106-GHZ ELECTRON-CYCLOTRON HEATING-SYSTEM FOR HELIOTRON-E

A new high-power electron cyclotron heating system has been installed for the Heliotron-E helical device. This system is designed to operate at 106-GHz frequency with a half-megawatt output power. The system consists of a pulse gyrotron with TE12,2 whispering gallery mode (WGM) output, conversion system of the WGM into the Gaussian-like beam, transmission line for HE11 mode, and launching system. From measurement of radiation patterns, it was confirmed that the WGM was effectively converted into the Gaussian-like beam, and the emergent radiation profile from the tubular oversized corrugated waveguide was close to a circular Gaussian one even when the beam coupled to the HE11 mode had the side lobes before the transmission. This indicates that the oversized corrugated waveguides act as a mode filter. The launching system effectively focuses the Gaussian beam in the free space to a 2-cm (poloidal) x 3-cm (toroidal) e-folding power spot size. These are small enough compared with the plasma minor radius (approximately 15 cm). It is expected that the power deposition can be well localized in the plasma central region.