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Journal article

'Profile consistency' features in shaped sawtoothing ohmic TCV plasmas

A large variety of plasma conditions has been created in TCV (Tokamak a Configuration Variable, B-T < 1.5 T, R-0 = 0.88 m, a < 0.25 m). They include limited and diverted discharges with elongations in the range 1-2.58, triangularities between -0.7 and 1 as well as 'square' shapes with plasma currents in the range 0.1-1 MA. Over the entire range of quasi-stationary ohmic conditions investigated we observe a correlation between electron pressure profiles and conductivity profiles, suggesting that [p]/p(0) approximate to (j)/j(0), where [] refers to an average over the volume or respectively, the cross sectional area of the plasma. The profiles become broader as the average current density is increased. These 'profile consistency' features are in apparent agreement with theoretical considerations based on minimum energy states of the plasma or on stationary entropy. Further analysis of the experimental evidence, together with a model of the current profile consistent with neoclassical conductivity in the confinement zone and corresponding to a safety factor 0.8 less than or equal to q less than or equal to 1 inside the sawtoothing core, however, shows that the observations can be accounted for by the effects of sawtooth activity.

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