INTERFEROMETER SYSTEMS ON LHD

INTERFEROMETER SYSTEMS ON LHD

INTERFEROMETER SYSTEMS ON LHD 150 150 Mathew

This paper describes the interferometer systems on the Large Helical Device (LHD). LHD is equipped with five interferometer systems, each of which has a different operational purpose and measurable electron density range. A single-channel millimeter-wave interferometer is mainly used for low-density plasmas along a horizontal line of sight on the equatorial plane. Wavelengths of 1 and 2 mm are used for vibration compensation based on two-color interferometry, which has been used since the first operation of LHD. A 13-channel CH 3 OH laser interferometer (wavelength of 119 mm) covers almost the whole poloidal cross sections of LHD plasmas with a chord separation of 90 mm. It routinely provides temporal behavior and profiles of the electron density. The laser has been developed as a collaboration between the National Institute for Fusion Science (NIFS) and Chubu University. An 80-channel CO 2 laser interferometer (10.6 mm) is employed for high-density plasmas such as superdense core plasmas. It adopts an imaging technique with three slablike beams and array detectors to measure the density profile precisely. A phase contrast imaging interferometer, which measures density fluctuations, is combined with the CO 2 laser interferometer. Since LHD has strong magnetic shear, a distribution of the density fluctuations is evaluated by using shear technique. A conventional millimeter-wave (4 mm) interferometer is also installed at a divertor region to measure dynamic density responses in a divertor leg. The phase counter used on these interferometers was originally developed at NIFS. The phase resolution of a typical phase counter is 1/100 fringe with a temporal response of 10 ms.

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28/10/2009