Speaker
Description
The development of suitable materials for structural and plasma-facing components is a decisive challenge on the path towards nuclear fusion as a future energy source. In particular, the transport and retention of hydrogen isotopes is of relevance as they have a significant influence on the tritium inventory. The Soret effect describes diffusion processes driven by a temperature gradient, which are also expected to occur in the actively cooled components of a future fusion reactor. To estimate the resulting hydrogen transport, the Soret coefficient $S_T$ is required, which not only depends on the material combination but also varies with temperature and the temperature gradient. However, it is largely unknown for the fusion-relevant materials tungsten and copper.
In this contribution, the development and validation of a novel approach for determining $S_T$ for deuterium in metals is presented. Rod-shaped samples are gas-loaded with deuterium and subsequently coated with a diffusion barrier layer. After long-term exposure to a constant temperature gradient, the concentration distribution is determined using ion beam analysis. This has the advantage that $S_T$ can be determined for a wide temperature range using a single sample.
A dedicated experimental setup was developed to expose rod-shaped samples to a constant temperature gradient over a prolonged time period. The cold side is maintained at room temperature, while the hot side can reach temperatures of up to 500°C. Depending on the thermal conductivity of the material, a heat flux of up to 600 W is possible. In order to prevent oxidation of the sample, the process is performed under vacuum.
To validate the measurement concept and setup, the Soret coefficient of deuterium in niobium was determined and compared with known literature values. 30 mm long samples were gas-loaded in a deuterium atmosphere, coated with a copper diffusion barrier layer and exposed to a stationary temperature gradient for 21 days. The deuterium concentration was determined both before and after with a lateral resolution of 1 mm using the $\textrm{D}(^3\textrm{He},\textrm{p})^4\textrm{He}$ nuclear reaction. The concentration profile was then used to determine $S_T$, whereby a high degree of consistency with the literature values could be observed.