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 (∼15 cm). It is expected that the power deposition can be well localized in the plasma central region. 21 refs., 10 figs