New Approximations and Calibration Methods to Provide Routine Real-Time Polarimetry on JET

The increasing importance of providing reliable polarimetric measurements in real time, for both machine protection and plasma control, has motivated the development of a quick version of the calibration algorithms for JET polarimeter. This new code, which interprets the calibration procedure performed before each shot, is based on a physical equivalent model of the diagnostic optical path and is valid for any operational regime of JET. It provides results before the plasma breakdown, and, with its estimates of the optical paths parameters, the polarimetric measurements have an accuracy more than sufficient for real-time purposes. New approximate equations have been validated in order to obtain the line integrated density from the newly calibrated horizontal chords, so that also these polarimetric measurements can also be used for density feedback and machine protection. The availability of reliable polarimetric measurements in real time opens new perspectives also to the determination of the plasma boundary, the magnetic equilibrium, and their use in advanced feedback control schemes.