Kelvin-Helmholtz instability in systems with large effective Larmor radius
The Kelvin-Helmholtz instability is examined for weakly magnetized systems where the effective ion Larmor radius, u/[omega][sub i], is larger than the velocity shear scale (u is the flow speed and [omega][sub i] is the ion gyrofrequency). Two cases are considered: the case for which the flow, u, is transverse to the ambient magnetic field, B, (u [center dot] B = 0), and the case for which (u [center dot] B [ne] 0). Each case is treated separately, and, in each case, the properties are modified compared to the small Larmor radius (magnetohydrodynamic) case. In the first case, the classical, MHD instability is recovered independent of the size of the Larmor radius, unless a perpendicular density gradient is present. When a density gradient is present, the instability has two modes: a long wavelength mode which is similar to the classical Kelvin-Helmholtz mode, and a new short wavelength mode. The dispersion relation for both these modes exhibits an asymmetry with respect to the sign of B [center dot] [del] [times] u. In the second case, u [center dot] B [ne] 0, the large Larmor radius Kelvin-Helmholtz instability exhibits a very strong asymmetry with respect to the sign of B [center dot] [del] [times] u. In contrast to the classical, MHD case, where, if the Alfven speed exceeds the flow speed the system is stable, the plasma supports a strong instability even when the Alfven speed far exceeds the flow speed provided B [center dot] [del] [times] u < 0. Conversely, for B [center dot] [del] [times] u > 0, the system is stabilized even for sub-Alfvenic flows. The transition from the case u [center dot] B [ne] 0 to the case u [center dot] B = 0 for long wavelengths is found to occur in a singular manner in that the critical value of u [center dot] B where this transition occurs scales as one half the power of the width of the velocity shear layer. Implications for experiments are discussed.
- Research Organization:
- Maryland Univ., College Park, MD (United States)
- OSTI ID:
- 5637024
- Resource Relation:
- Other Information: Thesis (Ph.D.)
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
SUPERCONDUCTIVITY AND SUPERFLUIDITY
ALFVEN WAVES
VELOCITY
FLUID FLOW
HELMHOLTZ INSTABILITY
IONS
LARMOR RADIUS
GYROFREQUENCY
MAGNETIC FIELDS
MAGNETOHYDRODYNAMICS
CHARGED PARTICLES
FLUID MECHANICS
HYDRODYNAMICS
HYDROMAGNETIC WAVES
INSTABILITY
MECHANICS
PLASMA INSTABILITY
PLASMA MACROINSTABILITIES
665510* - Magnetohydrodynamics- (1992-)