The Motional Stark Effect diagnostic on Alcator C-Mod

A ten channel Motional Stark Effect diagnostic has been installed on Alcator C-Mod to measure the plasma internal magnetic pitch angle profile. The C-Mod MSE measures the local electric field direction by measuring the polarization angle of Balmer-[alpha] n=2) emission from a radially injected hydrogen Diagnostic Neutral Beam (50 keV, 5 A, 50 ms). The Lorentz electric field (EL = v ) and the magnetic field cause the nominally fully degenerate Balmer-[alpha] to split into a partially degenerate multiplet whose components are polarized relative to the local fields. Through careful spectral filtering, MSE measures the polarization angle of select multiplet components using a photoelastic modulator based polarimeter. Investigation of hydrogenic Balmer-[alpha] transitions in crossed E and B fields typical of MSE has led to the discovery of new features of the Stark-Zeeman Balmer-[alpha] multiplet. Three different transitions are found for this EB = ( ... ) configuration. In the regime where the Stark effect dominates over the Zeeman effect, transitions polarize parallel to E, B, or ... with ellipticity a function of the beam velocity. More important for MSE diagnostics is the discovery that multiplet lines (summed over degenerate transitions) will be observed to be orthogonally polarized only for statistical (i.e. equally) upper hybrid state populations.

Department dc:contributor.department

Massachusetts Institute of Technology. Department of Nuclear Engineering

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2005

Author dc:creator

• Yuh, Howard Yung-Hao

Advisor dc:contributor.advisor

• Steven D. Scott.

• Nuclear Engineering.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/34976

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/34976