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- 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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| 6. |
- Hobirk, J., et al.
(författare)
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The JET hybrid scenario in Deuterium, Tritium and Deuterium-Tritium
- 2023
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Ingår i: Nuclear Fusion. - : Institute of Physics Publishing (IOPP). - 0029-5515 .- 1741-4326. ; 63:11
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Tidskriftsartikel (refereegranskat)abstract
- The JET hybrid scenario has been developed from low plasma current carbon wall discharges to the record-breaking Deuterium-Tritium plasmas obtained in 2021 with the ITER-like Be/W wall. The development started in pure Deuterium with refinement of the plasma current, and toroidal magnetic field choices and succeeded in solving the heat load challenges arising from 37 MW of injected power in the ITER like wall environment, keeping the radiation in the edge and core controlled, avoiding MHD instabilities and reaching high neutron rates. The Deuterium hybrid plasmas have been re-run in Tritium and methods have been found to keep the radiation controlled but not at high fusion performance probably due to time constraints. For the first time this scenario has been run in Deuterium-Tritium (50:50). These plasmas were re-optimised to have a radiation-stable H-mode entry phase, good impurity control through edge Ti gradient screening and optimised performance with fusion power exceeding 10 MW for longer than three alpha particle slow down times, 8.3 MW averaged over 5 s and fusion energy of 45.8 MJ.
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| 7. |
- Kiptily, V. G., et al.
(författare)
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Observation of alpha-particles in recent D-T experiments on JET
- 2024
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Ingår i: Nuclear Fusion. - : Institute of Physics (IOP). - 0029-5515 .- 1741-4326. ; 64:8
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Tidskriftsartikel (refereegranskat)abstract
- The fusion reaction between deuterium and tritium, D(T,n)4 He is the main source of energy in future thermonuclear reactors. Alpha-particles (4 He-ions) born with an average energy of 3.5 MeV transferring energy to the thermal plasma during their slowing down, should provide the self-sustained D-T plasma burn. The adequate confinement of alpha-particles is essential to provide efficient heating of the bulk plasma and steady burning of a reactor plasma. That is why the fusion-born alpha-particle studies have been a priority task in the second D-T experiments (DTE2) on the Joint European Torus (JET) to understand the main mechanisms of their slowing down, redistribution and losses and to develop optimal plasma scenarios. JET with Be-wall and W-divertor, enhanced auxiliary heating systems and improved energetic-particle diagnostic capabilities, producing significant population of alpha-particles, provided the possibility for comprehensive studying of the alpha-particle behaviour. Selected results of the confined and lost alpha-particle measurements, evidence of alpha-particle self-heating and assessments of the fusion performance are presented in this paper giving an opportunity for further modelling and extrapolation to the International Thermonuclear Experimental Reactor and burning plasma reactors.
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| 8. |
- Mantsinen, M. J., et al.
(författare)
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Experiments in high-performance JET plasmas in preparation of second harmonic ICRF heating of tritium in ITER
- 2023
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Ingår i: Nuclear Fusion. - : Institute of Physics (IOP). - 0029-5515 .- 1741-4326. ; 63:11
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Tidskriftsartikel (refereegranskat)abstract
- The reference ion cyclotron resonance frequency (ICRF) heating schemes for ITER deuterium-tritium (D-T) plasmas at the full magnetic field of 5.3 T are second harmonic heating of T and 3He minority heating. The wave-particle resonance location for these schemes coincide and are central at a wave frequency of 53 MHz at 5.3 T. Experiments have been carried out in the second major D-T campaign (DTE2) at JET, and in its prior D campaigns, to integrate these ICRF scenarios in JET high-performance plasmas and to compare their performance with the commonly used hydrogen (H) minority heating. In 50:50 D:T plasmas, up to 35% and 5% larger fusion power and diamagnetic energy content, respectively, were obtained with second harmonic heating of T as compared to H minority heating at comparable total input powers and gas injection rates. The core ion temperature was up to 30% and 20% higher with second harmonic T and 3He minority heating, respectively, with respect to H minority heating. These are favourable results for the use of these scenarios in ITER and future fusion reactors. According to modelling, adding ICRF heating to neutral beam injection using D and T beams resulted in a 10%-20% increase of on-axis bulk ion heating in the D-T plasmas due to its localisation in the plasma core. Central power deposition was confirmed with the break-in-slope and fast Fourier transform analysis of ion and electron temperature in response to ICRF modulation. The tail temperature of fast ICRF-accelerated tritons, their enhancement of the fusion yield and time behaviour as measured by an upgraded magnetic proton recoil spectrometer and neutral particle analyser were found in agreement with theoretical predictions. No losses of ICRF-accelerated ions were observed by fast ion detectors, which was as expected given the high plasma density of n e approximate to 7-8 x 1019 m-3 in the main heating phase that limited the formation of ICRF-accelerated fast ion tails. 3He was introduced in the machine by 3He gas injection, and the 3He concentration was measured by a high-resolution optical penning gauge in the sub-divertor region. The DTE2 experiments with 3He minority heating were carried with a low 3He concentration in the range of 2%-4% given the fact that the highest neutron rates with 3He minority heating in D plasmas were obtained at low 3He concentrations of similar to 2%, which also coincided with the highest plasma diamagnetic energy content. In addition to 3He introduced by 3He gas injection, an intrinsic concentration of 3He of the order of 0.2%-0.4% was measured in D-T plasmas before 3He was introduced in the device, which is attributed to the radioactive decay of tritium to 3He. According to modelling, even such low intrinsic concentrations of 3He lead to significant changes in ICRF power partitioning during second harmonic heating of T due to absorption of up to 30% of the wave power by 3He.
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| 9. |
- Kazakov, Ye O., et al.
(författare)
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Physics and applications of three-ion ICRF scenarios for fusion research
- 2021
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Ingår i: Physics of Plasmas. - : American Institute of Physics (AIP). - 1070-664X .- 1089-7674. ; 28:2
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Forskningsöversikt (refereegranskat)abstract
- This paper summarizes the physical principles behind the novel three-ion scenarios using radio frequency waves in the ion cyclotron range of frequencies (ICRF). We discuss how to transform mode conversion electron heating into a new flexible ICRF technique for ion cyclotron heating and fast-ion generation in multi-ion species plasmas. The theoretical section provides practical recipes for selecting the plasma composition to realize three-ion ICRF scenarios, including two equivalent possibilities for the choice of resonant absorbers that have been identified. The theoretical findings have been convincingly confirmed by the proof-of-principle experiments in mixed H–D plasmas on the Alcator C-Mod and JET tokamaks, using thermal 3He and fast D ions from neutral beam injection as resonant absorbers. Since 2018, significant progress has been made on the ASDEX Upgrade and JET tokamaks in H–4He and H–D plasmas, guided by the ITER needs. Furthermore, the scenario was also successfully applied in JET D–3He plasmas as a technique to generate fusion-born alpha particles and study effects of fast ions on plasma confinement under ITER-relevant plasma heating conditions. Tuned for the central deposition of ICRF power in a small region in the plasma core of large devices such as JET, three-ion ICRF scenarios are efficient in generating large populations of passing fast ions and modifying the q-profile. Recent experimental and modeling developments have expanded the use of three-ion scenarios from dedicated ICRF studies to a flexible tool with a broad range of different applications in fusion research.
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| 10. |
- Kirov, K. K., et al.
(författare)
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Analysis of fusion alphas interaction with RF waves in D-T plasma at JET
- 2024
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Ingår i: Nuclear Fusion. - : Institute of Physics Publishing (IOPP). - 0029-5515 .- 1741-4326. ; 64:8
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Tidskriftsartikel (refereegranskat)abstract
- This work studies the influence of radio frequency (RF) waves in the ion cyclotron resonance heating (ICRH) range of frequencies on fusion alphas during the recent JET D-T campaign. Fusion alphas from D-T reactions are created with energies of about 3.5 MeV and therefore have significant Doppler shifts enabling synergistic interactions between them and RF waves at a broad range of frequencies, including the ones foreseen for future fusion machines in ITER (Schneider et al 2021 Nucl. Fusion 61 126058) and SPARC (Creely et al 2020 J. Plasma Phys. 86 865860502). Resonant interactions between RF waves and alphas, also called synergistic effects, will modify the alpha distribution and ultimately will have an impact on alpha orbit losses and heating. Data from JET 3.43 T/2.3 MA pulses based on the hybrid scenario (Hobirk et al 2023 Nucl. Fusion; Hobirk et al 29th IAEA FEC23 Conf. (16-21 October 2023); Challis et al 48th EPS Conf. on Plasma Physics (27 June-1 July 2022) during the DTE2 campaign (Maggi et al 2023 Nucl. Fusion)) were used for the analysis in this study. The impact of synergistic effects on alpha orbit losses and alpha heating are assessed. The conclusions are based on the analysis of experimental data for fast alpha losses, i.e. measurements from neutral particle analyser (NPA), fast ion losses scintillator detector, Faraday cups (FCs), and TRANSP (Hawryluk et al 1980 Physics of Plasmas Close to Thermonuclear Conditions vol 1 (CEC) pp 19-46) simulations. Experimental data and TRANSP analysis indicates that there are indeed changes in the alpha distribution function (DF) due to interaction with RF waves. Data from the NPA show increased 4He flux in the range from a few hundred keV up to 800 keV for pulses with RF power, while TRANSP clearly shows modifications in the fast alpha DF for these energies. Data from the scintillator detector and the FCs were compared for pulses with and without ICRH power and versus cases with enhanced alpha losses due to MHD activity. The trends from these diagnostics consistently show no additional alpha losses due to interaction with RF waves. TRANSP predictions for the impact of ynergistic effects on alpha heating show up to a 42% increase in alpha electron heating and up to a 25% increase in alpha ion heating. These effects, however, become negligibly small, less than 1%, when alpha heating is compared to the total auxiliary heating power in the investigated JET pulses.
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