Spectral modification of laser-accelerated proton beams by self-generated magnetic fields

Robinson, A.P.L. and Foster, P. and Adams, D. and Carroll, D.C. and Dromey, B. and Hawkes, S. and Kar, S. and Li, Y.T. and Markey, K. and Mckenna, Paul and Spindloe, C. and Streeter, M. and Wahlström, C-G and Xu, M. H. and Zepf, M. and Neely, D. (2009) Spectral modification of laser-accelerated proton beams by self-generated magnetic fields. New Journal of Physics, 11. ISSN 1367-2630

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    Abstract

    Target normal measurements of proton energy spectra from ultrathin (50-200 nm) planar foil targets irradiated by 10(19) W cm(-2) 40 fs laser pulses exhibit broad maxima that are not present in the energy spectra from micron thickness targets (6 mu m). The proton flux in the peak is considerably greater than the proton flux observed in the same energy range in thicker targets. Numerical modelling of the experiment indicates that this spectral modification in thin targets is caused by magnetic fields that grow at the rear of the target during the laser-target interaction.