Nonlinear evolution of helical plasma waves*

Electron plasma waves are inherent to several of the laser-plasma instabilities that inhibit the performance of inertial confinement fusion (ICF). When driven to large amplitudes, these waves can trap and accelerate a substantial population of electrons. The resulting modification to the electron distribution function produces a nonlinear frequency shift that allows for plasma wave self-action and, in some cases, enhanced instability growth. While these processes are relatively well understood for planar-like plasma waves, the three-dimensional topology of helical plasma waves offers an additional degree of freedom to control or mitigate the nonlinear evolution. More specifically, these waves feature an integer multiple l of azimuthal phase windings per period. Here, the nonlinear evolution of helical electron plasma waves is studied in ICF relevant plasma conditions using three-dimensional particle-in-cell simulations. To study these processes independently of a particular laser-plasma instability, the waves are resonantly excited using an external driving field. Preliminary results reveal the dependence of the trapped particle frequency shift and plasma wave self-action on the helical mode number l and show that the accelerated electrons generate an azimuthal magnetic field that persists well after the wave has damped.