Experimental study of heating scheme effect on the inner divertor power footprint widths in EAST lower single null discharges

A comprehensive work of the effects of plasma current and heating schemes on divertor powerfootprint widths is carried out in the experimental advanced superconducting tokamak (EAST). Thedivertor power footprint widths, i.e., the scrape-off layer heat flux decay length λ q and the heatspreading S, are crucial physical and engineering parameters for fusion reactors. Strong inversescaling of λ q and S with plasma current have been demonstrated for both neutral beam (NB) andlower hybrid wave (LHW) heated L-mode and H-mode plasmas at the inner divertor target. Forplasmas heated by the combination of the two kinds of auxiliary heating schemes (NB and LHW),the divertor power widths tend to be larger in plasmas with higher ratio of LHW power. Comparisonbetween experimental heat flux profiles at outer mid-plane (OMP) and divertor target for NB heatedand LHW heated L-mode plasmas reveals that the magnetic topology changes induced by LHW maybe the main reason to the wider divertor power widths in LHW heated discharges. The effect ofheating schemes on divertor peak heat flux has also been investigated, and it is found that LHWheated discharges tend to have a lower divertor peak heat flux compared with NB heated dischargesunder similar input power. All these findings seem to suggest that plasmas with LHW auxiliaryheating scheme are better heat exhaust scenarios for fusion reactors and should be the priorities forthe design of next-step fusion reactors like China Fusion Engineering Test Reactor.