The motional electric fieldE=vtimes;B, wherevis the velocity andBis the tokamak magnetic field, produces a strong Stark effect in spectral lines emitted by hydrogenic neutral beams. The tilt angle of the magnetic field line, a quantity related directly to the distribution of the plasma toroidal current, is deduced from a measurement of the direction of polarization of the Stark components. In the DIIIhyphen;D tokamak, the Balmerhyphen;agr; line of deuterium emitted by one of the highhyphen;power heating beams is analyzed. A multichord polarimeter measures the magnetic field pitch angle at eight spatial locations covering sim;0.6 of the nominal plasma diameter at the midplane outboard side. The diagnostic offers 2ndash;8hyphen;cm resolution in the major radius and 1hyphen;ms integration time. The accuracy of the measurement of the polarization direction necessary for an adequate reconstruction of the current profiles is obtained with the use of active polarizing elements which produce highhyphen;frequency intensity modulation with an amplitude related to the direction of linear polarization of the plasma radiation. The current profiles in highly shaped (noncircular) plasmas cannot be determined solely from the tilt angle measurements because they do not provide any information about the shape of magnetic surfaces. Thus, the polarization measurements are used in conjunction with a large set of external magnetic measurements (magnetic field and flux probes, diamagnetic loops, and Rogowski coils) by the magnetic field equilibrium code EFIT, and provide a constraint on the possible solutions for the current profile. thinsp;
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