Characteristics of internal transport barriers in JT-60U reversed shear plasmas

Abstract

The characteristics of internal transport barrier (ITB) structures are studied and active ITB control has been developed in JT-60U reversed shear plasmas. The following results are found. Outward propagation of ITBs with steep T_i gradients is limited to the minimum safety factor location ρ_qmin. However, ITBs with reduced T_i gradients can move to the outside of ρ_qmin. The lower boundary of the ITB width is proportional to the ion poloidal gyroradius at the ITB centre. Furthermore, active control of the ITB strength based on modification of the radial electric field shear profile is successfully demonstrated by toroidal momentum injection in different directions or an increase of heating power by neutral beams.