W. M. Sharp, D. A. Callahan-Miller, M. Tabak
Lawrence Livermore National Laboratory, Livermore, CA 94550, USA
wmsharp
lbl.gov
S. S. Yu, Lawrence Berkeley National Laboratory
M. S. Armel, P. F. Peterson, University of California, Berkeley
D. V. Rose, D. R. Welch, Mission Research Corporation
R. C. Davidson, I. D. Kaganovich, E. Startsev, Princeton Plasma Physics Laboratory
C. L. Olson, Sandia National Laboratory
R. E. Olson, University of Missouri, Rolla
In a typical thick-liquid-wall scenario for heavy-ion fusion (HIF), between twenty and two hundred high-current beams enter the target chamber through ports and propagate about three meters to the target. They first heat the target for about 30 ns, then deposit a total of 3-7 MJ in the final 8-10 ns. Since crisscrossed 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. Due to this stripping, beams for heavy-ion fusion are expected to require substantial neutralization in a target chamber. Simulations with no electron sources other than collisions show an acceptable focal spot only for beam currents far below the values assumed in recent HIF driver scenarios. 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 pre-neutralization 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.
