High recycling steady H-mode regime in the JFT-2M tokamak

Abstract

A new operating regime, ‘high recycling steady’ (HRS) H-mode regime, has been discovered in the JFT-2M tokamak. It is easily reproduced with neutral beam heating of any co-, balanced-, or counter-injection under wall fuelling from the boronized first wall. The HRS is characterized by good energy confinement (H89P ∼ 1.6) at a high density (ne/nGW ∼ 0.7; nGW is the Greenwald density), low radiation loss power fraction (, typically), and the complete disappearance of large ELMs. Accompanying the HRS H-mode transition, the coherent magnetic fluctuations in the frequency range of the order of 10–100 kHz with significant variation are seen on magnetic probes at the vessel wall. In addition, the HRS H-mode edge condition is compatible with an improved core confinement. We have demonstrated that an internal transport barrier can be produced under a HRS H-mode edge condition, achieving βNH89P ∼ 6 at ne/nGW ∼ 0.7–1.0, transiently.