Development of high-performance discharges with transport barriers in JT-60U

Abstract

In order to provide greater confidence in the advanced steady-state operation in ITER, recent high-performance campaign in JT-60U has emphasized maximizing the capabilities of internal and edge transport barriers by the elaborate profile control using NB, electron cyclotron heating and other non-inductive current drive (CD) schemes as well as the strong shaping. Accordingly, it is highlighted by the reliable reproduction of the D–T equivalent fusion amplification gain (QDTeq) of over 1.2 transiently and sustainment of QDTeq at 0.8 for 0.55 s in reversed shear plasmas. On the other hand, increased triangularity up to 0.6 has also provided the improved confinement at higher density and sustainment of high normalized β (βN) above 2.7 for over 7 s in high-β poloidal H-mode. In addition, increased negative ion based neutral beam heating and CD power up to 5.7 MW contributed much to achieve the βN of 2.4 and confinement enhancement factor of 1.2 over the ITER98(y, 2) scaling simultaneously under full non-inductive CD at 1.8 MA. Furthermore, impact of electron heating on transport barriers was investigated, and it was found that strong barriers survive Te⩾Ti. With regard to the exploratory control of transport barriers using the perturbative schemes, the effect of asymmetric pressure fluctuations and Maxwell stress has been investigated. The suggested approaches could be applied in steady-state burning plasmas with transport barriers, where the external heating fraction is reduced and electron heating is predominant.