Progress on LMJ targets for ignition

Abstract

Targets designed to produce ignition on the Laser Megajoule (LMJ) are being simulated in order to set specifications for target fabrication. The LMJ experimental plans include the attempt of ignition and burn of an ICF capsule with 160 laser beams, delivering up to 1.4 MJ and 380 TW. New targets needing reduced laser energy with only a small decrease in robustness have then been designed for this purpose. Working specifically on the coupling efficiency parameter, i.e. the ratio of the energy absorbed by the capsule to the laser energy, has led to the design of a rugby-ball shaped cocktail hohlraum; with these improvements, a target based on the 240-beam A1040 capsule can be included in the 160-beam laser energy-power space. Robustness evaluations of these different targets shed light on critical points for ignition, which can trade off by tightening some specifications or by preliminary experimental and numerical tuning experiments.

Progress in indirect and direct-drive planar experiments on hydrodynamic instabilities at the ablation front

“…Current Laser M egajoule (LMJ) and NIF plastic ablator (CHGe) point designs 16,59 rely on the so-called graded dopant ablator 15 to minimize RTI growth during the capsule implosion. The graded dopant allows for both a minimal instability at the ablation front, and little or no instability at the fuel-ablator interface, where the dopant gradient brings the ablator density smoothly in agreement with the fuel density.…”

Hugoniot and mean ionization of laser-shocked Ge-doped plastic

“…[6][7][8] CEA also developed similar capsules for the Laser M egajoule. 9 These graded dopant capsules pusher material structure consists of an external undoped plastic layer (typically 100 lm thick) above deeper layers doped with varying atomic fractions of Ge. Getting closer to the fuel, dopant fraction increases then decreases to zero leaving an undoped plastic layer in contact with the cryogenic fuel (Fig.…”