| 1. |
- Stroth, U., et al.
(författare)
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Progress from ASDEX Upgrade experiments in preparing the physics basis of ITER operation and DEMO scenario development
- 2022
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 62:4
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Tidskriftsartikel (refereegranskat)abstract
- An overview of recent results obtained at the tokamak ASDEX Upgrade (AUG) is given. A work flow for predictive profile modelling of AUG discharges was established which is able to reproduce experimental H-mode plasma profiles based on engineering parameters only. In the plasma center, theoretical predictions on plasma current redistribution by a dynamo effect were confirmed experimentally. For core transport, the stabilizing effect of fast ion distributions on turbulent transport is shown to be important to explain the core isotope effect and improves the description of hollow low-Z impurity profiles. The L-H power threshold of hydrogen plasmas is not affected by small helium admixtures and it increases continuously from the deuterium to the hydrogen level when the hydrogen concentration is raised from 0 to 100%. One focus of recent campaigns was the search for a fusion relevant integrated plasma scenario without large edge localised modes (ELMs). Results from six different ELM-free confinement regimes are compared with respect to reactor relevance: ELM suppression by magnetic perturbation coils could be attributed to toroidally asymmetric turbulent fluctuations in the vicinity of the separatrix. Stable improved confinement mode plasma phases with a detached inner divertor were obtained using a feedback control of the plasma β. The enhanced D α H-mode regime was extended to higher heating power by feedback controlled radiative cooling with argon. The quasi-coherent exhaust regime was developed into an integrated scenario at high heating power and energy confinement, with a detached divertor and without large ELMs. Small ELMs close to the separatrix lead to peeling-ballooning stability and quasi continuous power exhaust. Helium beam density fluctuation measurements confirm that transport close to the separatrix is important to achieve the different ELM-free regimes. Based on separatrix plasma parameters and interchange-drift-Alfvén turbulence, an analytic model was derived that reproduces the experimentally found important operational boundaries of the density limit and between L- and H-mode confinement. Feedback control for the X-point radiator (XPR) position was established as an important element for divertor detachment control. Stable and detached ELM-free phases with H-mode confinement quality were obtained when the XPR was moved 10 cm above the X-point. Investigations of the plasma in the future flexible snow-flake divertor of AUG by means of first SOLPS-ITER simulations with drifts activated predict beneficial detachment properties and the activation of an additional strike point by the drifts.
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| 2. |
- Meyer, H.F., et al.
(författare)
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Overview of physics studies on ASDEX Upgrade
- 2019
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 59:11
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Forskningsöversikt (refereegranskat)abstract
- The ASDEX Upgrade (AUG) programme, jointly run with the EUROfusion MST1 task force, continues to significantly enhance the physics base of ITER and DEMO. Here, the full tungsten wall is a key asset for extrapolating to future devices. The high overall heating power, flexible heating mix and comprehensive diagnostic set allows studies ranging from mimicking the scrape-off-layer and divertor conditions of ITER and DEMO at high density to fully non-inductive operation (q 95 = 5.5, ) at low density. Higher installed electron cyclotron resonance heating power 6 MW, new diagnostics and improved analysis techniques have further enhanced the capabilities of AUG. Stable high-density H-modes with MW m-1 with fully detached strike-points have been demonstrated. The ballooning instability close to the separatrix has been identified as a potential cause leading to the H-mode density limit and is also found to play an important role for the access to small edge-localized modes (ELMs). Density limit disruptions have been successfully avoided using a path-oriented approach to disruption handling and progress has been made in understanding the dissipation and avoidance of runaway electron beams. ELM suppression with resonant magnetic perturbations is now routinely achieved reaching transiently . This gives new insight into the field penetration physics, in particular with respect to plasma flows. Modelling agrees well with plasma response measurements and a helically localised ballooning structure observed prior to the ELM is evidence for the changed edge stability due to the magnetic perturbations. The impact of 3D perturbations on heat load patterns and fast-ion losses have been further elaborated. Progress has also been made in understanding the ELM cycle itself. Here, new fast measurements of and E r allow for inter ELM transport analysis confirming that E r is dominated by the diamagnetic term even for fast timescales. New analysis techniques allow detailed comparison of the ELM crash and are in good agreement with nonlinear MHD modelling. The observation of accelerated ions during the ELM crash can be seen as evidence for the reconnection during the ELM. As type-I ELMs (even mitigated) are likely not a viable operational regime in DEMO studies of 'natural' no ELM regimes have been extended. Stable I-modes up to have been characterised using -feedback. Core physics has been advanced by more detailed characterisation of the turbulence with new measurements such as the eddy tilt angle - measured for the first time - or the cross-phase angle of and fluctuations. These new data put strong constraints on gyro-kinetic turbulence modelling. In addition, carefully executed studies in different main species (H, D and He) and with different heating mixes highlight the importance of the collisional energy exchange for interpreting energy confinement. A new regime with a hollow profile now gives access to regimes mimicking aspects of burning plasma conditions and lead to nonlinear interactions of energetic particle modes despite the sub-Alfvénic beam energy. This will help to validate the fast-ion codes for predicting ITER and DEMO.
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| 3. |
- Blösch, Günter, et al.
(författare)
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Twenty-three unsolved problems in hydrology (UPH) - a community perspective
- 2019
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Ingår i: Hydrological Sciences Journal. - : Informa UK Limited. - 0262-6667 .- 2150-3435. ; 64:10, s. 1141-1158
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Tidskriftsartikel (refereegranskat)abstract
- This paper is the outcome of a community initiative to identify major unsolved scientific problems in hydrology motivated by a need for stronger harmonisation of research efforts. The procedure involved a public consultation through online media, followed by two workshops through which a large number of potential science questions were collated, prioritised, and synthesised. In spite of the diversity of the participants (230 scientists in total), the process revealed much about community priorities and the state of our science: a preference for continuity in research questions rather than radical departures or redirections from past and current work. Questions remain focused on the process-based understanding of hydrological variability and causality at all space and time scales. Increased attention to environmental change drives a new emphasis on understanding how change propagates across interfaces within the hydrological system and across disciplinary boundaries. In particular, the expansion of the human footprint raises a new set of questions related to human interactions with nature and water cycle feedbacks in the context of complex water management problems. We hope that this reflection and synthesis of the 23 unsolved problems in hydrology will help guide research efforts for some years to come.
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| 4. |
- Sourikopoulos, Ilias, et al.
(författare)
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The H2020-SPACE-SIPHODIAS project: Space-grade optoelectronic interfaces for photonic digital and analogue very-high-throughput satellite payloads
- 2021
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Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 11852
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Konferensbidrag (refereegranskat)abstract
- The EU-SIPhoDiAS project deals with the development of critical photonic building blocks needed for high-performance and low size, weight, and power (SWaP) photonics-enabled Very High Throughput Satellites (VHTS). In this presentation, we report on the design and fabrication activities during the first year of the project concerning the targeted family of digital and microwave photonic components. This effort aims to demonstrate components of enhanced reliability at technology readiness level (TRL) 7. Specifically, with respect to microwave photonic links, we report: (i) the design of Ka and Q-bands analogue photodetectors that will be assembled in compact packages, allowing for very high bandwidth per unit area and (ii) on the design of compact V-band GaAs electro-optic modulator arrays, which use a folded-path optical configuration to manage all fiber interfaces packaged opposite direct in-line RF feeds for ease of board layouts and mass/size benefits. With respect to digital links, we report on the development of 100 Gb/s (4 x 25 Gb/s) digital optical transceiver sub-assemblies developed using flip-chip mounting of electronic and opto-parts on a high-reliability borosilicate substrate. The transceiver chipset developed specifically for this project refers to fully-custom 25 Gb/s radiation hard (RH) VCSEL driver and TIA ICs designed in IHP’s 130 nm SiGe BiCMOS Rad-Hard process.
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| 5. |
- Fice, Jason, 1985, et al.
(författare)
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Neck Muscle and Head/Neck Kinematic Responses While Bracing Against the Steering Wheel During Front and Rear Impacts
- 2021
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Ingår i: Annals of Biomedical Engineering. - : Springer Science and Business Media LLC. - 1573-9686 .- 0090-6964. ; 49:3, s. 1069-1082
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Tidskriftsartikel (refereegranskat)abstract
- Drivers often react to an impending collision by bracing against the steering wheel. The goal of the present study was to quantify the effect of bracing on neck muscle activity and head/torso kinematics during low-speed front and rear impacts. Eleven seated subjects (3F, 8 M) experienced multiple sled impacts (Delta v = 0.77 m/s; a(peak) = 19.9 m/s(2), Delta t = 65.5 ms) with their hands on the steering wheel in two conditions: relaxed and braced against the steering wheel. Electromyographic activity in eight neck muscles (sternohyoid, sternocleidomastoid, splenius capitis, semispinalis capitis, semispinalis cervicis, multifidus, levator scapulae, and trapezius) was recorded unilaterally with indwelling electrodes and normalized by maximum voluntary contraction (MVC) levels. Head and torso kinematics (linear acceleration, angular velocity, angular rotation, and retraction) were measured with sensors and motion tracking. Muscle and kinematic variables were compared between the relaxed and braced conditions using linear mixed models. We found that pre-impact bracing generated only small increases in the pre-impact muscle activity (< 5% MVC) when compared to the relaxed condition. Pre-impact bracing did not increase peak neck muscle responses during the impacts; instead it reduced peak trapezius and multifidus muscle activity by about half during front impacts. Bracing led to widespread changes in the peak amplitude and timing of the torso and head kinematics that were not consistent with a simple stiffening of the head/neck/torso system. Instead pre-impact bracing served to couple the torso more rigidly to the seat while not necessarily coupling the head more rigidly to the torso.
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| 6. |
- Siegmund, Gunter P., et al.
(författare)
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Letter to the editor
- 2019
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Ingår i: Spine. - Malmö : Malmö universitet. - 1528-1159 .- 0362-2436. ; 44:2, s. E133-E133:1, s. i-i
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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| 7. |
- Jones, Geraint H., et al.
(författare)
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The Comet Interceptor Mission
- 2024
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Ingår i: Space Science Reviews. - : Springer Nature. - 0038-6308 .- 1572-9672. ; 220:1
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Tidskriftsartikel (refereegranskat)abstract
- Here we describe the novel, multi-point Comet Interceptor mission. It is dedicated to the exploration of a little-processed long-period comet, possibly entering the inner Solar System for the first time, or to encounter an interstellar object originating at another star. The objectives of the mission are to address the following questions: What are the surface composition, shape, morphology, and structure of the target object? What is the composition of the gas and dust in the coma, its connection to the nucleus, and the nature of its interaction with the solar wind? The mission was proposed to the European Space Agency in 2018, and formally adopted by the agency in June 2022, for launch in 2029 together with the Ariel mission. Comet Interceptor will take advantage of the opportunity presented by ESA’s F-Class call for fast, flexible, low-cost missions to which it was proposed. The call required a launch to a halo orbit around the Sun-Earth L2 point. The mission can take advantage of this placement to wait for the discovery of a suitable comet reachable with its minimum Δ V capability of 600 ms − 1 . Comet Interceptor will be unique in encountering and studying, at a nominal closest approach distance of 1000 km, a comet that represents a near-pristine sample of material from the formation of the Solar System. It will also add a capability that no previous cometary mission has had, which is to deploy two sub-probes – B1, provided by the Japanese space agency, JAXA, and B2 – that will follow different trajectories through the coma. While the main probe passes at a nominal 1000 km distance, probes B1 and B2 will follow different chords through the coma at distances of 850 km and 400 km, respectively. The result will be unique, simultaneous, spatially resolved information of the 3-dimensional properties of the target comet and its interaction with the space environment. We present the mission’s science background leading to these objectives, as well as an overview of the scientific instruments, mission design, and schedule.
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| 8. |
- Åström, Karl Johan, et al.
(författare)
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Control in an Information Rich World: Report of the Panel on Future Directions in Control, Dynamics, and Systems
- 2003
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Bok (övrigt vetenskapligt/konstnärligt)abstract
- The field of control provides the principles and methods used to design physical and information systems that maintain desirable performance by sensing and automatically adapting to changes in the environment. This report spells out some of the prospects for control in the current and future technological environment, describes the role the field will play in military, commercial, and scientific applications over the next decade, and recommends actions required to enable new breakthroughs in engineering and technology through the application of control research. This brief yet thorough report provides renewed vision, a detailed list of new application areas, and specific recommendations for future research directions in control, dynamics, and systems, compiled by experts in the field.
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