Simulations of dynamic laser / plasma X-ray production

A high fluence X-ray diagnostic is being developed by Sandia National Laboratories for use as a point-projection X-ray source for imaging high-density load dynamics on the ZR pulsed power facility. The LSP 3D PIC code was used to model the dynamic interaction, between the Z-Petawatt IR laser and a high-atomic-number thin foil, which generates the intense short-duration bremsstrahlung X-ray pulse. Particle kinematics are explicit for densities near and below critical and implicit for higher densities through solid. Sufficiently small cell-sizes and timesteps were used to fully resolve the laser-plasma interaction and subsequent electron dynamics in the foil - 15 million cells and 400 million particles were required. An optional treatment of high-energy electrons as non-interacting test particles was also examined. The particle-field solution used matrix inversion techniques as opposed to a conventional ADI scheme. The effect of parameters such as foil radius, tilt angle, foil support structure, and net laser energy on the X-ray fluence and energy spectrum were evaluated in both cylindrical and 3D Cartesian coordinates for all angle leaving the target. The simulated X-ray fluence produced a peak X-ray dose in excess of 200 mRad, consistent with experimental measurements.