Simulations of Tokamak sputtering conditions with high energy particle beams

Physical sputtering of first wall and impurity control surfaces results in a substantial impurity source to a tokamak plasma. Unfortunately, only a limited sputtering yield data base exists for currently proposed impurity control surface materials. The variation of sputtering yields caused by hydrogen isotope and helium contamination due to ion implantation and adsorption is virtually unknown. This lack of fundamental data has hindered present efforts to model particle transport in the plasma edge region. This situation exists because plasma edge conditions and plasma-surface interactions are intimately coupled. Sputtering yield data for contaminated and redeposited surfaces can provide valuable information for improved edge modeling and impurity control design. In order to expand the sputtering yield data base for fusion impurity control materials a refined ion-surface interaction system has been developed at the Westinghouse Research and Development Center. This facility has the capabilities necessary to condition impurity control test samples to simulate some prior exposure to tokamak plasmas. This is achieved through ion implantation and subsequent sputtering using a 30keV ion beam complete with deceleration optics. A quartz crystal oscillator microbalance functions as the transducer. The in situ conditioning capabilities of the system will be discussed alone with data obtained for a preliminary series of sputtering experiments