No abstract

Microballoons filled with an equimolar deuterium-tritium mixture and coated with a plastic ablator of variable thickness are imploded by the eight-beam Octal laser (X = 1.06 jum; 0.6 TW). An X-ray r diagnostic with space-time resolution is used to analyse the implosion of the targets designed to the highest /pdr. The experimental results are compared with numerical simulations performed by a one-dimensional J Lagrangian code. A DT density of about 2 gem" 3 is obtained; the transition from an exploding-pusher regime to a more ablative one is analysed on the basis of the evolution of the preheat, the hydrodynamic efficiency and the density and temperature performance.

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The laser program developed at the Centre d'Etudes de Limeil-Valenton, Saint-Georges, France (CEL-V) is concentrated on a systematic investigation of indirect drive fusion; by comparison with direct drive, this process is expected to provide the required irradiation uniformity with relaxed constraints on laser beam quality. The main concerns are radiative transfer and preheat, hydrodynamic instabilities, and high-density X-ray driven implosions. Ablative implosion experiments have been conducted with the two beams at the Phebus facility (5 kJ, 1.3 ns, 0.35 jim). Symmetry was proved to be controlled by the casing structure, following scaling laws describing hohlraum physics. A compressed DT densitỹ 100 p 0 (fio liquid DT density) has been deduced from activation measurements. Different aspects of the soft X-ray transfer processes, and particularly of the ablation of a low-Z material, which drives the capsule implosion, are dealt with in detailed investigations. Reported here are results on X-ray reemission and penetration in several materials, and on induced hydrodynamics of accelerated foils. The laser energy required to reach fuel ignition conditions has been evaluated from numerical simulations as well as from analytical models, taking into account hohlraum physics, capsule implosion, hot spot formation, and burn propagation. Several crucial parameters have been drawn, the most important being the radiation temperature. A target gain in the order of 10 appears achievable with a 2-MJ laser.