The drift wave stability of pellet enhanced performance modes in Tore Supra has been investigated. It is found that these discharges are characterized by a combination of three different stabilizing mechanisms: density peaking, E × B shear and magnetic shear. Drift wave stability appears to be very sensitive to magnetic shear, with the most favourable configuration corresponding to a slightly negative magnetic shear. The conclusions are compatible with the results from JET and TFTR.
Convective modes driven by density gradients