Development and test of a millimeter-wave MW-power bolometric load for CW gyrotrons and high-power transmission lines

The development of high-power dummy loads with calorimetric capabilities started in IFP with short pulse loads and continued with the design of a 2MW CW load in the frame of EGYC Consortium activities on the development of the European Gyrotron for ITER, coordinated by F4E. The loads are characterized by a spherical shape, with the cavity internal surface coated by a ceramic absorber. Special care has been devoted to the design of the power distribution on the surface and on the selection of the coating thickness. For the CW version, the cooling channels cover completely the external surface, for a fast heat removal. A prototype load with partial coating of the internal surface has been tested successfully in pulses up to 300 sec. at the 170 GHz JAEA ITER transmission line test bed, proving the capability of a full-coated version at power levels exceeding 1 MW. Load design and test results are discussed.