A systematic experimental study is conducted in order to measure the density and configuration of the plasma by holographic interferometry, and the ion temperature and level of turbulence by cooperative laser scattering. The two measurements are done in various phases of the plasma, before, during, and after the filament breakup. Suprathermal scattering during the filament phase and the successive development of an ionizing wave are evidenced for the first time. The anisotropy of the neutron emission is found to exist in all regimes by the simultaneous measurement of the energy spectra in two directions. A possible explanation of the neutron emission is given. It is concluded that nonthermal processes play an essential role in the plasma focus.
A significant effort has been made recently at CEL-V to improve laser facilities. OCTAL, the eight beam, 2 kJ laser, has been equipped with phosphate glass and KDP frequency tripling systems. PHEBUS, a two beam 20 kJ neodymium glass laser based on NOVA technology was denned and built and will be tested in early 1986 in close collaboration with Lawrence Livermore National Laboratory.In the field of diagnostics, the development of soft X-ray emission analysis has been emphasized.Most of the recent experimental results have been obtained at a short wave-length (0·35 μm). They deal with the effect of non-uniform illumination, 2D hydrodynamics with either plane or spherical targets, and the study of thermal transport inhibition.
1.3-keV X-ray backlighting of microballoons imploded with 0.8-TW, 50-ps Nd-glass-laser pulses has been performed early during the irradiation. Transmission measurements have been interpreted in terms of fast-electron energy deposition. Targets with the thinnest walls are shown to be pre-heated up to more than 200 eV.
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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