19. 04. 2006
Jirí Matejícek, Vladimír Weinzettl, Edita Dufková, Vojtech Piffl, Vratislav Perina
Tungsten is a candidate material for plasma facing components for ITER and other fusion devices. Plasma spraying is among prospective fabrication technologies, thankls to its ability to coat large areas and the possibility of in-situ repair. Several types of tungstenbased coatings were produced at IPP Prague, using water-stabilized plasma spraying. Their structure, porosity, oxide content and mechanical and thermal properties were characterized. Several stages of the spraying process optimization towards the foreseen application were performed.
The usage of these coatings as plasma facing materials (covering different diagnostic tools) in the edge plasma region was tested at the CASTOR tokamak at IPP. Behavior of 0.4-2mm thick plasma-sprayed surfaces and their influence on the discharge quality was studied. Plasma sprayed tungsten-based samples, solid tungsten and graphite were inserted into the plasma at various radii and exposed to tokamak discharges (30 ms pulse length, 30kW ohmic heating). Moreover, the samples were biased by positive and negative voltages to increase electron and ion interaction with the sample surface. Broad scans over the biasing voltages (from 300V to +200 V) and sample surface locations (from the plasma edge up to the core region) were performed. Afterwards, the sample surfaces were imaged by electron microscopy. Only a moderate surface modi cation was observed - narrow bright tracks, probably caused by unipolar arcing. Compositional changes in sprayed surfaces were also measured by RBS and ERDA methods. Hydrogen and carbon deposition, and oxygen content decrease were observed. Generally, pure tungsten coatings are suitable for covering di erent edge plasma diagnostics because of their low surface erosion and negligible in uence on the discharge parameters.