Subpercent-Scale Control of 3D Low Modes of Targets Imploded in Direct-Drive Configuration on OMEGA

Abstract

Multiple self-emission x-ray images are used to measure tomographically target modes 1, 2, and 3 up to the end of the target acceleration in direct-drive implosions on OMEGA. Results show that the modes consist of two components: the first varies linearly with the laser beam-energy balance and the second is static and results from physical effects including beam mistiming, mispointing, and uncertainty in beam energies. This is used to reduce the target low modes of low-adiabat implosions from 2.2% to 0.8% by adjusting the beam-energy balance to compensate these static modes.

Impact of stalk on directly driven inertial confinement fusion implosions

“…The goal with the time-resolved x-ray imaging was to get an x-ray measurement of the target motion during the implosion for comparison with the nuclear measurements, using the method described in Ref. 54. This also involved fielding a solid (non-imploding) CH sphere as a time-resolved position reference (shot 87050).…”

The National Direct-Drive Inertial Confinement Fusion Program

“…Direct measurements will eliminate any assumptions associated with diagnosing the on-target intensity using equivalent-target-plane diagnostics. Proof-of-principle experiments using implosions of gas-filled plastic shell targets have demonstrated subpercent-scale control of low modes at a CR of 3 with 3D gated x-ray imaging [12]. This target-physics experimental technique provides an independent check on the direct measurements of the laser drive.…”

“…The strategy of the enhanced-capability approach is highlighted in figure 3 showing the areal density plotted as a function of the primary neutron yield with the calculated contours of hot-spot pressure overlaid. It involves improvements to the OMEGA laser [1][2][3], targets [8], and diagnostics [9][10][11][12], and new modeling and simulation capabilities [13][14][15][16][17][18], to increase the areal density and yield of the implosion. These improvements will be applied to the α ~ 3.5 DT cryogenic implosion where the highest hot-spot pressure (56 ± 7 Gbar) was achieved with an energy-scaled generalized Lawson parameter of 0.6-0.64 [27], which extrapolates to 125 kJ of fusion yield on a symmetric NIF LDD implosion [30].…”

“…The 100 Gbar Campaign on OMEGA explores the formation of hot-spot conditions relevant for ignition at the megajoule (MJ) scale using hydrodynamically scaled implosions of layered DT cryogenic targets [1][2][3]. The enhancedcapability approach of the 100 Gbar Campaign involves improvements to the OMEGA laser [1][2][3], targets [8], diagnostics [9][10][11][12] along with new modeling and simulation capabilities [13][14][15][16][17][18] to increase the areal density and yield of the implosion. While these improvements are underway, the 100 Gbar Campaign has a parallel effort using a statistical approach to search for the optimum DT cryogenic implosion on OMEGA having the highest combination of areal density and primary neutron yield using the current capabilities [19].…”

3D Simulations Capture the Persistent Low-Mode Asymmetries Evident in Laser-Direct-Drive Implosions on OMEGA

“…These may arise from target defects, small-scale structure in the intensity profile of the laser, and other experimental constraints and errors. Control and mitigation of low-mode (long wavelengths) perturbations is a key milestone to improving implosion performances, be it in Indirect-Drive (ID) [1][2][3][4][5] or Direct-Drive (DD) configurations [6][7][8]. In experiments, many different sources of low-modes may contribute to the final hotspot shape.…”