The power threshold of H-mode access in mixed hydrogen–tritium and pure tritium plasmas at JET with ITER-like wall

The heating power to access the high confinement mode (H-mode), PLH, scales approximately inversely with the isotope mass of the main ion plasma species as found in (protonic) hydrogen, deuterium and tritium plasmas in many fusion facilities over the last decades. In first dedicated L–H transition experiments at the Joint European Torus (JET) tokamak facility with the ITER-like wall (ILW), the power threshold, PLH, was studied systematically in plasmas of pure tritium and hydrogen–tritium mixtures at a magnetic field of 1.8 T and a plasma current of 1.7 MA in order to assess whether this scaling still holds in a metallic wall device. The measured power thresholds, PLH, in Ohmically heated tritium plasmas agree well with the expected isotope scaling for metallic walls and the lowest power threshold was found in Ohmic phases at low density. The measured power thresholds in ion cyclotron heated plasmas of pure tritium or hydrogen–tritium mixtures are significantly higher than the expected isotope mass scaling due to higher radiation levels. However, when the radiated power is taken into account, the ion cyclotron heated plasmas exhibit similar power thresholds as a neutral beam heated plasma, and are close to the scaling. The tritium plasmas in this study tended to higher electron heating fractions and, when heated with ion cyclotron waves, to relatively higher radiation fractions compared to other isotopes potentially impeding access to sustained H-modes.The authors thank P.A. Schneider, F. Ryter, A. Nielsen, and A. Kappatou for fruitful discussions and for help with data analysis tools. This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom Research and Training Programme 2014–2018 and 2019–2020 under Grant Agreement No. 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission. G. Birkenmeier received funding from the Helmholtz Association under Grant No. VH-NG-1350.Peer Reviewed"Article signat per 27 autors/es: G. Birkenmeier, E.R. Solano, E. Lerche, D. Taylor, D. Gallart, M.J. Mantsinen, E. Delabie, I.S. Carvalho, P. Carvalho, E. Pawelec, J.C. Hillesheim, F. Parra Diaz, C. Silva, S. Aleiferis, J. Bernardo, A. Boboc, D. Douai, E. Litherland-Smith, R. Henriques, K.K. Kirov, C.F. Maggi, J. Mailloux, M. Maslov, F.G. Rimini, S.A. Silburn, P. Sirén, H. Weisen and JET Contributors"Postprint (published version

The role of isotope mass and transport for H-mode access in tritium containing plasmas at JET with ITER-like wall

Special Issue Featuring the Invited Talks from the 48th EPS Conference on Plasma Physics, 27 June - 1 July 2022The required heating power, , to access the high confinement regime (H-mode) in tritium containing plasmas is investigated in JET with ITER-like wall at a toroidal magnetic field of T and a plasma current of MA. , also referred to as the L-H power threshold, is determined in plasmas of pure tritium as well as mixtures of hydrogen with tritium (H-T) and mixtures of deuterium with tritium (D-T), and is compared to the L-H power threshold in plasmas of pure hydrogen and pure deuterium. It is found that, for otherwise constant parameters, is not the same in plasmas with the same effective isotope mass, , when they differ in their isotope composition. Thus, is not sufficient to describe the isotope effect of in a consistent manner for all considered isotopes and isotope mixtures. The electron temperature profiles measured at the L-H transition in the outer half of the radius are very similar for all isotopes and isotope mixtures, despite the fact that the L-H power threshold varies by a factor of about six. This finding, together with the observation of an offset linear relation between the L-H power threshold, , and an effective heat diffusivity, , indicates that the composition-dependent heat transport in the low confinement mode (L-mode) determines, how much power is needed to reach the necessary electron temperatures at the edge, and hence PLH.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). 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. G Birkenmeier received funding from the Helmholtz Association under Grant No. VH-NG-1350Peer Reviewed"Article signat per 50 autors/es: G Birkenmeier, E R Solano, I S Carvalho, J C Hillesheim, E Delabie, E Lerche, D Taylor, D Gallart, M J Mantsinen, C Silva, C Angioni, F Ryter, P Carvalho, M Fontana, E Pawelec, S A Silburn, P Sirén, S Aleiferis, J Bernardo, A Boboc, D Douai, P Puglia, P Jacquet, E Litherland-Smith, I Jepu, D Kos, H J Sun, A Shaw, D King, B Viola, R Henriques, K K Kirov, M Baruzzo, J Garcia, A Hakola, A Huber, E Joffrin, D Keeling, A Kappatou, M Lennholm, P Lomas, E de la Luna, C F Maggi, J Mailloux, M Maslov, F G Rimini, N Vianello, G Verdoolaege, H Weisen, M Wischmeier and JET Contributors"Postprint (published version

Implementation of synthetic fast-ion loss detector and imaging heavy ion beam probe diagnostics in the 3D hybrid kinetic-MHD code MEGA

A synthetic fast-ion loss (FIL) detector and an imaging Heavy Ion Beam Probe (i-HIBP) have been implemented in the 3D hybrid kinetic-magnetohydrodynamic code MEGA. First synthetic measurements from these two diagnostics have been obtained for neutral beam injection-driven Alfvén Eigenmode (AE) simulated with MEGA. The synthetic FILs show a strong correlation with the AE amplitude. This correlation is observed in the phase-space, represented in coordinates (P, E), being toroidal canonical momentum and energy, respectively. FILs and the energy exchange diagrams of the confined population are connected with lines of constant E, a linear combination of E and P. First i-HIBP synthetic signals also have been computed for the simulated AE, showing displacements in the strike line of the order of ∼1 mm, above the expected resolution in the i-HIBP scintillator of ∼100 μm.This work received funding from the European Starting Grant (ERC) from project 3D-FIREFLUC and from the Spanish Ministry of Science under Grant No. FPU19/02267. This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014-2018 and 2019-2020 under grant agreement No 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission

Characterization of scintillator screens under irradiation of low energy 133Cs ions

An imaging heavy ion beam probe (i-HIBP) diagnostic, for the simultaneous measurement of plasma density, magnetic field and electrostatic potential in the plasma edge, has been installed at ASDEX Upgrade. Unlike standard heavy ion beam probes, in the i-HIBP the probing (heavy) ions are collected by a scintillator detector, creating a light pattern or strike-line, which is then imaged by a camera. Therefore, a good characterization of the scintillator response is needed. Previous works focused on the scintillator behaviour against irradiation with light ions such as hydrogen and alpha particles. In this work we present the characterization of several scintillator screens — TG-Green (SrGa2S4:Eu2+), YAG-Ce (Y3Al5O12:Ce3+) and P11 (ZnS:Ag) — against irradiation with 133Cs+ ions, in an energy range between 5 and 70 keV and ion currents between 105 and 107ions/(s·cm2). Three main properties of the scintillators have been studied: the ionolumenescence efficiency or yield, the linearity and the degradation as a function of the fluence. The highest yield was delivered by the TG-Green scintillator screen with > 8·103 photons/ion at 50 keV. All the samples showed a linear response with increasing incident ion flux. The degradation was quantified in terms of the fluence F1/2, which leads to a reduction of the emissivity by a factor of 2. TG-Green showed the lowest degradation with F1/2= 5.4·1014ions/cm2. After the irradiation the samples were analyzed by Scanning Electron Microscopy (SEM), Rutherford Backscattering Spectrometry (RBS) and Particle Induced X-ray Emission (PIXE). No trace of Cs was found in the irradiated regions. These results indicate that, among the tested materials, TG-Green is the best candidate for the i-HIBP detector.European Union’s Horizon 2020 (grant agreement No. 805162)Helmholtz Association VHNG-1350Spanish Ministry of Science and Innovation FJC2019-041092-I

Characterization of scintillator screens under irradiation of low energy 133Cs ions

An imaging heavy ion beam probe (i-HIBP) diagnostic, for the simultaneous measurement of plasma density, magnetic field and electrostatic potential in the plasma edge, has been installed at ASDEX Upgrade. Unlike standard heavy ion beam probes, in the i-HIBP the probing (heavy) ions are collected by a scintillator detector, creating a light pattern or strike-line, which is then imaged by a camera. Therefore, a good characterization of the scintillator response is needed. Previous works focused on the scintillator behaviour against irradiation with light ions such as hydrogen and alpha particles. In this work we present the characterization of several scintillator screens - TG-Green (SrGa2S4:Eu2+), YAG-Ce (Y3Al5O12:Ce3+) and P11 (ZnS:Ag) - against irradiation with 133Cs+ ions, in an energy range between 5 and 70 keV and ion currents between 105 and 107 ions/(s·cm2). Three main properties of the scintillators have been studied: the ionolumenescence efficiency or yield, the linearity and the degradation as a function of the fluence. The highest yield was delivered by the TG-Green scintillator screen with > 8·103 photons/ion at 50 keV. All the samples showed a linear response with increasing incident ion flux. The degradation was quantified in terms of the fluence F1/2, which leads to a reduction of the emissivity by a factor of 2. TG-Green showed the lowest degradation with F1/2= 5.4·1014 ions/cm2. After the irradiation the samples were analyzed by Scanning Electron Microscopy (SEM), Rutherford Backscattering Spectrometry (RBS) and Particle Induced X-ray Emission (PIXE). No trace of Cs was found in the irradiated regions. These results indicate that, among the tested materials, TG-Green is the best candidate for the i-HIBP detector.This work received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No. 805162). G. Birkenmeier acknowledges funding from the Helmholtz Association under grant no. VHNG-1350. J. Galdon-Quiroga acknowledges funding from the Spanish Ministry of Science and Innovation under grant no. FJC2019-041092-I

Experimental investigations of structure and dynamics of drift-wave turbulence in stellarator geometry

Seit über 60 Jahren versucht man in der Fusionsforschung ein Plasma mit Hilfe von Magnetfeldern einzuschliesen, so dass die erforderlichen hohen Dichten und Temperaturen für die Zündung der Kernfusion erreicht werden können. Trotz großartiger Fortschritte bewährter Einschlusskonzepte, die Energieeinschlusszeiten an der Zündschwelle der Kernfusion in Bälde erwarten lassen, wird neuartigen Magnetfeldgeometrien von Seiten der theoretischen Plasmaphysik ein enormes zusätzliches Potential an Einschlussverbesserung zugesprochen. Der Schlüssel dafür liegt in der Minimierung des turbulenten Transports durch geeignete Wahl der Magnetfeldgeometrie, wofür ein grundlegendes Verständnis des Einflusses der Magnetfeldgeometrie auf die Plasmaturbulenz essenziell ist. Neben einer stattlichen Anzahl von theoretischen Arbeiten über die turbulente Plasmadynamik in dreidimensionalen Geometrien gibt es nur wenige experimentelle Studien zur Überprüfung der theoretischen Resultate. Das Ziel der vorliegenden Arbeit ist daher, experimentelle Daten zu liefern, die für den Vergleich mit der Theorie und für tiefere Einblicke in das Wechselspiel zwischen Driftwellenturbulenz und Magnetfeldgeometrie dienen. Dafür werden mit Hilfe zweier Multi-Sondenanordnungen an 128 Stellen auf einer Flussfläche des Stellarators TJ-K in Niedertemperaturplasmen lokale Dichte- und Potentialfluktuationen mit hoher zeitlicher Auflösung gemessen. Daraus bestimmte senkrechte Strukturgrößen sind in Bereichen hoher absoluter lokaler Magnetfeldverscherung reduziert. Zudem wird ein poloidaler Versatz relativ zu den Magnetfeldlinien und ein komplexes Propagationsmuster der parallel ausgedehnten Turbulenzstrukturen gefunden. Aus den Sondendaten können auch Poloidalprofile des turbulenten Transports bestimmt werden. Die Transportmaxima werden dabei poloidal lokalisiert im Bereich negativer Normalenkrümmung (ungünstiger Krümmung) gefunden. Darüber hinaus gibt es Hinweise, dass auch die geodätische Krümmung eine Rolle für den Transport spielen könnte. Die transportverursachenden Bereiche sind parallel entlang einer Magnetfeldlinie auf der Flussfläche ausgedehnt. Die Sondenanordnungen erlauben erstmals auch globale Messungen von Zonalströmungen. Diese deuten auf ein Räuber-Beute-Schema zwischen Zonalströmung und Turbulenz hin, wobei eine signifikante Reduktion des turbulenten Transports um 30 % durch die Zonalströmungen nachgewiesen werden kann. Dabei wirkt die Zonalströmung zunächst auf die Kreuzphase ƒzwischen Dichte und elektrischem Feld, danach erst auf die Fluktuationsamplituden.For more than 60 years, fusion scientists try to confine a plasma by means of external magnetic fields in order to achieve appropriately high densities and temperatures for the ignition of nuclear fusion. Despite of great progress in the design of confinement concepts, which are considered for the confinement of burning plasmas in the near future, theoretical plasma physics promises further confinement improvements using novel magnetic field geometries. Therefor, the key is the minimization of turbulent transport by choosing appropiate magnetic field geometries, which necessitates a fundamental understanding of the influence of magnetic field geometry on plasma turbulence. There are several theoretical works on turbulent plasma dynamics in three-dimensional geometries, but only a few experimental studies for validation of the theoretical results exist. Hence, the present work aims at providing experimental data for comparison with theory and to gain insights into the interplay between drift-wave turbulence and magnetic field geometry. By means of two multi-probe arrays, local density and potential fluctuations are measured in low-temperature plasmas at 128 positions on a single flux surface of the stellarator TJ-K with high temporal resolution. Using methods of statistical timeseries analysis structure sizes and dynamic properties of the drift-wave turbulence in TJ-K are determined. Thereby, it is shown that the size of turbulent structures perpendicular to the magnetic field is reduced in regions of high absolute local magnetic shear. In addition, a poloidal displacement with respect to the magnetic field lines and a complex propagation pattern of parallelly extended turbulent structures is found. Also, poloidal profiles of turbulent transport are calculated from the probe data. The maximum transport is found to be poloidally localized in a region of negative normal curvature (unfavourable curvature). In addition, the results point to an influence of geodesic curvature on turbulent transport. Regions of maximum transport are parallely elongated along the field line. For the first time, the multi-probe arrays allow global measurements of zonal flows. These point to a predator-prey scheme between zonal flows and turbulent transport associated with a significant reduction of turbulent transport induced by zonal flows by a factor of 30 %. In the early phase of transport reduction, the zonal flow acts mainly on the cross-phase between density and electric field. In a later phase, the fluctuation levels are reduced, too

Hardware developments and commissioning of the imaging heavy ion beam probe at ASDEX upgrade

The imaging heavy ion beam probe (i-HIBP) is a new diagnostic concept realized at the tokamak ASDEX Upgrade (AUG) in order to obtain two-dimensional information about the density, the magnetic field and the electrostatic potential at the plasma edge. Although the two main components of the i-HIBP, an alkali beam based injector and a scintillator based detector, involve well-developed technologies, further developments were necessary to realize the i-HIBP at AUG. In dedicated laboratory tests, a new type of cesium source was characterized and the neutralization efficiency and properties of the primary cesium beam were found to be similar to alkali beams made of lighter elements. The use of cesium had also impact on the choice of the scintillator material, which was experimentally investigated in terms of photon yield, energy dependence and degradation revealing significant differences under irradiation with cesium ions compared to irradiation with hydrogenic beams. Due to constrictions of the AUG experiment setup, the high voltage components, the in-vessel shutter technology and the maintenance capabilities of the i-HIBP required new developments for the commissioning of the diagnostic.This work received funding from the Helmholtz Association under grant no. VH-NG-1350. This work received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No. 805162). This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014–2018 and 2019–2020 under grant agreement No 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission

Conceptual design of a scintillator based Imaging Heavy Ion Beam Probe for the ASDEX Upgrade tokamak

Trabajo presentado en el 2nd European Conference on Plasma Diagnostics, celebrado en Bordeaux (Francia), del 18 al 22 de abril de 2017A conceptual design of a new diagnostic for the simultaneous space and time resolved measurement of plasma density, potential and poloidal magnetic field fluctuations at ASDEX Upgrade is proposed. The diagnostic combines the detection techniques of standard heavy ion beam probes (HIBP) and scintillator based fast ion loss detectors (FILD), making use of an atomic beam to probe plasma parameters with high spatio-temporal resolution. This new approach takes advantage of using a neutral probe beam and a scintillator plate as detection system. The combination of these two techniques makes the diagnostic more compact than standard HIBP facilitating its integration in the machine. Simulations using an orbit following code have been carried out to investigate the viability of the proposed detection method based on the displacement of the beam strike-line on the scintillator plate. Relative plasma potential fluctuations from 10% to 100% in the potential well induce localized displacements in the strike line in the range of 0.1-1.0 mm, while poloidal magnetic field fluctuations such as those arising from edge currents produce displacements in the order of mm. The use of a scintillator screen provides virtually infinite spatial resolution together with a temporal resolution up to the MHz range, needed for the identification of internal fluctuationsPeer reviewe

Conceptual design of a scintillator based Imaging Heavy Ion Beam Probe for the ASDEX Upgrade tokamak

A conceptual design of a new diagnostic for the simultaneous space and time resolved measurement of plasma density, potential and poloidal magnetic field fluctuations at ASDEX Upgrade is proposed. The diagnostic combines the detection techniques of standard heavy ion beam probes (HIBP) and scintillator based fast ion loss detectors (FILD), making use of an atomic beam to probe plasma parameters with high spatio-temporal resolution. This new approach takes advantage of using a neutral probe beam and a scintillator plate as detection system. The combination of these two techniques makes the diagnostic more compact than standard HIBP facilitating its integration in the machine. Simulations using an orbit following code have been carried out to investigate the viability of the proposed detection method based on the displacement of the beam strike-line on the scintillator plate. Relative plasma potential fluctuations from 10% to 100% in the potential well induce localized displacements in the strike line in the range of 0.1-1.0 mm, while poloidal magnetic field fluctuations such as those arising from edge currents produce displacements in the order of mm. The use of a scintillator screen provides virtually infinite spatial resolution together with a temporal resolution up to the MHz range, needed for the identification of internal fluctuations.Ministerio de Economía y Competitividad RYC-2011-09152, FIS2015-69362-P, ENE2012- 31087Marie Curie FP7 Integration PCIG11-GA-2012-32145