| 1. |
- Joffrin, E., et al.
(författare)
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Overview of the JET preparation for deuterium-tritium operation with the ITER like-wall
- 2019
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 59:11
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Forskningsöversikt (refereegranskat)abstract
- For the past several years, the JET scientific programme (Pamela et al 2007 Fusion Eng. Des. 82 590) has been engaged in a multi-campaign effort, including experiments in D, H and T, leading up to 2020 and the first experiments with 50%/50% D-T mixtures since 1997 and the first ever D-T plasmas with the ITER mix of plasma-facing component materials. For this purpose, a concerted physics and technology programme was launched with a view to prepare the D-T campaign (DTE2). This paper addresses the key elements developed by the JET programme directly contributing to the D-T preparation. This intense preparation includes the review of the physics basis for the D-T operational scenarios, including the fusion power predictions through first principle and integrated modelling, and the impact of isotopes in the operation and physics of D-T plasmas (thermal and particle transport, high confinement mode (H-mode) access, Be and W erosion, fuel recovery, etc). This effort also requires improving several aspects of plasma operation for DTE2, such as real time control schemes, heat load control, disruption avoidance and a mitigation system (including the installation of a new shattered pellet injector), novel ion cyclotron resonance heating schemes (such as the three-ions scheme), new diagnostics (neutron camera and spectrometer, active Alfven eigenmode antennas, neutral gauges, radiation hard imaging systems...) and the calibration of the JET neutron diagnostics at 14 MeV for accurate fusion power measurement. The active preparation of JET for the 2020 D-T campaign provides an incomparable source of information and a basis for the future D-T operation of ITER, and it is also foreseen that a large number of key physics issues will be addressed in support of burning plasmas.
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| 2. |
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| 3. |
- Bruckner, Barbara, et al.
(författare)
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A note on extracting electronic stopping from energy spectra of backscattered slow ions applying Bragg's rule
- 2018
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Ingår i: Nuclear Instruments and Methods in Physics Research Section B. - : ELSEVIER SCIENCE BV. - 0168-583X .- 1872-9584. ; 423, s. 82-86
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Tidskriftsartikel (refereegranskat)abstract
- Electronic stopping measurements in chemically reactive targets, e.g., transition and rare earth metals are challenging. These metals often contain low Z impurities, which contribute to electronic stopping. In this article, we present two ways how one can correct for the presence of impurities in the evaluation of proton and He stopping in Ni for primary energies between 1 and 100 keV, either considering or ignoring the contribution of the low Z impurities to multiple scattering. We find, that for protons either method leads to concordant results, but for heavier projectiles, e.g. He ions, the influence on multiple scattering must not be neglected.
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| 4. |
- Carvalho, D. D., et al.
(författare)
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Deep neural networks for plasma tomography with applications to JET and COMPASS
- 2019
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Ingår i: Journal of Instrumentation. - : Institute of Physics Publishing (IOPP). - 1748-0221. ; 14
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Tidskriftsartikel (refereegranskat)abstract
- Convolutional neural networks (CNNs) have found applications in many image processing tasks, such as feature extraction, image classification, and object recognition. It has also been shown that the inverse of CNNs, so-called deconvolutional neural networks, can be used for inverse problems such as plasma tomography. In essence, plasma tomography consists in reconstructing the 2D plasma profile on a poloidal cross-section of a fusion device, based on line-integrated measurements from multiple radiation detectors. Since the reconstruction process is computationally intensive, a deconvolutional neural network trained to produce the same results will yield a significant computational speedup, at the expense of a small error which can be assessed using different metrics. In this work, we discuss the design principles behind such networks, including the use of multiple layers, how they can be stacked, and how their dimensions can be tuned according to the number of detectors and the desired tomographic resolution for a given fusion device. We describe the application of such networks at JET and COMPASS, where at JET we use the bolometer system, and at COMPASS we use the soft X-ray diagnostic based on photodiode arrays.
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| 5. |
- Goebl, D., et al.
(författare)
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Quasi-resonant neutralization of He+ ions at a germanium surface
- 2013
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Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 25:48, s. 485006-
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Tidskriftsartikel (refereegranskat)abstract
- When low-energy He ions are scattered from a Ge surface, the fraction of positive ions exhibits characteristic oscillations as a function of ion energy. These oscillations are caused by quasi-resonant neutralization (qRN), a process which is active for materials with a narrow band nearly resonant with the unperturbed He 1s-level. In this paper we measure the fraction of He+ backscattered from Ge(100). In conjunction with recently developed theoretical methods, we extract quantitative information on the efficiency of qRN. Our evaluation reveals that qRN is a highly efficient process leading to ion fractions two orders of magnitude lower than in systems for which neutralization is only due to Auger processes.
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| 6. |
- Hans, M., et al.
(författare)
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Effect of oxygen incorporation on the structure and elasticity of Ti-Al-O-N coatings synthesized by cathodic arc and high power pulsed magnetron sputtering
- 2014
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 116:9, s. 093515-
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Tidskriftsartikel (refereegranskat)abstract
- Ti-Al-O-N coatings were synthesized by cathodic arc and high power pulsed magnetron sputtering. The chemical composition of the coatings was determined by means of elastic recoil detection analysis and energy dispersive X-ray spectroscopy. The effect of oxygen incorporation on the stress-free lattice parameters and Young's moduli of Ti-Al-O-N coatings was investigated by X-ray diffraction and nanoindentation, respectively. As nitrogen is substituted by oxygen, implications for the charge balance may be expected. A reduction in equilibrium volume with increasing O concentration is identified by X-ray diffraction and density functional theory calculations of Ti-Al-O-N supercells reveal the concomitant formation of metal vacancies. Hence, the oxygen incorporation-induced formation of metal vacancies enables charge balancing. Furthermore, nanoindentation experiments reveal a decrease in elastic modulus with increasing O concentration. Based on ab initio data, two causes can be identified for this: First, the metal vacancy-induced reduction in elasticity; and second, the formation of, compared to the corresponding metal nitride bonds, relatively weak Ti-O and Al-O bonds.
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| 7. |
- Pöllmann, P. J., et al.
(författare)
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Metastable phase formation of (Mo,Cr)2AlB2 MAB phase thin films revealed by theory and experiments
- 2024
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Ingår i: Materials Research Letters. - : Taylor & Francis. - 2166-3831. ; 12:1, s. 58-66
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Tidskriftsartikel (refereegranskat)abstract
- A (Mo0.24Cr0.76)0.40Al0.32B0.28 thin film was deposited by direct current magnetron sputtering at 600 °C substrate temperature. Analysis by X-ray diffraction, energy-dispersive X-ray spectroscopy, elastic recoil detection analysis, and high-resolution scanning transmission electron microscopy revealed the formation of the previously unreported (Mo,Cr)2AlB2 MAB phase, along with Cr3AlB4, CrB4, and Mo, in good agreement with density functional theory (DFT) calculations. Hence, the MAB phase family in the Mo-Cr-Al-B system is extended by a novel, quaternary member.
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| 8. |
- Roth, D., et al.
(författare)
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A procedure to determine electronic energy loss from relative measurements with TOF-LEIS
- 2013
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Ingår i: Nuclear Instruments and Methods in Physics Research Section B. - : Elsevier BV. - 0168-583X .- 1872-9584. ; 317:Part A, s. 61-65
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Tidskriftsartikel (refereegranskat)abstract
- The electronic stopping cross section of protons in polycrystalline Ge is deduced from TOF-LEIS measurements using an amorphized Ge wafer and a thick Cu reference sample. The evaluation is based on the comparison of height ratios of backscattering spectra from both, experiment and Monte Carlo simulations, which allow for multiple scattering of the protons in the sample. This procedure yields the electronic stopping cross section of Ge for protons with a relative uncertainty of less than 10% per data point. In the velocity regime 0.07–0.56 a.u., corresponding to proton energies in the range 120 eV–8 keV, the electronic stopping cross section is linear in the ion velocity. Extrapolation of the data yields a velocity threshold of vth = 0.0274 a.u. ± 10%. At velocities below 0.18 a.u., i.e. at proton energies below 810 eV, electronic stopping in Ge is – compared to Cu – found to be more efficient by up to a factor of 2.6.
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| 9. |
- Roth, D., et al.
(författare)
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Electronic Stopping of Slow Protons in Oxides : Scaling Properties
- 2017
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 119:16
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Tidskriftsartikel (refereegranskat)abstract
- Electronic stopping of slow protons in ZnO, VO2 (metal and semiconductor phases), HfO2, and Ta2O5 was investigated experimentally. As a comparison of the resulting stopping cross sections (SCS) to data for Al2O3 and SiO2 reveals, electronic stopping of slow protons does not correlate with electronic properties of the specific material such as band gap energies. Instead, the oxygen 2p states are decisive, as corroborated by density functional theory calculations of the electronic densities of states. Hence, at low ion velocities the SCS of an oxide primarily scales with its oxygen density.
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| 10. |
- Roth, D., et al.
(författare)
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Electronic Stopping of Slow Protons in Transition and Rare Earth Metals : Breakdown of the Free Electron Gas Concept
- 2017
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 118:10
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Tidskriftsartikel (refereegranskat)abstract
- The electronic stopping cross sections (SCS) of Ta and Gd for slow protons have been investigated experimentally. The data are compared to the results for Pt and Au to learn how electronic stopping in transition and rare earth metals correlates with features of the electronic band structures. The extraordinarily high SCS observed for protons in Ta and Gd cannot be understood in terms of a free electron gas model, but are related to the high densities of both occupied and unoccupied electronic states in these metals.
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