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taiichi_icc_proceedings_p2_016.pdf2011-08-18 02:30:38Taiichi Shikama

Design and development of a polarization resolved spectroscopy for measurements of the magnetic field in Caltech spheromak

Author: Taiichi Shikama
Requested Type: Poster Only
Submitted: 2011-05-28 20:41:16

Co-authors: Paul M. Bellan

Contact Info:
California Institute of Technology
1200 East California Boulevard
Pasadena, California   91125

Abstract Text:
A polarization resolved visible emission spectroscopy system is being developed for non-perturbing measurement of the magnetic field in the Caltech coaxial magnetized plasma gun experiment. By separately observing the Zeeman-split +/-sigma components of emissions from the plasma, the field strength in a dynamically evolving magnetic flux tube can be determined. The collection optics, designed to simultaneously observe the left- and right-circularly polarized +/-sigma components, consists of a quartz lens combined with an achromatic quarter wave plate and a beam-splitting Glan-Thompson prism. This arrangement provides both high extinction ratio and high throughput. The collected optical emission is transferred via a quartz optical fiber to a 1 meter spectrometer (JY Horiba 1000M, 3600 grooves/mm grating) and the spectra are recorded by an intensified gated CCD camera (Andor DH520-25F-03, 800 x 256 active pixels, 26 micro meter square pixel).
Expected nitrogen ionic spectra NII 2p3p ^1P_1-2p^3 ^1D_2 (489.5 nm) will be interpreted using quantum mechanical perturbation calculations involving the Zeeman effect. For typical experimental conditions (electron density ~10^21-22 m^-3, electron and ion temperatures ~1-3 eV, magnetic field ~0.2 T) it is expected that the difference in wavelengths between the +/-sigma components will be about 5 pm. This is to be compared with Doppler broadening of about 10-17 pm, Stark broadening of less than 50 pm, and instrumental function of about 50 pm at FWHM. The Zeeman splitting should be detectable by separation of the polarization components.

Characterization: D1,D5

Please add a footnote for Taiichi Shikama.

*On leave from Department of Mechanical Engineering and Science, Graduate School of Engineering, Kyoto University, Kyoto 606-8501, Japan.

University of Washington

Workshop on Innovation in Fusion Science (ICC2011) and
US-Japan Workshop on Compact Torus Plasma
August 16-19, 2011
Seattle, Washington

ICC 2011