MEASUREMENTS OF THE EFFECT OF LASER-BEAM SMOOTHING ON DIRECT-DRIVE INERTIAL-CONFINEMENT-FUSION CAPSULE IMPLOSIONS

We present measurements of the effect of various levels of laser beam smoothing on both burnthrough time and the neutron yield in layered, deuterium-filled imploding microballoons. Burnthrough times are found to improve as smoothing is increased. This effect is believed to result from a reduction in the seeding of the Rayleigh-Taylor (RT) instability with increasing smoothing. The results are in agreement with simulations that model the development of the RT instability from initial perturbation spectra consistent with measured changes in uniformity. The neutron yields are also observed to increase in the presence of smoothing, but are much less sensitive to uniformity changes than the burnthrough rates.