JET polari-interferometer

Journal Article · Fri Sep 01 00:00:00 EDT 1989 · Review of Scientific Instruments; (USA)

DOI:https://doi.org/10.1063/1.1140666· OSTI ID:5537464

Braithwaite, G; Gottardi, N; Magyar, G; O'Rourke, J; Ryan, J; Veron, D ^[1]

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1. JET Joint Undertaking, Abingdon, Oxon OX14 3EA, United Kingdom (GB)

A multichannel far-infrared interferometer used on the Joint European Torus (JET) is described. The light source is a 195-{mu}m DCN laser. The instrument is of the Mach--Zehnder type, with a heterodyne detection system. The modulation frequency (100 kHz) is produced by diffraction from a rotating grating. There are six vertical and two oblique channels. The latter rely on retroreflection from mirrors mounted on the vessel wall. Their vibration is compensated by a second wavelength interferometer at 118.8 {mu}m. The various subsystems are described, with emphasis on features necessitated by (a) large path lengths, (b) remote handling requirements, (c) fluctuations in atmospheric humidity, and (d) 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{times}10{sup 17} m{sup {minus}2}. 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 pickup, the flux geometry, and the density profile are considered. The Faraday angle is measured with an accuracy of 5% and a time resolution of 1--10 ms. The poloidal magnetic field is deduced with an accuracy of {plus minus}15%.

• OSTI ID: 5537464
• Journal Information: Review of Scientific Instruments; (USA), Vol. 60:9; ISSN 0034-6748
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
JET TOKAMAK
ELECTRON DENSITY
MACH-ZEHNDER INTERFEROMETER
PERFORMANCE
PLASMA DIAGNOSTICS
BEAM OPTICS
DESIGN
FAR INFRARED RADIATION
FARADAY EFFECT
OPERATION
ELECTROMAGNETIC RADIATION
INFRARED RADIATION
INTERFEROMETERS
MEASURING INSTRUMENTS
RADIATIONS
THERMONUCLEAR REACTORS
TOKAMAK TYPE REACTORS
700102* - Fusion Energy- Plasma Research- Diagnostics