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.

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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.

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An XTREME Technologies XTS 13-35 extreme ultraviolet (EUV) light source creates a xenon z pinch that generates 13.5nm light. Due to the near x-ray nature of light at this wavelength, extremely smooth metal mirrors for photon collection must be employed. These are exposed to the source debris. Dissolution of the z-pinch gas column results in high-energy ion and neutral release throughout the chamber that can have adverse effects on mirror surfaces. The XTREME commercial EUV emission diagnostic chamber was designed to maximize diagnostic access to the light and particulate emissions from the z pinch. The principal investigation is characterization of the debris field and the erosive effects on optics present. Light emission from the z pinch is followed by ejection of multiply charged ions and fast neutral particles that make up an erosive flux to chamber surfaces. Attenuation of this erosive flux to optical surfaces is attempted by inclusion of a debris mitigation tool consisting of foil traps and neutral buffer gas flow. Characterization of the z-pinch ejecta is performed with a spherical sector energy analyzer (ESA) that diagnoses fast ion species by energy-to-charge ratio using ion time-of-flight (ITOF) analysis. This is used to evaluate the debris tool’s ability to divert direct fast ions from impact on optic surfaces. The ITOF-ESA is used to characterize both the energy and angular distribution of the direct fast ions. Xe+ up to Xe+4 ions have been characterized along with Ar+ (the buffer gas used), W+, Mo+, Si+, Fe+, and Ni+. Energy spectra for these species from 0.5 up to 13keV are defined at 20° and 30° from the pinch centerline in the chamber. Results show a drop in ion flux with angular increase. The dominant species is Xe+ which peaks around 8keV. Ion flux measured against buffer gas flow rate suggests that the direct fast ion population is significantly attenuated through increases in buffer gas flow rate. This does not address momentum transfer from scattered ions or fast neutral particles. These results are discussed in the context of other investigations on the effects of total particle flux to normal incidence mirror samples exposed for 1×107 pulses. The samples (Si∕Mo multilayer with Ru capping layer, Au, C, Mo, Pd, Ru, and Si) were exposed to the source plasma with 75% argon flow rate in the debris mitigation tool and surface metrology was performed using x-ray photoelectron spectroscopy, atomic force microscopy, x-ray reflectivity, and scanning electron microscopy to analyze erosion effects on mirrors. These results are compared to the measured direct ion debris field.

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