Energy increase in multi-MeV ion acceleration in the interaction of a short pulse laser with a cluster-gas target

Fukuda, Yuji; Faenov, A. Y.; Tampo, Motonobu; Pikuz, T. A.*; Nakamura, Tatsufumi; Kando, Masaki; Hayashi, Yukio; Yogo, Akifumi; Sakaki, Hironao; Kameshima, Takashi*; Pirozhkov, A. S.; Ogura, Koichi; Mori, Michiaki; Esirkepov, T. Z.; Koga, J. K.; Boldarev, A. S.*; Gasilov, V. A.*; Magunov, A. I.*; Yamauchi, Tomoya*; Kodama, Ryosuke*; Bolton, P.; Kato, Yoshiaki* ; Tajima, Toshiki*; Daido, Hiroyuki; Bulanov, S. V.

A new approach for accelerating ions, based on the use of a cluster-gas target and a compact ultrashort pulse laser, is presented. It is shown that ions with energy 10-20 MeV per nucleon having a small divergence (full angle) of 3.4 are generated, corresponding to an approximately tenfold increase in the ion energies compared to previous experiments using solid targets. It is inferred from a particle-in-cell code simulation that the high energy ions are generated at the rear side of the target due to the formation of a strong dipole vortex structure in near-critical density plasmas.