ECH propagation and absorption experiments at 140 GHz in MTX

Single pass absorption experiments using fundamental, O-mode ECH waves have been performed in the Microwave Tokamak Experiment (MTX) and found to be consistent with linear absorption theory, as predicted for the ECH source which is a 140 GHz, 400 kW CW gyrotron. These experiments provide the basis for comparison with future Free Electron Laser (FEL) experiments in which the absorption is predicted to be in the non-linear regime for P{sub FEL} {ge} 1 GW. The gyrotron power is coupled into a quasi-optical transmission line to the tokamak by a Vlasov antenna. The input power is measured by calorimeters located just outside the injection port and on the vacuum wall opposite the port. For plasma shots, the total transmitted power and its profile are measured. Temporal analysis of the thermistor signals compared with a heat diffusion model for the tiles gives the spatial profile of transmitted power. These measurements are compared with the stored energy increase by diamagnetism measurements, 3-D vacuum fields calculations and ray-tracing calculations of the transmitted power. 5 refs., 4 figs