Accurate Modeling of Laser-Plasma Accelerators with Particle-In-Cell Codes

Particle-In-Cell (PIC) codes are often used to study systems where the details of phasespace are important; for example, self trapping or optical injection in laser-plasma accelerators. Here we investigate the numerical heating and macro-particle trajectory errors in 2D PIC simulations of laser-plasma accelerators. The effects of grid resolution and laser polarization on the momentum spread and on subsequent spurious trapping in a plasma wave is studied. It is shown that when the laser is polarized in the plane of the simulation, which mimics the 3D behavior, the macroparticles are subject to trajectory errors resulting in a high momentum spread. The phase-space error associated with this momentum spread results in unphysical trapping. Smoother particle shapes are considered to reduce the interpolation errors. With these schemes, the macro-particle trajectories are more accurately modeled and unphysical momentum spread is reduced.