Recent Publications

Neoclassical impurity transport in the tokamak transport barrier and pedestal with SOLPS-ITER

Veronika Korzueva, Elizaveta Kaveeva, Vladimir A Rozhansky, Nikita Shtyrkhunov, Xavier Pierre Bonnin

New neoclassical corrections are implemented in the SOLPS-ITER code package and can be used for modelling with drifts. These corrections are introduced to obtain standard neoclassical impurity flux in the core for non-steep main ion density and temperature gradients if drifts are switched on. ITER, JET and ASDEX Upgrade H-modes are simulated with SOLPS-ITER. It is demonstrated that standard neoclassical theory is not applicable inside a transport barrier with steep density and temperature gradients, at least for JET and ASDEX Upgrade. High Field Side-Low Field Side asymmetry in impurity distribution is observed, which is consistent with analytical results. Resulting radial convective fluxes significantly differ from predictions of the standard neoclassical theory. Ne transport in the ITER pedestal is discussed. Standard neoclassical theory of impurity transport should not be applicable to Ne here, yet SOLPS-ITER modelling shows a Ne drift flux that is close to the standard neoclassical prediction in the pedestal. Additional discussion of tungsten transport in the JET and ITER pedestals is provided. According to the provided estimates, collisional tungsten will exhibit HFS-LFS asymmetry in the pedestal, and its radial transport will be suppressed compared to standard neoclassical predictions.

Identifying non-performing or Dud Plasmas for Burning Plasma Control: Insights from JET and TFTR Deuterium-Tritium Campaigns

Lidia Piron, Nicolò Ferron, Eric Fredrickson, Morten Lennholm, Alessandro Pau, Timo Ravensbergen, Olivier Sauter, Fulvio Auriemma, Matteo Baruzzo, Krassimir K. K Kirov, et al.

Consorzio RFX, Culham Centre for Fusion Energy, United Kingdom Atomic Energy Authority, Max-Planck-Institut fuer Plasmaphysik, PPPL

Among the burning plasma controllers for research fusion reactors, the dud detector will be of primary importance as it determines whether the plasma is performing well or if it is a dud. In the latter case, the discharge needs to be terminated to remain within tritium and neutron activation limits. To this scope, monitors which track the plasma performance will be integrated in the plasma control system. In this work, we present a novel dud detector that has been empirically identified based on Deuterium-Tritium campaigns carried out at JET and TFTR. This controller estimates a proxy of the neutron rate using a combination of the diamagnetic energy and the density peakedness. If the predicted neutron rate deviates from the real-time measurement, then the dud detector will trigger an alarm leading to a safe plasma termination if plasma recovery is not expected or, to actuator requests when adjustment is possible. This monitoring function can also be coupled with equilibrium solver and control-oriented models, such as RAPDENS, as proposed in the 15 MA plasma current, 5.3 T toroidal magnetic field baseline Deuterium-Tritium ITER scenario.

The physics of ballooning-limited ELM-free regimes in EUROfusion tokamaks

Mike G Dunne, Michael Faitsch, Olivier Sauter, Eleonora Viezzer, Benoit Labit, Athina Kappatou, David Keeling, Branka Vanovac, Itziar Balboa, Petra Bilkova, et al.

Culham Centre for Fusion Energy, Max-Planck-Institut für Plasmaphysik, Ecole Polytechnique Federale de Lausanne, Academy of Sciences of the Czech Republic, University of Seville

The development of operational scenarios without large Type-I ELMs is of utmost importance for the stable operation and longevity of future tokamaks. The EUROfusion tokamak exploitation program has therefore made the understanding of ELM-free regimes a major topic of exploration across all its contributing devices (ASDEX Upgrade, JET, MAST-Upgrade, TCV, and WEST). An integrated program to investigate a range of Type-I ELM-free regimes has been developed covering the enhanced D-alpha (EDA), magnetic perturbations (MP), negative triangularity (NT), quasi-continuous exhaust (QCE), quiescent H-mode (QH), the baseline small ELMs (SE), I-mode, and X-point radiator (XPR) regimes. This contribution focuses on the development and understanding of the NT and QCE regimes on ASDEX Upgrade, JET, and TCV. The importance of transport via ballooning modes in both regimes is highlighted, as well as the progress in developing access models based on ideal-MHD. In the case of the QCE, this can also be expressed as a minimum separatrix density, which corresponds well to experimentally measured separatrix densities. Particular focus is paid to the performance of the QCE in terms of the achieved pedestal top values, which, when appropriately normalised, do not differ significantly from ELMy H-mode plasmas. This, combined with the predicted minimum separatrix density for the 15~MA ITER baseline plasma, highlight the relevance of the QCE as a potential operational scenario for both ITER and future reactors.

Development of a high-current, high fusion performance scenario on JET: physics insights and operational challenges

Luca Garzotti, Domenico Frigione, Peter J Lomas, Fernanda Rimini, Dirk Van Eester, Vito Konrad Zotta, Spyridon Aleiferis, Edoardo Alessi, Fulvio Auriemma, Rennan Bianchetti Morales, et al.

Culham Centre for Fusion Energy, United Kingdom Atomic Energy Authority, Institute of Plasma Physics and Laser Microfusion, Consiglio Nazionale delle Ricerche, Sapienza University of Rome

Since the installation of a beryllium-tungsten(Be/W) first wall on JET an intense scenario development programme has taken place to realize a high-current (3.5-4 MA) scenario, denominated JET baseline scenario, with $q_{95} \sim 3$, $\beta_N \sim 1.8$ and capable of delivering high fusion performance ($P_{fusion} > 10$ MW) for 5 s in the D-T campaigns conducted in 2021 and 2023. The JET baseline scenario was realized in D-T at 3.5 MA in 2021 (DTE2 campaign), but, despite achieving transitorily $P_{fus} \sim 8$ MW, it could not be sustained for more than 3 s. In this paper we will revisit and expand the analysis of the baseline scenario at 3.5 MA and present new results obtained in D-T at 3.0 MA in DTE3, where we were able to sustain the scenario for 5 s. We will also present recent modelling results showing how available semi-empirical and first-principles transport models can explain a variety of phenomena ranging from fusion performance, impurity transport and control of the fuelling mix. Many of these points are potentially relevant for bigger machines such as ITER. Finally, we will discuss open questions and improvements to our present modelling capabilities required to extrapolate the results to power plant devices.

First wall particle fluxes and Be erosion in high-performance JET-ITER baseline plasmas

Eduardo de la Cal, Carine Giroud, Henri Aaron Kumpulainen, Juri Romazanov, Itziar Balboa, Scott Alan Silburn, Pedro Carvalho, Juuso Karhunen, Beth Thomas, Alex Tookey, et al.

Culham Centre for Fusion Energy, VTT, Consorzio RFX, Forschungszentrum Juelich GmbH, Centro de Investigaciones Energeticas Medioambientales y Tecnologicas

In next step large fusion devices with a tungsten (W) first wall such as ITER, impurity control will be a challenge to avoid strong core radiation from highly ionized metals. Here we analyse the deuterium (D) fluxes impacting on the beryllium (Be) first wall limiters and the resulting surface erosion in high-performance neon (Ne) seeded ITER-baseline plasmas with up to 35 MW heating power in JET tokamak. Visible cameras are used to quantify the fluxes using the spectroscopic S/XB method at the regions of strongest plasma-wall interaction: the Outer Midplane (OMP) and the Upper Dump Plates (UDP). We first describe how Ne seeding, which significantly improves core plasma performance and power exhaust control, modifies the plasma flux dynamics and ELM properties at the walls. It is then shown, that the global Be erosion by sputtering is not significantly affected by Ne seeding. This is because the time-averaged fluxes are dominated by the inter-ELM phase, where the main erosion precursor is deduced to be D+. Furthermore, we observe a beneficial strong decrease of the fluxes at the OMP when slightly increasing the Separatrix-limiter clearance, indicating short far scrape-off layer (SOL) decay lengths. We also describe, how the fluxes change with average plasma density and toroidal magnetic field and plasma current. Regarding the fluxes at the UDP, we show the critical effect of the magnetic topology at the top of the chamber. The formation of a secondary Separatrix in this region enhances the parallel plasma fluxes to the UDP, which eventually becomes the main plasma-wall interaction area. Finally, we compare the experimentally estimated Be effective sputtering yields at the OMP for the inter- and intra-ELM phases with the values calculated using the SDTrim code to infer information on the mean ion impinging energies Ei and to show that the main global erosion precursor is D+. The obtained Ei values are in the range or at least compatible with those expected for the plasmas analysed: approximately 30 eV for the inter- and 1 keV for the intra-ELM periods respectively.

Machine learning aided neutron yield for dud detection based on JET and TFTR Deuterium-Tritium plasmas

Lidia Piron, Alessandro Pau, Nicolò Ferron, Eric Fredrickson, Olivier Sauter, Matteo Baruzzo, Clive D Challis, Remi Dumont, Dirk Van Eester, Michael Fitzgerald, et al.

Culham Science Centre, Consorzio RFX, Ecole Polytechnique Federale de Lausanna, Laboratory for Plasma Physics, Max-Plank-Institut für Plasma Physik

as it indicates fusion performance. To optimize Tritium consumption and limit neutron activation, a support function included in the plasma control system called a dud detector will trigger an alarm if the plasma fails to achieve expected fusion performance. This function has been developed and routinely employed at JET during DT campaigns. This study presents machine-learning methods based on a surrogate model of the neutron rate, which can be used as an advanced dud detector. In preparation for DT operations in BEST, HL-3, ITER, and SPARC, we investigate the portability and inherent limitations of these ML methods by analysing similar DT experiments conducted at TFTR.

Diagnostics for large tokamaks: from JET to JT-60SA 1

Carlo Sozzi, A Jokinen, G Phillips, K Tanaka, Juan Ayllon-Guerola, Andrea Belpane, Attila Buzás, Santiago Cabrera, mario - cavinato, Daniel Carralero, et al.

Fusion for Energy, Consorzio RFX, Hungarian Academy of Sciences Centre for Energy Research, Centro de Investigaciones Energeticas Medioambientales y Tecnologicas, Consiglio Nazionale delle Ricerche

The main scientific purpose of JT-60SA is complementing ITER in the preparation of the operation of a DEMOnstration fusion reactor, in particular investigating the conditions for a controllable high beta steady-state regime able to optimize the fusion gain. In order to accomplish this task, a sequence of operation and machine enhancement periods in the next few years are planned to reach the target performance of the machine before a transition to a full tungsten wall. EUROfusion and Fusion for Energy are jointly contributing to the enhancement plan of JT-60SA, in particular, for what concerns the present contribution, to provide JT-60SA with state-of-art diagnostics in support of its scientific and technical objectives. This paper reports the status of the projects being implemented in view of the next scientific campaigns or under consideration through the various stages from feasibility to detailed design.

Integrated core-SOL modelling of JET baseline plasmas in D/D-T/T: impact of ELMs and isotopic composition on Tungsten sputtering

Rachele Cicioni, Luca Garzotti, Lidia Piron, Vito Konrad Zotta, Vassili Parail, Agata Chomiczewska, Domenico Frigione, Alexander Huber, Florian Koechl, Henri Aaron Kumpulainen, et al.

University of Padova, United Kingdom Atomic Energy Authority, Consorzio RFX, Institute of Plasma Physics and Laser Microfusion, Institute of Fusion Energy and Nuclear Waste Management-Plasma Physics, Forschungszentrum Jülich GmbH

The JET DTE2 experimental campaign revealed an isotopic dependence in the baseline scenario, where the target stationary conditions achieved in deuterium plasmas could not be maintained in tritium and deuterium-tritium mixtures. This loss of stationarity was associated with a gradual increase in plasma density, reduced ELM activity, and rising core radiation. This work investigates whether isotope-dependent tungsten sputtering contributes to the loss of stationarity observed in JET DTE2 baseline plasmas. The analysis focuses on the tungsten sputtering source and on tungsten transport during inter- and intra-ELM phases, as a function of the isotopic species of the main plasma. The study is carried out using the integrated core-edge-SOL framework COCONUT/JINTRAC, which was used to evolve the plasma self-consistently across the entire domain. The simulations show a clear isotopic dependence of the tungsten sputtering source, which increases with the mass of the main plasma ion and reaches the highest levels in tritium plasmas. Despite the enhanced tungsten source, most of the sputtered tungsten remains confined to the SOL, and no substantial net increase of the tungsten content is observed in the plasma core over the ELM time window. Pedestal onditions affect tungsten transport across the separatrix and the transient tungsten response during the ELM cycle. The results also indicate that ELM dynamics, in particular the ELM frequency, can modify the transient tungsten content in the core. Overall, the simulations suggest that isotope composition and ELM activity affect the tungsten sputtering source and its short-time redistribution, but that ELM-induced sputtering alone does not explain the loss of stationarity observed experimentally.

Implementation and verification of the avalanche source in a 3D full-f particle-in-cell model of relativistic electrons for studies of tokamak disruptions

Fiona Wouters, Hannes Bergström, Matthias Hoelzl, Guido T. A. Huijsmans, Jan van Dijk, the JOREK team

Disruptions threaten tokamak operation not only because of large in-vessel forces and thermal heat loads, but also because some electrons may be accelerated to relativistic energies. These so-called runaway electrons (REs) can multiply exponentially via knock-on collisions with thermal electrons. As the resulting RE avalanche is exponentially sensitive to the pre-disruption plasma current, multi-MA RE beams may form in large future devices, risking severe localized wall damage. Detailed understanding of RE beam formation and the particle phase-space distribution requires a self-consistent treatment of the RE avalanche and competing losses in the stochastic fields of MHD-active plasmas. Such simulations including the RE sources in 3D fields are needed to develop viable mitigation scenarios. For this, the 3D nonlinear MHD code JOREK includes a hybrid fluid-kinetic model, describing REs with a full-f relativistic particle-in-cell (PiC) approach using full-orbit or drift-kinetic descriptions. In this work, an energy and momentum conserving knock-on collision operator is implemented to enable accurate modeling of the RE phase-space dynamics in 3D electromagnetic fields. To make such novel high-fidelity simulations computationally viable, a resampling technique was also implemented to restrict the number of markers. The avalanche model is verified using analytical expressions from literature and applied to a JET-like termination scenario, demonstrating its applicability to realistic 3D MHD active scenarios. Future work on porting to accelerated high-performance computing systems will be needed to cross the long time scales involved, e.g., in periodic termination and re-avalanching that could occur in large devices like ITER.

Measurements and analysis of short-term activation of ITER samples exposed in irradiation-end during DT operations at JET

Ewa Łaszyńska, Jakub Piotr Włodarczyk, Sabahattin Akbas, Barbara Bieńkowska, Zamir Ghani, Callum Grove, Xavier L Litaudon, Lee William Packer, Chantal Shand, Rosaria Villari, et al.

United Kingdom Atomic Energy Authority, Institute of Plasma Physics and Laser Microfusion, AGH University of Krakow, CEA, ENEA

Short-lived activation products in fusion materials are critical for assessing radiological safety and maintenance planning in future fusion reactors like ITER. These products influence shutdown dose rates, impact maintenance procedures, and provide essential validation for nuclear data and activation models in the short term. Understanding their formation and decay behavior under deuterium-tritium (DT) plasma conditions allows for more accurate predictions of material performance and safety constraints. This study analyzes the short-term activation of ITER materials exposed at the KN2 6U irradiation end in the JET (Joint European Torus) tokamak during the DTE2 and DTE3 campaigns. CuCrZr, IWS A286, and SS316L(N) samples were activated during DTE2, while tungsten monoblock, a key ITER divertor material, was irradiated during DTE3. Activated samples were promptly transported via a pneumatic post system for gamma spectrometry measurements using UKAEA’s 190% relative efficiency HPGe (High-Purity Germanium) detector. The efficiency calibration was performed with the MCNP 6.1 code, employing an MCNP detector model validated by a certified multi-gamma calibration source. The experimental data were compared with FISPACT-II activation calculations, enabling the determination of calculation-to-experiment (C/E) ratios. This study provides key validation data for nuclear activation models and improves the accuracy of computational predictions for material behavior in fusion reactors.

3D modelling of thermal loads during unmitigated vertical displacement events in ITER and JET

F.J. Artola, A. Redl, S.N. Gerasimov, R.A. Pitts, I.S. Carvalho, M. Kong, G. Simic, A. Loarte, J. Van Blarcum

ITER Organization, Max Planck Institute for Plasmaphysics, UKAEA, Ecole Polytechnique Fédérale de Lausanne (EPFL)

Predicting three-dimensional thermal loads during tokamak disruptions is essential for ITER yet remains weakly developed. We present a physics-based workflow that couples MHD simulations of vertical displacement events with field line tracing on a realistic 3D first wall model and a transient wall thermal response. The approach is validated against JET discharges with beryllium main chamber armour, reproducing key global dynamics, non-axisymmetric current features, and the occurrence (or absence) of melting, thereby building confidence in the methodology. We then apply the same workflow to ITER-relevant conditions with tungsten (W) armour, consistent with the new 2024 ITER re-baseline, to assess disruption heat loads and their 3D localization. The resulting analysis demonstrates the resilience of the ITER W first wall against these events and provides predictions for the energy deposition and current flow profiles. Beyond these studies, the workflow enables scenario-by-scenario estimates of disruption-induced thermal loading, allowing to assess the disruption-budget consumption for these events in future devices.

A new model for runaway electron transport based on chaotic Hamiltonian systems

Dániel Jánosi, Anikó Horváth, Hannes Bergström, Matthias Hölzl, Gergely Papp, Gábor Veres, Gergo I. Pokol, György Károlyi

The transport of runaway electrons (RE) in ergodic magnetic geometries is an area of active study. Computing the transport from the direct simulation of particle trajectories is computationally expensive. Instead, diffusion models, such as the one by Rechester and Rosenbluth, are often employed to incorporate transport effects into reduced simulations. However, the comparison of diffusion-based to direct simulations reveals that the transport is typically not purely diffusive. In this paper, we introduce a simple transport model, based on chaos theory, which goes beyond the Rechester-Rosenbluth approximation. Besides chaotic diffusion, our model takes into account the effect of so-called sticky regions, a trapping layer around magnetic islands, where particle escape slows down to a power-law decay rather than an exponential decay. We demonstrate the applicability of the model both in the Ullmann-Caldas map with parameters corresponding to the TBR-1 tokamak, and in a JOREK simulation of a JET disruption scenario, with remarkably good fits achieved in both cases.

Integrated numerical analysis of impurity transport and sources for high current—high power baseline pulses with T in JET-ILW

I. Ivanova-Stanik, A. Chomiczewska, G. Telesca, E. Kowalska-Strzęciwilk, L. Garzotti, G. Pucella, D. Van Eester, R. Zagorski, V.K. Zotta

Institute of Plasma Physics and Laser Microfusion, National Centre for Nuclear Research, UKAEA, ENEA, Association EUROFUSION-Belgian State

This work consists of integrated numerical modelling applied to JET high-current, high-power baseline pulses with 92% tritium + 8% hydrogen with tungsten divertor and beryllium wall in corner configuration. These simulations are performed using the COREDIV code, which self-consistently solves one-dimensional radial transport equations for the plasma and impurities in the core region, coupled with two-dimensional multi-fluid transport in the scrape-off layer. It should be noted that the simulations are ‘semi-interpretative’, in the sense that transport coefficients are tuned in order to match experimental data: profile of the radiation, Ni concentration, radiation in SOL and Z eff . The simulations suggest that, within the assumptions of the COREDIV model and the available experimental constraints, the observed increase in core plasma radiation can be most consistently reproduced by changes in impurity transport rather than by an increase in the impurity source. The simulations show that sputtering of tungsten due to tritium is negligible. The Be is the main source of sputtering and the dominant contribution to tungsten sputtering comes from Be 2+ .

Analysis of the alpha particle transport induced by Alfven eigenmodes and fish-bones in JET DT discharges: multiple energetic particle simulations

J. Varela, J. Garcia, D. Zarzoso, S. Mazzi, Y. Kazakov, Z. Stancar, M. Baruzzo, J. Ongena, D.A. Spong, L. Garcia, et al.

United Kingdom Atomic Energy Authority, University of Texas at Austin, Universidad Carlos III de Madrid, CEA, Oak Ridge National Laboratory

The present study is dedicated to analyze the extensive fast ion (FI) induced perturbations in ion cyclotron resonance heating (ICRH) dominated plasmas in JET deuterium–tritium (D–T) discharges, the closest experiment to reactor-like operation. A set of nonlinear simulations are performed with the gyro-fluid FAR3d code to reproduce the FI induced activity and energetic particle (EP) transport observed in the discharge 99896 by multiple EP populations. Well validated simulations with JET D–T diagnostics show that Toroidal Alfvén eigenmodes (TAEs) and fish-bone are destabilized by ICRH accelerated passing D and trapped H ions, respectively. Multiple EP simulations show important nonlinear couplings between EP species, leading to a strong effect on the alpha particle confinement even in the alpha particles do not destabilize EP modes. Simulations including trapped H and alpha particles indicate fish-bones may induce alpha particle losses up to 3 % . The situation is different with respect to TAEs, which have a smaller impact on the alpha particle transport, leading to negligible losses. In addition, the generation of shear flows during the saturation phase of TAE and fish-bones is observed in the simulations. Shear flows induced by TAEs in the inner-middle plasma region are almost two times larger compared to the shear flows caused by the fish-bone in the inner plasma region. Shear flow generation by AE/fish-bones may have an important impact in the thermal plasma and alpha particle confinement of devices as ITER and JT60SA. Consequently, nonlinear effects in multiple EP populations must be considered in the analysis of EP transport. It is shown that this is a fundamental result that has to be considered to be properly evaluate fusion power in reactor relevant plasmas.

Investigating long-duration plasma operation with the international multi-machine CICLOP database

Xavier L Litaudon, Ernesto A Lerche, Olaf Grulke, Christopher Thomas Holcomb, Juan Huang, Marcin Jakubowski, Hyun-Seok Kim, Pierre Manas, Tomohiro Morisaki, Francesca Turco, et al.

IRFM, Max-Planck-Institut für Plasmaphysik, Chinese Academy of Sciences, General Atomics, Culham Science Centre

Combined high-fusion performance and long-pulse operation is one of the key integration challenges for fusion energy development in magnetic devices. Addressing these challenges requires an integrated vision of physics and engineering aspects with the purpose of simultaneously increasing time duration and fusion performance. Since the previous 2023 IAEA Fusion Energy Conference, significant progresses have been made in tokamaks and stellarators including very recent achievement in duration and/or performance. These progresses are reviewed by analyzing the experimental data provided by 10 tokamaks and two stellarators. The published database [Litaudon X. et al 2024 Nucl. Fusion 64 015001], which initially included data up to January 2022, has been significantly updated for the 2025 IAEA Fusion Energy Conference to incorporate the latest 2023-2025 experiments (up to May 2025) including recent records performance with new entries provided by DIII-D, EAST, JET, KSTAR, WEST, and W7-X. The update dataset has been gathered and coordination have been provided by the IEA-IAEA international CICLOP group (Coordination on International Challenges on Long duration OPeration). An overview of the recent progress toward long pulse operation analysing the CICLOP database is provided in this publication.

Interaction between locked modes and plasma rotation during error field identification experiments

Alessandra Tonel, Lidia Piron, Paolo Zanca, David Terranova, Ephrem Delabie, Krassimir K. K Kirov, Morten Lennholm, Sheena Menmuir, Piero Martin

Acciaierie Venete SpA, University of Padova, UKAEA, CCFE, Oak Ridge

The interplay between externally induced locked modes and the plasma toroidal rotation is studied in JET L-mode plasmas, through the analysis of shots in which the non-disruptive compass scan technique [Piron L. et al. Nuclear Fusion 64 (2024) 066029] was performed. In these experiments, an external magnetic field perturbation was applied up to the onset of a locked mode, with toroidal mode number n = 1, at constant plasma density. In Ohmic plasmas, during the execution of the compass scan, it is observed that the toroidal rotation brakes in a wide range of the core. In the case of Neutral Beam Injection (NBI)-heated shots, the rotation braking is significantly reduced. The experimental analyses have been interpreted by the RFXlocking code adapted to the JET tokamak [Zanca P. et al. Nuclear Fusion 55 (2015) 043020], which also allowed to investigate the roles of the electromagnetic force and of the neoclassical toroidal viscosity, in the rotation braking phenomenon. Plasma rotation has been analyzed also during a density variation in the absence of external magnetic field perturbations, highlighting that a profile transition occurs in the core.

Experimental observation and integrated modelling of proton-beryllium fusion in He and D plasmas at JET

Žiga Štancar, Jacob Eriksson, James Oliver, Vasily Kiptily, Sean Conroy, Aljaz Cufar, Anders Hjalmarsson, Yevgen Kazakov, Zamir Ghani, Marina Gorelenkova, et al.

United Kingdom Atomic Energy Authority, Uppsala University, Jožef Stefan Institute, Ecole Royale Militaire, Princeton Plasma Physics Laboratory

Validated integrated modelling of JET ITER-like wall experiments in which fusion performance is driven by reactions between fast ions and intrinsically present metal wall impurities is presented. A steady-state L-mode plasma with dominant proton-beryllium fusion and neutron yields of up to ≈ 6·10 13 s -1 is developed in He and D, via radiofrequency heating of a H minority. The fusion drive is unambiguously confirmed by the neutral particle analyser, fast ion loss detector, and γ-ray diagnostics. Experiments are analysed via an integrated modelling framework, developed to model the two-stage proton beryllium-fusion chain and produce high-fidelity fusion product source terms. The modelling chain comprises TRANSP and JETTO for plasma core modelling, LOCUST for full orbit product tracking and collisional slowing-down, DRESS to resolve two- and three-body fusion kinematics, and MCNP for neutron transport calculations. Modelling shows that the primary 9 Be(p,n) 9 B reaction is the dominant neutron emitter at naturally present concentrations of beryllium in these experiments. The yield contribution of secondary reactions between fusion products and beryllium, 9 Be(d,n) 10 B and 9 Be(α,n) 12 C, is found to be negligible. The proton-deuteron knock-on effect in D plasmas is modelled, which is calculated to contribute ≈ 25 % to the total neutron yield. For both He and D discharges the total computed neutron rates match fission chamber measurements within the combined experimental and computational uncertainty, with an average discrepancy of ≈ ± 20 %. Realistic proton-beryllium neutron sources are propagated through JET's MCNP neutron transport model which shows that 235 U fission chambers' response is sensitive to p-Be source changes, with up to ≈ 10 % variation compared to a D-D neutron source. We show that the high-energy tail of the fast proton minority can be studied with multi-foil neutron activation. The framework is also applied to the study of interactions between fast protons and boron impurities, of relevance to ITER. We calculate that in JET conditions a significant alpha source with DT-like energies could be generated through 11 B(p,α)2α, and detected via γ-emission in secondary interactions between fast alphas and boron. The work represents an important step towards validating predictive integrated modelling capabilities for non-standard fusion reactions.

Integrated modelling simulations of Ohmic and L-mode JET discharges in H, D and T using JETTO-TGLF

Harry George Dudding, Francis J Casson, David Dickinson, Colin M Roach, Bhavin S Patel, Tom W Bache, Ephrem Delabie, Costanza F Maggi, Pablo Rodriguez-Fernandez, Maria Filomena Ferreira Nave

UKAEA, University of York, Oak Ridge National Laboratory, MIT Plasma Science and Fusion Center, Universidade de Lisboa

The ability to capture the isotope mass scaling of core confinement seen in experiment is validated with JETTO-TGLF for low power JET-ILW discharges across H, D and T. The cases analysed include Ohmic discharges spanning the linear and saturated Ohmic confinement regimes as well as a trio of L-modes. The TGLF saturation rules SAT1-SAT3 are seen to predict a similar isotope scaling across both the ITG- and TEM-dominated discharges simulated, despite for the latter case the inclusion of the TEM branch of SAT3. The models demonstrate good agreement with experiment for the scaling between D and T plasmas, however a discrepancy is observed for H in the ITG-dominated discharges of higher density, as well as a systematic overprediction of the confinement time on the order of 20% in most cases. A retuned version of the SAT3 model, which was fit to better recreate fluxes close to the transport threshold, is seen to improve the magnitude of confinement predictions across all shots owing to an increased transport stiffness. This retuning was not seen to influence the confinement isotope scaling however, and possible transport mechanisms responsible for the continued discrepancy of higher density Ohmic and L-mode discharges in H are discussed.

Dimensional isotope scaling of heat and particle transport between JET deuterium and tritium L-mode plasmas

T. Tala, A. Mariani, A.E. Järvinen, A. Salmi, F. Albert, I.S. Carvalho, A. Chomiczewska, E. Delabie, J. Ferreira, W. Gromelski, et al.

UKAEA, VTT, CNR, IPPLM, Aalto University

The dimensionally matched deuterium–tritium pulse pair under JET L-mode conditions showed 13%–16% improvement in the energy confinement time in favour of the tritium pulse. This favourable isotope scaling can be seen clearly in the effective diffusion coefficients throughout the radius. The isotope scaling originates dominantly from the electron heat transport channel and from the edge part of the plasma. The phase and amplitude profiles in response to the gas puff modulation robustly show that there is no room for a large isotope scaling in the particle transport channel in the core plasma at ρ tor ⩽ 0.95 . This can also be seen in the derived particle transport coefficients between the deuterium and tritium pulses. EDGE2D-EIRENE simulations found that the radial ionisation profiles are very similar between the dimensionally matched deuterium and tritium identity pulses. A similar deviation from the gyro-Bohm scaling, i.e. strong isotope scaling favouring tritium in heat transport was found with gyrokinetic simulations in the edge at ρ tor = 0.95 under the JET L-mode conditions. The strong edge isotope scaling favouring tritium is consistent with the experimental observation. This edge isotope effect ρ tor = 0.95 in the GENE simulations is also much larger than found in the core plasma ρ tor = 0.6 when comparing similarly deuterium and tritium simulation results. Both the experimental results and the GENE simulations suggest that the isotope mass scaling is a nonlinear function of the isotope mass itself, being significantly stronger between deuterium and tritium than between hydrogen and deuterium, at least in JET L-mode conditions.

Heating D ions to optimal D–T fusion energies in JET-ILW

E. Lerche, M. Maslov, P.H. Jacquet, I. Monakhov, D. King, D. Keeling, C.D. Challis, D. Van Eester, P. Mantica, C. Maggi, et al.

Culham Campus, ERM/KMS, Institute of Plasma Science and Technology, IRFM, Consorzio RFX ISTP-CNR

In JET-ILW, beam-target reactions contribute to a large fraction of the fusion power generated in deuterium–tritium (D–T) plasmas, with core ion temperatures of 10–12 keV and large neutral-beam injection (NBI) power. Previous modelling done in preparation for the recent D–T campaigns in JET have shown that injecting D beam ions with energies of ∼120 keV in T–rich plasmas produces larger 14 MeV fusion yield than in 50:50 D:T plasmas, but such scenario had never been tested in past D–T experiments. In addition, the simulations showed that fundamental ion cyclotron resonance heating (ICRH) of the D ions can significantly boost the net fusion reactivity, since both the D-bulk ions and the fast D-beam ions are accelerated to energy ranges that are optimal for the D–T reactions to take place. In the last JET D–T campaigns (DTE2 and DTE3), dedicated experiments confirmed—for the first time—the improved fusion performance of T-rich plasmas with high D-NBI power and highlighted the key impact of fundamental D ICRH on the fusion performance. This new scenario led to the world-wide D–T fusion energy record ever achieved in a fusion device and allowed to sustain more than 12 MW of fusion power averaged over 5 s. The main results of these unprecedented experiments will be presented and the NBI + ICRF physics responsible for the high fusion performance achieved will be highlighted through numerical modelling.