, the maximum parallel and perpendicular correlation lengths, and the saturation amplitude of the turbulence. This study also seeks to benchmark GryfX with GS2. GryfX runs on NVIDIA GPUs, giving it more than a 70 times performance advantage over a CPU gyrofluid code. Compared to a gyrokinetic code, GryfX also has the advantage of evolving only six moments as opposed to six hundred grid points in velocity space for a kinetic calculation. Combined, these two factors give a seven thousands times performance advantage that allows the use of GryfX to efficiently guide the choice of resolution and other parameters of interest for gyrokinetic simulations.\\[4pt] [1] Barnes et al, Phys. Rev. Lett. 107, 115003 (2011) [Preview Abstract] |
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JP8.00066: Development of the Dynamic Programming Technique to Analyze BES Fluctuation Data A.J. Creely, G.R. McKee, Z. Yan Detecting and accurately quantifying turbulence flows is important to understanding turbulent transport dynamics in magnetically confined plasmas. The Dynamic Programming (DP) mathematical technique has been adapted from fluid dynamics to measure rapidly time-varying turbulent flows that arise from radial electric fields and related turbulent processes. The DP technique enables more precise evaluation of the time- and space-resolved velocity of turbulent eddy structures from 2D BES measurements of local long-wavelength density fluctuations than previous Time-Delay-Estimation methods. The method adapts and optimizes a vector-to-vector matching transformation to reveal underlying high-frequency flows. This analysis technique will be tested and applied to the study of interactions between applied magnetic perturbations and Geodesic Acoustic Modes (GAMs), as well as poloidal flow and flow shear dynamics at the L-H transition and during limit cycle oscillations. [Preview Abstract] |
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JP8.00067: ABSTRACT WITHDRAWN |
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JP8.00068: Analysis of a Measurement of $^{12}$C(n,2n)$^{11}$C Cross Sections Garrett Hartshaw, Ian Love, Mark Yuly, Stephen Padalino, Megan Russ, Mollie Bienstock, Angela Simone, Drew Ellison, Holly DeSmitt, Thomas Massey, Craig Sangster In inertial confinement fusion (ICF), nuclear fusion reactions are initiated by bombarding a small fuel pellet with high power lasers. One ICF diagnostic tool involves placing graphite discs within the reaction chamber to determine the number of high-energy neutrons. This diagnostic requires accurate $^{12}$C(n, 2n)$^{11}$C cross sections, which have not been previously well measured. An experiment to measure this cross section was conducted at Ohio University, in which DT neutrons irradiated polyethylene and graphite targets. The neutron flux was determined by counting recoil protons from the polyethylene in a silicon dE-E detector telescope. Preliminary cross sections were calculated using the incident neutron flux and the number of $^{11}$C nuclei in the graphite and polyethylene targets determined by counting, in a separate counting station, the gamma rays resulting from the positron decay of $^{11}$C. This poster will present the data analysis techniques used to determine these cross sections and the MCNPX simulation used to compute the corrections needed to account for the detector and target geometry. Funded in part by a LLE contract through the DOE. [Preview Abstract] |
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JP8.00069: New Apparatus to Launch Ion Acoustic Waves in 10$^{12}$ /cm$^3$ Density Plasmas Rebecca Roycroft, Seth Dorfman, Troy A. Carter, Shreekrishna Tripathi A new apparatus has been designed and constructed to launch ion acoustic waves in the $\sim$ 10$^{12}$/cm$^3$ density plasma in the small plasma device (SMPD) at UCLA. It consists of a plasma source made of lanthanum hexaboride (LaB6) and a chamber with an anode at the end. Gas will be ionized in this chamber and will diffuse out into the main SMPD chamber. By modulating the anode-cathode voltage on the wave launcher, the density in the wave launcher chamber will be made to oscillate. This plasma will then diffuse out into the main chamber, launching an ion acoustic wave. Design and preliminary results will be presented. Future studies will focus on both linear acoustic mode behavior and nonlinear interactions with Alfven waves in the large plasma device (LAPD) at UCLA. [Preview Abstract] |
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JP8.00070: A 3D high-speed probe for measuring the magnetic components of a whistler wave Pakorn Wongwaitayakornkul, Xiang Zhai, Paul M. Bellan In the Caltech astrophysical jet experiment, observations show that a burst of wave activity in the whistler frequency regime (10-30 MHz) occurs at the time of a fast magnetic reconnection. The whistler wave magnetic component is expected to be circularly polarized even for oblique propagation and also contains most of the energy.\footnote{Bellan, P. M. (2013) \textit{Circular polarization of obliquely propagating whistler wave magnetic field} (submitted for publication).} An inductive whistler wave detector has been designed using B-dot probes to measure the 3D high frequency magnetic field fluctuation. Each probe component consists of two miniature commercial oppositely oriented inductor coils connected to a miniature transformer. The transformer subtracts the signals of the two coils to cancel the unwanted capacitive component and retain the inductive component. The three coil pairs are arranged orthogonally and are adjacent to each other. The probe has excellent rejection of capacitive coupling and should resolve the whistler wave polarization. The measurements will be compared with other diagnostics, namely a capacitively coupled probe, an ultra-high-speed camera and a EUV detector. [Preview Abstract] |
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JP8.00071: DC Studies of Coaxial Vacuum Gap Breakdown for Pulsed Power Liners C.M. Meisenhelder, S.C. Bott-Suzuki, D.M. Haas Previously, pulsed power loads for inertial fusion have been envisioned as cylindrical wire arrays, which could easily be constrained to be in contact with both electrodes for a good electrical connection. Recently, solid liners have become the load of choice for Magnetized Liner Inertial Fusion (MagLIF) experiments which are currently being conducted on the Z-Machine at Sandia National Laboratory. These liners cannot easily be constrained as previous wire loads were, particularly for a repetitive system. The result is a vacuum gap between the driver electrodes and load, which may have unknown effects on the stability and development of the plasma system. DC voltages up to 30 kV will be applied to coaxial electrodes in vacuum to simulate a variety of possible gap parameters for pulsed power liners. This work investigates the breakdown-timing, azimuthal symmetry and coupling of the driver energy to the load as a function of gap parameters to better understand the subsequent behavior of a liner load. [Preview Abstract] |
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JP8.00072: Boron Carbide Materials for Inertial Confinement Fusion C. Mattsson, G.C. Randall, H. Xu, H. Streckert, C. Hill, A. Nikroo Boron carbide shows promise as an inertial confinement fusion (ICF) ablator material because it is light enough that it can be driven efficiently to high velocity, yet strong enough that is may suppress Rayleigh-Taylor instabilities. We seek to fabricate strong, homogeneous boron carbide foils with thicknesses $\sim$0.1 mm, relevant to the production of future ICF targets. We analyze the material properties of various chemical vapor deposition (CVD), sputtered, and hot-pressed boron carbide samples. [Preview Abstract] |
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JP8.00073: Differences in Predictions using the MMM8.1 and MMM7.1 Multi-Mode Transport Models C. Wilson, A.H. Kritz, T. Rafiq, A.Y. Pankin The updated Multi-Mode anomalous transport module version 8.1 (MMM8.1)~[1] includes several advancements over the previous version (MMM7.1). In particular, the new version of the Multi-Mode transport model includes improved formulations of the flow shear effects and of the toroidal and poloidal momentum diffusivities. The MMM8.1 model can be used to compute toroidal and poloidal angular momentum transport as well as thermal and particle transport in tokamaks. To facilitate the research carried out, a new efficient tool has been developed to examine simulation results obtained using the PTRANSP code. The effective diffusivities are computed for several DIII-D discharges using the MMM8.1 model. These diffusivities are compared with those predicted using the previous model, MMM7.1. In addition, systematic scans over a range of plasma parameters such as plasma collisionality, magnetic shear, and \hbox{\bf{E}$\times$\bf{B}} flow shear are carried out. These scans are used to identify those plasma parameters that would result in the most significant differences in predictions using the MMM8.1 transport model in contrast to using the MMM7.1 model. \\[4pt] [1] T. Rafiq, A.H. Kritz, J. Weiland, A.Y. Pankin, and L. Luo, Phys.~Plasmas 20, 032506 (2013). [Preview Abstract] |
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JP8.00074: Charge Exchange Measurements of Impurity Density Asymmetry in DIII-D B.F. Kraus, K.H. Burrell, C. Chrystal, N. Commaux Poloidal asymmetries of impurity density have been investigated using charge exchange spectroscopy measurements of carbon density on both the low- and high-field sides of DIII-D plasmas. In tokamak plasmas with high toroidal rotation, neoclassical theory predicts that centrifugal effects can cause accumulation of impurities on the low-field side of flux surfaces. The magnitude of the poloidal asymmetry is set by a balance between centrifugal effects and the poloidal electric field required to maintain charge neutrality. Accordingly, measurements of impurity density asymmetry, which can be made in the core of DIII-D, can be used to infer poloidal asymmetries of the electrostatic potential. Density asymmetries can be an important component of impurity transport for plasmas with high rotation as well as plasmas with significant fast ion content. Results will be presented for plasmas with both high and low rotation and for plasmas with minimal and significant neutral beam injection. These charge exchange measurements have been supplemented by visible bremsstrahlung measurements of Z-effective on the low- and high-field sides of the plasma. [Preview Abstract] |
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JP8.00075: Comparison of Reported and Inferred Neutral Beam Performance by Neutron and Spectroscopic Measurements on DIII-D R.N. Rozansky, B.A. Grierson, W.W. Heidbrink The DIII-D tokamak is equipped with eight sources for neutral beam injection (NBI). Recent studies of neutron rates indicate that the power injected by each source can differ from the values derived from NBI transmission calculations. During experimental operation, the first discharge of each day is a ``reference shot" that provides information on wall conditions and neutral beam performance. During this reference shot all NBI sources are injected into steady plasma conditions enabling qualitative comparison between sources, and absolute comparison with fusion neutron counters. Spectroscopic diagnostics measure the neutral beam emission from up to six of the eight sources, as well as the circulating fast-ion content injected from all sources by the fast-ion D-alpha (FIDA) technique. Comparison of the neutron rate, beam emission, and fast-ion emission will be made with theoretical models of these processes in order to determine qualitative and quantitative agreement with expectations derived from reported NBI powers. [Preview Abstract] |
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JP8.00076: Correcting for Background Emission Effects in \mbox{DIII-D} LIBEAM Measurements K. Kaplan, D.M. Thomas, H. Stoschus, X. Chen A novel background correction technique has been developed for the DIII-D neutral lithium beam diagnostic (LIBEAM) which is used for diagnosing the local density profile $n_e(r)$ and current density $j(r)$ in the edge ($\rho \ga 0.8$) region of the plasma. The diagnostic relies on the Zeeman splitting of the collisionally excited lithium 2S-2P line in the tokamak magnetic field. Combined spectroscopy and polarimetry are then used to determine the magnetic field components and thence $j(r)$. Background plasma light due to imperfect spectral filtering can represent a significant systematic error in these measurements in some cases. To correct for this effect, a beam splitter was used in conjunction with 670.3$\,$nm and 649.9$\,$nm filters. The output signals from these two filters were then used to determine the non-beam background in real time at the observation point and account for it in the analysis. This process of correcting for background noise allows a more accurate determination of the pitch angle of the plasma under high-density conditions. [Preview Abstract] |
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JP8.00077: Phase-space Characterization of Fast Ion Loss Detectors in the DIII-D Tokamak R.M. Pipes, D.C. Pace, R.K. Fisher Scintillator-based fast ion loss detectors (FILDs) measure the energy and pitch angle of lost energetic ions along the outer wall in DIII-D. The FILDs operate as magnetic spectrometers in which the escaping ions pass through a collimator and strike the scintillator surface according to their gyroradius and pitch angle with respect to the local magnetic field. The mapping of gyroradius/pitch across the scintillator surface, or strike map, is dependent on the primary magnetic field, plasma current, and potentially the toroidal field ripple or applied magnetic perturbations. These parameters vary during experiments, requiring unique Monte Carlo-calculated strike maps. The validity of strike map calculations is demonstrated through experiments in which neutral beams generate well described, and measurable, losses. A computational study of FILD phase-space sensitivity is performed, compared with measurements, and used to quantify uncertainties in the diagnostic. These results serve to constrain transport codes that simulate fast ion losses. [Preview Abstract] |
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JP8.00078: Prediction of Transport Phenomena in Plasmas with Neural Networks C.J. Luna, O. Meneghini, S.P. Smith For our analysis, a multi-layer feed-forward back-propagation neural network is built and trained using data that is taken from the DIII-D database. It is observed that given the same parameters that the most sophisticated numerical codes use, the neural network model is able to accurately predict the heat transport profiles observed in the DIII-D experiments across the whole plasma radius. Consistent results have been obtained over a broad spectrum of plasma configurations, including L-mode discharges that gyro-kinetic models are unable to reproduce. Furthermore, by investigating the weights of the input parameters that are selected by the trained neural network, we are able to more accurately gauge the physical importance of any given input parameter. This poster reports a systematic study of the neural network performance for different input signals, training data sets, and plasma configurations. [Preview Abstract] |
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JP8.00079: Implementation of a Microwave Imaging Reflectometer on DIII-D D.M. Kriete, B.J. Tobias The microwave imaging reflectometer (MIR) is a new plasma diagnostic system on DIII-D that will make localized measurements of density fluctuations on a poloidal cross section of the tokamak. The data from these measurements will provide a quantitative picture of plasma turbulence and MHD instabilities. This project's focus is to install the MIR system on DIII-D, perform calibration tests on it, and develop data analysis tools to process MIR data, with a focus on estimating measurement error. Tests include taking dark shots to subtract out passive noise from the measurements and taking plasma shots to better quantify active noise. Synthetic diagnostics based on numerical codes will also be used to evaluate the MIR system. The MIR uses the same optics as the existing electron cyclotron emission imaging (ECEI) system so, after completion, physicists will have access to a 2D image of both density and temperature fluctuations within the plasma. The MIR thus has broad utility across experiments seeking to understand turbulent transport. [Preview Abstract] |
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JP8.00080: Validation of EFIT++ MHD Equilibrium Reconstructions on DIII-D B. Cornille, M.J. Lanctot, L.L. Lao, L.C. Appel, O. Meneghini, C.T. Holcomb MHD force balance calculations play a key role in the optimization of transport and stability in tokamaks. In high confinement tokamak plasmas, reconstructions of the MHD plasma equilibrium are needed to resolve key profile features including the edge pressure pedestal and resulting bootstrap current. The EFIT code [1] is the standard tool for calculating MHD force balance in DIII-D and many tokamaks. This code has recently been rebuilt to be machine-independent in order to facilitate cross-machine comparisons [2]. This update, EFIT++, is in its late stages of development and requires validation for widespread use. Benchmarking of EFIT++ against the established EFIT cases including motional Stark effect measurements from DIII-D will be presented.\par \vskip3pt \noindent [1] L.L.\ Lao, et al., Fusion Sci.\ Technol.\ {\bf 48}, 968 (2005).\par \noindent [2] L.C.\ Appel, et al., ``Equilibrium Reconstructions on Multiple Tokamaks," to be submitted to Nucl.\ Fusion (2013). [Preview Abstract] |
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JP8.00081: Synthetic Soft X-ray Imaging With 3D Perturbations in DIII-D M.D. Brown, A. Wingen, E.A. Unterberg, M.W. Shafer, N.M. Ferraro, T.E. Evans A synthetic soft x-ray (SXR) diagnostic is applied to the \mbox{DIII-D} tokamak to model measurements of SXR emissions from the lower X-point and divertor region during an resonant magnetic perturbation (RMP) H-mode discharge with intermittent edge-localized modes (ELMs). The synthetic diagnostic takes into account the computed vacuum 3D magnetic field structure in the tokamak as well as linear, resistive, two-fluid MHD. The latter calculates self-consistently the plasma response to the applied RMP field. A $2-3\,$s time series is modeled. The evolution of the discharge is studied, especially focusing on the change in plasma response with evolving plasma parameters. Also ELMs reappear in the second half of the discharge. Therefore, the synthetic diagnostic may help to illuminate RMP ELM suppression. The latter is crucial to ELM control in ITER. [Preview Abstract] |
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JP8.00082: Modeling of Radiative Divertor Dynamics and Control N.A. Sutton-Smolin, D.A. Humphreys, T.W. Petrie, M.E. Fenstermacher A simple control-level model has been constructed for analysis and design of divertor radiation control. The intent is to represent dynamics sufficient to enable design of controllers for divertor radiation, target heat flux, and eventually detachment state. Experimental observations were used to qualitatively characterize the responses of various plasma quantities. Based on the model, a controller was developed for regulating divertor heat flux with PID control algorithms. Four inputs were used: core fueling rate, impurity species flow rates to both core and divertor, and core heating power. High accuracy dynamic control was demonstrated in simulation for core electron density, core stored energy, and divertor target heat flux, simultaneously. The model assumes fully ionized argon gas, uses confinement times inferred from experiment, and describes divertor radiation with a heuristic function of core electron and divertor impurity densities. Simplified control-level models enable design and study of different approaches to integrated core-divertor radiation control. [Preview Abstract] |
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JP8.00083: Converging Resonance Cones in the LAPTAG plasma Cami Katz, Chris Ha, Walter Gekelman, Patrick Pribyl, Nathan Agmon, Joe Wise, Bob Baker The LAPTAG laboratory is a high school outreach effort that has a 1.5m long 50 cm diameter magnetized plasma device. The plasma is produced by an ICP source (1X10$^{9}$ \textless\ n \textless\ 5X10$^{11}$ cm$^{-3})$ and has computer controlled data acquisition. Ring antennas are used to produce converging resonance cones.\footnote{R.L Stenzel, W. Gekelman, Phys. Fluids, 20, 108 (1977).} The experiment was performed in the quiescent plasma afterglow. The electrostatic cones were produced by rf applied to the rings (80 \textless\ f \textless\ 120 MHz), where f$_{\mathrm{RF}}$ \textless\ f$_{\mathrm{ce}}$,f$_{\mathrm{pe}}$. A movable three-axis electric dipole probe, was used to measure the field at thousands of locations and times (dt $=$ 0.4 ns) on a x-z plane where the z axis is parallel to the background field. (50G \textless\ B \textless\ 100 G). Two resonance cones were clearly measured as well as reflections from the density gradient at the plasma edge. The cone angle compares well to the theoretical value. The two focal points, far removed from the antenna are ideal locations for generating hotspots and density perturbations when the rf power is high. Graphics and movies showing the cone generation at different frequencies will be shown. [Preview Abstract] |
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JP8.00084: Nonlinear Resonance Cones and Converging Plasma Blobs Nathan Agmon, Patrick Pribyl, Walter Gekelman, Joe Wise, Cami Katz, Chris Ha, Bob Baker Electric field resonance cones have been shown to create density disturbances in cold, magnetized plasmas.\footnote{W. Gekelman, R.L. Stenzel, Phys. Fluids, 20, 1316 (1977).} Two circular antennas in the LAPTAG experimental plasma device were used to create converging, nonlinear resonance cones. The nonlinear electrostatic field is produced by large amplitude RF (E$_{\mathrm{RF}}$/nkT$_{\mathrm{e}}$ $\gg$ 1). A movable probe, powered by a computerized motor and consisting of three mutually orthogonal electric dipoles, is used to measure the electric field of the cones which become distorted at large amplitudes. A 2D movable Langmuir probe was used to determine localized density perturbations after turn-off of the RF power. A density blob moving at 3-5 times the ion sound speed has been observed to propagate away (for at least 20 cm) from the focus of the cone. Two ring antennas produced colliding blobs. The physics of the collision will be described. [Preview Abstract] |
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JP8.00085: MMD, ALPHA HEATING AND COMPUTATIONAL METHODS |
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JP8.00086: TRANSP - TGLF predictions for ITER R.V. Budny, X. Yuan, B. Grierson, G. Staebler The GLF23 [1] and TGLF [2] quasilinear gyrofluid transport simulation models have been installed in TRANSP for analysis of experiments and for generating self-consistent integrated predictions [3]. A new parallel module PT-SOLVER was developed [4] for efficient solution of these and other numerically challenging transport models. A new spectral shift paradigm was added to TGLF [5] to strengthen the physics basis of toroidal rotation and flow shear simulations. Predictions of density, temperatures, and toroidal rotation are being verified and validated [6,7] with experimental data from JET and DIII-D. Verification and validation results, and predictions for ITER H-mode and hybrid plasmas are given. The ITER predictions are compared with previous TRANSP predictions [8] using the GLF23 model.\\[4pt] [1] R. Waltz, {\it et al.,} Phys. Plasmas {\bf 4} (1997) 2482\\[0pt] [2] G.M. Staebler, {\it et al.,} Phys. Plasmas {\bf 14} (2007) 055909\\[0pt] [3] R.V. Budny, {\it et al.,} IAEA Fus. Energy conf. (2012), San Diego\\[0pt] [4] X. Yuan, {\it et al.,} this conf\\[0pt] [5] G.M. Staebler, {\it et al.,} Phys. Rev. Letters. {\bf 110} 055003 (2013)\\[0pt] [6] R.V. Budny, {\it et al.,} EPS (2013) Espoo\\[0pt] [7] B. Grierson, {\it et al.,} this conf\\[0pt] [8] R.V. Budny, Nucl. Fus. {\bf 52} (2012) 013001 [Preview Abstract] |
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JP8.00087: Burn Control Mechanisms in Tokamaks Maxwell Hill, Weston Stacey Burn control and passive safety in accident scenarios will be an important design consideration in future tokamaks, especially those used as a neutron source for fusion-fission hybrid reactors, such as the Subcritical Advanced Burner Reactor (SABR) concept. At Georgia Tech, we are developing a new burning plasma dynamics code to investigate passive safety mechanisms that could prevent power excursions in tokamak reactors. This code solves the coupled set of balance equations governing burning plasmas in conjunction with a two-point SOL-divertor model. Predictions have been benchmarked against data from DIII-D. We are examining several potential negative feedback mechanisms to limit power excursions: i) ion-orbit loss, ii) thermal instabilities, iii) the degradation of alpha-particle confinement resulting from ripples in the toroidal field, iv) modifications to the radial current profile, v) ``divertor choking'' and vi) Type 1 ELMs. [Preview Abstract] |
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JP8.00088: Preconditioning of the HiFi Code by Linear Discretization on the Gauss-Lobatto-Legendre Nodes A.H. Glasser, V.S. Lukin The most challenging aspect of extended MHD simulation is the scaling of computational time as the problem size is scaled up. The use of high-order spectral elements, as in the HiFi code, is useful for handling multiple length scales and strong anisotropy, but detailed code profiling studies show that cpu time increases rapidly with increasing np, the polynomial degree of the spectral elements, due to the cost of Jacobian matrix formation and solution. We have implemented a method of matrix preconditioning based on linear discretization of the Jacobian matrix on the Gauss-Lobatto-Legendre interpolatory nodes.[J. Brown, J. Sci. Comput. 45, 48-63 (2010)] The resulting matrix has much fewer nonzero elements than the full Jacobian and shares the same vector format. The full solution is then obtained by matrix-free Newton-Krylov methods, which converges rapidly because the preconditioner provides an accurate approximation to the full problem. Scaling studies will be presented for a variety of applications. [Preview Abstract] |
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JP8.00089: A new drift-kinetic equation solver for coupled neoclassical- magnetohydrodynamic simulations in axisymmetric systems B.C. Lyons, S.C. Jardin, J.J. Ramos A set of time-dependent drift-kinetic equations (DKEs) is solved for the non-Maxwellian part of the distribution function ($f_{NM}$) for both electrons and ions using the full, linearized Fokker-Planck-Landau collision operator. The plasma is taken to be axisymmetric and in the neoclassical banana regime. The DKEs are formulated such that the resulting $f_{NM}$ carries no net density, parallel momentum, or kinetic energy. Rather, these quantities are contained within the background Maxwellian and are assumed to be evolved by an appropriate set of extended magnetohydrodynamics (MHD) equations. Computational methods and convergence results will be discussed. The calculated neoclassical conductivity and bootstrap current are benchmarked against theoretical models and other neoclassical codes. Moments of $f_{NM}$ are used to provide a neoclassical closure to the reduced, extended MHD equations, allowing for self-consistent simulations of the inductive formation of the Ohmic and bootstrap currents. Progress towards coupling with TSC and M3D-$C^1$ as well as plans for extensions to nonaxisymmetic geometries will be discussed. This future work will be ideally suited for coupled neoclassical-MHD simulations of core plasma instabilities (e.g., neoclassical tearing modes). [Preview Abstract] |
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JP8.00090: Benchmarking of the Gyrokinetic Microstability Codes GEM, GYRO, and GS2 including Equilibrium \textbf{ExB }Rotation Shear Ronald Bravenec, Yang Chen, Scott Parker, Jeff Candy, Michael Barnes, Christopher Holland, Nathan Howard The physics capabilities of gyrokinetic microstability codes are now so extensive that one cannot demonstrate that the codes correctly solve the gyrokinetic-Maxwell equations (verification) for realistic tokamak plasmas using purely analytic approaches. Instead, one must rely on comparing results from different codes, preferably using different algorithms, for identical plasmas and physics (benchmarking). We present linear and nonlinear comparisons of the Lagrangian particle-in-cell (PIC) code GEM with the Eulerian codes GYRO and GS2 for a low-power DIII-D discharge at the mid-radius. The benchmarking includes not only electron collisions, plasma shaping, kinetic electrons, and one impurity, but also equilibrium \textbf{ExB} rotation shear in the nonlinear simulations. We also present benchmarks for a low-$q$ Alcator C-Mod discharge with broad density profiles, low $q$ and shear, and for the DIII-D plasma at the location of a transport shortfall predicted by GYRO. [Preview Abstract] |
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JP8.00091: Toroidal Ampere-Faraday Equations Solved Consistently with the CQL3D Fokker-Planck Time-Evolution R.W. Harvey, Yu.V. Petrov A self-consistent, time-dependent toroidal electric field calculation is a key feature of a complete 3D Fokker-Planck kinetic distribution radial transport code for f(v,theta,rho,t). In the present CQL3D finite-difference model, the electric field E(rho,t) is either prescribed, or iteratively adjusted to obtain prescribed toroidal or parallel currents. We discuss first results of an implementation of the Ampere-Faraday equation for the self-consistent toroidal electric field, as applied to the runaway electron production in tokamaks due to rapid reduction of the plasma temperature as occurs in a plasma disruption. Our previous results assuming a constant current density (Lenz' Law) model [1] showed that prompt ``hot-tail runaways'' dominated ``knock-on'' and Dreicer ``drizzle'' runaways; we will examine modifications due to the more complete Ampere-Faraday solution.. \\[4pt] [1] R.W. Harvey et al., Physics of Plasmas 7, 4590 (2000). [Preview Abstract] |
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JP8.00092: Reacting Plasma-Neutral Fluid Simulations using the NIMROD Finite Element Code Peter Norgaard, Uri Shumlak NIMROD is being modified to solve fully-coupled neutral particle dynamics with MHD for 3D fusion configurations. Our approach is based on a generalized fluid model derived from the Boltzmann equation that captures the effects of plasma interacting with a gasdynamic neutral fluid. Three implementations are presented, in order of increasing complexity. In the ``static'' model, the neutral fluid properties are fixed and only the plasma dynamics are modified by the contribution of ionization, recombination, and charge exchange reactions to the MHD source terms. In the ``stationary'' model, a fully coupled neutral fluid density equation is evolved simultaneous with the plasma dynamics. The ``isothermal'' model solves the neutral density and momentum equations, but maintains a fixed neutral fluid temperature. Development of an implict leapfrog algorithm for these physical models is based on previous work by C.R. Sovinec and J.R. King. The equations are implemented in the NIMROD psuedospectral / finite element code, which has been used extensively for simulating MHD and two-fluid plasma physics. In this work, we present verification simulations for the static, stationary, and isothermal models, which confirm the collision operator coefficients and plasma-neutral couplings. Initial validation work is also presented for the isothermal model. [Preview Abstract] |
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JP8.00093: PSI-Center Simulations of Validation Platform Experiments B.A. Nelson, C. Akcay, A.H. Glasser, C.J. Hansen, T.R. Jarboe, G.J. Marklin, R.D. Milroy, K.D. Morgan, P.C. Norgaard, U. Shumlak, B.S. Victor, C.R. Sovinec, J.B. O'Bryan, E.D. Held, J.-Y. Ji, V.S. Lukin The Plasma Science and Innovation Center (PSI-Center - http://www.psicenter.org) supports collaborating validation platform 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), LTX (PPPL), MAST (Culham), Pegasus (U Wisc-Madison), PHD/ELF (UW/MSNW), SSX (Swarthmore College), TCSU (UW), and ZaP/ZaP-HD (UW). Modifications have been made to the NIMROD, HiFi, and PSI-Tet codes to specifically model these experiments, including mesh generation/refinement, non-local closures, appropriate boundary conditions (external fields, insulating BCs, etc.), and kinetic and neutral particle interactions. The PSI-Center is exploring application of validation metrics between experimental data and simulations results. Biorthogonal decomposition is proving to be a powerful method to compare global temporal and spatial structures for validation. Results from these simulation and validation studies, as well as an overview of the PSI-Center status will be presented. [Preview Abstract] |
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JP8.00094: NIMROD validation using 3-axis probe data from the TCSU experiment Richard Milroy, Katherine Velas Recent analysis the data from a 3-axis translatable magnetic probe on the TCSU experiment has revealed new details of the magnetic structure of rotating magnetic field (RMF) sustained FRCs. This data was acquired from TCSU just prior to its shutdown in 2011. This analysis which reveals the 3D structure of the magnetic field shows the field lines are opened and relatively short with even-parity current drive, but can be much longer with odd-parity current drive. A torque analysis has revealed new details about the flow of magnetic torque due to both the RMF field and the steady component of the field. This detailed magnetic data provides a good platform for the validation of numerical simulations, and will be compared with predictions from the NIMROD code, which 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)]. [Preview Abstract] |
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JP8.00095: Current Status and Development Plans for the PSI-TET Code George Marklin, Chris Hansen, Tom Jarboe The PSI-TET code is designed for MHD modeling on a tetrahedral mesh which can be quickly generated from a CAD representation of an arbitrary 3-dimensional geometry such as the HIT-SI spheromak experiment. It solves finite element equations using up to fourth order nodal Lagrange or vector Nedelec elements by fully implicit Newton-Krylov iteration with geometric and polynomial multigrid preconditioning. Physics modules currently exist for solving lineraized ideal MHD, non-linear resistive MHD and non-linear resistive Hall MHD (without density or temperature evolution). Boundary conditions allow for an insulator coated conductor and external circuits that drive flux and current in multiply connected regions like the helicity injectors of HIT-SI. Another poster [C. J. Hansen et. al. (this meeting)] will present results from simulations of injector coupling and current drive in HIT-SI. This poster will describe features of the code and documentation currently available, and plans for further development in the near term. This will include the addition of density and temperature equations, neutral interactions, interactive circuits and a new user interface that will simplify the procedure for changing or adding equations. [Preview Abstract] |
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JP8.00096: Integral parallel closures of electrons for arbitrary collisionality Jeong-Young Ji, Eric Held, Hogun Jhang In developing electron parallel closures for density, temperature, and flow velocity equations, we have analytically solved 1600 parallel moment equations for arbitrary collisionality. This is a generalization of our previous work on the heat flow responding to a temperature gradient\footnote{J.-Y. Ji, E. D. Held, C. R. Sovinec, Phys. Plasmas {\bf 15}, 022312 (2009).} and viscosity to a flow velocity gradient.\footnote{ J.-Y. Ji and E. D. Held, J. Fusion Energy {\bf 28}, 170 (2009).} Heat flow, viscosity, and friction force closures are expressed as integrals of the temperature gradient, the difference between electron and ion flow velocities, and the flow velocity gradient weighted by kernel functions. The kernel functions are sums of exponentially decaying functions, which are obtained by solving the eigensystem of the matrix of free streaming and collision terms. Our integral (nonlocal) closures agree well with the existing closures in the collisional and collisionless limits. Furthermore we have obtained fitted kernel formulas for arbitrary collisionality from the moment solution and asymptotic behaviour in the high and low collision limits. The formulas can be used conveniently without solving the higher order moment equations in closing electron fluid equations. [Preview Abstract] |
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JP8.00097: Towards optimal design of 2-D and 3-D shaping for linear microinstability Mordechai Rorvig, Chris Hegna, Harry Mynick, Pavlos Xanthopoulos Optimal design for linear, toroidal microinstability relies on understanding metrics for how geometry affects instability, and how 2-D and 3-D shaping mechanisms can be targeted to improve those metrics. To elucidate these goals, we apply local 3-D equilibrium theory, analytic instability theory, and local, numerical gyrokinetics solution using GENE. Geometric analytic targets and cost function scalings are found for adiabatic linear ion temperature gradient (ITG) modes. Maximum linear growth rates from numerical ITG calculations show reasonable agreement with those from an analytic model that employs a Gaussian estimate for the mode structure. Shaping may be characterized by how it controls the distribution of curvature null lines on the surface, i.e., the lines where the curvatures are zero. Rotation of the cross section mostly only rotates the nulls, whereas cross sectional deformation shifts their relative positioning, providing a shaping mechanism unique to 3-D. More recent efforts at extending and generalizing the results to other important instability channels, such as linear trapped electron modes (TEM), are presented. Application of these results in numerical optimization schemes is discussed. [Preview Abstract] |
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JP8.00098: Validating a 0D predator-prey model for LH Transition with its 1D-2D supersets: effects of heating and fueling on Hysteresis and transition dynamics Mikhail Malkov, Patrick Diamond, Kazuhiro Miki The LH transition crucially depends on the heat and particle deposition, transport and electric field shear suppression. Despite the inhomogeneity of these phenomena, a popular 0D predator-prey model seems to capture the essential transition dynamics, including the limit cycle pre-H-mode oscillations (or I-mode). However, its predictions regarding hysteresis are inconclusive. This is understandable at least because of the known deep fuel lowering of the transition threshold. The readily available fueling devices are the edge neutral penetration and an internal deposition via the supersonic molecular beam injection (SMBI). This suggests a minimal extension of the 0D model by using bi-modal particle distributions. To formulate this extension accurately, a step-by-step comparison with a 1D treatment is required. Fortunately a suitable 1D numerical model has been recently developed specifically for the LH transition studies. In this work, we use the 1D model for the following purposes. First, we explore fueling effects as occurring both by edge neutral penetration, and internal deposition (SMBI) at a finite depth within the separatrix. Second, as the 0D model responds positively to the oscillating heating power, we include a periodic repetitive SMBI firing. [Preview Abstract] |
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JP8.00099: Study of particle transport during application of resonant magnetic perturbations in the J-TEXT tokamak Qiming Hu, Ge Zhuang, Wei Chen, Qinquan Yu, Nengchao Wang, Jie Chen, Li Gao, Yonghua Ding, Bo Rao, Xiwei Hu In the J-TEXT tokamak, electron density pump-out is frequently observed during the application of resonant magnetic perturbations (RMPs). It is found that the applied RMPs cause obvious density pump-out in plasma core, while the edge plasma density changes little. In order to study the density pump-out caused by RMPs, the direct perturbed particle transport measurements are carried out during the application of RMPs in J-TEXT ohmic plasmas. It is found that, compared to the case without application of RMPs, the applied RMPs substantially decrease the pinch velocity V and increase the diffusion coefficient D. Stronger amplitude of applied RMPs results in more obvious change in both the transport coefficients. [Preview Abstract] |
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JP8.00100: New MHD feedback control schemes using the MARTe framework in RFX-mod Chiara Piron, Gabriele Manduchi, Lionello Marrelli, Paolo Piovesan, Paolo Zanca Real-time feedback control of MHD instabilities is a topic of major interest in magnetic thermonuclear fusion, since it allows to optimize a device performance even beyond its stability bounds. The stability properties of different magnetic configurations are important test benches for real-time control systems. RFX-mod, a Reversed Field Pinch experiment that can also operate as a tokamak, is a well suited device to investigate this topic. It is equipped with a sophisticated magnetic feedback system that controls MHD instabilities and error fields by means of 192 active coils and a corresponding grid of sensors. In addition, the RFX-mod control system has recently gained new potentialities thanks to the introduction of the MARTe framework and of a new CPU architecture. These capabilities allow to study new feedback algorithms relevant to both RFP and tokamak operation and to contribute to the debate on the optimal feedback strategy. This work focuses on the design of new feedback schemes. For this purpose new magnetic sensors have been explored, together with new algorithms that refine the de-aliasing computation of the radial sideband harmonics. The comparison of different sensor and feedback strategy performance is described in both RFP and tokamak experiments. [Preview Abstract] |
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JP8.00101: Two-Fluid Equilibrium Calculation and Applications Luca Guazzotto, Riccardo Betti Poloidal and toroidal flows are routinely found in tokamak equilibria. In ideal MHD, the axisymmetric equilibrium problem reduces to the solution of a PDE for the magnetic poloidal flux $\psi$ coupled with an algebraic equation for the plasma density. Plasma velocity is within magnetic surfaces. This picture is modified when two-fluid effects are considered. Neglecting electron inertia, plasma flow is found to lie on stream surfaces labeled by the stream function $\Psi \ne \psi$. Assuming quasi-neutrality, the equilibrium problem requires the solution of two coupled PDEs and an algebraic equation for the density. In this work, we present the status of the development of FLOW2, designed to solve the two-fluid equilibrium axisymmetric problem in arbitrary geometry. Applications, limiting cases and reduction to MHD are presented. In particular, we focus on transonic equilibria, that is equilibria in which the poloidal velocity in faster than the poloidal sound speed $(C_{sP} = C_s B_p/B)$ at the plasma edge, and slower in the center. The discontinuous MHD solution is modified by two-fluid effects. Comparison with theory and MHD solution are presented. [Preview Abstract] |
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JP8.00102: Can helical RFP states be explained by simple linear tearing mode theory? Jeffrey Freidberg, Luca Guazzotto One very interesting experimental observation in recent years is the transition of an RFP plasma from a cylindrically symmetric state to a helically symmetric state which occurs above a critical value of plasma current. Helical RFP states form even though the boundary conditions are cylindrically symmetric. We focuse on understanding the basic physics that leads to the formation of such states. Specifically, we pursue a ``minimal model,'' containing the minimum amount of physics necessary to explain the transition, even if only semi-quantitatively. Since it is believed that helical states form as saturated tearing modes, we need to include tearing stability in our model. We do not have the goal to explain helical states by a nonlinear analysis of tearing mode saturation. Rather, we try to obtain, by a combination of analytical linear stability theory and simple numerical calculations, a plausible trajectory in the $F - \Theta$ space for the slowly varying RFP equilibrium profiles that will ultimately bring the system to the onset of a dominant unstable tearing mode. Other critical elements in our model are stability analysis of ideal modes, the presence of an ideal wall and most importantly, the goal to obtain an unstable tearing mode with the same helicity as experiments. [Preview Abstract] |
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JP8.00103: Decay of runaway electron current Boris Breizman The population of relativistic runaway electrons in a tokamak tends to grow exponentially via avalanche mechanism when the inductive electric field exceeds a critical value determined by the background electron density. As a result of this avalanche growth, the current of runaway electrons can quickly replace the initial current carried by the bulk plasma electrons. In the absence of external current drive, the runaway current will then decay slowly in line with dissipation of the stored poloidal magnetic field energy. A noteworthy feature of this decay is that it occurs in a self-sustained mode of marginal criticality: the inductive electric field has to be close to its critical value at every location where the runaway current density is finite, and the current density should vanish at any point where the electric field drops below its critical value. Based on this nonlinear ``Ohms law'' for runaways, a complete description has been constructed in this work for the time evolution of the toroidal current profile. [Preview Abstract] |
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JP8.00104: M3D-K Simulations of Beam-Driven Fishbone Instability in DIIID Guoyong Fu, Benjamin Tobias, Michael Van Zeeland Fishbone instability is often observed between sawtooth crashes in DIII-D with sufficient on-axis neutral beam power. In this work, hybrid simulations with the global kinetic/MHD hybrid code M3D-K [1] have been carried out to investigate the linear stability and nonlinear dynamics of n=1 mode with effects of energetic beam ions for parameters and profiles of a DIII-D discharge. The results show that the n=1 internal kink mode is unstable in MHD limit. However, with kinetic effects of beam ions, a fishbone-like mode is found to be unstable with mode frequency about a few kHz, consistent with experimental observation. Nonlinear simulations are being performed to investigate mode saturation, frequency chirping as well as energetic particle transport. Numerical results will be compared with the experimental data from DIII-D.\\[4pt] [1] G.-Y. Fu et al., Phys. Plasmas 13, 052517 (2006). [Preview Abstract] |
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JP8.00105: M3D-K Simulations of Beam-Driven Alfven Eigenmodes in ASDEX-U Ge Wang, Guoyong Fu, Philipp Lauber, Mirjam Schneller Core-localized Alfven eigenmodes are often observed in neutral beam-heated plasma in ASDEX-U tokamak. In this work, hybrid simulations with the global kinetic/MHD hybrid code M3D-K [1] have been carried out to investigate the linear stability and nonlinear dynamics of beam-driven Alfven eigenmodes using experimental parameters and profiles of an ASDEX-U discharge. The safety factor q profile is weakly reversed with minimum q value about qmin$=$3.0. The simulation results show that the n$=$3 mode transits from a reversed shear Alfven eigenmode (RSAE) to a core-localized toroidal Alfven eigenmode (TAE) as qmin drops from 3.0 to 2.79, consistent with results from the stability code NOVA as well as the experimental measurement. The M3D-K results are being compared with those of the linear gyrokinetic stability code LIGKA [2] for benchmark. The simulation results will also be compared with the measured mode frequency and mode structure. \\[4pt] [1] G.-Y.Fu et.al., Phys. Plasmas 13, 052517(2006)\\[0pt] [2] Ph.Lauber et.al., J.Comp.Phys. 226(2007):447 [Preview Abstract] |
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JP8.00106: M3D-K Simulations of Sawteeth and Energetic Particle Transport in Tokamak Plasmas Wei Shen, Guoyong Fu, Zhengmao Sheng, Joshua Breslau, Feng Wang Nonlinear simulations of Sawteeth and energetic particle transport are carried out using the kinetic/MHD hybrid code M3D-K. MHD simulations show repeated sawtooth cycles due to a resistive (1,1) internal kink mode for a model tokamak equilibrium. Furthermore, test particle simulations are carried out to study the energetic particle transport due to a sawtooth crash. The results show that energetic particles are redistributed radially in plasma core depending on pitch angle and energy. For trapped particles, the redistribution occurs for particle energy below a critical value in agreement with previous theory. For co-passing particles, the redistribution is strong with little dependence on particle energy. In contrast, the redistribution level of counter-passing particles decreases as particle energy becomes large. [Preview Abstract] |
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JP8.00107: Energetic Particle Modes: example of Autoresonance and Superradiance in fusion plasmas Fulvio Zonca, Liu Chen Energetic Particle Modes (EPM) [1] are resonant non-normal modes born out of the shear Alfv\'en wave (SAW) continuous spectrum when the energetic particle (EP) drive overcomes continuum damping in nonuniform fusion plasmas. Their nonlinear evolution is characterized by radially convective amplification of the EPM wave-packet and secular EP radial transports [2]. Here, we demonstrate that EPM-EP phase locking [2,3] is an example of Autoresonance [4] in fusion plasmas; and that the corresponding EPM-EP nonlinear dynamics has interesting analogies with Superradiance [5]. These complex nonlinear behaviors are described, in a simple yet practically relevant limiting case, by a complex Nonlinear Schr\"odinger Equation.\\[4pt] [1] L. Chen, Phys. Plasmas {\bf 1}, 1519 (1994).\newline [2] F. Zonca et al., Nucl. Fusion {\bf 45}, 477 (2005). \newline [3] R. B. White et al., Phys. Fluids {\bf 26}, 2958 (1983). \newline [4] J. Fajans and L. Friedland, A. J. Phys. {\bf 69}, 1096 (2001). \newline [5] R. Bonifacio et al., Nucl. Inst. Meth. Phys. Res., Sect. A {\bf 296}, 358 (1990). [Preview Abstract] |
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JP8.00108: Nonlinear simulations of Alfv\'enic instabilities driven by energetic particles in a reversed shear tokamak plasmas Xin Wang, Sergio Briguglio, Liu Chen, Giuliana Fogaccia, Gregorio Vlad, Fulvio Zonca The extended version of nonlinear hybrid magnetohydrodynamic (MHD)-Gyrokinetic code HMGC~\footnote{S. Briguglio {\sl et al.}, Phys. Plasmas {\bf 2} 3711 (1995).}(XHMGC) is used to investigate the reversed shear Alfv\'en eigenmodes (RSAE)/energetic particle modes (EPM) driven by an anisotropic Maxwellian energetic particles with reversed shear q profiles. In the region near the minimum-q surface, EPM are shown to exist inside the kinetic low-frequency shear Alfv\'en continuum gap. Fast non-adiabatic down-ward chirping frequency is found for given equilibrium profiles, which is understood as consequence of nonlinear wave particle dynamics. In our current case, the mode structure is dominated by two neighbor poloidal components, while wave energetic particle interaction is dominated by the sidebands of the dominant transit resonance. [Preview Abstract] |
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JP8.00109: Analytical Model for the Thermonuclear Instability in IGNITOR* A. Cardinali, G. Sonnino, B. Coppi The non-linear energy balance equation for thermal equilibrium and stability, is analytically and numerically investigated in order to study the thermonuclear instability in the IGNITOR experiment facility. The expressions for the ion and the electron thermal coefficients, introduced in the thermal energy balance equation, are obtained by solving the nonlinear transport equations relevant to several collisional transport regimes (in particular the banana regime). The differential equation for the temperature profile at equilibrium is solved and the resulting profile is compared with the results obtained by a full transport code. The growth of the perturbation in the temperature is analyzed by integrating the equation in time. A scenario is considered where IGNITOR is led to operate in a slightly sub-critical regime by adding a small fraction of $^{3}$He to the nominal 50-50 Deuterium-Tritium mixture and heating the plasma by ICRH power. *Sponsored in part by the US DOE. [Preview Abstract] |
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JP8.00110: Nonlinear Numerical Modeling of Fast Controlled Shut-Down in IGNITOR in The Presence of 3D Structures* R. Albanese, G. Ambrosino, G. De Tommasi, A. Pironti, G. Rubinacci, F. Villone, G. Ramogida, B. Coppi In Ignitor. the avoidance and mitigation of plasma disruptions can play an important role in its safe operation. These objectives pose additional constraints on the performances of an accurate integrated plasma position, shape and current control. This system can indeed be an effective aid to disruption avoidance and mitigation as well as to achieve a fast controlled shut-down. In these cases, a suitable redistribution of the currents in the PF coils system is very effective. Previously, we analyzed a control strategy leading to the redistribution of the currents in the PF coil system without modifying too much the plasma shape. Here, we test the constraints affecting the time needed to implement a suitable dynamic currents allocation also in view of a fast controlled shutdown. To this purpose we use a computational tool, called CarMa0NL, with the unprecedented capability of simultaneously considering three-dimensional effects of conductors surrounding the plasma and the inherent nonlinearity of the plasma behaviour itself, in the presence of the complex set of circuit equations describing the control system. *Sponsored in part by the US DOE. [Preview Abstract] |
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JP8.00111: Hybrid simulation of fast ion dynamics in the presence of off-axis fishbone-like modes in high-beta JT-60U plasmas Andreas Bierwage, Nobuyuki Aiba, Go Matsunaga, Koji Shinohara, Yasushi Todo, Masatoshi Yagi The MHD-PIC hybrid code MEGA is used to simulate high-beta JT-60U plasmas in regimes near marginal MHD ballooning stability and driven by neutral beams. The goal of this research is to study the transport of fast ions caused by experimentally observed fishbone-like modes that peak off-axis (near the q=2 surface) and have frequencies well below the accumulation points of the beta-induced gap of the shear Alfv\'{e}n continuum. The approach chosen is as follows. Before examining the physics via parameter scans and case studies, the relevance of the simulation model is verified by checking whether the code can reproduce a plasma response with properties similar to those seen in the experiments. For this purpose, the simulation scenario is set up as realistically as currently possible: with realistic plasma shape and bulk pressure, and a fast ion distribution that is consistent with particle sources and collisions. The methods used and first results are reported and discussed. [Preview Abstract] |
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JP8.00112: Fast ion loss associated with perturbed field by resonant magnetic perturbation coils in KSTAR Jun Young Kim, Junghee Kim, Tongnyeol Rhee, S.W. Yoon, G.Y. Park, Y.M. Jeon, M. Isobe, A. Shimizu, K. Ogawa, J.-K. Park, M. Garcia-Munoz Resonant magnetic perturbation (RMP) is the most promising strategies for ELM mitigation/suppression. However, it has been found through the modeling and the experiments that RMP for the ELM mitigation can enhance the toroidally localized fast ion loss. During KSTAR experimental campaigns in 2011 and 2012, sudden increase or decrease of the fast ion loss has been observed by the scintillator-based fast ion loss detector (FILD) when the RMP is applied. Three-dimensional perturbed magnetic field by RMP coil in vacuum is calculated by Biot-Savart's law embedded in the Lorentz orbit code (LORBIT). The LORBIT code which is based on gyro-orbit following motion has been used for the simulation of the three-dimensional fast ion trajectories in presence of non-axisymmetric magnetic perturbation. It seems the measured fast ion loss rate at the localized position depends on not only the RMP field configuration but also the plasma profile such as safety factor and so on, varying the ratio between radial drift and stochastization of the fat-ion orbits. The simulation results of fast ion orbit under magnetic perturbation w/ and w/o plasma responses will be presented and compared with KSTAR FILD measurement results in various cases. [Preview Abstract] |
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JP8.00113: Long-time scale nonlinear simulation of RSAE/TAE instabilities Don Spong Both frequency sweeping and constant frequency fast ion driven Alfv\'{e}n instabilities are often observed to persist for a few times 100,000 Alven times. Simulations for these time intervals are challenging both due to computational issues (numerical stability, error accumulation) and physics considerations (source/sink balancing, avoiding bursting/decay, resolution of nonlinear energy cascades, etc.). The usually invoked quasilinear saturation mechanisms do not allow maintenance of such long-lived turbulence; some form of self-organization due to effects such as zonal flows/currents is necessary to nonlinearly sustain Alfv\'{e}n instabilities over these time intervals. The global mode structures of RSAE and TAE instabilities naturally drive such effects through the Reynold's and Maxwell stress terms. The TAEFL gyrofluid model is a useful tool for exploring such effects since it has the computational stability/efficiency and nonlinear Reynold's/Maxwell stress effects to follow long-time scale nonlinear Alfv\'{e}nic turbulence. Since the evolving nonlinear mode structure can be quite different from linear mode structure, such effects can be of importance in evaluating fast ion losses and wall heating caused by the nonlocal wave-induced fast ion transport. [Preview Abstract] |
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JP8.00114: Near threshold conditions justify critical gradient model for Alvenic mode driven relaxation of fast ions Nikolai Gorelenkov, Katy Ghantous, William Heidbrink, Michael Van Zeeland Future burning plasma performance will be limited by the constraints to confine energetic superalfvenic fusion products, which can drive several low frequency Alfv\'enic instabilities. Expected multiple resonances help to justify the model developed recently, called critical gradient or 1.5D reduced quasilinear diffusion model. Similar conditions are expected in burning plasmas with TAE instabilities in a non virulent nonlinear regime. The 1.5D model make use of TAE/RSAEs linear theory. One critical element of the presented model is that it requires averaging over the time comparable to the fast ion slowing down. Another element is that the fast ion diffusion near the resonance does not flatten the distribution function whose gradient is maintained by the collision scattering. Further validations of this model justify its use in case of relatively high collisions. With the parametric plasma dependencies embedded in the model and with the quantitative normalization to NOVA-K growth rates the 1.5D model application to DIII-D experiments is well positioned for validations. Good agreement is summarized here for absolute values of the deduced neutron rate and for the time behavior of fast ion losses near the AE activity thresholds. 1.5D model is applicable for ITER and other BPs. [Preview Abstract] |
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JP8.00115: Particle-in-Cell WARP simulation studies of positron plasmas in micro-Penning-Malmberg traps Alireza Narimannezhad, Marc H. Weber, Kelvin G. Lynn The charged particles storage capacity of microtraps with large length to radius aspect ratios and radii of the order of tens of microns was explored using particle-in-cell WARP code. The new design of the trap consisted of an array of microtraps with substantially lower end electrodes potential than conventional Penning-Malmberg traps, which makes this trap quite portable. It was shown that each microtrap with 50 $\mu$m radius immersed in a 7 T uniform, axial magnetic field, stored positrons with a density (1.6E11 cm$^{-3})$ even higher than that in conventional Penning-Malmberg traps ($\approx $ 1E11 cm$^{-3})$ while the confinement voltage was only 10 V. The trapped density scaled as r$^{-2}$ down to 3 $\mu$m radius. It was presented in this work how to evaluate and lower the numerical noise by controlling the modeling parameters so the simulated plasma can evolve toward computational equilibrium. The local equilibrium distribution was attained in time scales of the simulation for plasmas initialized with a uniform density and Boltzmann energy distribution. The charge clouds developed the expected radial soft edge density distribution and rigid rotation evolved to some extent. To reach global equilibrium (i.e. rigid rotation) longer runs are required. The plasma confinement time and its thermalization were independent of the length. [Preview Abstract] |
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JP8.00116: A high-temporal-order, asymptotic-preserving spectral deferred correction algorithm for the anisotropic heat transport equation L. Chacon, E. Endeve Modeling electron transport in magnetized plasmas is extremely challenging due to the extreme anisotropy between the parallel (to the magnetic field) and perpendicular directions (the transport-coefficient ratio $\chi_{\parallel}/\chi_{\perp} \sim 10^{10}$ in fusion plasmas). Recently, an asymptotic preserving semi-Lagrangian approach has been developed that is able to deal with arbitrary anisotropy ratios and non-trivial magnetic topologies in an accurate and efficient manner.\footnote{L. Chac\'on, D. del-Castillo-Negrete, C. Hauck, {\em JCP}, submitted (2013)} The approach is shown to avoid spatial discretization pollution, and to feature bounded numerical errors for {\em arbitrary} $\chi_{\parallel}/\chi_{\perp}$ ratios, which renders it asymptotic preserving. However, it is only first-order accurate in time. In this poster, we explore spectral deferred correction (SDC) methods\footnote{A. Dutt, L. Greengard, and V. Rokhlin, {\em BIT} {\bf 40}, 241 (2000)} to produce a high-order asymptotic preserving algorithm, using the first-order semi-Lagrangian algorithm as the inner solver for the corrector step. We will show that the combination SDC+semi-Lagrangian features a numerical stability constraint, but one which is benign for sufficiently large anisotropy ratios. [Preview Abstract] |
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JP8.00117: Status and Benchmarking of the Free Boundary Equilibrium Code FREEBIE Jakub Urban, Jean-Francois Artaud, Vincent Basiuk, Karim Besseghir, Philippe Huynh, Sunhee Kim, Jonathan Bryan Lister, Eric Nardon FREEBIE is a recent free boundary equilibrium (FBE) code, which solves the temporal evolution of tokamak equilibrium, described by the Grad-Shafranov equation and circuit equations for active and passive poloidal field components. FREEBIE can be run stand-alone, within the transport code CRONOS or on the ITM (European Integrated Tokamak Modelling) platform. FREEBIE with prescribed plasma profiles has already been successfully benchmarked against DINA simulations and TCV experiments. Here we report on the current status of the code coupling with transport solvers and benchmarking of fully consistent transport-FBE simulations. A benchmarking procedure is developed and applied to several ITER cases using FREEBIE, DINA and CEDRES++. The benchmarks indicate that because of the different methods and the complexity of the problem, results obtained from the different codes are comparable only to a certain extent. [Preview Abstract] |
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JP8.00118: Gyrokinetic simulation of the collisionless tearing mode instability Edward Startsev, Wei-li Lee A recently developed split-weight perturbative particle simulation scheme for finite-$\beta$ plasmas in the presence of background inhomogeneities [1] has been generalized to the sheared magnetic field geometry. The scheme is an improvement over the original split-weight scheme [2], which splits the perturbed particle response into adiabatic and non-adiabatic parts. In the new scheme, the additional adiabatic response of the particles associated with the quasi-static bending of the magnetic field lines in the presence of background inhomogeneities of the plasma is analytically separated. The new scheme has been implemented in a 2D particle-in-cell code in slab geometry with drift-kinetic electrons and gyrokinetic ions. In this paper the results of linear simulations of tearing mode for realistic mass ratio $m_i/m_e=1837$ and different values of plasma $\beta$ are presented and compared to the solution of the eigenvalue equation. The unstable mode structure has double-peaked shape corresponding to the positive tearing mode parameter $\Delta'$ consistent with the MHD requirement for the tearing mode instability [3].\\[4pt] [1] E. A. Startsev et. al, submitted to Phys. Plasmas, (2013).\\[0pt] [2] W. W. Lee et. al, Phys. Plasmas 8, 4435 (2001).\\[0pt] [3] H. P. Furth et. al., Phys. Fluids 6, 459 (1963) [Preview Abstract] |
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JP8.00119: Parallel computing aspect in TRANSP with PT-SOLVER Xingqiu Yuan, Steve Jardin, Greg Hammett, Robert Budny, Gary Staebler We describe a new parallel predictive profile time-advance in the TRANSP code, PT-SOLVER, which has been developed during last two-years. A multilevel parallelization paradigm is implemented in PT-SOLVER, with the computationally intensive transport routines (such as NEO and TGLF) treated as independent components with their own communicators. The SOLVER component, which advances the transport equation, controls the other components for synchronization and communication. A communication layer is dynamically established to exchange the data from the SOLVER component to the turbulent and neoclassical transport components, and to collect the neoclassical and turbulent fluxes from their respective components. We demonstrate the massively parallel computational aspect of TRANSP by presenting results using over 1,000 cores on NSERC supercomputers. Parallel scaling properties are illustrated. PT-SOLVER is fully compatible with utilizing parallel versions of NUBEAM (for neutral beam and fusion products heating) and TORIC (for RF heating) in the same TRANSP simulation. [Preview Abstract] |
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JP8.00120: A Lorentz ion/drift-kinetic electron model for particle-in-cell turbulence simulations in tokamaks Yang Chen, Scott Parker, Benjamin Sturdevant The gyrokinetic model faces a few limitations when applied to tokamak plasmas. First, in the steep gradient edge pedestal, the equilibrium scale lengths for the density and temperature profiles are on the scale of 10 $\rho_i$ or even shorter, which makes the small $\rho_i/L_n$ ordering inaccurate. Second, the presence of a sonic level ExB flow complicates the gyrokinetic formalism. Third, the long wavelength radial electric field requires equations derived and implemented to higher order accuracy.\footnote{F.~Parra and P.~Catto, Plasma Phys. Contr. Fusion 50, 065014 (2008)} For these reasons we have previously proposed a Lorentz ion/drift-kinetic electron model.\footnote{Y.~Chen and S.~E.~Parker, Phys. Plasmas 16, 052305 (2009)} This model is unlikely to solve all the problems gyrokinetics faces, but will provide an independent tool for verification. Here we consider the implementation of the model in toroidal geometry, with the goal of laying out a detailed plan of implementation. This includes the choice of a suitable coordinate system, the discretization of the field equations (the three components of a generalized Ohm's law) and parallelization. Integration techniques of the Lorentz ions, including subcycling and orbit averaging, will be discussed. [Preview Abstract] |
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JP8.00121: Fully Parallel MHD Stability Analysis Tool Vladimir Svidzinski, Sergei Galkin, Jin-Soo Kim, Yueqiang Liu Progress on full parallelization of the plasma stability code MARS will be reported. MARS calculates eigenmodes in 2D axisymmetric toroidal equilibria in MHD-kinetic plasma models. It is a powerful tool for studying MHD and MHD-kinetic instabilities and it is widely used by fusion community. Parallel version of MARS is intended for simulations on local parallel clusters. It will be an efficient tool for simulation of MHD instabilities with low, intermediate and high toroidal mode numbers within both fluid and kinetic plasma models, already implemented in MARS. Parallelization of the code includes parallelization of the construction of the matrix for the eigenvalue problem and parallelization of the inverse iterations algorithm, implemented in MARS for the solution of the formulated eigenvalue problem. Construction of the matrix is parallelized by distributing the load among processors assigned to different magnetic surfaces. Parallelization of the solution of the eigenvalue problem is made by repeating steps of the present MARS algorithm using parallel libraries and procedures. Preliminary results of the code parallelization will be reported. [Preview Abstract] |
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JP8.00122: Finite Volume Scheme for Anisotropic Diffusion Bram van Es, Barry Koren, Hugo de Blank In fusion plasmas there is extreme anisotropy of transport coefficients due to the high temperature and large magnetic field strength. This anisotropy puts stringent requirements on the numerical methods used to solve the MHD-equations since any misalignment of the grid with the fieldlines may cause numerical pollution of the perpendicular diffusion by the much larger parallel diffusion coefficient. The common approach of field-aligned coordinates runs into problems in case of x-point magnetic topology which makes local non-alignment unavoidable. The mimetic finite difference schemes and finite element schemes using the support operator method maintain the accuracy of the perpendicular diffusion particularly well on non-aligned grids. We address why these schemes maintain the accuracy so well. For this purpose we compared several finite-difference schemes and a special finite-volume scheme applied to the anisotropic heat conduction equation. [Preview Abstract] |
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JP8.00123: Helicity Conservation and Two-Fluid Relaxation Modeling for Reversed-Field Pinches Joshua Sauppe, Carl Sovinec, Chris Hegna, Vladimir Mirnov We report on NIMROD simulations of two-fluid relaxation relevant to RFP discharges. RFPs typically exhibit periodic relaxation events that flatten the parallel current profile. Taylor recognized that in a dissipative plasma the global magnetic helicity is a more robust invariant than the magnetic energy and postulated that the relaxation minimizes magnetic energy while conserving global helicity [Taylor, PRL Vol. 33, No. 19 (1974)]. The predicted relaxed state is force-free with a globally constant parallel current. Two-fluid physics is significant on the Madison Symmetric Torus RFP and this has consequences for magnetic relaxation [Kuritsyn et. al., PoP Vol. 16 No. 055903 (2009)]. Two-fluid relaxation theories make use of generalized species helicities and predict a relaxed state with both parallel current and parallel flow spatially constant [Hegna, PoP Vol. 5 No. 6 (1998)]. We compare NIMROD two-fluid results to these theories. The magnetic helicity and generalized species helicities are well-conserved relative to the energy over the relaxation event. The parallel current flattens as expected, but the parallel flow develops steeper gradients in some cases. [Preview Abstract] |
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JP8.00124: Vlasov-Poisson calculations of electron confinement times in Polywell(TM) devices using a steady-state particle-in-cell method Jeffrey Kollasch, Carl Sovinec, John Santarius Collisionless electron confinement times in polyhedral magnetic cusp configurations are investigated numerically with a particle-in-cell technique designed for steady-state conditions of the Vlasov-Poisson system. This method is based on iteratively solving particle trajectories in the time-independent electrostatic field produced by trajectories from a previous iteration. A new code based on this technique, SSUBPIC (steady-state unstructured-boundary particle-in-cell), is presented. It is found to converge rapidly for the cases investigated. The implementation is verified on computations of space-charge limited current in 1D and 2D configurations. Here, it is applied to study the effects of an ejecting virtual cathode potential well on a single electron species injected by guns into a Polywell(TM). Adverse effects of non-magnetically shielded structural members on confinement time are also calculated. [Preview Abstract] |
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JP8.00125: Verification of spectral stabilization and numerically modeled external vacuum in NIMROD C.R. Sovinec, K.J. Bunkers Revisions to the NIMROD algorithm (JCP 195, 355) aim to improve its utility for tokamak computations. The standard spectral-element expansion of all physical fields in continuous bases leads to convergence on MHD interchange from the unstable side in conditions of weak dissipation. This is a numerical impediment in nonlinear computations (Lutjens, CPC 95, 47). Adapting 1D numerical results (Sovinec, BAPS 57, No. 12) to NIMROD's elements, we consider incomplete modal expansions for auxiliary flow-divergence and parallel-vorticity fields. Their bases are just the highest order Legendre polynomial of each element. We show that convergence from the stable side is achieved when the auxiliary fields are used for either hyperbolic or parabolic correction terms, as verified in cylindrical interchange and toroidal ballooning computations. Separate development on applying distinct physical models to different regions of a domain allows coupling to external vacuum regions, suitable for modeling vertical displacement events and resistive wall modes. Results from initial tests are reported. [Preview Abstract] |
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JP8.00126: Progress on a new Fast Multipole Method based Grad-Shafranov solvers Antoine Cerfon, Zydrunas Gimbutas, Leslie Greengard In tokamaks, transport processes and MHD stability depend strongly on the magnetic field curvature and shear. Since both curvature and shear are functions of the second derivatives of the solution of the Grad-Shafranov equation (GS equation), it is critical to design highly accurate Grad-Shafranov solvers that can compute these derivatives with very good accuracy. We recently showed that an effective way to design a fast and highly accurate solver is to view the GS equation as a nonlinear Poisson equation [1]. We solved this Poisson problem combining conformal mapping techniques with Fourier and integral equation methods on the unit disk, and obtained high order accuracy for the second derivatives of the solution of the GS equation [1]. Conformal mapping techniques become more inefficient as the elongation of the plasma cross-section increases, and even fail if the surface has a separatrix. In order to handle arbitrary fusion-relevant geometries in a robust manner, we are designing a new fixed boundary Grad-Shafranov solver that relies on the Fast Multipole Method to solve the associated Poisson problem [2]. \\[4pt] [1] A. Pataki, A.J. Cerfon, J.P. Freidberg, L. Greengard, M. O'Neil, J. Comput. Phys. 243, 28 (2013)\\[0pt] [2] F. Ethridge and L. Greengard, SIAM J. Sci. Comput.23, 741 (2001) [Preview Abstract] |
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JP8.00127: Non-Canonical Symplectic Integration of Guiding Center Orbits C. Leland Ellison, John M. Finn, Hong Qin, William M. Tang The calculation of guiding center trajectories is an important aspect of evaluating particle confinement in a given magnetic configuration. An attractive approach to doing so involves the specification of a non-canonical guiding center Lagrangian which in turn requires novel methods to develop geometric (i.e. symplectic) algorithms. We present results from the progress made in the use of variational integrators applied to the guiding center problem. The stability of various classes of discrete Lagrangians is discussed using backwards error analysis, and new methods for controlling parasitic modes are introduced. Cross-benchmarking comparisons are carried out against standard Runge-Kutta methods applied to the calculation of guiding center orbits in 3-D toroidal geometries. The conserved quantities in the variational algorithms are shown to lead to good numerical fidelity in simulations of long duration. [Preview Abstract] |
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JP8.00128: A novel, semilagrangian, coarse solver for the Parareal technique and its application to 2D fluid drift-wave (BETA) and 5D gyrokinetic (GENE), turbulence simulations J.M. Reynolds-Barredo, D.E. Newman, R. Sanchez, Frank Jenko Parareal is a new parallelization technique that focuses on the time coordinate in order to parallelize it and allows us to use more processors than conventional parallelization techniques would. Parareal is based on an iterative process with two stages in every one of the iterations: In a first predictor stage, a fast coarse time propagator gives an approximated solution for all time. In a second stage, an accurate time propagator is used in order to correct the solution. The key of the success in the application of the algorithm to an specific problem depends on choosing an adequate coarse solver. In this work, we apply Parareal to convection dominated problems. In particular, to a 2D fluid drift wave case using the BETA code and in a 5D gyrokinetic simulation using the GENE code. Here, a new and promising coarse solver based on semilagrangian time advance is proposed and tested on both kind of simulations. The advantage of the semilagrangian solver is that it can be split into a piece that can run in parallel (the computation of the interpolation coefficients) and a piece that is computed serially (the application of the coefficients over the convected field). The second piece is the time limiting part (due to its sequential character) but can be computed much faster than the fine solver. [Preview Abstract] |
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JP8.00129: Gamma-gamma Counting Station dead time corrections Angela Simone, Megan Russ, Mollie Bienstock, Steven Padalino, Drew Ellison, Holly DeSmitt, Craig Sangster It has been proposed that neutron activation of graphite could be used to measure tertiary neutron production in ICF experiments. Graphite samples were activated by 20-26.4 MeV neutrons at the Edwards Accelerator Facility at Ohio University to simulate an ICF activation. Once activated by the 12C(n,2n)11C reaction the 11C decays via positron emission. The positron promptly annihilates with an electron producing two back-to-back gamma rays. A counting station consisting of a pair of onaxis NaI(Tl) detectors was constructed to measure the 511 keV gammas in coincidence. Due to the high initial specific activity of the graphite samples following intense neutron bombardment the dead time in the NaI-Thl detectors was high but tapered off over the duration of measurement. In order to correct for lost counts in the decay curve the dead-time as a function of dwell time must be known. A script was written to sort dead-time from the acquired data as a function of dwell time interval. These values were then used to correct the measured decay curve which produced an exceptionally good fit to the theoretical decay curve. Ultimately this information was used to determine the total number of activations in the graphite samples. Funded in part by a LLE contract through the DOE [Preview Abstract] |
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JP8.00130: 12C(n, 2n)11C Reaction Cross Section Measurements for Bombarding Energies 20-26.4 MeV Mollie Bienstock, M. Russ, Steven Padalino, A. Simone, D. Ellison, H. DeSmitt, M. Yuly, I. Love, G. Hartshaw, T. Massey, C. Sangster The (n,2n) threshold for 12C is nearly 6MeV above the primary neutron energy in DT ICF implosions. This makes it a good candidate for measuring the tertiary neutron yield above 20MeV using neutron activation of graphite. In order to use this method the 12C(n,2n)11C reaction cross section must be known accurately. However, the published data for this reaction is bifurcated in the energy range of 20-30MeV. An experiment to measure the cross section for these neutron energies has been performed at the Ohio University Accelerator. Deuterons from the accelerator struck a titanium tritide foil releasing neutrons via the T(d,n)4He reaction producing neutrons with energies between 20.0-26.4MeV. The geometry of the experiment was chosen so that the incident neutron energy would not vary by more than 0.5MeV across the graphite target. After neutron exposure, the decay of the 11C nuclei by positron emission was measured with an array of NaI detectors to determine the activity of the graphite. The neutron fluence through the carbon was measured using a particle telescope to detect recoil protons from CH2 target, allowing the absolute cross section for the 12C(n,2n)11C reaction to be determined. Funded in part by a LLE contract from the DOE [Preview Abstract] |
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JP8.00131: New Results for the Polarization Current Effect on NTM Threshold Koki Imada, Natalia Tronko, Howard Wilson For successful operation of future tokamaks, such as ITER, it is essential to control neoclassical tearing modes (NTMs): plasma instabilities characterized by the evolution of magnetic islands. Experimental observations show that sufficiently small magnetic islands heal themselves and shrink away. It has been suggested that the neoclassical polarization current, induced due to ion inertia, may contribute to the NTM threshold. However, the physics of polarization current is not fully understood in toroidal geometry. Slab model calculations show that the contribution from the narrow island separatrix layer opposes that away from the island, nearly cancelling each other out. However, no previous works have investigated this layer contribution in full toroidal geometry; this is essential for accurately determining the trapped particle effect and hence the overall sign of the polarization current. In this project, we aim to determine the full contribution of the polarization current in the tokamak toroidal geometry, including the separatrix layer contribution, using drift kinetic theory. If the polarization current contribution is found to be stabilizing, our new result will provide valuable information towards the development of effective NTM control system for ITER. [Preview Abstract] |
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