Propagation and collisionless absorption of linearly converted lower hybrid plasma waves

Abstract

Mode conversion and collisionless absorption of externally driven waves in the lower hybrid frequency range in an inhomogeneous plasma are described through numerical analysis of the locally evaluated linear dispersion relation for a homogeneous plasma. The effects of finite temperature and inhomogeneity of the plasma are emphasized since, according to the linear theory, these effects are responsible for the eventual absorption of the waves by the plasma. The exact forms of the dispersion relations, derived first from the two-fluid equations with an isotropic pressure law and then from the Vlasov equation, are analyzed for plasma parameters applicable to present day tokamaks. The two-fluid theory predicts that a mode conversion to an acoustic wave takes place near the lower hybrid resonance density layer. The Vlasov theory, in addition, predicts that this may be followed by a second mode conversion at a lower density. The results of the Vlasov theory also include electron Landau damping and ion cyclotron harmonic damping.