Use of X-Ray Preheated Foam Layers to Reduce Beam Structure Imprint in Laser-Driven Targets

A new direct-drive scheme is proposed, which substantially reduces initial laser-nonuniformity imprinting by surrounding conventional targets with a low-density foam jacket. The foam is ionized by a supersonic wave induced by a soft x-ray pulse prior to the arrival of the main optical drive. The variable-sized, supercritical foam plasma thus created acts to thermally smooth laser-drive structure. Hydrocode simulations are presented showing that the scheme is very effective at reducing target nonuniformities due to imprinting without significantly increasing target preheat and reducing hydrodynamic efficiency.