Numerical modeling of radiation physics in kinetic plasmas [III] - $\gamma$-ray transport via Bremsstrahlung in ultra-fast heated high Z matter

Radiation transport code coupled with fully relativistic collisional Particle-in-Cell (PIC) code, PICLS, has been developed to study the transport of X-ray photons produced in laser-solid interaction. We have implemented the radiation cross-section of relativistic Bremsstrahlung to simulate $\gamma$-ray transport in ultrafast heated high Z matter by an intense short pulse laser. We discuss the laser energy dependence of the emission energy and the intensity dependence of the angular distribution of $\gamma$-rays. By solving the transport of hard X-rays we find that high energy photons emitted by relativistic electrons are co-moving with the electrons and they are intensified continuously. As a result the $\gamma$-rays have the signature of the fast electrons' temporal and spatial distribution. We also calculate the number of pairs by solving the Bethe-Heitler cross-section in the radiation transport simulation. Comparing the details of $\gamma$-rays via Bremsstrahlung and pair creations with varying laser intensities in simulations, we will discuss the laser parameters and the target conditions (material) to produce the higher yield.