Advances in H-mode physics for long-pulse operation on EAST

TLDR

Since 2012, EAST has advanced both physics and technology toward a long‑pulse stable high‑confinement (H‑mode) plasma regime. The recent upgrades position EAST to investigate ITER‑relevant long‑pulse high‑performance operations with dominant electron heating and low torque input over the next five years. EAST’s experimental capabilities were enhanced with up to 26 MW source power, an ITER‑like tungsten divertor, a new internal cryopump, and 16 in‑vessel resonant magnetic perturbation coils. Remarkable progress has been achieved, including ELM mitigation via lower‑hybrid wave, supersonic molecular beam injection, RMPs, and Li aerosol; active steady‑state power control with LHW+SMBI; a 28‑s H‑mode pulse with H98≈1.2; βN≈2 and 220 kJ stored energy; NBI‑only or LHCD‑modulated H‑mode sustaining nearly full noninductive plasmas; a quasi‑snowflake divertor; and a newly observed edge‑coherent mode affecting transport.

Abstract

Since the 2012 International Atomic Energy Agency Fusion Energy Conference (IAEA-FEC), significant advances in both physics and technology has been made on the Experimental Advanced Superconducting Tomakak (EAST) toward a long-pulse stable high-confinement (H-mode) plasma regime. The experimental capabilities of EAST have been technically upgraded with the power enhancement (source power up to 26 MW) of the continuous-wave heating and current drive system, replacement of the upper graphite divertor with an ITER-like W monoblock divertor, and installation of a new internal cryopump in the upper divertor and a set of 16 in-vessel resonant magnetic perturbation (RMP) coils. This new upgrade enables EAST to be a unique operating device capable of investigating ITER-relevant long-pulse high-performance operations with dominant electron heating and low torque input within the next 5 years. Remarkable physics progress in controlling transient and steady-state divertor heat fluxes has been achieved on EAST, e.g. (i) edge-localized mode (ELM) mitigation/suppression with a number of attractive methods including lower hybrid wave (LHW), supersonic molecular beam injection (SMBI), RMPs, and real-time Li aerosol injection; and (ii) active control of steady-state power distribution by the synergy of LHW and SMBI. In the 2014 experimental campaign, a long-pulse high-performance H-mode plasma with H98 ∼ 1.2 has been obtained with a duration over 28 s (∼200 times the energy confinement time). In addition, several new experimental advances have been achieved in the last EAST campaign, including: (i) high-performance H-mode with βN ∼ 2 and stored plasma energy ∼220 kJ; (ii) H-mode plasma sustained by neutral beam injection (NBI) alone or modulated NBI with lower hybrid current drive (LHCD), for the first time in EAST; (iii) high current drive efficiency and nearly full noninductive plasmas maintained by the new 4.6 GHz LHCD system; (iv) demonstration of a quasi-snowflake divertor configuration; and (v) observation of a new edge-coherent mode and its effects on edge transport in H-mode plasmas.