Numerical modeling of fast electron transport in short pulse laser–solid interactions with long scale-length pre-formed plasma

Abstract

Results of numerical modeling of the experiment carried out to investigate the effect of long scale pre-plasma on fast electron transport are presented. A peculiar ring-like structure in Cu Kα x-ray emission was seen experimentally when a short pulse laser (intensity ∼3 × 1018 W cm−2) interacted with a long scale pre-plasma. The long scale pre-plasma, produced by irradiation of a long pulse laser on a flat target having copper fluorescence layer sandwiched between aluminum layers, is modeled with the radiation hydrodynamic code, h2d. Fast electron transport modeling performed with the hybrid particle-in-cell code, LSP, suggests that the ring structure is due to the refluxing of low energy (∼50 keV) fast electrons traveling in the pre-formed plasma back to the solid target. Modeling shows that the excitation of strong electrostatic fields near the transverse plasma boundary is responsible for this refluxing. Details of the modeling along with the exact mechanism of formation of ring-like Kα x-ray emission are discussed.