Beam Final Transport and Direct-Drive Pellet Implosion in Heavy-Ion Fusion

Abstract

Key issues of heavy-ion beam (HIB) inertial confinement fusion (ICF) include an efficient beam transport, beam focus, uniform fuel pellet implosion, etc. The HIB final transport and a direct-drive fuel pellet implosion by computer simulations in HIB ICF are examined. To realize a fine focus on a fuel pellet, space charge neutralization of incident-focusing HIBs may be required at HIB final transport. First, an insulator annular tube guide is proposed at the final portion of the transport, through which an HIB is transported. The physical mechanism of HIB charge neutralization based on an insulator guide is as follows: The local electric field created by HIB induces local discharges, and a plasma is produced on the insulator inner surface. Then electrons are extracted from the plasma by HIB net space charge. The emitted electrons neutralize the beam space charge and move together with the HIB. After the final transport, the HIBs enter a reactor gas and illuminate a fuel pellet. Direct-drive DT pellet implosion were also simulated. The simulation results present a density valley formation by a Pb HIB deposition in a fuel pellet energy absorber layer and a radiation-smoothing effect along the density valley. The density valley provides radiation confinement, and beam nonuniformity can be smoothed along the valley.