Ion sources for light-ion fusion (invited)

Light-ion drivers offer a potentially efficient and low-cost method to compress and heat an inertial-confinement fusion (ICF) target. In order to produce a significant thermonuclear burn of the fuel, focused ion-beam intensities of 100 TW/cm2 are required. The ion sources for these pulsed-power drivers should produce a single-ion species and should be capable of providing current-density levels up to 5 kA/cm2, in pulse widths of 10–20 ns, at voltages up to several tens of megavolts. Most ion sources used in the past have produced multiple-ion species, including protons and heavier ions, such as carbon and oxygen. In the last few years there has been a substantial research effort to produce single-species sources. The major effort since 1983 has been directed towards developing a pure, high-current Li+ source for the light-ion fusion accelerator, PBFA II. There are two types of ion sources being used for intense ion-beam generation: (1) passive sources which are produced directly or indirectly by the diode voltage itself; and (2) active sources, in which a preformed plasma is generated before the arrival of the power pulse. A survey of existing ion sources and those under development will be given. Emphasis will be given to the lithium-ion sources being developed at Sandia National Laboratories (SNL).