A dimensionless criterion for characterizing internal transport barriers in JET

Analysis of experiments performed at different heating powers and magnetic field intensities shows that the existence of internal transport barriers in JET can be inferred in regions of space-time where the ratio of the ion gyroradius to the local gradient scale length exceeds some critical value. A possible interpretation leading to the theoretical relevance of this dimensionless parameter as a local indicator of a bifurcated plasma state is the stabilization of turbulence by the E x B shear flows associated with large pressure gradients and plasma rotation. Large database analysis and real time plasma control are envisaged as attractive applications.