The DIII–D program is presently commissioning the first MW gyrotron of a planned 3 MW, 110 GHz electron cyclotron heating (ECH) system for off-axis electron heating and current drive. Advanced tokamak (AT) research in DIII–D and other tokamaks requires the ability to control the current density profile. ECH offers the ability to localize the heating and driven current in a controllable manner and is not dependent upon, the local plasma conditions, so it appears to be an ideal tool for AT research. The planned rf sources for the DIII-D system are I MW state-of-the-art internal mode-converter gyrotrons, with one gyrotron being manufactured by GYCOM, a Russian company, and two gyrotrons being manufactured by CPI (formerly Varian). The GYCOM gyrotron has been tested at the factory to 960 kW, 2 seconds and has been shipped to GA where it is now undergoing initial checkout and testing. The first CPI gyrotron has been assembled and factory tested to 530 kW, 2 seconds and 350 kW, 10 seconds. Both the Gycom and CPI gyrotrons are limited in pulse length at full power by thermal limits on the output window. The second CPI gyrotron is expected to be ready for testing in April 1996.

This paper will report on the initial experiences of using the GYCOM I MW, 110 GHz internal mode-converter gyrotron, at General Atomics, and the observed effects the ECRH power has on the DIII-D plasma.