Parametric decay of lower hybrid waves in a plasma: Effect of ion nonlinearity

The contribution of ion nonlinearity to the coupling coefficients for parametric decay, quasi‐mode decay, oscillating two‐stream instability, and modulational instability of a lower hybrid pump (k0≠0) has been obtained by solving the full Vlasov equation for magnetized ions. It is seen that the contribution of ions is important only for decay into a Bernstein wave of short perpendicular wavelength (ω≫k z v e , k ⊥ρ i ≫1). A comparative study of various channels of decay reveals that the oscillating two‐stream instability and nonlinear Landau damping by electrons are the predominant channels in the high density region. Modulational instability and the decay into an ion acoustic wave are seen to be irrelevant to tokamaks.