Fringe jump analysis and electronic corrections for the Tore Supra far infrared interferometer
- CEA, IRFM, F-13108 Saint Paul Lez Durance (France)
On the Tore Supra tokamak, the ten-channel far infrared interferometer consists of a double color (119 and 195 {mu}m) system with two detectors for each channel to measure the plasma density. The phase measurement is obtained by combining a 100 kHz shifted reference beam with the probing beam that has crossed the plasma. The achieved precision--a few percent of a fringe--is very good compared with the expected variations due to plasma, which are on the order of several fringes. However, the counting of the fringe variations can be affected when the signal is perturbed by electromagnetic interferences or when it deviates in the presence of strong plasma refraction changes occurring during ICRH breakdowns, pellet injections, or disruptions. This induces a strong decrease in the reliability of the measurement, which is an important concern when the diagnostic is used for density control. We describe in this paper the renewing of the electronics that has been achieved to reduce and correct the number of the so-called fringe jumps. A new zero crossing method for phase measurement is used, together with a field programable gate array semiconductor integration, to measure the phase and activate the algorithm of corrections every 10 {mu}s. Comparisons between a numerical oscilloscope analysis and the corrected acquired data in the case of laboratory amplitude modulation tests and in the case of real plasma perturbations are also discussed.
- OSTI ID:
- 21266535
- Journal Information:
- Review of Scientific Instruments, Vol. 79, Issue 10; Other Information: DOI: 10.1063/1.2956824; (c) 2008 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); ISSN 0034-6748
- Country of Publication:
- United States
- Language:
- English
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