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

Abstract

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.

Authors:
 [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
Publication Date:
Research Org.:
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 Org.:
USDOE Office of Science (SC), Fusion Energy Sciences (FES); National Magnetic Confinement Fusion Program of China; National Natural Science Foundation of China (NSFC)
OSTI Identifier:
1526019
Alternate Identifier(s):
OSTI ID: 1417939
Grant/Contract Number:  
SC0010469; 2014GB106002; 11375237; 11505238; 11261140328
Resource Type:
Accepted Manuscript
Journal Name:
Review of Scientific Instruments
Additional Journal Information:
Journal Volume: 89; Journal Issue: 1; Journal ID: ISSN 0034-6748
Publisher:
American Institute of Physics (AIP)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; 46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY

Citation Formats

Zou, Z. Y., Liu, H. Q., Ding, W. X., Chen, J., Brower, D. L., Lian, H., Wang, S. X., Li, W. M., Yao, Y., Zeng, L., and Jie, Y. X. Effects of stray lights on Faraday rotation measurement for polarimeter-interferometer system on EAST. United States: N. p., 2018. Web. https://doi.org/10.1063/1.5012820.
Zou, Z. Y., Liu, H. Q., Ding, W. X., Chen, J., Brower, D. L., Lian, H., Wang, S. X., Li, W. M., Yao, Y., Zeng, L., & Jie, Y. X. Effects of stray lights on Faraday rotation measurement for polarimeter-interferometer system on EAST. United States. https://doi.org/10.1063/1.5012820
Zou, Z. Y., Liu, H. Q., Ding, W. X., Chen, J., Brower, D. L., Lian, H., Wang, S. X., Li, W. M., Yao, Y., Zeng, L., and Jie, Y. X. Wed . "Effects of stray lights on Faraday rotation measurement for polarimeter-interferometer system on EAST". United States. https://doi.org/10.1063/1.5012820. https://www.osti.gov/servlets/purl/1526019.
@article{osti_1526019,
title = {Effects of stray lights on Faraday rotation measurement for polarimeter-interferometer system on EAST},
author = {Zou, Z. Y. and Liu, H. Q. and Ding, W. X. and Chen, J. and Brower, D. L. and Lian, H. and Wang, S. X. and Li, W. M. and Yao, Y. and Zeng, L. and Jie, Y. X.},
abstractNote = {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.},
doi = {10.1063/1.5012820},
journal = {Review of Scientific Instruments},
number = 1,
volume = 89,
place = {United States},
year = {2018},
month = {1}
}

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Figures / Tables:

FIG. 1 FIG. 1: The one chord optical layout used by the POINT system.

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Works referenced in this record:

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    Works referencing / citing this record:

    A Faraday-effect polarimeter for fast magnetic dynamics measurement on DIII-D
    journal, October 2018

    • Chen, J.; Ding, W. X.; Brower, D. L.
    • Review of Scientific Instruments, Vol. 89, Issue 10
    • DOI: 10.1063/1.5035276

    Non-inductive vertical position measurements by Faraday-effect polarimetry on EAST tokamak
    journal, October 2018

    • Ding, W. X.; Liu, H. Q.; Qian, J. P.
    • Review of Scientific Instruments, Vol. 89, Issue 10
    • DOI: 10.1063/1.5035280

    Error correction associated with stray light for Faraday-effect polarimetry system on EAST
    journal, May 2019

    • Lian, H.; Liu, H. Q.; Ding, W. X.
    • Review of Scientific Instruments, Vol. 90, Issue 5
    • DOI: 10.1063/1.5089699

    Theoretical assessment of the OTDR detector noise on plasma current measurement in tokamaks
    journal, January 2019

    • Motuz, Rastislav; Leysen, Willem; Moreau, Philippe
    • Applied Optics, Vol. 58, Issue 11
    • DOI: 10.1364/ao.58.002795

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