Internal transport barrier dynamics with plasma rotation in JET

At JET the dynamics of internal transport barriers (ITBs) has been explored by trying to decouple the effects of heating on the one hand and torque on the other with the ultimate objective of identifying the minimum torque required for the formation of transport barriers. The experiments shed light on the physics behind the initial trigger for ITBs, which often shows to be linked to the shape of the q profile and magnetic shear, while the further development was influenced by the strength of the rotational shear. In discharges with a small amount of rotational shear ITBs were triggered, which suggest that the overall rotational shear is not the dominant factor in the triggering process. However, the subsequent growth of the barrier was limited if the rotational shear was too low at the time of triggering. This growth phase may be highly non-linear, with several possible positive feedback loops, such as the increases in the toroidal and poloidal component of the rotational shear caused by the ITB itself.