Bulletin of the American Physical Society
63rd Annual Meeting of the APS Division of Plasma Physics
Volume 66, Number 13
Monday–Friday, November 8–12, 2021; Pittsburgh, PA
Session NO03: HED: Pulsed Power and Magnetized PlasmasOn Demand
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Chair: Patrick Knapp, Sandia National Laboratories Room: Rooms 302-303 |
Wednesday, November 10, 2021 9:30AM - 9:42AM |
NO03.00001: Pulsed power method for determining the electrical conductivities of metals from ambient to HED conditions Andrew J Porwitzky, Kyle Cochrane, Brian Stoltzfus Simulation of a wide range of astrophysical and high energy density (HED) phenomenon requires accurate modeling of the electrical conductivity of materials at elevated pressures and temperatures. Existing techniques for probing electrical conductivities are limited to the moderate pressures achievable under static compression (DAC), and often can’t capture high temperature states. We present ongoing work on a magnetic direct drive (MDD) planar flyer technique to infer the electrical conductivity of metals – in this case copper – from ambient conditions up to temperatures and pressures in excess of 4000 K and 10 GPa, respectively. Minor modifications (<10%) were found to be necessary to the previous Lee-More-Desjarlais model isotherms in the vicinity of the high pressure/temperature melt transition as a result of our experimental data. This work uses the Sandia National Laboratories’ 2 MA Thor pulsed power driver, which presents the possibility of conducting experiments of this class at university scale facilities. |
Wednesday, November 10, 2021 9:42AM - 9:54AM |
NO03.00002: Investigation of Visbile Line Emission in Gas PUFF Z-pinches at 1-MA on Cobra Niansheng Qi, Eric S Lavine, Jay S Angel, Euan Freeman, Chiatai Chen, William M Potter, John B Greenly, David A Hammer, Bruce Kusse In high current (>1MA) z-pinches, it is a challenge to use visible spectroscopy because there are not many detectable visible lines in the hot plasmas. We have identified several visible spectral lines in 1 MA 200 ns COBRA z-pinch plasmas. These pairs of visible lines are Ar VIII 5168 and 5181 Å, and C IV 5801 and 5812Å, which have been observed from the imploding plasma shell. The other possible line pair is Ne IX 4650 and 4672 Å. In these experiments, a triple-gas puff z-pinch is imploded with and without an external Bz field. Radially resolved Thomson Scattering is used to measure the imploding plasma density, temperature and velocity and to locate the plasma boundary. Visible light from the plasma is focused onto 20-channel fiber linear optical linear arrays. It views cross over the diameter of the plasma. Emission vs. chord radius is dispersed by a 0.75M imaging spectrometer and the spectra are recorded by gated ICCD cameras. The spatially resolved double line-profiles of Ar VIII, C IV, and/or Ne IX are captured. A de-convolution model for the spectrum is used to deduce the Zeeman, and Doppler shifts in the plasma as well as the rotation velocity due to the external Bz field. Details of the experiments will be presented. |
Wednesday, November 10, 2021 9:54AM - 10:06AM |
NO03.00003: Turbulence in Gas-Puff Z-Pinches: Applying Thomson Scattering to Diagnosing Turbulent Density and Velocity Fluctuations Sophia Rocco, David A Hammer, Jacob T Banasek, Eric S Lavine, William M Potter We present measurements of velocity distributions and electron density fluctuations in a neon gas-puff z-pinch. These experiments were performed on the 0.9 MA, 240 ns rise-time COBRA generator at Cornell University. Time-resolved electron plasma wave (EPW) and ion acoustic wave (IAW) Thomson scattering data were obtained using a 526.5 nm laser (E=10 J, $\Delta$t= 2.3 ns) and two streak cameras. IAW spectra from two differently sized scattering volumes at the same radius were also collected. We observe that including a velocity distribution in the IAW fit improves the fit pre-pinch. The width of the distribution does not scale with the size of the scattering volume, indicating that the distribution is not due to a continuous velocity gradient, but more likely to turbulent eddies. |
Wednesday, November 10, 2021 10:06AM - 10:18AM Not Participating |
NO03.00004: Observation of a field orientation dependent instability in preconditioned wire obstacles Lee G Suttle, Jacob Davies, Bartosz Krawczyk, Danny R Russell, Jack W Halliday, Mark E Koepke, Stefano Merlini, Vicente Valenzuela-Villaseca, Adam Frank, Sergey V Lebedev We present experiments from a new pulsed-power driven platform demonstrating interactions of magnetized, supersonic plasma flows with low-ionization plasma columns formed by pre-pulsed wire targets. |
Wednesday, November 10, 2021 10:18AM - 10:30AM |
NO03.00005: Subcritical Shock Structure in a Highly Collisional Plasma Danny R Russell, Guy C Burdiak, Jack W Halliday, Jack D Hare, Stefano Merlini, Lee G Suttle, Vicente Valenzuela-Villaseca, Eric Blackman, Jonathan Carroll-Nellenback, Adam Frank, Sergey V Lebedev Shock interactions are common in astrophysical systems, for example HH objects in protostellar jets. We present results from a laboratory study of interacting bow shocks in magnetised collisional HED plasmas. Shocks are produced by placing cylindrical obstacles into the supersonic, super-Alfvénic outflow from an inverse wire array z-pinch at the MAGPIE pulsed power facility. Magnetic field pile-up at the obstacles leads to the formation of subcritical bow shocks which are supported by downstream magnetic pressure. Optical Thomson scattering measurements show that the flow remains supersonic across the subcritical shocks and hydrodynamic-like shocks are seen in the downstream. We compare experiments with multiple obstacles both with and without magnetic field pile-up and discuss the differences in shock interaction geometry. New measurements of the magnetic field by Faraday rotation imaging confirm the importance of magnetic field compression. Radiative MHD simulations show good agreement with the experimental results, paving the way for MHD simulations of astrophysical shock reflection which include a magnetic field. |
Wednesday, November 10, 2021 10:30AM - 10:42AM |
NO03.00006: Structure and dynamics of quasi-Keplerian, differentially rotating HED laboratory plasmas Vicente Valenzuela-Villaseca, Lee G Suttle, Francisco Suzuki-Vidal, Stefano Merlini, Jeremy P Chittenden, S. Reza Mirfayzi, Jack W Halliday, Danny R Russell, Jack D Hare, Mark E Koepke, Sergey V Lebedev We present results from the Rotating Plasma Experiment (RPX) developed on the MAGPIE pulsed-power generator (1.4 MA, 500 ns duration). The goal is to interpret and model the rotation profile and pressure balance of differentially rotating plasmas driven by the slightly off-radial inward-convergence of 8 magnetized ablation flows. |
Wednesday, November 10, 2021 10:42AM - 10:54AM |
NO03.00007: HADES ramp-up Pierre-Alexandre Gourdain, Marissa B Adams, Aidan Bachmann, Matthew C Evans, Hannah R Hasson, James Young, Imani West-Abdallah
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Wednesday, November 10, 2021 10:54AM - 11:06AM |
NO03.00008: Pulsed-power magnetized shocks under an external magnetic field Raul F Melean, Rachel Young, Sallee Klein, Akash Shah, Trevor J Smith, George Dowhan, Brendan J Sporer, Paul C Campbell, Nicholas M Jordan, Ryan D McBride, R P Drake, Carolyn C Kuranz We present the results from our second experimental campaign with the goal of characterizing magnetized plasma jets and magnetized shocks on the Michigan Accelerator for Inductive Z-Pinch Experiments (MAIZE) in the Plasma, Pulsed Power, and Microwave Laboratory at the University of Michigan. We show the interactions of magnetized plasma jets created by conical wire-arrays and the behavior of shocks generated by collisions with a solid obstacle in the presence of an external magnetic field. We show how the structure and behavior of the shock layer, as well as flow instabilities, vary as a function of magnetic field strength. To generate the magnetized plasma flows, we used MAIZE to ablate 100-micron, aluminum wire arrays with currents in the order of 500 kA with a rise time of 250 ns. We use a conical array to drive an axial plasma jet, while an externally powered Helmholtz coil provides a uniform axial magnetic field which we can vary from 0.5 to 5 T. Our primary diagnostic consists of laser shadowgraphy (532 nm), captured by an intensified, fast framing camera, showing the structure and evolution of the plasma flow. In addition, preliminary results from a newly installed laser interferometry diagnostic identify density features that may correspond to a bow-shock layer. |
Wednesday, November 10, 2021 11:06AM - 11:18AM |
NO03.00009: Experimental Measurement of Surface Motion and Emission on Metal Rods Driven by Intense Current Aidan W Klemmer, Seth E Kreher, Bruno S Bauer, Trevor M Hutchinson, Thomas J Awe, Dan Dolan, Brian T Hutsel, Maren W Hatch, Kevin C Yates Complex plasma-material interactions are found in many fusion and HEDP experiments that may dramatically affect the performance of the device through both material and MHD instabilities. Accurate modeling of electrically driven conductors is challenging due to uncertainties in the equation-of-state (EOS) and electrical conductivity during the metal-insulator transition. Photonic Doppler velocimetry was used to measure the surface motion of extremely smooth mm-diameter 5N Al rods driven to 0.8 MA in 100 ns by the Sandia Mykonos generator. For the first time, uncoated Al rods were measured to compress 40 nm radially before expanding. Subsequently, the reflective surface experiences several changes in acceleration during the current rise. Taking advantage of PDV's sensitivity to multiple simultaneous velocities, the time dependence of the distribution of velocities in the reflective material is being investigated. Visual emission data from photodiodes and streaked-visual-spectroscopy diagnostics is being used to investigate the temperature and radiation of the metal rods. The experimental measurements are being used to benchmark MHD calculations, and thereby inform the choice of EOS and conductivity tables for modeling. |
Wednesday, November 10, 2021 11:18AM - 11:30AM |
NO03.00010: 1-D MHD simulation of an argon gas puff implosion with time-dependent non-LTE kinetics* Nicholas D Ouart, Arati Dasgupta, Alexander L Velikovich, John Giuliani, Varun Tangri, Marc-Andre Schaeuble, Jens Schwarz, David J Ampleford, Roger A Vesey, Christopher A Jennings, Brent M Jones Ar gas puff implosions have been performed on SNL’s Z machine. One frequently fielded platform has a mass profile of 1:1.6 from an 8 cm dia. nozzle, 1 mg/cm mass, and a 2.5 cm height. These experiments produced K-shell yields >300 kJ. The 2-D MHD code Mach2+TCRE reproduced the measured powers, yields, and emission region. The ratio of the Lyα to the Heα+IC lines from the simulation matched the experiment after peak power. Yet, the simulation had higher line ratios earlier. This difference was attributed to 3-D effects or on the assumption of steady-state kinetics [1]. This presentation will explore the effect of time-dependent kinetics using the NRL DZAPP code. DZAPP is a coupled 1-D MHD, non-LTE atomic kinetics, and radiation transport code that incorporates a transmission line to drive the load. Line ratios from steady-state and time-dependent kinetics will be presented and compared. |
Wednesday, November 10, 2021 11:30AM - 11:42AM |
NO03.00011: Sensitivity of electrically exploding metal rods to tabular equation of state and electrical conductivity models in magnetohydrodynamic calculations Seth E Kreher, Christopher L Rousculp, Bruno S Bauer, Aidan W Klemmer, Charles Starrett The fundamental limits of high-current conduction in metals to large, fast current pulses are of interest to magnetically driven DMP and ICF. An electrically thick (R ~ 400-mm > skin-depth) cylindrical metal rod platform in a Z-pinch configuration was fielded on the Sandia 100-ns, 900-kA Mykonos LTD. PDV expansion velocity measurements of the aluminum rod surface benchmarked equation of state (EOS) and electrical conductivity models used in MHD simulations. The metal surface in simulation expanded along the liquid-vapor coexistence curve for all EOS models. These expansion velocities were compared against the PDV data to validate the EOS used. Several tabular electrical conductivity models were also compared. The models predicted varying surface velocities due to differing Ohmic heating rates. Once the surface vaporized, the expansion behaviors varied widely by table with some simulations showing thermal plasma formation in 1D simulations and others not. |
Wednesday, November 10, 2021 11:42AM - 11:54AM |
NO03.00012: Development of a diagnostic based on ruby luminescence for pressure measurement during dynamic loading experiments on high-pulsed power drivers Jérémy Vich, Thierry D'Almeida, Camille Chauvin, Yohan Barbarin, Thierry Duvaut, Gaël Le Blanc The CEA Gramat dedicates a significant part of its activities to study the dynamic behavior of various materials of interest. Dynamic loading experiments, mainly quasi-isentropic compression experiments, are achieved on several High-Pulsed Power (HPP) drivers. In order to constrain Equation of State (EOS) and elastic-plastic behavior parameters, physical quantities such as wave velocity, temperature and pressure are valuable measurements. In our HPP driver experiments, wave velocities are routinely measured and temperature measurements can be obtained under certain conditions. Due to the severe electromagnetic environements associated with these experiments, fielding pressure gauges proved more difficult. However, such measurements are very useful for characterizing the dynamic response of the materials studied.. Hence, we studied the feasibility of a diagnostic based on ruby luminescence for HPP drivers. Ruby luminescence spectra were recorded during a microsecond scale ramp-compression experiment on the ICE16 driver. A 0.5 mm thick ruby disk served as sample. The ruby luminescence was recorded using a CCD camera coupled to a dispersive spectrometer over 500 ns. Based on associated numerical simulations, a pressure of 4.06 GPa was inferred across the bulk of the ruby sample. During the recording period, the fluorescence spectroscopic measurements give a R1 shift of 0.73 nm. |
Wednesday, November 10, 2021 11:54AM - 12:06PM |
NO03.00013: Staged Z-pinch experiments at a 0.5MA LTD pulsed power generator using Ar and Kr liners Emil Ruskov, Hafiz U Rahman, Fabio Conti, Farhat N Beg We report on our first Staged Z-pinch experiments at Cezar, a 0.5 MA Linear Transformer Driver (LTD) at UC San Diego. In these experiments Ar or Kr liners compress a deuterium target. The pinch stability is monitored with a multi-frame X-ray pinhole camera and with Schlieren imaging. Soft X-rays are measured with silicon diodes covered with thin metal foils. Extensive set of neutron time of flight detectors (nTOFs) are deployed to assess the neutron flux isotropy and to measure the neutron yield. The neutron yield is also measured with a LaBr detector. |
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