Helical Plasma Wave Damping and Magnetic Field Generation*

An accurate description of plasma waves is essential to the understanding of many aspects of plasma phenomena. We demonstrate both analytically, and using 3D Particle-In-Cell (PIC) simulations, that it is possible to twist a plasma wave such that, in addition to having longitudinal motion, it can possess quantized orbital angular momentum. This feature implies a helix like density perturbation that rotates about a central axis and can be described using a Laguerre-Gaussian mode. Such perturbations can be driven by Laguerre-Gaussian laser modes. This work is of increasing importance due to developing capabilities for generating such laser modes at high-energy high-intensity laser facilities.

The talk presents novel phenomena associated with helical plasma waves. Using 3D PIC simulations, we demonstrate that these waves can be stable and long-lived. We then show that, while at low amplitudes these waves are electrostatic, as the wave amplitude increases they generate large-amplitude static magnetic fields with unique longitudinal twisted structures. The second part of the talk focuses on the key phenomena that are found from deriving an accurate analytical description of the Landau damping of the helical plasma waves. In order to fully understand the differences these waves are compared to plane plasma waves. The first comparison is a significant increase in damping rate that can be as large as the thermal correction. Planar plasma waves, when subjected to Landau damping, transfer their purely longitudinal momentum to electrons traveling close to the phase velocity of the wave. Helical plasma waves are additionally shown to transfer the orbital angular momentum to electrons proportionately to the longitudinal momentum. In the particle-trapping regime particles are also seen to form phase-space islands, similar to those for planar plasma waves, but twisted about the central axis.