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The relative accuracy of the electron temperature profiles measured on JET using ECE is improved by reducing the relative systematic error in the spectral calibration of the Michelson interferometer which is used to measure the ECE spectrum. The improvement technique does not change the absolute level of the spectral calibration, but reduces fluctations in the calibration which distort the temperature profiles. The toroidal field is varied and the development of the measured emission spectrum from a plasma with a fixed-shape temperature profile is analysed. The change in magnetic field causes a corresponding frequency shift of the ECE spectrum, while the calibration errors are fixed in frequency. During a ramp of the toroidal field, the spectrum traverses the calibration errors, allowing them to be distinguished from real spectral features. The effectiveness of the technique is investigated theoretically and by analysis of real data. Examples are presented which illustrate the substantial improvements which are obtained. Sawteeth and other fast temperature profile changes appear not to disturb the correction process, although profile changes correlated with the variation of magnetic field must be minimised.

Additional information

Authors: BINDSLEV H, Riso National Laboratory, Roskilde (DK)
Bibliographic Reference: Report: JET-R(88)04 EN (1988)
Availability: Available from the Publications Officer, JET Joint Undertaking Abingdon, Oxon. OX14 3EA (GB)
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