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- Bombarda, F., et al.
(författare)
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Runaway electron beam control
- 2019
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Ingår i: Plasma Physics and Controlled Fusion. - : IOP Publishing. - 1361-6587 .- 0741-3335. ; 61:1
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Tidskriftsartikel (refereegranskat)
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- Bowman, C., et al.
(författare)
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Pedestal evolution physics in low triangularity JET tokamak discharges with ITER-like wall
- 2018
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 0029-5515 .- 1741-4326. ; 58:1
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Tidskriftsartikel (refereegranskat)abstract
- The pressure gradient of the high confinement pedestal region at the edge of tokamak plasmas rapidly collapses during plasma eruptions called edge localised modes (ELMs), and then re-builds over a longer time scale before the next ELM. The physics that controls the evolution of the JET pedestal between ELMs is analysed for 1.4 MA, 1.7 T, low triangularity, delta = 0.2, discharges with the ITER-like wall, finding that the pressure gradient typically tracks the ideal magneto-hydrodynamic ballooning limit, consistent with a role for the kinetic ballooning mode. Furthermore, the pedestal width is often influenced by the region of plasma that has second stability access to the ballooning mode, which can explain its sometimes complex evolution between ELMs. A local gyrokinetic analysis of a second stable flux surface reveals stability to kinetic ballooning modes; global effects are expected to provide a destabilising mechanism and need to be retained in such second stable situations. As well as an electronscale electron temperature gradient mode, ion scale instabilities associated with this flux surface include an electro-magnetic trapped electron branch and two electrostatic branches propagating in the ion direction, one with high radial wavenumber. In these second stability situations, the ELM is triggered by a peeling-ballooning mode; otherwise the pedestal is somewhat below the peeling-ballooning mode marginal stability boundary at ELM onset. In this latter situation, there is evidence that higher frequency ELMs are paced by an oscillation in the plasma, causing a crash in the pedestal before the peeling-ballooning boundary is reached. A model is proposed in which the oscillation is associated with hot plasma filaments that are pushed out towards the plasma edge by a ballooning mode, draining their free energy into the cooler plasma there, and then relaxing back to repeat the process. The results suggest that avoiding the oscillation and maximising the region of plasma that has second stability access will lead to the highest pedestal heights and, therefore, best confinement-a key result for optimising the fusion performance of JET and future tokamaks, such as ITER.
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| 13. |
- 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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| 19. |
- Lygnerud, Kristina, et al.
(författare)
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Handbook for increased recovery of urban excess heat
- 2022
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The aim of this book is to consolidate information from low temperature waste heat recovery demonstration sites. Apart from technical validation, the ReUseHeat project has generated knowledge about the urban waste heat potential in Europe, main stakeholders and different business aspects. Five stakeholder groups are targeted. These are urban waste heat owners, District Heating (DH) companies, policy makers, investors and customers. In the first chapter of the book, the concept of urban waste heat is introduced and the urban waste heat potential in Europe is presented. Thereafter (chapter two), information on business aspects is provided (stakeholders, value chain, risks, contracts and business model characteristics). Chapter three showcases the demonstrator concepts (waste heat recovery from data centre, hospital, metro and awareness creation about urban waste heat recovery) and performance data. Throughout the writing of the handbook, it was identified that it is important to compare the cost of different heating alternatives, to facilitate customer decision making. Therefore, a model was derived to compare costs of heating alternatives. It is presented in chapter four. Urban waste heat recovery is news. It is therefore important that stakeholders are made aware of the possibility to use the locally available heat and to start collaborating in new ways. To ensure as much stakeholder engagement as possible, the writing process of this book encompassed a six-month stakeholder involvement process. The stakeholder input is presented in chapter five. In chapter six, thoughts on the future development of district energy, policy implications and major learnings from the project are presented. This book was written within the ReUseHeat project. The work on the book was initiated after the first out of five years of activity to ensure that the consortium would be engaged in its development and to capture the knowledge generated on an ongoing basis. The final version of the book was ready and placed on the ReUseHeat webpage in September 2022. The project webpage remains in operation until 2024. The book not only exists in digital format. 600 copies were also printed and distributed to relevant stakeholders. All partners of the consortium have contributed to the writing of the book.
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| 25. |
- Wynn, A., et al.
(författare)
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Investigation into the formation of the scrape-off layer density shoulder in JET ITER-like wall L-mode and H-mode plasmas
- 2018
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Ingår i: Nuclear Fusion. - : IOP PUBLISHING LTD. - 0029-5515 .- 1741-4326. ; 58:5
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Tidskriftsartikel (refereegranskat)abstract
- The low temperature boundary layer plasma (scrape-off layer or SOL) between the hot core and the surrounding vessel determines the level of power loading, erosion and implantation of material surfaces, and thus the viability of tokamak-based fusion as an energy source. This study explores mechanisms affecting the formation of flattened density profiles, so-called 'density shoulders', in the low-field side (LFS) SOL, which modify ion and neutral fluxes to surfaces-and subsequent erosion. We find that increases in SOL parallel resistivity, Lambda(div) (=[L-parallel to nu(ei)Omega(i)]/c(s)Omega(e)), postulated to lead to shoulder growth through changes in SOL turbulence characteristics, correlates with increases in SOL shoulder amplitude, A(s), only under a subset of conditions (D-2-fuelled L-mode density scans with outer strike point on the horizontal target). Lambda(div) fails to correlate with As for cases of N-2 seeding or during sweeping of the strike point across the horizontal target. The limited correlation of Lambda(div) and A(s) is also found for H-mode discharges. Thus, while it may be necessary for Lambda(div) to be above a threshold of similar to 1 for shoulder formation and/or growth, another mechanism is required. More significantly, we find that in contrast to parallel resistivity, outer divertor recycling, as quantified by the total outer divertor Balmer D-alpha emission, I-D-alpha, does scale with A(s) where Lambda(div) does and even where Lambda(div) does not. Divertor recycling could lead to SOL density shoulder formation through: (a) reducing the parallel to the field flow (loss) of ions out of the SOL to the divertor; and (b) changes in radial electric fields which lead to E x B poloidal flows as well as potentially affecting SOL turbulence birth characteristics. Thus, changes in divertor recycling may be the sole process involved in bringing about SOL density shoulders or it may be that it acts in tandem with parallel resistivity.
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| 26. |
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- 2018
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 58:9
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Tidskriftsartikel (refereegranskat)
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| 27. |
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- 2018
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 58:1
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Forskningsöversikt (refereegranskat)
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