Measurements of residual power of EC waves propagating in FTU tokamak during ECRH experiments at 140 GHz

The measure of residual power of electron cyclotron (EC) waves propagating in FTU tokamak during ECRH experiments at 140 GHz is provided by three low-gain probes facing the tokamak walls. One probe is located in the same poloidal section of the EC launching system; the other two are toroidally displaced by 60 and 90°, respectively. A model for the estimate of the e.m. power coupled to the probes has been developed. Several discharges with two gyrotrons at 140 GHz, delivering 0.5 MW each for up to 0.5 s, and with different polarizations have been analyzed. Calculations of the power deposition and e.m. residual power are found to be in very good agreement with the experimental measurements.