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Effect of target-emitted ions on the focal spot of an intense electron beam

Published online by Cambridge University Press:  15 October 2009

Dale R. Welch  and
Thomas P. Hughes
Dale R. Welch
Affiliation:
Mission Research Corporation, Albuquerque, NM 87106-4245, USA
Thomas P. Hughes
Affiliation:
Mission Research Corporation, Albuquerque, NM 87106-4245, USA
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Abstract

Intense electron beams are known to produce surface plasmas when they strike typical target materials. The beam space charge then draws an ion current that can substantially affect the beam dynamics. We consider these effects for two intense-beam sources: (1) a needle-tip cathode immersed in a strong magnetic field, and (2) an induction accelerator-produced beam that is focused onto a field-free target. For the first case, the dominant effect is an electrostatic dipole instability between the beam and the ions. A sufficiently large magnetic field can keep the oscillation amplitude to a low level. For the second case, the dominant effect is that the focal length changes in time. For the “worst case” of space-charge-limited proton emission, the predicted effect is severe. The actual abundance and charge state of the target-plasma ions will need to be measured or inferred from planned experiments. Mitigation schemes also are discussed briefly.

Type
Research Article
Information
Laser and Particle Beams , Volume 16 , Issue 2 , June 1998 , pp. 285 - 294
Copyright
Copyright © Cambridge University Press 1998

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