Measurements of the internal magnetic field on DIII-D using intensity and spacing of the motional Stark multiplet

We describe a version of a motional Stark effect (MSE) diagnostic based on the relative line intensities and spacing of Stark split D(alpha) emission from the neutral beams. This system, named B-Stark, has been recently installed on the DIII-D tokamak. To find the magnetic pitch angle, we use the ra...

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Bibliographic Details
Published in:Review of scientific instruments 2008-10, Vol.79 (10), p.10F517-10F517
Main Authors: Pablant, N A, Burrell, K H, Groebner, R J, Kaplan, D H, Holcomb, C T
Format: Article
Language:English
Subjects:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY
BEAMS
COMPARATIVE EVALUATIONS
DIAGNOSTIC TECHNIQUES
DOUBLET-3 DEVICE
ITER TOKAMAK
MAGNETIC FIELDS
MAGNETOHYDRODYNAMICS
PLASMA
PLASMA DIAGNOSTICS
POLARIMETRY
STARK EFFECT
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Summary:We describe a version of a motional Stark effect (MSE) diagnostic based on the relative line intensities and spacing of Stark split D(alpha) emission from the neutral beams. This system, named B-Stark, has been recently installed on the DIII-D tokamak. To find the magnetic pitch angle, we use the ratio of the intensities of the pi(3) and sigma(1) lines. These lines originate from the same upper level and so are not dependent on the level populations. In future devices, such as ITER, this technique may have advantages over diagnostics based on MSE polarimetry. We have done an optimization of the viewing direction for the available ports on DIII-D to choose the installation location. With this placement, we have a near optimal viewing angle of 59.6 degrees from the vertical direction. All hardware has been installed for one chord, and we have been routinely taking data since January 2007. We fit the spectra using a simple Stark model in which the upper level populations of the D(alpha) transition are treated as free variables. The magnitude and direction of the magnetic field obtained using this diagnostic technique compare well with measurements from MSE polarimetry and EFIT.
ISSN:0034-6748
1089-7623
DOI:10.1063/1.2966596