Initiation of long electrical discharge in ICF reactor dense atmospheres

There is significant interest in using light-ion beams (LIB) as drivers for inertial confinement fusion (ICF). Typical commercial target yields are on the order of 0.1 to 1 GJ, which requires the driver to be shielded adequately from the implosion-associated energy. The LIB can be guided through a gaseous shield via current carrying reduced density plasma channels surrounded with ambient gas envelop. The plasma serves as a conductor for the confinement current and for beam neutralization while the envelope counteracts inertially the core pressure. The optimum channel density for reactor-grade LIB propagation (a few torr) has triggered researchers to choose low-pressure gas doped with high-Z material to fill the reactor. Channeling simplicity and minimum pellet heating from the channels were among the motivations for this choice. Although such a shield absorbs the target soft x ray, it is incompatible with power reactor requirements. Factors like channel susceptibility to various hydrodynamic instabilities, maximum attainable LIB power density, and the reactor dimensions seem to require much higher gas pressure. An additional shielding and breeding blanket has to be built around the activated reactor vessel, adding cost and maintenance complexity to the plant design. Recently, a new concept for a commercial LIB reactor has been suggested. The concept is based on a rotating body of boiling heavy water, which serves simultaneously as the first wall, working fluid, shock wave absorber, biological shielding, and tritium breeding blanket. The LIB propagate in 0.5- to 1-m-long reduced density channels formed in the high-pressure superheated steam, which fills a vortex cavity formed at the water surface center