Studies of the Plasma Edge in Tokamaks Using Passive Probes

This paper briefly reviews the use of ion beam analysis techinques to study the interaction between the plasma edge and wall materials in present magnetic confinement plasma experiments. In these studies, samples are exposed to the plasma edge and subsequently analysed for hydrogen isotopes and heavier impurity elements deposited during the exposure. Recent experiments of this kind have provided the first values for the energies and fluxes of hydrogen isotopes and impurities incident on materials in the edge plasma in several machines. Values for deuterium ion temperatures range from ~ 50 to ~ 500 eV and deuterium fluxes in the range 1016-1018(cm2s)-l have been observed. Some measurements have been made as a function of distance from the plasma or of time during single discharges. This information together with results from laboratory studies on hydrogen retention in materials, and reflection and sputtering yields for hydrogen in the energy range of interest, are providing a better understanding of plasma-wall interactions.