Electron Temperature and Density Inferred from JET ECE Diagnostics
At JET the electron cyclotron emission (ECE) spectrum of several harmonics (up to 500GHz) mainly in X-mode polarisation is probed by a Michelson interferometer and a heterodyne radiometer. For a wide range of plasma parameters the optical thickness of the medium for the spectral range 100­200GHz is assumed to be suited to justify the black-body approach used as a standard at JET. This links the radiative temperature associated with the measured ECE spectrum in the domain of the second harmonic with the electron temperature profile. However, from theoretical point of view the full ECE spectrum provides additional information: about the electron density, and also about the equilibrium. To exploit this information the ECE ray-tracing code SPECE and TRAVIS have been used to model the measured ECE spectrum dependent on the profiles and equilibrium. Due to the embedding of the ray-tracing code SPECE into the Bayesian framework Minerva a powerful tool is available to infer the density and temperature profile relying only on the ECE diagnostic model. A proof of principle was demonstrated. With this approach, corrected temperature profiles not relying on the assumption of optical thickness, can be inferred, and compared to the results derived from the standard approach. It will also be shown how much information about the electron density profiles can be derived from the measured spectra. Besides those profiles, a correction of the vacuum magnetic field and the wall reflection properties are considered as free parameters in the probabilistic approach presented.