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

TLDR

The study investigates internal transport barrier structures and develops active control in JT‑60U reversed‑shear plasmas. Active ITB control is achieved by altering radial electric field shear through toroidal momentum injection or increased neutral beam heating. ITBs with steep Ti gradients propagate only to the minimum‑q surface, whereas those with weaker gradients can extend beyond it, and the minimum ITB width scales with the ion poloidal gyroradius at the barrier center.

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 Ti gradients is limited to the minimum safety factor location ρqmin. However, ITBs with reduced Ti gradients can move to the outside of ρqmin. 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.