Ion-cyclotron waves in nonuniform plasmas and parametric instabilities

A general formalism for studying waves propagating in a plasma with density and magnetic field gradients in slab geometry is discussed. Specializing to electrostatic ion-cyclotron waves propagating perpendicular to the gradients, it is shown that a density profile can lead to local or nonlocal structure around points where N′ (x)/N (x) has a local maximum while inhomogeneous magnetic fields provide the wave with the profile of an Airy function. Application of the formalism to parametric instabilities driven by magnetosonic waves and with kyρi≫1 is discussed. In particular, it is concluded that density and magnetic field gradients should not be critical in the development of the cyclotron decay instability in the FM-1 (floating multipole-1), ATC (adiabatic toroidal compressor), and PLT (Princeton large torus) devices of Princeton.