TJ-II:Magnetic surface mapping

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The fluorescent rod system used for flux surface mapping experiments at TJ-II.

After construction of TJ-II was completed, the accuracy of the magnetic field was checked by measuring the vacuum flux surface mapping and comparing to theoretical predictions. The mapping was done at a magnetic field strength of 10% of the nominal value. The detection process involved imaging <ref>J. Marin et al, Real time image integrator for magnetic surface mapping experiments in TJ-I U torsatron, IEEE Trans. Nucl. Science 43, 1 (1996) 234</ref> the spots produced by electrons, emitted from an electron gun, when these intersected an array of fluorescent rods that swept the vacuum vessel cross section. <ref>E. Ascasíbar et al, Magnetic surface mapping experiments in TJ-II Heliac, J. Plasma Fusion Res. SERIES 1 (1998) 183</ref> The agreement was found to be good. <ref name="Fraguas">A. López Fraguas et al, Magnetic surface mapping experiments in TJ-II, Proc. 13th International Stellarator Workshop (Australia, 2001) P1-6</ref>

Flux surfaces. Left column: measured. Right column: calculated. Top row: n=4, m=3. Middle row: n=8, m=5. Bottom row: n=3, m=2. <ref name="Fraguas" />


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