Fast polarizers installation for ECRH and ECE in TCV

We report on the installation of fast polarizers for ECRH injection and ECE diagnostics, in the TCV tokamak. The main goal is to change the polarization during a plasma shot and react to changing conditions such as: plasma current and position, ECRH injection angles as well as ECE oblique observation angle and correlation ECE frequency. This will allow tracking of plasma variations, find optimum parameters to maximize ECRH absorption and improve the quality and consistency of ECE measurements. The polarization is varied using two fast polarizers, from General Atomics, positioned either in the evacuated transmission line for ECRH, or in a similar non-evacuated line near a real-time moveable directional antenna for ECE. A programmable driver is used to control a servo-motor and allows three operation modes during a plasma shot: fixed angle position, pre-programmed reference waveform and following of a real-time reference waveform. Preliminary tests of the motor controller achieved an 8 Hz bandwidth for a 4 +/-degrees amplitude motion and a 2.2 Hz bandwidth for a +/- 4 degrees amplitude motion. The fast polarizers are presently in the ECE system and the control hardware is being installed. (C) 2011 Elsevier B.V. All rights reserved.