Linear coupling of the fast extraordinary wave to electrostatic plasma oscillations: A revised theory

Abstract

We study analytically the resonant absorption of the extraordinary wave related to its coupling to the upper-hybrid plasma oscillations in finite but low magnetic field. Common approaches based on a local dispersion relation and WKB approximation are proved to be insufficient for plasma with ωce ≪ ωpe; thus, a full wave problem dealing with exact Maxwell's equations is considered. A new formula for the absorption efficiency is derived analytically basing on the formalism of Frobenius forms and Stokes diagrams. Meanwhile, a new universal technique is proposed that adds an extra relation to the Stokes constants owning the fact that resonant absorption in a linear system may always be canceled due to interference of two counter-propagating waves. The proposed theory complements the recent extensive numerical studies of the resonant heating of high-β plasma.