Bulletin of the American Physical Society
23rd Biennial Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 68, Number 8
Monday–Friday, June 19–23, 2023; Chicago, Illinois
Session R04: Warm Dense Matter |
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Chair: Andrew Krygier, Lawrence Livermore National Laboratory Room: Sheraton Grand Chicago Riverwalk Chicago 6 & 7 |
Wednesday, June 21, 2023 11:15AM - 11:30AM |
R04.00001: Reflectivity extinction in strongly-shocked liquid deuterium Peter M Celliers, Marius Millot, Harry F Robey, Thomas R Boehly, Gilbert W Collins, Otto L Landen Optical velocimetry from reflecting shock fronts in transparent media is a common application at high energy density facilities such as the National Ignition Facility (NIF). The primary application on the NIF is to tune the shock sequence for capsule implosions in inertial confinement fusion experiments. Shock tuning on the NIF is limited by reflectivity extinction or self-blanking to a maximum shock pressure of 3 TPa and velocity of 150 km/s in liquid deuterium. With the possibility for driving shocks well into the multi-TPa range for many materials at current and future facilities an understanding of the limits of optical velocimetry is becoming important. The underlying mechanism for reflectivity extinction is upstream photoionization of the unshocked material; however, the details involve a level of complexity that is not immediately evident. We describe a model for shock front reflectivity in liquid deuterium that matches observations and predicts a wavelength dependence. Application of the same modeling framework is possible for other common transparent shock materials such as quartz, fused silica, diamond and plastics. |
Wednesday, June 21, 2023 11:30AM - 11:45AM |
R04.00002: Measurements of super-sonic to sub-sonic transition within SiO2 foams at OMEGA Dean R Rusby, Shon T Prisbrey, Felicie Albert, Allen Toreja, Robert E Tipton, Stephen D Murray A comparison of simulated shock interactions with x-ray ablation fronts to experimental data has shown some disagreement. Specifically, the measured shock front history produced does not show the sharp increase in velocity predicted by a reflected shock interacting with an x-ray ablation front. To study the interaction of strong shocks interacting with diffuse pressure fronts, we developed a platform to study the transition of a supersonic shock into a subsonic shock within silica aerogel on the OMEGA laser facility. The target package consists of a halfraum that is driven by 21 Omega beams to create an ~110 eV radiation drive, and a cylinder that contains a low density (32 mg/cc) silica (SiO2) aerogel. The radiation from the halfraum induces a supersonic radiation transport within the aerogel that travels along the cylinder. Reduction of the energy density in the radiation front along the cylinder transitions radiation transport from the supersonic to the subsonic regime and creates a pressure front which creates a pressure-induced density perturbation within the aerogel. The time history of the density change is studied by using X-ray radiography and a time-gated , 4-strip, x-ray detector. Using hydrodynamic simulations of the entire experiment, we can match the experimental results with simulations. |
Wednesday, June 21, 2023 11:45AM - 12:00PM |
R04.00003: A comparison of hydrodynamic code simulations with experimental data for short pulse laser driven shocks in aluminum Sophie E Parsons, Michael R Armstrong, Ross E Turner, Ka Ming Woo, Harry B Radousky, Javier E Garay, Farhat N Beg In order to better understand the impact of the laser absorption physics and equation of state tables used in hydrodynamic simulations on the maximum simulated pressures at the ultrafast (100ps) time scale, we conducted a joint theoretical and experimental campaign. Using a 500$mu$m aluminum ablator and a 1mm sapphire tamper, we conducted a series of experiments on an ultrafast table top laser system to determine how pressure generation varied with laser intensity. The samples were shocked to a maximum pressure randing from 20-40 GPa, corresponding to laser energies ranging from 10$mu$J to 40$mu$J. We then used this experimental data to compare it to two different hydrodynamic codes: DRACO and FLASH. These codes were chosen to compare an inverse bremstralung code (FLASH) to a code that includes more laser absorption and initial plasma formation physics (DRACO). |
Wednesday, June 21, 2023 12:00PM - 12:15PM |
R04.00004: Observation of Laser Ablation in Al Using Ultrafast X-Ray Diffraction Harry B Radousky, Michael R Armstrong, Sophie E Parsons, Ka Ming Woo, Farhat N Beg The mechanisms of laser matter interactions with an ablator such as Al, are fundamental to understanding how strong shock waves are driven into materials as a function of laser energy and pulse duration. Using 130 fs x-rays at the LCLS Materials at Extreme Conditions (MEC) beamline, we interrogated the initial ablation of Al driven by 120 ps pulses and observed the strength of the shock induced and the amount of material which was ablated. The samples consisted of 2 microns of Al deposited on 2 microns of Zr, which for this study served as a calibrant. The Al samples were dynamically compressed to pressures up to 100 GPa, driven with energies in the range of 2.5-250 mJ. The experimental observations were compared to laser matter interaction simulations using two different hydrodynamic codes: DRACO and FLASH. These codes were chosen to compare the impact of laser absorption physics included in the simulation on the predicted ablation depths. |
Wednesday, June 21, 2023 12:15PM - 12:30PM |
R04.00005: Proposed Code Validation of Convergent Shock Interactions Shon T Prisbrey, Felicie Albert, Dean R Rusby, Allen Toreja, Robert E Tipton Simulation in 2D radiation hydrodynamic codes of experimental convergent geometries, such as those found in hohlraum simulations, inertial confinement fusion, or converging, cylindrical experiments (Sauppe, J. P. et al, Phys. Plasmas 26, 042701 (2019); doi: 10.101063/1.5083851) can lead to the prediction of on-axis features that may not be experimentally present. Of concern is the numerical nature of physics models and their interactions near the axis of symmetry where computational, numerical noise can impact the calculations occurring in the simulations. We propose a possible experimental platform that could be fielded at the National Ignition Facility that can measure the formation of an on-axis feature with sufficient resolution that it could be compared to simulation and used to validate the predicted on-axis shock interaction in a cylindrically convergent geometry. We will show that the radiation from a hohlraum can be used to create a cylindrically converging shock and that experimental measurements can be taken to characterize the uniformity of the converging shock and the resultant interaction. Such measurements can be used to validate a simulation approach that accurately captures the results of an on-axis, convergent-shock interaction. |
Wednesday, June 21, 2023 12:30PM - 12:45PM |
R04.00006: Line Positions in Warm Dense Matter Trinity Thelen, Christopher J Fontes, Daniel A Rehn, Charles Starrett Transition energies in dense plasmas, in which an atom is excited from some initial state to a final state, are challenging to model due to the need for an accurate treatment of both atomic and plasma physics. Experiments have been carried out at the LCLS that measured the K-edge and K-alpha emission from magnesium, aluminum, and silicon plasmas [Ciricosta et al, Nat. Comm. 2016]. We use a modified version of the Tartarus average atom code [Starrett et al, CPC 2019] to model ions in dense plasmas and calculate the K-edges and K-alpha to compare with these experiments. We find that our calculations agree with the experiments if we assume K-shell ionization from a cold plasma (1eV), and the subsequent K-alpha de-excitation from a heated plasma. The results give insight into the timescale and temperature dependence of electron transitions and ionization, as well as the plasma effects that must be taken into consideration. |
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