In–out asymmetry of divertor particle flux in H-mode with edge localized modes on EAST

Abstract

The in–out divertor asymmetry in the Experimental Advanced Superconducting Tokamak (EAST), as manifested by particle fluxes measured by the divertor triple Langmuir probe arrays, is significantly enhanced during type-I edge localized modes (ELMs), favoring the inner divertor in lower single null (LSN) for the normal toroidal field (B t) direction, i.e. with the ion B × ∇ B direction towards the lower X-point, while the in–out asymmetry is reversed when the ion B × ∇ B is directed away from the lower X-point. The plasma flow measured by the Mach probe at the outer midplane is in the ion Pfirsch–Schlüter (PS) flow direction, opposite to both B × ∇ B and E × B drifts, i.e. towards the inner divertor for normal B t, and the outer divertor for reverse B t, consistent with the observed in–out divertor asymmetry in particle fluxes. Since the particle source from an ELM event is predominantly located near the outer midplane, this new finding suggests a critical role of the PS flow in driving the in–out divertor asymmetry. The divertor asymmetry during type-III ELMs exhibits a similar trend to that during type-I ELMs. Strong in–out divertor asymmetry is also present during inter-ELM and ELM-free phases for the normal field direction, i.e. with more particle flux to the lower inner divertor target, but the peak particle flux merely becomes more symmetric, or slightly reversed, for reverse B t, i.e. reversed B × ∇ B drift direction.

Effect of ∇B drift on the H-mode power threshold in upper single null plasmas with ITER-like tungsten divertor on EAST

“…38 In EAST, the SOL parallel flow has been analyzed, suggests a critical role of the Pfirsch-Schl€ uter (PS) flow as one of the most flowdriving mechanisms. [39][40][41][42] However, previous results are mainly achieved under the carbon wall divertor.…”

“…Still, it is not clear why the SOL flow is not reversed with reversing field direction, which is different from previous results on EAST under all carbon divertors. [39][40][41][42] This may be related to the up-down asymmetry divertors, in both material and geometry. In this paper, the role of neutral particle density on the L-H transition is qualitatively analyzed using the normalized divertor Da emission, however, diagnostics for the local T e , n e profile in the divertor region are needed.…”

Modeling study of divertor particle and heat flux asymmetries for EAST H-mode discharges

“…For the H-mode discharges, since the heating power is relatively high, resulting in the arcing faults in some of the probe channels, which make the heat flux profiles from the divertor Langmuir probes unreliable. For the DOIA of particle flux for EAST H-mode discharges, the main finding is the reversed asymmetry behavior with the reverse of toroidal magnetic field 27 . In this section, we will study the effects of diamagnetic and E × B drifts on the DOIAs of particle and heat fluxes through modeling.…”

“…As aforementioned, the experimental studies of the DOIA of heat flux for L-mode discharges 24 – 26 and the DOIA of particle flux for H-mode discharges 27 , 28 have been carried out in EAST in recent years. There is still a lack of study on the DOIA of heat flux for EAST H-mode discharges due to the unreliability of heat flux measurement from the divertor Langmuir probes.…”

“…EAST is the first superconducting tokamak in China with ITER-like divertor and configuration. Experimental studies on the DOIA of heat flux for the L-mode discharges 24 – 26 and DOIA of particle flux for the H-mode discharges 27 , 28 have been carried out recently. The results also show that the DOIAs could be reversed by reversing the toroidal magnetic field.…”