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Title: Effects of stray lights on Faraday rotation measurement for polarimeter-interferometer system on EAST

Journal Article · · Review of Scientific Instruments
DOI: https://doi.org/10.1063/1.5012820 · OSTI ID:1526019
 [1]; ORCiD logo [2];  [3];  [3];  [3];  [1];  [1];  [1];  [2];  [2];  [2]
  1. Chinese Academy of Sciences (CAS), Hefei (China). Inst. of Plasma Physics; Univ. of Science and Technology of China, Hefei (China)
  2. Chinese Academy of Sciences (CAS), Hefei (China). Inst. of Plasma Physics
  3. Univ. of California, Los Angeles, CA (United States). Dept. of Physics and Astronomy

A double-pass radially view 11 chords polarimeter-interferometer system has been operated on the experimental advanced superconducting tokamak and provides important current profile information for plasma control. Stray light originating from spurious reflections along the optical path (unwanted reflections from various optical components/mounts and transmissive optical elements such as windows, waveplates, and lens as well as the detectors) and also direct feedback from the retro-reflector used to realize the double-pass configuration can both contribute to contamination of the Faraday rotation measurement accuracy. Modulation of the Faraday rotation signal due to the interference from multiple reflections is observable when the interferometer phase (plasma density) varies with time. Direct reflection from the detector itself can be suppressed by employing an optical isolator consisting of a λ/4-waveplate and polarizer positioned in front of the mixer. A Faraday angle oscillation during the density ramping up (or down) can be reduced from 5°–10° to 1°–2° by eliminating reflections from the detector. Residual modulation arising from misalignment and stray light from other sources must be minimized to achieve accurate measurements of Faraday rotation.

Research Organization:
Univ. of California, Los Angeles, CA (United States); Chinese Academy of Sciences (CAS), Hefei (China); Univ. of Science and Technology of China, Hefei (China)
Sponsoring Organization:
USDOE Office of Science (SC), Fusion Energy Sciences (FES); National Magnetic Confinement Fusion Program of China; National Natural Science Foundation of China (NSFC); USDOE
Grant/Contract Number:
SC0010469; 2014GB106002; 11375237; 11505238; 11261140328
OSTI ID:
1526019
Alternate ID(s):
OSTI ID: 1417939
Journal Information:
Review of Scientific Instruments, Vol. 89, Issue 1; ISSN 0034-6748
Publisher:
American Institute of Physics (AIP)Copyright Statement
Country of Publication:
United States
Language:
English
Citation Metrics:
Cited by: 13 works
Citation information provided by
Web of Science

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Cited By (4)

A Faraday-effect polarimeter for fast magnetic dynamics measurement on DIII-D journal October 2018
Non-inductive vertical position measurements by Faraday-effect polarimetry on EAST tokamak journal October 2018
Error correction associated with stray light for Faraday-effect polarimetry system on EAST journal May 2019
Theoretical assessment of the OTDR detector noise on plasma current measurement in tokamaks journal January 2019

Figures / Tables (4)