| 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. |
- Murari, A., et al.
(författare)
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A control oriented strategy of disruption prediction to avoid the configuration collapse of tokamak reactors
- 2024
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Ingår i: Nature Communications. - 2041-1723 .- 2041-1723. ; 15:1
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Tidskriftsartikel (refereegranskat)abstract
- The objective of thermonuclear fusion consists of producing electricity from the coalescence of light nuclei in high temperature plasmas. The most promising route to fusion envisages the confinement of such plasmas with magnetic fields, whose most studied configuration is the tokamak. Disruptions are catastrophic collapses affecting all tokamak devices and one of the main potential showstoppers on the route to a commercial reactor. In this work we report how, deploying innovative analysis methods on thousands of JET experiments covering the isotopic compositions from hydrogen to full tritium and including the major D-T campaign, the nature of the various forms of collapse is investigated in all phases of the discharges. An original approach to proximity detection has been developed, which allows determining both the probability of and the time interval remaining before an incoming disruption, with adaptive, from scratch, real time compatible techniques. The results indicate that physics based prediction and control tools can be developed, to deploy realistic strategies of disruption avoidance and prevention, meeting the requirements of the next generation of devices.
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| 4. |
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| 5. |
- Fenstermacher, M.E., et al.
(författare)
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DIII-D research advancing the physics basis for optimizing the tokamak approach to fusion energy
- 2022
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 0029-5515 .- 1741-4326. ; 62:4
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Tidskriftsartikel (refereegranskat)abstract
- DIII-D physics research addresses critical challenges for the operation of ITER and the next generation of fusion energy devices. This is done through a focus on innovations to provide solutions for high performance long pulse operation, coupled with fundamental plasma physics understanding and model validation, to drive scenario development by integrating high performance core and boundary plasmas. Substantial increases in off-axis current drive efficiency from an innovative top launch system for EC power, and in pressure broadening for Alfven eigenmode control from a co-/counter-I p steerable off-axis neutral beam, all improve the prospects for optimization of future long pulse/steady state high performance tokamak operation. Fundamental studies into the modes that drive the evolution of the pedestal pressure profile and electron vs ion heat flux validate predictive models of pedestal recovery after ELMs. Understanding the physics mechanisms of ELM control and density pumpout by 3D magnetic perturbation fields leads to confident predictions for ITER and future devices. Validated modeling of high-Z shattered pellet injection for disruption mitigation, runaway electron dissipation, and techniques for disruption prediction and avoidance including machine learning, give confidence in handling disruptivity for future devices. For the non-nuclear phase of ITER, two actuators are identified to lower the L-H threshold power in hydrogen plasmas. With this physics understanding and suite of capabilities, a high poloidal beta optimized-core scenario with an internal transport barrier that projects nearly to Q = 10 in ITER at ∼8 MA was coupled to a detached divertor, and a near super H-mode optimized-pedestal scenario with co-I p beam injection was coupled to a radiative divertor. The hybrid core scenario was achieved directly, without the need for anomalous current diffusion, using off-axis current drive actuators. Also, a controller to assess proximity to stability limits and regulate β N in the ITER baseline scenario, based on plasma response to probing 3D fields, was demonstrated. Finally, innovative tokamak operation using a negative triangularity shape showed many attractive features for future pilot plant operation.
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| 13. |
- Buller, Stefan, 1991, et al.
(författare)
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Collisional transport of impurities with flux-surface varying density in stellarators
- 2018
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Ingår i: Journal of Plasma Physics. - 0022-3778 .- 1469-7807. ; 84:4
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Tidskriftsartikel (refereegranskat)abstract
- High-Z impurities in magnetic-confinement devices are prone to develop density variations on the flux surface, which can significantly affect their transport. In this paper, we generalize earlier analytic stellarator calculations of the neoclassical radial impurity flux in the mixed-collisionality regime (collisional impurities and low-collisionality bulk ions) to include the effect of such flux-surface variations. We find that only in the homogeneous density case is the transport of highly collisional impurities (in the Pfirsch-Schlhter regime) independent of the radial electric field. We study these effects for a Wendelstein 7-X (W7-X) vacuum field, with simple analytic models for the potential perturbation, under the assumption that the impurity density is given by a Boltzmann response to a perturbed potential. In the W7-X case studied, we find that larger amplitude potential perturbations cause the radial electric field to dominate the transport of the impurities. In addition, we find that classical impurity transport can be larger than the neoclassical transport in W7-X.
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| 14. |
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| 15. |
- Harsanyi, I., et al.
(författare)
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On the hydration structure of LiCl aqueous solutions : A Reverse Monte Carlo based combination of diffraction data and Molecular Dynamics simulations
- 2011
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Ingår i: Journal of Molecular Liquids. - : Elsevier BV. - 0167-7322 .- 1873-3166. ; 158:1, s. 61-67
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Tidskriftsartikel (refereegranskat)abstract
- Reverse Monte Carlo (RMC) calculations have been carried out on aqueous LiCl solutions at several concentrations, comparing experimental X-ray and neutron diffraction data with partial radial distribution functions (prdf) from Molecular Dynamics (MD) simulations based on conventional ion-ion, ion-water, and water-water pair potentials. The RMC calculations indicate that the hydration shell of the Li+ ions could be even more structured than computer simulations predict, containing at high concentrations unusually few water molecules, of the order of 2 to 3. Concerning the consistency between the structures based on potential models and diffraction data: the ion-water partial radial distribution functions (prdf) from MD are found to be consistent with the experimental data whereas the water-water and ion-ion partials are more problematic. The most serious deficiency is that at high salt concentrations the O-O prdf cannot be made consistent with the present X-ray diffraction data.
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| 20. |
- Mollén, Albert, 1985, et al.
(författare)
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Impurity peaking in tokamaks
- 2013
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Ingår i: Proceedings of 40th European Physical Society meeting on Plasma Physics. - 9781632663108 ; 2, s. 1034-1037
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Konferensbidrag (refereegranskat)
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| 21. |
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| 22. |
- Moradi, Sara, 1981, et al.
(författare)
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Core micro-instability analysis of JET hybrid and baseline discharges with carbon wall
- 2014
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 54:12, s. 123016-
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Tidskriftsartikel (refereegranskat)abstract
- The core micro-instability characteristics of hybrid and baseline plasmas in a selected set of JET plasmas with carbon wall are investigated through local linear and non-linear and global linear gyro-kinetic simulations with the GYRO code (Candy and Belli 2011 General Atomics Report GA-A26818). In particular, we study the role of plasma pressure on the micro-instabilities, and scan the parameter space for the important plasma parameters responsible for the onset and stabilization of the modes under experimental conditions. We find that a good core confinement due to strong stabilization of the micro-turbulence driven transport can be expected in the hybrid plasmas due to the stabilizing effect of the fast ion pressure that is more effective at the low magnetic shear of the hybrid discharges. While parallel velocity gradient destabilization is important for the inner core, at outer radii the hybrid plasmas may benefit from a strong quench of the turbulence transport by E×B rotation shear.
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| 23. |
- Nemeskeri, R. L., et al.
(författare)
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Dynamic site characterization for brownfield risk management
- 2017
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Ingår i: Engineering Tools for Environmental Risk Management -3 : Site Assessment and Monitoring Tools - Site Assessment and Monitoring Tools. - 9781138001565 - 9781317697459 ; , s. 343-360
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Bokkapitel (refereegranskat)abstract
- Common remediation and land management approaches often preclude economically attractive and low risk brownfield redevelopment. The authors argue that recently developed dynamic site characterization techniques can greatly improve sound decision making on land revitalization options. A number of these in-situ soil and groundwater test methods, such as MIP, ROST™/UVOST™, XRF and BAT, based on geotechnical cone pressure testing and developed by Fugro and its partners, are introduced.
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| 24. |
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| 25. |
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| 26. |
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| 27. |
- Pusztai, L, et al.
(författare)
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MCGR: An inverse method for deriving the pair correlation function from the structure factor
- 1997
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Ingår i: PHYSICA B. - : ELSEVIER SCIENCE BV. - 0921-4526. ; 234, s. 357-358
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- MCGR is a Monte-Carlo program for determining the pair correlation function (pcf), G(r), of a material from the total structure factor (tsf), F(Q), by an inverse method. Some of the latest developments are reviewed here: (a) coordination constraints, (b)
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| 28. |
- Pusztai, L, et al.
(författare)
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The structure of molten ZnCl2 and MgCl2
- 2001
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Ingår i: JOURNAL OF PHYSICS-CONDENSED MATTER. - : IOP PUBLISHING LTD. - 0953-8984. ; 13:33, s. 7213-7222
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Tidskriftsartikel (refereegranskat)abstract
- The structures of molten MgCl2 and ZnCl2 have been modelled using the reverse Monte Carlo method, based on neutron and x-ray diffraction data. We show that, although the structures are similar in terms of two-body correlations (e.g. partial radial distrib
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| 29. |
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| 34. |
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| 35. |
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| 36. |
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| 37. |
- Sundstrom, A., et al.
(författare)
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Fast collisional electron heating and relaxation in thin foils driven by a circularly polarized ultraintense short-pulse laser
- 2020
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Ingår i: Journal of Plasma Physics. - : Cambridge University Press (CUP). - 0022-3778 .- 1469-7807. ; 86:2
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Tidskriftsartikel (refereegranskat)abstract
- The creation of well-thermalized, hot and dense plasmas is attractive for warm dense matter studies. We investigate collisionally induced energy absorption of an ultraintense and ultrashort laser pulse in a solid copper target using particle-in-cell simulations. We find that, upon irradiation by a 2 x 10(20) Wcm(-2) intensity, 60 fs duration, circularly polarized laser pulse, the electrons in the collisional simulation rapidly reach a well-thermalized distribution with similar to 3 :5 keV temperature, while in the collisionless simulation the absorption is several orders of magnitude weaker. Circular polarization inhibits the generation of suprathermal electrons, while ensuring efficient bulk heating through inverse bremsstrahlung, a mechanism usually overlooked at relativistic laser intensity. An additional simulation, taking account of both collisional and field ionization, yields similar results: the bulk electrons are heated to similar to 2:5 keV, but with a somewhat lower degree of thermalization than in the pre-set, fixed-ionization case. The collisional absorption mechanism is found to be robust against variations in the laser parameters. At fixed laser pulse energy, increasing the pulse duration rather than the intensity leads to a higher electron temperature.
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| 38. |
- Sundström, Andréas, 1994, et al.
(författare)
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Collisional effects on the electrostatic shock dynamics in thin-foil targets driven by an ultraintense short pulse laser
- 2020
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Ingår i: Plasma Physics and Controlled Fusion. - : IOP Publishing. - 0741-3335 .- 1361-6587. ; 62:8
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Tidskriftsartikel (refereegranskat)abstract
- We numerically investigate the impact of Coulomb collisions on the ion dynamics in high-Z, solid density caesium hydride and copper targets, irradiated by high-intensity (I approximate to 2-5x10(20) W cm(-2)), ultrashort (similar to 10 fs), circularly polarized laser pulses, using particle-in-cell simulations. Collisions significantly enhance electron heating, thereby strongly increasing the speed of a shock wave launched in the laser-plasma interaction. In the caesium hydride target, collisions between the two ion species heat the protons to similar to 100-1000 eV temperatures. However, in contrast to previous work (A E Turrellet al2015Nat. Commun.68905), this process happens in the upstream only, due to nearly total proton reflection. This difference is ascribed to distinct models used to treat collisions in dense/cold plasmas. In the case of a copper target, ion reflection can start as a self-amplifying process, bootstrapping itself. Afterwards, collisions between the reflected and upstream ions heat these two populations significantly. When increasing the pulse duration to 60 fs, the shock front more clearly decouples from the laser piston, and so can be studied without direct interference from the laser. The shock wave formed at early times exhibits properties typical of both hydrodynamic and electrostatic shocks, including ion reflection. At late times, the shock is seen to evolve into a hydrodynamic blast wave.
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| 39. |
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| 40. |
- Vallhagen, Oskar, 1997, et al.
(författare)
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Drift of ablated material after pellet injection in a tokamak
- 2023
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Ingår i: Journal of Plasma Physics. - 0022-3778 .- 1469-7807. ; 89:3
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Tidskriftsartikel (refereegranskat)abstract
- Pellet injection is used for fuelling and controlling discharges in tokamaks, and it is foreseen in ITER. During pellet injection, a movement of the ablated material towards the low-field side (or outward major radius direction) occurs because of the inhomogeneity of the magnetic field. Due to the complexity of the theoretical models, computer codes developed to simulate the cross-field drift are computationally expensive. Here, we present a one-dimensional semi-analytical model for the radial displacement of ablated material after pellet injection, taking into account both the Alfven and ohmic currents which shortcircuit the charge separation creating the drift. The model is suitable for rapid calculation of the radial drift displacement, and can be useful for e.g. modelling of disruption mitigation via pellet injection.
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| 41. |
- Vallhagen, Oskar, 1997, et al.
(författare)
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Effect of two-stage shattered pellet injection on tokamak disruptions
- 2022
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 62:11
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Tidskriftsartikel (refereegranskat)abstract
- An effective disruption mitigation system in a tokamak reactor should limit the exposure of the wall to localized heat losses and to the impact of high current runaway electron beams, and avoid excessive forces on the structure. We evaluate with respect to these aspects a two-stage deuterium-neon shattered pellet injection in an ITER-like plasma, using simulations with the DREAM framework (Hoppe et al 2021 Comput. Phys. Commun. 268 108098). To minimize the obtained runaway currents an optimal range of injected deuterium quantities is found. This range is sensitive to the opacity of the plasma to Lyman radiation, which affects the ionization degree of deuterium, and thus avalanche runaway generation. The two-stage injection scheme, where dilution cooling is produced by deuterium before a radiative thermal quench caused by neon, reduces both the hot-tail seed and the localized transported heat load on the wall. However, during nuclear operation, additional runaway seed sources from the activated wall and tritium make it difficult to reach tolerably low runaway currents.
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