Effects of stray lights on Faraday rotation measurement for polarimeter-interferometer system on EAST
- Chinese Academy of Sciences (CAS), Hefei (China). Inst. of Plasma Physics; Univ. of Science and Technology of China, Hefei (China)
- Chinese Academy of Sciences (CAS), Hefei (China). Inst. of Plasma Physics
- 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
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