Nonlinear variations of the reflexion coefficient for lower-hybrid heating

The effect of the ponderomotive depression of the plasma density on the power reflexion coefficient is calculated in the first space harmonic approximation. Numerical results demonstrate a considerable growth of the reflexion coefficient when increasing the RF power. Exceptionally, the reflexion coefficient can be almost invariable up to high RF power densities ( 10kW cm^-2), if the unperturbed plasma density gradient is high ( 5 × 10¹² cm^-4). The relation of the present theory to experiments is discussed.