Chemical erosion behaviour of carbon materials in fusion devices

Published data on chemical erosion of graphite in present fusion devices obtained by spectroscopy are discussed in view of existing ion beam data. In addition, new data from TEXTOR for an intermediate flux range and from JET at different wall temperatures are presented. A distinction of data measured under erosion dominated, generally attached plasma conditions and under deposition dominated, mostly detached conditions is proposed. Under attached conditions yields are between 1% and 5% with only a moderate temperature dependence. Under deposition conditions connected with cold plasmas chemical erosion depends more strongly on the target temperature and the yields are more uncertain. In general, yields evaluated by CD spectroscopy still suffer from significant uncertainties of the effective photon efficiency (D/XB) of the CD radical. A definitive conclusion on a flux dependence of the chemical erosion is not possible from the present database.