Particle-in-cell simulations of ion acceleration in high contrast and high intensity laser-solid target interactions at intensities above 1020 Wcm-2

Experiments conducted on the Trident laser facility show strongly ionized, directional and monoenergetic heavy ion bunches generated from ultrathin (60-140 nm) solid Titanium targets shined by high contrast short laser pulses $( \sim 650$ fs) with intensities above $10 ^{20}\mathrm {W}/$cm
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. Here we performed 2-Dimensional PIC simulations with EPOCH code to study the effect of target thickness on the ion acceleration physics. The simulation with 100nmthick target shows that during laser-solid target interaction, the dominant Ti $^{+20}$ ions are accelerated through mixed mechanisms of target normal sheath acceleration (TNSA) and acceleration caused by relativistic transparency effect. Along the target normal direction (on-axis), we observed quasi mono-energetic Ti $^{+20}$ beams with energy spike of about 160 MeV at the end of the simulation at 3ps. Mono-energetic spike is also observed at about 200 MeV between $\pm 10 \sim 20$ degrees off-axis at 2ps before the energetic Ti $^{+20}$ ions on the spike leave the simulation box. Both mono-energetic spikes are in good agreement with the experimental measurements in angle and energy. As the laser goes through the target, the longitudinal and transverse electric fields are formed during the propagation of Ti $^{+20}$ and electron filaments. These fluctuating fields stay until the end of the simulation, and may affect the propagation of Ti $^{+20}$ ions after the end of the laser pulse at 1.3ps. Detailed simulation results will be presented at the meeting. Simulations for this work were performed using HPC resources provided by the Texas Advanced Computing Center at the University of Texas.