ICRH coupling experiment in Big D

A 10 MW, 40 to 80 MHz ICRH experiment has been proposed for Big D (at General Atomic). Compact loop antennas have been chosen to convey this power. In order to verify that the antenna will have sufficient loading, a prototype low-power antenna has been designed and will be installed in January 1986. The antenna is a cavity antenna that will operate from 30 to 80 MHz with a 50 Ohm match at R = 1 Ohm. The antenna can be moved from a position flush with the wall to flush with the limiter. By these means, we will establish the maximum acceptable gap from the coupler to the plasma. The electrical, mechanical, and thermal characteristics of this antenna system will be discussed. In addition to experimental exploration of coupling, we have investigated wave propagation and absorption in Big D by using a cold collisional plasma model in straight tokamak geometry with rotational transform. Although loading is dependent on the plasma position, both the reactive and real loads (10 to 20 and 1 to 2 Ohms) are comparable to other experiments. Loading and power deposition profiles as a function of frequency, density, and species mix will be presented. The reportmore » consists of viewgraphs of the presentation.« less