Plasma-wall interaction studies within the EUROfusion consortium: Progress on plasma-facing components development and qualification

This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014-2018 under grant agreement No 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission.The provision of a particle and power exhaust solution which is compatible with first-wall components and edge-plasma conditions is a key area of present-day fusion research and mandatory for a successful operation of ITER and DEMO. The work package plasma-facing components (WP PFC) within the European fusion programme complements with laboratory experiments, i.e. in linear plasma devices, electron and ion beam loading facilities, the studies performed in toroidally confined magnetic devices, such as JET, ASDEX Upgrade, WEST etc. The connection of both groups is done via common physics and engineering studies, including the qualification and specification of plasma-facing components, and by modelling codes that simulate edge-plasma conditions and the plasma-material interaction as well as the study of fundamental processes. WP PFC addresses these critical points in order to ensure reliable and efficient use of conventional, solid PFCs in ITER (Be and W) and DEMO (W and steel) with respect to heat-load capabilities (transient and steady-state heat and particle loads), lifetime estimates (erosion, material mixing and surface morphology), and safety aspects (fuel retention, fuel removal, material migration and dust formation) particularly for quasi-steady-state conditions. Alternative scenarios and concepts (liquid Sn or Li as PFCs) for DEMO are developed and tested in the event that the conventional solution turns out to not be functional. Here, we present an overview of the activities with an emphasis on a few key results: (i) the observed synergistic effects in particle and heat loading of ITER-grade W with the available set of exposition devices on material properties such as roughness, ductility and microstructure; (ii) the progress in understanding of fuel retention, diffusion and outgassing in different W-based materials, including the impact of damage and impurities like N; and (iii), the preferential sputtering of Fe in EUROFER steel providing an in situ W surface and a potential first-wall solution for DEMO.European Commission; Consortium for Ocean Leadership 633053; Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART

Electron screening in the

We have measured the cross-section for the 1H(7Li,$\alpha$)4He reaction at lithium beam energies from 0.34 to 1.05MeV. Hydrogen was forced by diffusion into Pd and PdAg alloy foils. A large electron screening effect was observed only when foils were under tensile stress. A dependence of the screening potential on hydrogen concentration or Hall coefficient of the metallic host could not be established

Deuterium retention in tungsten simultaneously damaged by high energy W ions and loaded by D atoms

Deuterium retention was for the first time measured in tungsten samples simultaneously irradiated by W ions and exposed to D atoms at five different temperatures from 450K to 1000K. In order to obtain information on the defect concentration, samples were afterwards exposed to D atoms at 600K to populate the created defects. The results were compared to different sequential damaging/exposure experiments. Synergistic effects were observed, namely, higher D concentrations were found in the case of simultaneous damaging and D-atom loading as compared to sequential damaging at elevated temperatures and populating the defects afterwards. However, the deuterium retention is still lower as compared to sequential damaging at room temperature and post-damaging annealing. The observations are explained by stabilization of defects by the presence of solute hydrogen in the bulk that would annihilate at high temperatures without the presence of hydrogen. Results of simultaneous W-ion damaging and D exposure at elevated temperatures were also compared to a sequential experiment of W-ion damaging at room temperature and then D-atom loading at high temperatures showing that thermal D de-trapping dominates deuterium retention at high temperatures. Keywords: Tungsten, Deuterium retention, Displacement damage, Neutral atoms, NR

Field dependence of T2* contrast in human substantia nigra

MRI holds high promise to diagnose Parkinson’s disease (PD) at clinical field strength B0.However, it remains unclear which B0 optimizes T2* contrast in substantia nigra, which provideshigh diagnostic accuracy. We used quantitative MRI at B0=1.5T-9.4T, MR microscopy, andhistochemistry to characterize the field dependence of the major contributors to R2* (1/T2*):dopaminergic neurons, ferritin, and myelin. R2* maps were similar at B0=3T-9.4T, and allcontributions scaled approximately linearly with B0. Hence, the contrast mechanisms are similaracross currently available MRI field strengths in vivo, which informs the design of novel PDbiomarkers

Magnetic properties of dopaminergic neurons in human substantia nigra quantified with MR microscopy

MRI-based quantification of dopaminergic neurons (DN) and their neuromelanin (NM) in substantia nigra (SN) has great potential to serve as a specific biomarker for neurodegeneration in movement disorders. We used 22-µm-resolution post mortem MR microscopy combined with ion beam microscopy to characterize the magnetic properties of DN. MR microscopy visualized individual DN and provided 3D cellular maps of the entire SN. Static dephasing was determined as main effective transverse relaxation mechanism of DN. We characterized the susceptibility of iron in DN and estimated that the contribution of DN to R2* and QSM may also be detected with in vivo MRI