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

Kar, S. and Markey, K. and Simpson, P. T. and Bellei, C. and Green, J. S. and Nagel, S. R. and Kneip, S. and Carroll, D. C. and Dromey, B. and Willingale, L. and Clark, E. L. and McKenna, P. and Najmudin, Z. and Krushelnick, K. and Norreys, P. and Clarke, R. J. and Neely, D. and Borghesi, M. and Schiavi, A. and Zepf, M. (2008) Laser driven MeV proton beam focussing by auto-charged electrostatic lens configuration. AIP Conference Proceedings, 1024. pp. 173-182. ISSN 0094-243X

Abstract

Significant reduction of inherent large divergence of the laser driven MeV proton beams is achieved by strong (of the order of 10(9) V/m) electrostatic focussing field generated in the confined region of a suitably shaped structure attached to the proton generating foil. The scheme exploits the positively charging of the target following an intense laser interaction. Reduction in the proton beam divergence, and commensurate increase in proton flux is observed while preserving the beam laminarity. The underlying mechanism has been established by the help of particle tracing simulations. Dynamic focussing power of the lens, mainly due to the target discharging, can also be exploited in order to bring up the desired chromaticity of the lens for the proton beams of broad energy range.