Edge cooling experiments and non-local transport phenomena in Tore Supra

Edge cooling experiments have been performed in Tore Supra by impurity injection and oblique pellet injection. Non-local transport (NLT) features have been confirmed in both cases in the ohmic regime. The pellet injection experiments have shown the existence of a threshold on the plasma density 〈n_e〉 and current I_p for the observation of this effect: 〈n_e〉/I_p^1/2≤1.0×10¹⁶ (m^-3 A^-1/2). A second threshold on the relative density variation caused by the pellet injection has also been observed: Δ〈n_e〉/〈n_e〉≤0.5. It has been observed that in the L regime during lower hybrid current drive (LHCD) experiments these limits are extended: [〈n_e〉/I_p^1/2]_crit = 1.4×10¹⁶ (m^-3 A^-1/2) and [Δ〈n_e〉/〈n_e〉]_crit≥0.65. Observations in a LHCD scheme with fully non-inductive plasma current seem to indicate that the mechanism governing the NLT is unlikely to be linked to the plasma current profile effects including the spatial redistribution, the magnetic shear, and the low-m MHD modes.