[en] The source of the broad radiation of fast hydrogen atoms in plasmas containing noble gases remains one of the most discussed problems relating to plasma–solid interface. In this paper, we present a detailed study of Balmer lines emission generated by fast hydrogen and deuterium atoms in an energy range between 40 and 300 eV in a linear magnetised plasma. The experiments were performed in gas mixtures containing hydrogen or deuterium and one of the noble gases (He, Ne, Ar, Kr or Xe). In the low-pressure regime (0.01–0.1 Pa) of plasma operation emission is detected by using high spectral and spatial resolution spectrometers at different lines-of-sight for different target materials (C, Fe, Rh, Pd, Ag and W). We observed the spatial evolution for H_α, H_β and H_γ lines with a resolution of 50 μm in front of the targets, proving that emission is induced by reflected atoms only. The strongest radiation of fast atoms was observed in the case of Ar–D or Ar–H discharges. It is a factor of five less in Kr–D plasma and an order of magnitude less in other rare gas mixture plasmas. First, the present work shows that the maximum of emission is achieved for the kinetic energy of 70–120 eV/amu of fast atoms. Second, the emission profile depends on the target material as well as surface characteristics such as the particle reflection, e.g. angular and energy distribution, and the photon reflectivity. Finally, the source of emission of fast atoms is narrowed down to two processes: excitation caused by collisions with noble gas atoms in the ground state, and excitation transfer between the metastable levels of argon and the excited levels of hydrogen or deuterium. (paper)

[en] Optical isolation of the clockwise or the counter-clockwise circular polarization of spectral lines was applied to emission of sputtered tungsten atoms. As a result one measures the weak magnetic field at plasma-surface interface resulting in splitting of spectral lines (W I at 4008.751 Å and 4982.593 Å) being negligibly small with respect to the Doppler broadening. One relies only on the phase rotation of a reflected circular polarized light propagating at the normal incidence to the mirror-like surface. The spectral shift of the signal from sputtered W atoms on the detector using high-resolution spectrometer provides the value of the magnetic field at a known dispersion, i.e. no further modeling or additional assumption on the distribution of atoms is required. The isolation of spectral line components is equivalent to isolation of the effect of the magnetic field from the measured line shape. It is complete for Zeeman triplet lines and partial for other lines. The results are found to be in a very good agreement of 3% with calculations and the Zeeman resolved laser absorption spectroscopy (10%) on metastable levels of Ar I atoms. (paper)

[en] An interferometer structure was realized based on a GaAs/InAs core/shell nanowire and Nb superconducting electrodes. Two pairs of Nb contacts are attached to the side facets of the nanowire allowing for carrier transport in three different orientations. Owing to the core/shell geometry, the current flows in the tubular conductive InAs shell. In transport measurements with superconducting electrodes directly facing each other, indications of a Josephson supercurrent are found. In contrast for junctions in diagonal and longitudinal configuration a deficiency current is observed, owing to the weaker coupling on longer distances. By applying a magnetic field along the nanowires axis pronounced h/2e flux-periodic oscillations are measured in all three contact configurations. The appearance of these oscillations is explained in terms of interference effects in the Josephson supercurrent and long-range phase-coherent Andreev reflection. (paper)

[en] The erosion from plasma-facing components has to be monitored in many kind of laboratory and fusion plasmas. For this purpose, spectroscopy is an essential tool. Under certain conditions the particle flux can be calculated from the absolute line intensities of the sputtered material using so-called S/XB values. The impact of light reflection on the emission induced by sputtered particles at the mirror-grade polished surface of tungsten (W) and aluminum (Al) was investigated in a low-density (n _e ≈ 2 × 10¹² cm⁻³) and low-temperature (T _e ≈ $3\mathrm{e}\mathrm{V}$) argon (Ar) plasma in the linear plasma device PSI-2 using high-resolution spectroscopy. Using the line shape affected by Doppler shift we show that the light reflection has a considerable impact on the number of measured photons and has to be taken into account for calculating particle fluxes. The Al target was sputtered by Ar ions at the incident ion energy of $120\mathrm{e}\mathrm{V}$. The measured profile of the Al I line ($3961.52\stackrel{˚<!--\; ??\; -->}{\mathrm{A}}$) was compared with a Doppler-shifted emission model based on the Thompson energy distribution function. In this new model, the instrumental broadening and the impact of the Zeeman effect were also taken into account. The parameter for the high-energy fall-off n of the energy distribution function ($\propto <!--\; ???\; -->1/E^{n+1}$), the surface binding energy E _b and the surface reflectance were derived by comparing the experimental and the synthetic spectrum. The W target was sputtered by Ar ions at incident ion energies in the range of $30$–$160\mathrm{e}\mathrm{V}$. The influence of the ion impact energy on the energy distribution of the sputtered particles was demonstrated. (topical issue article)

[en] Tunable diode laser absorption spectroscopy was applied at the linear plasma device PSI-2 to measure the magnetic field, temperature of argon and density of metastable species in a low density gas discharge. The measurements on the two metastable levels of Ar were performed by scanning the plasma column of PSI-2 at different radii. The obtained magnetic field using the lines at 763 and 772 nm (Ar) was found to be systematically lower (by 5% to 17%) than the calculated vacuum field. Part of the deviation arises from the line integration of the absorption signal. The radial gradient of the magnetic field strength combined with the radial metastable density determines the magnitude of this contribution (2%–3%). The temperature of the neutral gas was found to be essentially constant within the discharge chamber. The gas temperature rises with increasing cathode current and magnetic field due to an increase in the plasma density and, consequently, an increase in the energy transferred to the neutral gas by collisions with the charged particles. The density of the 4 s metastable level with J = 2 was found to be 8–9 times higher than that of the level with J = 0 similarly to observations by others in non-magnetized plasmas. To understand this trend a simple collisional-radiative model for the metastable argon 4s J = 2 level was developed. Depending on the treatment of the 4p levels it predicts a lower and an upper limit of the metastable density. The experimental values are within the limits predicted by the model indicating that the complex kinetics of the excitation and deexcitation collisional-radiative processes lead to this deviation from the statistical equilibrium. (paper)

[en] The surface morphology of plasma-facing components (PFCs) and its evolution during plasma irradiation has been shown to have a significant effect on the erosion and subsequent transport of sputtered particles in plasma. This in turn can influence the resulting lifetime of PFCs. A model for treatment of the effect of surface roughness on the erosion of PFCs has recently been incorporated into the three-dimensional Monte Carlo code ERO2.0. First simulations have confirmed a significant influence of the assumed surface roughness (for both regular and stochastic numerically constructed samples) on both the effective sputtering yields Y _eff and the effective angular distributions of sputtered particles. In this study, a series of experiments at the linear plasma device PSI-2 are conducted to test the effect of surface roughness on the sputtering parameters. Graphite samples prepared with a 100 nm molybdenum layer with various surface roughness characteristic sizes (R _a = 110 nm, 280 nm, 600 nm and R _a < 20 nm) were exposed to a helium plasma in the PSI-2 linear plasma device at a magnetic field B = 0.1 T. These PSI-2 experiments were simulated using ERO2.0 with a surface morphology model. Simulations are able to reproduce the experimentally observed significant suppression of erosion for higher R _a values. (topical issue article)