Plasma filling in reduced-scale hohlraums irradiated with multiple beam cones

Abstract

The radiation temperature achieved inside a hohlraum, a high-Z cylindrical cavity heated by high-power lasers, is limited by plasma filling of ablated wall material. Recent work [Dewald et al., Phys. Rev. Lett. 95, 215004 (2005)] tested radiation temperature limits in a simple on-axis laser-hohlraum geometry and validated an analytic plasma-fill model. The experiments reported here use several cones of beams to heat a 600μm diameter hohlraum. Thin-walled images show the time evolution: plasma stagnation followed by plasma filling of the hohlraum cavity. Features in the Raman backscatter spectra are correlated to the thin-walled images to measure a fill time. The quantity of hard x rays produced by hot electrons is proportional to the time left in the laser pulse after the fill time. Simulations using the radiation-hydrodynamic code LASNEX and the analytic plasma-fill model predict plasma filling consistent with the data. LASNEX predicts a much higher electron temperature than the analytic model.