Shock propagation, preheat, and x-ray burnthrough in indirect-drive inertial confinement fusion ablator materials

Abstract

The velocities and temperatures of shock waves generated by laser-driven hohlraum radiation fields have been measured in indirect-drive inertial confinement fusion (ICF) capsule ablator materials. Time-resolved measurements of the preheat temperature ahead of the shock front have been performed and included in the analysis. Measurements of the x-ray burnthrough of the ablation front and the ablator x-ray re-emission have also been made in the Cu-doped beryllium, polyimide, and Ge-doped CH ablator samples. The experiments utilize 15 beams of the University of Rochester Omega Laser [Soures et al., Phys. Plasmas 3, 2108 (1996)] to heat hohlraums to radiation temperatures of ∼120–200 eV. In the experiments, planar samples of ablator material are exposed to the hohlraum radiation field, generating shocks in the range of 10–50 Mbars. The experimental results are compared to integrated two-dimensional Lasnex [G. B. Zimmerman and W. L. Kruer, Comments Plasma Phys. Control. Fusion 2, 51 (1975)] calculations, in which the measured laser pulse is used as input and the time-dependent ultraviolet shock breakout and soft x-ray ablator burnthrough are calculated quantities. It is found that proper calculation of the time-dependent hohlraum x-ray flux, including spectral content, and the ablator opacity will be essential for obtaining the level of predictive capabilities required for the thermonuclear ignition of an ICF capsule at the U.S. National Ignition Facility [E. I. Moses, Fusion Technol. 44, 11 (2003)].