Particle simulation study on the transport of laser-accelerated proton beams in high-density plasmas

Ion beam has important applications in inertial confinement fusion and high energy density physics. In this work, we used EPOCH (Extendable PIC Open Collaboration) to simulate the transport of laser-accelerated proton beams in high density plasmas with different ion charge numbers. Especially in the plasma with a high ion charge number, where the plasma collision frequency approaches electron oscillation frequency, the beam protons are strongly decelerated by the electric field induced by plasma return current. The energy deposition is further enhanced as the beam travel distance increases due to beam density selfsteeping, which is also confirmed by three-dimensional simulation. Interestingly, in the transverse direction, we observed that proton beams evolved into multiple current filaments due to current filamentation instability (CFI). Following that, we found through two-dimensional transverse simulations that Coulomb collisions can accelerate the merging process of current filaments. We preliminarily attribute this to Coulomb collisions causing plasma heating, thereby accelerating the nonlinear process of CFI.