Influence of lithium and silicon coatings on tungsten erosion in arc plasma

Abstract

• Arc erosion of W substrate can be effectively mitigated by Li and Si coatings. • Selective formation of spots on coatings is responsible for erosion mitigation. • Vapor shielding of Li coating provides effective mitigation of tungsten erosion. Arc spots formed on a plasma-facing component (PFC) have a stunning resemblance with the arc spots formed on a cathode of a vacuum arc. Hence, in this paper, a laboratory-scale vacuum arc process is used to get a better understanding of the arc erosion process of the tungsten (W) material. The performance of lithium (Li) and silicon (Si) coatings in erosion mitigation of W material is analyzed. The virgin W substrate was eroded significantly by arc spots and numerous W droplets were ejected into the interelectrode plasma from cathode with velocity of tens m/s. However, the W substrates can be effectively protected by Li and Si coatings from arc erosion. Preferential formation of arc spots on the coatings is responsible for the arc erosion mitigation. Compared with the virgin W substrate, no ejection of W droplets from the cathode was observed in the cases of coatings. Li and Si droplets were accidently ejected from the cathode and the ejected droplets were rapidly ablated in the arc plasma. For the case of Si coating, the W substrate was slightly melted and eroded due to the arc spots formed on the coating. By contrast, no obvious melting and erosion were observed on the W substrate for the case of Li coating, which is possibly due to the vapor shielding effect of Li between the W substrate and arc spots. These results confirm coatings served as a sacrificial protective layer and can reduce tungsten surface erosion caused by arcs, which provides a new reference for protecting first wall materials in future fusion devices.