Ray tracing and absorption of microwaves in connection with electron-cyclotron resonance heating of the plasma in the L-2 stellarator

Plasma heating by microwaves at the first and second harmonics of the electron gyrofrequency is considered. Results are presented from simulations of the propagation and absorption of electromagnetic waves in the plasma of the L-2 stellarator. The calculations were carried out in the geometrical-optics approximation. The characteristics of absorption of the ordinary wave at the first harmonic and the extraordinary wave at the second harmonic have been obtained. The calculations were carried out for input angles close to {pi}/2. The results apply to microwave power fed into an external port in the L-2 stellarator, which corresponds to input of electromagnetic waves from the direction of the weak magnetic field. The single-pass absorption coefficient and the power absorption profiles are obtained as functions of the plasma parameters (the magnetic field, density, and electron temperature). The contribution to the absorption coefficient is estimated due to absorption of the power not absorbed in the first pass by estimating the reflection of waves from the wall of the vacuum chamber and calculating the absorption during the second pass of the microwave through the plasma. For resonant heating when the electron temperature in the center of the plasma is T{sub e}(0)=400 eV the one-pass absorptionmore » coefficient for an ordinary wave at the first harmonic is less than 0.6, and for an extraordinary wave at the second harmonic it is close to unity. The power density deposited by the microwave radiation in the center of the plasma reaches several W/cm{sub 3} for the ordinary wave. 12 refs., 6 figs.« less