Development of Langmuir probe array for the new lower tungsten divertor in EAST

Abstract

The divertor Langmuir probes (Div-LPs) system is a key diagnostic, which is widely used in advanced tokamaks including ITER, for divertor plasma measurement. With the improvement of EAST performance by more available heating power, the lower graphite divertor has been upgraded to a new tungsten structure recently. Therefore, the Div-LPs for the EAST lower divertor have undergone an overall upgrade, including the structure of the probe tip, the layout of the probe arrays and the optimized power supply. In the EAST 2021 experimental campaign, the new Div-LPs, which can measure the electron temperature, plasma density, heat and particle fluxes at the divertor plates, have been tested by long-term discharges with long-pulse plasmas. In the strike point sweeping experiments, the particle flux distribution and evolution measured by the Div-LPs match the inversed strike point by EFIT code excellently. In addition, the Div-LPs have been successfully employed in long-pulse plasmas over 100 s with high core electron temperature operation. In the long-pulse discharges, the data measured by Div-LPs are reliable by cross-validation with key plasma parameters. Moreover, it is observed that the electron temperature, particle and heat fluxes measured by Div-LPs significantly drop after impurity seeding, which is consistent with the surface temperature measured by the infrared camera. These experimental results demonstrate the success on the upgrade of the new divertor Langmuir probe system, which will provide essential diagnostic data for divertor physics study and plasma control, especially for long-pulse high-performance operation.