Upgrade Design of Lower Divertor Langmuir Probe Diagnostic System in the EAST Tokamak

A flush-mounted Langmuir probe system has been built on the lower graphitic divertor targets in the experimental advanced superconducting tokamak (EAST) in 2016, which is revised from the previous divertor Langmuir probes, aimed to reduce the erosion from high-energy particle and strong heat flux on the probe surfaces exposed in the plasma, and explore new structure applications. The theories of single and triple flush-mounted probes relevant to their dimensions and the plasma parameters in the EAST divertor region are reviewed. During the 2016 EAST campaign, the flush-mounted probe system measured the plasma parameters by using single and triple probes, respectively, to obtain plasma parameters. The results were compared with the previous measurements by the domed probe in the similar condition. The results showed a good agreement between measurements using different probe geometries and techniques. This demonstrated the reliability of the flush-mounted probe system as a diagnostic tool in the EAST divertor. Optimization of these Langmuir probe system for the next generation of EAST lower divertor, which will be upgraded to a full tungsten divertor with active water cooling, is also discussed.