Status and Plans for the DIII-D ECH/ECCD System

Abstract

The DIII-D electron cyclotron heating and current drive (ECH/ECCD) system has been operating with an annual average of 4268 individual gyrotron pulses into the plasma in the last four years and 3-3.6 MW average yearly power availability in the last ten years. This allowed an increase in the number and the range of experiments involving injection of 110 and 117.5 GHz EC power into the DIII-D tokamak plasma. Some of the operational limitations encountered for the 110 GHz X-mode second harmonic resonance scenario launched in overdense plasmas were bypassed with the alternative use of O-mode second harmonic launch and the addition of a new higher frequency gyrotron at 117.5 GHz. A new launcher that will inject the EC waves downward nearly parallel to the resonance layer with higher current drive efficiency and a long absorption path was built and is now installed. Some of the remaining gyrotrons have been successfully in service as long as 14 years and need to be replaced; major plans for commissioning and purchasing a new series of gyrotrons in addition to the repair and refurbishment of the older ones are under way. The number of gyrotrons will increase bringing the generated power up to 10 MW in the next few years.