First Measurements of the Oblique ECE system at JET.
Anomalies in the ECE spectra and discrepancies among different measurements in plasmas with high electron temperature have been reported in several experiments, suggesting that the electron distribution function could be significantly different from the Maxwellian one in the range of 1-3 times the thermal velocity. In this respect the new Oblique Electron Cyclotron Emission (ObECE) system at JET, entered operations during 2006, aims to resolve relatively small discrepancies among the ECE spectra measured at three toroidal angles, 0, 10 and 22 degrees with respect to the perpendicular to the toroidal field with 2 linear polarizations each. This technique enables the study of the electron distribution function in the low energy range. The spectral analysis of the EC radiation is performed over an extended bandwidth (75-800GHz) using a six-channel Martin-Puplett interferometer. The time resolution is usually set at 10ms/profile and the single line equivalent spectral resolution at 7.5-15GHz. At present results from several experiments performed at different magnetic fields (1.8-3.2T) and aimed to reach high Beta normalized values with high fraction of non inductive plasma current are being analyzed. This paper deals particularly with a set of shots of the "hybrid regime with high electron heating" experiment. In all cases a substantial amount of auxiliary heating (up to 24MW of NBI and ICRF) was used, with electron temperature in the range of 5-10keV and electron density of 3-6 1019 m-3.