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The four major processes involved in hydrogen retention in graphite are reviewed. These processes are saturation of the near-surface region, diffusion on surface-connected porosity, intragranular diffusion, and erosion of carbon with concomitant formation of codeposited hydrogen-carbon films. It is suggested that in the retention of tritium in a fusion experiment the fourth process will dominate; therefore, from that point of view, it is the most important. To address the question of plasma fuel purity, more data are needed on ion-induced release of hydrogen isotopes by hydrogen isotopes and by heavier ions (e.g. carbon and oxygen) as a function of temperature. >

The total erosion yields of 304 stainless steel by low energy hydrogen and deuterium have been determined by 4He ion backscattering spectroscopy at energies ranging from 0.33 to 9.0 keV. This experimental method determines the number of atoms removed by sputtering by measuring the change in depth of implanted Xe marker atoms. Data for 304 stainless steel are compared with the extensive published data obtained using the weight loss technique. The Xe marker method is used to make the first measurements of deuterium erosion on polycrystalline graphite. Deuterium erosion measurements of thermally-prepared oxide layers on Be were also made using 4He backscattering spectroscopy to determine directly the number of removed atoms. These new data for the sputtering yields of deuterium on carbon and BeO range from 0.016 to 0.052 atoms/ ion. A previously proposed semi-empirical curve derived from theory and fitted to existing physical sputtering data fits the stainless steel data quite well, but much of the existing carbon sputtering data using hydrogen and all of the results obtained here are substantially greater than predicted using the semi-empirical theory.

A review of particle-solid processes pertinent to modelling plasma-wall interactions is presented, and sets of recommended data are given. Analytic formulas are used where possible; otherwise, data are presented in the form of tables and graphs. The incident particles considered are e−, H, D, T, He, C, O, and selfions. The materials include the metals aluminum, beryllium, copper, molybdenum, stainless steel, titanium, and tungsten and the nonmetals carbon and TiC. The processes covered are light ion reflection, hydrogen and helium trapping and detrapping, desorption, evaporation, sputtering, chemical effects in sputtering, blistering caused by implantation of helium and hydrogen, secondary electron emission by electrons and particles, and arcing.

A technique using nuclear microanalysis has been developed to determine 2D an 3He concentrations versus depth profiles in the near surface regions (∼2 μm) of solids. Ultimate near-surface depth resolutions of (≈100 A) should be attainable by these techniques. A probing beam of 3He ions is used to analyze for the deuterium. By energy analyzing the emitted 4He ions from the reaction d(3He,p)4He and by simple computer analysis, deuterium concentration versus depth profiles are obtained. The same methods are applicable for 3He profiling except in that case a 2D probing beam is used. The techniques is currently being developed using Er hydride and Sc hydride films. It is particularly suited for the study of the transition metals with high hydrogen solubility such as Nb and V which are of interest for CTR reactor applications.

Measurements of electron-capture cross sections ${\ensuremath{\sigma}}_{10}$ and electron-loss cross sections ${\ensuremath{\sigma}}_{01}$ for protons and atomic hydrogen in ${\mathrm{H}}_{2}$, He, Ar, Kr, ${\mathrm{N}}_{2}$, ${\mathrm{O}}_{2}$, CO, C${\mathrm{O}}_{2}$, ${\mathrm{H}}_{2}$O, C${\mathrm{H}}_{4}$, ${\mathrm{C}}_{2}$${\mathrm{H}}_{4}$, ${\mathrm{C}}_{2}$${\mathrm{H}}_{6}$, and ${\mathrm{C}}_{4}$${\mathrm{H}}_{10}$ are reported and compared with published theoretical estimates and experimental results. The energy range was 100 to 2500 keV. The results are presented in graphical form. By applying the additive rule, the cross sections ${\ensuremath{\sigma}}_{10}$ and ${\ensuremath{\sigma}}_{01}$ are estimated for hydrogen particles in carbon.

The global recombination rate coefficient k/sub r/ for hydrogen has been measured in the TEXT tokamak vacuum vessel for various surface conditions. An attempt was made to correlate the measured values of k/sub r/ with residual gas analyzer (RGA) data taken before each measurement of k/sub r/ and with the power radiated during tokamak discharges produced after each measurement of k/sub r/. The results show that k/sub r/ increases during a series of tokamak discharges, k/sub r/ is relatively insensitive to power radiated during tokamak discharges, and k/sub r/ increases with the RGA measurements of mass 28 and 40 but not with those of mass 18. In addition, it was found that the mass 18 (H/sub 2/O) signal decreases as glow discharge experiments with hydrogen were performed.