Gyrokinetic Theory and Simulations of Alfvénic Instabilities in Dipole Plasmas

Details Gyrokinetic Theory and Simulations of Alfvénic Instabilities in Dipole Plasmas Gyrokinetic Theory and Simulations of Alfvénic Instabilities in Dipole Plasmas

Publishing date

Dec 2001

URL

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agufmsm11a0786d&link_type=abstract

Journals

American Geophysical Union, Fall Meeting 2001, abstract #SM11A-0786

Science

Physics

Additional info 3

2720 Energetic Particles, Trapped, 2752 Mhd Waves And Instabilities, 2778 Ring Current

Type

Scientific paper

Abstract

We study the effect of energetic ring current protons on the stability of magnetospheric shear Alfvén waves. Motivated by satellite observations of Pc 4--5 geomagnetic pulsations, our model plasma consists of a core ( ~ 100eV) component and an energetic ( ~ 10 keV) component described by a gyrokinetic model from earlier perturbative analytic studies [Chen and Hasegawa; JGR 96, 1503 (1991)]. We have developed a hybrid gyrokinetic-magnetohydrodynamic δ f PIC initial-value simulation scheme in which full kinetic effects such as finite Larmor radii and particle magnetic bounce and precessional drift motions are retained nonperturbatively. We present numerical growth rates, real mode frequencies, and critical beta values for odd and even parity modes with reference to the azimuthal wavenumber and the plasma equilibrium parameters. We have also carried out analytical studies demonstrating the possible existence of energetic-particle modes (EPM) due to energetic ring-current protons. These EPM's are intrinsic to the energetic-particle dynamics and hence require non-perturbative treatment of interactions between waves and energetic particles. EPM's have thus not been investigated in previous theoretical analyses, which as a rule treat the wave-particle interactions as perturbations to the background Alfvén eigenmodes. We show that, given sufficiently steep pressure gradient, the even-mode EPM's, with frequencies scaling with the typical precessional frequency, can be destabilized even though the corresponding Alfvén-ballooning mode is stabilized by the trapped-particle compression.

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