Experimental investigation of radiation transport in soft-x-ray-heated aluminum plasma

Radiation transport in soft-x-ray-heated aluminum plasma was experimentally investigated. A thin foil was heated by intense soft x rays. We measured spectral transmittance of the foil with time-resolving spectroscopically probing technique. Occurrence of ionization burnthrough was clearly shown. The spectral transmittance and its temporal behavior were understood with two-layer model and burnthrough-front propagation. Velocity of the burnthrough-front propagation was consistent with the previous shock-wave experiment. The investigation reported here concludes that soft-x-ray-driven low-Z plasma ablation can be regarded as subcritical-limit deflagration. (author)