Study of Spatial Distribution of Microwave Power Deposition for Plug ECRH in GAMMA 10

Wave propagation around the ECR layer in the GAMMA 10 plug region is analyzed by calculating the dispersion relation of an electron cyclotron wave in a hot plasma. Then, the spatial distribution of microwave power deposition and the absorption rate along each microwave ray are calculated. The absorption rate is experimentally evaluated by using an array of waveguide antennas. The calculated value well agrees with the experimental one on reasonable assumption that the extraordinary mode shares about 90% of the injected microwave power. This analysis is used to obtain an axisymmetric power deposition distribution. It is shown that the heating wave should be directed somewhat upward than the direction to the on-axis point on the resonance layer. This is because a larger power is deposited in the injection side lower side to the machine axis. For the plug in GAMMA 10, an injection beam with an elliptic cross section is suitable to obtain a circular distribution of power deposition.