Formation of Hydrocarbon Films in the Plasma Generator PSI-2

Introduction The question of whether graphite can be used as target or wall material in a fusion reactor – or at first in ITER – is essentially related to two adverse properties of graphite: its high erosion probability in general and the high inventory of tritium that is possibly stored in hydrocarbon layers being formed either on the target plates proper or on other surfaces remote from the plasma. With respect to the inventory of hydrogen and its isotopes stored in the cooler parts of the target surfaces carbon-co-deposition (instead of diffusion) has been identified as the dominating process [1]. Whereas the ions play an essential role in this plasma-target interaction the formation of hydrocarbon layers (C:H films) on the remote surfaces can be caused only by fluxes of neutral particles. It is this second problem which is investigated in this paper.