644 research outputs found
X-mode reflectometry measurements in the JET plasma core region
No full textCRPPSPC16th HTPD Topical Conference on High Temperature Plasma Diagnostics, Williamsburg, USA, 07-11 May 200
Quasi coherent modes: a signature of trapped Electron Mode contribution
No full textQuasi coherent modes: a signature of trapped Electron Mode contribution. R. Sabot1, H. Arnichand1, S. Hacquin1, A. Krämer-Flecken2, X. Garbet1, C. Bourdelle1, J. Citrin1, J.C. Giacalone1, G. Hornung3, C. Bottereau1, F. Clairet1, and J. Bernardo31 CEA, IRFM, F-13108 Saint-Paul-Lez-Durance, France 2Institute for Energy Research (Plasma Physics) Forschungszentrum Jülich, D-52425 Jüulich, Germany 3Department of Applied Physics, Ghent University, Ghent, B-9000, Belgium 4Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade de Lisboa, 1049-001 Lisboa, PortugalCore turbulence in tokamak plasmas is driven by two main instabilities: Ion Temperature Gradient (ITG) and Trapped Electron Modes (TEM). Experimental identification is challenging because both instabilities are unstable in the limit of long wavelengths [1]. However, apparition of quasi-coherent modes in the reflectometry signal can be used to mark the onset of turbulent regime dominated by TEM [2].First studied on T-10 [3] and Textor Tokamak [4], quasi-coherent modes appear as a secondary peak on the density fluctuation spectrum measured by reflectometry. They exhibit wavelength lower than the inverse of the ion Larmor radius. They were termed quasi-coherent due to marked poloidal and toroidal correlation. On Tore Supra and Textor, this extra peak which is centred between 40-120 kHz with a bandwidth of few tens kilohertz, could be observed from the edge to the core on the low field side; stabilized on the high field side, its amplitude is damped at the top of the machine. All these characteristics point to a link with drift wave instabilities. In Ohmic plasmas in Tore Supra and Textor, quasi-coherent modes are detected only in Low Ohmic Confinement (LOC) regime. They are stabilized at LOC SOC transition and they disappear in the Saturated Ohmic Confinement (SOC) regime where one expects TEM stabilization. Perpendicular velocity measurements made from the top of TEXTOR by correlation reflectometry show that QC modes rotate 300 m/s faster in the electron diamagnetic direction than density fluctuations at lower frequency. Non-linear gyrokinetic simulation performed for Tore Supra LOC-SOC transition reproduced the double peak spectrum observed by reflectometry [5].Quasi-Coherent modes could also be observed in electron heated discharges at localisation where gyrokinetic simulations pedict TEM dominance. The temporal dynamic of quasi-coherent modes will also be presented using tools developed for Doppler reflectometry analysis [6, 7]. [1] X. Garbet et al, Plasma Physics and Controlled Fusion 46, B557–B574 (2004) [2] H. Arnichand, et al, Nuclear Fusion 54, 123017 (2014). [3] V. Vershkov et al, Nuclear Fusion 45, S203-226 (2005) [4] A. Krämer-Flecken et al, Nuclear Fusion 44, 1143-1157 (2004) [5] S. Hacquin, et al, this workshop [6] L. Vermare, Nuclear Fusion 52, 063008 (2012) [7] A. Sorelli, PhD thesis, (2015)
Frequency modulation continuous wave reflectometry measurements of plasma position in ASDEX Upgrade ELMy H-mode regimes
No full textSimulation of amplitude and phase variations induced by magnetic islands with turbulence on reflectometry signals
No full textInternational audienceReflectrometry is influenced by plasma perturbations and turbulence, making the understanding of how signals are affected by such phenomena of prime importance. In this work we look at the effect magnetic islands with turbulence have on the amplitude and phase of reflectometry signals. For this purpose we resort to a two-dimensional finite difference time domain code and use a turbulence model based on experimental data. We investigate the possibility of occurrence of destructive interference due to a chain of islands and the role turbulence plays. The simulation of an island with turbulence present at the resonant surface q=2, with dimensions of the same order of magnitude as the phenomena observed on ASDEX Upgrade on Tore Supra, is also done with results which are in agreement with experimental observations
The JET hybrid scenario in Deuterium, Tritium and Deuterium-Tritium
No full textThe 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.The BSC part of this work has contributed through the Spanish National R&D Project PID2019-110854RB-I00 and the CIEMAT part through grant PID2021-127727OB-I00, funded through MCIN/AEI/10.13039/501100011033 and ERDF "A way of making Europe". This scientific paper has been published as part of the international project co-financed by the Polish Ministry of Science and Higher Education within the programme called 'PMW' for 2018–2023. This work has been carried out within the framework of the EUROfusion Consortium, funded by the European Union via the Euratom Research and Training Programme (Grant Agreement No. 101052200 - EUROfusion) and from the EPSRC [Grant Number EP/W006839/1]. Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or the European Commission. Neither the European Union nor the European Commission can be held responsible for them. Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the ITER organization.Peer Reviewed"Article signat per més de 50 autors/es:" J. Hobirk, C.D. Challis, A. Kappatou, E. Lerche, D. Keeling, D. King, S. Aleiferis, E. Alessi, C. Angioni, F. Auriemma, M. Baruzzo, É. Belonohy, J. Bernardo, A. Boboc, I.S. Carvalho, P. Carvalho, F.J. Casson, A. Chomiczewska, J. Citrin, I.H. Coffey, N.J. Conway, D. Douai, E. Delabie, B. Eriksson, J. Eriksson, O. Ficker, A.R. Field, M. Fontana, J.M. Fontdecaba, L. Frassinetti, D. Frigione, D. Gallart, J. Garcia, M. Gelfusa, Z. Ghani, L. Giacomelli, E. Giovannozzi, C. Giroud, M. Goniche, W. Gromelski, S. Hacquin, C. Ham, N.C. Hawke, R.B. Henriques, J.C. Hillesheim, A. Ho, L. Horvath, I. Ivanova-Stanik, P. Jacquet, F. Jaulmes, E. Joffrin, H.T. Kim, V. Kiptily, K. Kirov, D. Kos, E. Kowalska-Strzeciwilk11, H. Kumpulainen24, K. Lawson2, M. Lennholm2,25, X. Litaudon14, E. Litherland-Smith2, P.J. Lomas, E. de la Luna, C.F. Maggi, J. Mailloux, M.J. Mantsinen, M. Maslov, G. Matthews, K.G. McClements, A.G. Meigs, S. Menmuir, A. Milocco, I.G. Miron, S. Moradi, R.B. Morales, S. Nowak, F. Orsitto, A. Patel, L. Piron, C. Prince, G. Pucella, E. Peluso, C. Perez von Thun, E. Rachlew, C. Reux, F. Rimini, S. Saarelma, P. A Schneider, S. Scully, M. Sertoli, S. Sharapov, A. Shaw, S. Silburn, A. Sips, P. Siren, C. Sozzi, E.R. Solano, Z. Stancar, G. Stankunas, C. Stuart, H.J. Sun, G. Szepesi, D. Valcarcel, M. Valisa, G. Verdoolaege, B. Viola, N. Wendler, M. Zerbini and JET Contributors"Postprint (published version
Optimization of the FM-CW reflectometry W-band antenna for core density profile measurements on ASDEX Upgrade
No full textA numerical study of the focused hog-horn antenna used for the W-band channel of the ASDEX Upgrade frequency modulated continuous wave reflectometry system is performed here. A mode matching code is used to accuretely model wave propagation in waveguide and antenna structures. Then the field distribution (amplitude and phase) in the horn aperture given by this code is used as an input for other codes computing wave propagation in the plasma. Evaluating the received energy in the antenna, we first analyze plasma effects as the nonalignment between the antenna and the plasma equatorial plane. We show in the case of an unfocused antenna that ray-tracing results are in qualitative agreement with full wave calculations. Simulations also confirm that hog-horn antennas allow improving the measurement performances in comparison with unfocused antennas. The role of location of the focusing point of a hog-horn antenna (depending on the antenna design) is then studied. It appears that the focusing point position should be optimized to maximize the energy received in the antenna. Finally, we show that a new design for the W-band antenna on the ASDEX Upgrade broadband reflectometry system could improve the performances of this diagnostic
Frequency modulation continuous wave reflectometry measurements of plasma position in ASDEX Upgrade ELMy H-mode regimes
No full textFrequency modulation continuous wave reflectometry measurements of plasma position in ASDEX Upgrade ELMy H-mode regimes
No full textIsotope removal experiment in JET-ILW in view of T-removal after the 2nd DT campaign at JET
No full textA sequence of fuel recovery methods was tested in JET, equipped with the ITER-like beryllium main chamber wall and tungsten divertor, to reduce the plasma deuterium concentration to less than 1% in preparation for operation with tritium. This was also a key activity with regard to refining the clean-up strategy to be implemented at the end of the 2nd DT campaign in JET (DTE2) and to assess the tools that are envisaged to mitigate the tritium inventory build-up in ITER. The sequence began with 4 days of main chamber baking at 320 °C, followed by a further 4 days in which Ion Cyclotron Wall Conditioning (ICWC) and Glow Discharge Conditioning (GDC) were applied with hydrogen fuelling, still at 320 °C, followed by more ICWC while the vessel cooled gradually from 320 °C to 225 °C on the 4th day. While baking alone is very efficient at recovering fuel from the main chamber, the ICWC and GDC sessions at 320 °C still removed slightly higher amounts of fuel than found previously in isotopic changeover experiments at 200 °C in JET. Finally, GDC and ICWC are found to have similar removal efficiency per unit of discharge energy. The baking week with ICWC and GDC was followed by plasma discharges to remove deposited fuel from the divertor. Raising the inner divertor strike point up to the uppermost accessible point allowed local heating of the surfaces to at least 800 °C for the duration of this discharge configuration (typically 18 s), according to infra-red thermography measurements. In laboratory thermal desorption measurements, maintaining this temperature level for several minutes depletes thick co-deposit samples of fuel. The fuel removal by 14 diverted plasma discharges is analysed, of which 9, for 160 s in total, with raised inner strike point. The initial D content in these discharges started at the low value of 3%-5%, due to the preceding baking and conditioning sequence, and reduced further to 1%, depending on the applied configuration, thus meeting the experimental target
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