A 70-GHz Electron Cyclotron Resonance Heating System for Heliotron J

A 70-GHz electron cyclotron resonance heating (ECRH) system has been constructed in a helical-axis heliotron device, Heliotron J, in order to realize localized heating and current drive experiments. Since the Heliotron J plasma has a threedimensional complex shape, the ECRH system is designed to satisfy the requirement of wide steering capability in both the toroidal and poloidal directions. The low-power transmission test shows that the beam radius of the focused Gaussian beam is 22 mm at the magnetic axis, which is small enough compared to the averaged minor plasma radius (170 mm), and the launching system covers a wide toroidal steering range from perpendicular to tangential injection by replacing the steering plane mirror. Since these characteristics satisfy the condition for controlling the power localization in the three-dimensional helical-axis configuration, it is possible to explore the on- and off-axis heating over most of the plasma radius (0 < r/a < 0.7) and the electron cyclotron current drive. In the high-power transmission test, the transmission efficiency of the 20-m corrugated waveguide is 92%, and the available output power to the vacuum vessel is up to 0.4 MW. Plasma production and heating are successfully performed using this ECRH system.