Calibration of the Joint European Torus energetic ion and alpha particle collective Thomson scattering diagnostic receiver

The receiver of the Joint European Torus (JET) energetic ion and alpha part icle collective Thomson scattering diagnostic is calibrated assuming blackb ody emission from the torus vacuum vessel (VV) and using electron cyclotron emission (ECE). The 32 receiver channels are absolutely calibrated with a mechanical chopper in the quasioptical arm of the receiver, alternating the receiver view between the torus vacuum at 320 degrees C and room temperatu re. This calibration is noisy due to the small difference between torus and room temperatures. A more accurate relative calibration is achieved with t he ECE during plasma shots. The intensity of the ECE is found to be a smoot h function of frequency, which enables the combination of the ECE calibrati on with the VV calibration. The accuracy of the absolute VV calibration is hereby improved to nearly the same standard as the relative ECE calibration . ECE signals measured by the calibrated receiver agree well with standard JET ECE diagnostics. Based on mathematical considerations presented here, n oise is injected into the receiver final intermediate frequency stage durin g VV calibrations to provide more bit transitions for accurate analog-to-di gital (AD) conversion of the low level calibration signals. This yields a r esolution which is better than 1% of an (AD) step. (C) 1999 American Instit ute of Physics. [S0034-6748(99)75701-1].