Comparison of measurements with different types of divertor Langmuir probe in EAST tokamak

Divertor Langmuir probes (Div-LPs), embedded in the divertor target plates, are the important diagnostic tools to measure the plasma parameters in EAST divertor region. A series of measurement methods, i.e., single-probe, double-probe and triple-probe schemes, are applied and compared for the Div-LPs on EAST, to get the electron temperature T-e and the electron density n(e) at the same poloidal position, respectively. It is found that the electron temperature T-e and the electron density n(e) measured by the single-probe and the double-probe schemes are basically the same during the plasma discharge phase. Further analysis of the electron energy distribution function (EEDF) represented by the first derivative curve method shows that the electrons conform to a Maxwell distribution, which indicate that the three methods can be applied in the EAST divertor region. Besides, the domed and flush-mounted probe tips for measuring the plasma parameters are also compared, and the results show a good match. The sheath potential coefficient Lambda is also calculated from the I-V characteristic curves by two ways, i.e. Lambda(p) = (V-plasma-V-f)/T-e and Lambda(I) = ln(vertical bar I-es/I-is vertical bar), and compared with the traditional value Lambda = 2.8, the results indicate that the similar to 1.5 Lambda(I) and Lambda = 2.8 are available to replace the Lambda(p) under the different strength of toroidal magnetic field in EAST tokamak.