Collisionless, phase-mixed, dispersive, Gaussian Alfven pulse in transversely inhomogeneous plasma

Abstract

In the previous works harmonic, phase-mixed, Alfven wave dynamics was considered both in the kinetic and magnetohydrodynamic regimes. Up today only magnetohydrodynamic, phase-mixed, Gaussian Alfven pulses were investigated. In the present work we extend this into kinetic regime. Here phase-mixed, Gaussian Alfven pulses are studied, which are more appropriate for solar flares, than harmonic waves, as the flares are impulsive in nature. Collisionless, phase-mixed, dispersive, Gaussian Alfven pulse in transversely inhomogeneous plasma is investigated by particle-in-cell (PIC) simulations and by an analytical model. The pulse is in inertial regime with plasma beta less than electron-to-ion mass ratio and has a spatial width of 12 ion inertial length. The linear analytical model predicts that the pulse amplitude decrease is described by the linear Korteweg de Vries (KdV) equation. The numerical and analytical solution of the linear KdV equation produces the pulse amplitude decrease in time as t −1 . The latter scaling law is corroborated by full PIC simulations. It is shown that the pulse amplitude decrease is due to dispersive effects, while electron acceleration is due to Landau damping of the phase-mixed waves. The established amplitude decrease in time as t −1 is different from the MHD scaling of t −3/2 . This can be attributed to the dispersive effects resulting in the different scaling compared to MHD, where the resistive effects cause the damping, in turn, enhanced by the inhomogeneity. Reducing background plasma temperature and increase in ion mass yields more efficient particle acceleration.

Electron acceleration from the interaction of three crossed parallel Alfvén waves

“…Phase mixing has been associated with density depletion or cavity (plasma under-density) in auroral regions (Génot et al 1999(Génot et al , 2000Mottez & Génot 2011) or more recently in interplume regions (Daiffallah & Mottez 2017). This mechanism has been associated also with the density bump or plasma over-density in solar coronal loops (Tsiklauri 2007(Tsiklauri , 2011(Tsiklauri , 2012(Tsiklauri , 2016 or in a solar coronal holes (Wu & Fang 2003). However, APAWI density gradients N e (X, Y) show a longitudinal modulation-like profile for all our simulations (see figure 7a).…”

Electron acceleration and small‐scale coherent structure formation by an Alfvén wave propagating in coronal interplume region

“…For the smallest positive slopes, we have found V x ≈0.033 for the stripes at x = 15, and V x ≈0.0286 for the weak stripes situated between x = 90 and x = 108 ( t >334). This shows that another part of the electron population propagates around the phase velocity of the Alfvén wave ( V A =0.0315), which indicates a signature of Landau damping due to the wave–particle interaction (see, e.g., Tsiklauri ).…”