Plasma exposure of tungsten in the linear plasma device PSI-2 produced via powder injection molding

Tungsten is envisaged as plasma facing material in fusion reactors because of its small tritium retention and low erosion rate as well as its high melting point and high thermal conductivity. However, it is very hard and brittle, which makes it difficult and expensive to fabricate and prone to crack formation under transient heat loads. The first disadvantage can be ameliorated using Powder Injection Molding (PIM) as fabrication route . With its near-net-shape precision the method offers particularly the advantage of cost saving. Furthermore PIM is an ideal tool for scientific investigations and efficient production of new oxide and carbide doped materials. In this contribution, we report on the initial exposure of pure tungsten produced via PIM (sintered at 2400 °C, density 98,6 - 99%, with equiaxed grain orientation) in the linear plasma device PSI-2 using deuterium and neon plasmas (to enhance physical sputtering) with a moderate plasma flux density of 4x10 21 m-2s-1 to the targets. For the neon plasma exposure, the targets were biased to obtain an ion impact energy of 110 eV and the fluence was 1.6x10 25 m-2, for deuterium to 200 eV at a fluence of 5.2x10 25 m-2, respectively. ... mehrThe sample temperature has been kept to 150 – 200°C during these exposures. In addition, the samples have been exposed to transient heat loads by a Nd:YAG- laser to simulate ELM-like heat pulses of 0.38 GWm-2 and a duration of 1 ms with a frequency of 0.5 Hz. 1000 pulses have been applied with and without plasma exposure. Reference samples (Plansee W, density > 99.97%, rolled, with a grain elongation perpendicular to the loaded surface and W with density > 99.95%, rolled, grain elongation parallel to the loaded surface) were exposed under the same conditions for comparison. Net erosion has been measured by determination of the mass loss, the surface roughness by laser profilometry and the resulting fuel inventory has been determined by nuclear reaction analysis. The surface morphology has been analyzed prior and after the exposure by secondary electron microscopy. We observe in all cases a slightly enhanced erosion yield of the PIM material to about 10-20%, the response of the material to the transient heat loads is similar in terms of roughness and surface morphology with a larger damage during neon exposure compared to deuterium exposure. The most significant difference between PIM and reference material is observed for the fuel retention which was about a factor of 5 larger for the exposed PIM samples (determined by NRA). A modest porosity observed for the PIM samples could be a possible explanation of this finding.