Speaker
Description
The application of flowing liquid metal for plasma-facing components (PFCs) in fusion reactors has attracted interest due to its potential heat removal capabilities, self-healing surface, and the expectation of improved plasma confinement. However, research on the interaction between liquid metal and plasma in well-controlled laboratory-scale experiments is not sufficient to understand the interaction comprehensively. To assess the feasibility of its application for PFCs, understanding of some key factors are needed, such as droplet ejection mechanisms and their suppression, the influence of local recycling rates on plasma, liquid metal related MHD phenomena, differences between flowing and steady liquid metal and so on.
In this study, our new experimental device with linear plasma and liquid Sn, along with the preliminary results, will be presented. A liquid metal free-surface flow system was integrated into the downstream end of the linear plasma device TPD-II to study plasma-liquid Sn free-surface interaction and droplet ejection. Liquid Sn is injected from the top of the vacuum chamber, forming a thin vertical free-surface flow with a width of about 50 mm. The plasma is incident perpendicular to the Sn free-surface flow. In the experiments, the Sn free-surface flow was exposed to cylindrical pure He plasma (ne ~ 1 x 1018 /m3, Te ~ 5 eV). Plasma at about 12 mm upstream from the exposure surface were measured by a scanning Langmuir probe.
Spectroscopic observation showed no significant peaks from Sn in the range of 300–600 nm wavelength. However, apparent peaks from Zn were observed. The origin of the Zn is likely an impurity in the Sn (99.9 % purity) in the system. When the Sn inlet was stopped while maintaining the He plasma, numerous bubbles of visible size (< 1 mm) were observed on the plasma-exposed surface (the surface of adhered molten Sn) after several tens of seconds. Many adhered Sn droplets were also observed on the stainless steel thin plate installed in the exposure chamber. Even when bubbles were observed, no peaks from Sn were detected, indicating that our measurement was insufficient to capture the release of Sn droplets. The fact that there were no observable bubbles during Sn flow indicates suppression of foaming and/or growth of bubbles. However, further research is needed to understand the conditions for the bubbling mechanism and to confirm the suppression of bubbling.