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Hollow microspheres as targets for staged laser-driven proton acceleration

Burza, M. and Gonoskov, A. and Genoud, G. and Persson, A. and Svensson, K. and Quinn, M. and McKenna, P. and Marklund, M. and Wahlstrom, C-G (2011) Hollow microspheres as targets for staged laser-driven proton acceleration. New Journal of Physics, 13 (Januar). 013030. ISSN 1367-2630

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Abstract

A coated hollow core microsphere is introduced as a novel target in ultra-intense laser-matter interaction experiments. In particular, it facilitates staged laser-driven proton acceleration by combining conventional target normal sheath acceleration (TNSA), power recycling of hot laterally spreading electrons and staging in a very simple and cheap target geometry. During TNSA of protons from one area of the sphere surface, laterally spreading hot electrons form a charge wave. Due to the spherical geometry, this wave refocuses on the opposite side of the sphere, where an opening has been laser micromachined. This leads to a strong transient charge separation field being set up there, which can post-accelerate those TNSA protons passing through the hole at the right time. Experimentally, the feasibility of using such targets is demonstrated. A redistribution is encountered in the experimental proton energy spectra, as predicted by particle-in-cell simulations and attributed to transient fields set up by oscillating currents on the sphere surface.