Differential interferometry for measurement of density fluctuations and fluctuation-induced transport (invited)

Journal Article · Fri Oct 15 00:00:00 EDT 2010 · Review of Scientific Instruments

DOI:https://doi.org/10.1063/1.3464480· OSTI ID:22058665

Lin, L; Ding, W X; Brower, D L; Bergerson, W F; Yates, T F ^[1]

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1. University of California at Los Angeles, Los Angeles, California 90095 (United States)

Differential interferometry employs two parallel laser beams with a small spatial offset (less than beam width) and frequency difference (1-2 MHz) using common optics and a single mixer for a heterodyne detection. The differential approach allows measurement of the electron density gradient, its fluctuations, as well as the equilibrium density distribution. This novel interferometry technique is immune to fringe skip errors and is particularly useful in harsh plasma environments. Accurate calibration of the beam spatial offset, accomplished by use of a rotating dielectric wedge, is required to enable broad application of this approach. Differential interferometry has been successfully used on the Madison Symmetric Torus reversed-field pinch plasma to directly measure fluctuation-induced transport along with equilibrium density profile evolution during pellet injection. In addition, by combining differential and conventional interferometry, both linear and nonlinear terms of the electron density fluctuation energy equation can be determined, thereby allowing quantitative investigation of the origin of the density fluctuations. The concept, calibration, and application of differential interferometry are presented.

• OSTI ID: 22058665
• Journal Information: Review of Scientific Instruments, Vol. 81, Issue 10; Other Information: (c) 2010 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); ISSN 0034-6748
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY
BEAM PROFILES
CALIBRATION
DENSITY
DETECTION
DIELECTRIC PROPERTIES
ELECTRON DENSITY
FLUCTUATIONS
INTERFEROMETRY
LASER RADIATION
MHZ RANGE
MIXERS
MST DEVICE
OPTICS
PELLET INJECTION
PHOTON BEAMS
PLASMA
REVERSE-FIELD PINCH