γ -ray ‘bang-time’ measurements with a gas-Cherenkov detector for inertial-confinement fusion experiments

Abstract

In a laser driven inertial-confinement fusion experiment, bang time is defined as the time between the laser light impinging the target and the peak of the fusion reactions. Bang time is often used to compare computed predictions to experiment. Large laser facilities, such as NIF and LMJ, which are currently under construction, will produce yields far in excess of any previous inertial-confinement fusion experiment. One of the implications of such high yields is that fusion γ rays, which have branching ratios four orders of magnitude less than that of fusion neutrons, may be used to diagnose bang time. This article describes the first of such γ-ray bang-time measurement made using the OMEGA laser facility at the Laboratory for Laser Energetics, University of Rochester. The diagnostic used for this was a gas Cherenkov detector. The experimental setup, data and error analyses, and suggested improvements are presented.