PIC simulations of the damping of nonlinear electron plasma waves propagating in magnetic fields*

Nonlinear electron plasma waves propagating perpendicular to magnetic fields can be damped due to the fact that trapped electrons get accelerated perpendicularly across the wave front, continually extracting energy from it.  We present particle-in-cell simulations of externally driven electron plasma waves showing how the initial damping of the wave, the evolution of the wave after several bounces, and its long-time evolution after many bounce times are all effected by even weak magnetic fields (ω_c/ω_p << 1).  This behavior can have significant consequences for instabilities that are sensitive to the nonlinear evolution of electron plasma waves.  We use these results to inform simulations of backward stimulated Raman scattering in which small normalized magnetic fields applied perpendicularly to a light wave increase the instability’s kinetic threshold and decrease the total reflectivity.