In this article we report on surface scattering experiments at graphite as to model the interactions at divertor surfaces in tokamaks and conversion electrodes in negative ion sources. The formation of negative and positive hydrogen ions on a graphite surface during positive hydrogenous ion scattering at a projectile energy of 400 eV is observed. A remarkably high H ¯ and H+ on fraction, both varying between 10% and 30% of all scattered particles, is found during scattering of positive hydrogenous ions.

J. Appl. Phys.

Tsumori, K., Koppers, W. R., Heeren, R., Kadodwala, M., Beijersbergen, J. H. M., & Kleyn, A. W. (1997). Large ion yields in hydrogen scattering from a graphite surface. J. Appl. Phys., 81, 6390–6396.