| 321. |
- Ström, Petter, et al.
(författare)
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Energy deposition by nonequilibrium charge states of MeV 127I in Au
- 2021
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - : American Physical Society. - 1050-2947 .- 1094-1622. ; 103
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Tidskriftsartikel (refereegranskat)abstract
- The energy loss of iodine ions at initial charge states up to 25+ and energies up to 36 MeV in self-supporting gold foils between 37 and 107 nm of thickness was measured with an electron mirror type time-of-flight detector. An excess energy loss of 130 keV was observed at 36MeV for charge state 25+ compared to 16+, and an energy loss deficit of 100 keV was observed for charge state 8+. The charge state equilibration length for 36-MeV iodine was estimated to lie between 3 and 7 nm, corresponding to an equilibration time between 0.4 and 0.9 fs. This result is relevant both for nanostructure fabrication with MeV ion beams and for depth profiling based on ion beam analysis data in cases where the charge state of the primary ion is far from the equilibrium value in the sample under study. A comparison to published data on charge state equilibration for various projectile-target combinations and energies from 10 keV to 6 GeV indicated that the energy scaling of the equilibration length observed at high energy is invalid for projectile velocities on the order of the Bohr velocity and below. The measurement further provided equilibrium values of the electronic stopping power for iodine in gold at ten energies between 10 and 36 MeV.
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| 322. |
- Ström, Petter, et al.
(författare)
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In-situ measurement of diffusion and surface segregation of W and Ta in bare and W-coated EUROFER97 during thermal annealing
- 2021
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Ingår i: Nuclear Materials and Energy. - : Elsevier. - 2352-1791. ; 27
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Tidskriftsartikel (refereegranskat)abstract
- The near-surface composition of polished EUROFER97 samples was measured by Rutherford backscattering spectrometry while maintaining the analyzed surface at temperatures up to 1188 K. A sample pre-coated with less than a monolayer of tungsten by magnetron sputter deposition was included in the study. A shifting equilibrium due to diffusion and segregation of tungsten and tantalum was observed, with segregation being most important between 900 K and 1040 K, which is near the known transition temperature between the martensitic and austenitic phases. Diffusion counteracted any increase of the near-surface concentration of the elements of interest both above and below the temperature range in which segregation dominated. An asymmetry in the diffusion-segregation balance was observed when approaching the same temperature from above and below. The largest segregation peak measured at elevated temperature in this work indicated an increased amount of tungsten and/or tantalum near the sample surface with an areal atom density corresponding to 70-80% of a monolayer. Additional measurements were performed on bare EUROFER97 after annealing at 1089 K and 1553 K followed by rapid cooling to near room temperature which, if carried out at a critical rate, is expected to restore a martensitic microstructure. In the former case a similar enrichment peak was seen as that measured while the sample temperature was elevated, while in the latter case an increased concentration of tungsten and tantalum from 0.4 to 0.55 atomic percent in a layer of at least 300 nanometers thickness near the surface was observed.
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| 323. |
- Ström, Petter, et al.
(författare)
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Ion beam analysis of tungsten layers in EUROFER model systems and carbon plasma facing components
- 2016
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Ingår i: Nuclear Instruments and Methods in Physics Research Section B. - : Elsevier. - 0168-583X .- 1872-9584. ; 371, s. 355-359
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Tidskriftsartikel (refereegranskat)abstract
- The tungsten enriched surface layers in two fusion-relevant EUROFER steel model samples, consisting of an iron-tungsten mixture exposed to sputtering by deuterium ions, were studied by Rutherford backscattering spectrometry and medium energy ion scattering. Exposure conditions were the same for the two samples and the total amount of tungsten atoms per unit area in the enriched layers were similar (2e15 and 2.4e15 atoms/cm2 respectively), despite slightly different initial atomic compositions. A depth profile featuring exponential decrease in tungsten content towards higher depths with 10-20 atomic percent of tungsten at the surface and a decay constant between 0.05 and 0.08 Å-1 was indicated in one sample, whereas only the total areal density of tungsten atoms was measured in the other. In addition, two different beams, iodine and chlorine, were employed for elastic recoil detection analysis of the deposited layer on a polished graphite plate from a test limiter in the TEXTOR tokamak following experiments with tungsten hexafluoride injection. The chlorine beam was preferred for tungsten analysis, mainly because it (as opposed to the iodine beam) does not give rise to problems with overlap of forward scattered beam particles and recoiled tungsten in the spectrum.
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| 324. |
- Ström, Petter, et al.
(författare)
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Ion beam tools for nondestructive in-situ and in-operando composition analysis and modification of materials at the Tandem Laboratory in Uppsala
- 2022
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Ingår i: Journal of Instrumentation. - : IOP Publishing. - 1748-0221. ; 17:4
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Tidskriftsartikel (refereegranskat)abstract
- Ion accelerators have demonstrated tremendous versatility in their research applications throughout several decades. Starting predominantly as nuclear physics tools, they subsequently provided novel insights into fundamental atomic physics. Nowadays small and medium size accelerators are routinely employed in several branches of materials science. As research questions increasingly drive the need for analyses and material modification experiments performed in-situ and/or in-operando, facilities must adapt to service such a need. In this work, we highlight capabilities for in-situ and in-operando composition depth profiling and materials modification, developed with instrumentation at the Tandem Laboratory at Uppsala University. An overview of available ion sources and accelerators is given. We then exemplify the specific capabilities of the available end stations for materials synthesis, sample modification and device operation either during simultaneous ion beam based characterization or with such characterization performed in-situ before and after the application of various modification steps. Describing specific recent examples and potential future applications, we illustrate the impact of the present national research infrastructure.
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| 325. |
- Ström, Petter, 1989-
(författare)
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Material characterization for magnetically confined fusion : Surface analysis and method development
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The dream of abundant clean energy has brought scientists and laypeople alike to ponder the possibilities of nuclear fusion since it was established as the energy source of the stars in 1939. Starting from the mid-twentieth century, significant effort has been put into overcoming the technological challenges related to the construction of a power plant, but initial optimism has faded somewhat due to a notable absence of practical outcomes. Nevertheless, the research continues and progress is made slowly but surely.The present work deals with a small part of the fusion puzzle, namely the materials to be used in the first wall surrounding a magnetically confined plasma. Carbon, which has historically been considered as the most viable element for this role, has been ruled out due to issues with plasma-induced erosion, hydrocarbon formation and a buildup of thick deposited material layers on wall components. The latter two lead to an unacceptable accumulation of radioactive tritium, both in the deposited layers and in dust particles. A metal wall, which would alleviate these particular problems but increase the severity of others, is therefore envisioned for a future demonstration reactor.Three contributions to the overall research effort are made through this thesis. First, an increased understanding of plasma-induced erosion of so-called reduced activation ferritic-martensitic steels and preferential sputtering of light material components is provided. High-resolution ion beam analysis and microscopy methods are used to examine samples of such a steel after exposure to plasma under controlled circumstances. Model films consisting of a mixture of iron and tungsten deposited on silicon substrates are also studied as they constitute simpler systems where the effects of interest may be simulated. The knowledge obtained is necessary for an assessment of the possibility to use reduced activation steel as a plasma-facing material in specific regions of a reactor wall.The second contribution consists of reports on the composition of deposited material layers on wall components retrieved from the plasma confinement experiments JET and TEXTOR. These provide limited conclusions on the range and rate of material erosion, transport and deposition in two cases.Finally, a detection system for the ion beam technique elastic recoil detection analysis has been assembled, tested and put into operation. In addition to improving the quality of analyses performed on fusion-related materials, the system has become an established tool available for users of the 5 MV electrostatic pelletron accelerator at Uppsala University’s Tandem Laboratory.”
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| 326. |
- Ström, Petter, et al.
(författare)
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Position‐Selective Introduction of Ferromagnetism on the Micro‐ and Nanoscale in a Paramagnetic Thin Palladium Film
- 2024
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Ingår i: Physica Status Solidi. Rapid Research Letters. - : John Wiley & Sons. - 1862-6254 .- 1862-6270. ; 18:8
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Tidskriftsartikel (refereegranskat)abstract
- Postsynthetic, position-selective addition of properties to materials constitutes a paradigm shifting step in materials engineering. The approach enables creation of material systems inaccessible by equilibrium and near-equilibrium synthesis and can be applied in novel practical applications as well as fundamental physics studies over a range of length and energy scales. Ion implantation is a versatile, scalable, industry-compatible tool, enabling the next step in this development. Herein, ion implantation is used to design and functionalize a mesoscopic magnetic architecture. A self-supporting mask is combined with implantation of 60 keV Fe ions to create an embedded array of ≈8 μm-wide circular ferromagnetic regions in a Pd film. The approach is contactless, free from surface residues, and requires no focusing or scanning of the beam. Magnetic properties of the array are probed with longitudinal magneto-optic Kerr effect measurement while varying sample temperature and applied magnetic field. Microstructures are visualized with Kerr microscopy and compared to the Fe distribution measured with microbeam proton-induced X-Ray emission. Sample topography after implantation is obtained by atomic force microscopy, while ion beam analysis is used to probe concentration depth profiles of implanted Fe, impurities, and to investigate material mixing.
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| 327. |
- Ström, Petter, et al.
(författare)
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Sputtering of polished EUROFER97 steel : Surface structure modification and enrichment with tungsten and tantalum
- 2018
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Ingår i: Journal of Nuclear Materials. - : Elsevier. - 0022-3115 .- 1873-4820. ; 508, s. 139-146
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Tidskriftsartikel (refereegranskat)abstract
- Surface structure modification and enrichment with tungsten and tantalum were measured for polished EUROFER97 samples after exposure to a deuterium ion beam. Time-of-flight medium energy ion scattering and time-of-flight elastic recoil detection analysis were implemented for measuring atomic composition profiles. Atomic force microscopy and optical microscopy were used to investigate surface morphology. The deuterium particle fluence was varied between 1021 D/m2 and 1024 D/m2, projectile energy was 200 eV/D and exposure temperatures up to 1050 K were applied. The average fraction of tungsten plus tantalum to total metal content in the 2 nm closest to the sample surface was increased from an initial 0.0046 to 0.12 for the sample exposed to the highest fluence at room temperature. The enrichment was accompanied by an increase in surface roughness of one order of magnitude and grain dependent erosion of the material. The appearance of protrusions with heights up to approximately 40 nm after ion beam exposure at room temperature was observed on individual grains. Samples exposed to 1023 D/m2 at temperatures of 900 K and 1050 K displayed recrystallization and cracking while changes to the total surface fraction of tungsten and tantalum were limited to less than a factor of two compared to the sample exposed to the same fluence at room temperature.
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| 328. |
- Ström, Petter, et al.
(författare)
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Surface oxide and roughness on test samples for the Ultra High Vacuum section of the Laser Heater for the European XFEL
- 2018
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Ingår i: Vacuum. - : Elsevier. - 0042-207X .- 1879-2715. ; 149, s. 83-86
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Tidskriftsartikel (refereegranskat)abstract
- The European X-ray Free Electron Laser has recently started with operation for users. An approximately 3 m long ultra high vacuum laser heater section is implemented to overcome possible electron bunch instabilities. We describe the process of determining the oxide layer thickness and surface roughness on test samples of the internal surface material in the laser heater vacuum chambers using elastic recoil detection analysis and optical surface profiling. The results are compared to specified values and show that surface roughness on the samples is larger than the requested maximum, with RMS deviations from a mean plane of up to 1.76 mu m for 0.60 x 0.45 square millimeter scans. The maximum oxide layer thickness is 5.5 nm on non-electropolished surfaces assuming cuprous oxide with density 6.0 g per cubic centimeter and 4.0 nm on electropolished surfaces.
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| 329. |
- Ström, Petter, et al.
(författare)
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Synthesis of ferromagnetic thin films and engineering of their magnetic properties by Fe ion implantation in polycrystalline Pd
- 2022
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Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier. - 0304-8853 .- 1873-4766. ; 552
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Tidskriftsartikel (refereegranskat)abstract
- Ferromagnetic thin films were synthesized by implantation of Fe ions with energies between 40 keV and 120 keV in 60 nm of polycrystalline Pd. The possibility to engineer magnetic properties in such films through the Fe concentration depth profile was demonstrated. In-plane magnetic moments were measured both while varying the sample temperature at constant applied magnetic field, and varying the applied field at constant temperature. All samples were explicitly shown to exhibit ferromagnetism at sufficiently low temperature, with threshold temperatures in the range from 35 K to 140 K. Saturation moments at 5 K were between 3.5 and 4.6 Bohr magnetons per implanted Fe atom for implantation fluences between 5 × 1015 and 2.3 × 1016 ions/cm2. Coercivities were between 1 and 3 mT. The samples included in the study were carefully characterized with Rutherford backscattering spectrometry, and selected samples with elastic recoil detection analysis and cross-sectional transmission electron microscopy, providing information on Fe concentration profiles, impurity fractions, structure as well as sample modification during implantation. A new model was proposed to calculate the scaling of the films’ magnetic moments with temperature from the Fe concentration profiles. The model qualitatively reproduced the data and quantitative differences were explained. It can thus be applied to predict the modification of the magnetic moment at a given temperature for a similar film when the implantation parameters are varied.
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| 330. |
- Tegnered, Daniel, 1987, et al.
(författare)
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Comparative gyrokinetic analysis of JET baseline H-mode core plasmas with carbon wall and ITER-like wall
- 2016
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Ingår i: Plasma Physics and Controlled Fusion. - : IOP Publishing. - 0741-3335 .- 1361-6587. ; 58:4
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Tidskriftsartikel (refereegranskat)abstract
- Following the change of plasma facing components at JET from a carbon wall (CW) to a metal ITER-like wall (ILW) a deterioration of global confinement has been observed for H-mode baseline experiments. The deterioration has been correlated with a degradation of pedestal confinement with lower electron temperatures at the top of the edge barrier region. In order to investigate the change in core confinement, heat transport due to Ion Temperature Gradient (ITG)/Trapped Electron Mode (TEM) turbulence is investigated using the gyrokinetic code GENE. Two pairs of CW and ILW discharges that are matched according to several global parameters are simulated at mid radius. The simulations included effects of collisions, finite beta, realistic geometries, and impurities. A sensitivity study is performed with respect to the key dimensionless parameters in the matched pairs. The combined effect of the relative change in these parameters is that the ITG mode is destabilized in the ILW discharges compared to the CW discharges. This is also reflected in nonlinear simulations where the ILW discharges show higher normalized ion and electron heat fluxes and larger stiffness. The ion energy confinement time within rho = 0.5 is found to be comparable while the electron confinement time is shorter for the ILW discharges. The core confinement in the ILW discharges is expected to improve if the edge pedestal is recovered since that would favourably change the key plasma parameters that now serve to destabilize them.
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