In-situ impurity measurements in PDX edge plasma

The surface analysis station on PDX combines several surface analysis techniques (AES, XPS, and SIMS) for in-situ measurement of impurity fluxes in the edge plasma. The major impurities deposited on a sample surface during nondiverted PDX discharges are oxygen, titanium (limiter material), and chlorine. The impurity fluxes measured at different radial positions decrease by a factor of ten from the plasma edge to the wall. The sample surface collecting the impurity ions is located behind a circular aperture. The observed broadening of the deposition profile of Ti relative to the aperture diameter enables an estimate to be made of the ratio of charge state/energy of Ti ions in the edge plasma. Time-resolved analyses of the deposited impurities are presented which indicate that the time behaviour for various impurities may be quite different for different impurity species. This aspect is discussed in relation to probable impurity release mechanisms. (orig.)