Pulsed ion sources for acceleration inertial fusion

Experimental results are reported on an extractor for pulsed, high-intensity beams of intermediate-mass ions. Aluminum and indium plasmas were generated using a metal-vapor vacuum arc. A method for electrostatic separation of ions from electrons at the anode was utilized to generate constant current beams, insensitive to plasma flux variations. Electrostatic separation also prevented plasma prefill of the extraction gap, allowing rapid and quiet beam initiation. A maximum extraction voltage of 30 kV was applied across a 1.6-cm gap. Voltage pulse length ranged from 10 to 50 μsec. Peak current densities of 15 mA/cm2 for Al+ and In+ were achieved from an anode with an area of 20 cm2. Time-of-flight measurements indicated that beam ions were predominantly in the +1 ionization state with no observable species contamination. A divergence measure with a channel-electron-multiplier arrays implies a normalized emittance of εn<3x10-7 πm-rad. The technology may have application to the induction linac approach to accelerator inertial fusion. (author)