High resolution ECE radiometer for electron temperature profile and fluctuation measurements on Alcator C-Mod

A broadband heterodyne radiometer has been installed on Alcator C-Mod to me asure second harmonic electron cyclotron emission at 234-306 GHz. The high- resolution diagnostic is now operational with 32 channels separated by <1 c m and a frequency response of 1 MHz, measuring T-e on the low field side, f or typical machine operation at B-T = 5.4 T. We describe the operation of t he radiometer based on two novel second harmonic mixers appropriate for the se high frequencies. We discuss the design and implementation of the optica l system, heterodyne mixer and intermediate frequency sections. First resul ts are presented along with the calibration of the diagnostic and compariso n to other ECE diagnostics. Future plans for the diagnostic as a correlatio n radiometer for temperature fluctuation measurements are also discussed. ( C) 2001 Published by Elsevier Science B.V.