Vlasov simulations of plasma-wall interactions in a weakly collisional plasma

International audienceAn Eulerian Vlasov code is used to model plasma-wall interactions in a weakly collisional plasma. The different numerical methods used to solve the Vlasov and Poisson equations are described in detail. The code is used to simulate measurements of the ion distribution and ion temperature in a low-pressure argon plasma. In particular, it is shown that the presence of material walls can lead to significant errors in the measurements, if the effect of the sheaths is not properly taken into account

Kinetic simulations of ion temperature measurements from retarding field analyzers

International audienceRetarding 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 perturbatio

Gas adsorption on carbon nanotubes

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Characterization of single wall carbon nanotubes by means of rare gas adsorption

International audienceBased 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

Accessibility of Nanotube Inner Channels Investigated by Krypton Adsorption

International audienceBecause of their remarkable properties, single wall carbon nanotubes (SWCNTs) have been considered for many potential applications in nanoelectronics, as scanning probes, as gas sensors or for field emission displays. Such bulk applications demand large quantities of this material with high purity and homogeneous properties. A high pressure carbon monoxide disproportionation (HiPco) process is one of the several approaches currently attempting to meet these demands. This technique has been shown to produce nanotubes of good purity. However purification procedures involving acid treatment and/or air-oxidation are still indispensable to remove impurities. But it is well known that purification introduces some detrimental effects such as damaging the tubes or modifying their surfaces through addition of functional groups. Consequently, characterization of purified samples is necessary. In this work, we report the characterization of HiPco SWCNTs by krypton Kr adsorption at 77.3 K in order to analyze the effects of purification on the bundle surface

Determination of the single wall carbon nanotube opening ratio by means of rare gas adsorption

International audienc

Accessibility of Nanotube Inner Channels Investigated by Krypton Adsorption

International audienceBecause of their remarkable properties, single wall carbon nanotubes (SWCNTs) have been considered for many potential applications in nanoelectronics, as scanning probes, as gas sensors or for field emission displays. Such bulk applications demand large quantities of this material with high purity and homogeneous properties. A high pressure carbon monoxide disproportionation (HiPco) process is one of the several approaches currently attempting to meet these demands. This technique has been shown to produce nanotubes of good purity. However purification procedures involving acid treatment and/or air-oxidation are still indispensable to remove impurities. But it is well known that purification introduces some detrimental effects such as damaging the tubes or modifying their surfaces through addition of functional groups. Consequently, characterization of purified samples is necessary. In this work, we report the characterization of HiPco SWCNTs by krypton Kr adsorption at 77.3 K in order to analyze the effects of purification on the bundle surface