Anisotropic Alfven-ballooning modes in the Earth's magnetosphere

Technical Report · Sat May 01 04:00:00 EDT 1993

DOI:https://doi.org/10.2172/6327525· OSTI ID:6327525

Chan, A A ^[1]; Xia, Mengfen ^[2]; Chen, Liu ^[3]

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1. Dartmouth Coll., Hanover, NH (United States). Dept. of Physics and Astronomy
2. Beijing Univ., BJ (China). Dept. of Physics
3. Princeton Univ., NJ (United States). Plasma Physics Lab.

We have carried out a theoretical analysis of the stability and parallel structure of coupled shear-Alfven and slow-magnetosonic waves in the Earth's inner magnetosphere including effects of finite anisotropic plasma pressure. Multiscale perturbation analysis of the anisotropic Grad-Shafranov equation yields an approximate self-consistent magnetohydrodynamic (MHD) equilibrium. This MHD equilibrium is used in the numerical solution of a set of eigenmode equations which describe the field line eigenfrequency, linear stability, and parallel eigenmode structure. We call these modes anisotropic Alfven-ballooning modes. The main results are: The field line eigenfrequency can be significantly lowered by finite pressure effects. The parallel mode structure of the transverse wave components is fairly insensitive to changes in the plasma pressure but the compressional magnetic component can become highly peaked near the magnetic equator due to increased pressure, especially when P[perpendicular] > P[parallel]. For the isotropic case ballooning instability can occur when the ratio of the plasma pressure to the magnetic pressure, exceeds a critical value [beta][sub o][sup B] [approx] 3.5 at the equator. Compared to the isotropic case the critical beta value is lowered by anisotropy, either due to decreased field-line-bending stabilization when P[parallel] > P[perpendicular], or due to increased ballooning-mirror destabilization when P[perpendicular] > P[parallel]. We use a [beta]-6 stability diagram'' to display the regions of instability with respect to the equatorial values of the parameters [bar [beta]] and [delta], where [bar [beta]] = (1/3)([beta][sub [parallel]] + 2 [beta][perpendicular]) is an average beta value and [delta] = 1 - P[parallel]/P[perpendicular] is a measure of the plasma anisotropy.

• Research Organization: Princeton Univ., NJ (United States). Plasma Physics Lab.
• Sponsoring Organization: DOE; DOD; NASA; NSF; USDOE, Washington, DC (United States); Department of Defense, Washington, DC (United States); National Aeronautics and Space Administration, Washington, DC (United States); National Science Foundation, Washington, DC (United States)
• DOE Contract Number: AC02-76CH03073
• OSTI ID: 6327525
• Report Number(s): PPPL-2911; ON: DE93014819; CNN: NAGW-1098; F49620-93-1-0101; ATM-9211999
• Country of Publication: United States
• Language: English

Related Subjects

661320* -- Auroral
Ionospheric
& Magnetospheric Phenomena-- (1992-)
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ALFVEN WAVES
BALLOONING INSTABILITY
EARTH ATMOSPHERE
EARTH MAGNETOSPHERE
EQUILIBRIUM
HYDROMAGNETIC WAVES
INSTABILITY
MATHEMATICS
MHD EQUILIBRIUM
NUMERICAL ANALYSIS
PLASMA INSTABILITY
PLASMA MACROINSTABILITIES
PLASMA PRESSURE