Scaling model for high-aspect-ratio microballoon direct-drive implosions at short laser wavelengths

Abstract

A scaling model for hot spherical ablative implosions in direct-drive mode is presented. The model results have been compared with experiments from LLE, ILE, and LLNL. Reduction of the neutron yield due to illumination nonuniformities is taken into account by the assumption that the neutron emission is cut off when the gas shock wave reflected off the center meets the incoming pusher, i.e., at a time when the probability of shell breakup is greatly enhanced. The main advantage of this semiempirical scaling model is that it elucidates the principal features of these simple implosions and permits one to estimate very quickly the performance of a high-aspect-ratio direct-drive target illuminated by short-wavelength laser light.

Radiochemistry measurements on the Phebus laser

“…If we assume 1-D fuel-pusher assembly, without mixing, from mass conservation, continuity of pressure, and temperature at the D-T-glass interface, the fuel compression is given by (Storm et al 1980) M DT and M p are, respectively, the fuel and pusher masses, (pAR) the pusher areal density, p m and pj the fuel densities, the index / corresponds to initial condition and m to the measured value at the burn time, Z p is the average pusher ionization, and a is approximate to 2. It can also be more simply evaluated from the pusher areal density by using a simple model.…”

“…Numerous elements have been examined to be a tracer candidate to measure the areal density of either the fuel or the pusher (Campbell 1977;Lane 1980). The most commonly used for the pusher is 28 Si, but also used are Pr oxide by ILE (Miyanaga et al 1986) and at the present time Rb by LLNL (Lane et al 1990) on the powerful NOVA laser facility.…”

“…From the point of view of the 24 Na collection, Ti is the best material (Lane 1980). We assume that Na and Si collection efficiencies have the same value (Lane et al 1990) because Si and Na have almost the same atomic number although they are two different elements.…”

“…This method, developed for the first time at LLNL (Campbell 1977;Lane et al 1980), was also used at LLE (Richardson et al 1986). The neutron yield obtained with the Phebus laser allows the silicon radiochemistry analysis method to be used for measuring pusher areal density of imploded glass microballoons.…”