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A model of collisional processes of hydrocarbons in hydrogen plasmas has been developed to aid in computer modeling efforts relevant to plasma-surface interactions. It includes 16 molecules ͑CH up to CH 4 , C 2 H to C 2 H 6 , and C 3 H to C 3 H 6) and four reaction types ͑electron impact ionization/ dissociative ionization, electron impact dissociation, proton impact charge exchange, and dissociative recombination͒. Experimental reaction rates or cross sections have been compiled, and estimates have been made for cases where these are not available. The proton impact charge exchange reaction rates are calculated from a theoretical model using molecular polarizabilities. Dissociative recombination rates are described by the equation A/T B where parameter A is fit using polarizabilities and B is estimated from known reaction rates. The electron impact ionization and dissociation cross sections are fit to known graphs using four parameters: threshold energy, maximum value of the cross section, energy at the maximum, and a constant for the exponential decay as energy increases. The model has recently been used in an analysis of the Joint European Torus ͓P. H. Rebut, R. J. Bickerton, and B. E. Keen, Nucl. Fusion 25, 1011 ͑1985͔͒ MARK II carbon inner divertor using the WBC Monte Carlo impurity transport code. The updated version of WBC, which includes the full set of hydrocarbon reactions, helps to explain an observed asymmetry in carbon deposition near the divertor.

The absolute sputtering yields of D + , He + and Li + on deuterium saturated solid lithium have been measured and modelled at 45 • incidence in the energy range 100-1000 eV. The Ion-surface InterAction Experiment (IIAX) was used to measure the absolute sputtering yield of lithium in the solid phase from bombardment with a Colutron ion source. The lithium sample was treated with a deuterium plasma from a hollow cathode source. Measurements also include bombardment of non-deuterium-saturated lithium surfaces. The results lead to the conclusion that the chemical state of the deuterium treated lithium surface plays a major role in the decrease of the lithium sputtering yield. Specifically, preferential sputtering of implanted deuterium atoms over lithium atoms in deuterium treated samples results in a decrease of at least 60% of the lithium sputtering yield, in the case of He + bombardment. These results also demonstrate that lithium self-sputtering is well below unity and that the fraction of sputtered species in an ionic state ranges from 55 to 65% for incident particle energies between 100 and 1000 eV. Furthermore, correlation of Monte Carlo VFTRIM-3D simulations and IIAX experimental data demonstrate that the surface composition has a one to one ratio between deuterium and lithium components.

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Reflection coefficients for carbon and hydrocarbon atoms/molecules on carbon-based surfaces are critically needed for plasma-surface interaction analysis in fusion devices, as carbon will continue to be used in next step devices like ITER. These have been calculated at different energies and angles with a molecular dynamics code using the Brenner hydrocarbon potential. Hydrogen saturated graphite was prepared by bombarding a graphite lattice with hydrogen, until a saturation at $ 0:42 H:C. Carbon at 458 has a reflection coefficient ðRÞ of 0:64 AE 0:01 at thermal energy, decreasing to 0:19 AE 0:01 at 10 eV. Carbon dimers ðR thermal ¼ 0:51; R >1 eV $ 0:10Þ tend to stick more readily than carbon trimers ðR thermal ¼ 0:63; R 10 eV ¼ 0:16Þ: Hydrocarbons reflect as molecules at thermal energies and break up at higher energies. The total reflection via these fragments decreases with energy, the number of unpaired electrons, and changing hybridization from sp 3 to sp 2 to sp. The results compare reasonably well with binary collision modeling for higher energies and experimental sticking data at thermal energies. A second surface, representing a ''soft'' redeposited carbon layer formed by the deposition of hydrocarbons onto a graphite surface, is also analyzed. In general, reflection is lower from the ''soft'' surface by 0.1-0.2. This reflection data can and has been incorporated in erosion/redeposition codes to allow improved modeling of chemically eroded carbon transport in fusion devices.

Effect of capacitive coupling in a miniature inductively coupled plasma source J. Appl. Phys. 112, 093306 (2012) Time dependent behaviors of ion-ion plasmas exposed to various voltage waveforms in the kilohertz to megahertz frequency range Phys. Plasmas 19, 103501 (2012) Electron scattering in helium for Monte Carlo simulations Phys. Plasmas 19, 093511 (2012) Generation of high-energy (>15 MeV) neutrons using short pulse high intensity lasers Phys. Plasmas 19, 093106 (2012) Improved modeling of relativistic collisions and collisional ionization in particle-in-cell codes Phys. Plasmas 19, 083104 (2012) Additional information on Phys. Plasmas Monte Carlo neutral transport simulations of hydrogen velocities in the Tokamak Fusion Test Reactor ͑TFTR͒ ͓K. M. McGuire et al., Phys. Plasmas 2, 2176 ͑1995͔͒ are compared with experiment using the Doppler-broadened Balmer-␣ spectral line profile. Good agreement is obtained under a range of conditions, validating the treatment of charge exchange, molecular dissociation, surface reflection, and sputtering in the neutral gas code DEGAS ͓D. Heifetz et al., J. Comput. Phys. 46, 309 ͑1982͔͒. A residual deficiency of 10-100 eV neutrals in most of the simulations indicates that further study of the energetics of H 2 ϩ dissociation for electron energies in excess of 100 eV is needed.

Observation of liquid lithium flow in metal trenches has been made using a lithium-metal infused trench (LiMIT) tile and is reported here. The flow is self-pumping and uses thermoelectric magnetohydrodynamics to remove heated lithium and replenish it at a lower temperature. Flow velocities have been measured and compared with theoretical predictions.