The effect of rate of rise to peak power on x-radiation drive in hohlraums at the National Ignition Facility

Modern hohlraum simulations of inertial confinement fusion (ICF) experiments must incorporate empirical multipliers on the laser input power to match experimental data. The laser pulse has a low-power picket, and a long, low-power trough before rising to peak power, and each portion of the laser pulse incorporates separate multipliers. To understand the physical mechanisms involved in the discrepancies, a two-shot campaign investigated the effect of the rate of rise to peak power on the resulting x-radiation drive. The experiments used a ViewFactor hohlraum (truncated hohlraum, cut open at ~75% of its length) to measure the x-radiation drive as observed by the target on standard hohlraums by viewing the ViewFactor hohlraum interior through the “open” end, without a laser entrance hole. A secondary goal is to measure the charge state of gold in the bubble region using gold L band spectroscopy as a first step in the development of a diagnostic for electron temperature distributions in the multi-KeV regime. The experimental configuration will be described, and results will be discussed and compared to simulations.