WAVE-GUIDE TRANSMISSION-LINE FOR 106-GHZ ELECTRON-CYCLOTRON HEATING IN HELIOTRON-E

A 106-GHz electron cyclotron heating system is installed and operated for plasma production and heating of the Heliotron-E helical device. T he Gaussian beam radiated from the gyrotron is coupled to the HE11 wav eguide mode by the matching optics unit (MOU), then transmitted throug h 15-m corrugated waveguides and four miter bends. The system is close d for safety to prevent spurious modes from radiating into the free sp ace and is operated at atmospheric pressure. The transmitted wave is l aunched from the outside of the torus, and the launched beam is focuse d on the magnetic axis so that the power deposition is expected to be localized at the desired resonance region. The measured transmission e fficiency from the MOU output to the launcher output is 86%, which is in good agreement with the theoretical estimate. The power losses aris e mainly at the waveguide mouth where the Gaussian beam is coupled to the HE11 mode, at the miter bends and in the launching system.