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Proceedings Paper

The Multichannel Submillimeter Wave Interferometer Of The Tokamak De Varennes.
Author(s): J L Lachambre
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Paper Abstract

We have developed a six-beam submillimeter wave interferometer at 214 μm to be installed on the Varennes tokamak for plasma shape and density fluctuation measurements (ne 3x1019 m-3, Te 450 eV). The number of chords and their distribution in the plasma cross-section are chosen for optimum density profile reconstruction through Abel inversion. Each channel consists of a frequency-modulated Mach-Zehnder interferometer derived from the same dualbeam submillimeter source. This source is an optically pumped twin CH2F2 laser featuring three stabilizing feedback loops: Stark-cell tuning of the pump CO2 laser, beat frequency control of the two output carriers and power locking of the submillimeter wave cavities. At a total pump power of 22 W, each laser delivers 25 mW of radiation at 214 μm. The beat frequency is maintained to 1 MHz with a long term stability of ± 15 kHz. Using corner-cube Schottky diodes optimized for 250 μm, the interferometer attains a line-integrated density resolution of 5x1016 m-2, a factor of 300 below the line density corresponding to the center chord passing through the plasma axis. The fringe-free line-integrated density signals as well as the amplified fluctuation signals are produced by a 0-8n electronic phase detector. Its 200-kHz output bandwidth makes the interferometer suitable for density fluctuation correlation studies in the .001 sn/n range. The extension of the present interferometer to polarimetry is discussed.

Paper Details

Date Published: 26 September 1986
PDF: 14 pages
Proc. SPIE 0666, Far-Infrared Science and Technology, (26 September 1986); doi: 10.1117/12.938833
Show Author Affiliations
J L Lachambre, Institut de Recherche d'Hydro-Quebec (Canada)

Published in SPIE Proceedings Vol. 0666:
Far-Infrared Science and Technology
Jerald A. R. Izatt, Editor(s)

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