Wave Propagation near Electron Cyclotron Harmonics in Nonuniform Plasmas

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Abstract
Equations are derived that describe the excitation and propagation of longitudinal waves (Bernstein modes) in nonuniform plasmas with a uniform applied magnetic field perpendicular to the direction of wave propagation and to the gradients of the unperturbed plasma. Certain features of the microwave absorption by plasma columns have recently been explained on the basis of such modes. Comparison shows that the equations derived by most other authors are correct only when the scale of the plasma inhomogeniety is long compared to the wavelength considered; this is primarily because they ignore the ambipolar electric field and the anisotropy of the unperturbed electron velocity distribution. The inclusion of these effects does not complicate the equations.