Recent Developments of the JET Far Infrared Interferometer-Polarimeter Diagnostic

The Far Infrared diagnostic provides essential internal measurements of the plasma density and magnetic field topology (q-profile via Faraday rotation angle) in real-time. The diagnostic capabilities have recently been extended in a number of key areas. Fast interferometer data, with 10ms time resolution, and a new Matlab code, have allowed improved analysis of the evolution of density profiles during fast events such as vertical plasma displacements, ELM, pellet fuelling and disruptions. Using the polarimeter measurements in realtime, a new calibration procedure has been developed, based on a propagation code using the Mueller matrix formalism. This approach leads to good estimates of the Faraday rotation (F) and Cotton-Mouton (C-M) angle in all JET plasma regimes and particularly for high performance discharges (plasma current of 4.5MA and large F and C-M angles).A further major upgrade of the system is presently underway: adding a second colour laser to the vertical channels and implementing a new phase counter based on analogue zero crossing and FPGA.
Name Size  
EFDC100306 1.10 Mb