The JET polari-interferometerFunded under: FP1-FUSION 9C
A multichannel far infrared interferometer used on the Joint European Torus (JET) is described. The light source is a 195micron DCN laser. The instrument is of the Mach-Zehnder type, with a heterodyne detection system. The modulation frequency (100kHz) is produced by diffraction from a rotating grating. There are 6 vertical and 2 oblique channels. The latter rely on retro-reflection from mirrors mounted on the vessel wall. Their vibration is compensated by a second wavelength interferometer at 118.8micron. The various subsystems are described, with emphasis on features necessitated by large path lengths; remote handling requirements; fluctuations in atmospheric humidity, and unmanned automatic operation. Typical measurements, along with real-time and off-line data analysis, are presented. The phase-shift measurement is made with an accuracy of (1/20) of a fringe, corresponding to a line integrated electron density of 5 x 1.0 E17/m2. Comparison with other electron density diagnostics are shown. The introduction of additional optics allows measurements of the Faraday effect and a determination of the poloidal magnetic field distribution. The signal processing and data analysis are described. Errors introduced by the calibration procedure, birefringence of the probing beams, toroidal field pick-up, flux geometry, and the density profile are considered. The Faraday angle is measured with an accuracy of 5%, and a time resolution of 1-10ms. The poloidal magnetic field is deduced with an accuracy of +- 15%.
Bibliographic Reference: Report: JET-P(89)15 EN (1989)
Availability: Available from the Publications Officer, JET Joint Undertaking, Abingdon, Oxon. OX14 3EA (GB)
Record Number: 198911014 / Last updated on: 1994-12-01
Original language: en
Available languages: en