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Tungsten is foreseen for a full W-divertor of JET where tungsten will totally replace carbon as the material for the target plate. Also ITER operation is planned to be carried out with tungsten as one of the first wall materials, e.g. in the upper regions of the lower divertor. For the characterization of the accompanying plasma surface interaction a thorough spectroscopic diagnostic of the W influx into the plasma is of utmost importance. In order to upgrade the experimental and theoretical spectroscopic data beyond the present use of the W I transition (5d 5 6s 7 S 3 -5d 5 6p 7 P 4 ) at 4008 Å, an extension to lines of other (preferably longer) wavelengths has experimentally been carried out and accompanied by calculations. The survey resulted in an assessment of four additional lines in the longer (4294.61, 4886.90, 4982.59 and 5053.28 Å) and two in the shorter wavelength range (2551.35 and 2681.42 Å). The lines emitted from tungsten particles which were released by the plasma from tungsten plates and limiters in the TEXTOR edge plasma were observed with different (also high resolution) spectrometers and the Zeeman pattern was studied in order to identify possible influences of nearby interfering plasma spectral lines. The effect of the ground state level population as well as cascading from higher levels is included in the calculation of the relative line intensities and of the respective S/XB-values, the conversion factor for photon into particle fluxes. Measured and calculated S/XB-values for the 4008 Å line agrees well whereas some of the other lines are probably strongly affected by not yet identified factors.

We consider a narrow magneto-dipole transition in the 169 Tm atom at the wavelength of 1.14 µm as a candidate for a 2D optical lattice clock. Calculating dynamic polarizabilities of the two clock levels [Xe]4f13 6s 2 (J = 7/2) and [Xe]4f 13 6s 2 (J = 5/2) in the spectral range from 250 nm to 1200 nm, we suggest the "magic" wavelength for the optical lattice at 807 nm. Frequency shifts due to blackbody radiation (BBR), the van der Waals interaction, the magnetic dipole-dipole interaction, and other effects which can perturb the transition frequency are calculated. The transition at 1.14 µm demonstrates low sensitivity to the BBR shift corresponding to 8 × 10 −17 in fractional units at room temperature which makes it an interesting candidate for high-performance optical clocks. The total estimated frequency uncertainty is less than 5 × 10 −18 in fractional units. By direct excitation of the 1.14 µm transition in Tm atoms loaded into an optical dipole trap, we set the lower limit for the lifetime of the upper clock level [Xe]4f 13 6s 2 (J = 5/2) of 112 ms which corresponds to a natural spectral linewidth narrower than 1.4 Hz. The polarizability of the Tm ground state was measured by the excitation of parametric resonances in the optical dipole trap at 532 nm.

The influence of the target density on the electron-capture (EC) processes in collisions of fast ions with atoms and molecules is considered. The partial EC cross sections σn on the principal quantum number n of the scattered projectile, as well as the total σtot = Σnσn values, are calculated for highly charged ions interacting with gaseous and solid targets in the energy range of E = 100 keV u−1 to 10 MeV u−1. It is shown that with the target density increasing, the populations of the excited states of the scattered projectiles, formed via the EC channel, are drastically suppressed due to projectile ionization by the target particles and, as a result, the total EC cross sections decrease by orders of magnitude at low energies, while the reduction is less prominent at high energies.

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Electron-impact double-ionization processes of multi-electron heavy ions from Ti up to Bi (nuclear charge from Z = 22 up to Z = 83) are investigated for incident electron energies E < 50 Ith where Ith is the threshold energy for double ionization. The following ions are considered: Tiq+ (q = 1–6), Feq+ (q = 1, 3–6), Niq+ (q = 1–6), Gaq+ (q = 1–6), Krq+ (q = 1–4), Moq+ (q = 1–6), Prq+ (q = 1–4), Smq+ (q = 1–6), Wq+ (q = 1–6), Pbq+ (q = 1–9) and Biq+ (q = 1–10, 12). On the basis of experimental data, mostly obtained at an electron–ion crossed-beams set-up in Giessen, and quantum-mechanical considerations, a simple semi-empirical formula with six fitting parameters is developed taking into account the contribution of direct double ionization of two outer-shell electrons of the ions and also of single inner-shell ionization processes followed by autoionization with additional ejection of an electron as was suggested in our previous paper (Shevelko et al 2005). The formula obtained there was found to describe well the available experimental double-ionization cross sections within an accuracy of 20–30%. However, for multi-electron, very heavy ions significant deviations of that formula from experiment are found in the low-energy region. These deviations are most likely caused by higher order processes, including inner-shell excitation and subsequent double autoionization (EDA). The tabulated parameters can be used for easy analytical representation of the double-ionization cross sections of heavy positive ions in the modelling of laboratory and astrophysical plasmas.