Fuel-shell interface instability growth effects on the performance of room temperature direct-drive implosions

Abstract

Performance degradation in direct-drive inertial confinement fusion implosions is caused by several effects, one of which is Rayleigh–Taylor (RT) instability growth during the deceleration phase. In room-temperature plastic target implosions, deceleration-phase RT growth is enhanced by the density discontinuity and finite Atwood number at the fuel–shell interface. In this paper, the Atwood number of the interface is systematically varied by altering the ratio of deuterium to tritium (D:T) within the DT gas fill. It is shown that the stability of the interface is best characterized by the effective Atwood number, which is primarily determined by radiation heating of the shell and not by the composition of the fuel. Both simulation and experimental data show that yield performance scales with the fraction of D and T present in the fuel and that the observed inferred ion temperature asymmetry (ΔTi=Timax−Timin), which indicates the presence of long-wavelength modes, has a small sensitivity to the different D:T ratios.