Thermal Transport Measurements in Six-Beam, Uv Irradiation of Spherical Targets

摘要

Thermal transport, mass ablation rates, and preheat have been studied in spherical irradiation at lambda = 351 nm, using six of the 24 beams of OMEGA. Mass ablation rates are higher in 351 nm than at 1054 nm irradiation, even when compared at the same absorbed irradiance. Similarly to the case of 1054 nm irradiation essentially uninhibited transport was found at 351 nm. However, the low gradient temperature profile at the heat front characteristic of the experiments at 1054 nm was not observed here nor was observed the large difference between uniform and tight focus irradiation of spherical targets as at 1054 nm irradiation. Ablation pressures derived from charge collector data (more conservative than by using the spectroscopic results) rise from 10 to 100 Mbar for irradiance in the range of 4 x 10 exp 13 to 9 x 10 exp 14 W/cm exp 2 . Preheat as measured by K/sub alpha / radiation from titanium is shown to be due to radiative rather than fast electron preheat. Plastic coating of the target can reduce preheat to less than 1% of the absorbed laser energy. (ERA citation 09:042433)