Analysis of target implosion on irradiation by proton beams I Beam interaction with target plasma

Abstract

Numerical simulations and analyses are given for the implosion of a hollow shell target driven by proton beams. The target consists of three layers of Pb, Al and DT. The Pb and Al layers play roles of a tamper and a pusher, respectively. The main part of the beam energy is deposited in the Al layer. But the process of deposition depends strongly on the distribution of incident angles and particle energies. As the Al layer is heated by proton beams, the layer expands and pushes the DT layer toward the target centre. This type of implosion motion is examined by using a similarity solution for the slab model. To obtain an optimum velocity for the DT implosion, the optimum target size and optimum layer thicknesses are determined. The Rayleigh–Taylor instability, accompanied by the implosion motion is investigated, and the implosion is found to be stable with respect to the chosen target structure. The effects of inhomogeneities on implosion are shown to be severe. The initial fluctuation of the temperature or the density in the Al layer must be less than 3% and the maximum amplitude of the ripples on the initial boundary surface should be less than 3 μm with a view to achieving a high target gain.