Bulletin of the American Physical Society
60th Annual Meeting of the APS Division of Plasma Physics
Volume 63, Number 11
Monday–Friday, November 5–9, 2018; Portland, Oregon
Session NO6: Z-pinch, X-pinch, Exploding Wire Plasma, Dense Plasma Focus, and Magnetized Target Fusion |
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Chair: Farhat Beg, University of California, San Diego Room: OCC B115-116 |
Wednesday, November 7, 2018 9:30AM - 9:42AM |
NO6.00001: Charged particle acceleration experiments in a dense plasma focus driven by a high-inductance generator* S. L. Jackson, J. T. Engelbrecht, A. S. Richardson, E. E. Petkov, B. V. Weber, J. L. Giuliani, J. W. Schumer, A. A. Mamonau, A. Beresnyak, D. Klir, K. Rezac, J. Cikhardt, Y. Maron, E. Stambulchik Charged particle acceleration is being investigated in a dense plasma focus (DPF) driven by the Hawk pulsed-power generator at the Naval Research Laboratory. The high inductance (607 nH) and associated high voltage (640 kV) and fast rise time (1.2 µs) of Hawk are unusual for a DPF driver, as is the initialization of the DPF using local injection of neutral gas and plasma into a vacuum chamber, rather than a conventional neutral gas fill. Neutron yields of up to 3.6×1010 at a peak current of I=670 kA have been measured using rhodium foil activation counters, significantly above the yield expected based on purely I4.4 scaling from conventional DPFs. Evidence of deuteron and x-ray acceleration has been recorded, respectively, in ion multi-pinhole images obtained with filters of varying thickness and in the form of x-ray pinhole images of emission from the pinch and surrounding hardware. The initial conditions established by the injected gas and plasma have also been varied to accentuate the observed neutron or x-ray emission. |
Wednesday, November 7, 2018 9:42AM - 9:54AM |
NO6.00002: Current disruption and electric field in dense plasma focus Andrey Beresnyak, John L Giuliani, Stuart L Jackson, Steve Richardson, Alexander L. Velikovich Plasma Physics Division at NRL is running a Dense Plasma Focus (DPF) experiment on the HAWK pulsed power generator (640 kV, 665 kA peak current). This experiment and many similar devices in the past produced neutron yields orders of magnitude above the thermal neutron yield suggesting that some mechanisms accelerate ions to energies well above thermal energy. We modeled the experiment using MHD code Athena coupled to an equivalent circuit model for HAWK and confirmed that the thermal yield is indeed much smaller than the observed yields. In addition we modeled particles accelerated in the motional vxB fields with the code Hephaestus and confirmed that this acceleration can only give particles with energies up to 0.2 MeV. To study potential non-MHD mechanisms of acceleration we introduced physically motivated, but artificial current disruption and calculated resulting electric and magnetic fields. We will report on the morphology and the energy spectrum of the neutron source described by such model. |
Wednesday, November 7, 2018 9:54AM - 10:06AM |
NO6.00003: Radiation physics and particle beam research on a medium-class dense plasma focus generator with complex diagnostics Victor L Kantsyrev, Alla Safronova, Christopher Butcher, Jeff Rowland, Ishor Shrestha, Veronica Shlyaptseva, Austin Stafford, Amandeep Gill, Mahadevan Krishnan A newly developed dense plasma focus (DPF) Sparky III device is a medium class generator at UNR. Typical operation parameters are: current up to 450 kA in 1 - 1.5 microsecond rise time, voltage charge up to 25 kV, stored energy in capacity banks up to 10 kJ, and repetition rate up to 0.2 Hz. The operation gases are Ne, Ar, Kr, Xe, and their mixtures, with a pressure of 1 - 10 Torr. The diagnostics consist of high resolution optical interferometer, time resolved x-ray and particles detectors, soft x-ray and hard x-ray spectrometers and spectropolarimeters, and x-ray pinhole cameras. Present and future objectives of this research are: study radiation yield with mixed gases to reach maximum radiation yield in soft and hard x-rays (> 100 keV); perform extensive electron and ion beams studies on a DPF device; carry out the unique studies on statistics in Z-pinches by using DPF at high repetitive rate to understand the reproducibility of Z-pinches, radiation yields, and plasma parameters in a thousand shots. Comparison of new DPF results with data obtained in previous experiments with mixed gases jets irradiated by ultrashort laser pulses are discussed. |
Wednesday, November 7, 2018 10:06AM - 10:18AM |
NO6.00004: Electron Plasma Wave Thomson Scattering on Laboratory Plasma Jets Jacob Banasek, Sophia Rocco, William Potter, Tom Byvank, Bruce Kusse, David A Hammer Thomson scattering in the collective regime can be used for plasma electron density measurements by using the electron plasma wave feature. Such measurements have been performed on plasma jets created from a 15 μm thick radial Al foil load on COBRA, a 1 MA pulsed power machine. The scattering from the electron plasma wave was used to measure the electron density and temperature inside and outside of a plasma jet created by the radial foil. The laser used for these measurements had a maximum energy of 10 J at 526.5 nm. Previous experiments observing the stronger ion acoustic wave feature have shown that the full laser energy significantly heats the estimated 5×1018 cm-3 jet by inverse bremsstrahlung from 20 eV to 90 eV. By using scattering from the electron plasma wave in tandem with scattering from the ion acoustic wave a more accurate picture of the plasma jet and its heating can be achieved. Results will be presented comparing time resolved ion acoustic wave features with time gated electron plasma wave features. |
Wednesday, November 7, 2018 10:18AM - 10:30AM |
NO6.00005: Examining energy partitioning in gas-puff z-pinches using Thomson scattering Sophia Rocco, Jacob T Banasek, William Potter, Bruce Kusse, David A Hammer The conditions of gas puff z-pinch plasmas near pinch time are studied on the COBRA pulsed power generator (current rise time of 240 ns and 0.9 MA peak current). A 526.5 nm, 10 J, 2.3 ns (FWHM) Thomson scattering diagnostic laser enables probing the plasma conditions with spatial and temporal resolution. Electron and ion temperatures, flow velocity, and electron density can be obtained from the ion acoustic and electron plasma wave features. Splitting the laser into two pulses allows observation of time-resolved spectra for more of the implosion time. Spectra from the same scattering volume but collected by optics at differing angles to the laser imply ion temperatures that are inconsistent across viewing angles if the width of the ion features in the spectral profile are interpreted as only due to ion temperature. This suggests an additional source of peak broadening that scales with angle. Multiple methods of fitting the Thomson scattering spectral profile show that the presence of flow velocity distributions in the plasma at stagnation can, along with ion temperature, give a better fit to the observed ion feature peak widths than ion temperature alone. |
Wednesday, November 7, 2018 10:30AM - 10:42AM |
NO6.00006: Study of Z-pinch Magnetic Fields and Sources of MeV Ions via Ion Deflectometry Vojtech Munzar, Daniel Klir, Jakub Cikhardt, Balzhima Cikhardtova, Josef Kravarik, Pavel Kubes, Karel Rezac, Alexandr Viktorovich Shishlov, Vladimir Alexeyevich Kokshenev, Rustam Koshalievich Cherdizov, Nikolay Alexadrovich Ratakhin, Karel Turek In the deuterium gas-puff MA Z-pinch experiments on GIT-12, >30 MeV hydrogen ion beams are detected. Pinhole detectors show that the fast ions originate from annular sources. Ion deflectometry is used to investigate B-fields and ion sources by simulating deflected ion trajectories in Z-pinch plasmas. Analysis and interpretation of experimental and synthetic pinhole images demonstrate effects of magnetic fields and ion beam divergence. Thus, the spatial distribution of the ion source and magnitude of the averaged magnetic field are estimated. |
Wednesday, November 7, 2018 10:42AM - 10:54AM |
NO6.00007: Experimental and Computational Exploration of the Effects of Non-Uniform Applied Axial Magnetic Field on Z-Pinch Imploding Cylindrical Foils Jeff M Woolstrum, Paul C Campbell, Stephanie M Miller, Akash P Shah, Nicholas B Ramey, Nicholas M Jordan, Charles E Seyler, Ryan D McBride We use X-pinch radiography and PERSEUS [1], an extended magneto-hydrodynamic simulation code developed by Seyler et al., to explore the effect that an applied non-uniform axial magnetic field has on a z-pinch imploding cylindrical liner as compared to a uniform magnetic field. The effect of magnetic field geometry is of importance to inertial confinement fusion efforts being explored at Sandia National Laboratories on the Z-machine, which uses z-pinch cylindrical liners to compress fusion fuel. We present results of radiographic imaging of cylindrical foils imploded on the MAIZE facility at the University of Michigan, a 1-MA, 100-ns rise time pulsed power machine, as well as results from simulation work using PERSEUS. [1] C.E. Seyler and M.R. Martin.Relaxation model for extended magnetohydrodynamics: Comparison to magnetohydrodynamics for dense Z-pinches.Physics of Plasmas 18, 012703 (2011). |
Wednesday, November 7, 2018 10:54AM - 11:06AM |
NO6.00008: Abstract Withdrawn. TBD TBD TBD |
Wednesday, November 7, 2018 11:06AM - 11:18AM |
NO6.00009: Power Modeling Using Perseus Extended-MHD Simulation Code For Hed Plasmas Nathaniel D Hamlin, Charles E Seyler We discuss the use of the PERSEUS extended-MHD simulation code for high-energy-density (HED) plasmas in modeling power flow in coaxial transmission lines and in the Magnetized Liner Inertial Fusion (MagLIF) experiment at Sandia National Labs. By formulating the fluid equations as a relaxation system in which the current is semi-implicitly time-advanced using the Generalized Ohm’s Law (GOL), PERSEUS enables modeling of two-fluid phenomena in dense plasmas without the need to resolve the smallest electron length and time scales. We find that Hall physics is required in order to model differences arising from plasma initialization against the cathode versus anode. In particular, compared to cathode initialization, substantially greater current losses result from anode-initialized plasma, for which electron ExB drift currents produce filaments streaming away from the anode. The MagLIF results exhibit sensitivity to the treatment of the vacuum and low-density regions, which is improved by Hall physics but remains an unsolved problem in fluid modeling. |
Wednesday, November 7, 2018 11:18AM - 11:30AM |
NO6.00010: The development of high repetition x-pinches using a fast, compact pulsed power driver Roman Shapovalov, Matthew Evans, Brandon Foy, Daniel Mager, Imani West-Abdallah, James Young, Pierre-Alexandre Gourdain The x pinch is an excellent source for point-projection radiography. Its radiation source size is a few microns, the probing pulse duration is a few nanoseconds, and the brightness is sufficient to backlight warm dense matter samples or biological objects. However, the repletion rate of x pinches is limited, at best, to a few shots per hour. Every time the x pinch is fired, wires are vaporized and the x pinch must be replaced. Here, we investigate a new way of creating x pinches inside the vacuum chamber. In this approach, a nano-particle metal powder is injected directly in the load section by mixing it inside a rapid flow of low-density inert gas. The inert gas is pre-ionized to create two virtual conical electrodes, and the current from a compact driver is applied to nano-particle gas flow. This approach eliminates the needs of electrode and wires potentially increasing the x-pinch repetition rate. |
Wednesday, November 7, 2018 11:30AM - 11:42AM |
NO6.00011: General Fusion Overview Michel Laberge General Fusion is a private company developing Magnetized Target Fusion (MTF). Using the General Fusion MTF method, we first form a spherical tokamak inside a cavity in liquid metal. The compressed gas pushes on pistons that rapidly inject more liquid metal in the chamber and therefore compress the plasma to higher density and temperature. After a brief description of our system, we will look at General Fusion’s latest results forming a spherical tokamak by coaxial helicity injection (no center solenoid). We have achieved plasma with sufficient density, temperature and lifetime to be good candidates for compression. The results from compressing some of these plasmas to higher density and temperature will be presented. Finally, we will look at our future plans and extrapolation to a point design for an MTF power plant. |
Wednesday, November 7, 2018 11:42AM - 11:54AM |
NO6.00012: Developments in Compression of Magnetized Plasmas Peter O'Shea Magnetized Target Fusion (MTF) involves compressing an initial magnetically confined plasma on a timescale faster than the thermal confinement time of the plasma. Volumetric compression of 350X or more of a 500 eV target plasma would achieve a final plasma temperature exceeding 10 keV. Power plant relevant fusion gains could be achieved provided the compressed plasma has sufficient density and dwell time. General Fusion is developing a compression system using pneumatic pistons to collapse a cavity formed in liquid metal containing a magnetized plasma target. This approach offers a low-cost driver, straightforward heat extraction, good tritium breeding ratio and excellent neutron protection in power plant designs. Through an active plasma and compression R&D program, General Fusion is conducting full scale and reduced scale plasma experiments and simulation of both. Although pneumatic driven compression of full scale plasmas is the end goal, present compression studies use reduced scale plasmas and chemically accelerated aluminum liners. We will review results from our plasma target development and dynamic compression program. In particular we will focus on the two most recent tests in which we have detected significant increases in fusion neutron rates. |
Wednesday, November 7, 2018 11:54AM - 12:06PM |
NO6.00013: A New Pre-Ionization Technique for the HJ1 Coaxial Plasma Gun for PJMIF Y.C. F. Thio, E. Cruz, A. Case, S. Brockington, Ajoke Williams, F. Witherspoon, M. Luna We are exploring a new technique for preparing and pre-ionizing the initial gas slab before turning on the main discharge in a coaxial plasma gun for driving PJMIF. The present pre-ionization scheme used an annular array of capillary discharges driven by a capacitor storing up to 1.5kJ of energy and tend to produce long jets. In the new scheme, a capacitor storing about 50 J of energy applies a voltage across the gap between the electrodes. As the working gas (e.g. Ar) is introduced into the gap, a sharp trigger voltage is given to an annular array of 20 tungsten pins positioned in the gap to emit electrons by field-enhanced emission, in order to facilitate the Townsend avalanche. The Townsend discharge is appropriately limited by external circuit impedance to control its growth rate to allow time for the avalanching electrons to diffuse annularly. When the annular spread of the glow is complete the main discharge to the gun is turned on. |
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