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- 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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| 6. |
- Stahl, Adam, 1985, et al.
(författare)
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Kinetic modelling of runaway-electron dynamics
- 2015
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Ingår i: Proceedings of the 14th IAEA Technical Meeting on Energetic Particles in Magnetic Confinement Systems.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Improved understanding of runaway-electron formation and decayprocesses are of prime interest for the safe operation of large tokamaks, and theirdynamics during dynamical scenarios such as disruptions are of particular concern. Inthis contribution, we present kinetic modelling of scenarios with time-dependent plasmaparameters – in particular, we investigate hot-tail runaway generation during a rapiddrop in plasma temperature. With the goal of studying runaway-electron generationwith a self-consistent electric field-evolution, we also discuss the implementation ofa conservative collision operator and demonstrate its properties. An operator foravalanche runaway-electron generation which includes the proper energy dependenceof the runaway distribution, is investigated, and the avalanche growth rate is shownto be significantly affected in some parameter regimes. These developments all pavethe way for an improved modelling of runaway-electron dynamics during disruptionsor other dynamic events.
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| 8. |
- Hesslow, Linnea, 1993, et al.
(författare)
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Effect of partially-screened nuclei on fast-electron dynamics
- 2017
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Ingår i: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 118:25, s. article no. 5501-
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Tidskriftsartikel (refereegranskat)abstract
- We analyze the dynamics of fast electrons in plasmas containing partially ionized impurity atoms, where the screening effect of bound electrons must be included. We derive analytical expressions for the deflection and slowing-down frequencies, and show that they are increased significantly compared to the results obtained with complete screening, already at sub-relativistic electron energies. Furthermore, we show that the modifications to the deflection and slowing down frequencies are of equal importance in describing the runaway current evolution. Our results greatly affect fast-electron dynamics and have important implications, e.g. for the efficacy of mitigation strategies for runaway electrons in tokamak devices, and energy loss during relativistic breakdown in atmospheric discharges.
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| 9. |
- Hesslow, Linnea, 1993, et al.
(författare)
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Kinetic effects of partially screened impurities in runaway-electron mitigation scenarios
- 2017
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Ingår i: International Sherwood Fusion Theory Conference, Annapolis, USA.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Runaway electrons constitute a significant threat to tokamak devices. Their mitigation by heavy-impurity injection has been experimentally shown to be more effective than would be expected from standard collisional theory [1]. In order to understand this effect and develop runaway mitigation schemes, more accurate kinetic models are needed to describe the interaction between electrons and partially ionized atoms. Such models require the partial screening of the nuclei by the bound electrons to be taken into account.In this contribution, we analyze the dynamics of fast electrons in plasmas containing partially ionized impurity atoms. A generalized collision operator is derived from first principles using quantum-mechanical models. We obtain analytical expressions for the deflection and slowing-down frequencies. Even at sub-relativistic energies, these are increased by more than an order of magnitude compared to the results obtained with complete screening. Moreover, we implement the generalized collision operator in the continuum kinetic-equation solver CODE [2, 3] and demonstrate that interaction with partially ionized atoms greatly affects fast-electron dynamics by enhancing the rates of angular deflection and energy loss. In particular, we investigate the decay of a runaway-electron current coupled to a self-consistent electric field. The effect of the interaction with partially ionized impurities has important implications for the efficacy of mitigation strategies for runaway electrons in tokamak devices.References[1] E. M. Hollmann et al., Physics of Plasmas 22, 056108 (2015).[2] M. Landreman, A. Stahl and T. Fülöp, Comp. Phys. Comm. 185, 847 (2014).[3] A. Stahl et al., Nuclear Fusion 56, 112009 (2016).
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| 10. |
- Labit, B., et al.
(författare)
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Dependence on plasma shape and plasma fueling for small edge-localized mode regimes in TCV and ASDEX Upgrade
- 2019
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 59:8
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Tidskriftsartikel (refereegranskat)abstract
- © 2019 Institute of Physics Publishing. All rights reserved. Within the EUROfusion MST1 work package, a series of experiments has been conducted on AUG and TCV devices to disentangle the role of plasma fueling and plasma shape for the onset of small ELM regimes. On both devices, small ELM regimes with high confinement are achieved if and only if two conditions are fulfilled at the same time. Firstly, the plasma density at the separatrix must be large enough (ne,sep/nG ∼ 0.3), leading to a pressure profile flattening at the separatrix, which stabilizes type-I ELMs. Secondly, the magnetic configuration has to be close to a double null (DN), leading to a reduction of the magnetic shear in the extreme vicinity of the separatrix. As a consequence, its stabilizing effect on ballooning modes is weakened.
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