Plasma exposures of a high-conductivity graphitic foam for plasma facing components. (December 2018)

• Record Type: Journal Article
• Authors: Youchison, D.L.; Brezinsek, S.; Lumsdaine, A.; Klett, J.W.; Coenen, J.W.; Parish, C.; Ievlev, A.V.; Oelmann, J.; Li, C.; Rasinski, M.; Martynova, Y.; Linsmeier, Ch.; Ertmer, S.; Kreter, A.
• Is Part Of: Nuclear materials and energy. Volume 17(2018)
• Page Start: 123
• Page End: 128
• Publication Date: 2018-12
• Subjects: Graphitic foam -- Graphite -- Plasma facing component -- Plasma exposure -- Monoblock; Nuclear energy -- Periodicals; Nuclear fuels -- Periodicals; Nuclear reactors -- Materials -- Periodicals; Radioactive substances -- Periodicals; 621.4833
• DOI: 10.1016/j.nme.2018.10.002
• Languages: English
• ISSNs: 2352-1791

Abstract

Highlights: No measurable erosion or cracking of graphitic foam at 500 °C was observed in W7-X exposures to hydrogen and helium plasmas. Higher fluence exposures (5 × 10 25 D/m 2 ) over a 4 h period to deuterium plasmas on graphitic foam at 190 °C with a 120 V target bias resulted in a 5 mg of mass loss which is roughly 43 µm of depth. Most of the retained deuterium was found in the first micron of the graphitic foam. ToF-SIMS revealed only the presence of C2 D2 and/or C2 H4 on the surface which could not be differentiated. No CD4 was detected. Sample outgassing was insignificant and no deleterious effects on the plasmas were noted. Abstract: The plasma-surface interactions from samples of high-conductivity graphitic foam biased to 120 V and placed in 6–8 eV deuterium plasmas with densities as high as 10 19 m −3 were investigated at the PSI-2 linear plasma device in Jülich. Graphitic foam-plasma interactions were also studied at the Wendelstein 7-X (W7-X) stellarator in Greifswald by exposure to hydrogen and helium plasmas using the Jülich multi-purpose manipulator. The purpose was to explore the possibility of using the material in a plasma facing component, and initial results were encouraging. In W7-X, no measurable erosion or cracking was observed. The PSI-2 samples received a deuterium fluence of 5 × 10 25 m −2 resulting in an average erosion of 43 µm or about 5 mg per sample. Residual gas analysis (RGA) data were acquired to monitor sample outgassing. Laser-induced Breakdown Spectroscopy (LIBS) was used to measure deuterium retention in the porous foam. After exposure, the surfaces were characterized with scanning electron microscopy, energy dispersive x-ray analysis and time-of-flight secondary ion mass spectrometry (ToF-SIMS). The graphitic foam has a thermal conductivity as high as 287 W/mK and is considered as a replacement to more exotic carbon fiber composites such as SepCarb NB31 or isotropic graphites like ATJ that are no longer produced but used in present-day tokamak experiments. Actively cooled monoblocks were made from the foam and underwent extensive materials characterization including infrared response studies at Oak Ridge National Laboratory. This material is under consideration for the proposed actively-cooled W7-X divertor scraper element.