Baking and helium glow discharge cleaning of SST-1 Tokamak with graphite plasma facing components

10th Asia Plasma and Fusion Association Conference

Semwal, P.^1 ; Khan, Z.^1 ; Raval, D.C.^1 ; Dhanani, K.R.^1 ; George, S.^1 ; Paravastu, Y.^1 ; Prakash, A.^1 ; Thankey, P.^1 ; Ramesh, G.^1 ; Khan, M.S.^1 ; Saikia, P.^1 ; Pradhan, S.^1

Institute for Plasma Research, Near Indira Bridge, Bhat, Gandhinagar

382 428, India^1

关键词: Desorption yield;    Glow discharge cleaning;    Graphite surfaces;    Particle-induced desorption;    Plasma discharge;    Plasma operations;    Plasma-facing components;    Porous structures;   

Others  :  https://iopscience.iop.org/article/10.1088/1742-6596/823/1/012061/pdf
DOI  :  10.1088/1742-6596/823/1/012061

来源: IOP

【 摘 要 】

Graphite plasma facing components (PFCs) were installed inside the SST-1 vacuum vessel. Prior to installation, all the graphite tiles were baked at 1000 °C in a vacuum furnace operated below 1.0 × 10-5mbar. However due to the porous structure of graphite, they absorb a significant amount of water vapour from air during the installation process. Rapid desorption of this water vapour requires high temperature bake-out of the PFCs at ≥ 250 °C. In SST-1 the PFCs were baked at 250 °C using hot nitrogen gas facility to remove the absorbed water vapour. Also device with large graphite surface area has the disadvantage that a large quantity of hydrogen gets trapped inside it during plasma discharges which makes density control difficult. Helium glow discharge cleaning (He-GDC) effectively removes this stored hydrogen as well as other impurities like oxygen and hydrocarbon within few nano-meters from the surface by particle induced desorption. Before plasma operation in SST-1 tokamak, both baking of PFCs and He-GDC were carried out so that these impurities were removed effectively. The mean desorption yield of hydrogen was found to be 0.24. In this paper the results of baking and He-GDC experiments of SST-1 will be presented in detail.