Bulletin of the American Physical Society
56th Annual Meeting of the APS Division of Plasma Physics
Volume 59, Number 15
Monday–Friday, October 27–31, 2014; New Orleans, Louisiana
Session JP8: Poster Session IV: Education and Outreach; Undergraduate/High School Research; Fundamental Theory and Computation; Magnetic ICF & HEDP; Z-Pinch, X-Pinch, Exploding Wire Plasma and Dense Plasma Focus |
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Room: Preservation Hall |
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JP8.00001: EDUCATION AND OUTREACH |
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JP8.00002: A Seven-Year Longitudinal Study of the Research Outcomes for the CASPER Physics Circus Jorge Carmona-Reyes, Anna Land-Zandstra, Gary Stark, Lisa Tarman, Matt Menefee, Li Wang, Mike Cook, Jimmy Schmoke, Lorin Matthews, Truell Hyde The CASPER Physics Circus was specifically designed to increase student interest in science, technology, engineering and mathematics (STEM) careers where the current generation of scientists and engineers is rapidly approaching retirement age. The Physics Circus followed Waco and LaVega ISD students starting in the sixth grade and ending in the twelfth grade with this cohort group attending the Physics Circus event on the Baylor University campus, interacting with CASPER graduate students and participating in hands-on instructional activities. The event was designed as an informal learning environment intervention and operated under the discovery, project and guided-inquiry base framework wrapped in a learner-center ideology. Participating students were allowed to experiment with hands-on manipulatives while interacting with physicists, science educators and graduate students in both STEM and science education fields. Professional Development was also a part of the Physics Circus for all science teachers within the cohort. This paper presents the results of a seven-year longitudinal study on the Physics Circus and presents future plans to expand the program's effectiveness and impact. [Preview Abstract] |
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JP8.00003: The Suitability of 3D Printed Plastic Parts for Laboratory Use Andrew Zwicker, Josh Bloom, Robert Albertson, Sophia Gershman 3D printing has become popular for a variety of users including scientists and engineers interested in producing their own laboratory equipment. Pearce and his group have tested a variety of different objects, developed a library of open-source files for printing optics equipment and found a cost savings of up to 97\% compared to the equivalent objects purchased commercially.\footnote{Joshua M. Pearce, Open-Source Lab: How to Build Your Own Hardware and Reduce Research Costs, (Elsevier, 2014).J} In order to determine the suitability of 3D printed parts for our plasma physics laboratory, we measured the accuracy, strength, vacuum compatibility, and electrical properties of test pieces printed in PLA plastic. For example, samples could be printed with a dimensional accuracy on the order of 50$\mu$m and had an average tensile strength of 60 MPa, similar to bulk plastic. For pressures greater than $10^{-6} $ torr a residual gas analyzer showed no increase above background until samples were heated to greater than 75$^{\circ}$C. While clearly not for all applications, the flexibility of rapidly creating custom parts has led to the 3D printer becoming an invaluable resource in our laboratory. [Preview Abstract] |
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JP8.00004: Advances in the Remote Glow Discharge Experiment Arturo Dominguez, A. Zwicker, L. Rusaits, M. McNulty, Carl Sosa The Remote Glow Discharge Experiment (RGDX) is a DC discharge plasma with variable pressure, end-plate voltage and externally applied axial magnetic field. While the experiment is located at PPPL, a webcam displays the live video 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 RGDX is designed as an outreach tool that uses the attractive nature of a plasma in order to reach a wide audience and extend the presence of plasma physics and fusion around the world. In March 2014, the RGDX was made publically available [1] and, as of early July, it has had approximately 3500 unique visits from 107 countries and almost all 50 US states. We present recent upgrades, including the ability to remotely control the distance between the electrodes. These changes give users the capability of measuring Paschen's Law remotely and provides a comprehensive introduction to plasma physics to those that do not have access to the necessary equipment. \\[4pt] [1] http://www.pppl.gov/news/2014/03/students-try-out-pppl-plasma-physics-experiment-can-be-accessed-anywhere-world [Preview Abstract] |
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JP8.00005: UNDERGRADUATE AND HIGH SCHOOL RESEARCH |
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JP8.00006: Measurements of the relative transmission properties of optical fiber for use on Proto-MPEX T.M. Biewer, K. Collins, B. Johnson, A. Lancaster, R. Mosby, H. Ray, G. Shaw, B. Young The prototype Material Plasma Exposure eXperiment (Proto-MPEX) is a linear plasma device being developed at Oak Ridge National Laboratory (ORNL). This machine plans to study plasma-material interaction (PMI) physics relevant to future fusion reactors. Measurements of plasma emission will be made on Proto-MPEX using spectrometers and filterscopes, which are coupled to the plasma by fiberoptic cables. The transmission properties of these fiberoptics are critical to the accurate estimation of the plasma emission levels. This presentation will highlight some of the issues encountered during calibration of hardware for use on Proto-MPEX. [Preview Abstract] |
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JP8.00007: The simple map - equilibrium, safety factor on magnetic axis, and perturbation from map parameter Nakeisha Johnson, Tanzania Guest, LaToya Pressley, Halima Ali, Alkesh Punjabi The simple map is the simplest symplectic map that has the generic magnetic topology of divertor tokamaks. The generating function of the simple map is $S(x$,$y)=x^{\mathrm{2}}$/2$+y^{\mathrm{2}}$/2-$y^{\mathrm{3}}$/3. The equilibrium magnetic surfaces of the simple map are calculated from the generating function. 0 \textless $S $\textless 1/6 gives closed surfaces and private flux surfaces; $S=$1/6 gives the separatrix, and $S $\textgreater 1/6 gives open surfaces. The scaling of safety factor on the magnetic axis, $q_{\mathrm{0}}$, with map parameter $k$ is calculated. The scaling of root mean square deviation of energy on the $q_{\mathrm{95}}$ 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 homoclinic tangle of the separatrix of simple map. This work is supported by grants DE-FG02-01ER54624, DE-FG02-04ER54793, and DE-FG02-07ER54937. [Preview Abstract] |
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JP8.00008: Homoclinic tangle of separatrix of the simple map LaToya Pressley, Tanzania Guest, Nakeisha Johnson, Alkesh Punjabi, Halima Ali The simple map is the simplest symplectic map that has the generic magnetic topology of divertor tokamaks. The generating function of the simple map is $S(x$,$y)=x^{2}$/2$+y^{2}$/2-$y^{3}$/3. $S=$1/6 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 simple 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 simple maps to calculate the homoclinic tangle of the separatrix of 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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JP8.00009: Construction of a hybrid rf/dc discharge source for dusty plasma studies Justin Krupa, Jeremiah Williams A complex (dusty) plasma is a four-component system composed of ions, electrons, neutral particles and charged microparticles. The presence of the microparticles gives rise to new plasma phenomena at time scales on the order of Hertz. Over the last several years, the Wittenberg University Plasma Laboratory has studied these dusty plasma systems in a dc discharge plasma. In this poster, we present work on a dual rf/dc hybrid discharge system to replace the dc glow discharge system currently in use. Details of the design and use of 3D printing in the construction will be presented. [Preview Abstract] |
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JP8.00010: Comparison of open-source particle image velocimetry (PIV) programs for dusty plasma studies Megan Heitkemper, Jeremiah Williams Particle Image Velocimetry (PIV) is a non-invasive diagnostic technique that provides a quantitative measure of fluid flow and particle transport. Recent advances in imaging technology have led to the development of a time-resolved version of this diagnostic technique, which replaces a dedicated PIV diagnostic setup with a high-speed camera and a CW laser. This technique has been used to examine a wide range of phenomena in the dusty plasma community. Additionally, the availability of open-source PIV software has made this diagnostic technique accessible at a relative modest cost. This poster will present an overview of how the PIV technique can be applied to image data acquired with a high speed camera, the image requirements, and will provide a comparison of a number of open-source PIV software. [Preview Abstract] |
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JP8.00011: Spectral characterization of Compact Toroidal Hybrid plasmas in preparation for Thomson scattering measurements M.M. Goforth, S.D. Loch, D.A. Maurer, A.J. Pearce, P.J. Traverso A Thomson scattering system is in development for the Compact Toroidal Hybrid (CTH) experiment to provide localized, internal electron temperature and density measurements. Thomson scattering yields accurate information on the internal plasma electron pressure profile, which will aid in the equilibrium reconstruction of CTH plasmas using the V3FIT code [1]. The expected Thomson scattered signal is approximately 10$^{15}$ times less than the incident laser light, and can be overwhelmed by stray laser light, background plasma emission, and intrinsic detector noise. Background plasma emission measurements in the visible spectral region near the planned laser wavelength of 532nm are underway using a Holospec f/1.8 spectrometer and an Andor iStar image intensified CCD camera to quantify line and continuum background levels. In addition, impurity line identification and plans for a separate line-of-sight averaged impurity temperature and density measurement capability employing the Thomson spectrometer are in progress. \\[4pt] [1] J.D. Hanson, et. al., Nuclear Fusion 49 (2009) 075031 [Preview Abstract] |
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JP8.00012: Determining Point of Structural Failure of a Foil Liner Under High Magnetic Fields Hannah Moore, Emma Bell, Robbert Duggan, Nathan Lambert, Daniel Liang, Lauren Ransohoff, Grigoriy Tabak, Pierre Gourdain, William Potter, John Greenly At the National Ignition Facility (NIF), the path to nuclear fusion relies on indirect drive, where the fuel capsule is irradiated by x-rays produced by a MJ laser heating the wall of a hohlraum. However laser plasma interactions prevent optimal focusing and the quality of the implosion may suffer from it. One way to mitigate this issue is to impose an external magnetic field on the hohlraum, reducing plasma outflows thereby limiting plasma-laser interaction. While the optimal magnetic field strength is still under debate, one major issue is the effect of the field on hohlraum integrity. Our goal is to study the effect of large magnetic fields ($>$100 T) on a thin aluminum liner (thickness 10 microns) and identify the maximum magnetic field ($<$150T) where the liner maintains its structural integrity. In past COBRA experiments using a coaxial coil design, we were able to consistently produce magnetic fields above 150 T. We will use this setup coupled with the liner and use a B-dot probe to measure the field penetration inside of the liner. From laser interferometry and XUV measurements we will also be able to observe how the liner reacts to the different magnetic field strengths. [Preview Abstract] |
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JP8.00013: Designing and testing a high power rf matching network circuit for helicon plasma antennas Kyle Adriany, Ryan De Leon, Saikat Chakraborty Thakur, George Tynan Controlled Shear Decorrelation eXperiment [CSDX] is a helicon plasma device dedicated to basic plasma studies of turbulence and transport in a very controlled and well diagnosed plasma environment. Previous studies in argon helicon plasmas were performed at relatively low power thresholds, typically 1.5 kWatts (maximum of 1.8 kWatts), mainly because of arcing in the rf matching circuit at higher powers. We are designing a completely new rf matching network circuit with new higher power rated capacitors and better insulation to prevent arcing even at much higher powers. We shall report initial results of using this new matching network circuit to couple rf power, up to 5 kwatts, to the helicon antenna in CSDX. We believe that this capability shall significantly improve upon the range of plasma parameters previously studied at CSDX. [Preview Abstract] |
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JP8.00014: Characterizing ICF Neutron Diagnostics on the nTOF line at SUNY Geneseo Angela Simone, Stephen Padalino, Ethan Turner, Mary Kate Ginnane, Natalie DuBois, Kurtis Fletcher, Michael Giordano, Patrick Lawson-Keister, Hannah Harrison, Hannah Visca, Craig Sangster, Sean Regan Charged particle beams from the Geneseo 1.7 MV tandem Pelletron accelerator produce nuclear reactions that emit neutrons in the range of 0.5 to 17.9 MeV via the d(d,n)3He and 11B(d,n)12C reactions. The neutron energy and flux can be adjusted by controlling the accelerator beam current and potential. This adjustable neutron source makes it possible to calibrate ICF and HEDP neutron scintillator diagnostics. However, gamma rays which are often present during an accelerator-based calibration are difficult to differentiate from neutron signals in scintillators. To identify neutrons from gamma rays and to determine their energy, a permanent neutron time-of-flight (nTOF) line is being constructed. By detecting the scintillator signal in coincidence with an associated charged particle (ACP) produced in the reaction, the identity of the neutron can be known and its energy determined by time of flight. Using a 100{\%} efficient surface barrier detector to count the ACPs, the absolute efficiency of the scintillator as a function of neutron energy can be determined. This is done by determining the ratio of the ACP counts in the singles spectrum to coincidence counts for matched solid angles of the SBD and scintillator. Funded in part by a LLE contract through the DOE. [Preview Abstract] |
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JP8.00015: Design of a triple plasma device for double layer and turbulence investigations Justin Kim, Cory Jackson, Noah Hershkowitz, M. Umair Siddiqui A triple plasma device is being constructed at the University of Wisconsin- Madison for basic plasma physics investigations. The device consists of two outer chambers and a central chamber. Separate plasmas are generated in the two outer chambers, and their interactions are measured in the central chamber. DC plasma is generated via thermionic emission of electrons from a hot-filament and rf plasma is generated either capacitively or inductively. The device is used to investigate double layer structures [Coakley and Hershkowitz, Physics of Fluids \textbf{22,} 1171 (1979)] and beam plasma instabilities. The design, construction, and operation of this device are discussed. Initial results are presented here. [Preview Abstract] |
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JP8.00016: ABSTRACT WITHDRAWN |
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JP8.00017: Permutation entropy analysis of dynamical turbulence in the SSX MHD wind tunnel and the solar wind P.J. Weck, E.R. Hudson, D.A. Schaffner, M.R. Brown, R.T. Wicks, V.S. Lukin The statistical character of turbulence in the plasma wind-tunnel configuration at the Swarthmore Spheromak Experiment (SSX) and the solar wind is evaluated using ordinal pattern-based measures of complexity. The SSX MHD wind tunnel measures fluctuations in magnetic field, velocity, and density as highly magnetized spheromaks (typical values are $B\approx 0.1$ T, $n\geq10^{20}$ m$^{-3},$ and $T \geq 20$ eV) evolve dynamically into a relaxed state. Flow speeds are measured with a visible light array. $\dot{B}$ time series for 3 spatial directions recorded by a 16-channel, high-resolution probe array embedded in the chamber are analyzed using the permutation entropy and Jensen-Shannon statistical complexity. By calculating the position of signals on a complexity-entropy plane,\footnote{Rosso, et al. PRL 99, 154102 (2007).} the degree of stochastic, periodic, or chaotic dynamics can be evaluated. Complexity-entropy positions of SSX signals are compared to those of turbulent fluctuations in the solar wind and the Large Plasma Device (LAPD) as well as Hall-MHD simulations of the SSX plasma, and it is found that the dynamics in the SSX plasma source are more truly turbulent than those in the LAPD but less stochastic than fluctuations in the solar wind. [Preview Abstract] |
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JP8.00018: Study of the probe-induced plasma perturbation on magnetic field measurements using an insertable probe M. Leeds, J.B. Triana, J.C. Titus, A.F. Almagri, J.S. Sarff One of the most utilized diagnostics in magnetized plasma research is an insertable probe with pickup loops to measure the local magnetic field. When an insulated probe is inserted into the plasma, the plasma current is forced to flow around the probe body. The geometry of both the particle shield and the coil arrangement within the current-free probe volume affect the measurement's sensitivity to this perturbation. A probe has been constructed for use in 200 kA, n$_{\mathrm{e}}$ $\sim$ 10$^{13}$cm$^{-3}$ MST plasmas with interchangeable particle shields (diameters of 1.6-2.5 cm) to investigate the influence of the probe's perturbation of measured fields. Magnetic pickup coils are arranged both centered and offset inside the probe body to measure all field components including the perturbation. The impact on both large-scale equilibrium and short wavelength magnetic fluctuations is studied. A simple lump-current wire model will be presented to interpret the data. [Preview Abstract] |
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JP8.00019: Magnetic field and velocity fluctuations with and without a reversal surface in the RFP D. Martin, D. Craig, D.J. Den Hartog, M.R. Nornberg, J.A. Reusch Fluctuations in the standard Reversed Field Pinch (RFP) are dominated by poloidal mode numbers m$=$0 and m$=$1. The velocity and magnetic fluctuations generate an emf which redistributes current in the plasma. In experiments, the m$=$0 mode amplitude and the emf due to m$=$1 modes are both highly dependent on the existence of the reversal surface in the plasma. We investigate the role of the reversal surface on magnetic and velocity fluctuations using the DEBS resistive magnetohydrodynamic (MHD) code. As in the experiment, we find that m$=$0 modes are suppressed through the removal of the reversal surface but m$=$1 magnetic fluctuation amplitudes are not strongly affected. However, the suppression of m$=$0 fluctuations is much more sudden in the experiment than in the code. Using the outputs of the code, we calculate the line-integrated velocity fluctuation correlated with specific magnetic modes measured at the edge. This facilitates comparisons between experimental and computational measures of velocity fluctuations. As in experiment, decreased m$=$1 velocity fluctuations are observed in the code without a reversal surface present but the change in phase between v and b observed in experiment is not reproduced in the code. We speculate that the phase change observed in the experiment may be due to the contribution of advection of the mean flow profile by the magnetic fluctuations, an effect not present in the code. This work has been supported by the USDOE and NSF. [Preview Abstract] |
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JP8.00020: Absolute Wavelength Calibration of the IDSII Spectrometer for Impurity Ion Velocity Measurements in the MST M. Baltzer, D. Craig, D.J. Den Hartog, M.D. Nornberg The MST operates two Ion Doppler Spectrometers (IDS) for high time-resolution passive and active measurements of impurity ion emission. Absolutely calibrated measurements of flow are difficult because the spectrometers record data within 0.3 nm of the line of interest, and commercial calibration lamps do not produce lines in this narrow range$.$ Four calibration methods were investigated. First, emission along the chord bisecting the poloidal plane was measured as it should have no time-averaged Doppler shift. Second, a calibrated CCD spectrometer and the IDSII were used to observe the same plasma from opposing sides so as to measure opposite Doppler shifts. The unshifted line is located halfway between the two opposing measurements. Third, the two fibers of the IDSI were positioned to take absolute flow measurements using opposing views. Substituting the IDSII for one of the IDSI fibers, absolute measurements of flow from the IDSI were used to calibrate the IDSII. Finally, an optical system was designed to filter an ultraviolet LED, providing a known wavelength source within the spectral range covered by the IDSII. The optical train is composed of an air-gapped etalon and fused silica lenses. The quality of calibration for each of these methods is analyzed and their results compared. Preliminary impurity ion velocity measurements are shown. This work has been supported by the US DOE and the NSF. [Preview Abstract] |
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JP8.00021: The High Fidelity Plasma Speaker James McGall A plasma speaker is a device that uses ionized gas as the driving source of sound production, rather than the traditional magnetic coil and membrane setup found on a standard speaker. Similar to how lightning produces sound, or even a small static shock, a plasma speaker uses a modulating electric arc between two electrodes to produce sound. An electric circuit is built that allows the variance of the high voltage electric potential to be controlled by a 3.5mm standard audio headphone jack, allowing sound energy to be transferred from the plasma to the air by means of pulse width modulation. For my summer project I have built two different models of plasma speakers and am working on a third. The speaker benefits from having a nearly massless driver, and I hypothesize that it should show a response rate faster than that of a traditional speaker and a decreased impulse response while having the drawbacks of inefficiency and a low maximum decibel output. The speakers are currently being optimized with magnetic stabilization of the plasma and will be tested soon for impulse response, frequency generation, efficiency, and audio coloration. [Preview Abstract] |
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JP8.00022: Measurement of Ion Temperature in a Laboratory Plasma Jiachen Liu, Seth Dorfman, Troy Carter, Walter Gekelman, Patrick Pribyl, Anton Bondarenko Alfv\'{e}n waves are low-frequency oscillating waves in a magnetized plasma. These modes may play a significant role in the heating of the solar corona, solar wind turbulence, and in fast ion transport in tokamaks. Effects that arise in a hot ion plasma are of particular interest; a new plasma source has been installed in the Large Plasma Device (LAPD) at UCLA to study this regime. In the present work, the ion temperature in this new plasma is measured using the width of the Helium ion spectral line emission. A monochromator is first used to measure cold ($\sim$0.1ev) spectral lines of a mercury lamp to account for instrumental broadening. After acquiring this calibration data, we convolve it with plasma simulation (PrismSPECT) data for a series of known ion temperatures. The result is then compared to the actual plasma measurements to obtain the plasma ion temperature. Currently, we are working to implement a matching F-number lens system to improve the resolution of the spectral line. Results of these measurements will aid future Alfv\'{e}n wave research in hot ion plasmas; this research may shed light on some of the plasma physics problems mentioned above. [Preview Abstract] |
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JP8.00023: ABSTRACT WITHDRAWN |
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JP8.00024: A Variable Frequency, Mis-Match Tolerant, Inductive Plasma Source Anthony Rogers, Don Kirchner, Fred Skiff Presented here is a survey and analysis of an inductively coupled, magnetically confined, singly ionized Argon plasma generated by a square-wave, variable frequency plasma source. The helicon-style antenna is driven directly by the class ``D'' amplifier without matching network for increased efficiency while maintaining independent control of frequency and applied power at the feed point. The survey is compared to similar data taken using a traditional exciter---power amplifier---matching network source. Specifically, the flexibility of this plasma source in terms of the independent control of electron plasma temperature and density is discussed in comparison to traditional source arrangements. [Preview Abstract] |
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JP8.00025: Plasma Globe Filamentary Structure and Propagation Trends by Voltage Waveform Change H.G. Ceja, M.J. Burin, G.G. Simmons, A. Nagy, S.J. Zweben Filamentary structures are seen in many types of plasma discharges. However, principal aspects of their physics are unclear. In order to study plasma filaments we have used popular commercial plasma globes, which typically have a Neon based mixture near atmospheric pressure. Previous work has provided initial estimates of the speed of plasma globe filaments [Campanell et al. 2010]. Our work analyzes the effects of voltage amplitude and frequency on filament speed and structure using a programmable high voltage supply with phase triggered high-speed photography. Observed trends are discussed in detail along with their possible relation to discharge structures found in nature (e.g. lightning leaders) and various industrial applications. [Preview Abstract] |
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JP8.00026: Fast Method for Radial Electric Field Correction of Motional Stark Effect Data in DIII-D L.J. Bergsten, C.C. Petty, T.C. Luce, C.T. Holcomb A fast and easy method to correct the motional Stark effect (MSE) data used in equilibrium reconstruction on the DIII-D tokamak by including the radial electric field effect in the determination of the magnetic pitch angles has been created. Previously, two methods for calculating motional stark effect were possible - one in which the radial electric field is completely ignored and the other in which the radial electric field is determined by manually fitting the radial force balance equation. This project develops a new equilibrium reconstruction procedure that is automatic and easy to use, in which only the toroidal rotation component of radial force balance is used to correct the MSE data for the radial electric field. This is expected to give a more accurate result than ignoring the radial electric field effect for discharges with co-neutral beam injection. Comparisons of equilibrium reconstructions using the approximate and complete determination of the radial electric field will be made. [Preview Abstract] |
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JP8.00027: Analysis of Sawtooth Post-Cursor Oscillations in Low Safety Factor DIII-D Plasmas J.D. Cabrera, C. Paz-Soldan, E.J. Strait, D. Shiraki Large sawtooth oscillations are a commonly observed phenomenon in very low safety factor ($q_{95}\sim $2) plasmas. Following the sawtooth crash phase, low frequency ($\sim$200 Hz) post-cursor oscillations in the magnetic field, with amplitudes $\sim$2 G decaying in time, are excited. These post-cursor oscillations do not exhibit the usual m=odd poloidal structures of sawtooth oscillation, but instead are found to be m=even in structure, suggesting the excitation of global kink modes. A novel means of modeling such post-cursor oscillations is presented via computational analysis of data obtained from high-resolution magnetic sensors installed at the DIII-D tokamak facility. Nonlinear regression analysis is used to obtain modeling parameters such as rates of decay and rotation. Trends in parameters over many oscillations are then compared with equilibrium plasma parameters. The impact of measured parameters on global instability onset and disruption prediction is considered. [Preview Abstract] |
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JP8.00028: Power Law Regression Analysis of Heat Flux Width in Type I ELMs C.D. Stephens, M.A. Makowski, A.W. Leonard, T.H. Osborne In this project, a database of Type I ELM characteristics has been assembled and will be used to investigate possible dependencies of the heat flux width on physics and engineering parameters. At the edge near the divertor, high impulsive heat loads are imparted onto the surface. The impact of these ELMs can cause a reduction in divertor lifetime if the heat flux is great enough due to material erosion [1]. A program will be used to analyze data, extract relevant, measurable quantities, and record the quantities in the table. Care is taken to accurately capture the complex space/time structure of the ELM. Then correlations between discharge and equilibrium parameters will be investigated. Power law regression analysis will be used to help determine the dependence of the heat flux width on these various measurable quantities and parameters. This will enable us to better understand the physics of heat flux at the edge.\par \vskip6pt \noindent [1] H. Thomsen et al 2011 Nucl. Fusion {\bf 51} 123001 [Preview Abstract] |
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JP8.00029: Evolution of Phase Space Sensitivity for Energetic Ion Loss Measurements in DIII-D N. Cothard, D.C. Pace The Fast Ion Loss Detector (FILD) diagnostic system installed on the DIII-D tokamak is a scintillator-based magnetic spectrometer that measures the energy and pitch angle of energetic ions that escape confinement and reach the diagnostic on the outer wall. Different areas of the FILD scintillator correspond to the energies and pitch angles of the impacting ions. This strike map is dependent on the local magnetic field vector that sets the geometry of the ion orbits upon entering the detector. The phase space sensitivity of the FILD, therefore, varies with plasma conditions. The FILD combines a slow camera (100 Hz) viewing the entire scintillator simultaneously with narrow viewing photomultiplier tubes that provide fast time-resolved (1$\,$MHz) measurements in narrow bands of energy and pitch angle. New analysis methods allow for tracking the phase space coverage throughout shots, thereby improving the fidelity of ion loss measurements due to plasma instabilities that change in time. [Preview Abstract] |
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JP8.00030: Time-Dependent DIII-D Heat Transport Simulations Using Neural-Network Models J.M. Penna, S.P. Smith, O. Meneghini, C.J. Luna The neural network transport model BRAINFUSE has been developed to produce transport fluxes based on local parameters [1]. The BRAIN-FUSE model has been integrated into the transport modeling framework ONETWO [2,3] in order to develop time dependent solutions and has been validated by artificially varying the input neutral beam power and comparing the output to DIII-D scans. These efforts have led to the development of a time-dependent workflow within the OMFIT integrated modeling framework. The new work flow can evolve the electron and ion temperatures as a function of time dependent sources and equilibria. The effects of different engineering parameters can be explored and optimized in support of DIII-D operations. The efficiency of this workflow enables planning plasma operations of next-day experiments, as will be required for ITER.\par \vskip6pt \noindent [1] O.~Meneghini et al., Phys.\ Plasmas {\bf 21}. 060702 (2014).\par \noindent [2] W.W.\ Pfeiffer et al., General Atomics Report GA-A16178 (2980).\par \noindent [3] O.~Meneghini et al., Bull.\ Am.\ Phys.\ Soc.\ {\bf 58}, 109 (2014). [Preview Abstract] |
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JP8.00031: Emittance Analysis of the DIII-D Neutral Beam Source N.A. Lopez, B. Crowley In a high powered neutral beam system ions are extracted from a low temperature plasma, through apertures in the arc chamber, by application of a potential to an external electrode. It has been determined that to increase the beam energy of the DIII-D neutral beam system beyond 95 keV the accelerator must be reconfigured to avoid excessive electrical breakdown in the grid gaps. Deciding exactly what modifications are to be made requires modeling and experimental effort. A basic problem is to find a geometry with which the extracted beam is intense, low divergence, free of aberrations, and does not strike the focusing electrodes. We present the results of modeling proposed reconfigurations to the accelerator geometry and source conditions. The quality of the beam produced from the various accelerator configurations is quantified through metrics such as the beam emittance and the average divergence per beamlet. By comparing the beam quality and power delivered for each proposed reconfiguration an optimal design is selected and recommended.\par [Preview Abstract] |
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JP8.00032: Optimization of a GPU Field Line Integration Code for Tokamak Transprt Simulation A. Steinhebel, T.E. Evans, W. Wu A basic knowledge of transport and diffusion physics processes in fusion plasmas is essential for the understanding and optimization of fusion confinement devices. Classical transport theory disagrees with experiment in predictions of the time necessary for electrons to exit the plasma. This anomalous transport is not yet understood. The TRIP3DGPU code is used to incorporate realistic magnetic field perturbations and trace the resulting magnetic field lines. The more accurately these lines can be traced, the more precisely the electron position and time of diffusion can be calculated through a series of electron-ion collisions. Accurate line tracing requires a small computational spatial integration step that does not result in a long computation time. To meet wishes for accuracy and speed, a varied step will be introduced into TRIP3DGPU and tested. The goal is to allow for quick, accurate magnetic field line tracing which can then be used to compare electron transport simulations to theory and experiment. [Preview Abstract] |
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JP8.00033: Transition From High Harmonic Fast Wave to Whistler/Helicon Regime in Tokamaks S.P. Harris, R.I. Pinsker, M. Porkolab Experiments are being prepared1 on DIII-D in which fast waves (FWs) at 0.5 GHz will be used to drive current noninductively in the mid-radius region. Previous DIII-D experiments used FWs at $\sim$0.1 GHz to drive central current; in this work we examine the frequency dependence of wave propagation and damping in the 0.1--1.0 GHz range with the goal of identifying the optimum frequency range for a particular application. Strongly enhanced electron damping and reduced ion damping at higher frequencies must be weighed against increasing coupling difficulties at higher frequencies and more restrictive wave accessibility at low toroidal field. Wave propagation and accessibility is studied with ray tracing models in slab, cylindrical, and fully toroidal geometries. Analytic expressions for electron and ion damping will be derived with an emphasis on understanding the transition from the moderate-to-high ion cyclotron harmonic regime to the very high harmonic or ``whistler"/``helicon"/lower hybrid FW regime.\par \vskip6pt \noindent [1] R.~Prater et al., Nucl.\ Fusion {\bf 54}, 083024 (2014). [Preview Abstract] |
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JP8.00034: Parametric Study of Anomalous Thermal, Particle and Momentum Transport in Tokamak Plasmas C. Wilson, T. Rafiq, A.H. Kritz, A.Y. Pankin A new tool is developed to obtain experimental, predictive, and interpreted values from the TRANSP/PTRANP code in order to study the parameter dependence of transport models. This tool is used to investigate the parameter dependence of the new Multi-mode anomalous transport model 8.1 (MMM8.1). A number of scans are carried out and the parameters chosen are those typical for DIII-D discharges. A stiffness study reveals that large values of shear flow and low values of magnetic shear lead to reduced stiffness and reduced thermal diffusivity as well as to an increase in the temperature gradient threshold. In addition, collisionality and temperature gradient scans indicate that the transport associated with the ITG/TEM modes decrease with large electron collisionality while transport associated with DRIBM diffusivity components increase with collisionality. In contrast, in the temperature gradient scan carried out, the behavior observed is that the transport associated with ITG/TEM modes increase with increased temperature gradient and the DRIBM transport decreases. The anomalous poloidal momentum diffusivity is found to be smaller than the toroidal momentum diffusivity. Additional scans carried out include density gradient, $q$, plasma beta, and plasma elongation. Results from the scans can be used to identify conditions for achieving optimal tokamak discharge performance. [Preview Abstract] |
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JP8.00035: Time-Resolved Tandem Faraday Cup for High Energy TNSA Particles Stephen Padalino, Angela Simone, Ethan Turner, Mary Kate Ginnane, Natalie DuBois, Craig Sangster, Sean Regan MTW and OMEGA EP Lasers at LLE utilize ultra-intense laser light to produce bursts of high-energy ions through Target Normal Sheath Acceleration (TNSA). A Time Resolved Tandem Faraday Cup (TFC) is being designed to collect and differentiate protons and alphas from heavy ions produced during TNSA. The TFC will be comprised of a replaceable thickness absorber capable of stopping a range of user-selectable heavy ions. Ions heavier than alphas emitted from the TNSA plasma will stop within the primary TFC, while less massive particles will continue through and deposit their remaining charge in the secondary TFC. The time-resolved beam current generated in each cup will be measured on a fast storage scope in multiple channels. Secondary electrons released from the impact of heavy ions with the cups will be suppressed by magnetic and electrostatic fields. A charge-exchange foil at the TFC entrance will modify the charge state distribution of the heavy ions produced by the plasma to a known distribution. Using the known distribution and the time of flight of the heavy ions, the total heavy ion current can be determined. Ultimately the TFC will be used to normalize a variety of nuclear physics cross sections and stopping power measurements. Funded in part by a LLE contract through the DOE. [Preview Abstract] |
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JP8.00036: Coincidence Efficiency of Sodium Iodide Detectors for Positron Annihilation Thomas Eckert, Laurel Vincett, Mark Yuly, Stephen Padalino, Megan Russ, Mollie Bienstock, Angela Simone, Drew Ellison, Holly Desmitt, Craig Sangster, Sean Regan One possible diagnostic technique for characterizing inertial confinement fusion reactions uses tertiary neutron activation of $^{\mathrm{12}}$C via the $^{\mathrm{12}}$C(n, 2n)$^{\mathrm{11}}$C reaction. A recent experiment to measure this cross section involved counting the positron annihilation gamma rays from the $^{\mathrm{11}}$C decay by using sodium iodide detectors in coincidence. To determine the number of $^{\mathrm{11}}$C decays requires an accurate value for the full-peak coincidence efficiency for the detector system. A new technique has been developed to measure this coincidence efficiency by detecting the positron prior to its annihilation, and vetoing events in which decay gamma rays other than the 511 keV annihilation gamma rays could enter the detectors. Measurements and simulation results for the absolute coincidence total and full-peak efficiencies are presented. [Preview Abstract] |
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JP8.00037: Measurements of proton energy spectra using a radiochromic film stack T.M. Filkins, Jessica Steidle, D.M. Ellison, Jeffrey Steidle, C.G. Freeman, S.J. Padalino, G. Fiksel, S.P. Regan, T.C. Sangster The energy spectrum of protons accelerated from the rear-side of a thin foil illuminated with ultra-intense laser light from the OMEGA EP laser system at the University of Rochester's Laboratory for Laser Energetics (LLE) was measured using a stack of radiochromic film (RCF). The film stack consisted of four layers of Gafchromic HD-V2 film and four layers of Gafchromic MD-V2-55 film. Aluminum foils of various thicknesses were placed between each piece of RCF in the stack. This arrangement allowed protons with energies of 30 MeV to reach the back layer of RCF in the stack. The stack was placed in the detector plane of a Thomson parabola ion energy (TPIE) spectrometer. Each piece of film in the stack was scanned using a commercially available flat-bed scanner (Epson 10000XL). The resulting optical density was converted into proton fluence using an absolute calibration of the RCF obtained at the SUNY Geneseo 1.7 MV Pelletron accelerator laboratory. In these calibration measurements, the sensitivity of the radiochromic film was measured using monoenergetic protons produced by the accelerator. Details of the analysis procedure and the resulting proton energy spectra will be presented. Funded in part by a grant from the DOE through the Laboratory for Laser Energetics. [Preview Abstract] |
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JP8.00038: Analysis of CME and CIR driven storms based on observations made by TWINS Bianca Trigo, Gunner Robinson, Jerry Carr Jr., Amy Keesee Geomagnetic storms are categorized into two different groups: coronal mass ejection (CME) and corotating interaction regions (CIR) driven storms. This work will analyze a CIR-driven storm observed on 13 Oct 2012 to see if it follows similar patterns observed in a superposed epoch analysis discussed in Keesee et al. (2014)\footnote{Keesee, A.M., et al., Superposed epoch analyses of ion temperatures during CME and CIR/HSS driven storms. J. Atmos. Sol. Terr. Phys. (2014), doi:10.1016/j.jastp.2013.08.009} and compared to the 22 July 2009 CIR-driven storm discussed in Keesee et al. (2012).\footnote{Keesee, A. M., et al., Inner magnetosphere convection and magnetotail structure of hot ions imaged by ENA during a HSS-driven storm. J. Geophys. Res. (2012), doi:10.1029/2011JA017319} The temperature and movement of the ions will be studied as the storm progresses. The ion temperature will be monitored during the recovery phase of the storm and the ion temperatures of the night side and the day side will be evaluated. To verify the accuracy of the analysis for the October storm, the data from the CME driven September storm on the 26 in 2011 referenced by Keesee et al. (2014)\footnote{Keesee (2014)} will be used as a baseline model for comparison. [Preview Abstract] |
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JP8.00039: High Duty Factor (DF) Testing of a Saddle Antenna Radio Frequency Surface Plasma Ion Source (SA RF SPS) Jeffrey Breitschopf, Vadim Dudnikov, Rol Johnson, Jerry Carr Jr., Robert Welton, Baoxi Han, Sydney Murray Jr., Terry Pennisi, Chip Piller, Manuel Santana, Martin Stockli, Galina Dudnikova A SA RF SPS was tested at the Spallation Neutron Source (SNS) at Oak Ridge National Lab. Hydrogen ions were extracted from the source as described in Dudnikov et al. (2011).\footnote{Dudnikov, V., et al., AIP Conf. Proc. 1390, 411 (2011).}$^{\mathrm{\thinspace }}$ Modifications were installed to increase ion beam output and optimize cooling. The source was tested under a DF of 5-20\% at 150 Hz as well as a continuous beam with power ranging from 0.8 kW to 3.3 kW. Cesium was also used to optimize H- beam output.\footnote{Dudnikov, V., Method of Negative Ion Production, Patent cccp 411542, 10 March, 1972.}$^{\mathrm{\thinspace }}$ The highest beam produced was 13 mA at 2.5 kW. The SA RF SPS has an ion production efficiency of $\sim$5 mA/kW while the current ion source at the SNS produces $\sim$1 mA/kW.\footnote{Welton, R. F., et.al. AIP Conf. Proc. 925, 87 (2007).}$^{\mathrm{\thinspace }}$ The SA RF SPS will be tested with the conditions of the linear accelerator at the SNS so the recent accelerator-based pulsed neutron record of 20 GW (1.4 MW average power)\footnote{A Record-Breaking Month for ORNL's Spallation Neutron Source www.ornl.gov/ornl/news/features/2014}$^{\mathrm{\thinspace }}$ can be surpassed. [Preview Abstract] |
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JP8.00040: Offline Development of Plasma Boundary Controllers for the KSTAR Tokamak S. Ballinger, N.W. Eidietis, D.A. Humphreys, A.W. Hyatt, A.S. Welander, S.H. Hahn The KSTAR TokSys [1] tokamak simulator, implemented in Matlab\textsuperscript{\textregistered}/Simulink, has been extended to include a plasma boundary control system to allow automated offline tuning of shape control feedback loops. Offline control development minimizes resources expended tuning controllers during actual run time, and automated tuning is desirable in order to optimize the large number of shape control gains. The new simulation includes simplified versions of the rtEFIT/Isoflux [2] controller used in the KSTAR plasma control system, allowing full-closed-loop analysis of the plasma shape control. Results presented include application of robust design methods to optimizing control of KSTAR's plasma boundary, and analysis to understand observed differences in boundary control between KSTAR and other superconducting devices.\par \vskip6pt \noindent [1] D.A.\ Humphreys {\em et al.}, Nucl.\ Fusion {\bf 86}, 1116 (2007).\par \noindent [2] J.R.\ Ferron {\em et al.}, Nucl.\ Fusion {\bf 38}, 1055 (1998). [Preview Abstract] |
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JP8.00041: Particle-in-cell Simulations of Cross-field Propagation by a Beam Composed of Positive and Negative Ions Ryan Gale, Nathaniel Hicks Particle-in-cell simulations of a beam composed of positive and negative ions are performed to explore beam propagation in the presence of a transverse magnetic field. The dependences of propagation on parameters such as beam density and energy, spatial profiles of magnetic field and beam, and beam species are investigated. Initially, 2-D simulations of a slab beam are performed, with the possibility of moving to 3-D to assess effects on the head of the beam. The ability of such a beam to achieve cross-field propagation without dramatic beam losses may be of interest for applications in which delivery of a charge-neutral beam to a target in the presence of a magnetic field is desired. [Preview Abstract] |
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JP8.00042: Measurements of the Absorption of Atmospheric Gases in Bulk Lithium Metal using a Mass Balance Connor A. Hart, Charles H. Skinner, Angela M. Capece, Bruce E. Koel Lithium conditioning of plasma facing components has enhanced the performance of several fusion devices. However, metallic lithium is very reactive and it is important to quantify the processes leading to the passivation of lithium upon exposure to air. Passivation, as used here, refers to the absorption of atmospheric gases by lithium to ultimately form~lithium species including lithium hydroxide, carbonate, and oxide. The current work uses a mass balance with microgram sensitivity to measure the mass gain during the absorption of atmospheric gases by bulk lithium. Metallic lithium films with thicknesses of 0.3 and 1.0 mm are exposed to humid air as well as dry synthetic air at atmospheric conditions in order to reproduce the environment of a tokamak exposed to air during maintenance activities and venting. The data yield the reaction rates and interdiffusion of these~lithium species~as functions of thickness and time. These results provide critical insight into the chemical state of a lithiated surface after air exposure. In addition, the depth of passivation versus time is of interest in determining the length of exposure required to completely passivate a lithium layer of a given thickness, making it safe to handle. [Preview Abstract] |
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JP8.00043: Electron beam modeling on LTX Gregory Szalkowski, Richard Majeski, John Schmitt The lithium tokamak experiment (LTX) is a low aspect ratio tokamak with a steel clad copper shell that can be heated to 300-400 $^{\circ}$C and coated with lithium. The lithium coating has been shown to decrease impurities in the plasma and decrease the recycling coefficient, improving plasma performance. The coating is applied to the walls by heating the shells, then using an electron beam to evaporate a pool of lithium located at the bottom of the shell. The beam is steered using the magnetic field generated by the field coils. This method allows for rapid evaporation of the lithium, producing a 50-100 nm coating in approximately 5 minutes. The current electron beam system can only coat half of the shell surface. A new electron beam system has been installed on LTX to coat the remaining shell surface. A model of this electron gun has been created using the AMaze program series (Field Precision LCC). The model will be used to find the magnetic fields needed to steer the electron beam produced by the gun to the lithium pool. The model will also show the electropotential produced both at the electron gun head and in the vessel. The model may also be used to find the dispersion of the beam and therefore the effective power density of the beam as it impacts the lithium pool. [Preview Abstract] |
(Author Not Attending)
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JP8.00044: Investigation of Liquid Metal Embrittlement of Materials for use in Fusion Reactors Daniel Kennedy, Michael Jaworski Liquid metals can provide a continually replenished material for the first wall and extraction blankets of fusion reactors. However, research has shown that solid metal surfaces will experience embrittlement when exposed to liquid metals under stress [1]. Therefore, it is important to understand the changes in structural strength of the solid metal materials and test different surface treatments that can limit embrittlement. Research was conducted to design and build an apparatus for exposing solid metal samples to liquid metal under high stress and temperature. The apparatus design, results of tensile testing, and surface imaging of fractured samples will be presented.\\[4pt] [1] B.A. Benson and R.G. Hoagland, Scr. Metall. 23 (1989) 1943-1948. [Preview Abstract] |
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JP8.00045: Reconstruction of electron temperature and density profiles from Thomson scattering system using neural networks Vetri Velan, Ahmed Diallo, Benoit LeBlanc Neural networking analysis is implemented on NSTX Thomson scattering measurements in order to provide fast, real-time control of temperature and density profiles. Raw voltages from an array of 30 radially-variant polychrometers [1] are transformed into T$_{\mathrm{e}}$ and N$_{\mathrm{e}}$ measurements by using a multi-layer perceptron approach. The neural net, designed with the Torch7 package, is trained on Thomson Scattering data taken between 2008 and 2011, and tested on different data taken during the same period. The net can be modified by changing the number of hidden layers, the optimization procedure used, the size of each epoch, or the batch size (in the case of batch optimization methods); different permutations of these are tested to optimize accuracy and computation time. If the analysis succeeds, the next step is to use it on 2012 data, which contains an array of 42 polychrometers, to predict temperatures and densities and compare them to actual calculations. Furthermore, the analysis's success will motivate inclusion of the neural net into the NSTX-Upgrade, so that electron temperatures and densities can be extracted in real time. \\[4pt] [1] B. LeBlanc et. al. Rev Sci Instrum. 2012 \textbf{83}(10):10D527. [Preview Abstract] |
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JP8.00046: Development of a GPU-Accelerated 3-D Full-Wave Code for Electromagnetic Wave Propagation in a Cold Plasma D. Woodbury, S. Kubota, I. Johnson Computer simulations of electromagnetic wave propagation in magnetized plasmas are an important tool for both plasma heating and diagnostics. For active millimeter-wave and microwave diagnostics, accurately modeling the evolution of the beam parameters for launched, reflected or scattered waves in a toroidal plasma requires that calculations be done using the full 3-D geometry. Previously, we reported on the application of GPGPU (General-Purpose computing on Graphics Processing Units) to a 3-D vacuum Maxwell code using the FDTD (Finite-Difference Time-Domain) method. Tests were done for Gaussian beam propagation with a hard source antenna, utilizing the parallel processing capabilities of the NVIDIA K20M. In the current study, we have modified the 3-D code to include a soft source antenna and an induced current density based on the cold plasma approximation. Results from Gaussian beam propagation in an inhomogeneous anisotropic plasma, along with comparisons to ray- and beam-tracing calculations will be presented. Additional enhancements, such as advanced coding techniques for improved speedup, will also be investigated.\newline [1] K.S. Reuther, et al., Poster JP8.00021, APS DPP13 Meeting, Nov. 11-15, 2013, Denver, CO [Preview Abstract] |
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JP8.00047: Carbon Density Asymmetry and Beam Density Verification in DIII-D R.S. Bielajew, C. Chrystal, B.A. Grierson, K.H. Burrell Carbon density asymmetry in DIII-D plasmas has been measured using charge exchange spectroscopy coupled with main ion measurements. These main ion charge exchange measurements are used to verify the neutral beam density. Centrifugal effects in plasmas with high toroidal rotation and electrostatic effects due to trapped fast ions can both drive impurity density asymmetries within flux surfaces. Measuring impurity density asymmetry is important for verifying theories of parallel impurity transport. New main ion charge exchange measurements implemented on the high field side of the plasma are instrumental to this work. Impurity density asymmetry is measured in plasmas with low and high [$V_\phi/V_{t,imp}=O (1)$] rotation and low and high ($\eta_{fast}/\eta_e>0.2$). [Preview Abstract] |
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JP8.00048: Progress on Pre-Stage Magnetic Coil to Enhance Helicon Mode Excitation and Data Acquisition Software on the Helicon Plasma Experiment (HPX) Justin Sherman, Phillip Azzari, P.B. Crilly, Omar Duke-Tinson, Royce W. James, Jackson Karama, E.J. Page, Carter Schlank, Jonathan Zuniga CGAPL is conducting small investigations in plasma physics and magneto-hydrodynamics buoy positioning. For data management, we are developing capability to analyze/digitize data with a National Instruments Data Acquisition board, 2MS/s sampling rate (long time scale), and an Express Octopus card, 125MS/s sampling rate (short scale). Sampling at 12bits precision, we use LabVIEW as a programing language; GUIs will control variables in 1 or more concurrent runs and monitor of diagnostics. HPX utilizes high density(10$^{13}$cm$^{3}$ up), low pressure(.01 T) [1] Ar gas (fill pressure: on 10$^{4}$mTorr order). Helicon/W Mode plasmas become a diagnostics test-bed for other investigations and a tool for future spacecraft propulsion devices. Plasmas created by directing energy into gas-filled Pyrex tube; power supply and matching box, up to 250W power in 20-100MHz frequencies, provide energy to ignite. Uniform magnetic field needed to reach the W-Mode [1]. We employ an electromagnet to B-field while an acceleration coil positions plasma in vacuum chamber, facilitating analysis. Initial field requirements and accuracy calibration have been completed. Progress on development and implementation of probes and DAQ/GUI system will be reported. [1] K.Toki, et al, Thin Solid Films 506-507(2005) [Preview Abstract] |
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JP8.00049: Updates on the Optical Emission Spectroscopy and Thomson Scattering Investigations on the Helicon Plasma Experiment (HPX) Omar Duke-Tinson, Jackson Karama, Phillip Azzari, James Royce, Eric Page, Carter Schlank, Justin Sherman, Brooke Stutzman, Jonathan Zuniga HPX at the Coast Guard Academy Plasma Laboratory (CGAPL) have set up spectral probes to verify plasma mode transitions to the W-mode. These optical probes utilize movable filters, and ccd cameras to gather data at selected spectral frequency bands. Raw data collected will be used to measure the plasma's relative density, temperature, structure, and behavior during experiments. Direct measurements of the plasma's properties can be determined through modeling and by comparison with the state transition tables, using Optical Emission Spectroscopy (OES). The spectral probes will take advantage of HPX's magnetic field structure to define and measure the plasma's radiation temp as a function of time and space. In addition, the Thomson Scattering (TS) device will measure internal temperature and density data as the HPX plasma transitions through capacitive and inductive modes while developing into helicon plasma. Currently CGAPL is focused on building its laser beam transport and scattered light collection optical systems. Recently, HPX has acquired an Andor ICCD spectrometer for the spectral analysis. Data collected by the TS system will be logged in real time by CGAPL's Data Acquisition (DAQ) system with LabView remote access. Further progress on HPX will be reported. [Preview Abstract] |
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JP8.00050: FUNDAMENTAL THEORY AND COMPUTATION |
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JP8.00051: Particle-In-Cell Modeling of Hall-Driven Magnetic Penetration and Species Separation in Two-Species Plasmas Andrew Richardson, Stephen Swanekamp, Paul Ottinger, Justin Angus, Ian Rittersdorf, Joseph Schumer Understanding the interaction of a strong magnetic field with a plasma is a key problem in plasma physics. In this poster we report on a new systematic study using two-dimensional particle-in-cell simulations designed to explore the interplay between magnetic pushing and Hall-driven magnetic field penetration. In plasma where the ions are infinitely massive and $\nabla n \times B > 0$, the magnetic field penetrates into the plasma at a specific fraction of the Hall speed, $v_b$. When the ions have finite mass, the penetrating magnetic field gives an impulse to the ions, accelerating them to speed $v_i$. In a two-species plasma, simulations show simultaneous pushing of the light-ion species and magnetic field penetration through the heavy-ion species when $v_{heavy} < v_b < v_{light}$. This leads to a separation of the two ion species. If the mass of the light ions is increased, a transition to magnetic penetration of both species is observed when $v_{heavy} < v_{light} < v_b$. Analytic estimates for both $v_i$ and the mass at which this transition occurs agree well with simulations. [Preview Abstract] |
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JP8.00052: Plasma Model V\&V of Collisionless Electrostatic Shock Robert Martin, Hai Le, David Bilyeu, Stephen Gildea A simple 1D electrostatic collisionless shock was selected as an initial validation and verification test case for a new plasma modeling framework under development at the Air Force Research Laboratory's In-Space Propulsion branch (AFRL/RQRS). Cross verification between PIC, Vlasov, and Fluid plasma models within the framework along with expected theoretical results will be shown. The non-equilibrium velocity distributions (VDF) captured by PIC and Vlasov will be compared to each other and the assumed VDF of the fluid model at selected points. Validation against experimental data from the University of California, Los Angeles double-plasma device\footnote{R.J. Taylor, D.R. Baker, H. Ikezi, \textbf{PRL} 24:5, 206-209, 1969.} will also be presented along with current work in progress at AFRL/RQRS towards reproducing the experimental results using higher fidelity diagnostics to help elucidate differences between model results and between the models and original experiment.\\[4pt] DISTRIBUTION A: Approved for public release; unlimited distribution; PA (Public Affairs) Clearance Number 14332. [Preview Abstract] |
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JP8.00053: High-Performance Kinetic Plasma Simulations with GPUs and load balancing Kai Germaschewski, Narges Ahmadi, Stephen Abbott, Liwei Lin, Liang Wang, Amitava Bhattacharjee, Will Fox We will describe the Plasma Simulation Code (PSC), a modern particle-in-cell code with GPU support and dynamic load balancing capabilities. For 2-d problems, we achieve a speed-up of up to $6\times$ on the Cray XK7 ``Titan'' using its GPUs over the well-known VPIC code, which has been optimized for conventional CPUs with SIMD support. Our load-balancing algorithm employs a space-filling Hilbert-Peano curve to maintain locality and has shown to keep the load balanced within approximately 10\% in production runs which otherwise slow down up to $5\times$ with only static load balancing. PSC is based on the {\sc libmrc} computational framework, which also supports explicit and implicit time integration of fluid plasma models. Applications include magnetic reconnection in HED plasmas, particle acceleration in space plasmas and the nonlinear evolution of anisotropy-based kinetic instabilities like the mirror mode. [Preview Abstract] |
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JP8.00054: A new PIC noise reduction technique D.C. Barnes Numerical solution of the Vlasov equation is considered in a general situation in which there is an underlying static solution (equilibrium). There are no further assumptions about dimensionality, smallenss of orbits, or disparate time scales. The semi-characteristic (SC) method for Vlasov solution is described. The usual characteristics of the equation, which are the single particle orbits, are modified in such a way that the equilibrium phase-space flow is removed. In this way, the shot noise introduced by the usual discrete particle representation of the equilibrium is static in time and can be removed completely by subtraction. An almost exact algorithm for this is based on the observation that a (infinitesimal or) discrete time step of any equilibrium MC realization is again a realization of the equilibrium, building up strings of associated simulation particles. In this way, the only added discretization error arises from the need to extrapolate backward in time the chain end points one dt using a canonical transformation. Previously developed energy-conserving time-implicit methods are applied without modification. 1D ES examples of Landau damping and velocity-space instability are given to illustrate the method. [Preview Abstract] |
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JP8.00055: Particle-in-cell simulations on graphic processing units C. Ren, X. Zhou, J. Li, M.C. Huang, Y. Zhao We will show our recent progress in using GPU's to accelerate the PIC code OSIRIS [Fonseca et al. LNCS \textbf{2331}, 342 (2002)]. The OISRIS parallel structure is retained and the computation-intensive kernels are shipped to GPU's. Algorithms for the kernels are adapted for the GPU, including high-order charge-conserving current deposition schemes with few branching and parallel particle sorting [Kong et al., JCP \textbf{230}, 1676 (2011)]. These algorithms make efficient use of the GPU shared memory. This work was supported by U.S. Department of Energy under Grant No. DE-FC02--04ER54789 and by NSF under Grant No. PHY-1314734 [Preview Abstract] |
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JP8.00056: Comparison of velocity distribution function errors introduced by particle reweighting schemes in PIC-DSMC simulations Christopher Moore, Jeremy Boerner, Stan Moore, Keith Cartwright, Timothy Pointon Many PIC simulations span many orders of magnitude in the plasma density and therefore a constant particle weight results in too few particles in regions (or time periods) of low density or too many particles when the density is high. The standard solution is to employ a reweighting scheme in which low-weight particles are merged in order to keep the number of particles per cell roughly constant while conserving mass and momentum. Unfortunately merger schemes distort a general velocity distribution function (VDF) of particles (one can conserve arbitrarily higher moments such as energy flux by merging N to M particles for N\textgreater M\textgreater 1) and often merge routines act like artificial collisions that thermalize the distribution and lead to simulation error. We will compare the accuracy of the unique reweighting scheme used in our PIC-DSMC code and common reweighting schemes (e.g. redrawing from a constructed VDF or rouletting) through two benchmarks. The first compares the time varying VDF from various merge routines to an analytic solution for relaxation of a bimodal VDF to a Maxwellian through elastic collisions. The second benchmark compares error introduced in the VDF due to merging electrons during a breakdown simulation. [Preview Abstract] |
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JP8.00057: A Variational Formulation of Particle Algorithms for Kinetic E{\&}M Plasma Simulations in the Moving Window Alexander Stamm, Bradley Shadwick The recent variational technique [1] for rigorously deriving discrete, self-consistent equations for electromagnetic particle codes has been further developed in the moving window. The primary advantage of the Lagrangian formulation is the connection between symmetries of the system and conservation laws, which in the present case resolves the grid-heating issue. However, the approach also simplifies coordinate transformations and enables the particle method to be formulated in moving window coordinates. For some laser-plasma interaction scenarios, this leads to computational savings from working in a coordinate system where the evolution of the laser is intrinsically slow. New time advance integrators were developed in this coordinate system and compared to one another; namely, a symplectic method and a split explicit particle and implicit field advance method were developed in the moving window to show the extent of available optimization and improvements over the traditional particle-in-cell (PIC) method. In addition, we examine the phase-space fidelity of our method in cases where the conventional PIC algorithm exhibits unphysical particle trapping [2]. [1] E. G. Evstatiev et al., J. Comput. Phys. \textbf{245}, 376 (2013); B. A. Shadwick et al., Phys. Plasmas \textbf{21}, 055708 (2014); A. B. Stamm et al., IEEE Trans. Plasma Sci. \textbf{42}, 1747 (2014). [2] E. Cormier-Michel et al., Phys. Rev. E \textbf{78}, 016404 (2008). [Preview Abstract] |
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JP8.00058: Finite Time Step and Finite Grid Size Numerical Analysis of Warm Plasmas in $\delta f$ Simulations Benjamin Sturdevant, Scott Parker, Yang Chen The effects on the dispersion relation for warm plasmas due to numerical time integration methods and finite spatial grids can be analyzed for many conventional particle in cell(PIC) models using the mathematical framework developed by Langdon [1,2]. This analysis can be useful to gain an understanding of overall system accuracy and nonphysical behaviors including instabilities caused by numerical integration and finite difference methods. To derive a numerical dispersion relation for $\delta f$ method simulations, however, a different approach is required for the time integration analysis. Here, this analysis is performed using a discrete version of the method of characteristics applied to an implicit $\delta f$ particle weight equation. A numerical dispersion relation including both finite time step size and finite grid size effects has been derived for an implicit ion acoustic wave model which shows agreement with simulation results and reduces to the continuous result in the limits that the discrete time and spatial sizes go to zero. Comparisons with conventional PIC will be performed to determine differences in the numerical dispersion between the two simulation models.\\[4pt] [1] A.B. Langdon, J. Comput. Phys. 6 (1970), 247\\[0pt] [2] A.B. Langdon, J. Comput. Phys. 30 (1979), 202 [Preview Abstract] |
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JP8.00059: Gyrokinetic Simulations of Low-$n$ Tearing Modes Yang Chen, Jugal Chowdhury, Weigang Wan, Scott Parker Low-n tearing modes in cylintrical plasmas are studied with the GEM code using the gyrokinetic ion/fluid electron model. Particle trajectories and the evolution equations for $A_\parallel$ and $\phi$ are advanced in the field-line-following coordinates, but new field solvers for the vorticity equation and the Ampere's law are developed for global, low-n modes to avoid the usual high-n approximations made in the Laplacian $\nabla_\perp^2$ operator in gyrokinetic simulations. Since the tearing mode growth rate is small, numerical dissipation must be minimized. The hybrid model properly reduces to the reduced MHD model when ion kinetic effects are neglected. Eigenmode analysis for the reduced MHD cylindrical tearing mode problem has been developed to provide a direct verification of the simulation algorithms. Excellent agreement between the simulation and the eigenmode analysis is obtained for the tearing mode growth rate. When the finite-Larmor-radius effect in the ion polarization term in the vorticity equation is fully retained, simulations show an increase of the growth rate. The effects of gyrokinetic ions on the tearing mode stability will be studied and reported. [Preview Abstract] |
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JP8.00060: Gyrokinetic description of high intensity beams in cyclotrons Joseph Guadagni, Antoine Cerfon Continuum kinetic and fluid theories are a useful complement to Particle-in-Cell simulations to study the dynamics of intense beams in cyclotrons. We recently derived a reduced fluid model for cyclotron beams in the regime in which 1) the ratio of the self-electric field force to the externally imposed magnetic force is small; 2) the amplitude of the mismatch oscillations is small compared to the characteristic size of the beam. The fluid equations in this model are formally identical to the vorticity-streamfunction form of the incompressible 2D-Euler equations. Based on this analogy, we were able to use well-known results of fluid dynamics to offer intuitive explanations for beam spiraling and breakup. In our present work, we relax assumption 2) to include the effects of large mismatch oscillations in our model. We still assume that the beam is strongly magnetized, corresponding to a large scale separation between the betatron time scale and the space charge time scale. Averaging over the betatron time scale, we show that the evolution of the beam on the space charge time scale is determined by the gyrokinetic Vlasov-Poisson system. We describe the numerical scheme we developed to solve these equations and present initial results. [Preview Abstract] |
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JP8.00061: Deviations from Axisymmetry in Rotating Multiscale Gyrokinetics Ian Abel, Matt Landreman We extend Multiscale Rotating Gyrokinetics [Abel et. al. Rep. Prog. Phys. 2013] to include small non-axisymmetric magnetic fields, including both ripple and applied magnetic fields. We develop a framework in which neoclassical toroidal viscosities can compete with turbulent momentum fluxes in regulating the size of the global toroidal flow. In addition, we gain the capability to study the effects of small non-axisymmetric magnetic fields on the gyrokinetic turbulence itself. This work will also enable the study of how turbulence can affect the penetration of non-axisymmetric fields into the plasma. [Preview Abstract] |
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JP8.00062: Discontinuous Galerkin schemes for a class of Hamiltonian evolution equations with applications to gyrokinetic edge turbulence problems Ammar Hakim, Gregory Hammett, Eric Shi, Ian Abel We present a new gyrokinetic code, Gkeyll, for use in edge plasma simulations. The code implements novel energy conserving discontinuous Galerkin schemes, applicable to a general class of Hamiltonian equations. The inclusion of magnetic fluctuations with kinetic electrons has been challenging for many gyrokinetic algorithms in the past, requiring special treatment to reduce the Ampere cancellation problem. An important feature of this work is that we have developed novel versions of DG that can handle gyrokinetic magnetic fluctuations in an efficient way while preserving the energy invariant. To illustrate our improved algorithm, we show that Gkeyll reproduces the Alfven wave dispersion relation even at very low $k_\perp \rho_s$ in an efficient way with just the normal time step needed to resolve the electron dynamics. Initial results will be shown for a 1D axisymmetric problem and a higher dimensional turbulent problem with a simple geometry, to illustrate the applications of this approach for fusion problems. [Preview Abstract] |
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JP8.00063: Extension of Gkeyll Discontinuous Galerkin Kinetic Code to 2D E.L. Shi, A. Hakim, G.W. Hammett Gkeyll is a discontinuous Galerkin (DG) code under development for modeling the edge plasma in fusion devices and basic plasma experiments. High-order accurate, energy-conserving numerical algorithms for general Hamiltonian systems are implemented in Gkeyll. Details of the recent extension of the code dimensionality to 2D2V will be presented. Since DG schemes allow for flexibility in the choice of basis functions, we will discuss how various types of basis functions affect code accuracy and efficiency. Test problems in 2D, such as toroidal ITG instabilities and turbulence in a local limit, will be presented. We will also show initial results from 2D kinetic simulations of transport in a scrape-off layer plasma, using a specified diffusion coefficient to model radial transport. [Preview Abstract] |
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JP8.00064: Gyrokinetic Magnetic Fluctuations in an ELM Heat Pulse Scrape-Off-Layer Test Problem G.W. Hammett, A.H. Hakim, E.L. Shi, I.G. Abel, T. Stoltzfus-Dueck We have applied an electromagnetic gyrokinetic-based model to simulate parallel plasma transport in the scrape-off layer (SOL) to a divertor plate, employing the Discontinuous-Galerkin code Gkeyll. We focus on a test problem that has been studied previously,\footnote{E. Havl{\'\i}{\v c}kov{\'a}, W. Fundamenski, D. Tskhakaya, et al., PPCF 54, 045002 (2012)} using parameters chosen to approximate a heat pulse driven by an edge localized mode (ELM) in JET. With the use of the gyrokinetic quasineutrality equation and logical sheath boundary conditions, spatial and temporal resolution requirements are no longer set by the electron Debye length and plasma frequency. This test problem also helps illustrate some of the physics contained in the Hamiltonian form of the gyrokinetic equations and some of the numerical challenges in developing an edge gyrokinetic code. In particular, we will describe some of the special techniques needed to handle magnetic fluctuations in this nonlinear gyrokinetic problem. [Preview Abstract] |
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JP8.00065: Nonlinear bounce-gyrokinetic formulation of Neoclassical Tearing Modes N. Tronko, A.J. Brizard The nonlinear bounce-gyrokinetic formulation of neoclassical tearing modes in axisymmetric tokamak geometry is presented. The guiding-center/gyrocenter and bounce-center/bounce-gyrocenter phase-space transformations are successively introduced in order to self-consistently describe the nonlinear bounce-gyrocenter dynamics of trapped/passing-particle orbits in axisymmetric tokamak geometry in the presence of a magnetic-island perturbation. The bounce-gyrokinetic Poisson (i.e., quasineutrality condition) and parallel Ampere equations are written explicitly in terms of magnetic flux-surface-averaged expressions that clearly highlight the role of the reduced polarizations that result from dynamical reduction. This work generalizes previous reduced kinetic descriptions of neoclassical tearing modes [1,2]. \\[4pt] [1] H.R. Wilson, J.W. Connor, R.J. Hastie, and C.C. Hegna, PoP {\bf 3}, 248 (1996).\\[0pt] [2] J.W. Connor, R.J. Hastie, and P. Helander, PPCF {\bf 51}, 015009 (2009). [Preview Abstract] |
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JP8.00066: Energy-momentum-conserving Landau form of the guiding-center Fokker-Planck collision operator J. Burby, A.J. Brizard, E. Hirvijoki The guiding-center Fokker-Planck collision operator [1] describes particle collisions in the five-dimensional guiding-center phase space [2], where the fast gyroangle is asymptotically eliminated at lowest order in the slow collisional time scale. The test-particles and field-particles are treated independently in terms of full guiding-center distributions without the need of linearization. For the field-particle guiding-center representation, guiding-center Rosenbluth potentials are introduced. The phase-space divergence form of the guiding-center Fokker-Planck collision operator immediately guarantees its particle-conserving property, while its Landau form guarantees its energy-momentum-conserving properties, even when the guiding-center transformation is truncated at finite order. A linearized guiding-center Fokker-Planck collision operator suitable for gyrokinetic particle simulations is derived and compared with recent linearized gyrokinetic collision operators [3,4].\\[4pt] [1] A.J. Brizard, PoP {\bf 11}, 4429 (2004).\\[0pt] [2] E. Hirvijoki, A.J. Brizard, A. Snicker, and T. Kurki-Suonio, PoP {\bf 20}, 092505 (2013).\\[0pt] [3] B. Li and D.R. Ernst, PRL {\bf 106}, 195002 (2011).\\[0pt] [4] J. Madsen, PRE {\bf 87}, 011101 (2013). [Preview Abstract] |
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JP8.00067: Gyrokinetic investigation of ITG turbulence in helical RFPs I. Predebon, P. Xanthopoulos, D. Terranova Micro-instabilities in reversed field pinch (RFP) plasmas have been investigated in the last years from several viewpoints and with various numerical tools. So far, axisymmetry of the magnetic equilibrium has always been postulated. Nevertheless, experimental evidence suggests that the physical conditions mostly favoring the onset of electrostatic/electromagnetic turbulence, e.g., the occurrence of large pressure gradients, emerge when magnetic surfaces become helical, during the single helicity states [1]. In this work, we investigate ion-temperature-gradient driven turbulence focusing on the 3D feature, with the aim to describe its distinct properties compared to the axisymmetric geometry. For this study, we will apply the 3D nonlinear gyrokinetic code GENE [2,3] to RFP equilibria generated by the VMEC code.\\[4pt] [1] Carraro et al, Nucl. Fusion 53, 073048 (2013);\\[0pt] [2] http://www.ipp.mpg.de/$\sim$fsj/gene;\\[0pt] [3] http://www.ipp.mpg.de/$\sim$pax [Preview Abstract] |
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JP8.00068: Effects of collisions on conservation laws in gyrokinetic field theory H. Sugama, T.-H. Watanabe, M. Nunami In gyrokinetic field theory [1], the gyrokinetic Vlasov equation, Poisson's equation, and Ampere's law are all obtained from the Lagrangian formulation, and conservation laws of energy and momentum for collisionless magnetized plasmas are derived by applying the Noether's theorem [2,3]. In this work, effects of collisions on conservation laws are investigated by using the gyrokinetic Boltzmann equation which includes Landau's collision operator represented in the gyrocenter coordinates. Particle, energy, and momentum transport equations including collisional transport fluxes are systematically derived by modifying Noether's theorem. Then, the ensemble-averaged transport equations of particles, energy, and toroidal momentum given in the present work are shown to include both collisional and turbulent transport fluxes which agree with those derived from the conventional recursive formulation with the WKB representation.\\[4pt] [1] H. Sugama, Phys. Plasmas 7, 466 (2000).\\[0pt] [2] H. Sugama, T.-H. Watanabe, and M. Nunami, Phys. Plasmas 20, 024503 (2013).\\[0pt] [3] H. Sugama, T.-H. Watanabe, and M. Nunami, Phys. Plasmas 21, 012515 (2014). [Preview Abstract] |
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JP8.00069: Global Microtearing Modes in Collisionless Large Aspect Ratio Tokamaks Aditya Krishna Swamy, Rajaraman Ganesh, Jugal Chowdhury, S. Brunner, J. Vaclavik, L. Villard Microtearing Modes (MTM) are high-n electromagnetic microinstabilities in tokamak plasmas deriving their free energy from the equilibrium electron temperature gradient. The modes exhibit an even (tearing) parity in ${\tilde A}_\parallel$ and odd parity in $\tilde{\varphi}$ about the mode rational surface and rotate in electron diamagnetic direction, whereas the Kinetic Balloning modes exhibit the opposite parity. Gyrokinetic simulations have found these unstable modes in spherical tokamaks, reversed field pinch configurations as well as Standard tokamaks, typically driven by collisional mechanisms. However, recent simulations point to the existence of these modes in the absence of collisions in tokamak plasmas, with a drive coming mainly from the magnetic drift resonance of trapped electrons in spherical tokamaks. In the present work, in context of large aspect ratio tokamaks, global gyrokinetic stability studies show that MTMs are unstable in purely collisionless plasmas, driven by magnetic drift resonance of passing electrons. Trapped electrons are found to change the nature of linear growth rate spectrum. The effect of trapped electrons on the scaling with the plasma $\beta$ and electron temperature gradient $\eta_e$ will be presented. [Preview Abstract] |
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JP8.00070: One and two dimensional electromagnetic gyrokinetic PIC simulation by $\delta f$ method C.M. Chen, Y. Nishimura, C.Z. Cheng An electromagnetic gyrokinetic Particle-in-Cell simulation is studied aiming at long-wave-length magnetohydrodynamic instabilities. A fully nonlinear characteristic method ($\delta f$ method) of electrostatic gyrokinetic theory is employed.\footnote{S. E. Parker and W. W. Lee, Phys. Fluids B {\bf 5}, 77 (1993) } For a one dimensional geometry, ``0.5 dimension'' is taken in ``$y$-direction'' of the configuration space and another ``0.5 dimension'' is taken in the ``$v_z$-direction'' of the velocity space. Recent electromagnetic $\delta f$ simulation shows optimistic results.\footnote{A.Mishchenko and A. Zocco, Phys. Plasmas {\bf 19}, 122104, 2012; A. Bottino, T. Vernay, and B.Scott, Plasma Phys. Controlled Fusion {\bf 53}, 124027 (2011).} We revisit the importance of the conservation properties in the low dimensional geometries. This work is supported by National Science Council of Taiwan, NSC 100-2112-M-006-021-MY3 and NSC 103-2112-M-006-021-MY3. [Preview Abstract] |
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JP8.00071: A multi-dimensional nonlinearly implicit, electromagnetic Vlasov-Darwin particle-in-cell (PIC) algorithm Guangye Chen, Luis Chac\'on For decades, the Vlasov-Darwin model has been recognized to be attractive for PIC simulations (to avoid radiative noise issues) in non-radiative electromagnetic regimes.\footnote{Nielson and Lewis, Methods Comput. Phys.,16 (1976)} However, the Darwin model results in elliptic field equations that renders explicit time integration unconditionally unstable.\textsuperscript{1} Improving on linearly implicit schemes, fully implicit PIC algorithms for both electrostatic and electromagnetic regimes, with exact discrete energy and charge conservation properties, have been recently developed in 1D.\footnote{Chen, Chac\'on, and Barnes, J. Comput. Phys. 230 (2011)}\textsuperscript{,}\footnote{Chen and Chac\'on, Comput. Phys. Commun. (2014)} This study builds on these recent algorithms to develop an implicit, orbit-averaged, time-space-centered finite difference scheme for the particle-field equations in multiple dimensions. The algorithm conserves energy, charge, and canonical-momentum exactly, even with grid packing. A simple fluid preconditioner allows efficient use of large timesteps, $O(\sqrt{\frac{m_i}{m_e}}\frac{c}{v_{eT}})$ larger than the explicit CFL. We demonstrate the accuracy and efficiency properties of the of the algorithm with various numerical experiments in 2D3V. [Preview Abstract] |
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JP8.00072: Performance of VPIC on Sequoia William Nystrom Sequoia is a major DOE computing resource which is characteristic of future resources in that it has many threads per compute node, 64, and the individual processor cores are simpler and less powerful than cores on previous processors like Intel's Sandy Bridge or AMD's Opteron. An effort is in progress to port VPIC\footnote{K. J. Bowers, B. J. Albright, L. Yin, B. Bergen, and T. J. T. Kwan, Phys. Plasmas 15, 055703 (2008)} to the Blue Gene Q architecture of Sequoia and evaluate its performance. Results of this work will be presented on single node performance of VPIC as well as multi-node scaling. [Preview Abstract] |
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JP8.00073: High-gain aneutronic fusion M.J. Hay, N.J. Fisch Fusion reactions which release most of their energy in charged particles are desirable for power applications. The proton-boron reaction $p+^{11}\!B\to3\alpha+8.7\,{\rm MeV}$ is ideal due to the low incidence of neutron-generating side reactions and the natural abundance of the reactants. However, an optically thin proton-boron plasma radiates a substantial amount of energy via bremsstrahlung. To compensate, we consider ways of increasing the fusion reactivity above the Maxwellian value. Using the fusion alpha particle energy to heat specific parts of the proton velocity distribution is one such approach. In principle, waves could channel the alpha energy to protons near the cross section maximum in energy, resulting in a substantial reactivity gain. By making aggressive assumptions regarding how energy might be channeled, we present upper bounds on the extent to which a proton-boron fusion reaction can be self-sustaining. [Preview Abstract] |
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JP8.00074: Spectral method for the solution of the Vlasov equation based on Hermite polynomials Ben Bergen, Gian Luca Delzanno, J. David Moulton, Bhuvana Srinivasan, Enrico Camporeale We present a spectral method for the solution of the Vlasov equation for a collisionless plasma by means of an expansion of the distribution function in Hermite polynomials, which leads to a system of partial differential equations for the coefficients of the expansion. With a spectral (Fourier) technique for the spatial discretization and a fully-implicit time integrator, the numerical scheme can achieve exact mass, momentum and energy conservation. In the one-dimensional electrostatic limit, comparisons with a Particle-In-Cell (PIC) method on standard test cases show that the Hermite method can be much more accurate and faster than PIC [1]. We also discuss our further development of this method, which includes a finite element spatial discretization, the extension of the method to multi-dimensions and to the fully electromagnetic case and the use of preconditioning techniques to speed-up the convergence of the inner iterations of the Newton-Krylov method used to solve the discrete non-linear system. \\[4pt] [1] E. Camporeale, G.L. Delzanno, B. Bergen, J.D. Moulton, ``On the velocity space discretization for the Vlasov-Poisson system: comparison between Hermite spectral and Particle-in-Cell methods. Part 2: fully-implicit scheme,'' under review (2014). [Preview Abstract] |
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JP8.00075: Efficient simulation of pitch angle collisions in a 2+2-D Eulerian Vlasov code Jeff Banks, R. Berger, S. Brunner, T. Tran Here we discuss pitch angle scattering collisions in the context of the Eulerian-based kinetic code LOKI that evolves the Vlasov-Poisson system in 2+2-dimensional phase space (Banks et al., Phys. Plasmas 18, 052102 (2011)). The collision operator is discretized using 4th order accurate conservative finite-differencing. The treatment of the Vlasov operator in phase-space uses an approach based on a minimally diffuse, fourth-order-accurate discretization (Banks and Hittinger, IEEE T. Plasma Sci. 39, 2198--2207). The overall scheme is therefore discretely conservative and controls unphysical oscillations. Some details of the numerical scheme will be presented, and the implementation on modern highly concurrent parallel computers will be discussed. We will present results of collisional effects on linear and non-linear Landau damping of electron plasma waves (EPWs). In addition we will present initial results showing the effect of collisions on the evolution of EPWs in two space dimensions. [Preview Abstract] |
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JP8.00076: Solving the 1D1P relativistic Vlasov-Poisson system of equations: case study of the linear Landau damping and two-stream instability Michael Carrie, Bradley Shadwick We present the initial development of an implicit method to solve the collisionless relativistic Vlasov-Poisson system of equations on a 1D1P Eulerian grid and we benchmark the numerical results against the relativistic Landau damping and two-stream instability linear theory. Since the code is dissipation free, oscillations can be produced in the solution --- when the characteristic gradient length becomes comparable to the grid size --- and the distribution function can take negative values. One would expect negative values to give unphysical results: particles number, total momentum and enstrophy ($\int f^{2}$) are perfectly conserved down to the machine precision, damping and growing rates and frequency are recovered, even when negative values are produced, and the energy conservation is surprisingly good. For electron distribution parameters relevant to the ICF context, the two-stream instability study shows excellent agreement with the linear theory and highlights the detrimental effect of low energy, low temperature counter-propagating electron beams. [Preview Abstract] |
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JP8.00077: High-order continuum kinetic Vlasov-Poisson simulations of magnetized plasmas G.V. Vogman, P. Colella, U. Shumlak Continuum methods offer a high-fidelity means of simulating plasma kinetics as modeled by the Boltzmann-Maxwell equation system. These methods are advantageous because they can be cast in conservation law form, are not susceptible to noise, and can be implemented using high-order numerical methods. Thereby the methods can conserve mass, momentum, and energy to a high degree. A fourth-order accurate finite volume method has been developed to solve the continuum kinetic Vlasov-Poisson equation system in one spatial and two velocity dimensions. The method is validated in cartesian coordinates using the Dory-Guest-Harris instability, which is a special case of a perpendicularly-propagating kinetic electrostatic wave in a warm uniformly magnetized plasma. The instability dispersion relation, and its generalization to arbitrary distribution functions, are demonstrated to be well-suited benchmarks for continuum algorithms in higher-dimensional phase space. The numerical method has also been extended to two spatial dimensions, and has been implemented in cylindrical coordinates to simulate axisymmetric configurations such as a Z-pinch. [Preview Abstract] |
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JP8.00078: Continuum kinetic plasma modeling by the Vlasov-Maxwell system in multiple dimensions Noah Reddell, Uri Shumlak A kinetic plasma model for multiple particle species described by the Vlasov equation and coupled to fully dynamic electromagnetic forces is presented. The model is implemented as evolving continuous PDFs (probability density functions) in particle phase space (position-velocity) as opposed to particle-in-cell (PIC) methods which discretely sample the PDF. The hyperbolic model is evolved using a high-order finite element method (discontinuous Galerkin), with excellent conservation of system mass, momentum, and energy -- an advantage compared to PIC. Simulations of two- to six-dimensional phase space while resolving the plasma frequency and cyclotron frequency are computationally expensive. To maximize performance and scaling to large simulations, a new framework, WARPM, has been developed for many-core (e.g.\ GPU) computing architectures. WARPM supports both multi-fluid and continuum kinetic plasma models as coupled hyperbolic systems with nearest neighbor predictable communication. Simulation results are compared to existing benchmark problems and newly achievable studies of wave-particle interactions are presented. [Preview Abstract] |
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JP8.00079: Capturing marginally collisional effects with the 13N-moment plasma model Sean Miller, Uri Shumlak Fluid-based plasma models have typically been applied to parameter regimes where a local thermal equilibrium is assumed. While this parameter regime is valid for low temperature applications, it begins to fail as plasmas enter the collisionless regime and kinetic effects dominate the physics. This research extends the validity of the collisional fluid regime using an anisotropic 13-moment fluid model derived from the Pearson type-IV probability distribution. The model explicitly evolves the heat flux hyperbolically alongside the density, momentum and an energy tensor to capture dynamics usually restricted to costly Boltzmann models. Each particle species is modeled individually and collectively coupled through electromagnetic and collision operators. Electromagnetic fields are evolved using Maxwell's equations. The model is implemented within the the University of Washington's WARPXM code for use on accelerated clusters using an unstructured central essentially non-oscillatory finite volume method, and is currently being extended to an unstructured discontinuous Galerkin method. [Preview Abstract] |
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JP8.00080: Integration of Full Particle Orbit in Toroidal Plasmas Using Boris Scheme Xishuo Wei, Yong Xiao When studying particle dynamics in high frequency electromagnetic waves, such as low hybrid wave heating, it is important to integrate full particle orbit accurately to very long time in tokamaks. Here we derived a formulation under magnetic coordinate based on the Boris Scheme, which can be used effectively to push particles in long time scale. After several hundred gyro-periods, the banana orbit can be observed and the toroidal precession frequency can be measured. The toroidal precession frequency is found to match that from the guiding center simulation. This new method shows superior numeric properties than the traditional Runge-Kutta method in terms of conserving particle energy and magnetic moment. [Preview Abstract] |
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JP8.00081: Simulations of Laboratory Astrophysics Experiments using the CRASH code Matthew Trantham, Carolyn Kuranz, Mario Manuel, Paul Keiter, R.P. Drake Computer simulations can assist in the design and analysis of laboratory astrophysics experiments. The Center for Radiative Shock Hydrodynamics (CRASH) at the University of Michigan developed a code that has been used to design and analyze high-energy-density experiments on OMEGA, NIF, and other large laser facilities. This Eulerian code uses block-adaptive mesh refinement (AMR) with implicit multigroup radiation transport, electron heat conduction and laser ray tracing. This poster/talk will demonstrate some of the experiments the CRASH code has helped design or analyze including: Kelvin-Helmholtz, Rayleigh-Taylor, imploding bubbles, and interacting jet experiments. This work is funded by the Predictive Sciences Academic Alliances Program in NNSA-ASC via grant DEFC52- 08NA28616, by the NNSA-DS and SC-OFES Joint Program in High-Energy-Density Laboratory Plasmas, grant number~DE-NA0001840, and by the National Laser User Facility Program, grant number~DE-NA0000850. [Preview Abstract] |
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JP8.00082: Relabeling symmetry in relativistic fluids and plasmas Yohei Kawazura, Zensho Yoshida, Yasuhide Fukumoto The conservation of the recently formulated relativistic canonical helicity\footnote{Z. Yoshida, Y. Kawazura, and T. Yokoyama, J. Math. Phys. \textbf{55} 043101 (2014).}$^,$\footnote{Y. Kawazura, Z. Yoshida and Y. Fukumoto, arXiv:1405.3544 [math-p.plasm-ph]} is derived from Noether's theorem with the fluid elements' relabeling symmetry. Upon Eulerianizing the Noether current, the purely spatial volume integral on the Lagrangian coordinates is mapped to a space-time mixed three-dimensional integral on the four-dimensional Eulerian coordinates. The relativistic conservation law in the Eulerian coordinates is no longer represented by any divergence-free current. We have also formulated a relativistic action principle of MHD on the Lagrangian coordinates, and have derived the relativistic MHD cross helicity. [Preview Abstract] |
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JP8.00083: Dissipative Ballooning Modes in Accretion Disks and Toroidal Configurations Eliezer Hameiri Recently there has been an attempt [1] to investigate the stability of dissipative rotating accretion disks imbued with a magnetic field, with respect to localized (i.e., ballooning) modes. Some mistakes were made in the analysis, which we correct in this work. The more technically challenging issue is the choice of the dependent variables to be used. In ideal MHD stability analyses, it is common to use the Lagrange displacement vector {\boldmath $\xi$}, but in dissipative systems this choice does not appear obvious since it is not possible to solve most other perturbed quantities in terms of {\boldmath $\xi$}. We nevertheless show that the perturbation equations are simplified this way, and in particular, if we are interested in small diffusivity, the {\boldmath $\xi$}-equations lend themselves to more easily obtaining the small deviation of the growth rate from ideal plasma. \\[4pt] [1] A. Kirillov and F. Stefani, Phys.\ Rev.\ Lett.\ \textbf{111}, 061103 (2013). [Preview Abstract] |
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JP8.00084: Quasineutrality, self-adjointness and parallel force balance in Kinetic-MHD Jesus J. Ramos An alternative to the traditional formulations of Kinetic-MHD is presented, based on drift-kinetic equations in the reference frame of the complete fluid velocity. In this approach, the electric field is eliminated by exact algebraic transformations and the quasineutrality condition is satisfied without the need of any explicit enforcement. The moving frame drift-kinetic equations provide only the variables needed to close the fluid moment equations and are not redundant with any information contained in the fluid system such as the parallel force balance. Linearization about a Maxwellian equilibrium without flow yields a standard eigenvalue problem for the normal mode squared frequencies. A transparent proof of real squared frequency spectrum follows, when the plasma is spatially bound by either a rigid superconducting wall or a plasma-vacuum interface where the equilibrium density goes continuously to zero. At zero-frequency marginal stability, the Rosenbluth-Rostoker closures for the parallel and perpendicular pressures are obtained, in a solution with vanishing parallel electric field and non-zero fluid displacement that is identically consistent with quasineutrality and parallel force balance. [Preview Abstract] |
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JP8.00085: Derivation of Hamiltonian magnetofluid models with gyroviscous-like contributions using a gyro-map Alexander Wurm, Manasvi Lingam, P.J. Morrison Ideal MHD and various reduced magnetofluid models exhibit a noncanonical Hamiltonian structure when expressed in Eulerian variables [1]. Extending the work of Ref.[2], we investigate the possibility of systematically including contributions due to finite ion gyro-radii in three dimensions while preserving a noncanonical Hamiltonian structure. Starting with the Morrison-Greene 3D ideal MHD noncanonical Poisson bracket[1] and a Hamiltonian including gyroviscous terms, we derive equations of motion using a three-dimensional generalization of the gyro-map introduced in Ref.[2]. The origin of the gyro-map is motivated and explained using an action principle formulation as in Ref.[3]. Through a systematic reduction procedure, we also recover the (noncanonical) bracket and the gyroviscous tensor, which are identical to the ones obtained via the Hamiltonian formalism. \\[4pt] [1] P.J.~Morrison and J.M.~Greene, Phys. Rev. A {\bf 45},790 (1980).\\[0pt] [2] P.J.~Morrison, I.L.~Caldas, and H.~Tasso, Z. Naturforsch. {\bf 39a}, 1023 (1984).\\[0pt] [3] P.J.~Morrison, M.~Lingam, and R.~Acevedo, arXiv:1405.2326 (to appear in Phys. Plasmas) [Preview Abstract] |
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JP8.00086: Two-Dimensional Current Carrying Bernstein-Greene-Kruskal (BGK) Modes for the Vlasov-Poisson-Ampere System C.S. Ng Electrostatic structures have been observed in many regions of space plasmas, including the solar wind, the magnetosphere, the auroral acceleration region. One possible theoretical description of some of these structures is the concept of Bernstein-Greene-Kruskal (BGK) modes, which are exact nonlinear steady-state solutions of the Vlasov-Poisson system of equations in collisionless kinetic theory. We generalize exact solutions of two-dimensional BGK modes in a magnetized plasma with finite magnetic field strength [Ng, Bhattacharjee, and Skiff, Phys. Plasmas 13, 055903 (2006)] to cases with azimuthal magnetic fields so that these structures carry electric current as well as steady electric and magnetic fields. Such nonlinear solutions now satisfy exactly the Vlasov-Poisson-Ampere system of equations. [Preview Abstract] |
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JP8.00087: Anomalous diffusion of field lines and charged particles in Arnold-Beltrami-Childress force-free magnetic fields B. Dasgupta, A.K. Ram, F. Holguin, V. Krishnamurthy The cosmic magnetic fields in regions of low plasma pressure and large currents, such as in interstellar space and gaseous nebulae, are force-free in the sense that the Lorentz force vanishes. The three-dimensional Arnold-Beltrami-Childress (ABC) field is an example of a force-free, helical magnetic field. The ABC magnetic field lines exhibit a complex and varied structure that is a mix of regular and chaotic trajectories in phase space [1]. The characteristic features of field line trajectories are illustrated through the phase space distribution of finite-distance and asymptotic-distance Lyapunov exponents. In regions of chaotic trajectories, the field lines are superdiffusive. The time evolution of an ensemble of charged particles moving in the chaotic ABC fields is divided into three time domains. For short times, the motion of the particles is essentially ballistic. The intermediate times are characterized by a decay of the velocity autocorrelation function. For longer times, the particles undergo anomalous superdiffusion. Detailed theoretical and numerical results will be presented.\\[4pt] [1] A. K. Ram et al., {\it Phys. Plasmas} to be published in August 2014. [Preview Abstract] |
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JP8.00088: Refined Calculations of Secondary Nuclear Reactions in Magneto-Inertial Fusion Plasmas Paul Schmit, Patrick Knapp, Stephanie Hansen, Matthew Gomez, Kelly Hahn, Daniel Sinars, Kyle Peterson, Stephen Slutz, Adam Sefkow, Thomas Awe, Eric Harding, Christopher Jennings Diagnosing the degree of magnetic flux compression at stagnation in magneto-inertial fusion (MIF) is critical for charting the performance of any MIF concept. In pure deuterium plasma, the transport of high-energy tritons produced by the aneutronic DD fusion reaction depends strongly on the magnetic field. The tritons probe and occasionally react with the fuel, emitting secondary DT neutrons. We show that the DT/DD neutron yield ratio and the secondary DT neutron spectra can be used to infer the magnetic field-radius product (BR), the critical confinement parameter for MIF [1,2]. The amount of fuel-pusher mix also can be constrained by secondary reactions. We discuss the sensitivity to plasma inhomogeneities of the calculations and outline methods to relate secondary yields to alpha particle energy deposition in ignition-relevant experiments employing DT fuel. We compare our calculations to recent tests of the Magnetized Liner Inertial Fusion (MagLIF) concept [2] on the Z Pulsed Power Facility. [1] M.M. Basko et al., Nuclear Fusion, Vol. 40, No. 1 (2000). [2] S.A. Slutz et al., Phys. Plasmas 17, 056303 (2010). [Preview Abstract] |
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JP8.00089: Plasma-Jet-Driven Magneto-Inertial Fusion (PJMIF): Physics and Design for a Plasma Liner Formation Experiment Scott Hsu, Jason Cassibry, F. Douglas Witherspoon Spherically imploding plasma liners are a potential standoff compression driver for magneto-inertial fusion, which is a hybrid of and operates in an intermediate density between those of magnetic and inertial fusion. We propose to use an array of merging supersonic plasma jets to form a spherically imploding plasma liner. The jets are to be formed by pulsed coaxial guns with contoured electrodes that are placed sufficiently far from the location of target compression such that no hardware is repetitively destroyed. As such, the repetition rate can be higher (e.g., 1 Hz) and ultimately the power-plant economics can be more attractive than most other MIF approaches. During the R\&D phase, a high experimental shot rate at reasonably low cost (e.g., $<$\$1k/shot) may be achieved with excellent diagnostic access, thus enabling a rapid learning rate. After some background on PJMIF and its prospects for reactor-relevant energy gain, this poster describes the physics objectives and design of a proposed 60-gun plasma-liner-formation experiment, which will provide experimental data on: (i) scaling of peak liner ram pressure versus initial jet parameters, (ii) liner non-uniformity characterization and control, and (iii) control of liner profiles for eventual gain optimization. [Preview Abstract] |
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JP8.00090: Contoured-gap coaxial guns for imploding plasma liner experiments F.D. Witherspoon, A. Case, S. Brockington, J.T. Cassibry, S.C. Hsu Arrays of supersonic, high momentum flux plasma jets can be used as standoff compression drivers for generating spherically imploding plasma liners for driving magneto-inertial fusion, hence the name plasma-jet-driven MIF (PJMIF). HyperV developed linear plasma jets for the Plasma Liner Experiment (PLX) at LANL where two guns were successfully tested. Further development at HyperV resulted in achieving the PLX goal of 8000 $\mu$g at 50 km/s. Prior work on contoured-gap coaxial guns demonstrated an approach to control the blowby instability and achieved substantial performance improvements. For future plasma liner experiments we propose to use contoured-gap coaxial guns with small Minirailgun injectors. We will describe such a gun for a 60-gun plasma liner experiment. Discussion topics will include impurity control, plasma jet symmetry and topology (esp. related to uniformity and compactness), velocity capability, and techniques planned for achieving gun efficiency of $>$50\% using tailored impedance matched pulse forming networks. Mach2 and UAH SPH code simulations will be included. [Preview Abstract] |
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JP8.00091: Ram-pressure scaling and non-uniformity characterization of a spherically imploding liner formed by hypervelocity plasma jets Jason Cassibry, Jesse Dougherty, Seth Thompson, Scott Hsu, F.D. Witherspoon Three-dimensional modeling of plasma liner formation and implosion is performed using the Smoothed Particle Hydrodynamics Code (SPHC) with radiation, thermal transport, and tabular equations of state (EOS), accounting for ionization, in support of a proposed 60-gun plasma liner formation experiment for plasma-jet driven magneto-inertial fusion (PJMIF). Previous SPHC modeling showed that ideal gas law scaling of peak stagnation pressure increased linearly with density and number of jets, quadratically with jet radius and velocity, and inversely with the initial jet length, while results with tabular EOS, thermal transport, and radiation have greater sensitivity to the initial jet distribution. A series of simulations are conducted to study the effects of initial jet conditions on peak ram pressure and liner non-uniformity during plasma liner implosion. The growth rate of large-amplitude density perturbations introduced by the discrete jets are computed and compared with predictions by the Bell-Plesset equation. [Preview Abstract] |
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JP8.00092: High Speed Argon PlasmaJet Merging Studies in Support of PLX Andrew Case, Sarah Messer, Samuel Brockington, Linchun Wu, F. Douglas Witherspoon, Raymond Elton Formation of an imploding plasma liner such as for the Plasma Liner Experiment (PLX) requires individual plasma jets to merge into a uniform shell of plasma converging on the target region. Understanding dynamics of the merging process requires knowledge of the plasma phenomena involved. We present here results from the study of the merging of six plasma jets in three dimensional geometry. The experiments were performed using HyperV Technologies Corp. one centimeter MiniRailguns using a preionized Argon plasma armature on a vacuum chamber designed to partially reproduce the port geometry of the PLX vacuum chamber. Diagnostics include fast imaging, spectroscopy, B-dot probes, and high speed spatially resolved photodiodes, permitting measurements of temperature, velocity, and magnetic field. These experimental results are compared with simulation results from the LSP 3D hybrid PIC code.\footnote{Work supported by the US DOE OFES under grants DE-FG02-05ER54810 and DE-FG02-08ER85114.} [Preview Abstract] |
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JP8.00093: ABSTRACT WITHDRAWN |
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JP8.00094: Theoretical investigation of Laser Beatwave Magnetization of Liner-Compressed High Energy Density Plasmas Carsten Thoma, Dale Welch, Robert Clark The interaction of two lasers with difference frequencies equal that of the ambient plasma frequency produces beat waves. These waves can be used to drive electron current and remotely embed magnetic fields. This method can provide standoff magnetization in an imploding high energy density plasma as envisioned in magnetized target fusion schemes. We discuss the results of particle-in-cell simulations of laser beatwave current drive and magnetization in plasmas with densities on the order of 10$^{18}$ cm$^{-3}$. At such densities, lasers with $\sim$ 1~$\mu$m wavelength can generate magnetic fields on the order of a Tesla, for powers $\sim$ 10$^{15}$ W/cm$^2$, and pulse lengths of several ps. We consider the generation varied magnetic topologies by using multiple laser pairs. The evolution of current channels over timescales longer than the laser pulse duration is also described. We illustrate the effects of liner-driven hydrodynamic compression on the embedded magnetic fields in 1D and 2D simulations using the Lsp code. [Preview Abstract] |
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JP8.00095: MAGNETIC ICF \& HEDP |
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JP8.00096: Plasma Jets Subject to Adjustable Current Polarities and External Magnetic Fields Tom Byvank, Peter Schrafel, Pierre Gourdain, Charles Seyler, Bruce Kusse In the present research, collimated plasma jets form from ablation of a radial foil (Al 20 $\mu $m thin disk) using a pulsed power generator (COBRA) with 1 MA peak current and 100 ns rise time. Plasma dynamics of the jet are diagnosed with and without an applied uniform external field (1-1.5 T) and under a change of current polarities, which correspond to current moving either radially outward or inward from the foil's central axis. Experimental results are compared with numerical simulations (PERSEUS). The influence of the Hall effect on the jet development is observed under opposite current polarities. Additionally, the magnetic field compression within the jet is examined. Further studies will compare the laboratory-generated plasma jets and astrophysical jets with embedded magnetic fields. [Preview Abstract] |
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JP8.00097: Pulsed-power driven reconnection and the inverse skin effect John Greenly, Charles Seyler, Xuan Zhao The COBRA 1 MA generator at Cornell is used to drive magnetic reconnection experiments using wire plasmas. Typically two parallel wires are driven, accumulating magnetic and thermal energy during the current rise. This stored energy is converted into plasma flow kinetic energy by reconnection, driven by the ``inverse skin effect'' when the driving voltage reverses after peak current. The reversed voltage reverses the Poynting flux so that magnetic energy is being removed from the load, reducing the magnetic field at the boundary on a time scale short compared with resistive penetration time. Reversed current in the outer plasma drives reconnection of flux and creates supersonic and superalfvenic outflows. This effect may have relevance to other pulsed-power driven plasmas, such as the phenomenon of ``trailing mass'' in imploding Z-pinches. Recent measurements including first data from Thomson scattering will be presented. [Preview Abstract] |
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JP8.00098: Particle energization in magnetic reconnection in high-energy-density plasmas W. Deng, W. Fox, A. Bhattacharjee Significant particle energization is inferred to occur in many astrophysical environments and magnetic reconnection has been proposed to be the driver in many cases. Recent observation of magnetic reconnection in high-energy-density (HED) plasmas on the Vulcan, Omega and Shenguang laser facilities has opened up a new regime of reconnection study of great interest to laboratory and plasma astrophysics. In these experiments, plasma bubbles, excited by laser shots on solid targets and carrying magnetic fields, expand into one another, squeezing the opposite magnetic fields together to drive reconnection. 2D particle-in-cell (PIC) simulations have been performed to study the particle energization in such experiments. Two energization mechanisms have been identified. The first is a Fermi acceleration process between the expanding plasma bubbles, wherein the electromagnetic fields of the expanding plasma bounce particles, acting as moving walls. Particles can gain significant energy through multiple bounces between the bubbles. The second mechanism is a subsequent direct acceleration by electric field at the reconnection X-line when the bubbles collide into each other and drive reconnection. [Preview Abstract] |
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JP8.00099: Magnetic field generation and evolution in high-energy-density plasmas C. Moissard, W. Deng, W. Fox, A. Bhattacharjee Magnetic reconnection has been proposed to account for many astrophysical phenomena and is inferred to play an important role in fusion. Recent experiments have studied magnetic reconnection in high-energy-density (HED) plasmas at the Vulcan, Omega and Shenguang laser facilities. Plasma bubbles are created by laser irradiation of solid targets. These bubbles self-generate MG-scale magnetic fields, and the collision of pairs of bubbles drives reconnection of this magnetic field. 2D first principles particle-in-cell (PIC) simulations with a collision operator have been used to study the evolution of the magnetic field in these experiments. The ablation of the target is modeled by a Gaussian heating function acting on an initially cold, high density plasma. It is shown that the Biermann battery effect ($\nabla T \times \nabla n$ in generalized Ohm's law) can account quantitatively for the magnetic field produced. However, special attention must be given to the temperature, which can no longer be considered as a scalar in the regime of the experiments. In simulations with a collision operator, the evolution of the magnetic field is compared to Braginskii's transport theory. Results of 3D simulations of magnetic reconnection with the self-consistent Biermann effect will be reported. [Preview Abstract] |
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JP8.00100: Magnetic field measurements for study of fast electron transport in magnetized HED plasma Hiroshi Sawada, Brandon Griffin, Radu Presura, Showera Haque, Yasuhiko Sentoku Interaction of megagauss magnetic fields with high energy density (HED) plasma is of great interest in the field of magnetized plasma. The field changes fundamental properties of the HED plasma such as thermal and magnetic diffusion. A coupled capability utilizing the 1.0 MA Zebra pulsed power generator and the 50 TW Leopard laser at Nevada Terawatt Facility enables to create such a condition for studies of magnetized plasma properties. We have conducted an experiment to measure magnetic fields generated by a 1.0 MA, 100 ns Zebra pulsed current in stainless steel coils. Using a 532 nm continuous laser from a single longitudinal mode laser system, the temporal change in the magnetic field was measured with the Faraday rotation in F2 glass. The probe laser passing through the 1.5 mm in radius and 1.75 mm thick glass placed in the vicinity of the inductive coils was split with a Glan-Taylor prism to measure vertical and horizontal polarization components with photodiodes. We will present the analysis of the experimental result and a design of a coupled experiment for study of fast electron transport in the magnetized plasma. [Preview Abstract] |
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JP8.00101: Z-PINCH, X-PINCH, EXPLODING WIRE PLASMA AND DENSE PLASMA FOCUS |
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JP8.00102: New Planar Wire Array Experiments on the LTD Generator at U Michigan M.E. Weller, A.S. Safronova, V.L. Kantsyrev, I. Shrestha, V.V. Shlyaptseva, M.C. Cooper, M.Y. Lorance, A. Stafford, E.E. Petkov, N.M. Jordan, S.G. Patel, A.M. Steiner, D.A. Yager-Elorriaga, R.M. Gilgenbach Experiments on planar wire array z-pinches have been carried out on the MAIZE Linear Transformer Driver (LTD) generator at the University of Michigan (UM) for the first time. Specifically, Al (Al 5056, 95{\%} Al, 5{\%} Mg) double planar wire arrays (DPWAs) comprising six wires in each plane with interplanar gaps of 3.0 mm and 6.0 mm and interwire gaps of 0.7 mm and 1.0 mm were imploded with x-ray time-integrated spectra indicating electron temperatures of over 450 eV for K-shell Al and Mg, while producing mostly optically thin lines. In addition to x-ray time-integrated spectra, the diagnostics included x-ray time-integrated pinhole cameras, two silicon diodes, and shadowgraphy, which are analyzed and compared. The MAIZE LTD is capable of supplying up 1.0 MA, 100 kV pulses with 100 ns rise time into a matched load. However, for these experiments the LTD was charged to $+$-70 kV resulting in up to 0.5 MA with a current rise time of approximately 150 ns. Future experiments and the importance of studying planar wire arrays on LTD devices are discussed. [Preview Abstract] |
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JP8.00103: Spectroscopic Measurements of Planar Foil Plasmas Driven by a MA LTD Sonal Patel, David Yager-Elorriaga, Adam Steiner, Nick Jordan, Ronald Gilgenbach, Y.Y. Lau Planar foil ablation experiments are being conducted on the Linear Transformer Driver (LTD) at the University of Michigan. The experiment consists of a 400 nm-thick, Al planar foil and a current return post. An optical fiber is placed perpendicular to the magnetic field and linear polarizers are used to isolate the pi and sigma lines. The LTD is charged to $+$/-70 kV with approximately 400-500 kA passing through the foil. Laser shadowgraphy has previously imaged the plasma and measured anisotropy in the Magneto Rayleigh-Taylor (MRT) instability. Localized magnetic field measurements using Zeeman splitting during the current rise is expected to yield some insight into this anisotropy. Initial experiments use Na D lines of Al foils seeded with sodium to measure Zeeman splitting. Several ion lines are also currently being studied, such as Al III and C IV, to probe the higher temperature core plasma. In planned experiments, several lens-coupled optical fibers will be placed across the foil, and local magnetic field measurements will be taken to measure current division within the plasma. [Preview Abstract] |
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JP8.00104: Experimental Investigation of the Effects of an Axial Magnetic Field on the Magneto-Rayleigh-Taylor Instability in Ablating Planar Foils D.A. Yager-Elorriaga, S.G. Patel, A.M. Steiner, N.M. Jordan, M.R. Weiss, R.M. Gilgenbach, Y.Y. Lau Experiments are underway to study the effects an axial magnetic field on the magneto-Rayleigh-Taylor instability (MRT) in ablating planar foils on the 1-MA LTD at the Michigan Accelerator for Inductive Z-pinch Experiments (MAIZE) facility at the University of Michigan. For 600 kA drive current, a 15 T axial magnetic field is produced using helical return current posts. During the current pulse, the magnetic field may diffuse into the foil, creating a sheared magnetic field along with the possibility of shear stabilization of the MRT instability. Theoretical investigation at UM has shown that a sheared azimuthal magnetic field coupled with an axial magnetic field reduces the MRT growth rate in general. In order to study this effect, the amount of magnetic shear is controlled by offsetting the initial position of the foil. A 775 nm Ti:sapphire laser will be used to shadowgraph the foil in order to measure the MRT growth rate. By comparing these results to previous experiments at UM, the effects of magnetic shear and an axial magnetic field will be determined. [Preview Abstract] |
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JP8.00105: Experimental Investigation of the Electrothermal Instability on Planar Foil Ablation Experiments Adam Steiner, Sonal Patel, David Yager-Elorriaga, Nicholas Jordan, Ronald Gilgenbach, Y.Y. Lau The electrothermal instability (ETI) is an important early-time physical effect on pulsed power foil ablation experiments due to its ability to seed the destructive magneto-Rayleigh-Taylor (MRT) instability. ETI occurs whenever electrical resistivity has temperature dependence; when resistivity increases with temperature, as with solid metal liners or foils, ETI forms striation structures perpendicular to current flow. These striations provide an initial perturbation for the MRT instability, which is the dominant late-time instability in planar foil ablations. The MAIZE linear transformer driver was used to drive current pulses of approximately 600 kA into 400 nm-thick aluminum foils in order to study ETI in planar geometry. Shadowgraph images of the aluminum plasmas were taken for multiple shots at various times within approximately 50 ns of current start. Fourier analysis extracted the approximate wavelengths of the instability structures on the plasma-vacuum interface. Surface metrology of pre-shot foils was performed to provide a comparison between surface roughness features and resulting plasma structure. [Preview Abstract] |
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JP8.00106: Temporal and Spatial Measurements of a Z-Pinch Magnetic Field and Comparison with Simulations Eyal Kroupp, Guy Rosenzweig, Amnon Fisher, Yitzhak Maron, John Giuliani, Ward Thornhill, Alexander Velikovich, Arati Dasgupta Magnetic forces drive the implosion of a linear Z-pinch. The finite conductivity of the plasma means that the azimuthal field can diffuse into the accelerated material and the current is distributed. We have performed detailed measurements of the evolution of the azimuthal magnetic field within an oxygen z pinch on a 500 kA generator. Polarization spectroscopy is used to record the individual line profiles of the left and right circularly polarized component of Zeeman-split emission lines from OIII and OVI ions. The magnetic field spatial distribution down to \textless 5 mm radius is presented for four times within 26 ns of stagnation. Numerical simulations using a 2D radiation MHD code are compared with the data. Implications for the current distribution and plasma resistivity will be discussed in light of the simulations and data. [Preview Abstract] |
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JP8.00107: Magnetized jets and shocks in radial foil Z-pinches: experiments and numerical simulations S.V. Lebedev, F. Suzuki-Vidal, L.A. Pickworth, G.F. Swadling, G. Burdiak, J. Skidmore, G.N. Hall, M. Bennett, S.N. Bland, J.P. Chittenden, P. de Grouchy, J. Derrick, J. Hare, T. Parker, F. Sciortino, L. Suttle, A. Ciardi, R. Rodriguez, J.M. Gil, G. Espinosa, E. Hansen, A. Frank, J. Music Different variations of the radial foil Z-pinch configuration have been investigated in the recent years on the MAGPIE generator (1.4 MA, 250 ns), particularly using over-massed aluminum foils with thicknesses of $\sim$ 15$\mu$m. This setup is characterized by a highly collimated, supersonic jet on the axis of the foil surrounded by low-density ablated plasma, both moving with the same axial velocity of $\sim$ 60 km/s. Latest results show that the formation and collimation of the jet is directly related to toroidal magnetic field advected with the flow. We present new experimental results that include Thomson scattering measurements of plasma flow velocity and temperature, and a first study on the effect of foil material on jet formation. The effect of advected toroidal magnetic field in the plasma flow is clearly evidenced using a new experimental configuration that produces counter-streaming jets. The results are characterized by the formation of shocks in which the effect of magnetic field and radiative cooling are significant. The setup also allows controlling the polarity of the advected fields at the interaction point between the counter-streaming flows, and results from experiments and numerical simulations will be presented and discussed. [Preview Abstract] |
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JP8.00108: Magnetic flux compression experiments on the Z pulsed-power accelerator R.D. McBride, M.R. Gomez, S.B. Hansen, C.A. Jennings, D.E. Bliss, P.F. Knapp, P.F. Schmit, T.J. Awe, M.R. Martin, D.B. Sinars, J.B. Greenly, T.P. Intrator, T.E. Weber We report on the progress made to date for diagnosing magnetic flux compression on Z. Each experiment consisted of an initially solid Be or Al liner (cylindrical tube), which was imploded using Z's drive current (0--20 MA in 100 ns). The imploding liner compresses a 10-T axial seed field, $B_{z}$\textit{(0)}, supplied by an independently driven Helmholtz coil pair. Assuming perfect flux conservation, the axial field amplification should be well described by $B_{z}(t)=B_{z}$\textit{(0) $\times$ [R(0)/R(t)]}$^{2}$, where $R$ is the liner's inner surface radius. With perfect flux conservation, $B_{z}$ and \textit{dB}$_{z}$\textit{/dt} values exceeding 10$^{4}$ T and 10$^{12}$ T/s, respectively, are expected. These large values, the diminishing liner volume, and the harsh environment on Z, make it particularly challenging to measure these fields. We report our latest efforts to do so using three primary techniques: (1) micro B-dot probes, (2) streaked visible Zeeman spectroscopy, and (3) fiber-based Faraday rotation. We will also briefly highlight some recent developments using neutron diagnostics (ratio of secondary DT to primary DD neutrons and secondary DT neutron energy spectra) to assess the degree of magnetization in fully integrated magnetized liner inertial fusion (MagLIF) experiments on Z. This project was funded in part by Sandia's LDRD program and US DOE-NNSA contract DE-AC04-94AL85000. [Preview Abstract] |
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JP8.00109: Studies of Cylindrical Liner Z-Pinches at 1 MA on COBRA Levon Atoyan, Tom Byvank, Adam Cahill, William Potter, Philip De Grouchy, Bruce Kusse, David Hammer Tests of the magnetized liner inertial fusion (MagLIF) concept will make use of the 27 MA Z-machine to implode a cylindrical metal liner onto a preheated plasma contained within it [1]. While most pulsed power machines produce much lower currents than the Z-machine, there are questions that can be addressed on smaller scale facilities. Recent work on the 1 MA Cornell Beam Research Accelerator (COBRA) has made use of 10 mm long cylindrical metal liners having a 4 mm diameter and a varying wall thickness to study the initiation of plasma on the liner's outer surface as well as axial magnetic field compression [2]. We will present experimental results with both imploding and non-imploding liners, investigating the impact the liner's external surface structure has on initiation, outer surface ablation, and implosion. The effect of a uniform axial external magnetic field on observed surface striations [3] will also be discussed.\\[4pt] [1] S. A. Slutz, et al., Phys. Plasmas \textbf{17}, 056303 (2010).\\[0pt] [2] P.-A. Gourdain, et al., Nucl. Fusion \textbf{53}, 083006 (2013). \\[0pt] [3] T. J. Awe, et al., Phys. Rev. Lett. \textbf{111}, 235005 (2013). [Preview Abstract] |
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JP8.00110: Study of the 3D Structure of the Stagnated Z-Pinch Austin Anderson, Vladimir Ivanov Z pinches are the most powerful laboratory sources of x-ray radiation. Z pinches represent an unstable plasma configuration and are subjected by strong plasma instabilities at the ablation, implosion, and stagnation stages. MHD instability produce necks, kinks, and micropinches at stagnation. Knowledge of the 3D plasma distribution is important for interpreting 2D images of the pinch, as well as understanding the effectiveness of models that assume azimuthal symmetry using Abel inversion. Recent experiments were conducted with 266nm laser shadowgrams from 4 channels, evenly spaced in 45 degree increments. Channels were timed with 100 ps temporal accuracy to provide simultaneous imaging. Results and discussion on the azimuthal non-uniformity of the Z pinch are presented. [Preview Abstract] |
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JP8.00111: The First Pulsed-Power Z-Pinch Liner-On-Target Hydrodynamics Experiment Diagnosed with Proton Radiography C.L. Rousculp, W.A. Reass, D.M. Oro, J.R. Griego, P.J. Turchi, R.E. Reinovsky, A. Saunders, F.G. Mariam, C. Morris The first pulse-power driven, dynamic, liner-on-target experiment was successfully conducted at the Los Alamos proton radiography (pRad) facility. 100{\%} data return was achieved on this experiment including a 21-image pRad movie. The experiment was driven with the PHELIX pulsed-power machine that utilizes a high-efficiency (k $\sim $ 0.93) transformer to couple a small capacitor bank (U $\sim $ 300 kJ) to a low inductance condensed-matter experimental load in a Z-pinch configuration. The current pulse (I$_{peak} = $ 3.7 MA, $\delta $t $\sim $10 $\mu $s) was measured via a fiber optic Faraday rotation diagnostic. The experimental load consisted of a cylindrical Al liner (6 cm diam, 3 cm tall, 0.8 mm thick) and a cylindrical Al target (3 cm diam, 3 cm tall, 0.1 mm thick) that was coated with a thin (0.1 mm) uniform layer of tungsten powder (1 micron diam). It is observed that the shock-launched powder layer fully detaches from the target into a spatially correlated, radially converging (v$_{r} \sim $ 800 m/s) ring. The powder distribution is highly modulated in azimuth indicating particle interactions are significant. Results are compared to MHD simulations. [Preview Abstract] |
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JP8.00112: Diagnostics of deuterium gas-puff z-pinch experiments on the GIT-12 generator J. Cikhardt, D. Klir, K. Rezac, P. Kubes, J. Kravarik, B. Batobolotova, O. Sila, K. Turek, A. Shishlov, A. Labetsky, V. Kokshenev, R. Chedizov, N. Ratakhin, V. Varlachev, A. Garapatsky, G. Dudkin, V. Padalko Z-pinch experiments with a deuterium gas-puff and an outer plasma shell generated by plasma guns were carried out on the GIT-12 generator at the IHCE in Tomsk. Using this novel configuration of the load, the neutron yields from the DD reaction were significantly increased from 2x10$^{\mathrm{11}}$ up to 3x10$^{\mathrm{12}}$ neutrons per shot at the current level of about 3 MA. In addition to recent experiments, the threshold activation detectors were used in order to get the information about the energy spectrum of the generated neutrons. The copper, indium, and lead samples were irradiated by the pulse of the neutrons generated during the experimental shot. The decay radiation of the products from the reactions $^{\mathrm{63}}$Cu(n,2n)$^{\mathrm{62}}$Cu, $^{\mathrm{115}}$In(n, $\gamma )^{\mathrm{116m}}$In and $^{\mathrm{206}}$Pb (n,3n)$^{\mathrm{204m}}$Pb was observed using gamma spectrometer. According to the used neutron ToF scintillation detectors, the energy of neutrons reaches up to 20~MeV. [Preview Abstract] |
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JP8.00113: Small-amplitude magnetic Rayleigh-Taylor instability growth in cylindrical liners and Z-pinches imploded in an axial magnetic field A.L. Velikovich, J.L. Giuliani, R.W. Clark, D. Mikitchuk, E. Kroupp, Y. Maron, A. Fisher, P.F. Schmit Recent progress in developing the MagLIF approach to pulsed-power driven inertial confinement fusion has stimulated the interest in observation and mitigation of the magnetic Rayleigh-Taylor instability (MRTI) of liners and Z-pinches imploded in an axial magnetic field. Theoretical analysis of these issues is particularly important because direct numerical simulation of the MRTI development is challenging due to intrinsically 3D helical structure of the fastest-growing modes. We review the analytical small-amplitude theory of the MRTI perturbation development and the weakly nonlinear theory of MRTI mode interaction, emphasizing basic physics, opportunity for 3D code verification against exact analytical solutions, and stabilization criteria. The theory is compared to the experimental results obtained at Weizmann Institute with gas-puff Z pinches and on the Z facility at Sandia with solid liners imploded in an axial magnetic field. Work supported by the US DOE/NNSA, and by the US-Israel Binational Science Foundation. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. [Preview Abstract] |
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JP8.00114: Focused X-ray Thomson Scattering Experiments using the Hybrid X-pinch Radiation Source Cad Hoyt, Sergei Pikuz, Tania Shelkovenko, Bruce Kusse, Dave Hammer X-ray Thomson scattering (XRTS) experiments require intense sources of radiation to probe the high densities present in warm dense matter experiments. Past experiments have utilized free-electron lasers or kilojoules of laser energy coupled to foils to produce these sources. The brightness of X-pinch X-ray sources is shown to be comparable to the X-ray sources used in these previous experiments and suitable for application as an XRTS source with the Ti hybrid x-pinch providing $10^{15}-10^{16}$ photons into 4$\pi$ steradian. We present results of the first XRTS experiments utilizing the hybrid x-pinch as a probe source incorporated in a novel focusing scheme. We use a primary Bragg optic (Ge400) to collect and focus radiation onto a target and a secondary high-efficiency HAPG/HOPG optic to collect the scattered radiation. Results of scattering from heated targets driven by an independent pulser circuit are compared with cold scattering in the non-collective scattering regime. [Preview Abstract] |
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JP8.00115: Heat Transport in the Precursor of Carbon and Metallic Wire Arrays Jack Hare, Sergey Lebedev, Matthew Bennett, Simon Bland, Guy Burdiak, Lee Suttle, Francisco Suzuki-Vidal, George Swadling, Alexander Velikovich The complex interplay between the transport of heat and magnetic fields in high-\(\beta\), magnetised plasmas is crucial to the feasibility of Magnetised Liner Inertial Fusion (MagLIF). We consider using the precursor plasma in a cylindrical wire array to reach the relevant dimensionless parameters for the initial state of the MagLIF plasma. The precursor is a hot, dense, stable plasma formed on the axis by the collision of material ablated from the wires. Simple models show that an axial magnetic field of $\approx$ 5 T could magnetise the precursor ($\omega_{e}\tau_{e}\approx10$) at high-beta ($\beta\approx10$). In this regime, the Nernst term may dominate the transport of the magnetic field, affecting the heat transport. The experiments are conducted on MAGPIE (1.4 MA, 250 ns rise time). Metallic wire arrays are standard, but to reduce radiative losses and the electron-ion thermalisation time, we will also consider carbon in the form of 0.3 mm diameter graphite rods. The axial magnetic field can either be provided by external coils or by the drive current. We study the evolution of the plasma density and temperature using laser interferometry and Schlieren imaging, an optical streak camera and Thomson scattering. The magnetic field can be studied using fibre-based polarimetry. [Preview Abstract] |
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JP8.00116: A study of runaway electrons on a university scale generator* Nicholas Ouart, John Giuliani, Arati Dasgupta, George Petrov, David Ampleford, Stephanie Hansen, Alla Safronova, Victor Kantsyrev, Ishor Shrestha Wire array implosions have produced characteristic K-shell emission. These K-alpha and K-beta photons are a result of high energy electrons removing an n$=$1 bound electron from lower ionization stages (e.g. Ne-like). The motivation for studying this emission is the possibility of producing an alternative plasma radiation source with photon energies above 10 keV. However, the mechanism producing these fast runaway electrons still remains elusive. We show results from following electrons in uniform cylindrical plasma with an axial electric field and an azimuthal magnetic field. Elastic and inelastic collisions are included via Monte Carlo techniques. Comparison with experimental Zebra data previously reported [1] will be discussed. *Work supported by DOE/NNSA. This work is partially funded by Sandia LDRD project 165733. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. \\[4pt] [1] N.D. Ouart, J.L. Giuliani, A. Dagupta et al. Phys. Plasmas 21, 031207 (2014) [Preview Abstract] |
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JP8.00117: Investigation of the role of ion stopping power in Z-pinch stagnation physics Thomas Mehlhorn, John Giuliani, Ward Thornhill, Yitzhak Maron A recently published paper examining the pressure and energy balance of stagnating plasmas in K-shell radiating z-pinch experiments shows that the stagnating plasma pressure is balanced by the implosion pressure and the radiation energy is provided by the imploding-plasma kinetic energy. This result is shown to be valid for both neon gas-puff loads on the 500 kA, 500 ns Weizmann pulsed power generator and for nested aluminum-titanium wire array experiments on Sandia's Z- machine at 20 MA, 100 ns. Multi-frame pinhole photography and spectroscopic analysis of the neon gas puff has shown that the radius of the stagnation plasma increases from 0.2 mm to 0.45 mm over a 3.5 ns time period and that the density is nearly constant during the K-shell emission period. A very similar phenomenology of constant density and growing radius is observed on Sandia's Z machine for imploding wire array experiments with radius growing from 0.6 to 2.1 mm over a 6 ns period. In this poster we will study what role the kinetic energy loss of the imploding ions in the stagnation plasma may play in determining the initial scale, density, and evolution of the stagnation plasmas in these two K-shell emission systems. [Preview Abstract] |
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JP8.00118: Effect of Doubly-excited States on Simulation of K- and L-shell Kr Gas Puff on ZR Arati Dasgupta, Ward Thornhill, John Giuliani, Nick Ouart, Robert Clark, Brent Jones, Dave Ampleford, Adam Harvey-Thompson, Stephanie Hansen, Christine Coverdale A number of recent shots employing multi-shell gas puffs of Ar and Kr on the Sandia National Laboratories ZR accelerator have demonstrated unprecedented K-shell yields. The KAP TIXTL spectra of Ar gas puff shots with a Kr dopant in the middle shell show Kr L-shell lines near 2 keV. There have been also pure Kr shots on ZR. Krypton spectra from Z pinch implosions provide a wealth of information about the pinch dynamics and ionization history of the plasma. These spectra can be used together with experimental spectroscopic data to analyze the presence and dynamics of the emitting regions, which could dominate the Kr K- and L-shell yields. We will present synthetic K- and L-shell spectra with a detailed radiation transport scheme from the emission regions determined from Kr 1D simulations, employing a non-LTE collisional-radiative ionization kinetics model. We will also investigate the effects of state-specific dielectronic recombination on the populations and spectra of Z pinch Kr plasma. *Work supported by DOE/NNSA. Sandia National laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation for the US Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. [Preview Abstract] |
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JP8.00119: ZaP-HD: High Energy Density Z-Pinch Plasmas using Sheared Flow Stabilization U. Shumlak, B.A. Nelson, R.P. Golingo, C.A. Bowers, S.A. Doty, E.G. Forbes, D. Goldstone, M.C. Hughes, B. Kim, S.D. Knecht, K.K. Lambert, W. Lowrie, M.P. Ross, J.R. Weed The ZaP-HD flow Z-pinch project investigates scaling the sheared flow Z-pinch to HEDP conditions by using sheared flow stabilization. Z-pinch plasmas have been produced that are 100 cm long with a 1 cm radius and are quiescent for many radial Alfven times and axial flow times. Quiescent periods are characterized by low magnetic mode activity measured at several locations along the plasma column and by stationary visible plasma emission. Plasma evolution is modeled with high-resolution simulation codes: Mach2, WARPX, and NIMROD. A sheared flow profile is observed to be coincident with the quiescent period and is consistent with classical plasma viscosity. Equilibrium is determined by diagnostic measurements of density, flow, electron \& ion temperature, and magnetic field. Wall stabilization is investigated computationally and experimentally by removing 70\% of the surrounding conducting wall. The flow Z-pinch concept provides an approach to achieve HED plasmas, which are large and persist for extended durations. The new experiment, ZaP-HD, has been built to investigate this approach. Experimental results and scaling analyses are presented. [Preview Abstract] |
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JP8.00120: Modifications to the ZaP Experiment: Quasi-Steady Accelerator and ZaP-HD Operation M.C. Hughes, U. Shumlak, B.A. Nelson, R.P. Golingo, M.P. Ross, K.K. Lambert, J.R. Weed, C.A. Bowers, S.A. Doty, E.G. Forbes, S. Funke, D. Goldstone, B. Kim, S.M. Swofford The ZaP Flow Z-Pinch Experiment studies the stabilization of an unstable plasma by utilizing flow shear. The most recent operations of the original ZaP machine investigated a mechanism to increase the gas supply to the plasma source to prevent depletion during pulses. As the power through the machine increased, the density from the accelerator would drop off, leading to a lack of flow into the pinch and a loss of stability. The alteration created a quasi-steady operational mode that persists for the duration of the current pulse to the machine. Results are presented on this mode. In order to investigate scaling the ZaP concept to HEDP conditions, the ZaP-HD machine has been constructed. The new design has the flexibility to power the plasma source and Z-pinch separately. The design also takes lessons learned from the quasi-steady operational configuration. Initial operations of the machine focus on creating similar conditions to the ZaP machine. Recent results from the new ZaP-HD machine are presented. [Preview Abstract] |
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JP8.00121: Spectroscopy Measurements on the ZaP-HD Experiment Raymond Golingo, U. Shumlak, B.A. Nelson, S.A. Doty, D. Goldstone, M.C. Hughes, S.D. Knecht, M.P. Ross The ZaP-HD experiment is studying the scaling relationships necessary to bring a sheared-flow stabilized Z-pinch into the HEDP regime. In the ZaP experiment, a single spectrometer was used to measure velocities of up to $10^5$ m/s, ion temperatures of up to 100~eV, magnetic fields of 1 T, and densities of $10^{21}$ m$^{-3}$ using the Doppler shift and broadening, Zeeman splitting, and Stark broadening of the impurity line radiation. Local quantities are found with a deconvolution method. The success of the measurements was partially due to an accurate calibration of the spectrometer using an image warping technique and a collection system that uses telecentric telescopes. The adiabatic scaling relations predict that an increase of the pinch current from 50 kA to 750 kA will lead to velocities of $10^5$ m/s, temperatures of 4.5 keV, pinch radius of 0.17 mm, and densities of $2\times 10^{26}$ m$^{-3}$ in the Z-pinch. A review of the results from the ZaP experiment will be given. The improvements to the system necessary to make measurements of the smaller, hotter plasma will be shown. Initial velocity and temperature measurements will also be presented. [Preview Abstract] |
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JP8.00122: Investigating the density structure of the ZaP-HD Flow Z-Pinch with digital holographic interferometry Michael Ross, Uri Shumlak, Brian Nelson, Raymond Golingo, Michal Hughes, Eleanor Forbes, Matt Paliwoda The ZaP-HD Flow Z-Pinch experiment investigates how flow shear stabilized Z-pinches scale to higher densities and temperatures. Determining how such plasmas scale up may reveal their utility as test beds for HEDP physics. Scaling towards HEDP conditions requires compressing the plasma to a smaller size with increased plasma current. Measuring the internal structure of a smaller, hotter plasma requires high-resolution diagnostics. To measure electron density profiles, the ZaP-HD team uses holographic interferometry with 30 micron resolution. A new Nd:YAG laser is employed in concert with a consumer digital camera to record holograms, which are numerically reconstructed to obtain the phase shift caused by the interaction of the laser with the plasma. The numerical reconstruction provides a two-dimensional map of chord-integrated electron density, which can be inverted to radial profiles under the assumption of axisymmetry. Measurements of Z-pinch density structure are presented. [Preview Abstract] |
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JP8.00123: Wire array K-shell sources on the SPHINX generator Thierry d'Almeida, Francis Lassalle, Julien Grunenwald, Patrick Maury, Fr\'ed\'eric Zucchini, Nicolas Niasse, Jeremy Chittenden The SPHINX machine is a LTD based Z-pinch driver operated by the CEA Gramat (France) and primarily used for studying K-shell radiation effects. We present the results of experiments carried out with single and nested large diameter aluminium wire array loads driven by a current of $\sim$ 5 MA in $\sim$ 800 ns. The dynamic of the implosion is studied with filtered X-UV time-integrated pin-hole cameras. The plasma electron temperature and the characteristics of the sources are estimated with time and spatially dependent spectrographs and PCDs. It is shown that Al K-shell yields (\textgreater 1 keV) up to 27 kJ are obtained for a total radiation of $\sim$ 230 kJ. These results are compared with simulations performed using the latest implementation of the non-LTE DCA code Spk in the 3D Eulerian MHD framework Gorgon developed at Imperial College. Filtered synthetic bolometers and PCD signals, time-dependent spatially integrated spectra and X-UV images are produced and show a good agreement with the experimental data. The capabilities of a prospective SPHINX II machine (20 MA $\sim$ 800ns) are also assessed for a wider variety of sources (Ti, Cu and W). [Preview Abstract] |
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JP8.00124: Lasnex Predictions for Z Opacity Experiments Using Tampers of Increased Mass (LA-UR-14-24932) Heidi Morris, Manolo Sherrill, Chris Fontes, Jim Bailey, Greg Rochau, Taisuke Nagayama 2-D Lasnex radiation hydrodynamics simulations have been performed for opacity experiments carried out at Sandia National Laboratories' Z facility. The Z facility has a demonstrated capability for obtaining opacity measurements for iron in the 800-1800 eV x-ray range by showing agreement with PRISMSPECT, MUTA, and OPAL opacity models within experimental error bars. These experiments have been successfully repeated on the upgraded Z machine, ZR. More recently, efforts have focused on achieving opacity measurements for various materials with increased electron density and temperature. Increased mass CH and Be tampers have recently been used to attempt to increase the sample electron density and temperature to 8 $\times$ 10$^{22}$ e-/cm$^{3}$ and 193eV. The time-dependent sample conditions and hydrodynamics will be discussed for CH and Be tampers. Instantaneous and time integrated simulated transmission spectra for both tampers will be presented. Measurement of the spatially and temporally resolved x-ray spectrum is in progress for the new ZR, and could help constrain the simulations. [Preview Abstract] |
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JP8.00125: Z-pinch X-ray spectra obtained with a polarization splitting crystal R. Presura, M.S. Wallace, N.R. Pereira Anisotropy in a plasma may cause polarization of the spectral lines emitted. For example, the X-rays emitted by Z-pinch plasmas may be polarized if electron beams are present. To detect the polarization, we developed an X-ray spectropolarimeter using a single polarization-splitting crystal. Reflections on intersecting internal planes of the crystal select lines with mutually orthogonal linear polarization. The (10-10) internal planes of a quartz crystal can be used to split several lines of the Al K-shell spectrum according to polarization. We applied this technique to several types of Al wire arrays (cylindrical, conical, and X-pinches), expected to produce increasing beam contributions to the electron population. Peculiarities of the instrument set-up and of the spectra analysis will be presented. [Preview Abstract] |
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JP8.00126: Spatially-Resolved Argon and Neon K-Shell X-Ray Spectra from Triple-Nozzle Gas-Puff Z-Pinches on Cobra Niansheng Qi, Philip de Grouchy, Cad Hoyt, Tania Shelkovenko, Sergei Pikuz, Levon Atoyan, William Potter, Adam Cahill, John Greenly, Bruce Kusse, David Hammer We present the x-ray spectra obtained during Ar/Ne gas puff z-pinch experiments on the 1MA, 200ns COBRA pulsed power generator at Cornell University. A triple-nozzle gas-puff, which produces two annular (``outer'' and ``inner'') gas puffs and a high density center jet, is used to tailor the radial mass density distribution. Argon and/or neon plasmas are imploded. Filtered x-ray photo-conducting detectors are used for timing the neon and argon K-shell emission and a filtered x-ray pinhole camera images the K-shell x-ray source size. A spectrometer with three spherical mica crystals is used to capture the K-shell x-ray emission. Our objective is to diagnose the Ar and Ne pinch plasma densities (10$^{19}$-10$^{20}$ cm$^{-3}$) and temperatures (0.5 - 2 keV) with 0.1 mm axial and/or radial spatial resolution from the K-shell X-ray spectra. The He-like resonance to intercombination line ratio will be used to estimate the electron density and the He-like resonance to Li-like satellite line ratio will be used to estimate the electron temperature. We will also add Cl as a dopant in either the center Ar gas jet or inner annular puff for K-shell x-ray spectrum studies. [Preview Abstract] |
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JP8.00127: ABSTRACT WITHDRAWN |
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JP8.00128: Pulsed power produced counter-propagating plasma flows and the study of shock wave formation for laboratory astrophysical phenomena Julio Valenzuela, Gilbert Collins, Tom Zick, Jeff Narkis, Igor Krasheninnikov, Farhat Beg We report on counter-propagating plasma flows produced by two vertically opposing conical wire arrays using a compact current driver capable of producing 250 kA in about 150 ns. Laser interferometry and extreme ultraviolet imaging were performed to study the collision of the jets. A shock formed by jets interaction was clearly observed and remained stationary for at least 50 ns, after this period a bow shock developed propagating downwards at $\sim$ 20km/s. Interferometry data showed that the ion density of the jets prior to collision was of the order of 2 $\times$ 10$^{17}$cm$^{-3}$ and a jump in density of $\sim$ 4 was observed at the shock region. A lower limit of $\sim$ 100 km/s has been measured for the jets velocity. The inter ions mean free path has been estimated to be $\sim$ 12 mm, which is larger than the shock wave scale $\sim$ 5 mm, and hence the shock is not mediated by collisions. Magnetic field advection, which can drastically modify the conditions for shock formation, will be discussed. Kinetic particle-in-cell modeling using LSP code has also been implemented and benchmarked against the experimental results. [Preview Abstract] |
(Author Not Attending)
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JP8.00129: Dense Plasma Focus With High Energy Helium Beams for Radiological Source Replacement Andrea Schmidt, Jennifer Ellsworth, Steve Falabella, Anthony Link, Brian Rusnak, Jason Sears, Vincent Tang A dense plasma focus (DPF) is a compact accelerator that can produce intense high energy ion beams (multiple MeV). It could be used in place of americium-beryllium (AmBe) neutron sources in applications such as oil well logging if optimized to produce high energy helium beams. AmBe sources produce neutrons when 5.5 MeV alphas emitted from the Am interact with the Be. However, due to the very small alpha-Be cross section for alphas \textless 2 MeV, an AmBe source replacement would have to accelerate $\sim$0.15 $\mu $C of He to 2$+$ MeV in order to produce 10$^7$ neutrons per pulse. We are using our particle in cell (PIC) model in LSP of a 4 kJ dense plasma focus discharge to guide the optimization of a compact DPF for the production of high-energy helium beam. This model is fluid for the run-down phase, and then transitions to fully kinetic prior to the pinch in order to include kinetic effects such as ion beam formation and anomalous resistivity. An external pulsed-power driver circuit is used at the anode-cathode boundary. Simulations will be benchmarked to He beam measurements using filtered and time-of-flight Faraday cup diagnostics. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. This work supported by US DOE/NA-22 Office of Non-proliferation Research and Development. Computing support for this work came from the LLNL Institutional Computing Grand Challenge program. [Preview Abstract] |
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