EAST steady-state long pulse H-mode with core-edge integration for CFETR

Abstract

Recent EAST experiment has successfully demonstrated long pulse steady-state high plasma performance scenario and core-edge integration since the last IAEA in 2018. A discharge with a duration over 60s with βP ~2.0, βN ~1.6, H98y2~1.3 and internal transport barrier on electron temperature channel is obtained with multi-RF power heating and current drive. A higher βN (βN~1.8, βp~2.0, H98y2~1.3, ne/nGW~0.75) with a duration of 20s is achieved by using the modulated neutral beam and multi-RF power, where several normalized parameters are close or even higher than the phase III 1GW scenario of CFETR steady-state. High-Z impurity accumulation in the plasma core is well controlled in a low level by using the on-axis ECH. Modelling shows that the strong diffusion of TEM turbulence in the central region prevents tungsten impurity to accumulate. More recently, EAST has demonstrated compatible core-edge integration discharges in the high βp scenario: high confinement H98y2>1.2 with high βP~2.5/βN~2.0 and fbs~50% is sustained with reduced divertor heat flux at high density ne/nGW~0.7 and moderate q95~6.7. By combining active impurity seeding through radiative divertor feedback control and strike point splitting induced by resonant perturbation coil, the peak heat flux is reduced by 20-30% on the ITER-like tungsten divertor, here a mixture of 50% neon and 50% D2 is applied.

Progress on physics understanding of improved confinement with fishbone instability at low q 95 < 3.5 operation regime in EAST

“…The profiles of basic plasma parameters, n e (dotted line, reconstructed from POINT diagnostic [20]), T e (dashed line, measured by Thomson scattering diagnostic) and T i (solid line, measured by XCS), are compared between the fishbone instability (red color) and sawtooth oscillation (blue color) at constant heating power and identical plasma configuration, shown in figure 4(a). Under the condition of the sawtooth, the T e profile exhibits a central peaked shape and T e /T i > 1 is kept in the region of ρ < 0.6, which is quite similar to the plasma performance of the high poloidal beta scenario developed on EAST [21]. When the fishbone instability appears, the ion temperature in the region of ρ < 0.4 is elevated significantly compared to the sawtooth, along with the reduction in T e resulting in T e /T i < 1, indicating the formation of ITB in the ion thermal channel.…”

Characteristics of grassy ELMs and their impact on the divertor heat flux width

“…BOUT++ simulations for DIII-D, EAST, ITER and CFETR show consistent trends and demonstrate consistent divertor heat flux width broadening and peak amplitude reduction in the grassy ELM regimes [12][13][14][15][16]. A 60 s steady-state long pulse high β p EAST grassy ELM discharge has been achieved with high performance in 2019 [17]. Therefore, H-mode plasma regimes with small ELMs offers a potential solution to future reactor power exhaust as it features many aspects required for the operation of future fusion reactors and has been proposed as the primary ELM-mitigation solution for the Chinese Fusion Engineering Test Reactor (CFETR) [18,19].…”

Achievements of actively controlled divertor detachment compatible with sustained high confinement core in DIII-D and EAST

“…The strong ITB formation mechanism in DIII-D to be shown in section 4.3 and the EAST results in reference [35], suggesting that neon seeding may offer a more promising tool for favorable core-edge integration in the high β P plasma conditions in EAST, with respect to Ar seeding. In the EAST 2019 winter campaign, the compatible core-edge integration in the high β P scenario has been extended and demonstrated with H 98 > 1.2 at β P ∼ 2.5, β N ∼ 2.0, f bs ∼ 50%, f gw ∼ 0.7 at moderate q 95 ∼ 6.7 (EAST #94437) [33,34], with the peak heat flux on the divertor reduced by ∼30%, using a mixture of 50% neon and 50% D 2 seeding.…”

“…The EAST has demonstrated long-pulse high β P scenario over 1 min with ITER-like tungsten divertor [33,34]. To resolve the critical divertor PWI challenge with even higher heating power injection for future steady-state operation, the active detachment feedback control has also been successfully developed in the high β P scenario since the EAST 2019 spring campaign, showing favorable core-edge-divertor integration.…”