THE CONDITION FOR CUTOFF LAYER VANISHING IN MINORITY FUNDAMENTAL HEATING

The dispersion relation of a fast wave in a thermal (minority) hydroge n-deuterium plasma is investigated near the ion cyclotron frequency of hydrogen. It is found that the plasma shield for waves between the tw o-ion hybrid resonance and the minority fundamental resonance may be r educed by the thermal effects of plasma. By using zero Larmor radius a pproximations, the condition for cutoff layer vanishing due to the the rmal effects of plasma is obtained analytically. The formula derived i s compared with the numerical results from the full thermal-plasma dis persion relation, and excellent agreement is found. The results show t hat the cutoff layer may disappear in practical minority hydrogen-deut erium heating experiments.