High-flux positron generation via the ultra-intense laser irradiating density-modulated plasmas

To investigate plasma density during the Breit-Wheeler positron generation, a comparative study of four plasma targets is performed via the PIC (particle-in-cell) code EPOCH. When an ultra-intense laser (2.8 x 10(23) Wcm(-2)) is incident, more positrons with high energy are generated in the increasing density plasmas. The positron yield is already 1.5 x 10(8) with a cutoff energy of 2 GeV at t = 37T(0). It is demonstrated that increasing density plasmas will enhance gamma photon radiation and positron generation. In increasing density plasmas, under-dense plasmas favor electron acceleration, and over-dense plasmas will induce laser reflection. Cross sections of the Compton back-scattering and the BW positron generation are both increased via high-energy electrons colliding with the reflected laser. In addition, increasing the laser intensity will directly enhance positron generation. This investigation will further facilitate high -flux positron generation and application.