S. Cernusca

Sputtering of Au and Al2O3 surfaces by slow highly charged ions

Abstract A quartz crystal microbalance technique was used for measuring total sputtering yields for polycrystalline Au and Al 2 O 3 under impact of slow (100–1500 eV) multiply charged Ar and Xe ions. Up to the highest charge states investigated (Xe 25+ ), the sputter yield for the Au target remains independent on the projectile charge state and can be well described by kinetic sputtering only. For Al 2 O 3 , on the contrary, a dramatic increase in total sputtering yield with increasing projectile charge state was found, showing that in this case potential sputtering (PS), i.e., sputtering due to the potential energy of the projectile, clearly dominates over kinetically induced sputtering. Results can be explained within the defect-mediated desorption model of PS.

Edge plasma-relevant ion–surface collision processes

Abstract Graphite tiles or carbon-coated structures are largely used as wall or divertor materials in magnetically confined fusion devices. Laboratory work on plasma–wall interaction has so far mainly focused on obtaining physical and chemical sputtering yields for such materials. Much less is known on electron emission and molecular fragmentation and reactions during ion impact on graphite surfaces, despite the fact that both processes might play a decisive role in plasma–wall interaction. We therefore have measured such data for fusion-relevant ion species (e.g., Hn+, n=1–3 and Cz+, z=1,2,4,5) in the eV to keV impact energy region typical for fusion edge plasma conditions. As a target surface graphite tiles from the Tokamak experiment Tore Supra in CEA-Cadarache/France have been used. Implications of the experimental results for plasma edge modeling are also discussed.

Ion induced kinetic electron emission from highly oriented pyrolytic graphite by impact of H+, C+, N+, and O+

Total electron yields from highly oriented pyrolytic graphite (HOPG) have been measured for perpendicular impact of H+, C+, N+, and O+ projectile ions with kinetic energies from a few hundred eV up to 30 keV. The data are interpreted within a model for kinetic electron emission based on non-adiabatic time-dependent perturbation of valence-band electrons by the moving particle. The microscopical parameters of this excitation processes describe well the qualitative trends in the experimental data when changing the target from HOPG to polycrystalline gold.

Molecular projectile effects for kinetic electron emission from carbon- and metal-surfaces bombarded by slow hydrogen ions

Abstract Total yields for kinetic electron emission (KE) have been determined for impact of hydrogen monomer-, dimer- and trimer-ions (impact energy

Kinetic electron emission from highly oriented pyrolytic graphite surfaces induced by singly charged ions

Abstract We present total electron yields determined by current measurements for normal impact of H + , H 2 + , H 3 + , C + , N + and O + ions (E⩽10 keV) on a clean highly oriented pyrolytic graphite surface. The kinetic energy of the projectiles has been varied from near threshold up to 10 keV. By comparing the results to similar data obtained for a polycrystalline Au surface the role of different target properties for kinetic electron emission can be analysed.

Electron emission and molecular fragmentation during hydrogen and deuterium ion impact on carbon surfaces

Abstract Molecular fragmentation and electron emission during hydrogen ion impact on graphite surfaces has been investigated in the eV to keV impact energy region typical for fusion edge plasma conditions. As a target surface graphite tiles for the Tokamak experiment Tore Supra in CEA-Cadarache/France and highly oriented pyrolytic graphite (HOPG) have been used. For both surfaces studied, the experimentally observed threshold for electron emission is at about 50 eV/amu impact energy. Electron emission from the high conductivity side of the carbon tile is 15–20% less as compared to its low conductivity side, whereas results for HOPG are generally between these two cases. Deuterium and hydrogen ions are almost equally effective in liberating electrons from graphite when comparing results for the same impact velocity. Surface-induced dissociation of deuterium ions D3+ upon impact on Tore Supra graphite tiles, in the collision energy range of 20–100 eV, produced only atomic fragment ions D+. The other possible fragment ion D2+ could not be observed.