Design of a Thomson scattering diagnostic system to measure fast ion- and alpha-particle distributions in Jet

A diagnostic system to measure the velocity- and spatial distribution of fast ion populations in JET is being designed. The diagnostic is based on collective scattering of microwave radiation. A high power (up to 1MW), long pulse (up to CW) gyrotron is envisaged as the microwave power source at 140GHz, while the scattered radiation will be detected using a heterodyne system. The diagnostic is especially important for the measurement of the fast alpha particle distributions in the DT-phase of JET. This paper gives a short description of the diagnostic method, the expected performance for JET conditions and describes in some detail the technical design of the transmission line. In view of the frequency that was chosen and the high unit power, the design of the transmission line is highly relevant for possible next generation Electron Cyclotron Heating programmes