Measurement of the ³He Permeability of DT-Filled Fused Silica Inertial Confinement Fusion (ICF) Targets to Study the Effects of ³He on Neutron Emission During Implosion

A set of laser implosion experiments were conducted at the OMEGA laser at the University of Rochester, Laboratory for Laser Energetics (LLE) to study the effect of ³He concentration in DT-filled target shells on fusion yield in ICF implosions. Eleven laser fusion shells consisting of 1100-m diameter, hollow, fused silica spheres with 4.6 to 4.7-m-thick walls were loaded with 520 kPa of deuterium-tritium (DT) and then with ³He (101.3 or 520 kPa). The ³He permeabilities of the shells were determined by measuring the pressure rate of rise into a system with known volume. A mathematical method was developed that relied on the experimental fill pressure and time, and the rate of rise data to solve differential equations using MathCAD to simultaneously calculate ³He permeability and initial ³He partial pressure inside the shell. Because of the high permeation rate for ³He out of the shells compared to that for DT gas, shells had to be recharged with ³He immediately before being laser imploded or "shot" at LLE. The ³He partial pressure in each individual shell at shot time was calculated from the measured ³He permeability. Two different partial pressures of ³He inside the shell were shown to reduce neutron and gamma yields during implosion.