A Quasilinear Diffusion Model for Resonant WaveParticle Instability in Homogeneous Plasma
Abstract
In this paper, we develop a model to describe the generalized waveparticle instability in a quasineutral plasma. We analyze the quasilinear diffusion equation for particles by expressing an arbitrary unstable and resonant wave mode as a Gaussian wave packet, allowing for an arbitrary direction of propagation with respect to the background magnetic field. We show that the localized energy density of the Gaussian wave packet determines the velocityspace range in which the dominant waveparticle instability and counteracting damping contributions are effective. Moreover, we derive a relation describing the diffusive trajectories of resonant particles in velocity space under the action of such an interplay between the waveparticle instability and damping. For the numerical computation of our theoretical model, we develop a mathematical approach based on the CrankNicolson scheme to solve the full quasilinear diffusion equation. Our numerical analysis solves the time evolution of the velocity distribution function under the action of a dominant waveparticle instability and counteracting damping and shows a good agreement with our theoretical description. As an application, we use our model to study the oblique fastmagnetosonic/whistler instability, which is proposed as a scattering mechanism for strahl electrons in the solar wind. In addition, we numerically solve the full FokkerPlanck equation to compute the time evolution of the electronstrahl distribution function under the action of Coulomb collisions with core electrons and protons after the collisionless action of the oblique fastmagnetosonic/whistler instability.
 Publication:

The Astrophysical Journal
 Pub Date:
 October 2020
 DOI:
 10.3847/15384357/abb099
 arXiv:
 arXiv:2008.08169
 Bibcode:
 2020ApJ...902..128J
 Keywords:

 Space plasmas;
 Solar wind;
 Plasma astrophysics;
 1544;
 1534;
 1261;
 Physics  Space Physics;
 Physics  Plasma Physics
 EPrint:
 Astrophys. J. 902, 2, 2020