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Various steady state non-inductive plasmas, with strong electron heating and significant modification of the current density profile, have been routinely obtained in Tore Supra discharges with lower hybrid current drive (LHCD) and/or fast wave electron heating (FWEH) experiments. The dependence of the electron heat diffusivity on the electron temperature gradient, the magnetic shear and the safety factor is demonstrated. The increase of electron heat diffusivity with the electron temperature gradient indicates the existence of a critical temperature gradient. Moreover, the current density profile affects the global confinement and the local transport. The electron heat flux is found to be roughly proportional to the square of the safety factor. The effect of magnetic shear on electron heat diffusivity is studied in the improved confinement discharges obtained by modifying the current profile. When the magnetic shear increases in the confinement zone and/or vanishes in the plasma centre, electron heat diffusivity decreases. The effect of the current profile is also observed in the saturated ohmic regime. The results for electron heat diffusivity do not agree with the local transport models of Taroni et al or Rebut-Lallia-Watkins (RLW) for all ranges of electron heating.

Additional information

Authors: HOANG G T ET AL, CEA, CEN Cadarache, Saint-Paul-lez-Durance (FR)
Bibliographic Reference: Article: Nuclear Fusion, Vol. 38 (1998) No. 1, pp. 117-132
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