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Transport of relativistic electron beams along wire arrays

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4 Author(s)
Richardson, R.A. ; University of California, Lawrence Livermore National Laboratory, Livermore, California 94550 ; Denavit, J. ; Di Capua, M.S. ; Rambo, P.W.

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Theoretical prediction and particle simulations indicate that an array of longitudinal wires will allow electron beam propagation, without an external guiding magnetic field and above the drift tube limit, by providing a charge and current neutralizing background. This paper presents experimental tests of this transport concept by injecting a 60 ns, 18 kA pulse of 1.4 MeV electrons into an array of 1‐m long wires with a 1 cm spacing, filling a hexagon with 8.7‐cm average radius. Arrays were tested with wires of varying resistances and diameters ranging from 12 to 1.3 mil. Transport was tested with wires terminating on a common conducting beam collector and with wires terminating on individually insulated beam collectors. The data show good transport (up to 90% of injected current) without significant energy loss, for wire diameters 3 mil or less, while transport is cutoff after 10 ns when 12 mil wires are used. Particle simulations show that this cutoff is due to an instability fed by excess return current resulting from electron scattering by the wires. The arrays terminated on individually insulated beam collectors showed better transported beam profiles, with less pinching, than the arrays with a common conducting beam collector. Particle simulations also correlate well with this result and provide an understanding of the effect of scattering on transport and beam quality.

Published in:

Journal of Applied Physics  (Volume:69 ,  Issue: 9 )