Development of High Performance Discharges with Transport Barriers in JT-60U
T. Fukuda and the JT-60 Team
Naka Fusion Research Establishment, Japan Atomic Energy Research Institute Naka-machi, Naka-gun, Ibaraki-ken 311-0193, Japan
Abstract.
In order to provide greater confidence in the advanced steady-state operation in ITER, the recent high performance campaign in JT-60U has emphasized maximizing the capabilities of internal and edge transport barriers by the elaborate profile and shaping control. The expansion of internal barrier radius to enhance the confinement by an increase of feedback controlled normalized beta during the current ramp and deliberate tailoring of the safety factor profile with ECH preheat to improve the stability in reversed shear plasmas resulted in the DT equivalent fusion amplification gain of over unity transiently and its sustainment at 0.8 for 0.55 s. However, the H mode edge was not compatible with a strong internal barrier in highly elongated plasmas, which could have further extended the period of high fusion performance. On the other hand, increased triangularity up to 0.6 also provided the improved confinement at higher density and sustainment of high normalized beta above 2.5 for over 7 seconds in high beta-poloidal H mode. In addition, the full non-inductive current-drive capability has been extended, as a result of the increased N-NB power up to 5.7 MW, and normalized beta of 2.4 and HH factor of 1.2 were achieved.
The characteristic features of transport barriers found in JT-60U high performance discharges above will also be addressed, including (1) the influence of high-field-side shallow pellet and heavy gas puff on the internal barrier quality via possible interplay of the electron turbulence. In the case of pellet injection, further enhancement in the confinement was observed, whereas under the heavy gas puff, the barrier quality was damped by an increase of collisionality, as predicted by the gyro-kinetic simulation. In addition, (2) formation of the current hole, (3) width and location of the internal barriers, in relation with the ion poloidal Larmor radius and magnetic shear profile, and (4) compatibility of the edge and internal barrier formation will also be highlighted. Furthermore, necessary conditions for the acquirement of internal barrier as well as its active control capability in terms of the modification in the radial electric field shear are discussed for application in ITER.