Unphysical kinetic effects in particle-in-cell modeling of laser wakefield accelerators

Authors

Estelle Cormier-Michel, Lawrence Berkeley National Laboratory, Berkeley, California
Bradley Allan Shadwick, University of Nebraska-LincolnFollow
Cameron Guy Robinson Geddes, Lawrence Berkeley National Laboratory, Berkeley, CaliforniaFollow
Eric Esarey, Lawrence Berkeley National Laboratory, Berkeley, CaliforniaFollow
Carl B. Schroeder, Lawrence Berkeley National Laboratory, Berkeley, CaliforniaFollow
Wim P. Leemans, Lawrence Berkeley National Laboratory, Berkeley, CaliforniaFollow

Document Type

Article

Date of this Version

2008

Citation

PHYSICAL REVIEW E 78, 016404 (2008)

Comments

©2008 The American Physical Society

Abstract

Unphysical heating and macroparticle trapping that arise in the numerical modeling of laser wakefield accelerators using particle-in-cell codes are investigated. A dark current free laser wakefield accelerator stage, in which no trapping of background plasma electrons into the plasma wave should occur, and a highly nonlinear cavitated wake with self-trapping, are modeled. Numerical errors can lead to errors in the macroparticle orbits in both phase and momentum. These errors grow as a function of distance behind the drive laser and can be large enough to result in unphysical trapping in the plasma wake. The resulting numerical heating in intense short-pulse laser-plasma interactions grows much faster and to a higher level than the known numerical grid heating of an initially warm plasma in an undriven system. The amount of heating, at least in the region immediately behind the laser pulse, can, in general, be decreased by decreasing the grid size, increasing the number of particles per cell, or using smoother interpolation methods. The effect of numerical heating on macroparticle trapping is less severe in a highly nonlinear cavitated wake, since trapping occurs in the first plasma wave period immediately behind the laser pulse.