A High-Speed Optical Diagnostic that uses Interference Filters to Measure Doppler Shifts Page: 4 of 25
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I. Introduction
Measurements of plasma rotation have been important in fusion research for
decades with theories of parallel impurity velocity based on neoclassical effects first
developed in the 1970's.1 In neutral beam experiments in particular, the effects of
momentum transport are important as plasmas are accelerated to supersonic velocities.
Using a variety of techniques, including magnetic probes, Mach probes2, streak
photography, and spectroscopic measurements3 (including charge exchange
measurements on neutral beams4), physicists have used rotation measurements to
examine issues involving transport, instabilities, P-limits, and the effects of radial electric
fields. High-resolution, low throughput spectrometers' have been built and successfully
used for diagnosing fusion plasmas even with low rotation. The disadvantages are cost
and data collection speed. Other spectroscopic techniques developed more recently,
such as the MOSS camera system, employ time-delayed Fourier Transform
Spectroscopy and other optical coherence techniques in the time domain.' This
enhances the optical throughput by eliminating the need for an entrance slit.'
In this paper, a non-invasive velocity measurement is presented that also
eliminates the need for a grating spectrometer, allowing for reduced expense, high-
throughput and fast time response. This diagnostic has been developed for use on
Columbia's HBT-EP, a tokamak designed to examine the feasibility of high-beta
operation stabilized with a combination of close-fitting conducting walls, plasma
rotation, and active feedback.' In particular, the MHD stabilization program includes
using a biased edge probe as well as fast feedback control of the plasma rotation
relative to the conducting wall. The plasma parameters are: 92-97 cm major radius, 15-
19 cm minor radius, <15 kA plasma current, 3 kG toroidal field, <80 eV central
electron temperature, and < 1013 cm-3 electron density.- 2-
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Paul, S.F.; Cates, C.; Mauel, M.; Maurer, D.; Navratil, G. & Shilov, M. A High-Speed Optical Diagnostic that uses Interference Filters to Measure Doppler Shifts, report, August 9, 2004; Princeton, New Jersey. (https://digital.library.unt.edu/ark:/67531/metadc786058/m1/4/: accessed March 18, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.