FINITE LARMOR RADIUS STABILIZATION OF "WEAKLY" UNSTABLE CONFINED PLASMAS
The modifled '' magnetohydrodynamic equations of motion follow from the exact plasma kinetic theory in the limit of small Larmor radius and low frequency, so that a magnetohydrodynamic prediction of instability is usually valid. However, in weakly unstable systems such as mirror machines, slowly rotating plasmas, large-aspect-ratio torii, etc., the expansion is no longer correct since the growth rate is very small, i.e., (ka/sub i/)/sup 2/ may become comparable to omega / OMEGA /sub i/so that the growth rate omega must also be considered a small quantity. Here OMEGA /sub i/ is the ion cyclotron frequency, athe ion gyro-radius and k the wave number of the perturbaror machine, and a slowly rotating plasma-- are studied. In all these cases the characteristic flute type instability is effectively stabilized if (ka/sub i/)/sup 2/> OMEGA / where OMEGA /sub H/ is the growth rate predicted by the hydrodynamic theory. Mirror experiments and fast-compression experiments operating in t/e region (a/ sub i/ GAMMA )/sup 2 approximately omega /sub H/ OMEGA /sub i/ are discussed. The do minant physical oscillation-producing mechanism is the breakdown of the condition that ions and electrons move together across the magnetic field with characteristic velocity v == c sigma E x B/B/sup 2/, where sigma E is the perturbed electric field. As a esult of the finite ion Larmor radius the mean electric field seen by the ions is slightly different from the elec trons so that their velocity across the field is different. This builds up a charge separation that is out of phase with the characteristic charge separation arising from particle drifts, which drives the flute-type instability. If (ka/sub i/)/sup 2/ > omega /sub H// OMEGA , the result is a stable oscillation. (auth)
- Research Organization:
- General Dynamics Corp., San Diego, Calif.
- NSA Number:
- NSA-16-023224
- OSTI ID:
- 4808729
- Report Number(s):
- GA-2371
- Journal Information:
- Nuclear Fusion, Suppl., Journal Name: Nuclear Fusion, Suppl.
- Country of Publication:
- Country unknown/Code not available
- Language:
- English
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Related Subjects
DIFFERENTIAL EQUATIONS
DISTURBANCES
ELECTRIC FIELDS
ELECTRONS
FLUTE INSTABILITY
FREQUENCY
GRAVITATION
IONS
MAGNETIC COMPRESSION
MAGNETIC FIELDS
MAGNETIC MIRRORS
MAGNETOHYDRODYNAMICS
MOTION
ORBITS
OSCILLATIONS
PHYSICS
PLASMA
PRESSURE
ROTATION
STABILITY
THERMONUCLEAR DEVICES
TORUS
VARIATIONS
VELOCITY