A Compact Two-Frequency Notch Filter for Millimeter Wave Plasma Diagnostics

Sensitive millimeter wave diagnostics in magnetic confinement plasma fusion experiments need protection from gyrotron stray radiation in the plasma vessel. Modern electron cyclotron resonance heating (ECRH) systems take advantage of multifrequency gyrotrons. This means that the frequency band of some millimeter wave diagnostics contains more than one narrow-band gyrotron-frequency line, which needs to be effectively suppressed. A compact standard waveguide notch filter based on coupled waveguide resonators with rectangular cross-section is presented which can provide very high suppression of several gyrotron frequencies and has low insertion loss of the passband

Completion of the 8 MW Multi-Frequency ECRH System at ASDEX Upgrade

Over the last 15 years, the Electron Cyclotron Resonance Heating (ECRH) system at the ASDEX Upgrade tokamak has been upgraded from a 2 MW, 2 s, 140 GHz system to an 8 MW, 10 s, dual frequency system (105/140 GHz). Eight gyrotrons were in routine operation during the current experimental campaign. All gyrotrons are step-tunable operating at 105 and 140 GHz with a maximum output power of about 1 MW and 10 s pulse length. The system includes 8 transmission lines, mainly consisting of oversized corrugated waveguides (I.D. = 87 mm) with overall lengths between 50 and 70 meters including quasi-optical sections at both ends. Further improvements of the transmission lines with respect to power handling and reliability are underway