High performance experiments in JT-60U reversed shear discharges

TLDR

Operational schemes were developed to reproducibly achieve a low‑q regime. High‑current reversed‑shear discharges in JT‑60U reached a record QDTeq of 1.25 at 2.6 MA, the new W‑shaped pumped divertor reduced Zeff, power‑flow‑controlled ITB degradation broadened the pressure profile to lift the β limit in low‑q H‑mode, and an ELMy H‑mode discharge sustained the ITB and improved confinement for 5.5 s.

Abstract

The operation of JT-60U reversed shear discharges has been extended to a high plasma current, low q regime keeping a large radius of the internal transport barrier (ITB), and a record value of equivalent fusion multiplication factor in JT-60U, QDTeq = 1.25, has been achieved at 2.6 MA. Operational schemes to reach the low q regime with good reproducibility have been developed. The reduction of Zeff was obtained in the newly installed W shaped pumped divertor. The β limit in the low qmin regime, which limited the performance of L mode edge discharges, has been improved in H mode edge discharges with a broader pressure profile, which was obtained by power flow control with ITB degradation. Sustainment of the ITB and improved confinement for 5.5 s has been demonstrated in an ELMy H mode reversed shear discharge.