Josh May

Efficient modeling of laser–plasma interactions in high energy density scenarios

We describe how a new framework for coupling a full-particle-in-cell (PIC) algorithm with a reduced PIC algorithm has been implemented into the OSIRIS code. We show that OSIRIS, with this new hybrid-PIC algorithm, can efficiently and accurately model high energy density scenarios such as ion acceleration in laser–solid interactions and fast ignition of fusion targets. We model, for the first time, the full-density range of a fast ignition target in a fully self-consistent hybrid-PIC simulation, illustrating the possibility of stopping the laser generated electron flux at the core region with relatively high efficiencies. Computational speedups greater than 1000 times are demonstrated, opening the way for full-scale multi-dimensional modeling of high energy density scenarios and the guiding of future experiments.

Three-Dimensional Simulations of Laser–Plasma Interactions at Ultrahigh Intensities

Three-dimensional particle-in-cell simulations are used to investigate the interaction of ultrahigh-intensity lasers (>;1020 W/cm-2) with matter at overcritical densities. Intense laser pulses are shown to penetrate up to relativistic critical density levels and to be strongly self-focused during this process. The heat flux of the accelerated electrons is observed to have an annular structure when the laser is tightly focused, showing that a large fraction of fast electrons is accelerated at an angle. These results shed light into the multidimensional effects present in laser-plasma interactions of relevance to fast ignition of fusion targets and laser-driven ion acceleration in plasmas.

Particle-in-cell simulations for fast ignition

The hole-boring scheme in fast ignition is studied via largee-scale, two-dimensional particle-in-cell simulations in two steps. First, laser channeling in millimeter-scale underdense plasmas is simulated. The results show a highly nonlinear and dynamic process involving longitudinal plasma buildup, laser hosing, channel bifurcation and self-correction, and electron heating to relativistic temperatures. The channeling speed is much less than the linear group velocity of the laser. Low-intensity channeling pulses are preferred to minimize the required laser energy. The channel is also shown to significantly increase the transmission of an ignition pulse. In the second step, the interactions of the ignition pulse and a hundred-critical-density plasma are simulated to study hot electron generation and transport. The results show that at ultra-high intensities, I > 5 × 1019W/cm2, most of the electrons transporting energy through 50μm of 100 times critical density plasma are in a relatively low energy range. The fraction of laser power that transits the dense plasma and is deposited into a dense core increases with laser intensity. Overall these results show the promise of using ultra-high-intensity ignition pulses in the hole-boring scheme.