Chemical erosion of graphite (0001) surfaces with thermal H and D.
Zecho, Thomas; Fischer, Christian; Ehrenhaft, Gitta; Küppers, Jürgen Germany
Graphite tiles are in use as first-wall protection in experimental nuclear fusion devices. The major drawback is its reactivity towards hydrogen. Reactive hydrogen plasma species lead to the chemical erosion of the wall and to the retention of hydrogen in the graphitic material. In order to understand basic reactions we investigate interactions of thermal hydrogen atoms with graphite samples under ultra-high vacuum (UHV) conditions in laboratory-scale experiments.
For the present study highly oriented graphite (HOPG) surfaces were characterised with scanning electron microscopy (SEM) and thermal desorption spectroscopy (TDS) after exposure to D atoms. Thermal (2000 K) H and D atoms were produced with home build hot W-capillary type atom sources. Volatile erosion products were detected in-situ during hydrogen exposure with mass spectrometry. Hydrogen induced chemical erosion was measured between about 400 K and 800 K and was most effective at about 600 K sample temperature. The main erosion products were CHx, C2Hx and C3Hx species. A pronounced dependence of the hydrocarbon product distribution on the hydrogen isotope was found.