Statistical study of particle flux footprint widths with tungsten divertor in EAST

The study of the divertor heat flux is of great importance for the operation of ITER and future fusion devices. In this paper, the behaviors of the widths of the particle flux footprints on the tungsten divertor in EAST have been statistically studied for the first time. A large number of divertor Langmuir probe (Div-LP) data from EAST general discharges in the 2016 campaign have been stepwise selected and analyzed for both L- and H-mode plasmas. It is found that the scaling dependences on poloidal magnetic field for the particle flux fall-off width at the inner tungsten divertor agree well with those at the outer graphite divertor in both L- and H-mode plasmas. The difficulty of extracting reliable footprint widths has been overcome by fitting data from two Div-LP arrays distributed toroidally. The nonlinear regressions of the particle flux fall-off width and particle flux spreading width at the inner tungsten divertor in H-mode plasmas have then been performed. A negative dependence on the plasma stored energy is found in the regression of the particle flux fall-off width and the exponent of the stored energy in the regression is consistent with previous experimental studies. The comparison between the particle flux fall-off width at the tungsten divertor with that at the graphite divertor indicates that statistically the divertor material and the direction of the toroidal magnetic field seem to have no significant influence on the particle flux fall-off width at the inner divertor. In addition, the similar particle flux fall-off width in L- and H-mode plasmas and the in-out asymmetry of the particle flux fall-off width at the graphite divertor have also been shown.