Beam focusing by aperture displacement in multiampere ion sources

Results are given of an experimental study of beam focusing by aperture displacement (Δx) in duoPIGatron ion sources. Measurements with a single aperture, accel–decel electrode geometry show that the beam deflection angle is linear with Δx/z for the round aperture and with Δx/z*2 for the slit aperture, where z and z* are, respectively, the extraction gap distance and the effective gap distance. Applying the result of the single aperture study to the multiaperture duoPIGatron sources, it was possible to increase the neutral beam injection power to the Oak Ridge Tokamak (ORMAK) plasma by ?40%. Also presented are a discussion and comparison of other work on the effect of aperture displacement on beam deflection.