Direct indirect hybrid implosion of fuel pellet in heavy ion inertial fusion

Abstract

A direct-indirect hybrid implosion mode is proposed and discussed in heavy ion beam (HIB) inertial confinement fusion (HIF) in order to release sufficient fusion energy in a robust manner. The HIB illumination non-uniformity depends strongly on a target displacement dz from the centre of a fusion reactor chamber. In a direct-driven implosion mode, dz of about 20 micron m was tolerable, and in an indirect- implosion mode, dz of about 100 micron m was allowable. In the direct-indirect mixture mode target, a low-density foam layer is inserted, and the radiation energy is confined in the foam layer. In the foam layer the radiation transport is expected to smooth the HIB illumination non-uniformity in the lateral direction. Two-dimensional implosion simulations are performed, and show that the HIB illumination non- uniformity is well smoothed in the direct-indirect hybrid-mode target. Our simulation results present that a large pellet displacement of about a few hundred micron m is allowed in order to obtain a sufficient fusion energy output in HIF. In fuel target implosion, ICF has two ways of implosion schemes, which are indirect-driven scheme and direct-driven implosion scheme. Each implosion scheme has merits and demerits. The indirect-driven scheme may be robust against the beam non- uniformity and a beam number employed is low compared with that in the direct-driven scheme, though each HIB should carry a larger current and a target structure may be complicated and expensive relatively. The direct-driven pellet structure may be simple, though the scheme may be sensitive to the HIB illumination non-uniformity. In this paper, a direct- indirect mixture implosion mode is proposed and discussed in HIB ICF.