Gamma Reaction History ablator areal density constraints upon correlated diagnostic modeling of National Ignition Facility implosion experiments

Abstract

The inelastic neutron scattering induced γ-ray signal from 12C in an Inertial Confinement Fusion capsule is demonstrated to be an effective and general diagnostic for shell ablator areal density. Experimental acquisition of the time-integrated signal at 4.4 MeV using threshold detection from four gas Čerenkov cells provides a direct measurement of the 12C areal density near stagnation. Application of a three-dimensional isobaric static model of data acquired in a recent high neutron yield National Ignition Facility experimental campaign reveals two general trends: smaller remaining ablator mass at stagnation and higher shell density with increasing laser drive.

Higher velocity, high-foot implosions on the National Ignition Facility lasera)

“…We have a measure of the total areal density qr of the CH ablator using the Gamma Reaction History (GRH) diagnostic by measuring the c-ray signal from inelastic neutron scattering of 12 C in the ablator material. 20 The N140819 shot showed the lowest carbon qr of any high foot shot. In addition, the capsule x-ray spectrum measured by the Ross pair filters 21,22 can be fit to infer an optical depth (jqr).…”

Use of 41Ar production to measure ablator areal density in NIF beryllium implosions

“…The gamma ray signal can give the time dependence of the product of burn rate times the carbon areal density. Cerjan et al 2 concluded from GRH data that there were smaller remaining ablator mass and higher shell density than calculated. Radio-chemistry offers another method for measuring ablator areal density by using primary materials or adding dopants to the ablator and collecting products from neutron or charged particle induced nuclear reactions.…”

Gamma Ray Measurements at OMEGA with the Newest Gas Cherenkov Detector “GCD-3”

“…Techniques for determining the ρR of the unablated plastic or high density carbon (HDC) shell mass at bangtime using previous gas Cherenkov diagnostics have been reported by Hoffman [5,6] and Cerjan [7]. A graphite puck of known density mounted on the front of GCD-3 allows for an in situ calibration of the detector response to 4.44 MeV 12 C(n,n') inelastic scatter gamma rays.…”