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Low frequency stability of geotail plasma

2001; American Institute of Physics; Volume: 8; Issue: 5 Linguagem: Inglês

10.1063/1.1357828

1527-2419

H. Vernon Wong, W. Horton, J. W. Van Dam, Chris Crabtree,

Magnetic confinement fusion research

The local flux surface stability of magnetic dipole configurations is investigated in the magnetohydrodynamic (MHD) and drift frequency regimes. Solutions of the plasma equations in the very high beta limit are discussed. A novel procedure is developed for discussing stability in terms of the frequency ratio: the orbit averaged ion drift frequency divided by the ion diamagnetic frequency. This procedure is used to examine the stability of magnetospheric flux surfaces in the neighborhood of the equatorial plane at 6–10 Earth radii (where the plasma beta is ∼5 and where the onset of plasma instabilities may be responsible for triggering magnetic storms) with the following results: (1) MHD ballooning modes are predicted to be stable unless κvxp⩽2/5 where xp is the plasma pressure gradient scale length and κv the vacuum field line curvature at the equatorial plane; (2) drift modes may also be unstable unless η∼2/3, where η is the density gradient scale length divided by the temperature gradient scale length.