Chemical erosion behaviour of doped graphites under hydrogen impact: A comparison of ion beam experiments and planar inductively coupled RF plasmas

Carbide-doped and pure graphites were eroded by energy-and mass-separated hydrogen ion beams and by hydrogen containing planar inductively coupled RF plasmas. The erosion yield for 30 eV D impact on doped graphites and its fluence dependence are in the same order of magnitude for both exposure types. The D flux from the plasma onto the specimens (similar to 3.1 x 10(21) m(-2)s(-1)) contains energetic D ions and thermal D (650 K) in the ratio 1 to 5. The contribution of the thermal D to the erosion yield reaches at most the same magnitude as the erosion yield by ions only (30 eV). This contribution depends on the structure of the graphite. In the case of pure graphites the observed erosion yield is independent of the fluence for both types of exposure, although a rough surface morphology is created. For doped graphites reductions of the erosion yield with fluence by a factor of about 10 are observed, while the surfaces get rough and strongly enriched with dopants.