Parameter study of the diamagnetic relativistic pulse accelerator (DRPA) in slab geometry I: Dependence on initial frequency ratio and slab width

Two-and-a-half-dimensional particle-in-cell plasma simulations are used to study the particle energization in expanding magnetized electron-positron plasmas with slab geometry. When the magnetized relativistic plasma with high temperature (initial electron and positron temperature are $k_{B}T_{e}=k_{B}T_{p}=5MeV$) is expanding into a vacuum, the electromagnetic (EM) pulse with large amplitude is formed and the surface plasma particles are efficiently accelerated in the forward direction owing to the energy conversion from the EM field to the plasma particles. We find that the behavior of the DRPA (Diamagnetic Relativistic Pulse Accelerator) depends strongly on the ratio of the electron plasma frequency to the cyclotron frequency $\omega_{pe}/\Omega_{e}$ and the initial plasma thickness. In the high $\omega_{pe}/\Omega_{e}$ case, the EM pulse is rapidly damped and the plasma diffuses uniformly without forming density peaks because the initial thermal energy of the plasma is much larger than the field energy. On the contrary, in the low $\omega_{pe}/\Omega_{e}$ case, the field energy becomes large enough to energize all the plasma particles, which are confined in the EM pulse and efficiently accelerated to ultrarelativistic energies. We also find that a thicker initial plasma increases the maximum energy of the accelerated particles.