Measurement problems at 120 GHz

The authors discuss the problems they faced with transmission, reflection and spectral measurements at 120 GHz on the nuclear-fusion gyrotron microwave-power-source for their project at CRPP. They begin with the historical background to the gyrotron and then describe the tube itself (a 200kW quasi-optical gyroklystron, 70 eV, 2 x 5T coils). They present nine problem areas (including feedback, Q and coupling of the Fabry-Perot resonator, dielectric constant, beam duct to attenuate travelling waves, calorimeter for measuring output power, and output coupler for measuring output spectrum) and suggestions for their solution. (T.J.R.A.)