[en] The transport of molecules at the plasma edge in tokamaks is discussed in order to compare how light impurities enter the plasma if they are released either in atomic or molecular forms. Differences in their transport arise because of the dissimilarities between the atomic and molecular reactions with the bulk of the plasma. It is found that recycling to the walls is more efficient for the light impurities released in molecular form, but, also, that a substantial fraction of those atoms which originate from molecules may penetrate further into the plasma

[en] Interstellar SiO was discovered shortly after CO but it has been detected mainly in high density and high temperature regions associated with outflow sources. A new model of interstellar silicon chemistry that explains the lack of SiO detections in cold clouds is presented which contains an exponential temperature dependence for the SiO abundance. A key aspect of the model is the sensitivity of SiO production by neutral silicon reactions to density and temperature, which arises from the dependence of the rate coefficients on the population of the excited fine structure levels of the silicon atom. This effect was originally pointed out in the context of neutral reactions of carbon and oxygen by Graff, who noted that the leading term in neutral atom-molecule interactions involves the quadrupole moment of the atom. Similar to the case of carbon, the requirement that Si has a quadrupole moment requires population of the J = 1 level, which lies 111K above the J = 0 ground state and has a critical density n(cr) equal to or greater than 10(6)/cu cm. The SiO abundance then has a temperature dependence proportional to exp(-111/T) and a quadratic density dependence for n less than n(cr). As part of the explanation of the lack of SiO detections at low temperatures and densities, this model also emphasizes the small efficiencies of the production routes and the correspondingly long times needed to reach equilibrium. Measurements of the abundance of SiO, in conjunction with theory, can provide information on the physical properties of interstellar clouds such as the abundances of oxygen bearing molecules and the depletion of interstellar silicon

[en] We present the first self-consistent estimate of the magnitude of each term in a fluid treatment of plasma transport for a plasma lying in regions of open field lines in an axisymmetric tokamak. The fluid consists of a pure hydrogen plasma with sources which arise from its interaction with neutral hydrogen atoms. The analysis and results are limited to the high collisionality regime, which is optimal for a gaseous neutralizer divertor, or to a cold plasma mantle in a tokamak reactor. In this regime, both classical and neoclassical transport processes are important, and loss of particles and energy by diamagnetic flow are also significant. The prospect of extending the analysis to the lower collisionality regimes encountered in many existing experiments is discussed

[en] To model particle and heat loss terms at the edge of a tokamak with a divertor or pumped limiter, a simple two-chamber formulation of the scrapeoff has been constructed by integrating the fluid equations, including sources, along open field lines. The model is then solved for a wide range of density and temperature conditions in the scrapeoff, using geometrical parameters typical of the PDX poloidal divertor. The solutions characterize four divertor operating conditions for beam-heated plasmas: plugged, unplugged, blowthrough, and blowback

No abstract available

[en] The two-dimensional flow of a collision dominated hydrogen scrape-off plasma in an axisymmetric tokamak is examined. This flow is described by a set of equations which contain the dominant terms in a maximal ordering appropriate to high density experimental divertors and reactor scrape-off plasmas. Comparison of the theory to estimates of scrape-off parameters in the Doublet III expanded boundary plasmas suggests that analysis of classical and neoclassical processes alone may be sufficient to predict plasma transport in high density scrape-off plasmas of practical importance

[en] A quantitative theory of ionization in diffuse clouds is developed which includes H(+) charge exchange with O. Dissociative charge exchange of He(+) with H2 plays an important role in the densities of H(+) and He(+). The abundance of HD is also discussed. (U.S.)

[en] We have investigated the reactions of methane and its derivatives with hydrogen plasmas for use in modelling carbon and hydrocarbon transport in hydrogen plasmas. We provide quantitative information over the temperature range from 0.1 eV to 2 keV for the most significant reactions of methane and methane fragments with electrons and protons. We review the properties of each reaction, present graphs of the cross section and reaction rate coefficient, and give analytical fits for σ and [σv]. 34 refs

No abstract available

[en] Observations of molecular abundances and isotopic ratios are a primary means by which molecular interstellar clouds are studied. Understanding the chemistry responsible for producing the interstellar molecules is important for interpreting many of the physical and chemical properties of interstellar clouds. The author discusses the chemistry of interstellar clouds with the goal of understanding how to apply the theory of molecule formation to interpreting the physical and chemical properties, structure, and dynamics of these clouds. The emphasis is on the chemistry appropriate to molecular clouds which are almost all molecular hydrogen. (Auth.)