The development of conventional cavity gyrotrons at 140 GHz with 1-MW, CW output power at Forschungszentrum (FZK) Karlsruhe is mainly linked with the construction of the new superconducting stellarator W7-X at IPP Greifswald, Germany. For W7-X, 10 MW of electron cyclotron heating (ECRH) is planned and will be produced by ten gyrotrons each with a power of 1-MW. The gyrotrons are equipped with a diode-type magnetron injection gun, a conventional TE28,8 mode cavity, an advanced quasi-optical (qo) mode converter system, an RF output window with a single edge-cooled CVD-diamond disk and a depressed collector. Two prototype tubes have been built and tested successfully. The second one delivered an output power of 970kW for 11.7s (efficiency of 44% with single stage depressed collector), and 890kW for 180s (limit of the HV power supply). At reduced electron beam current (30A), the pulse length was 939s at 539 kW (506 MJ) and the limit was given by the increase of the internal gyrotron pressure. Based on these results seven gyrotrons were ordered. The first was delivered to FZK in February, has been installed into the testbed and is ready for tests. The result will be reported. For the use at ITER a 170 GHz coaxial cavity gyrotron with an output power of 2 MW, CW is under development in cooperation between European research institutions (FZK Karlsruhe, CRPP Lausanne and HUT Helsinki) and European tube industry (TED, France). The fabrication phase of a first prototype is in progress. The delivery of the first prototype is expected to be in summer 2006. Parallel to the industrial work the design of the main components as electron gun, cavity and the qo RF output system have been verified in a short pulse experiment under realistic conditions. Results will be reported. 110

Notch filters are required to protect sensitive millimeter wave diagnostics in fusion experiments from gyrotron stray radiation in the plasma vessel. A new type of notch filter based on a waveguide Bragg reflector is presented that can provide one or more defined stop bands in one standard waveguide frequency band.

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