Acceleration of background gas ions due to Coulomb explosion of clusters triggered by irradiation of ultrashort, intense laser pulses

Kanasaki, Masato; Jinno, Satoshi*   ; Sakaki, Hironao; Faenov, A. Ya.*; Pikuz, T. A.*; Nishiuchi, Mamiko; Kiriyama, Hiromitsu; Kando, Masaki; Kondo, Kiminori; Matsui, Ryutaro; Kishimoto, Yasuaki; Morishima, Kunihiro*; Watanabe, Yukinobu; Scullion, C.*; Smyth, A. G.*; Alejo, A.*; Doria, D.*; Borghesi, M.*; Oda, Keiji*; Yamauchi, Tomoya*; Fukuda, Yuji

In the laser-driven ion acceleration using cluster-gas target, the acceleration mechanism consists of different processes such as, (a) acceleration of ions due to Coulomb explosion of individual clusters, (b) compression and acceleration of background gas ions due to the Coulomb explosion of clusters, (c) magnetic vortex generation and associated pinching near the rear surface, and (d) sheath acceleration at the interface between the medium and vacuum. To reveal the synergetic interplay between the processes (a) and (b), we have conducted ion acceleration experiments using CO clusters embedded in background H gas with the J-KAREN laser. By a careful analysis of CR-39, we have found that the maximum energies of protons and carbon ions are 1.5 MeV and 1.1 MeV/u, respectively. Based on the experimental results, the acceleration mechanism of background gas ions induced by Coulomb explosion of clusters can be discussed with the help from numerical simulations.