Safety factor measurements on the magnetic axis of the Texas experimental tokamak plasma in Ohmic and electron-cyclotron-resonance heated discharges

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Abstract
Analysis of the circular polarization of a spectral line emission inside plasmas provides a measurement of the poloidal magnetic field on the Texas experimental tokamak (TEXT). Three sets of different polarimeters, using, respectively, the Ti XVII 3834-Å line of the intrinsic titanium impurity and the Li I 6708-Å line of a monoenergetic lithium beam, were developed and operated on TEXT. The safety factor q on the magnetic axis, determined from the measured magnetic field, was found to be near unity in all cases of Ohmically heated sawtoothing and nonsawtoothing discharges, and significantly below unity in the case of electron-cyclotron-resonance heating at the plasma center for high edge q discharges.