Laser driven MeV proton beam focussing by auto-charged electrostatic lens configuration

Kar, S. and Zepf, M. and Markey, K. and Simpson, P. and Bellei, C. and Green, J. and Dromey, B. and Nagel, S. and Kneip, S. and Williangle, L. and Carroll, D. C. and McKenna, P. and Najmuddin, Z. and Krushelnick, K. and Norreys, P. and Clark, E. and Clark, R. J. and Neely, D. and Borghesi, M. and Schiavi, A.; (2007) Laser driven MeV proton beam focussing by auto-charged electrostatic lens configuration. In: 34th EPS Conference on Plasma Physics 2007, EPS 2007 - Europhysics Conference Abstracts. European Physical Society (EPS), POL. ISBN 9788392629009

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Abstract

Laser driven multi-MeV proton beams from the rear surface of solid targets have been the subject of significant interest in last few years, due to their potential applications in various fields of science [1]. Despite of unique beam characteristics, such as low emittance, short burst duration and high particle energies there is still need for development. The large divergence angle and the broad energy spectrum are undesirable in most applications. Significant reduction of the inherent large divergence of the laser driven MeV proton beams has been achieved by strong (of the order of 109 V/m) electrostatic focusing field generated in the confined region of a ’washer’ type target geometry attached to the proton generating foil. In this scheme, the self charging of the target to multi-MV positive potential [2] is exploited to form a focusing field in suitable target geometries. A significant reduction in the proton beam divergence, and commensurate increase in the proton flux has been observed while preserving low beam emittance. The underlying mechanism has been verified using particle tracking simulations.

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