Surface processes in the production of negative hydrogen ions

Surface processes are very important in the production of intense beams D--ions. This is obvious for the surface conversion sources. By using Ba as converter material current densities for H--beams exceeding 40 mA/cm2 have been achieved. But also in volume sources surface effects are important, since the walls affect the vibrationally excited molecules and hydrogen atoms, which are very important components of the source plasma. In this report surface processes in the production of negative hydrogen ions will be discussed in the context of existing knowledge about these phenomena at the surface science level