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Thin films of silicon nanoparticles (diameter 5–10 nm) were deposited on highly oriented pyrolytic graphite (HOPG) by low-pressure DC magnetron sputtering. The effect of different room-temperature oxidation techniques was investigated using XPS sputter-depth profiling. Both oxygen treatment during deposition (using an argon–oxygen mixture in the sputter gas) as well as post-deposition oxidation techniques (exposure to oxygen plasma beam, ambient air conditions) were studied. In all cases oxidation was found to involve the whole film down to the film/substrate interface, indicating a network of open pores. Depending on the type of oxidation between 15 and 25 at% of oxygen, mostly associated with low oxidation states of silicon, were detected in the interior of the film and attributed to oxidized surfaces of the individual silicon nanoparticles. The highest oxygen concentrations were found at the very film surface, reaching levels of 25–30% for films exposed to air or prepared by reactive magnetron sputtering. For the oxygen plasma-treated films even oxygen surface concentrations around 45% and fully oxidized silicon (i.e., SiO 2 ) were achieved. At the Si/HOPG interface formation of silicon carbide was observed due to intermixing induced by Ar-ion beam used for sputter-depth profiling.

Sticking coefficients of deuterium from CD 2 + are quantified on fusion relevant plasma sprayed tungsten and carbon fibre composite in the incident energy range from about 0–100 eV. The samples that were cut from ASDEX-Upgrade tiles are exposed to a beam of CD 2 + of specific incident energy, Einc, in the tandem mass spectrometer BESTOF in Innsbruck. Nuclear reaction analysis is performed ex-situ at IPP Garching for the quantification of deuterium content. The deuterium content difference measured on a spot before and after ion-beam exposure of the sample is assigned to the above mentioned species of hydrocarbon molecules sticking on the surface, allowing the calculation of the sticking probability of a specific deuterated molecular ion. The sticking coefficient, S, is found to depend on the incident energy and shows a maximum of about S ∼ 0.4 around Einc = 30 eV on CFC and about S ∼ 0.1 near Einc = 20 eV in case of PSW.

Results of laboratory experiments of arcing on graphite tiles coated by a W-layer are reported. The samples have been taken from coated tiles manufactured for ASDEX Upgrade (AUG). The motion of the arcs was observed by high-speed cameras. Additionally, sample plates have been exposed to collect macro-particles emitted by the arc. The eroded surfaces of the cathodes were investigated after experiment to characterize surface changes, tracks, and re-deposited particles. On the cathode strongly radiating immobile spots are observed by the cameras acting as sources of numerous macro-particles. At the surface large holes (diameter 17 μm) are found that perforate the W-layer and extend into the graphite bulk. Subsequent arcs tend to locate at the pre-existing holes. Hence, locally the W-coating is quickly and effectively broken, the W erosion is enhanced as compared to bulk W, and carbon is locally liberated despite the existence of an undamaged W-coating outside the arcing region.

In a tokamak, plasma-wall interactions can result in production of dust. During operation, the tritium present in the Vacuum Vessel (VV) can then be trapped in the in-vessel materials but also in dust. The vacuum vessel represents the first confinement barrier to this radioactive material. In the event of a postulated accident involving ingress of steam into the VV, hydrogen could in principle be produced by chemical reaction with hot metal and dust. If the ingress of air into the VV is also postulated, reaction of air with hydrogen and/or dust cannot be completely excluded and could lead to a possible explosion which could challenge the VV tightness. In order to prevent such accidents and their radiological consequences, limitations on the accumulation of dust and tritium in the VV and on the air ingress are imposed. Correlatively, ITER has defined a strategy for the control of in-vessel dust and tritium inventories based on both measurement and removal techniques. In this context, this paper reports on the status of tasks under F4E responsibility aiming at developing some of the measurement systems and necessary R&D for the validation of the ITER strategy.

The transition from carbon to high-Z divertor devices reduces the erosion of the plasma facing components (PFC) strongly. Arcing as second erosion mechanism beside physical sputtering may now dominating the erosion. A procedure based on photographic techniques, profilometry and scanning electron microscopy was developed to investigate arc damage in ASDEX Upgrade. At the inner divertor baffle region erosion by arcing dominates the physical sputtering by a factor of 7. Whereas the number of arc traces only depends on the position of the tile, the effective erosion strongly depends on the surface resistivity of the PFCs. Video observations with high temporal and spatial resolution correlates the onset of arcing with the appearance of ELMs at the inner divertor baffle.

The ASDEX Upgrade programme is directed towards physics input to critical elements of the ITER design and the preparation of ITER operation, as well as addressing physics issues for a future DEMO design. After the finalization of the tungsten coating of the plasma facing components, the re-availability of all flywheel-generators allowed high-power operation with up to 20 MW heating power at I p up to 1.2 MA. Implementation of alternative ECRH schemes (140 GHz O2- and X3-mode) facilitated central heating above n e = 1.2 × 1020 m−3 and low q 95 operation at B t = 1.8 T. Central O2-mode heating was successfully used in high P/R discharges with 20 MW total heating power and divertor load control with nitrogen seeding. Improved energy confinement is obtained with nitrogen seeding both for type-I and type-III ELMy conditions. The main contributor is increased plasma temperature, no significant changes in the density profile have been observed. This behaviour may be explained by higher pedestal temperatures caused by ion dilution in combination with a pressure limited pedestal and hollow nitrogen profiles. Core particle transport simulations with gyrokinetic calculations have been benchmarked by dedicated discharges using variations of the ECRH deposition location. The reaction of normalized electron density gradients to variations of temperature gradients and the T e/T i ratio could be well reproduced. Doppler reflectometry studies at the L–H transition allowed the disentanglement of the interplay between the oscillatory geodesic acoustic modes, turbulent fluctuations and the mean equilibrium E × B flow in the edge negative E r well region just inside the separatrix. Improved pedestal diagnostics revealed also a refined picture of the pedestal transport in the fully developed H-mode type-I ELM cycle. Impurity ion transport turned out to be neoclassical in between ELMs. Electron and energy transport remain anomalous, but exhibit different recovery time scales after an ELM. After recovery of the pre-ELM profiles, strong fluctuations develop in the gradients of n e and T e. The occurrence of the next ELM cannot be explained by the local current diffusion time scale, since this turns out to be too short. Fast ion losses induced by shear Alfvén eigenmodes have been investigated by time-resolved energy and pitch angle measurements. This allowed the separation of the convective and diffusive loss mechanisms.

This addendum applies to papers authored by contributors from the Axially Symmetric Divertor Experiment (ASDEX) Upgrade Team published in Review of Scientific Instruments. This addendum provides the full list of ASDEX Upgrade Team contributors and their affiliations.

In this work we concentrate on the quantification of the sticking coefficient of CD 3 + on fusion relevant plasma-sprayed tungsten (PSW) surfaces in the collision energy range from about 0 up to 100 eV. PSW samples were cut from ASDEX Upgrade tiles and both untreated and electropolished surfaces are investigated. A collision energy, Ecoll, selected CD 3 + ion beam deposits hydrocarbon layers onto the target surfaces which are ex-situ analyzed by nuclear reaction analysis (NRA) via D(3He, p)4He at 800 kV and 2.5 MeV, respectively. The sticking coefficient, S, for deuterium has been found to be collision energy dependent, decreasing with increasing energy. It is in the order of S ∼ 0.4 for PSW and S ∼ 0.1 for electro polished PSW at Ecoll = 10 eV. Secondary ion mass spectra of charged particles are recorded after ion–surface collisions with the polished PSW surface for collision energies up to 100 eV. While at very low collision energies below about 10 eV only simple reflection of CD 3 + is observed, at higher collision energies both fragmentation of the projectile and fragmentation of ion–surface reaction products are observed. Concerning the stability of the layers we prove that hydrogen exchange plays a role on the time scale of weeks.

The dust collection and analysis strategy in ASDEX Upgrade (AUG) is described. During five consecutive operation campaigns (2007–2011), Si collectors were installed, which were supported by filtered vacuum sampling and collection with adhesive tapes in 2009. The outer and inner morphology (e.g. shape) and elemental composition of the collected particles were analysed by scanning electron microscopy. The majority of the ∼50 000 analysed particles on the Si collectors of campaign 2009 contain tungsten—the plasma-facing material in AUG—and show basically two different types of outer appearance: spheroids and irregularly shaped particles. By far most of the W-dominated spheroids consist of a solid W core, i.e. solidified W droplets. A part of these particles is coated with a low-Z material; a process that seems to happen presumably in the far scrape-off layer plasma. In addition, some conglomerates of B, C and W appear as spherical particles after their contact with plasma. By far most of the particles classified as B-, C- and W-dominated irregularly shaped particles consist of the same conglomerate with varying fraction of embedded W in the B–C matrix and some porosity, which can exceed 50%. The fragile structures of many conglomerates confirm the absence of intensive plasma contact. Both the ablation and mobilization of conglomerate material and the production of W droplets are proposed to be triggered by arcing. The size distribution of each dust particle class is best described by a log-normal distribution allowing an extrapolation of the dust volume and surface area. The maximum in this distribution is observed above the resolution limit of 0.28 µm only for the W-dominated spheroids, at around 1 µm. The amount of W-containing dust is extrapolated to be less than 300 mg on the horizontal areas of AUG.

Any plasma diagnostic in ITER must be able to operate at temperatures in excess of 200 °C and neutron loads corresponding to 0.1 dpa over its lifetime. To achieve this aim for the bolometer diagnostic, a miniaturized metal resistor bolometer detector based on Pt absorbers galvanically deposited on SiN membranes is being developed. The first two generations of detectors featured up to 4.5 μm thick absorbers. Results from laboratory tests are presented characterizing the dependence of their calibration constants under thermal loads up to 450 °C. Several detectors have been tested in ASDEX Upgrade providing reliable data but also pointing out the need for further optimization. A laser trimming procedure has been implemented to reduce the mismatch in meander resistances below 1% for one detector and the thermal drifts from this mismatch.

Collisions of SF 4 2+ and SF 4 + ions with hydrocarbon-covered stainless steel surface at room temperature were investigated. The projectile ions were mass selected by a two-sector-field mass spectrometer and decelerated to incident energies of 60 to a few eV. Product ions were measured with the use of a time-of-flight spectrometer and their relative abundances determined as a function of the incident energy of the projectile ions (collision-energy-resolved mass spectra, CERMS curves). The mass spectra of product ions were dominated by fragment ions SF 3 + , SF 2 + , and SF + at incident energies below 40 eV, while sputtering of contaminant adsorbates prevailed at higher energies. The results indicate that the likely major reaction sequence responsible for the observed CERMS curves of product ions from SF 4 2+ collisions is charge exchange to form singly charged projectile ions followed by subsequent unimolecular fragmentation. In addition, chemical reactions between projectile ions and hydrocarbon adsorbates were observed leading to SF 2 CH 3 + , SFCH 2 + , and SCH + ions.