Upgrades to and Recommissioning of the C-Mod FIR Polarimeter

The Alcator C-Mod 3-chord FIR polarimeter, with a 2 MHz bandwidth, is capable of responding to both fast changes in the plasma equilibrium and high frequency fluctuations. It operates under ITER-like plasma conditions and magnetic fields, and uses an optical layout similar to that proposed for ITER. After a brief discussion of this system, the design of the upgrade as installed on Alcator C-Mod will be presented. The laser table has been relocated from the cell to a shielded and climate controlled location, and improvements have been made to its acoustic isolation. New collimation optics, and an enclosed, humidity controlled beam-line needed to convey the FIR beams across the C-Mod cell, have been designed and installed. Results from phase calibrations and initial testing of the laser system and reference detectors during C-Mod operation will be presented.