Experimental scalings of scrape-off layer particle flux width by outboard divertor Langmuir probes for deuterium and helium plasmas on EAST

The scrape-off layer (SOL) power width (lambda(q)) is an important parameter for predicting the heat load on divertor targets for future magnetically confined devices. Currently, the underlying physics for lambda(q) scaling is not fully understood. This paper extends the previous SOL particle flux width (lambda(js), lambda(q) approximate to lambda(js) is assumed, j(s) is the measured ion current density used as a proxy for particle flux) scaling measured by the inboard divertor Langmuir probes (Div-LPs) in deuterium plasmas (Liu et al 2019 Plasma Phys. Control. Fusion 61 045001) to the.js scalings measured by the outboard Div-LPs in both deuterium and helium plasmas on EAST. A systematic method has been used to correct the upper-outer Div-LP measurements to reduce the measurement uncertainty of lambda(js). About 520 discharges are selected for the construction of six databases (H-mode, L-mode, and Ohmic for deuterium and helium plasmas) to scale.js. Since the published.q scalings do not fit EAST lambda(js) well in the databases, four separate lambda(js) scalings are proposed using statistical method to minimize the scaling parameters. It is found that lambda(js) has a robust scaling dependence on the plasma line-averaged density ((n) over bar (e)) for both deuterium and helium plasmas and a strong positive scaling dependence on the divertor leg length (L-div,L-leg). The scaling exponent of the stored energy agrees well with the previous lambda(q)/lambda(js) scalings for deuterium plasmas. The near unity scaling exponents of edge safety factor and L-div,L- leg reveal the importance of parallel connection length in determining lambda(js). The positive scaling dependence of.js on (n) over bar (e) and the 2 similar to 4 times larger scaling amplitude compared with the published.q scalings probably indicate the turbulence broadening of lambda(js) on EAST. The comparison of lambda(js) for deuterium and helium plasmas using the constructed databases shows no