HR: 1340h
AN: SM13A-1116    [Abstracts]
TI: Interchange Instability Criterion in the Plasma Sheet
AU: * Xing, X
EM: xyxing@rice.edu
AF: Department of Physics and Astronomy, Rice University, 6100 Main st. MS108, Houston, TX 77005, United States
AU: Wolf, R
EM: rawolf@rice.edu
AF: Department of Physics and Astronomy, Rice University, 6100 Main st. MS108, Houston, TX 77005, United States
AB: The interchange instability analysis of Xing and Wolf [2007] has been generalized to the case of arbitrary plasma β, where β is the ratio of plasma thermal pressure to magnetic pressure, averaged within a magnetic flux tube. The theoretical model focuses on a boundary layer between two plasma regions with uniform entropy parameters PV^5/3 on each side (where P is the plasma thermal pressure and V=\int ds/B is the flux tube volume); the gradients of PV^5/3 and V are at an angle α to each other in the boundary layer. The development of a small perturbation was investigated numerically and the results suggest that shorter wavelength (wave length λ compared with boundary layer thickness 2Δ) perturbations have a wider rage of stability in the plasma boundary layer than the longer wavelength perturbations do. For example when λ=100Δ, the plasma with β<<1 is unstable when α>π/2, but when λ=10Δ, the unstable angles are α>1.73. When λ=Δ, the unstable range goes to α>2.38, and the threshold angle keep getting closer to π as the wavelength decreases. The results for higher magnetic β values indicate more instability. The test calculation for λ=100Δ with β=10 shows that the plasma is unstable when α>1.03; for λ=10Δ the unstable range is α>1.45; and when λ=Δ, the unstable range becomes α>2.20. These critical angles are all reduced compare to the β<<1 cases. The overall conclusion is that increasing either β or wavelength increases the region of instability. Combined with the characteristic of the Earth's plasma sheet calculated from empirical models, our criterion shows that the statistical-average plasma sheet is interchange stable.
DE: 2730 Magnetosphere: inner
DE: 2744 Magnetotail
DE: 2764 Plasma sheet
DE: 3215 Instability analysis
SC: SPA-Magnetospheric Physics [SM]
MN: 2007 Fall Meeting