A high-current density contact ionization source for heavy-ion fusion

Abstract
Heavy ion fusion (HIF) sources will be low-emittance, high current (0.5-1A), and suitable for injection into a multiple beam induction linac, where the diameter of each beam aperture at the beginning of the accelerator is 3-6 cm. Practical transport limits involved in matching the beam to the accelerator aperture in a reasonably-sized structure correspond to several mA/cm 2 of space charge limited flow with an injector extraction voltage of 1-2.5 MV. We have built a J ∪ 8 mA/cm 2 Cs + contact ionization source for a 160kV diode; this represents a factor of four increase in the Cs + current density over previous sources for HIF. The emitter is sintered iridium, operating at 950 < T < 1150 ˚C. We are experimenting with several methods of alkali feeding capable of maintaining a fraction (<5%) of a monolayer coverage on the iridium surface.

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