The transition states of the elementary reactions for the dissociation of methane on the ruthenium (0001) surface have been investigated with DFT periodic calculations and the nudged elastic band method (NEB) for 25% coverages. The calculated barriers are 85 kJ mol-1 for methane decomposition, 49 kJ mol-1 for methyl decomposition, and 16 kJ mol-1 for methylene decomposition, respectively. The decomposition of CHads requires the highest activation energy from the series with 108 kJ mol-1. Discussion concerning chemical bonding aspects of the transition states structures is provided for.

Abstract.The surface morphology and deuterium retention were investigated of polycrystalline tungsten targets that were exposed to deuterium plasmas at widely varying conditions. By changing only one parameter at a time, the isolated effects of flux, time and pre-damaging on surface modifications and deuterium retention were studied. The sample exposed to low-flux plasma (10 20 m −2 s −1 ) is mostly smooth with only a few areas containing very large blisters (50 -500 µm). The samples exposed to high-flux plasmas (10 24 m −2 s −1 ) show large numbers of smaller blisters (1 -10 µm) and in addition even smaller protrusions (<750 nm). The size of the blisters and their density strongly increase with fluence. Pre-damaging tungsten with MeV ions leads to less blisters but to more protrusions. In addition to these (sub-)micrometer-sized structures, all samples show formation of nanostructures. Comparison of a low-flux and high-flux sample exposed to similar fluence showed that the variation in morphology is dominated by the flux differences. It is shown that the blisters and protrusions originate in inter-and intra-granular cavities, respectively. The depth of the cavities underneath the surface correlates well with the depth distributions of the retained deuterium. Trapping of significant amounts of deuterium therefore seems to take place in and/or close to these cavities and gives rise to an additional peak in the thermal desorption spectrum at 700 K.PACS numbers: 28.52.Fa, 28.52. Nh, 52.40.Hf, 52.77.Dq, 61.80.Jh, Submitted to: Nuclear Fusion Surface morphology and deuterium retention at high-flux deuterium plasmas 2

Effect of Ti-Al cathode composition on plasma generation and plasma transport in direct current vacuum arc Estimation of electron temperature and density of the decay plasma in a laser-assisted discharge plasma extreme ultraviolet source by using a modified Stark broadening method A magnetized hydrogen plasma beam was generated with a cascaded arc, expanding in a vacuum vessel at an axial magnetic field of up to 1.6 T. Its characteristics were measured at a distance of 4 cm from the nozzle: up to a 2 cm beam diameter, 7.5ϫ 10 20 m −3 electron density, ϳ2 eV electron and ion temperatures, and 3.5 km/ s axial plasma velocity. This gives a 2.6ϫ 10 24 H + m −2 s −1 peak ion flux density, which is unprecedented in linear plasma generators. The high efficiency of the source is obtained by the combined action of the magnetic field and an optimized nozzle geometry. This is interpreted as a cross-field return current that leads to power dissipation in the beam just outside the source.