Overview of JT-60U results leading to high integrated performance in reactor-relevant regimes

Abstract

Recent JT-60U results leading to high integrated performance are reported with emphasis on the projection to the reactor-relevant regime. Negative-ion-based neutral beam (NB) and electron cyclotron (EC) power increased up to 6.2 MW and 3 MW, respectively. A high βp H-mode plasma with full non-inductive current drive has been obtained at 1.8 MA, and the fusion triple product reached 3.1 × 1020 m−3 keV s. A high beta with βN = 2.7 was maintained for 7.4 s. Neoclassical tearing mode suppression with EC was accomplished using a real-time feedback control system, and improvement in βN was obtained. The stable existence of a current hole was observed. A high DT-equivalent fusion gain of 0.8 was maintained for 0.55 s in a plasma with a current hole. Current profile control in high bootstrap current reversed shear plasmas was demonstrated using N-NB and LH. A new operation scenario has been established in which a plasma with a high bootstrap current fraction and internal transport barriers (ITBs) is produced without the use of an OH coil. An ECCD study was undertaken in a reactor-relevant high Te regime. A new type of Alfvén eigenmode mode has been proposed and has been found to explain the observed frequency chirp quite well. High confinement reversed shear plasmas with Te > Ti were obtained. Ar exhaust with EC heating was obtained in a high βp mode plasma. Impurity accumulation related to strong ITBs in a reversed shear plasma and degradation of ITB by ECH in a weak positive shear plasma have been found. Dedicated measurement of edge localized mode dynamics and scrape-off-layer plasma flow have advanced understanding of the physics. N-NB heating in an Ar-seed plasma extended the density region to 95% of the Greenwald density, with HHy2 = 0.9. Enhancement of pedestal pressure was obtained with an increase in βp in a high triangularity configuration.