Proton emission imaging of the nuclear burn in inertial confinement fusion experiments

Abstract

A proton core imaging system has been developed and extensively used for measuring the nuclear burn regions of inertial confinement fusion implosions. These imaging cameras, mounted to the 60-beam OMEGA laser facility, use the penetrating 14.7-MeV protons produced from the fusion of deuterium and 3-helium to obtain spatial images of the nuclear burn. The technique relies on penumbral imaging, with symmetric or asymmetric reconstruction algorithms used to extract the source distribution. The hardware and design considerations required for the imaging cameras are described and the fidelity of the reconstructed burn profiles is verified. The spatial characteristics of the nuclear burn profile of directly driven capsule implosions were, for the first time, extensively studied. For thick plastic-shell capsules, with initial radii of-- 430 pun, the characteristic burn radii were found to be - 30 pun. The effects of gas pressure, shell thickness, laser energy, laser smoothing, capsule size, and capsule composition on the burn radius were systematically examined, resulting in radii ranging from 20 m to 80 pim. This new set of absolute burn profile measurements, in combination with other important implosion diagnostics, constitute a significant advance in that it imposes an exacting, integral test of the complex dynamics of imploding capsules.