Bulletin of the American Physical Society
62nd Annual Meeting of the APS Division of Plasma Physics
Volume 65, Number 11
Monday–Friday, November 9–13, 2020; Remote; Time Zone: Central Standard Time, USA
Session PI01: Invited: HED Fundamental Plasma PhysicsLive
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Chair: Cameron Geddes, LBNL |
Wednesday, November 11, 2020 2:00PM - 2:30PM Live |
PI01.00001: Liner Implosion Experiments Driven by a Dynamic Screw Pinch Invited Speaker: Paul Campbell Magnetically driven implosions are susceptible to magnetohydrodynamic instabilities, including the magneto-Rayleigh-Taylor instability (MRTI). The use of a dynamic screw pinch (DSP) has been proposed [1], to control the MRTI growth in sold-metal liner implosions. In a DSP configuration a helical return-current structure surrounds the liner, resulting in a helical magnetic field that drives the implosion. Using the 1-MA, 100--200-ns COBRA pulsed-power driver at Cornell, we present experimental tests of three DSP cases (with peak axial magnetic fields of 2 T, 14 T, and 20 T) as well as a standard z-pinch (SZP) case [2]. The liners had an initial radius of 3.2 mm and were made from 650-nm-thick aluminum foil. Micro B-dot probes measured the axial magnetic fields produced by the return current structures. A probe placed inside the liner measured the axial field injected into the liner's interior prior to the implosion and the degree of flux compression during the implosion. Load current measurements made in COBRA's power feed suggest that the amount of low-density plasma flowing in the power feed after peak current is reduced in the DSP cases. Imaging revealed that helical MRTI modes developed in the DSP cases while azimuthally correlated MRTI modes developed in the SZP case and that the MRTI amplitudes for the 14-T and 20-T DSP cases were smaller than in the SZP case. Specifically, when the liner had imploded to half of its initial radius, the MRTI amplitudes for the SZP case and for the 14-T and 20-T DSP cases were, respectively, 1.1\textpm 0.3 mm, 0.7\textpm 0.2 mm, and 0.3\textpm 0.1 mm. Relative to the SZP, the stabilization obtained using the DSP agrees reasonably well with theoretical estimates. This work was conducted in collaboration with T. M. Jones, J. M. Woolstrum, N. M. Jordan, and R. D. McBride (U. Michigan), P. F. Schmit (Sandia), and J. B. Greenly, W. M. Potter, E. S. Lavine, B. R. Kusse, D. A. Hammer (Cornell). This work was supported by NSF Grant PHY-1705418 of the NSF-DOE Partnership in Basic Plasma Science and Engineering. COBRA support was provided by the NNSA SSAP under DOE Cooperative Agreement DE-NA0003764. [1] P. F. Schmit \textit{et al.}, Phys. Rev. Lett. \textbf{117}, 205001 (2016). [2] P. C. Campbell \textit{et al.}, ``Stabilization of Liner Implosions via a Dynamic Screw Pinch'', accepted in Phys. Rev. Lett. (2020). [Preview Abstract] |
Wednesday, November 11, 2020 2:30PM - 3:00PM Live |
PI01.00002: Validation of heat transport modeling using directly driven beryllium and gold spheres Invited Speaker: William Farmer Simulations of inertial-fusion hohlraums are not yet predictive due to the complex interaction of atomic physics, radiation transport, kinetic plasma effects, magnetic fields, laser-plasma interactions, and microturbulence. It has been hypothesized that restricted heat transport is altering plasma conditions at the waist of the hohlraum, enhancing ``glint'' (specularly reflected light that exits the hohlraum), and that this can account for the drive-deficit. In an effort to determine whether restricted heat transport is occurring in relevant plasma conditions, a series of experiments in which either a beryllium or gold sphere was directly driven were performed on the OMEGA facility. Optical Thomson scattering was used to measure plasma conditions at several positions, and laser coupling was assessed using several calorimeters distributed throughout the machine. When driving gold spheres, the irradiated x-ray flux and spectrum are also measured using the Dante diagnostic. Radiation-hydrodynamic simulations in 2D are performed in order to account for heating of the plasma due to the presence of the probe beam. Simulations show that probe heating can alter the electron temperature by 20{\%} in beryllium at lower drive-intensities. It is found that the plasma conditions can be matched when driving a beryllium sphere at lower drive intensities (10$^{\mathrm{14}}$ -- 2.5\texttimes 10$^{\mathrm{14}}$ W/cm$^{\mathrm{2}})$ without restricting the heat flux. Laser-coupling is underpredicted by the simulations, but using a power multiplier to match the coupling data does not greatly alter the simulated plasma conditions. This same framework is also applied to the directly driven gold spheres with similar results. [Preview Abstract] |
Wednesday, November 11, 2020 3:00PM - 3:30PM Live |
PI01.00003: Measurements of ion-electron equilibration utilizing low-velocity ion stopping in High Energy Density Plasmas at OMEGA Invited Speaker: Patrick Adrian Obtaining a fundamental understanding of ion-electron (i-e) equilibration in High Energy Density Plasmas (HEDP) is essential for advancing basic plasma science and for correctly modeling the energy balance in Inertial Confinement Fusion (ICF) implosions. I-e equilibration has therefore been the subject of extensive analytical and numerical studies over decades. However, only a limited set of experimental data exists to test these theories. The lack of data is generally due to the dynamic and complex nature of HEDP, seriously compromising any methods that try to directly relate observables to the i-e equilibration process. To address this issue, we have developed and utilized a novel method for diagnosing i-e equilibration through low-velocity ion-stopping-power measurements. This method relies upon the fact that the cross section for the i-e energy transfer is identical for the ion-stopping power and i-e equilibration process when the ion velocity is less than the mean velocity of the thermal distribution of electrons, meaning that the information about the i-e equilibration is encoded in the energy loss of the low-velocity ions. Precision measurements of i-e equilibration were therefore conducted using 1-MeV tritons from DD reactions and 3.7-MeV alphas from D3He reactions in D3He gas-filled implosions. These implosions were doped with a trace amount of argon to diagnose the electron density and temperature, which fall in the ranges of 3x10$^{\mathrm{23}}$ -- 2x10$^{\mathrm{24}}$ cm$^{\mathrm{-3}}$ and 1.3 -- 2.1 keV, respectively. The i-e equilibration results observed in these experiments are well described by the Brown-Singleton and Gerkie-Murillo-Schlanges theories. Finally, future experiments are being planned to use this method to study i-e equilibration in higher-density plasmas where theories are more divergent. Co-authors: P. E. Grabowski, J. Frenje, S. D. Baalrud, B. Bachmann, A. Bose, R. Florido, V. Glebov, F. Graziani, S. X. Hu, M. G. Johnson, T. Joshi, N. V. Kabadi, B. Lahmann, C. K. Li, R. Mancini, S. P. Regan, F. H. Seguin, B. Srinivasan, C. Stoeckl, G. D. Sutcliffe, R. D. Petrasso [Preview Abstract] |
Wednesday, November 11, 2020 3:30PM - 4:00PM Live |
PI01.00004: First DC electrical conductivity measurements of warm dense matter using ultrafast THz radiation Invited Speaker: Benjamin Ofori-Okai The DC electrical conductivity is an important parameter for characterizing warm dense matter and dense plasmas as it is connected with carrier density and electron-electron and electron-ion collisional processes. Accurate knowledge is vital, for instance, for modeling the magnetic field produced by planetary dynamos, or for understanding instability growth in inertial confinement fusion implosions. However, investigations of the DC conductivity have remained a significant challenge due to the highly transient nature of laboratory generated warm dense matter. Probing transient states on ultrashort time scales is possible using ultrafast laser pulses, but these approaches measure the high frequency AC response which must then be extrapolated to the low-frequency near-DC regime. Additionally, theoretical models predict different results based on how the strong coupling of dense plasmas is handled. Taken together, these highlight the need for accurate measurements of the response close to DC. This talk presents recent measurements of the DC electrical conductivity of warm dense matter using terahertz (THz) pulses. THz fields are sufficiently slowly varying that they behave like DC fields on the timescale of electron-electron and electron-ion interactions, and hence probe DC-like responses. The THz pulses are produced using laser- or accelerator-based techniques and measured with high-fidelity single-shot electro-optic sampling. Using a pump-probe measurement, the electrical conductivity of laser generated warm dense matter is determined with $<$ 1 ps temporal resolution. The measurements demonstrate the influence of material density and changes in the collision frequency, and agree with density functional theory results in a controversial regime of warm dense aluminum.Finally, an outlook on using THz pulses for studies of dynamically compressed matter will be presented. [Preview Abstract] |
Wednesday, November 11, 2020 4:00PM - 4:30PM Live |
PI01.00005: Compression of Deuterium Along Isentropes to Multi-TPa Pressures Measured with an Absolute Technique. Invited Speaker: Peter Celliers Equation of state models for deuterium and other light elements have traditionally been tested experimentally along Hugoniots, primarily the principal Hugoniot. The compression path of DT fuel in inertial confinement fusion (ICF) follows isentropes to very high density, where little experimental data measuring the compression exist. We have developed an experimental platform to compress deuterium along isentropes similar to the ICF paths using the National Ignition Facility and to diagnose the density using a radiographic technique. Our approach combines spherical geometry with multi-shock reverberation to achieve near isentropic compression to multi-TPa pressures. Streaked radiography measures the volume of the compressed sample. We will report on initial results from the platform showing compression data at pressures approaching 10 TPa and we will discuss prospects for future improvements. [Preview Abstract] |
Wednesday, November 11, 2020 4:30PM - 5:00PM Live |
PI01.00006: Equation-of-state and transport properties of liquid and solid CO$_{\mathrm{2\thinspace }}$shock-compressed to 1 TPa and 93,000 K Invited Speaker: Linda Crandall Equation-of-state and transport measurements of shock-compressed CO$_{\mathrm{2}}$ at and above the insulating-to-conducting transition reveal new insight into the chemistry of simple molecular systems in the warm-dense-matter regime. In this work, we extend the measured CO$_{\mathrm{2}}$ liquid and solid Hugoniots to 1 TPa, and present the first temperature measurements of shocked CO$_{\mathrm{2}}$ to 93,000 K. CO$_{\mathrm{2}}$ was precompressed in diamond-anvil cells before being dynamically compressed with laser-driven shock waves. Uniquely, the different initial densities in these experiments allow us to extract thermodynamic derivatives, including specific heat and Gruneisen coefficient. At the most extreme conditions we reach, the data is inconsistent with a simple atomic fluid. A constant reflectivity implies a constant carrier density, but a rising specific heat implies increasing degrees of freedom. We conclude that at these conditions, CO$_{\mathrm{2}}$ is more likely an electrically conducting bonded fluid of increasing chemical complexity. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0003856, the University of Rochester, and the New York State Energy Research and Development Authority. A portion of this work was conducted at Lawrence Livermore National Laboratory under Contract Number DE-AC52-07NA27344. [Preview Abstract] |
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