• Energy Research

Using liquid metals confined in capillary porous structures (CPSs) as a plasma-facing component (PFC) could prolong the lifetime of the divertor in the high heat flux area. However, the high atomic number of tin (Sn) limits its acceptable fraction in the main plasma. Therefore, a crucial step in developing this concept is to test it in a tokamak environment, particularly in the diverted plasma region, e.g. ASDEX Upgrade (AUG). In this paper, the design of liquid tin module (LTM) is explained, and the testing in the high heat flux device GLADIS before its use in AUG is presented. The LTM was additively manufactured using selective laser melting, consisting of a 1.5mm porous layer tungsten (W) directly attached to a solid W bulk. The LTM has a plasma-facing area of 16×40mm2 and was filled with 1.54g of Sn. In GLADIS, the module was exposed to power loads between 2 and 8MWm−2 for 1 up to 10s, first unfilled and later filled with Sn. The surface temperature was monitored with infrared imaging and pyrometry. The thermal response was used to compare with simulations in Ansys Mechanical, enabling a determination of the module’s effective thermal properties. Sn droplets could be observed on the infrared camera, until a surface temperature of about a 1000°C was reached. The enhanced wetting of tin on the plasma-facing surface, which was observed by a visible camera, suggests that there is a conditioning of the surface, possibly due to the removal of impurities and oxides. Subsequent examinations of the adjacent tile revealed minor Sn leakages emanating from the module’s edge. Furthermore, the module showed no indication of mechanical failure. Therefore, these results indicated that the LTM qualifies for the heat fluxes expected in ASDEX Upgrade.

Arcing is a mechanism of dust production and erosion in fusion devices. The masses and velocities of tungsten (W) particles produced by arcing is of special interest given that W is used as wall material in current experimental devices and is planned for use in new machines such as ITER. This work presents a new technique for evaluation of the parameters of particles produced by vacuum arcs in laboratory conditions based on direct observation with a high-speed video camera. Tracking of particle trajectory provides a measurement of velocity and angle of emission. Additionally, the emitted thermal radiation of the particles is measured and its evolution over time is compared with a model of its cooling in order to obtain a measurement of size and temperature at the moment of emission for each individual particle. Surprisingly, temperature measurements reveal the production of initially solid particles. The newly established video technique allows automated measurement of a high number of particles in order to obtain distributions of the particle parameters.

Nuclear materials and energy 15, 214-219 (2018). doi:10.1016/j.nme.2018.05.001 Published by Elsevier, Amsterdam [u.a.]

Nuclear materials and energy 28, 101060 - (2021). doi:10.1016/j.nme.2021.101060 Published by Elsevier, Amsterdam [u.a.]

The preferred plasma-facing material in present-day and future magnetic confinement thermonuclear fusion devices is tungsten. This material is mainly chosen because of its high threshold energy for sputtering by hydrogen isotopes as well as its low retention of tritium within the material. From an engineering point of view, however, tungsten is a challenging material to work with as it is an inherently hard and brittle metal. In this respect, established fabrication technologies for tungsten and tungsten based materials are a limiting factor directly affecting the design of plasma-facing components. Against this background, additive manufacturing technologies could prove very beneficial with regard to plasma-facing component applications as they offer flexibilities beyond the possibilities that conventional manufacturing methods offer. Within the present contribution, we report on recent results regarding the additive manufacturing of tungsten by means of powder-bed based selective laser beam melting. In more detail, investigations on pure tungsten manufactured by using elevated substrate preheating temperatures up to 1000 ∘C are described. Keywords: Additive manufacturing, Refractory metal, Tungsten, Laser beam melting, Plasma-facing material

Nuclear materials and energy 37, 101514 - (2023). doi:10.1016/j.nme.2023.101514 Published by Elsevier, Amsterdam [u.a.]