The effects of pre-mix on burn in ICF capsules

Abstract

Directly driven implosions at the Omega laser have tested the effects of pre-mix of Ar, Kr, and Xe in D2 + 3He filled glass micro-balloons. Diagnostics included: D+D and D+T neutron yields, D+3He proton yields and spectra, Doppler broadened ion temperatures, time dependent neutron and proton burn rates, and time gated, high energy filtered, X-ray images. Yields are better calculated by XSN LTE than by non-LTE. Yields with a small amount of pre-mix, atom fractions of ∼5e-3 for Ar, 2e-3 Kr, and Xe for 5e-4, are more degraded than calculated, while the measured ion temperatures are the same as without pre-mix. There is also a decrease in fuel ρr. The neutron burn histories suggest that the early yield coming before the reflected shock strikes the incoming shell is un-degraded, with yield degradation occurring afterwards. Adding 20 atm % 3He to pure D fuel seems to produce a similar degradation. Calculated gated X-ray images agree with observed when the reflected shock strikes the incoming shell, but are smaller than observed afterward. This partially explains yield degradation and both the low fuel and whole capsule ρr's observed in secondary T+D neutrons and slowing of the D+3He protons. Neither LTE on non-LTE captures the degradation by 3He or at low pre-mix levels, nor matches the large shell radii after impact of the reflected shock.