Progress on Electron Cyclotron Heating and Electron Cyclotron Current Drive Experiments in LHD

The electron cyclotron resonance heating (ECH) system in the Large Helical Device consists of nine gyrotrons: two that are 82.7 GHz, 0.45 MW, and 2 s; two that are 84 GHz, 0.8 MW, and 3 s; one that is 84 GHz, 0.2 MW, and 1000 s; and four that are 168 GHz, 0.5 MW, and 1 s. ECH and electron cyclotron current drive (ECCD) experiments using this system have been conducted not only for plasma heating and current drive experiments but also for transport and power deposition studies with power modulation. The configuration of the recent ECH system including gyrotrons, high-voltage power supplies, and the transmission system is overviewed. The outstanding progress on the ECH/ECCD experimental results is described in detail, which includes an electron transport study in the plasma with an electron internal transport barrier, electron Bernstein wave heating through the mode conversion process, preliminary current drive experiments, and a steady-state plasma sustainment >1 h by only ECH.