The design of a second harmonic tangential array interferometer for C-Mod

Journal Article · Wed Jan 01 04:00:00 EST 1997 · Review of Scientific Instruments

DOI:https://doi.org/10.1063/1.1147683· OSTI ID:451847

Bretz, N; Jobes, F ^[1]; Irby, J ^[2]

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1. Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543 (United States)
2. Plasma Fusion Center, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States)

A design for a tangential array interferometer for C-Mod operating at 1.06 and 0.53 {mu}m is presented. This is a special type of two color interferometer in which a Nd:YAG laser is frequency doubled in a nonlinear crystal. Because the doubling efficiency is imperfect, two frequencies propagate collinearly through the plasma after which the 1.06 {mu}m ray is doubled again mixing in the optical domain with the undoubled ray. The resulting interference is insensitive to path length but is affected by plasma dispersion in the usual way. A typical central fringe shift in C-Mod is expected to be 0.1{endash}1.0, but the absolute and relative accuracy in n{sub e}l measurements can be as high as in a conventional interferometer. This design uses a repetitively pulsed laser which is converted to a fan beam crossing the horizontal midplane. The chordal array is defined by internal retroreflectors on the C-Mod midplane which return the beam to the second doubler and a detector array. This interferometer design has beam diameters of a few millimeters and element spacings of a few centimeters, uses a repetitively pulsed, TEM{sub 00} Nd:YAG laser, fiber optic beam transport, commercial components, and a compact optical design which minimizes port space requirements. An optical system design is presented which is based on the performance of a tabletop prototype at Princeton Plasma Physics Laboratory. {copyright} {ital 1997 American Institute of Physics.}

• Research Organization: Princeton Plasma Physics Laboratory
• DOE Contract Number: AC02-76CH03073; AC02-78ET51013
• OSTI ID: 451847
• Report Number(s): CONF-960543--
• Journal Information: Review of Scientific Instruments, Journal Name: Review of Scientific Instruments Journal Issue: 1 Vol. 68; ISSN RSINAK; ISSN 0034-6748
• Country of Publication: United States
• Language: English

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