In the latest research on Experimental Advanced Superconducting Tokamak (EAST), the EAST team in Institute of Plasma Physics, Hefei Institutes of Physical Science (ASIPP) found the critical role of Pfirsch-Schlüter (PS) flow in driving the in-out divertor asymmetry in the high confinement mode (H-mode).

The EAST team reported that the in-out divertor asymmetry in EAST, as manifested by particle fluxes measured by the divertor triple Langmuir probe arrays, is significantly enhanced during type-I 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, whilethein-out asymmetry is reversed when the ion B×▽B directs away from the lower X-point.

The plasma flow measured by the Mach probe at the outer midplane is in the ion 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.

Experiments found that the particle source from an edge localized modes (ELM) event is predominantly located near the outer midplane. This new finding suggests the critical role ofthe PS flow in driving the in-out divertor asymmetry. 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 reverseBt, i.e., reversed B×▽B drift direction.

The related work has been published recently in Nuclear Fusion with the title In–out asymmetry of divertor particle flux in H-mode with edge localized modes on EAST.

This finding sheds light on the in-out asymmetry of divertor particle flux and may contribute to the design and operation of future high-power long-pulse tokamak devices such as the International Thermonuclear Experimental Reactor (ITER).

Contours of ion saturation current density, js, at the lower inner and outer divertor targets for a type-I ELMy H-mode discharge in LSN configuration with normal Bt. The traces shown in the bottom panels (c), (d) are the peak current density js_peak, as an ELM indicator. The ELMs are manifested by the colorful stripes on the black background. (Image by LIU Jianbin)

Contours of js for a type-IELMy H-mode discharge in LSN configuration with reversed Bt. The ELMs areshown by the colorful stripes on theblack background. (Image by LIU Jianbin)

Contact:

Dr LIU Jianbin

The Institute of Plasma Physics

NO. 350, Shushanhu Road, Hefei, China

Email: jianbinliu@ipp.ac.cn

Tel: +86-551-65593282