Heavy ion acceleration in the radiation pressure acceleration and breakout afterburner regimes

We present a theoretical study of heavy ion acceleration from ultrathin (20 nm) gold foil irradiated by high-intensity sub-picosecond lasers. Using two-dimensional particle-in-cell simulations, three laser systems are modeled that cover the range between femtosecond and picosecond pulses. By varying the laser pulse duration we observe a transition from radiation pressure acceleration (RPA) to the relativistic induced transparency (RIT) regime for heavy ions akin to light ions. The underlying physics of beam formation and acceleration is similar for light and heavy ions, however, nuances of the acceleration process make the heavy ions more challenging. A more detailed study involving variation of peak laser intensity I-0 and pulse duration tau(FWHM) revealed that the transition point from RPA to RIT regime depends on the peak laser intensity on target and occurs for pulse duration tau(RPA -> RIT)(FWHM) [fs] congruent to 210/root I-0 [W cm (2)]/10(21) The most abundant gold ion and charge-to-mass ratio are Au51+ and q/M approximate to 1/4, respectively, half that of light ions. For ultrathin foils, on the order of one skin depth, we established a linear scaling of the maximum energy per nucleon (E/M)(max) with (q/M)(max), which is more favorable than the quadratic one found previously. The numerical simulations predict heavy ion beams with very attractive properties for applications: high directionality (<10 degrees half-angle), high fluxes (>10(11) ions sr(-1)) and energy (>20 MeV/nucleon) from laser systems delivering >20 J of energy on target.