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 GI01: Inertial Confinement Fusion ILive Streamed
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Chair: Brian Spears, LLNL Room: Ballroom 100 A |
Tuesday, October 18, 2022 9:30AM - 10:00AM |
GI01.00001: Measuring dark mix at stagnation of cryogenically layered capsule implosions at the NIF Invited Speaker: Benjamin Bachmann Understanding the physics and quantifying the impact of ice-ablator mix has been a decadal effort in Inertial Confinement Fusion. Here we present a measurement of the 'dark' mix that resides in the cool and dense fuel layer surrounding the fusion hotspot at capsule stagnation. The mix mass that we infer to be located outside of an ignition seeding hotspot can reduce fuel compression at stagnation and adversely affect burn-propagation when it turns into hot mix as the burn-wave propagates through the initially cool, mix contaminated, ice layer. These experiments are enabled by combining separated nuclear reactants and x-ray emission measurements which probe the burn-weighted amount of mix mass present in the hotspot periphery and the hotspot itself. Systematically changing the ice layer thickness effectively probes how much ablator material mixes into different ice layer depths of an equivalent full layer thickness ignition capsule and demonstrates how increasing the ice layer thickness is a promising lever for cleaner, more efficient burn propagation. |
Tuesday, October 18, 2022 10:00AM - 10:30AM |
GI01.00002: Gamma-Ray Measurements of Burning Plasmas achieved in Inertial Fusion Invited Speaker: Yongho Kim Reaction history measurements, such as the time of peak reaction rate (i.e., bang time) and how long thermonuclear conditions are maintained (i.e., burn width), are fundamental information indicating the dynamics of inertial confinement fusion. Fusion gammas provide a direct measure of nuclear reaction rates (unlike x-rays) without being compromised by Doppler spreading (unlike neutrons), however spectral information of fusion gammas is not readily available. In a deuterium-tritium fusion, the R-matrix nuclear analysis has predicted two branches of gamma rays (i.e., the transition to the ground state (g0) and the transition to the intermediate excited state (g1)). There have been large inconsistencies especially when determining state g1, the team of LANL/AWE were able to confirm for the first time the presence of two gamma branches and reported a ratio of g0 : g1 = (2.1 ± 0.4) : 1 and eliminate ambiguity in the fusion gamma measurement. |
Tuesday, October 18, 2022 10:30AM - 11:00AM |
GI01.00003: Experimental measurement of improved stability to achieve higher compression in ICF Invited Speaker: Alexandre Do A key objective toward achieving high gain in Inertial Confinement Fusion (ICF) is to achieve high compression. In recent indirect-drive capsule implosions on the National Ignition Facility (NIF), the SQ-n campaign is testing the hypothesis that reducing the hydrodynamic growth of perturbations is key to achieving higher compression of high-density carbon (HDC) based-ablators for ICF. The technique is designed around a 2-shock design, called BigFoot, tested on NIF in 2016 – 2019, which features good stability with the drawback of lower compression inherent to the intentional higher adiabat of this design. A “Scaling” and “Quality” importance of the implosion has led to a new campaign, called SQ-n, that is looking to reach higher compression using a ramped foot pulse shape to minimize early-time hydrodynamic instability growth and an optimized ablator dopant distribution. Three subsets of experiments were conducted within the SQ-n campaign to study the implosion symmetry, backscatter, stability, and compression. Keyhole experiments using VISAR enabled the development of a gently accelerating shock velocity as well as constraining models of foot drive and symmetry. The ice-ablator interface acceleration, important for managing the Richtmyer-Meshkov phase growth, was observed with Refraction Enhanced Radiography (RER) and the ablation front growth was measured using radiography of pre-imposed modulations. Finally, layered THD and DT implosions demonstrate higher compression has been achieved. Results of these experiments will be presented and discussed. LLNL-ABS-836109. |
Tuesday, October 18, 2022 11:00AM - 11:30AM |
GI01.00004: Theory and simulation of cross-beam energy transfer mitigation through increased laser bandwidth Invited Speaker: Alexander Seaton Recently, techniques have been proposed to increase laser bandwidth in inertial confinement fusion (ICF) implosions. These bandwidths could provide transformational improvements in ICF performance by mitigating laser-plasma and hydrodynamic instabilities. This talk will examine the impact of bandwidth on the cross-beam energy transfer (CBET) instability. A generalized linear theory for CBET will be presented that incorporates effects of bandwidth[1]. This is compared with data from linearized fluid simulations performed with the LPSE code, which satisfy many of the assumptions made by the theory and shows good agreement with the theoretical predictions. Particle-in-cell simulations of CBET using the VPIC code have also been performed, allowing an investigation of the nonlinear CBET regime. |
Tuesday, October 18, 2022 11:30AM - 12:00PM |
GI01.00005: Control of low-mode drive asymmetry in an efficient long pulse low-density filled hohlraum Invited Speaker: Nobuhiko Izumi One anticipated advantage of a 4-shock CH design (~2x longer laser pulses than typical HDC designs) is the ability to achieve high compression of the DT fuel, essential for the design of a high gain target. It has been shown experimentally that hohlraums filled with gas at low densities (< 0.6 mg/cc) have higher efficiency because of reduced backscatter losses due to laser plasma instabilities. Thus, combining longer drives in low gas-density hohlraum has been considered challenging since high-Z plasma ablated off the hohlraum wall is less tamped and will potentially interfere with the transport of the inner cone beam power during the last stages of the drive pulse. |
Tuesday, October 18, 2022 12:00PM - 12:45PM |
GI01.00006: Marshall N. Rosenbluth Ph.D. Thesis Award: Alpha-heating analysis of burning plasma experiments on the National Ignition Facility and their companion dudded fuel implosions. Invited Speaker: Alison R Christopherson In indirect drive inertial confinement fusion, a cryogenic layer of deuterium and tritium is compressed to high pressures and temperatures via irradiation by x-rays from a laser-driven hohlraum.At stagnation, the final fuel assembly consists of a relatively low density (~ 100 g/cc) and high temperature (~10 keV) “hot spot” confined by the relatively cooler (~ 1 keV) and denser (~1000 g/cc) “shell”.Last year, ignition was achieved in the laboratory for the first time whereby alpha particle heating of the hot spot propagated a burn wave into the dense shell.Here, we present a comprehensive analysis of the alpha-heating levels in this experiment which includes quantifying both the Lawson parameter and the fusion yield enhancement due to this alpha particle self-heating.We also report on a series of follow-up experiments where the DT fuel was replaced with a THD duded fuel mixture to measure the fusion yield output in the absence of alpha particle self-heating.
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