T. Ahlgren
A5004830987- Fusion materials and technologies
- Nuclear Materials and Properties
- Ion-surface interactions and analysis
- Semiconductor materials and devices
- Magnetic confinement fusion research
- Semiconductor materials and interfaces
- Nuclear reactor physics and engineering
- Metal and Thin Film Mechanics
- Diamond and Carbon-based Materials Research
- Silicon and Solar Cell Technologies
- X-ray Spectroscopy and Fluorescence Analysis
- GaN-based semiconductor devices and materials
- Integrated Circuits and Semiconductor Failure Analysis
- Advanced Materials Characterization Techniques
- Semiconductor Quantum Structures and Devices
- Nuclear Physics and Applications
- Advanced materials and composites
- Microstructure and mechanical properties
- Silicon Nanostructures and Photoluminescence
- Ga2O3 and related materials
- Hydrogen embrittlement and corrosion behaviors in metals
- Electron and X-Ray Spectroscopy Techniques
- Muon and positron interactions and applications
- Intermetallics and Advanced Alloy Properties
- Chalcogenide Semiconductor Thin Films
University of Helsinki
2014-2024
Helsinki Institute of Physics
2010-2024
Royal Military Academy
2020
Tekes
2002-2014
University of Sussex
2003
Abstract The JET 2019–2020 scientific and technological programme exploited the results of years concerted engineering work, including ITER-like wall (ILW: Be W divertor) installed in 2010, improved diagnostic capabilities now fully available, a major neutral beam injection upgrade providing record power 2019–2020, tested technical procedural preparation for safe operation with tritium. Research along three complementary axes yielded wealth new results. Firstly, plasma delivered scenarios...
First-principles calculations were used in determining the binding and trapping properties of hydrogen to point defects tungsten. Hydrogen zero-point vibrations taken into account. It was concluded that monovacancy can hold up five atoms at room temperature. The found distort self-interstitial atom configuration geometry. interaction with transmutation reaction impurities Re Os studied. substitutional have a negligible effect on whereas interstitial may increase inventory
First principle calculations were used to study the hydrogen migration properties in bulk bcc tungsten. Hydrogen has low solubility tungsten and occupies tetrahedral interstitial site with an energy difference of 0.38 eV compared octahedral site. The diffusion coefficient was evaluated using harmonic transition state theory found agree experimental results at temperatures above 1500 K. height barrier between two adjacent sites be 0.21 eV, which is lower than value 0.39 obtained for from...
The 2014–2016 JET results are reviewed in the light of their significance for optimising ITER research plan active and non-active operation. More than 60 h plasma operation with first wall materials successfully took place since its installation 2011. New multi-machine scaling type I-ELM divertor energy flux density to is supported by principle modelling. relevant disruption experiments modelling reported a set three mitigation valves mimicking setup. Insights L–H power threshold Deuterium...
The provision of a particle and power exhaust solution which is compatible with first-wall components edge-plasma conditions key area present-day fusion research mandatory for successful operation ITER DEMO. work package plasma-facing (WP PFC) within the European programme complements laboratory experiments, i.e. in linear plasma devices, electron ion beam loading facilities, studies performed toroidally confined magnetic such as JET, ASDEX Upgrade, WEST etc. connection both groups done via...
Abstract For the past several years, JET scientific programme (Pamela et al 2007 Fusion Eng. Des . 82 590) has been engaged in a multi-campaign effort, including experiments D, H and T, leading up to 2020 first with 50%/50% D–T mixtures since 1997 ever plasmas ITER mix of plasma-facing component materials. this purpose, concerted physics technology was launched view prepare campaign (DTE2). This paper addresses key elements developed by directly contributing preparation. intense preparation...
Following the IAEA Technical Meeting on 'Advanced Methodologies for Analysis of Materials in Energy Applications Using Ion Beam Accelerators', this paper reviews current status ion beam analysis (IBA) techniques and some aspects ion-induced radiation damage materials field relevant to fusion. Available facilities, apparatus development, future research options challenges are presented discussed. The beryllium radioactivity-containing samples from experiments JET or ITER represents not only...
Positron-annihilation measurements and nuclear reaction analysis [utilizing the N14(d,p)N15 N14(d,He)C12 reactions] in conjunction with Rutherford backscattering spectrometry channeling geometry were used to study defects as-grown Ga(In)NAs materials grown by molecular beam epitaxy using a radio-frequency plasma nitrogen source. Our data unambiguously show existence of vacancy-type defects, which we attribute Ga vacancies, interstitials nitride–arsenide epilayers. These point believe, are...
Reliable and accurate knowledge of the physical properties elementary point defects is crucial for predictive modeling evolution radiation damage in materials employed harsh conditions. We have applied positron annihilation spectroscopy to directly detect mono-vacancy created tungsten through particle irradiation at cryogenic temperatures, as well their recovery kinetics. find that efficient self-healing primary takes place Frenkel pair recombination already 35 K, line with an upper bound...
The objective of thermonuclear fusion consists producing electricity from the coalescence light nuclei in high temperature plasmas. most promising route to envisages confinement such plasmas with magnetic fields, whose studied configuration is tokamak. Disruptions are catastrophic collapses affecting all tokamak devices and one main potential showstoppers on a commercial reactor. In this work we report how, deploying innovative analysis methods thousands JET experiments covering isotopic...
A reactive interatomic bond-order potential for bcc tungsten is presented. Special attention in the development was given obtaining accurate formation and migration energies point defects, making useful atomic scale simulations of extended defects. The used to calculate binding trapping distances vacancies vacancy clusters recombination radius self-interstitial atom monovacancy.
We report in situ electron microscopy observations of the plastic deformation individual nanometer-sized Au, Pt, W, and Mo crystals. Specifically designed graphitic cages that contract under irradiation are used as nanoscopic cells. The correlation with atomistic simulations shows observed slow is due to dislocation activity. Our results also provide evidence vacancy concentration a nanoscale system can be smaller than bulk material, an effect which has not been studied experimentally before.
The first-principles calculations were used to study the hydrogen energetics on (100) tungsten $(\sqrt{2}\ifmmode\times\else\texttimes\fi{}\sqrt{2})R45\ifmmode^\circ\else\textdegree\fi{}$ surface. Two equilibrium sites for H at surface are identified, with a low migration barrier from energetically clearly higher long bridge site short site. At coverages, majority of diffusion events take place via sites. penetration solute in bulk was defined, showing that neighboring tetrahedral takes...
The interaction of fusion reactor plasma with the material first wall involves a complex multitude interlinked physical and chemical effects. Hence, modern theoretical treatment it relies to large extent on multiscale modelling, i.e. using different kinds simulation approaches suitable for length time scales in connection each other. In this review article, we overview briefly physics chemistry plasma–wall interactions tokamak-like reactors, present some most commonly used relevant topic. We...
We report a hydrogen induced vacancy formation mechanism in tungsten based on classical molecular dynamics simulations. demonstrate the due to presence of associated directly with stable hexagonal self-interstitial cluster as well linear crowdion. The stability different structures has been further studied and it is particularly shown that plays crucial role determining configuration SIAs, which structure preferred. Energetic analysis carried out prove SIA clusters facilitates vacancies....
The interstitial to substitutional nitrogen atoms as a function of concentration in GaNAs were determined by nuclear reaction analysis utilizing the N14(d,p) N15 and N14(d,α) C12 reactions using ion channeling technique. films with mean between 0.3% 3%, measured secondary mass spectrometry time-of-flight elastic recoil detection analysis, grown gas-source molecular-beam epitaxy. fraction occupying sites was observed increase linearly increasing amount, while nearly constant at 2×1019 cm−3...
Properties of small vacancy clusters in tungsten were studied with first-principles calculations. The binding and formation energies the increase cluster size. Dynamic characteristics a di-vacancy specified between room temperature 700 K lattice kinetic Monte Carlo calculations, which parametrised present results for dissociation barriers. An Arrhenius fit diffusion yielded , mean lifetime, ps. system was found to be stable up 500 K, due high energy needed its dissociation. Having carbon...
The fuel outgassing efficiency from plasma-facing components exposed in JET-ILW has been studied at ITER-relevant baking temperatures. Samples retrieved the W divertor and Be main chamber were annealed 350 240 °C, respectively. Annealing was performed with thermal desoprtion spectrometry (TDS) for 0, 5 15 h to study deuterium removal effectiveness nominal remained fraction determined by emptying samples fully of heating up 1000 775 °C,respectively. Results showed deposits having an...