Effects of phase-bunching in strongly turbulent plasmas

Abstract

The effects of phase bunching on the collisionless dissipation of nonlinear wave fields is explored, with emphasis on situations relevant to strong turbulence applications. It is argued that in a homogeneous, steady-state plasma, there is no preferred phase of the electric field experienced by particles as they enter a wave packet. However, an initially phase-uniform ensemble of particles will generally be phase-bunched after interacting with a wave packet. This can lead to a dramatically intensified interaction with subsequent packets encountered by the particles. Numerical calculations reveal that the local wave dissipation can increase by orders of magnitude if the transiting particles have been phase-bunched prior to entering a wave packet. The wave particle interactions, called transit-time dissipation, comprise Landau damping and a nonresonant type of damping. The nonresonant damping causes a redistribution of field energy within a wave packet. This effect is particularly strong in phase-bunched systems. These results may force modifications to previous treatments of strong turbulence which have assumed isotropy and homogeneity, and employed standard Landau damping.