| 1. |
- Ferreira, Diogo R., et al.
(författare)
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High temporal resolution of pedestal dynamics via machine learning on density diagnostics
- 2024
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Ingår i: Plasma Physics and Controlled Fusion. - 1361-6587 .- 0741-3335. ; 66:2
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Tidskriftsartikel (refereegranskat)abstract
- At the Joint European Torus, the reference diagnostic to measure electron density is Thomson scattering. However, this diagnostic has a low sampling rate, which makes it impractical to study the temporal dynamics of fast processes, such as edge localized modes. In this work, we use machine learning to predict the density profile based on data from another diagnostic, namely reflectometry. By learning to transform reflectometry data into Thomson scattering profiles, the model is able to generate the density profile at a much higher sampling rate than Thomson scattering, and more accurately than reflectometry alone. This enables the study of pedestal dynamics, by analyzing the time evolution of the pedestal height, width, position and gradient. We also discuss the accuracy of the model when applied on experimental campaigns that are different from the one it was trained on.
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| 2. |
- Jonsson, B. Lars G., et al.
(författare)
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On bandwidth bounds for periodic antenna elements with a ground plane
- 2021
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Ingår i: 2021 34th General Assembly and Scientific Symposium of the International Union of Radio Science, URSI GASS 2021. - : Institute of Electrical and Electronics Engineers (IEEE).
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Konferensbidrag (refereegranskat)abstract
- In this paper, we compare two different bandwidth bounds on array antennas with a ground plane. The first of these bounds is based on the fact that the antenna can be seen as a passive system, which implies that its response can be described in terms of a Herglotz function. This passivity-based bandwidth bound is closely related to a sum rule for lossless arrays over the ground plane. The second bound is a recently developed Q-factor based bound, valid for resonant structures. In this paper, it is shown that this latter bound strongly depends on the allowed shape and the electrical size of the element within the unit cell. It also depends on the size of the unit cell, corresponding to the interelement spacing. The Q-factor bound provides a sharper bound when the structure is resonant.
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| 3. |
- Kim, Hyun-Tae, et al.
(författare)
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Validation of D-T fusion power prediction capability against 2021 JET D-T experiments
- 2023
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Ingår i: Nuclear Fusion. - 0029-5515 .- 1741-4326. ; 63:11
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Tidskriftsartikel (refereegranskat)abstract
- JET experiments using the fuel mixture envisaged for fusion power plants, deuterium and tritium (D-T), provide a unique opportunity to validate existing D-T fusion power prediction capabilities in support of future device design and operation preparation. The 2021 JET D-T experimental campaign has achieved D-T fusion powers sustained over 5 s in ITER-relevant conditions i.e. operation with the baseline or hybrid scenario in the full metallic wall. In preparation of the 2021 JET D-T experimental campaign, extensive D-T predictive modelling was carried out with several assumptions based on D discharges. To improve the validity of ITER D-T predictive modelling in the future, it is important to use the input data measured from 2021 JET D-T discharges in the present core predictive modelling, and to specify the accuracy of the D-T fusion power prediction in comparison with the experiments. This paper reports on the validation of the core integrated modelling with TRANSP, JINTRAC, and ETS coupled with a quasilinear turbulent transport model (Trapped Gyro Landau Fluid or QualLiKiz) against the measured data in 2021 JET D-T discharges. Detailed simulation settings and the heating and transport models used are described. The D-T fusion power calculated with the interpretive TRANSP runs for 38 D-T discharges (12 baseline and 26 hybrid discharges) reproduced the measured values within 20 % . This indicates the additional uncertainties, that could result from the measurement error bars in kinetic profiles, impurity contents and neutron rates, and also from the beam-thermal fusion reaction modelling, are less than 20 % in total. The good statistical agreement confirms that we have the capability to accurately calculate the D-T fusion power if correct kinetic profiles are predicted, and indicates that any larger deviation of the D-T fusion power prediction from the measured fusion power could be attributed to the deviation of the predicted kinetic profiles from the measured kinetic profiles in these plasma scenarios. Without any posterior adjustment of the simulation settings, the ratio of predicted D-T fusion power to the measured fusion power was found as 65%-96% for the D-T baseline and 81%-97% for D-T hybrid discharge. Possible reasons for the lower D-T prediction are discussed and future works to improve the fusion power prediction capability are suggested. The D-T predictive modelling results have also been compared to the predictive modelling of the counterpart D discharges, where the key engineering parameters are similar. Features in the predicted kinetic profiles of D-T discharges such as underprediction of ne are also found in the prediction results of the counterpart D discharges, and it leads to similar levels of the normalized neutron rate prediction between the modelling results of D-T and the counterpart D discharges. This implies that the credibility of D-T fusion power prediction could be a priori estimated by the prediction quality of the preparatory D discharges, which will be attempted before actual D-T experiments.
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| 4. |
- McKelvey, Tomas, 1966, et al.
(författare)
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A Möbius Transform Approach for Improved MIMO Frequency Domain Identification
- 2021
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Ingår i: IFAC-PapersOnLine. - : Elsevier BV. - 2405-8963 .- 2405-8963. ; 54:7, s. 791-796
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Konferensbidrag (refereegranskat)abstract
- To improve the numerical conditioning of a frequency domain subspace algorithm (FSID) when identifying continuous time transfer functions a general Mobius transformation can be employed. The Mobius transformation is a more general class of transformations which include the bilinear transformation as a special case. For the state-space model class of MIMO transfer functions we derive the relations describing how the state-space realization of a transfer function is converted under a Mobius transformation. With an extensive numerical example we illustrate that a particular choice of the Mobius transformation leads to transfer function estimates with, in general, significantly improved accuracy. Copyright (C) 2021 The Authors.
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| 5. |
- Nedic, Mitja, et al.
(författare)
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Herglotz functions and applications in electromagnetics
- 2020
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Ingår i: Advances in Mathematical Methods for Electromagnetics. - : Institution of Engineering and Technology. - 9781785613845 - 9781785613852 ; , s. 491-514
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Herglotz functions inevitably appear in pure mathematics, mathematical physics, and engineering with a wide range of applications. In particular, they are the pertinent functions to model passive systems, and thus appear in modeling of electromagnetic phenomena in circuits, antennas, materials, and scattering. In this chapter, we review the basic theory of Herglotz functions and its applications to determine sum rules and physical bounds for passive systems.
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| 6. |
- Osipov, Andrei, 1991, et al.
(författare)
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Physical Limitations of Phased Array Antennas
- 2021
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Ingår i: IEEE Transactions on Antennas and Propagation. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-926X .- 1558-2221. ; In Press
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, the bounds on the Q-factor, a quantity inversely proportional to bandwidth, are derived and investigated for narrow-band phased array antennas. Arrays in free space and above a ground plane are considered. The Q-factor bound is determined by solving a minimization problem over the electric current density. The support of these current densities is on an element-enclosing region, and the bound holds for lossless antenna elements enclosed in this region. The Q-factor minimization problem is formulated as a quadratically constrained quadratic optimization problem that is solved either by a semi-definite relaxation or an eigenvalue-based method. We illustrate numerically how these bounds can be used to determine trade-off relations between the Q-factor and other design specifications: element form-factor, size, efficiency, scanning capabilities, and polarization purity.
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| 7. |
- Strand, Pär, 1968, et al.
(författare)
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A FAIR based approach to data sharing in Europe
- 2022
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Ingår i: Plasma Physics and Controlled Fusion. - : IOP Publishing. - 1361-6587 .- 0741-3335. ; 64:10
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Tidskriftsartikel (refereegranskat)abstract
- The European fusion research activities have, over recent decades, generated a vast and varied set of data. The volume and diversity of the data that need to be catalogued and annotated make the task of organising and making the data available within a broader environment very challenging. Nevertheless, there are strong scientific drivers as well as incentives and mandates from national research agencies suggesting that a more coherent approach to data referencing, dissemination and sharing would provide strong benefits to the fusion research community and beyond. Here, we discuss the technical requirements and developments needed to transition the current, and future, range of fusion research data to an open and Findable, Accessible, Interoperable, and Reusable data sharing structure guided by the principle 'as open as possible, as closed as necessary'. Here we propose a set of recommendations and technical implementations needed to form a European data sharing environment for the fusion research programmes. Consistency with the emerging IMAS (ITER Integrated Modelling and Analysis Suite) infrastructure is considered to facilitate future deployments.
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