Bulletin of the American Physical Society
64th Annual Meeting of the APS Division of Plasma Physics
Volume 67, Number 15
Monday–Friday, October 17–21, 2022; Spokane, Washington
Session YO04: Z-Pinch, X-Pinch, and Dense Plasma FocusLive Streamed
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Chair: Matthias Geissel, SNL Room: Ballroom 111 A |
Friday, October 21, 2022 9:30AM - 9:42AM |
YO04.00001: Fully kinetic simulations of effects beyond resisitive magnetohydrodynamics at the edge of a dense z-pinch Griffin Farrow, Jeremy P Chittenden, Brian Appelbe Low-density plasmas have an important role in pulsed-power experiments. They can divert power flow and change macroscopic plasma dynamics in lab astro experiments. However, the resistive magnetohydrodynamic (MHD) codes traditionally used to model these experiments cannot capture low-density effects, such as the Hall term or anomalous resistivity. Thus, it is not well understood which of these additional effects are relevant to current experiments and need to be included in models. In this work, we use fully kinetic particle-in-cell (PIC) simulations of the low-density edge region of a z-pinch to study beyond-MHD physics. By calculating electric field components, we show that the Hall and electron pressure terms are the dominant contributions to Ohm's law in this regime. We demonstrate that PIC can recreate both the microscopic behaviour of the Hall term as charge separation and macroscopic fluid-like behaviour. We compare PIC and Hall MHD simulations of a z-pinch m=0 mode, showing an axial shear in the direction of current flow due to the Hall effect. We conclude by discussing why PIC is a challenging tool for steep density gradients and highlight the ideal features for codes modelling this problem. |
Friday, October 21, 2022 9:42AM - 9:54AM |
YO04.00002: Modeling the CESZAR Gas-Puff Z Pinch in the Radiation-Magnetohydrodynamic FLASH Code David Michta, Marissa B Adams, Edward C Hansen, Kasper Moczulski, Adam Reyes, Petros Tzeferacos, Fabio Conti, Farhat N Beg The gas-puff Z pinch (GPZP) has a myriad of applications in high-energy-density physics as a source of intense x rays/neutrons and potential in nuclear fusion. Recent experiments at CESZAR1 drove GPZP’s with a linear transformer driver that achieves 0.5-MA current and <200-ns rise times without pulse compression, demonstrating high energy-coupling efficiency to the load. These properties, combined with the high shot rates possible, make CESZAR an ideal platform for parameter scans and benchmarking of models. Here we present the Z-pinch simulation capabilities in FLASH, which we verify with code-to-code comparisons to published HYDRA results2 and validate with CESZAR experimental data. We study the effects of thermal and radiative energy losses on instability growth and characterize the dynamical evolution in multiple gas-puff configurations to aid in experimental design. |
Friday, October 21, 2022 9:54AM - 10:06AM |
YO04.00003: Radiation from Tungsten Z-pinches influenced by using the alternating W and mid-atomic-number wires Alla S Safronova, Victor L Kantsyrev, Ryan R Childers, Austin Stafford, Christopher J Butcher, Veronica V Shlyaptseva Previously, it was demonstrated that compact wire arrays of 3-6 mm diameter/width are excellent radiation sources and can be useful for novel ICF applications, however currently there is very limited research on them. This study focuses on hard x-ray non-thermal inner-shell emission from compact cylindrical wire arrays (CCWA) and presents the analysis of radiation from tungsten (W) experiments performed on the 1 MA Zebra at the same conditions. Two W CCWA of 6 mm diameter with a similar array mass and the same number of wires (one with 24 W wires and another with alternating 12 W and 12 brass wires) are analyzed. Brass wires were chosen because characteristic W L-shell lines and Cu and Zn K-shell lines occupy the same spectral region between 1 and 1.6 Å, which makes their simultaneous observation possible using time-gated hard x-ray spectroscopy. A comprehensive comparison of x-ray diode signals, time-gated x-ray pinhole images and hard x-ray spectra, as well as soft x-ray spectra is presented to gain better understanding of changes in radiation from W Z-pinches when using alternating W and mid-atomic-number wires. |
Friday, October 21, 2022 10:06AM - 10:18AM |
YO04.00004: One-Dimensional FLASH Simulations of a Gas-Puff Staged Z-Pinch Edward C Hansen, Fernando Garcia Rubio, Kasper Moczulski, Marissa B Adams, Adam Reyes, Paul Ney, Hafiz U Rahman, Emil Ruskov, Petros Tzeferacos The staged Z-pinch (SZP) is an alternative, pulsed-power–driven magneto inertial fusion concept under development at Magneto-Inertial Fusion Technology, Inc. (MIFTI). While there have been several SZP variants proposed in the literature, a common property is the use of a high atomic number liner. In this talk we focus on FLASH simulations of a gas-puff Xe liner, a variant that has been referred to as SZP1 in the literature. The initial conditions and parameters used in the simulations we present differ in two key aspects compared to previous publications: (1) the use of a more-realistic double-Gaussian initial density profile, and (2) the use of a circuit model that can represent the pulsed-power Z machine at Sandia National Laboratories. Since MIFTI has used the MACH2 code for many of their calculations, we include code-to-code comparisons of FLASH and MACH2 on this new SZP1 setup. For the comparison runs, the two codes employ the same tables for the equation of state, ionization, and opacities, limiting the FLASH runs to gray opacities, i.e., single-group radiation diffusion, to match MACH2. We also present a FLASH run with a more-realistic multigroup diffusion configuration, with 40 energy groups and updated transport coefficients. The results show how the problem is affected by the choice of transport coefficient and that the SZP is worth further study as high convergence ratios and temperatures are achieved. |
Friday, October 21, 2022 10:18AM - 10:30AM |
YO04.00005: Understanding electrode plasma formation on wires and thin foils via vacuum ultraviolet spectroscopy of desorbed surface contaminants Trevor J Smith, Mark D Johnston, Nicholas M Jordan, Michael E Cuneo, Jens Schwarz, Ryan D McBride Power flow studies on the 30-MA, 100-ns Z facility at Sandia National Labs have shown that plasma in the facility’s magnetically insulated transmission lines can result in a loss of current delivered to the load.1 During the current pulse, thermal energy deposition into the electrodes causes neutral surface contaminant layers to desorb, ionize, and form plasma in the anode-cathode gap.2,3 We suspect that as the electrode thickness decreases relative to the skin depth of the current pulse (50−100 µm for aluminum and 100-500 µm for stainless steel, for a 100−500-ns pulse), the thermal energy delivered to the surface contaminant layers increases, and thus, faster desorption rates. |
Friday, October 21, 2022 10:30AM - 10:42AM |
YO04.00006: Quantifying data constraints for velocimetry-based load current determination for inertial confinement fusion targets Andrew J Porwitzky, Justin L Brown, David A Yager-Elorriaga Velocimetry-based load current inferences provide the most accurate method of determining delivered drive current on multi-mega-amp cylindrically imploding inertial confinement fusion platforms, allowing for drive uncertainties of < 2% for 20 MA targets. Low uncertainty current inferences are necessary inputs – along with high quality target metrology – for accurate multiphysics modeling postdictions. Velocimetry information is now routinely returned from cylindrical anode “return cans” concentric to the imploding gas filled cathode target across a wide variety of campaigns on the Z Machine. The standard 100 ns current rise results in shock formation in the return can, and current information is lost as wave characteristics coalesce. Understanding the uncertainty of the velocimetry-derived drive current in the region of the current constrained by the data lost to the shock formation requires advanced computational or mathematical methods. Here we discuss the application of Sobol indices – also referred to as variance-based sensitivity analysis – to identify the level of constraint of various portions of the derived current pulse. The Sobol indices approach is one of several methods under investigation at Sandia National Laboratories for quantifying constraining data of velocimetry-based load current inferences. |
Friday, October 21, 2022 10:42AM - 10:54AM |
YO04.00007: Measurement of hard x-rays at a staged Z-pinch using a 128-channel scintillator array Seth Pree, Paul M Bellan Z-pinch plasmas capable of sustaining nuclear fusion also generate X-rays with energies exceeding 5 keV. These X-rays can be generated by three different sources: the high average kinetic energy in the plasma, energetic particle beams, and as a secondary byproduct of fusion products scattering off of the environment. Each of these sources has characteristic spectra, timing, and origin, and their presence can be used to assess the suitability of a fusion concept for thermonuclear fusion. A scintillator-based, 128-channel, portable hard X-ray detector array with 40 ns time response has been built and deployed as one of ARPA-E’s fusion diagnostic capability teams. This array has been used to measure the hard X-rays from the staged Z-pinch driven by UCSD’s CESZAR linear transformer driver. The array has operated in three modes: a detector mode to correlate X-ray production with neutrons, a pinhole imaging mode to determine the X-ray origin, and a metal filter energy measurement mode. Measurements made using these three modes will be presented along with comparison to thermal and beam source X-ray models. |
Friday, October 21, 2022 10:54AM - 11:06AM |
YO04.00008: Dense Plasma Focus Controlled by Plasma and Gas Injection Andrey Beresnyak, Stuart L Jackson, Eric R Kaiser, Alexander L Velikovich, Paul E Adamson, Robert J Commisso, Joseph W Schumer, Arati Dasgupta Dense plasma focus (DPF) is a pulsed power plasma device in which the pinch is formed at the end of a cylindrical anode. Usually DPFs are filled with gas and the plasma parameters can only be controlled by the pressure of this gas fill. NRL DPF experiments explored the alternative - local plasma and gas injection into the DPF device, which prevents breakdown and short-circuiting of the generator at later times. Such injection gives a bigger control over implosion timing, independent of the device geometry. This will allow quick finetuning during the run of the experiment. In a series of MHD simulations using the Athena code, we study how different types of plasma and gas injection affect the implosion. For example, one may inject a plasma column perpendicular to the axis or at an angle, to counteract inhomogeneity of the jxB force. While injecting less gas, this produces longer delay times before the implosion as well as the different location for the implosion. Injecting the gas along the axis allows control of pinch density that is almost independent of the implosion time. |
Friday, October 21, 2022 11:06AM - 11:18AM |
YO04.00009: Pulsed neutron radiography using a Megajoule-class Dense Plasma Focus Energy Clement S Goyon, Owen B Drury, Jessica R Taylor, Christopher Cooper, Steven F Chapman, Paul C Campbell, David N Fittinghoff, Luis Frausto, Drew P Higginson, Anthony J Link, Brian H Shaw, Kurt Walters, Amanda E Youmans, Andrea E Schmidt The MegaJOuLe Neutron Imaging Radiography1 experiment uses dense plasma focus2 (DPF) as a source for flash neutron radiography. In a DPF, a high voltage is pulsed across a low-pressure gas between coaxial cylindrical electrodes. The gas is ionized and magnetically compressed to form a high-density plasma, called the pinch, at the tip of the central electrode. During the pinch event, magnetic instabilities generate electric fields that can accelerate ions up to several MeV. These ions produce neutrons via beam-target interaction with the dense plasma present on-axis. We present the first radiographs obtained using the MJOLNIR DPF as a neutron source. We also show measurements to characterize the neutron source using the suite of diagnostics implemented on MJOLNIR such as real-time neutron activation detectors, neutron time-of-flight detectors. This work was performed by LLNL under Contract DE-AC52-07NA27344, LLNL-ABS-837040. |
Friday, October 21, 2022 11:18AM - 11:30AM |
YO04.00010: Analysis of Radial Phase of Dense Plasma Focus with a Modified Electrode System Using Laser Interferometry and Electrical Measurements Jakub Malir, Daniel Klir, Jakub Cikhardt, Josef Kravarik, Pavel Kubes, Vojtech Munzar, Jan Novotny, Karel Rezac, Marian Paduch We focus on the analysis of implosion parameters - the implosion velocity and mass coupled with electrical parameters observed on the PF-1000 facility with a modified electrode system. The first two are based on the 16-frame Mach-Zehnder interferometer, which provides a spatial electron density distribution in a time sequence. This diagnostics also provided an inductance estimation since we registered imploding layer during the radial phase. Measuring electrical waveforms enables us to evaluate the total inductance and kinetic energy incoming from the capacitor bank. Then comparing the inductances and kinetic energies evaluated from the interferograms, and electrical waveforms provided a possible way to deal with the fact that only part of the total current flows through the layer. With the supposition that the rest of the current flows close to the insulator, we conclude that only 70 % of the total current flows through the pinch, which is in good agreement with the Lee model, for example. |
Friday, October 21, 2022 11:30AM - 11:42AM |
YO04.00011: Results and plan of research of plasma compression and total D-D fusion neutron emission for 16.8-kJ and 3.1-kJ plasma foci operated with D2, D2+Ne and D2+Ar gas mixtures Lukasz Marciniak, Karel Rezac, Agnieszka Kulinska, Jan Novotny, Mohamad Akel, Josef Kravarik, Sing Lee, Jakub Cikhardt, Marek Scholz, Daniel Klir, Sor H Saw A total of 269 discharges were performed on the 16.8-kJ Mather-type plasma focus device (called PF-24) filled with D2 and (100%-x)D2+xNe at a constant, initial, total mass of gas mixture in the experimental chamber. Magnetic and electric probes, Be activation neutron counter and 4-frame VUV/SXR plasma imaging system were used to study the plasma dynamics and radiation emission. The results showed a decrease in the radii of plasma columns (on average) in the initial phase of evolution and a decrease in the total D-D fusion neutron yields (on average) with increasing Ne fraction (x). Presently, similar new set of experiments is being planned and carried for the 3.1-kJ Mather-type plasma focus (called PFZ-200) which will operate with D2 and (100%-x)D2+xAr at the constant initial mass of deuterium in the mixture or at the constant initial total mass of gas mixture. For both PF-24 and PFZ-200 the 5-phase Lee model was used to design the discharges – chose the proper gas mixture composition and make predictions about the possible phenomena accompanying discharges. The main aims of these investigations are enhancement of plasma pinch compression and increase the total D-D fusion neutron emission, in plasma foci, by doping deuterium with noble gases. |
Friday, October 21, 2022 11:42AM - 11:54AM |
YO04.00012: Modeling the Effects of Radiation Reaction for a Next Generation Pulsed Power Machine Mark H Hess, Evstati G Evstatiev Next Generation Pulsed Power (NGPP) is a future machine being designed at Sandia National Laboratories for delivering >60MA of current to a load. When load radii, such as MagLIF, are less than or equal to 1mm, the peak magnetic fields in the load region are expected to be greater than 10,000T. Electrons that are in the load region will conduct small and fast cyclotron orbits in the magnetically insulated transmission line load region that will result in the emission of synchrotron radiation. The Lorentz-Abraham-Dirac Force Law describes the force that the electron experiences due to the emission of radiation and can be used to calculate its rate of cycloidal kinetic energy loss. In this presentation, we find that the e-folding time for electron kinetic energy loss at a magnetic field of 7200T is roughly 100ns, which corresponds to a possible pulse length design time scale for NGPP. We also show how the drift kinetic motion due to grad B drift of the electrons is modified due to the loss of cycloidal kinetic energy. Finally, we discuss the radiated energy spectrum in the load region where synchrotron radiation is expected to occur. |
Friday, October 21, 2022 11:54AM - 12:06PM |
YO04.00013: Faraday Rotation Imaging of X-Pinch Implosion Dynamics on the MAIZE Pulsed Power Facility George V Dowhan, Akash P Shah, Brendan J Sporer, Nicholas M Jordan, Simon N Bland, Sergey V Lebedev, Roland A Smith, Lee G Suttle, Sergei Pikuz, Ryan D McBride X-pinches, formed by driving intense current through the crossing of 2 or more wires, provide an excellent platform for the study of “micro-pinches” due to their propensity to generate a single micro-pinch at a predetermined location in space (i.e., where the wires cross) [1,2]. Ideally, micro-pinches are areas of run-away compression to very small radii (~1 µm) leading to pressures on the order of ~1 Gbar for currents on the order of ~0.1 MA. However, the fraction of the total current driven through the dense micro-pinch plasma at small radii versus shunted through the surrounding coronal plasma at larger radii is not well known. To allow for the study of micro-pinches and their current distribution on the 1-MA MAIZE facility, a high-magnification Faraday rotation imaging diagnostic (1064 nm) has been developed. Presented is the status of these developments including experimental results characterizing X-pinches on the MAIZE LTD. |
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