Modeling Chamber Transport for Heavy-Ion Fusion

In a typical thick-liquid-wall scenario for heavy-ion fusion (HIF), between 70 and 200 high-current beams approach the target chamber in entry pipes and propagate ~3 m to the target. Since molten-salt jets are planned to protect the chamber wall, the beams move through vapor from the jets, and collisions between beam ions and this background gas both strip the ions and ionize the gas molecules. Radiation from the preheated target causes further beam stripping and gas ionization. Because of this stripping, beams for HIF are expected to require substantial neutralization in a target chamber. Much recent research has, therefore, focused on beam neutralization by electron sources that were neglected in earlier simulations, including emission from walls and the target, photoionization by the target radiation, and preneutralization by a plasma generated along the beam path. When these effects are included in simulations with practicable beam and chamber parameters, the resulting focal spot is approximately the size required by a distributed radiator target.