Weakening of magnetohydrodynamic interchange instabilities by Alfv́n waves

Alfv́n waves, made to propagate along an ambient magnetic field and polarized transverse to a gravitational field g, with wave amplitude stratified along g, are shown to reduce the growth rate of interchange instability by increasing the effective inertia by a factor of 1+ (B- y′ B- z kz)2, where B-z is the ambient magnetic field, kz is the wavenumber, and B-y′ is the wave amplitude shear. Appropriately placed Alfv́n wave power could thus be used to enhance the stability of interchange and ballooning modes in tokamaks and other interchange-limited magnetically confined plasmas.