The 105/140 GHz Megawatt Waveguide Transmission Line at ASDEX Upgrade

The Electron Cyclotron Resonance Heating (ECRH) system at the ASDEX Upgrade tokamak employs 8 gyrotrons, each delivering 1 MW at 140 GHz and about 800 kW at 105 GHz with a maximum pulse length of 10s. The gyrotron output beams are coupled to 8 waveguide transmission lines via quasi-optical Matching Optics Units (MOUs). The oversized corrugated HE11 waveguides with an inner diameter of 87 mm are operated at atmospheric pressure with overall lengths between 65 and 103 meters. The number of quasi-optical miter bends per line is between 6 and 8. High mode purity in the transmission lines is critical with respect to both, losses and atmospheric breakdowns in the waveguides.