Linear stability of tearing modes

Cowley, S. C.; Kulsrud, R. M.; Hahm, T. S.

doi:doi:10.1063/1.865841

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Theory of beat‐resonant coupling of electrostatic modes

A general expression is derived for the beat‐resonant coupling electrostatic modes in a Vlasov plasma. The result for the coupling of two modes has a simple structure: the appropriate momentum gradient of the equilibrium particle distribution is weighted by a positive coupling coefficient and averaged over the resonance surface in momentum space. The contributions of all the resonance surfaces are then summed. This basic structure had been previously exhibited only for specific homogeneous plasm...

Magnetic pumping by magnetosonic waves in the presence of noncompressive electromagnetic fluctuations

In a quiescent collisionless plasma the motion of charged particles within a magnetosonic wave is reversible, but in the presence of electromagnetic plasma waves that pitch‐angle scatter the particles, this is no longer true, and the plasma may be magnetically pumped by the magnetosonic wave, extracting energy from the wave. The particles that are energized are in resonance with the catalyst electromagnetic waves but gain their energy from the magnetosonic wave. To study this mechanism, three ty...

This paper examines the stability of tearing modes in a sheared slab when the width of the tearing layer is much smaller than the ion Larmor radius. The ion response is nonlocal, and the quasineutrality retains its full integral form. An expansion procedure is introduced to solve the quasineutrality equation in powers of the width of the tearing layer over the ion Larmor radius. The expansion procedure is applied to the collisionless and semicollisional tearing modes. It is found that first‐order terms in the expansion are strongly stabilizing. The physics of the mode and of the stabilization are discussed. Tearing modes are observed in experiments even though the slab theory predicts stability. It is proposed that these modes grow from an equilibrium with islands at the rational surfaces. If the equilibrium islands are wider than the ion Larmor radius, the mode is unstable when Δ′ is positive.

KEYWORDS and PACS

Keywords

TEARING INSTABILITY, STABILITY, SHEAR, SLABS, IONS, LARMOR RADIUS, COLLISIONLESS PLASMA, COLLISIONAL PLASMA

PACS

52.35.Py

Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.30.Cv

Magnetohydrodynamics (including electron magnetohydrodynamics)
52.35.Bj

Magnetohydrodynamic waves (e.g., Alfven waves)