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

Abstract A broadband heterodyne radiometer has been installed on Alcator C-Mod to measure second harmonic electron cyclotron emission at 234–306 GHz. The high-resolution diagnostic is now operational with 32 channels separated by T e on the low field side, for typical machine operation at B T =5.4 T. We describe the operation of the radiometer based on two novel second harmonic mixers appropriate for these high frequencies. We discuss the design and implementation of the optical system, heterodyne mixer and intermediate frequency sections. First results are presented along with the calibration of the diagnostic and comparison to other ECE diagnostics. Future plans for the diagnostic as a correlation radiometer for temperature fluctuation measurements are also discussed.