Robust Direct-Indirect Hybrid Target Implosion in Heavy Ion Fusion

In inertial fusion target implosion, beam illumination non-uniformity must be reduced to less than a few percent. In this study a direct-indirect hybrid implosion mode is discussed in heavy ion beam (HIB) inertial confinement fusion (HIF) in order to release sufficient fusion energy in a robust manner. On the other hand, the HIB illumination non-uniformity depends strongly on a target displacement dz from the center 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 hybrid 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. Two-dimensional implosion simulations are performed, and show that the HIB illumination non-uniformity is well smoothed in the direct-indirect mixture target. The results also present that dz of a few hundred micron m is allowed in HIF.