Development of an in situ diagnostic system for mapping the deposition distribution on plasma facing components of the HL-2M tokamak.

The assessment of material deposition and fuel retention on Plasma Facing Components (PFCs) is of primary importance for the steady-state operations of future fusion devices. In this paper, an in situ diagnostic for mapping the deposition distribution (IMap) on a wide area of PFCs for HL-2M (Huan Liu Qi-2 Modification) is developed. The design, fabrication, integration, and lab test of the IMap have been implemented. This system is built with the laser-induced breakdown spectroscopy technique which is an in situ diagnostic technique to determine the constituents and the depth profile of deposition compositions on PFCs. With a molybdenum reflection mirror inside the chamber and its manipulator, the IMap system can scan from the inner wall across the lower divertor to the outer middle plane. The system can be remotely controlled, and its optical lenses, mirrors, and fibers can be adjusted automatically when scanning over the PFCs. Therefore, the wall properties over a wide area of the vessel can be measured. All elements with the emission lines in the range of 380-850 nm can be analyzed, and the isotope species H and D can also be identified clearly with this diagnostic. Moreover, the depth profiles of the deposited materials can be determined, and the fuel retention on PFCs can be evaluated in situ. This gives a clear picture of the deposition and retention over the wall of HL-2M.