Modeling and advances in the high bootstrap fraction regime on EAST towards the steady-state operation

Abstract

Experimental and modeling investigations on the Experimental Advanced Superconducting Tokamak (EAST) show attractive confinement and stability properties in fully non-inductive, high poloidal beta plasmas. In the 2018 EAST experimental campaign, extended operation regimes of steady-state scenario were obtained (β P ~ 1.9 & β N ~ 1.5 & H 98y 2 ~ 1.3 of using only RF heating) with a high bootstrap current fraction (f BS ~ 47%) and n e /n GW ~ 70%. The confinement quality, H 98y 2 ~ 1.3, is much better than standard H-mode, and stationary peaked electron temperature profiles and peaked current density profile when ~1 MW of ECH and ~2.6 MW of LHW are both deposited in the core region. The observed improvement in plasma confinement is much better (H 98y 2 ~ 1.3) when compared with the RF-dominant heating experiments in the EAST 2016-2017 experimental campaign (H 98y 2 ~ 1.1). Integrated modeling prediction suggests that high electron density would increase the plasma performance and bootstrap current fraction, which is consistent with the general experimental trend. Linear analysis shows that the high-k (k y > 1) modes instability (ETG) is suppressed in the core region. Also, the Shafranov shift is shown to play a role in the suppression of the electron turbulent energy transport. Besides the modeling predictions, the validation of the predicted of the effect of ECH on the plasma confinement in recent experiments was done and the experimental results were consistent with the modeling results. The validation results also suggest that when ECH is deposited in the core region in the RF heating experiments, increasing the ECH heating power from 0.5 MW to 1.0 MW does make a small improvement in the bootstrap current fraction. The high bootstrap fraction scenario realized on EAST and the investigation to achieve higher-performance plasma would help expanding the operation regime on EAST.

Characteristics of electron temperature profile stiffness in electron-heated plasmas on EAST

“…From the growth rate and frequency calculated by TGLF, we can find that the most unstable modes are the medium wavelength low-k(k y < 1) TEMs. As shown in figure 6, the normalized growth rate of the low-k(k y < 1) TEMs increased slightly after beginning the second ECRH injection at ρ = 0.4, which is mainly responsible for driving the electron energy flux [27]. This is consistent with the peaked T e profile, because the lowk(k y < 1) TEM is mainly driven by T e and n e gradients [32].…”

“…A detailed analysis of heating and driven current can be found in a dedicated manuscript [21]. On-axis ECRH power injection causes an obvious increase in the core LHW power density profile [19,27]. The LHW power deposition density has no obvious response to the second ECRH injection at 3.1 s, while the total RF current density in the core increases significantly.…”

Predictive multi-channel integrated modeling of a reversed magnetic shear H-mode discharge with internal transport barrier in EAST

“…Different from the previous modeling study on EAST with only some channels evolve, e.g. T e and T i evolve [58,60,61], or T e , T i and n e evolve [62], in this paper, n e , T e , T i and V t are evolved simultaneously and a good convergence is achieved (not shown in previous references [58,[60][61][62]). In fact, this is very difficult because the accurate calculation of equilibrium, source and sink must be guaranteed.…”

“…Based on the sensitivity study of the toroidal rotation effects on the background plasma transport, it is found that the V t < 30 km s −1 almost has no impact on the kinetic profiles prediction. Besides, the V t (∼30 km s −1 ) is also assumed as 0 in the predicting the kinetic profiles in EAST pure radio frequency wave heated discharges [60][61][62]. Therefore, the gap between the predicted and experimental V t in the region of 0.2 < ρ < 0.8 is not a big problem in our study.…”

Effect of electron temperature anisotropy on TEM in reversed-field-pinch plasmas

“…In fusion plasmas, the phenomena of plasma anisotropy in xperiments have also been found with the application of various heating and current drive schemes [4][5][6], such as neutral beam injection and ion/electron cyclotron resonance heating (ICRH/ECRH). Moreover, the anisotropy of electron temperature directly acts on the bootstrap current, which is closely related to the steadystate scenario in fusion experiments, and has been wildly studied in tokamaks [7], stellarators [8] and reversed-fieldpinch (RFP) plasmas [9]. Therefore, it is necessary to discuss the characteristics of microturbulence in anisotropic fusion plasmas.…”