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 BP12: Poster Session: ICF: Hydrodynamic Instabilities (9:30am - 12:30pm)On Demand
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BP12.00001: A Hydrodynamic Lengthscale for Characterizing Stagnation Seth Davidovits It is generally challenging to infer the hydrodynamic organization of the stagnation plasma in compression experiments, owing to the short timescales and small spatial scales in such plasmas and the frequent diagnostic necessity to integrate over sight lines. Here we present an analysis technique that, using time-resolved (through experimental repeatability), but spatially integrated, measurements of stagnating plasma, allows for the inference of a hydrodynamic length scale. We show that, theoretically, this inferred length scale can be related to the degree to which a stagnation is hydrodynamically ``ideal''. Applying this analysis technique to both data from a Z-pinch compression which may be turbulent at stagnation, and synthetic data from a 2D simulation of the same pinch, which stagnates axisymmetrically and without turbulence, we find initial evidence to support this theoretical prediction. [Preview Abstract] |
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BP12.00002: Instability Growth in Cylindrical Implosions at Convergence Ratio 5 Joshua Sauppe, Sasikumar Palaniyappan, Benjamin Tobias, Kirk Flippo, John Kline, Rebecca Roycroft, Paul Bradley, Steven Batha, Krista Stalsberg, William Gammel, Otto Landen, Dov Shvarts Hydrodynamic instability growth is a key factor limiting performance in inertial confinement fusion implosions, and growth is further enhanced in convergent geometry due to Bell-Plesset effects. Direct measurements in spherical systems are challenging, but cylindrical systems include the effects of convergence while retaining diagnostic access to the unstable interface. We present results from laser-driven cylindrical implosions at convergence ratio CR=5 (CR=initial radius/final radius), the highest yet achieved in these experiments, for three different sizes of target. Hydrodynamic growth of an initial perturbation occurs through a mix of the buoyancy-driven Rayleigh-Taylor instability during the deceleration phase and Bell-Plesset effects, and analytic models are employed to identify key differences in these targets and previous experiments at lower CR. The experimental results compare favorably with radiation-hydrodynamics modeling. Designs that push to higher CR through the use of gas-filled cylinders are presented. [Preview Abstract] |
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BP12.00003: Investigating hydrodynamic instabilities in high energy density systems on the Z Machine D. A. Yager-Elorriaga, P. F. Knapp, F. W. Doss, M. R. Martin, D. E. Ruiz, C. Jennings, A. J. Porwitzky, C. E. Myers, L. Shulenburger, T. Mattsson We present experimental data for two platforms investigating the Richtmyer-Mehskov process and interfacial feedthrough on the Z Machine at Sandia National Laboratories. Cylindrical liners filled with liquid deuterium are magnetically imploded with \textgreater 20 MA of current, driving a converging shock that propagates towards the central axis and generating a high plasma-beta system suitable for investigating HED hydrodynamical processes. The first platform investigates the interaction of this shock with a solid beryllium rod machined with sinusoidal perturbations that grow due to the Richtmyer-Meshkov process. The second platform replaces the on-axis rod with a cylindrical liner, enabling investigation of the feedthrough of these instabilities to the inner liner surface. Finally, future experimental platforms presently under development will be discussed, including (1) a variant where the outer cylindrical liner~is~replaced with a~quasi-spherical liner to drive strong converging shocks that interact with a nested spherical target, enabling the investigation of Bell-Plesset effects, and (2) an exploding cylindrical liner system to study the Rayleigh-Taylor instability driven for \textgreater 100 ns to a highly nonlinear regime. SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525 and LANL is managed and operated by Triad National Security under DOE NNSA contract 89233218CNA000001 [Preview Abstract] |
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BP12.00004: Evaluation of the use of two-photon polymerization printed structures in multi-shell ICF targets Brett Scheiner, Mark Schmitt, Derek Schmidt, Lynne Goodwin, Frederic Marshall, Philip Nilson Recent interest in the fielding direct drive multi-shell targets on the NIF[1,2] has highlighted the need for a low density support structure to support the inner shell inside of the ablator and to avoid energy loss in the acceleration and collision process. We evaluate the use of low density (5 mg/cc) two-photon polymerization printed lattices for this purpose. Simulations of 1D thin shells are used as a surrogate for the lattice struts and are used to illustrate qualitative behavior of the lattice under radiation driven heating by x-rays from the corona. Sufficiently fine lattices are shown to isotropize before the shell collision. High resolution Fresnel zone plate images from experiments on OMEGA are used to evaluate the uniformity of the post-collision inner shell. [1] Kim Molvig et al. Phys. Rev. Lett. 116, 255003 (2016) [2] S. X. Hu et al. Phys. Rev. E 100, 063204 (2019) [Preview Abstract] |
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BP12.00005: Preliminary Double Cylinder Target Design for Study of Hydrodynamic Instabilities in Multi-shell ICF Rebecca Roycroft, Joshua Sauppe, Paul Bradley The use of cylindrical implosions to study hydrodynamic instability growth for ICF applications [S. Palaniyappan, et al. Phys. Plasmas \textbf{27}, 042708 (2020)] is attractive, as cylindrical implosions allow for easier diagnostic access (on axis) while retaining convergence effects. In this work, we aim to use the established cylindrical implosion platform to inform the double shell ICF campaign [D. Montgomery, et al. Phys. Plasmas \textbf{25}, 092706 (2018)] and other multi-shell ICF concepts. We are designing a double cylindrical target as an analogue to the double shell ICF capsule in order to study hydrodynamic instability growth on the high-Z inner shell. We present preliminary design simulations from xRAGE [M. Gittings, et al. Comput. Science and Discovery \textbf{1}, 015005 (2008)], where we have scanned cylindrical target dimensions in 1D to optimize the surrogacy to spherical double shell implosions. In particular, we attempt to match the Atwood number and acceleration profile of the inner cylinder, as well as the kinetic energy transfer from the outer to the inner cylinder. We evaluate the feasibility of fielding this target at OMEGA, where we plan to measure the instability growth on the inner shell using radiography of the implosion. [Preview Abstract] |
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BP12.00006: Coupling Radiation-Hydrodynamics Simulation with Machine Learning for Double Shell Capsule Design Optimization Nomita Vazirani, Michael Grosskopf, Paul Bradley, Scott England, Wayne Scales Advances in machine learning provide the ability to leverage data from expensive simulation of high-energy-density experiments to significantly cut down on computational time and costs associated with the search for optimal design of inertial confinement fusion (ICF) experiments. Machine learning methods can use these predictive physics simulations to identify designs of high predicted performance as well as novel designs with high uncertainty in performance that may hold unexpected promise. Here we present our application of cutting-edge Bayesian optimization methods to the design optimization of inertial confinement fusion experiments - specifically the Los Alamos National Lab double shell campaign. This is an alternative approach to achieving fusion by indirectly driving a double shell target inside a hohlraum. The double shell target is significantly less sensitive to laser plasma interactions and able to achieve burn at lower convergence ratios and implosion velocities. However, the target is more complicated to build and analyze, resulting in lower potential yield and an increased number of hydrodynamically unstable interfaces. By applying machine learning tools to the simulation design, we aim to optimize the target geometry and experimental laser pulse to mitigate the hydrodynamic instabilities and improve yield. [Preview Abstract] |
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BP12.00007: Formation and Evolution of Fluid Instabilities in Double Shell Capsule Implosions using 2D Hydrodynamic Simulations with Surface Roughness Irina Sagert, R. Sacks, D. Stark, J. P. Sauppe, E. Loomis, D. Montgomery, B. Haines, P. Keiter, S. Palaniyappan, P. Amendt, H. Xu, H. Huang, T. Cardenas, S. Finnegan, J. Kline We study the formation and development of fluid instabilities in Double Shell capsule implosions via computational fluid dynamics simulations. In 1D simulations, we perform a systematic study regarding the role of the capsule's foam cushion, its density and material, where, for the latter, we use CH and SiO2 foam. In addition, we test the impact of Cr dopant in the Be tamper. These studies, which determine the Atwood numbers at the capsule material interfaces throughout the implosion, are followed up by 2D simulations with the hydrodynamics codes xRAGE and Hydra. We compare the outcomes of both codes in regard to the time evolution of Rayleigh-Taylor and Richtmyer-Meshkov instabilities that develop as a consequence of including experimentally obtained surface roughness spectra on the capsule's shells. Finally, we determine Reynolds numbers in Double Shell capsule implosions and evaluate the possible formation and role of turbulence in the fuel. [Preview Abstract] |
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