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Title: Measurements of DIII-D poloidal field by fiber-optic pulsed polarimetry

Abstract

A new technique for measuring the spatial and temporal structure of the poloidal field is presented, whereby the magnetic field causes the polarization of light traveling through an optical fiber to rotate via the Faraday effect by an amount proportional to the strength of the field oriented along the fiber. In fiber optic pulsed polarimetry, changes in the polarization of the backscatter light from the fiber are detected, thereby permitting measurement of the field as a function of position along the fiber. In this proof-of-principle experiment, specially prepared single-mode fibers with weak fiber Bragg gratings were installed in the poloidal direction on the outside of the thermal blanket on DIII-D. Light at 532 nm from a mode-locked Nd:YAG laser was injected into the optical fibers. The laser repetition rate was 895 kHz with a pulse length of <10 ps, resulting in ~1 μs temporal resolution. A photodetector system measured the Stokes polarization components necessary to determine the amount of polarization rotation. For this experiment, bandwidth limitations of the detectors resulted in a spatial resolution of ≈2 cm. The measured temporal and spatial distributions of the poloidal field are consistent with inductive probe measurements and Elastodynamic Finite Integration Technique reconstructions ofmore » the spatial distribution. Furthermore, this demonstrates the ability of this technique to provide real-time detection of the temporal and spatial variations of the poloidal field. Besides revealing more detailed information about the plasma, this new diagnostic capability can also help in detecting instabilities in real time, thereby enabling enhanced machine protection.« less

Authors:
ORCiD logo [1];  [1]; ORCiD logo [2];  [2];  [2]; ORCiD logo [3];  [3];  [3]
+ Show Author Affiliations
  1. STI Optronics, Redmond, WA (United States)
  2. General Atomics, San Diego, CA (United States)
  3. Polytechnique Montreal (Canada)
Publication Date:
Research Org.:
General Atomics, San Diego, CA (United States); STI Optronics, Inc., Redmond, WA (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
1609206
Alternate Identifier(s):
OSTI ID: 1459693
Grant/Contract Number:  
FC02-04ER54698; SC0009808
Resource Type:
Accepted Manuscript
Journal Name:
Review of Scientific Instruments
Additional Journal Information:
Journal Volume: 89; Journal Issue: 10; Journal ID: ISSN 0034-6748
Publisher:
American Institute of Physics (AIP)
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; instruments & instrumentation; physics; optical fibers; lasers; magnetic field sensors; optical polarimetry; birefringence; tokamaks; photodetectors; Faraday effect; fiber optics; polarization

Citation Formats

Kimura, W. D., Dhillon, D. S., Munaretto, S., Strait, E. J., Du, D., Loranger, S., Boisvert, J. -S., and Kashyap, R. Measurements of DIII-D poloidal field by fiber-optic pulsed polarimetry. United States: N. p., 2018. Web. doi:10.1063/1.5034777.
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Kimura, W. D., Dhillon, D. S., Munaretto, S., Strait, E. J., Du, D., Loranger, S., Boisvert, J. -S., & Kashyap, R. Measurements of DIII-D poloidal field by fiber-optic pulsed polarimetry. United States. https://doi.org/10.1063/1.5034777
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Kimura, W. D., Dhillon, D. S., Munaretto, S., Strait, E. J., Du, D., Loranger, S., Boisvert, J. -S., and Kashyap, R. Tue . "Measurements of DIII-D poloidal field by fiber-optic pulsed polarimetry". United States. https://doi.org/10.1063/1.5034777. https://www.osti.gov/servlets/purl/1609206.
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@article{osti_1609206,
title = {Measurements of DIII-D poloidal field by fiber-optic pulsed polarimetry},
author = {Kimura, W. D. and Dhillon, D. S. and Munaretto, S. and Strait, E. J. and Du, D. and Loranger, S. and Boisvert, J. -S. and Kashyap, R.},
abstractNote = {A new technique for measuring the spatial and temporal structure of the poloidal field is presented, whereby the magnetic field causes the polarization of light traveling through an optical fiber to rotate via the Faraday effect by an amount proportional to the strength of the field oriented along the fiber. In fiber optic pulsed polarimetry, changes in the polarization of the backscatter light from the fiber are detected, thereby permitting measurement of the field as a function of position along the fiber. In this proof-of-principle experiment, specially prepared single-mode fibers with weak fiber Bragg gratings were installed in the poloidal direction on the outside of the thermal blanket on DIII-D. Light at 532 nm from a mode-locked Nd:YAG laser was injected into the optical fibers. The laser repetition rate was 895 kHz with a pulse length of <10 ps, resulting in ~1 μs temporal resolution. A photodetector system measured the Stokes polarization components necessary to determine the amount of polarization rotation. For this experiment, bandwidth limitations of the detectors resulted in a spatial resolution of ≈2 cm. The measured temporal and spatial distributions of the poloidal field are consistent with inductive probe measurements and Elastodynamic Finite Integration Technique reconstructions of the spatial distribution. Furthermore, this demonstrates the ability of this technique to provide real-time detection of the temporal and spatial variations of the poloidal field. Besides revealing more detailed information about the plasma, this new diagnostic capability can also help in detecting instabilities in real time, thereby enabling enhanced machine protection.},
doi = {10.1063/1.5034777},
journal = {Review of Scientific Instruments},
number = 10,
volume = 89,
place = {United States},
year = {Tue Jul 10 00:00:00 EDT 2018},
month = {Tue Jul 10 00:00:00 EDT 2018}
}
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https://doi.org/10.1063/1.5034777
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Works referenced in this record:

Test of fiber optic based current sensors on the Tore Supra tokamak
journal, October 2011

Plasma Current Measurement in Thermonuclear Fusion Reactors Using a Photon-Counting POTDR
journal, March 2017

  • Wuilpart, Marc; Aerssens, Matthieu; Gusarov, Andrei
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All-fiber optical magnetic-field sensor based on Faraday rotation in highly terbium-doped fiber
journal, January 2010

Equilibrium analysis of current profiles in tokamaks
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journal, February 2006

  • Strait, E. J.
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Novel custom fiber Bragg grating fabrication technique based on push-pull phase shifting interferometry
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conference, April 2012

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  • DOI: 10.1117/12.922714

Nonperturbative measurement of the local magnetic field using pulsed polarimetry for fusion reactor conditions (invited)
journal, October 2008

  • Smith, Roger J.
  • Review of Scientific Instruments, Vol. 79, Issue 10
  • DOI: 10.1063/1.2981169
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