Scaling of high-Z laser plasmas with energy and pulselength

Abstract

The authors have used LASNEX modelling, which matches most current experiments, to study the scaling of high-Z laser-target interactions to the higher laser energies and longer pulses appropriate to future inertial fusion targets. Results are presented for the irradiation of gold disk targets with 0.26 μm light at a normal incident intensity of 3 × 1014W·cm−2 and incident energy varying from 102J to 107J. For both low- and high-energy cases, steep plasma profiles develop near the critical density of the laser light. In the absence of filamentation, the combination of large electron density gradients at densities substantially below the critical density and strong collisionality due to the high-Z plasma appears to suppress stimulated Raman backscattering and the 2ωpe instability. There is some possibility of stimulated Raman sidescatter in the high-energy case. Using one-dimensional plasma contours, filament generation is strongest at early times for the 107 J case, and weak at all times for the 102 J case. The radiation emission is largely generated near the critical surface, and the conversion efficiencies are of the order of 0.6 and constant to within ±0.1. There is weak variation with energy in global flow parameters.