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WEST database analysis shows a correlation of the recycled neutral source around the separatrix with core performances. This observation questions the causality chain between particle source and turbulent transport up to the core in L-mode, high recycling plasmas, an unavoidable phase of all scenarios. The best core performances correlate with the lowest values of the density at the separatrix, n sep , similarly to ASDEX Upgrade (AUG) tokamak and Joint European Torus (JET) tokamak in H-mode (Verdoolaege et al 2021 Nucl. Fusion 61 076006). Reflectometry in the midplane provides n sep , while the temperature at the separatrix, T sep is inferred by the ‘two-point model’ using Langmuir probe data on divertor targets. Lower separatrix resistivity does not correlate with better core performances, unlike H-mode observations (Eich et al 2020 Nucl. Fusion 60 056016). As expected in the presence of an efficient neutral source due to recycling fluxes, n sep correlates with the D recycled particle flux at the divertor measured by visible spectroscopy. Coherently, at a given controlled central line integrated density n ˉ , lower n sep correlates with a larger density gradient around the separatrix as well as a larger global density peaking, n ˉ / ⟨ n ⟩ , measured by interferometry. The latter correlates as well with lower collisionality in the core, similarly to JET and AUG H-modes (Angioni et al 2007 Nucl. Fusion 47 1326). The correlations reported allow phrasing the subsequent causality question: what is the interplay chain between low neutral recycling at the divertor plates, low density at the separatrix, high density peaking at the separatrix, high global density peaking, higher central temperature and better core energy confinement quality? Understanding the causality chain is essential to prepare ITER operation and design DEMO scenarios where the ratio of the divertor leg to the ionization length will be larger and where the pumped flux with respect to the plasma volume will be lower than presently operating tokamaks.

Reduced quasilinear and nonlinear (gradient-driven) models with scale separations, commonly used to interpret experiments and to forecast turbulent transport levels in magnetised plasmas, are tested against nonlinear models without scale separations (flux-driven). Two distinct regimes of turbulence—either above threshold or near marginal stability—are investigated with Boltzmann electrons. The success of reduced models hinges in particular on the reproduction of nonlinear fluxes. Good agreement between models is found above threshold, whilst reduced models significantly underpredict fluxes near marginality, overlooking mesoscale flow organisation and turbulence self-advection. Constructive prescriptions whereby to improve reduced models are discussed.

The magnetic drift and the electric potential play an important role in microtearing destabilization by increasing the growth rate of this instability in the presence of collisions, while in electrostatic plasma micro-turbulence, zonal electric potentials can have a strong impact on turbulent saturation. A reduced model has been developed, showing that the Rechester–Rosenbluth model is a good model for the prediction of electron heat diffusivity by microtearing turbulence. Here, nonlinear gyrokinetic flux-tube simulations are performed in order to compute the characteristics of microtearing turbulence and the associated heat fluxes in tokamak plasmas and to assess how zonal flows and zonal fields affect saturation. This is consistent with a change in saturation mechanism from temperature corrugations to zonal field- and zonal flow-based energy transfer. It is found that removing the electrostatic potential causes a flux increase, while linearly stabilization is observed.

The impact of the parallel flow shear on the tokamak plasma stability and turbulent transport driven by the ion temperature gradient (ITG) modes is analyzed by means of local gyrokinetic numerical analyses. It is shown that the parallel flow shear increases the ITG growth rate in the linear regime, and induces a broadening and shift of the radial spectrum. Then, the different effects of the finite parallel shear on the ITG turbulence characteristics are deeply analyzed in the nonlinear regime. These studies highlight that a reduction of the thermal-ion turbulent heat flux is induced by a complex mechanism involving the nonlinear generation of an enhanced zonal flow activity. Indeed, the turbulent sources of the zonal flows are increased by the introduction of the finite parallel flow shear in the system, beneficially acting on the saturation level of the ITG turbulence. The study has been carried out for the Waltz standard case below the critical threshold of the destabilization of the parallel velocity gradient instability, and then generalized to a selected pulse of a recent JET scenario with substantial toroidal rotation in the edge plasma region. It is, thus, suggested that the investigated complex mechanism triggered by the finite parallel flow shear reducing the ITG turbulent heat fluxes could be complementary to the well-established perpendicular flow shear in a region with sufficiently large plasma toroidal rotation.

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 Dα 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. 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. Peer Reviewed "Article signat per més de 50 autors/es: U. Stroth, D. Aguiam, E. Alessi, C. Angioni, N. Arden, R. Arredondo Parra, V. Artigues, O. Asunta, M. Balden, V. Bandaru, A. Banon-Navarro, K. Behler, A. Bergmann, M. Bergmann, J. Bernardo, M. Bernert, A. Biancalani, R. Bielajew, R. Bilato, G. Birkenmeier, T. Blanken, V. Bobkov, A. Bock, T. Body, T. Bolzonella, N. Bonanomi, A. Bortolon, B. Böswirth, C. Bottereau, A. Bottino, H. van den Brand, M. Brenzke, S. Brezinsek, D. Brida, F. Brochard, C. Bruhn, J. Buchanan, A. Buhler, A. Burckhart, Y. Camenen, B. Cannas, P. Cano Megias, D. Carlton, M. Carr, P. Carvalho, C. Castaldo, M. Cavedon, C. Cazzaniga, C. Challis, A. Chankin, C. Cianfarani, F. Clairet, S. Coda, R. Coelho, J.W. Coenen, L. Colas, G. Conway, S. Costea, D. Coster, T. Cote, A.J. Creely, G. Croci, D.J. Cruz Zabala, G. Cseh, A. Czarnecka, I. Cziegler, O. D'Arcangelo, A. Dal Molin, P. David, C. Day, M. de Baar, P. de Marné, R. Delogu, S. Denk, P. Denner, A. Di Siena, J.J. Dominguez Palacios Durán, D. Dunai, A. Drenik, M. Dreval, R. Drube, M. Dunne, B.P. Duval, R. Dux, T. Eich, S. Elgeti, A. Encheva, K. Engelhardt, B. Erdös, I. Erofeev, B. Esposito, E. Fable, M. Faitsch, U. Fantz, M. Farnik, H. Faugel, F. Felici, O. Ficker, S. Fietz, A. Figueredo, R. Fischer, O. Ford, L. Frassinetti, M. Fröschle, G. Fuchert, J.C. Fuchs, H. Fünfgelder, S. Futatani, K. Galazka, J. Galdon-Quiroga, D. Gallart Escolà, A. Gallo10, Y. Gao11, S. Garavaglia3, M. Garcia Muñoz16, B. Geiger21, L. Giannone1, S. Gibson32, L. Gil2, E. Giovannozzi18, S. Glöggler1, M. Gobbin8, J. Gonzalez Martin, T. Goodman, G. Gorini, T. Görler, D. Gradic, G. Granucci, A. Gräter, H. Greuner, M. Griener, M. Groth, A. Gude, L. Guimarais, S. Günter, G. Haas, A.H. Hakola, C. Ham, T. Happel, N. den Harder, G. Harrer, J. Harrison, V. Hauer, T. Hayward-Schneider, B. Heinemann, T. Hellsten, S. Henderson, P. Hennequin, A. Herrmann, E. Heyn, F. Hitzler, J. Hobirk, K. Höfler, J.H. Holm, M. Hölzl, C. Hopf, L. Horvath, T. Höschen, A. Houben, A. Hubbard, A. Huber, K. Hunger, V. Igochine, M. Iliasova, T. Ilkei, K. Insulander Björk, C. Ionita-Schrittwieser, I. Ivanova-Stanik, W. Jacob, N. Jaksic, F. Janky, A. Jansen van Vuuren, A. Jardin, F. Jaulmes, F. Jenko, T. Jensen, E. Joffrin, A. Kallenbach, S. Kálvin, M. Kantor, A. Kappatou, O. Kardaun, J. Karhunen4, C.-P. Käsemann, S. Kasilov, A. Kendl, W. Kernbichler, E. Khilkevitch, A. Kirk, S. Kjer Hansen, V. Klevarova, G. Kocsis, M. Koleva, M. Komm, M. Kong, A. Krämer-Flecken, K. Krieger, A. Krivska, O. Kudlacek, T. Kurki-Suonio, B. Kurzan, B. Labit, K. Lackner, F. Laggner, A. Lahtinen, P.T. Lang, P. Lauber, N. Leuthold, L. Li, J. Likonen, O. Linder, B. Lipschultz, Y. Liu, A. Lohs, Z. Lu, T. Luda di Cortemiglia, N.C. Luhmann, T. Lunt, A. Lyssoivan, T. Maceina, J. Madsen, A. Magnanimo, H. Maier, J. Mailloux, R. Maingi, O. Maj, E. Maljaars, P. Manas, A. Mancini, A. Manhard, P. Mantica, M. Mantsinen, P. Manz, M. Maraschek, C. Marchetto, L. Marrelli, P. Martin, A. Martitsch, F. Matos, M. Mayer, M.-L. Mayoral, D. Mazon, P.J. McCarthy, R. McDermott, R. Merkel, A. Merle, D. Meshcheriakov, H. Meyer, D. Milanesio, P. Molina Cabrera, F. Monaco, M. Muraca, F. Nabais, V. Naulin, R. Nazikian, R.D. Nem, A. Nemes-Czopf, G. Neu, R. Neu, A.H. Nielsen, S.K. Nielsen, T. Nishizawa, M. Nocente, J.-M. Noterdaeme, I. Novikau, S. Nowak, M. Oberkofler, R. Ochoukov, J. Olsen, F. Orain, F. Palermo, O. Pan, G. Papp, I. Paradela Perez, A. Pau, G. Pautasso, C. Paz-Soldan, P. Petersson, P. Piovesan, C. Piron, U. Plank, B. Plaum, B. Plöck, V. Plyusnin, G. Pokol, E. Poli, L. Porte, T. Pütterich, M. Ramisch, J. Rasmussen, G. Ratta, S. Ratynskaia, G. Raupp, D. Réfy, M. Reich1, F. Reimold, D. Reiser, M. Reisner, D. Reiter, T. Ribeiro, R. Riedl, J. Riesch, D. Rittich, J.F. Rivero Rodriguez, G. Rocchi, P. Rodriguez-Fernandez, M. Rodriguez-Ramos, V. Rohde, G. Ronchi, A. Ross, M. Rott, M. Rubel, D.A. Ryan, F. Ryter, S. Saarelma, M. Salewski, A. Salmi, O. Samoylov, L. Sanchis Sanchez, J. Santos, O. Sauter, G. Schall, K. Schlüter, K. Schmid, O. Schmitz, P.A. Schneider, R. Schrittwieser, M. Schubert, C. Schuster, T. Schwarz-Selinger, J. Schweinzer, E. Seliunin, A. Shabbir, A. Shalpegin, S. Sharapov, U. Sheikh, A. Shevelev, G. Sias, M. Siccinio, B. Sieglin, A. Sigalov, A. Silva, C. Silva, D. Silvagni, J. Simpson, S. Sipilä, E. Smigelskis, A. Snicker, E. Solano, C. Sommariva, C. Sozzi, G. Spizzo, M. Spolaore, A. Stegmeir, M. Stejner, J. Stober, E. Strumberge1, G. Suarez Lopez, H.-J. Sun, W. Suttrop, E. Sytova, T. Szepesi, B. Tál, T. Tala, G. Tardini, M. Tardocchi, D. Terranova, M. Teschke, E. Thorén, W. Tierens, D. Told, W. Treutterer, G. Trevisan, E. Trier, M. Tripský, M. Usoltceva, M. Valisa, M. Valovic, M. van Zeeland, F. Vannini, B. Vanovac, P. Varela, S. Varoutis, N. Vianello, J. Vicente, G. Verdoolaege, T. Vierle, E. Viezzer, I. Voitsekhovitch, U. von Toussaint, D. Wagner, X. Wang, M. Weiland, A.E. White, M. Willensdorfer, B. Wiringer, M. Wischmeier, R. Wolf, E. Wolfrum, Q. Yang, Q. Yu, R. Zagórski, I. Zammuto, T. Zehetbauer, W. Zhang, W. Zholobenko, M. Zilker, A. Zito, H. Zohm, S. Zoletnik and the EUROfusion MST1 Team "

The tokamak à configuration variable (TCV) continues to leverage its unique shaping capabilities, flexible heating systems and modern control system to address critical issues in preparation for ITER and a fusion power plant. For the 2019–20 campaign its configurational flexibility has been enhanced with the installation of removable divertor gas baffles, its diagnostic capabilities with an extensive set of upgrades and its heating systems with new dual frequency gyrotrons. The gas baffles reduce coupling between the divertor and the main chamber and allow for detailed investigations on the role of fuelling in general and, together with upgraded boundary diagnostics, test divertor and edge models in particular. The increased heating capabilities broaden the operational regime to include T e/T i ∼ 1 and have stimulated refocussing studies from L-mode to H-mode across a range of research topics. ITER baseline parameters were reached in type-I ELMy H-modes and alternative regimes with ‘small’ (or no) ELMs explored. Most prominently, negative triangularity was investigated in detail and confirmed as an attractive scenario with H-mode level core confinement but an L-mode edge. Emphasis was also placed on control, where an increased number of observers, actuators and control solutions became available and are now integrated into a generic control framework as will be needed in future devices. The quantity and quality of results of the 2019–20 TCV campaign are a testament to its successful integration within the European research effort alongside a vibrant domestic programme and international collaborations.

In recent years, a strong effort has been dedicated to the development of tokamak plasma regimes alternative to the standard high confinement mode (H-mode) with type-I edge localized mode (ELM), i.e. ELM-free and small-ELM regimes, given the associated hardly sustainable energy and particle fluxes on plasma facing components. In this work, we will focus on new H-mode regimes with small-ELMs, the so-called baseline small-ELMs (BSE), characterized by high thermal confinement and low core impurity accumulation, which have been recently found at JET. In order to characterize the micro-turbulence at play at the top of the pedestal, an extensive local linear gyrokinetic analysis with the GKW code has been carried out. In particular, a comparison between a reference type-I ELM (#97395) and two BSE plasmas (#96994 and #94442) has been performed. The ion-scale (0.1 ≤ k θ ρ i ≤ 2) micro-turbulence is found to have different characteristics in the two regimes. Indeed, kinetic-ballooning modes (KBM) are destabilized in the type-I ELM regime at k θ ρ i ∼ 0.1, while they are stable in BSE regimes. In addition, negative (i.e. electron-diamagnetic-direction) frequency modes, identified as electron-temperature-gradient (ETG) modes, are destabilized at k θ ρ i ∼ 1.5 in the type-I ELM regime while BSE regimes are characterized by positive (i.e. ion-diamagnetic-direction) frequency modes. Meanwhile, at electron-scale (10 ≤ k θ ρ i ≤ 700) ETG modes are the dominant micro-instabilities in both regimes. Then, since BSE regimes are characterized by a higher impurity concentration at the pedestal, particular attention has been given to the role played by them. We found that impurities represent a critical player in the linear dynamics, strongly affecting the nature of micro-instabilities at ion-scale.

Turbulent transport in the inner core of the high-β JET hybrid discharge 75225 is investigated extensively through linear and non-linear gyro-kinetic (GK) simulations using the GK code GKW in the local approximation limit. Compared to previous studies (Citrin et al 2015 Plasma Phys. Control. Fusion 57 014032; Garcia et al 2015 Nucl. Fusion 55 053007), the analysis has been extended towards the magnetic axis, ρ < 0.3, where the turbulence characteristics remain an open question. Understanding turbulent transport in this region is crucial to predict core profile peaking that in turn will impact the fusion reactions and the tungsten neoclassical transport, in present devices as well as in ITER. At ρ = 0.15, a linear stability analysis indicates that kinetic ballooning modes (KBMs) dominate, with an extended mode structure in ballooning space due to the low magnetic shear. The sensitivity of KBM stability to main plasma parameters is investigated. In the non-linear regime, the turbulence induced by these KBMs drives a significant ion and electron heat flux. Standard quasi-linear (QL) models are compared to the non-linear results. The standard reduced QL models work well for the E × B fluxes, but fail to capture magnetic flutter contribution to the electron heat flux induced by the non-linear excitation of low k θ ρ i micro-tearing modes that are linearly stable. An extension of the QL models is proposed allowing better capturing the magnetic flutter flux.

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The impact of plasma shaping on electron heat transport is investigated in TCV L-mode plasmas. The study is motivated by the observation of an increase in the energy confinement time with decreasing plasma triangularity which may not be explained by a change in the temperature gradient induced by changes in the geometry of the flux surfaces. The plasma triangularity is varied over a wide range, from positive to negative values, and various plasmas conditions are explored by changing the total electron cyclotron (EC) heating power and the plasma density. The mid-radius electron heat diffusivity is shown to significantly decrease with decreasing triangularity and, for similar plasma conditions, only half of the EC power is required at a triangularity of −0.4 compared with +0.4 to obtain the same temperature profile. Besides, the observed dependence of the electron heat diffusivity on the electron temperature, electron density and effective charge can be grouped in a unique dependence on the plasma effective collisionality. In summary, the electron heat transport level exhibits a continuous decrease with decreasing triangularity and increasing collisionality. Local gyro-fluid and global gyro-kinetic simulations predict that trapped electron modes are the most unstable modes in these EC heated plasmas with an effective collisionality ranging from 0.2 to 1. The modes stability dependence on the plasma triangularity is investigated.

Electron transport in fusion plasmas is intensively studied in coordinated experiments and great progress in physics understanding has been achieved during the past years. A threshold in normalized gradient explains most of the observations, both in steady-state and transient conditions. The results convincingly suggest that trapped electron modes (TEM) dominate electron transport at low and moderate collisionality, with electron heating. The stabilization of these modes at high collisionality predicted by theory is found in the experiments. Electron transport is then driven by the ion temperature gradient modes. At low collisionality, if TEM are stabilized by negative shear and Shafranov shift effects, electron internal transport barriers may develop.

The rapid formation of an electron internal transport barrier (eITB) is observed during a slow evolution (similar or equal to 200 ms) from a centrally peaked to a hollow current density profile, while all external actuators remain constant. The time constant for the barrier formation appears to be shorter than the electron energy confinement time. The improved confinement associated with the barrier formation occurs first in a localized region off-axis. Then the effects propagate to inner and outer flux surfaces on a confinement time scale. The temporal and spatial localizations of the barrier formation suggest a threshold in the magnetic shear profile that triggers the onset of the eITB. The threshold-like behaviour can be attributed to the sudden appearance of a minimum q (or zero-shear) flux surface in the safety factor profile. Based on modelling of the current profile evolution using the ASTRA transport code, the appearance of the zero-shear flux surface is correlated with the temporal and spatial formation of the barrier.

The existence of non-diffusive momentum transport can be considered as firmly established from transient transport analysis in several devices [1-4]. In NBI driven JET H-modes, the existence of a pinch has been established both using NBI modulation techniques [2] and using database analysis [3,4], with largely consistent results. Comparisons of the observations with linear gyrokinetic calculations using the GKW code [5,6] have shown similar parameter scalings with R/Ln, q and e = r/R, allowing the pinch to be identified as the theoretically predicted Coriolis pinch [6], but predicted pinch magnitudes are on the whole lower than observed. Several effects may be responsible for this difference: 1) systematic errors on the current profile reconstruction introducing a bias in the gyrokinetic modeling, 2) a difference between Carbon rotation (measured) and bulk ion rotation (predicted), 3) the presence of residual stresses (RS), 4) simplifying assumptions used in the gyrokinetic modeling in [3,4], namely the assumption of electrostatic fluctuations, a circular geometry and the simple quasilinear estimate for the ratio of heat and momentum fluxes. In order to address these points, the present work introduces several refinements into a subset of the data presented in [3,4], which are all from the JET Carbon wall phase (before 2010). It uses EFIT equilibria constrained by polarimetry and allowing for finite edge pressure and current. Torque and heat deposition profiles are calculated using the ion orbit code ASCOT [7] for all samples in the subset, thereby taking into account any classical fast ion transport. All gyrokinetic simulations are repeated with the improved magnetic equilibrium and electromagnetic perturbations. Last, but not least, the difference in neoclassical rotation velocity between the measured impurity (C6+) velocity and that of the main ion species (D+) is calculated using the NEOART code [8].

Through a diverse research programme, the Tokamak a Configuration Variable (TCV) addresses physics issues and develops tools for ITER and for the longer term goals of nuclear fusion, relying especially on its extreme plasma shaping and electron cyclotron resonance heating (ECRH) launching flexibility and preparing for an ECRH and NBI power upgrade. Localized edge heating was unexpectedly found to decrease the period and relative energy loss of edge localized modes (ELMs). Successful ELM pacing has been demonstrated by following individual ELM detection with an ECRH power cut before turning the power back up to trigger the next ELM, the duration of the cut determining the ELM period. Negative triangularity was also seen to reduce the ELM energy release. H-mode studies have focused on the L-H threshold dependence on the main ion species and on the divertor leg length. Both L- and H-modes have been explored in the snowflake configuration with emphasis on edge measurements, revealing that the heat flux to the strike points on the secondary separatrix increases as the X-points approach each other, well before they coalesce. In L-mode, a systematic scan of the auxiliary power deposition profile, with no effect on confinement, has ruled it out as the cause of confinement degradation. An ECRH power absorption observer based on transmitted stray radiation was validated for eventual polarization control. A new profile control methodology was introduced, relying on real-time modelling to supplement diagnostic information; the RAPTOR current transport code in particular has been employed for joint control of the internal inductance and central temperature. An internal inductance controller using the ohmic transformer has also been demonstrated. Fundamental investigations of neoclassical tearing mode (NTM) seed island formation by sawtooth crashes and of NTM destabilization in the absence of a sawtooth trigger were carried out. Both stabilizing and destabilizing agents (electron cyclotron current drive on or inside the q = 1 surface, respectively) were used to pace sawtooth oscillations, permitting precise control of their period. Locking of the sawtooth period to a pre-defined ECRH modulation period was also demonstrated. Sawtooth control has permitted nearly failsafe NTM prevention when combined with backup NTM stabilization by ECRH.

F.J. Casson, A.G. Peeters, C. Angioni, Y. Camenen, W.A. Hornsby, A.P. Snodin, G.Szepesi 1 Max Planck Institut fur Plasmaphysik, EURATOM association, Boltzmannstrasse 2, 85748 Garching, Germany 2 University of Bayreuth, Physics department, Universitatsstrasse 30 Bayreuth 3 Aix-Marseille Universite, CNRS, PIIM UMR 7345, 13397 Marseille, France 4 Department of Physics, Faculty of Science, Mahidol University, Bangkok 10400, Thailand and 5 Centre for Fusion, Space and Astrophysics, University of Warwick, CV4 7AL, Coventry, UK

Nuclear fusion reactor plasmas will need to exhaust a significant proportion of energy flux through radiative processes, to enable acceptable divertor loads. This can be obtained by line radiation from impurities, injected from the plasma edge. There are however limitations on the sustainable impurity content, since radiation from the core can lead to a deleterious electron heat sink. Moreover, dilution of the main ions reduces the available fuel. Simultaneously, impurities have an impact on the turbulent transport, both by dilution and by changes in the effective charge. Recent experiments at JET point towards an improvement in plasma confinement in neon seeded discharges with respect to purer equivalent plasmas. In this paper the impact of the impurities on the confinement is studied, isolating various effects. First-principle-based integrated modelling with the QuaLiKiz quasilinear turbulent transport model explains the improvement by a combination of higher pedestal temperature, increased rotation shear, and impurity-induced microturbulence stabilization. These results are optimistic with respect to the maximum impurity levels allowed in ITER and future reactors. Comparison between QuaLiKiz and higher fidelity gyrokinetics has exposed issues with QuaLiKiz impurity peaking predictions with rotation.

The JET 2019–2020 scientific and technological programme exploited the results of years of concerted scientific and engineering work, including the ITER-like wall (ILW: Be wall and W divertor) installed in 2010, improved diagnostic capabilities now fully available, a major neutral beam injection upgrade providing record power in 2019–2020, and tested the technical and procedural preparation for safe operation with tritium. Research along three complementary axes yielded a wealth of new results. Firstly, the JET plasma programme delivered scenarios suitable for high fusion power and alpha particle (a) physics in the coming D–T campaign (DTE2), with record sustained neutron rates, as well as plasmas for clarifying the impact of isotope mass on plasma core, edge and plasma-wall interactions, and for ITER pre-fusion power operation. The efficacy of the newly installed shattered pellet injector for mitigating disruption forces and runaway electrons was demonstrated. Secondly, research on the consequences of long-term exposure to JET-ILW plasma was completed, with emphasis on wall damage and fuel retention, and with analyses of wall materials and dust particles that will help validate assumptions and codes for design and operation of ITER and DEMO. Thirdly, the nuclear technology programme aiming to deliver maximum technological return from operations in D, T and D–T benefited from the highest D–D neutron yield in years, securing results for validating radiation transport and activation codes, and nuclear data for ITER. 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. Peer Reviewed Article signat per 1223 autors/autores: J. Mailloux1, N. Abid1, K. Abraham1, P. Abreu2, O. Adabonyan1, P. Adrich3, V. Afanasev4, M. Afzal1, T. Ahlgren5, L. Aho-Mantila6, N. Aiba7, M. Airila6, M. Akhtar1, R. Albanese8, M. Alderson-Martin1, D. Alegre9, S. Aleiferis10, A. Aleksa1, A.G. Alekseev11, E. Alessi12, P. Aleynikov13, J. Algualcil14, M. Ali1, M. Allinson1, B. Alper1, E. Alves2, G. Ambrosino8, R. Ambrosino8, V. Amosov15, E.Andersson Sunden16, P. Andrew13, B.M. Angelini17, C. Angioni18, I. Antoniou1, L.C. Appel1, C. Appelbee1, S. Aria1, M. Ariola8, G. Artaserse17, W. Arter1, V. Artigues18, N. Asakura7, A. Ash1, N. Ashikawa19, V. Aslanyan20, M. Astrain21, O. Asztalos22, D. Auld1, F. Auriemma23, Y. Austin1, L. Avotina24, E. Aymerich25, A. Baciero9, F. Bairaktaris26, J. Balbin27, L. Balbinot23, I. Balboa1, M. Balden18, C. Balshaw1, N. Balshaw1, V.K. Bandaru18, J. Banks1, Yu.F. Baranov1, C. Barcellona28, A. Barnard1, M. Barnard1, R. Barnsley13, A. Barth1, M. Baruzzo17, S. Barwell1, M. Bassan13, A. Batista2, P. Batistoni17, L. Baumane24, B. Bauvir13, L. Baylor29, P.S. Beaumont1, D. Beckett1, A. Begolli1, M. Beidler29, N. Bekris30,31, M. Beldishevski1, E. Belli32, F. Belli17, É. Belonohy1, M. Ben Yaala33, J. Benayas1, J. Bentley1, H. Bergsåker34, J. Bernardo2, M. Bernert18, M. Berry1, L. Bertalot13, H. Betar35, M. Beurskens36, S. Bickerton1, B. Bieg37, J. Bielecki38, A. Bierwage7, T. Biewer29, R. Bilato18, P. Bílková39, G. Birkenmeier18, H. Bishop1, J.P.S. Bizarro2, J. Blackburn1, P. Blanchard40, P. Blatchford1, V. Bobkov18, A. Boboc1, P. Bohm39, T. Bohm41, I. Bolshakova42, T. Bolzonella23, N. Bonanomi18, D. Bonfiglio23, X. Bonnin13, P. Bonofiglo43, S. Boocock1, A. Booth1, J. Booth1, D. Borba2,30, D. Borodin44, I. Borodkina39,44, C. Boulbe45, C. Bourdelle27, M. Bowden1, K. Boyd1, I.Bozicevic Mihalic46, S.C. Bradnam1, V. Braic47, L. Brandt48, R. Bravanec49, B. Breizman50, A. Brett1, S. Brezinsek44, M. Brix1, K. Bromley1, B. Brown1, D. Brunetti1,12, R. Buckingham1, M. Buckley1, R. Budny, J. Buermans51, H. Bufferand27, P. Buratti17, A. Burgess1, A. Buscarino28, A. Busse1, D. Butcher1, E.de la Cal9, G. Calabrò52, L. Calacci53, R. Calado2, Y. Camenen54, G. Canal55, B. Cannas25, M. Cappelli17, S. Carcangiu25, P. Card1, A. Cardinali17, P. Carman1, D. Carnevale53, M. Carr1, D. Carralero9, L. Carraro23, I.S. Carvalho2, P. Carvalho2, I. Casiraghi56, F.J. Casson1, C. Castaldo17, J.P. Catalan14, N. Catarino2, F. Causa12, M. Cavedon18, M. Cecconello16, C.D. Challis1, B. Chamberlain1, C.S. Chang43, A. Chankin18, B. Chapman1,57, M. Chernyshova58, A. Chiariello8, P. Chmielewski58, A. Chomiczewska58, L. Chone59, G. Ciraolo27, D. Ciric1, J. Citrin60, Ł. Ciupinski61, M. Clark1, R. Clarkson1, C. Clements1, M. Cleverly1, J.P. Coad1, P. Coates1, A. Cobalt1, V. Coccorese8, R. Coelho2, J.W. Coenen44, I.H. Coffey62, A. Colangeli17, L. Colas27, C. Collins29, J. Collins1, S. Collins1, D. Conka24, S. Conroy16, B. Conway1, N.J. Conway1, D. Coombs1, P. Cooper1, S. Cooper1, C. Corradino28, G. Corrigan1, D. Coster18, P. Cox1, T. Craciunescu63, S. Cramp1, C. Crapper1, D. Craven1, R. Craven1, M.Crialesi Esposito48, G. Croci56, D. Croft1, A. Croitoru63, K. Crombe51,64, T. Cronin1, N. Cruz2, C. Crystal32, G. Cseh22, A. Cufar65, A. Cullen1, M. Curuia66, T. Czarski58, H. Dabirikhah1, A.Dal Molin56, E. Dale1, P. Dalgliesh1, S. Dalley1, J. Dankowski38, P. David18, A. Davies1, S. Davies1, G. Davis1, K. Dawson1, S. Dawson1, I.E. Day1, M. De Bock13, G. De Temmerman13, G. De Tommasi8, K. Deakin1, J. Deane1, R. Dejarnac39, D. Del Sarto35, E. Delabie29, D. Del-Castillo-Negrete29, A. Dempsey67, R.O. Dendy1,57, P. Devynck27, A. Di Siena18, C. Di Troia17, T. Dickson1, P. Dinca63, T. Dittmar44, J. Dobrashian1, R.P. Doerner68, A.J.H. Donne´69, S. Dorling1, S. Dormido-Canto70, D. Douai27, S. Dowson1, R. Doyle67, M. Dreval71, P. Drewelow36, P. Drews44, G. Drummond1, Ph. Duckworth13, H. Dudding1,72, R. Dumont27, P. Dumortier51, D. Dunai22, T. Dunatov46, M. Dunne18, I. Duran39, F. Durodie51, R. Dux18, A. Dvornova27, R. Eastham1, J. Edwards1, Th. Eich18, A. Eichorn1, N. Eidietis32, A. Eksaeva44, H. El Haroun1, G. Ellwood13, C. Elsmore1, O. Embreus73, S. 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Galeani53, D. Gallart78, R. Galvao55, Y. Gao44, J. Garcia27, M. García-Muñoz79, M. Gardener1, L. Garzotti1, J. Gaspar80, R. Gatto81, P. Gaudio53, D. Gear1, T. Gebhart29, S. Gee1, M. Gelfusa53, R. George1, S.N. Gerasimov1, G. Gervasini12, M. Gethins1, Z. Ghani1, M. Gherendi63, F. Ghezzi12, J.C. Giacalone27, L. Giacomelli12, G. Giacometti54, C. Gibson1, K.J. Gibson72, L. Gil2, A. Gillgren74, D. Gin4, E. Giovannozzi17, C. Giroud1, R. Glen1, S. Glöggler18, J. Goff1, P. Gohil32, V. Goloborodko82, R. Gomes2, B. Gonçalves2, M. Goniche27, A. Goodyear1, S. Gore1, G. Gorini56, T. Görler18, N. Gotts1, R. Goulding43, E. Gow1, B. Graham1, J.P. Graves40, H. Greuner18, B. Grierson43, J. Griffiths1, S. Griph1, D. Grist1, W. Gromelski58, M. Groth59, R. Grove29, M. Gruca58, D. Guard1, N. Gupta1, C. Gurl1, A. Gusarov83, L. Hackett1, S. Hacquin27,30, R. Hager43, L. Hägg16, A. Hakola6, M. Halitovs24, S. Hall1, S.A. Hall1, S. Hallworth-Cook1, C.J. Ham1, D. Hamaguchi7, M. Hamed27, C. Hamlyn-Harris1, K. Hammond1, E. Harford1, J.R. Harrison1, D. Harting1, Y. Hatano84, D.R. Hatch50, T. Haupt1, J. Hawes1, N.C. Hawkes1, J. Hawkins1, T. Hayashi7, S. Hazael1, S. Hazel1, P. Heesterman1, B. Heidbrink85, W. Helou13, O. Hemming1, S.S. Henderson1, R.B. Henriques2, D. Hepple1, J. Herfindal29, G. Hermon1, J. Hill1, J.C. Hillesheim1, K. Hizanidis26, A. Hjalmarsson16, A. Ho60, J. Hobirk18, O. Hoenen13, C. Hogben1, A. Hollingsworth1, S. Hollis1, E. Hollmann68, M. Hölzl18, B. Homan45, M. Hook1, D. Hopley1, J. Horácek39, D. Horsley1, N. Horsten59, A. Horton1, L.D. Horton30,40, L. Horvath1,72, S. Hotchin1, R. Howell1, Z. Hu56, A. Huber44, V. Huber44, T. Huddleston1, G.T.A. Huijsmans13, P. Huynh27, A. Hynes1, M. Iliasova4, D. Imrie1, M. Imrísek39, J. Ingleby1, P. Innocente23, K. Insulander Björk73, N. Isernia8, I. Ivanova-Stanik58, E. Ivings1, S. Jablonski58, S. Jachmich13,30,51, T. Jackson1, P. Jacquet1, H. Järleblad86, F. Jaulmes39, J.Jenaro Rodriguez1, I. Jepu63, E. Joffrin27, R. Johnson1, T. Johnson34, J. Johnston1, C. Jones1, G. Jones1, L. Jones1, N. Jones1, T. Jones1, A. Joyce1, R. Juarez14, M. Juvonen1, P. Kalnin¸ a24, T. Kaltiaisenaho6, J. Kaniewski1, A. Kantor1, A. Kappatou18, J. Karhunen5, D. Karkinsky1, Yu Kashchuk87, M. Kaufman29, G. Kaveney1, Ye.O. Kazakov51, V. Kazantzidis26, D.L. Keeling1, R. Kelly1, M. Kempenaars13, C. Kennedy1, D. Kennedy1, J. Kent1, K. Khan1, E. Khilkevich4, C. Kiefer18, J. Kilpeläinen59, C. Kim32, Hyun-Tae Kim1,30, S.H. Kim13, D.B. King1, R. King1, D. Kinna1, V.G. Kiptily1, A. Kirjasuo6, K.K. Kirov1, A. Kirschner44, T. kiviniemi59, G. Kizane24, M. Klas88, C. Klepper29, A. Klix31, G. Kneale1, M. Knight1, P. Knight1, R. Knights1, S. Knipe1, M. Knolker32, S. Knott89, M. Kocan13, F. Köchl1, I. Kodeli65, Y. Kolesnichenko82, Y. Kominis26, M. Kong1, V. Korovin71, B. Kos65, D. Kos1, H.R. Koslowski44, M. Kotschenreuther50, M. Koubiti54, E. Kowalska-Strzeciwilk ˛ 58, K. Koziol3, A. Krasilnikov87, V. Krasilnikov13,15, M. Kresina1,27, K. Krieger18, N. 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Zychor3 // 1 United Kingdom Atomic Energy Authority, Culham Science Centre, Abingdon, Oxon, OX14 3DB, United Kingdom of Great Britain and Northern Ireland 2 Instituto de Plasmas e Fusao Nuclear, Instituto Superior Técnico, Universidade de Lisboa, 1049-001 Lisboa, Portugal 3 National Centre for Nuclear Research (NCBJ), 05-400 Otwock-Swierk, Poland 4 Ioffe Physico-Technical Institute, 26 Politekhnicheskaya, St Petersburg 194021, Russia 5 University of Helsinki, PO Box 43, FI-00014 University of Helsinki, Finland 6 VTT Technical Research Centre of Finland, PO Box 1000, FIN-02044 VTT, Finland 7 National Institutes for Quantum and Radiological Science and Technology, Naka, Ibaraki 311-0193, Japan 8 Consorzio CREATE, Via Claudio 21, 80125 Napoli, Italy 9 Laboratorio Nacional de Fusión, CIEMAT, Madrid, Spain 10 NCSR ‘Demokritos’ 153 10, Agia Paraskevi Attikis, Greece 11 NRC Kurchatov Institute, 1 Kurchatov Square, Moscow 123182, Russia 12 Institute for Plasma Science and Technology, CNR, via R. Cozzi 53, 20125 Milano, Italy 13 ITER Organization, Route de Vinon-sur-Verdon, CS 90 046, 13067 Saint Paul Lez Durance Cedex, France 14 Universidad Nacional de Educacion a Distancia, Dept Ingn Energet, Calle Juan del Rosal 12, E-28040 Madrid, Spain 15 Troitsk Insitute of Innovating and Thermonuclear Research (TRINITI), Troitsk 142190, Moscow Region, Russia 16 Department of Physics and Astronomy, Uppsala University, SE-75120 Uppsala, Sweden 17 Dip.to Fusione e Tecnologie per la Sicurezza Nucleare, ENEA C. R. Frascati, via E. Fermi 45, 00044 Frascati (Roma), Italy 18 Max-Planck-Institut für Plasmaphysik, D-85748 Garching, Germany 19 National Institute for Fusion Science, Oroshi, Toki, Gifu 509-5292, Japan 20 MIT Plasma Science and Fusion Center, Cambridge, MA 02139, United States of America 21 Universidad Politécnica de Madrid, Grupo I2A2, Madrid, Spain 22 Centre for Energy Research, POB 49, H-1525 Budapest, Hungary 23 Consorzio RFX, Corso Stati Uniti 4, 35127 Padova, Italy 24 University of Latvia, 19 Raina Blvd., Riga, LV 1586, Latvia 25 Department of Electrical and Electronic Engineering, University of Cagliari, Piazza d’Armi 09123 Cagliari, Italy 26 National Technical University of Athens, Iroon Politechniou 9, 157 73 Zografou, Athens, Greece 27 CEA, IRFM, F-13108 Saint Paul Lez Durance, France 28 Dipartimento di Ingegneria Elettrica Elettronica e Informatica, Università degli Studi di Catania, 95125 Catania, Italy 29 Oak Ridge National Laboratory, Oak Ridge, TN 37831, TN, United States of America 30 EUROfusion Programme Management Unit, Culham Science Centre, Culham, OX14 3DB, United Kingdom of Great Britain and Northern Ireland 31 Karlsruhe Institute of Technology, PO Box 3640, D-76021 Karlsruhe, Germany 32 General Atomics, PO Box 85608, San Diego, CA 92186-5608, United States of America 33 Department of Physics, University of Basel, Switzerland 34 Fusion Plasma Physics, EECS, KTH Royal Institute of Technology, SE-10044 Stockholm, Sweden 35 Institut Jean Lamour, UMR 7198, CNRS-Université de Lorraine, 54500 Vandoeuvre-lès-Nancy, France 36 Max-Planck-Institut für Plasmaphysik, Teilinsitut Greifswald, D-17491 Greifswald, Germany 37 Maritime University of Szczecin Faculty of Marine Engineering, Waly Chrobrego 1-2, 70-500 Szczecin, Poland 38 Institute of Nuclear Physics, Radzikowskiego 152, 31-342 Kraków, Poland 39 Institute of Plasma Physics of the CAS, Za Slovankou 1782/3, 182 00 Praha 8, Czech Republic 40 Ecole Polytechnique Fédérale de Lausanne (EPFL), Swiss Plasma Center (SPC), CH-1015 Lausanne, Switzerland 41 University of Wisconsin-Madison, Madison, WI 53706, United States of America 42 Magnetic Sensor Laboratory, Lviv Polytechnic National University, Lviv, Ukraine 43 Princeton Plasma Physics Laboratory, James Forrestal Campus, Princeton, NJ 08543, NJ, United States of America 44 Forschungszentrum Jülich GmbH, Institut für Energie- und Klimaforschung, Plasmaphysik, 52425 Jülich, Germany 45 Université Cote d’Azur, CNRS, Inria, LJAD, Parc Valrose, 06108 Nice Cedex 02, France 46 Ruder Boskovic Institute, Bijenicka 54, 10000 Zagreb, Croatia 47 The National Institute for Optoelectronics, Magurele-Bucharest, Romania 48 Mechanics, SCI, KTH SE-100 44 Stockholm, Sweden 49 Fourth State Research, 503 Lockhart Dr, Austin, TX, United States of America 50 University of Texas at Austin, Institute for Fusion Studies, Austin, TX 78712, United States of America 51 Laboratory for Plasma Physics LPP-ERM/KMS, B-1000 Brussels, Belgium 52 University of Tuscia, DEIM, Via del Paradiso 47, 01100 Viterbo, Italy 53 Università di Roma Tor Vergata, Via del Politecnico 1, Roma, Italy 54 Aix-Marseille University, CNRS, PIIM, UMR 7345, 13013 Marseille, France 55 Instituto de Física, Universidade de Sao Paulo, Rua do Mat˜ao Travessa R Nr.187, CEP 05508-090 Cidade Universitária, Sao Paulo, Brasil 56 University of Milano-Bicocca, Piazza della Scienza 3, 20126 Milano, Italy 57 Centre for Fusion, Space and Astrophysics, University of Warwick, Coventry, CV4 7AL, United Kingdom of Great Britain and Northern Ireland 58 Institute of Plasma Physics and Laser Microfusion, Hery 23, 01-497 Warsaw, Poland 59 Aalto University, PO Box 14100, FIN-00076 Aalto, Finland 60 FOM Institute DIFFER, Eindhoven, The Netherlands 61 Warsaw University of Technology, 02-507 Warsaw, Poland 62 Astrophysics Research Centre, School of Mathematics and Physics, Queen’s University, Belfast, BT7 1NN, United Kingdom of Great Britain and Northern Ireland 63 The National Institute for Laser, Plasma and Radiation Physics, Magurele-Bucharest, Romania 64 Department of Applied Physics, Ghent University, 9000 Ghent, Belgium 65 Slovenian Fusion Association (SFA), Jozef Stefan Institute, Jamova 39, SI-1000 Ljubljana, Slovenia 66 The National Institute for Cryogenics and Isotopic Technology, Ramnicu Valcea, Romania 67 Dublin City University (DCU), Dublin, Ireland 68 University of California at San Diego, La Jolla, CA 92093, United States of America 69 EUROfusion Programme Management Unit, Boltzmannstr. 2, 85748 Garching, Germany 70 UNED, Dpto. Informática y Automática, Madrid, Spain 71 National Science Center ‘Kharkov Institute of Physics and Technology’, Akademichna 1, Kharkiv 61108, Ukraine 72 York Plasma Institute, Department of Physics, University of York, York, YO10 5DD, United Kingdom of Great Britain and Northern Ireland 73 Department of Physics, Chalmers University of Technology, SE-41296 Gothenburg, Sweden 74 Department of Space, Earth and Environment, Chalmers University of Technology, SE-41296 Gothenburg, Sweden 75 European Commission, B-1049 Brussels, Belgium 76 University of Tennessee, Knoxville, TN 37996, TN, United States of America 77 Universitat Politècnica de Catalunya, Barcelona, Spain 78 Barcelona Supercomputing Center, Barcelona, Spain 79 Universidad de Sevilla, Sevilla, Spain 80 Aix-Marseille University, CNRS, IUSTI, UMR 7343, 13013 Marseille, France 81 Dipartimento di Ingegneria Astronautica, Elettrica ed Energetica, SAPIENZA Università di Roma, Via Eudossiana 18, 00184 Roma, Italy 82 Institute for Nuclear Research, Prospekt Nauky 47, Kyiv 03680, Ukraine 83 Studiecentrum voor Kernenergie—Centre d’Etude de l’Energie Nucléaire, Boeretang 200, 2400 Mol, Belgium 84 University of Toyama, Toyama, 930-8555, Japan 85 University of California, Irvine, Irvine, California 92697, United States of America 86 Department of Physics, Technical University of Denmark, Bldg 309, DK-2800 Kgs Lyngby, Denmark 87 Institution ‘Project Center ITER’, Moscow, 123182, Russia 88 Faculty of Mathematics, Department of Experimental Physics, Physics and Informatics Comenius University Mlynska dolina F2, 84248 Bratislava, Slovakia 89 University College Cork (UCC), Cork, Ireland 90 Institute of Physics, Opole University, Oleska 48, 45-052 Opole, Poland 91 Daegu University, Jillyang, Gyeongsan, Gyeongbuk 712-174, Republic of Korea 92 Department of Nuclear Engineering, Seoul National University, Seoul, Republic of Korea 93 Fusion for Energy Joint Undertaking, Josep Pl. 2, Torres Diagonal Litoral B3, 08019, Barcelona, Spain 94 PELIN LLC, 27a, Gzhatskaya Ulitsa, Saint Petersburg, 195220, Russia 95 Arizona State University, Tempe, AZ, United States of America 96 Politecnico di Torino, Corso Duca degli Abruzzi 24, I-10129 Torino, Italy 97 ICREA and Barcelona Supercomputing Center, Barcelona, Spain 98 Universidad Complutense de Madrid, Madrid, Spain 99 Istituto dei Sistemi Complessi—CNR and Dipartimento di Energia—Politecnico di Torino, C.so Duca degli Abruzzi 24, 10129 Torino, Italy 100 Eindhoven University of Technology, The Netherlands 101 Purdue University, 610 Purdue Mall, West Lafayette, IN 47907, United States of America 102 Department of Material Science, Shimane University, 1060 Nishikawatsu, Matsue, 690-8504, Japan 103 Faculty of Nuclear Sciences and Physical Engineering, Czech Technical University in Prague, Brehová 78/7, 115 19 Praha 1, Czech Republic 104 College of William and Mary, Williamsburg, VA 23185, United States of America 105 University of California, 1111 Franklin St., Oakland, CA 94607, United States of America 106 University of Strathclyde, Glasgow, G4 0NG, United Kingdom of Great Britain and Northern Ireland 107 Kindai University, Higashi-Osaka, 577-8502, Japan 108 Shizuoka University, Shizuoka, 422-8529, Japan 109 Rudolf Peierls Centre for Theoretical Physics, University of Oxford, Oxford OX1 3PU, United Kingdom of Great Britain and Northern Ireland 110 Columbia University, New York, NY 10027, United States of America 111 Dipartimento di Fisica ‘G. Galilei’, Universita’ degli Studi di Padova, Padova, Italy 112 Space and Plasma Physics, EECS, KTH SE-100 44 Stockholm, Sweden 113 University of Ioannina, Panepistimioupoli Ioanninon, PO Box 1186, 45110 Ioannina, Greece 114 Universidade do Porto, Faculdade de Engenharia, 4200-465 Porto, Portugal 115 The University of Tokyo, Kashiwa, Chiba, 277-0882, Japan 116 Lithuanian Energy Institute, Breslaujos g. 3, LT-44403, Kaunas, Lithuania 117 HRS Fusion, West Orange, NJ, United States of America 118 Ibaraki University Graduate School of Science and Engineering, Mito, Ibaraki 310-8512, Japan 119 Technische Universität Wien, Fusion@ÖAW Österreichische Akademie der Wissenschaften (ÖAW), Austria

This repository contains the source code of the publication "Fast modeling of turbulent transport in fusion plasmas using neural networks" by K.L. van de Plassche et al., submittedto Physics of Plasmas. Currently contains only the pre-print version. On publication, a reproduction package to reproduce all figures in this manuscript will be supplied. We present an ultrafast neural network (NN) model, QLKNN, which predicts core tokamak transport heat and particle fluxes. QLKNN is a surrogate model based on a database of 300 million flux calculations of the quasilinear gyroki- netic transport model QuaLiKiz. The database covers a wide range of realistic tokamak core parameters. Physical features such as the existence of a critical gradient for the onset of turbulent transport were integrated into the neural network training methodology. We have coupled QLKNN to the tokamak modelling framework JINTRAC and rapid control-oriented tokamak transport solver RAPTOR. The coupled frameworks are demonstrated and validated through application to three JET shots covering a representative spread of H-mode operating space, predicting turbulent trans- port of energy and particles in the plasma core. JINTRAC-QLKNN and RAPTOR-QLKNN are able to accurately reproduce JINTRAC-QuaLiKiz T i,e and n e profiles, but 3 to 5 orders of magnitude faster. Simulations which take hours are reduced down to only a few tens of seconds. The discrepancy in the final source-driven predicted profiles between QLKNN and QuaLiKiz is on the order 1%-15%. Also the dynamic behaviour was well captured by QLKNN, with differences of only 4%-10% compared to JINTRAC-QuaLiKiz observed at mid-radius, for a study of density buildup following the L-H transition. Deployment of neural network surrogate models in multi-physics integrated tokamak modelling is a promising route towards enabling accurate and fast tokamak scenario optimization, Uncertainty Quan- tification, and control applications.

International audience; Simultaneous measurements of binormal velocity of density fluctuations using two separate Doppler backscattering systems at the low field side and at the top of the plasma show significant poloidal asymmetry. The measurements are performed in the core region between the radii 0.7