Study of slow n=1, m=1 reconnection in JET discharges with low central magnetic shear
Buratti, P., B. Alper, S.V. Annibaldi, A. Becoulet, P. Belo, J. Bucalossi, M. de Baar, P. de Vries, D. Frigione, C. Gormezano, E. Joffrin, P. Smeulders e os contributos JET-EFDA
Experiments designed for the attainment of the hybrid advanced mode of
operation in JET revealed the existence of a new form of reconnecting modes
with toroidal number n = 1 and poloidal number m = 1, which have the
same radial structure as sawtooth precursors but are characterized by small
growth rate and low saturation amplitude. These modes develop in repetitive
cycles with typical growth times of 100 ms. Temperature perturbations are not
in the form of sawteeth; in fact, there is slow and mild erosion of the central
temperature without any crash. Comparison with theory of m = 1 modes
indicates that the slow growth observed in the hybrid regime is caused by low
magnetic shear (a measure of the radial variation of field line inclination) and
possibly by diamagnetic effects in the plasma core.