Retarding field analyzers (RFA) provide an integral of the ion velocity distribution in tokamak edge plasmas, leading, in principle, to an estimate of the ion temperature. However, the presence of the RFA itself perturbs the ambient plasma, such that the measured distribution is distorted with respect to the unperturbed one far from the probe. Here, collisionless kinetic modeling is employed to investigate the modification of the plasma characteristics (temperature, particle flux, density, and electric potential) in the presheath of the RFA. The kinetic equations are solved independently by means of two different numerical methods, which provide a reliable check of their results. Moreover, they are interpreted in light of a simplified kinetic analytical model. Systematic numerical studies are performed for a large range of values of the ion-to-electron temperature ratio and the parallel drift speed. In the same way that a Mach probe measures upstream–downstream asymmetries of ion saturation current in flowing plasmas, RFAs are expected to measure important asymmetries of sheath potential and ion temperature. These asymmetries can be used to estimate accurately the ion temperature in the absence of the probe perturbation.

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Based on the formalisms of Langmuir and Fowler, theoretical adsorption isotherms are calculated for different bundle geometries of single wall carbon nanotubes in a triangular lattice. The authors show the dependence of the adsorption properties on the nanotube diameter and on the specific morphology of the bundles they constitute. The authors demonstrate how isotherm curve analysis can help to experimentally determine what kinds of tubes form a given bundle and the ratio of open to closed tubes in a sample having undergone a complete or incomplete opening protocol. In spite of the model's simplicity, quite satisfactory agreement is observed between experiments and the authors' calculations.

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