Gyrokinetic particle simulation of drift-compressional modes in dipole geometry

Abstract

Gyrokinetic particle simulation of low frequency compressional modes has been developed using flux coordinates in the global magnetic dipole geometry. The compressional component is formulated in a scalar form of the parallel magnetic perturbation, and the gyro-averaging is performed explicitly in the configuration space. A reduced gyrokinetic model, in which the compressional perturbations are decoupled from the shear Alfvén and electrostatic perturbations, has been implemented. Linear simulation results have been verified using a numerical Nyquist analysis of the dispersion relation in the slab limit. Global simulations of unstable drift-compressional modes in the dipole geometry with kinetic ions find that finite Larmor radius (FLR) effects reduce the linear growth rate significantly but change little the real frequency. Global eigenmode structures show that the modes are even along the equilibrium magnetic field and broadened by the FLR effects in the radial direction. Radial propagation away from the region of excitation is observed.

First results of the high-resolution multibeam ULF wave experiment at the Ekaterinburg SuperDARN radar: Ionospheric signatures of coupled poloidal Alfvén and drift-compressional modes

“…In MHD theory, a compressional mode is represented by a slow magnetoacoustic mode coupled with the Alfvén mode due to the field line curvature and geodesic curvature (e.g., Cheremnykh et al, 2011). The applicability of MHD to long-period wave phenomena in hot collisionless plasmas is under question (Tur et al, 2010), but it was shown in gyrokinetics that another long-period compressional mode can exist in such plasmas, the drift-compressional mode (Porazik and Lin, 2011;. The characteristic frequency of this mode is of the order of the plasma diamagnetic drift frequency…”

“…Although usually high-m ULF waves were interpreted as Alfvén modes, there is another wave branch which can be identified with these pulsations -the drift-compressional mode (Crabtree and Chen, 2004;Porazik and Lin, 2011;. This mode has a kinetic nature and represents the most common kind of the compressional modes, demanding for its existence only finite pressure and plasma inhomogeneity across magnetic shells.…”

Magnetohydrodynamic Oscillations in the Solar Corona and Earth’s Magnetosphere: Towards Consolidated Understanding

“…(83) appears when the plasma inhomogeneity is taken into account. This oscillation branch is called the drift compressive mode (Ng et al 1984;Crabtree and Chen 2004;Porazik and Lin 2011). Its characteristic frequency is of the same order as the plasma diamagnetic drift frequency,…”

Gyrokinetic particle simulations of the effects of compressional magnetic perturbations on drift-Alfvenic instabilities in tokamaks

“…When the finite b effects are considered, the second order terms in the perturbed guiding center Hamiltonian contribute to extra polarization terms in the field equations. [7][8][9] At equilibrium and isotropic temperature, the conventional form of the component of Ampere's law parallel to the equilibrium magnetic field (hereafter, simply referred to as the parallel Ampere's law) is valid for arbitrary b. The perpendicular Ampere's law and gyrokinetic Poisson's equation become coupled for finite b.…”