Grid-controlled extraction of pulsed ion beams

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Abstract
Experimental results are presented on a method for extracting well‐focused ion beams from plasma sources with time‐varying properties. An electrostatic grid was used to stop the flow of plasma electrons so that only ions entered the extraction gap. In this case, ion flow in the gap was controlled by space‐charge effects as it would be with a thermionic ion source. Constant extracted current was observed even with large variations of source flux. An insulator spark source and a metal‐vapor vacuum arc were used to generate pulsed ion beams. With a hydrocarbon spark, current densities of 44 mA/cm2 were achieved at 20‐kV extractor voltage for an 8‐μs pulse. With an aluminum‐vapor arc, a current density of 15 mA/cm2 (0.3 A total) was measured for a 50‐μs pulse.

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