Magnetic shear effect on confinement and electron heat transport in dominant electron heating experiments in Tore Supra

摘要

Various steady-state non-inductive plasmas, with strong electron heating and significant modification of the current density profile, have been routinely obtained on Tore Supra in either Lower Hybrid Current Drive or Fast Ware Heating experiments. In those dominant electron heating discharges, the dependence of electron heat diffusivity((chi)(sub e)) on the electron temperature gradient, the magnetic shear (s) and the safety factor (q) has been investigated. The increase of (chi)(sub e) with (nabla)T(sub e) indicates the existence of a critical temperature gradient. Moreover, the current density profile effect on the global confinement and the local transport is clearly observed. The electron heat flux (q(sub e)) is found to be roughly proportional to q(sup 2). The effect of magnetic shear on (chi)(sub e) is studied in the improved confinement discharges obtained by modifying of the current profile. (chi)(sub e) decreases when the magnetic shear increases in the confinement zone and/or when it vanishes in the plasma center. When s becomes negative a decrease in (chi)(sub e) by two orders of magnitude is observed. The effect of the current profile is also observed in the saturated ohmic regime. Comparisons between experimental (chi)(sub e) and well known local transport models (Taroni, and Rebut - Lallia -Watkins) are reported. (authors). 31 refs.