Optimized shear (OS) experiments in JET can generate an internal transportbarrier (ITB) during a high power heating phase early in the plasma discharge.A strong link is generally observed between the formation of the barrier andthe location of an integer q magnetic surface within a low magnetic shear(s = r/q(dq/dr)) region of the plasma. However, if the q-profile forsuch experiments is modified by applying lower hybrid heating and currentdrive (LHCD) before the main heating pulse, to provide a region of reduced ornegative magnetic shear in the plasma core, ITBs can be formed the location ofwhich does not exhibit any apparent association with a particular internalmagnetic surface. Initial results suggest that q-profile modification usingan LHCD prelude can also be used to reduce the heating power level requiredfor ITB generation.
Effect of the q(r) profile on electron transport barrier formation in the T-10 tokamak