Infrared monitor of barrier window temperature during high power RF pulses

Barrier windows are critical components in electron cyclotron plasma heating/current drive (ECRH/ECCD) systems for fusion plasma experiments in which high frequency and high power microwave beams are used as additional heating or plasma profiles control. Even though material characteristics and thickness are chosen in order to reduce the absorbed power to a minimum, the window temperature is of major concern in high power, long pulse or CW operation. An infrared diagnostic device has been implemented on one of the boron nitride windows of the 140 GHz, 0.5 s, 0.5 MW per line ECRH system of the FTU tokamak. The evolution of the temperature of the barrier window can be monitored by acquisition of several IR emission profiles during the gyrotron pulse. Moreover, information on the beam pattern quality can be inferred.