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 YI01: High Energy Density/Laser PlasmasLive Streamed
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Chair: Mark Schmitt, LANL Room: Ballroom 100 A |
Friday, October 21, 2022 9:30AM - 10:00AM |
YI01.00001: First observations of distinct RM growth scenarios for successively shocked interfaces Invited Speaker: Elizabeth C Merritt Inertial Confinement Fusion (ICF) and High-Energy Density Physics (HEDP) experiments experience complicated forcing for instability growth and mix, due to the ubiquitous presence of multiple shocks interacting with perturbations on multiple material interfaces. One common driver of instability growth is successive shocks from the same direction. However, there is a severe lack of analytic work and modeling validation for same-sided successive shocks since they are extremely difficult to achieve with conventional (non-HED) drivers. Successive shocks access a large instability parameter space; idealized fluid theory [Mikaelian, PRA 31(1), 410 (1985)] predicts 15 different interface evolution scenarios for just a single mode. Growth becomes more complex for multi-mode, compressible HED systems. The Mshock campaign is the first experiment in any fluid regime to probe a wide portion of successive shock parameter space. This is enabled by our development of a hybrid direct/indirect drive capable of creating independently controllable successive shocks using a hybrid direct/indirect drive on the NIF. These experiments have delivered the first data capable of rigorously challenging our models and their ability to accurately capture Richtmyer-Meshkov growth under successive shocks. |
Friday, October 21, 2022 10:00AM - 10:30AM |
YI01.00002: Mix at the interface – Diffusion-dominated mixing phenomena probed by high-resolution separated reactant experiments Invited Speaker: Kevin D Meaney Mix is one of the most challenging problems in inertial confinement fusion (ICF). High-Z shell material mixed into the fuel degrades inertial fusion implosions by decreasing compressibility, increasing radiative and conductive losses and reducing confinement time. Because the processes that drive mix span from the scale of the full system down to Kolmogorov scale, it is extremely expensive to do complete simulations and instead simplified models must be used. To benchmark models, highly specific experimental data can be used to constrain and understand which mix mechanisms are important. |
Friday, October 21, 2022 10:30AM - 11:00AM |
YI01.00003: Three-dimensional Modeling of the Impact of Beam Incidence Angle in Laser-Driven Cylindrical Implosions Using the FLASH Code & Ramifications for HED Experiments Invited Speaker: Joshua P Sauppe The advent of high-power laser facilities such as the National Ignition Facility (NIF) has ushered in a new and exciting era in high-energy-density (HED) physics research, and the flexibility of the NIF allows many distinct targets to be fielded beyond the standard indirect-drive inertial confinement fusion (ICF) configuration. Often these physical systems are modeled in more tractable two-dimensional (2D) simulations with assumed symmetry, but this simplification risks inadvertently masking crucial features. Here, we show experimental evidence of a 3D asymmetry in directly driven cylindrical implosions which was not predicted with 2D modeling, and we accurately reproduce this feature in 3D radiation-hydrodynamics simulations. The asymmetry arises as a consequence of the NIF beam geometry and the dependence of laser absorption on beam incidence angle, and it clearly delineates the acceptable limits of 2D design work. This has significant implications for targets with off-normal beam pointing such as polar direct-drive ICF, and it may also be important for a more complete understanding of indirect-drive systems. In particular, differences between experimental data and synthetic data generated from 2D simulations can be misattributed to deficiencies in physics models rather than 3D effects. Our 3D simulations use the FLASH code, which is widely used in the design of laser driven HED systems, and they also show that there is a north/south skew to the drive asymmetry due to the beam configuration. This skew is obscured in radiographs that image down the cylinder axis, complicating inferences of instability growth. Recent experimental results control the drive asymmetry by increasing the power in the 45-degree beams to partially offset the reduced coupling efficiency, in agreement with FLASH simulations. More sophisticated asymmetry mitigation schemes are also discussed. |
Friday, October 21, 2022 11:00AM - 11:30AM |
YI01.00004: The first laboratory observation of transition from electrostatic toward electromagnetic collisionless shocks in laser driven plasmas Invited Speaker: Tim M Johnson
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Friday, October 21, 2022 11:30AM - 12:00PM |
YI01.00005: Laboratory Studies of Laser-Driven, Ion-Scale Magnetospheres on the Large Plasma Device Invited Speaker: Derek B Schaeffer Magnetospheres are a ubiquitous feature of magnetized bodies embedded in a plasma flow. Large planetary magnetospheres in the heliosphere have been studied for decades by spacecraft, while ion-scale ``mini'' magnetospheres have been observed around comets, weakly-magnetized asteroids, and localized regions on the Moon. These mini-magnetospheres provide a unique environment to study kinetic-scale plasma physics, in particular in the collisionless regime, but are difficult to study directly. Laboratory experiments on mini-magnetospheres can thus provide a controlled and reproducible platform for understanding fundamental magnetospheric physics while helping to validate models of larger, planetary magnetospheres. In this work, we present the results from experiments on ion-scale magnetospheres performed on a new high-repetition-rate (1 Hz) experimental platform developed on the Large Plasma Device (LAPD) at UCLA. The experiments utilize a high-energy laser to drive a supersonic plasma flow into a pulsed dipole magnetic field embedded in a uniform background magnetic field. 2D maps of magnetic field with high spatial and temporal resolution are measured with magnetic flux probes and examine the evolution of local and global magnetosphere and current density structures for a range of dipole and upstream parameters. The results are compared to PIC simulations to further identify the magnetospheric structure, kinetic-scale structures of the plasma current distribution, and dynamics of the laser-driven plasma. |
Friday, October 21, 2022 12:00PM - 12:30PM |
YI01.00006: Diffractive Plasma Optics via Ionization for the Generation and Control of High-Power Laser Pulses Invited Speaker: Matthew R Edwards The light intensity that can be produced by large lasers is limited by optical damage. Replacing standard optical components with plasma, which tolerates far higher intensity, provides a route to compact ultra-high-power lasers. However, creating plasma optics with adequate quality has proven difficult, and experimental efficiencies are often much lower than theoretical predictions. Diffractive ionization optics are a specific type of plasma optic that use interfering pump beams to generate wavelength-scale modulations of plasma density that control a delayed probe laser pulse. Because they average over a volume and avoid instabilities, diffractive optics should be more robust to plasma imperfections and inhomogeneity than alternative plasma approaches. Using two separate experimental approaches, avalanche-ionization gratings produced by 100-ps pump pulses and field-ionization gratings driven by femtosecond pulses, we have demonstrated substantially improved diffraction efficiency of intense femtosecond pulses from ionization gratings. For avalanche gratings, up to 60% of the incident probe energy can be redirected into a stable, focusable beam [1]. We have shown that the evolution of the grating affects the diffracted beam and directly measured the plasma fringes that make up the fine-scale grating structure. These experiments have produced ionization structures with plasma density and optical quality near what is required for diffractive plasma lenses [2] and compressors [3], suggesting the addition of ionization optics to the component toolkit for compact high-power laser systems. |
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