A 100-mA Low-Emittance Ion Source for Ion-Beam Fusion

A Penning-type ion source is described that meets the following requirements for ion-beam fusion: Pulsed capability, high currents of heavy ions, and low emittance. The source is a scaled version of a lower-current ion source that produces 2 mA of singly charged xenon ions with a normalized emittance of 0.0015 mrad-cm. The scaled source, which utilizes permanent magnets and a filament cathode, was tested with both multiple- and single-aperture extraction. In the former case, pulsed xenon-ion currents of 100 mA at 2.5 keV were achieved at a current density of 15 mA/cm2; in the latter case, 30 mA at 4.5 mA/cm2 was extracted at 100 keV. The 30-mA case represents the first-gap conditions of a high gradient 1.5 MeV dc pre-accelerator. In all tests, the pulse length was ~1 msec with a repetition rate of 0.2 to 1.0 Hz. The experimental perveance data are in good agreement with the theoretical calculations.