Recent Publications

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.

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.

Initial observations in X-point target divertor discharges on MAST-U

Nicola Lonigro, Kevin Verhaegh, James R Harrison, Bruce Lipschultz, Christopher Bowman, Fabio Federici, Jack Flanagan, Daniel Greenhouse, David Moulton, Peter Ryan, et al.

Culham Centre for Fusion Energy, United Kingdom Atomic Energy Authority, University of York, Eindhoven University of Technology, ORNL

The first high-power (≥ 3 MW) H-mode experiments using a double-null X-point-target (XPT) divertor configuration have been performed on MAST-U. The XPT geometry is obtained by combining a large strike point radius, similar to the Super-X divertor (SXD), with an additional X-point near the separatrix in the baffled outer divertor chambers and leads to additional exhaust benefits over the SXD. The broader electron density profile near the secondary X-point leads to additional plasma-neutral interactions, evidenced by a broader hydrogenic emission profile, and resulting in larger power and ion sinks. The increase in plasma-neutral interactions also leads to lower target electron temperatures and heat fluxes. These benefits appear to extend to transients, and preliminary evidence of improved ELM buffering in the XPT is presented. These results showcase how multiple alternative divertor configuration strategies can be combined to improve momentum, power, and particle losses, which may be required for the challenging exhaust conditions of future reactors.

On the transition to large fluxes and access to second stability in gyrokinetic simulations of electromagnetic turbulence in STEP

Daniel Kennedy, Yujia Zhang, Toby Adkins, Plamen Ivanov, Francis Casson, Harry Dudding, Bhavin Patel, Colin Roach, Howard Wilson

United Kingdom Atomic Energy Authority, PPPL, UK Industrial Fusion Solutions Ltd

This work investigates the nonlinear transition to large heat fluxes observed in local gyrokinetic simulations of electromagnetic turbulence in STEP. Using the stress-balance framework of Zhang et al. (arXiv:2606.04616, arXiv:2607.11789), we confirm that the onset of extreme transport correlates with a critical value of $q^{2}β_{e}$, where $q$ is the safety factor and $β_{e}$ is the ratio of electron thermal pressure to magnetic pressure, and relate this to a limit on the poloidal beta $β_{\mathrm{pol}}$. Crucially, this critical value lies below any relevant linear stability limit in the ($q$, $β_{e}$) space (e.g., the onset of ideal or kinetic ballooning modes). Using an extensive set of nonlinear gyrokinetic simulations, we demonstrate that the transition to large fluxes in STEP is governed by a balance between the electrostatic and magnetic-flutter stresses. We argue, and also show numerically, that larger-major-radius tokamaks reach the electromagnetic non-zonal regime at lower $β_{e}$, making this MHD-controlled saturation limit more accessible in reactor-scale devices than in small spherical tokamaks. We also demonstrate that access to a second-stable regime enables re-saturation at larger values of $β^{\prime}$. We further show that the ideal ballooning mode (IBM) threshold serves as a useful proxy for delineating this second-stable region and also as a qualitative guide for the onset of large fluxes. These results provide a predictive framework for identifying no-go zone predictions from local gyrokinetics and offer new insight into the electromagnetic saturation physics relevant to STEP and other high-$β_{e}$ devices.

First experimental realization of robust negative triangularity plasma control in a spherical tokamak

Andrey Lvovskiy, Charles Vincent, Himank Anand, Anders S Welander, Sam Blackmore, Martin Kochan, Graham McArdle, Scott Alan Silburn, Andrew Oakleigh Nelson

United Kingdom Atomic Energy Authority, General Atomics, Columbia University

In this work, we present the experimental realization of a plasma with a steady negative triangularity in a spherical tokamak (MAST-U) for the first time. An average triangularity of -0.1 was maintained for 100 ms in a double-null plasma with a plasma current of 600 kA, a neutral beam injected power of 3.2 MW, a normalized β of 2, and an elongation of 2 on the MAST-U spherical tokamak. Despite many constraints, this was made possible due to the development of a dedicated plasma shape control scheme and the validation and assessment of magnetic shape controllers in simulations. This effort lays the foundation for physics exploitation of the negative triangularity plasma in a spherical tokamak.

Space structure of the EGAM modes in TCV, experimental observations and modeling

Mykola Dreval, Alessandro Biancalani, Thomas Hayward-Schneider, Alexey Mishchenko, Alexander N Karpushov, Anton Jansen van Vuuren, Umar Ahmed Sheikh, Didier Gossard, Sergei E Sharapov, Baruch Rofman, et al.

Ecole Polytechnique Fédérale de Lausanne (EPFL), Léonard de Vinci Pôle Universitaire, Max-Planck-Institut für Plasmaphysik, Kharkov Institute of Physics and Technology, UKAEA

The complex spatial structure of EGAMs has been recently observed experimentally in the TCV tokamak [M.B. Dreval et al., 2025 Nucl. Fusion 65 016037]. In the present work, we model the spatial structure of EGAM modes in the TCV equilibrium using a realistic fast ion distribution function, implemented in the gyrokinetic particle-in-cell code ORB5. For a peaked radial profile of fast ions, the EGAM spatial structure coincides with that of the conventional GAM, characterized by an n/m=0/0 plasma potential perturbation and an m=1 standing density perturbation, where the amplitude of the density oscillations is proportional to the sine of the poloidal angle. In contrast, for a hollow fast-ion radial profile and a marginally stable mode, our simulations reproduce a complex EGAM spatial structure similar to that observed experimentally in TCV, with two coexisting density fluctuation frequencies at different radial locations.

Activation analysis on diagnostic windows and coating materials for HCPB and WCLL blankets in EU DEMO

Sabahattin Akbas, Barbara Bieńkowska, Ewa Łaszyńska, Jakub Piotr Włodarczyk, Matthew Lukacs, Sandrine Rosanvallon, Joelle Elbez-Uzan

Institute of Plasma Physics and Laser Microfusion, EUROfusion, CEA, AGH University of Krakow, UKAEA

Plasma diagnostics and reactor control systems in future fusion power plants, such as DEMO, will rely on optical windows to monitor key plasma characteristics under intense irradiation conditions. Selecting suitable window and coating materials such as quartz, fused silica, sapphire, HfO₂, and MgF₂ is therefore critical to ensuring component reliability and safety. This study investigates these candidate materials’ activation calculations in the DEMO environment. Using the MCNP code, neutron spectra have been calculated at window-relevant locations in the outboard equatorial port and upper port limiters, considering both Helium-Cooled Pebble Bed and Water-Cooled Lithium Lead breeding blankets. Activation analyses have been subsequently performed with the FISPACT-II inventory code to evaluate the activity, decay heat, contact dose rates, and dominant contributing nuclides under the initial DEMO irradiation scenario. The results provide insights into neutron irradiation effects relevant to the activation performance of window materials and coatings, and contribute valuable input to component design and safety evaluations within the EUROfusion Safety & Environment Work Package framework.

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.

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.

Real-time observation of toroidal current redistributions induced by three-dimensional MHD phenomena triggering vertical displacement events in tokamak plasmas

Matthew Tobin, Steve A Sabbagh, Veronika Zamkovska, Guillermo Bustos Ramirez, Hankyu Lee, Joseph R Jepson, Juan Riquezes, Frederick C Sheehan, Grant A Tillinghast, Keith Erickson, et al.

Columbia University, Korea Institute of Fusion Energy, Culham Centre for Fusion Energy, Princeton Plasma Physics Laboratory, UKAEA

Three-dimensional MHD instabilities, including edge-localized modes (ELMs) and internal reconnection events (IREs), have been observed to precipitate loss of vertical stability in tokamak plasmas, resulting in vertical displacement events (VDEs). This vertical destabilization can occur due to toroidal current redistributions and/or shape changes resulting from these phenomena. Using a recently introduced method for rapidly reconstructing the two-dimensional toroidal plasma current density profile in real-time, results are presented that demonstrate the specific current distribution changes that occur during ELMs (on KSTAR) and IREs (on MAST-U) that lead to loss of vertical control. The method most efficiently reconstructs the toroidal current density profile by doing so on a basis of principal components of historical profiles. These principal components isolate dominant current profile dynamics, improving interpretability, increasing speed, and reducing dimensionality of the profile computation. On KSTAR, this computation is executed in the real-time plasma control system at a rate of 10 kHz (limited by available CPU cycle times), allowing the current profile evolution to be assessed at several times over the course of each ELM event. Further, by incorporating the reconstructions into a novel vertical stability metric, the contribution of specific current profile dynamics to the loss of vertical stability can be assessed in real-time for VDE avoidance and improved understanding of the causal relationship between three-dimensional MHD phenomena and VDEs. The success of this method in approximating toroidal current density profiles from kinetic equilibrium reconstructions is also presented ($R^2=0.990$), along with its capability to produce other equilibrium quantities of interest in real-time at high time resolution.

Effect of neutron irradiation swelling on monoblock fracture in the DEMO reactor

M. Bruno, G. Cricrì, N. Mantel, J.H. You, R. Citarella

University of Napoli Federico II, United Kingdom Atomic Energy Authority (UKAEA), Max Planck Institute for Plasma Physics, University of Salerno

Neutronics, radiolysis and OSCAR-Fusion analysis for the design of a flow loop for Activated Corrosion Products studies

S. Noce, G. Bailey, L. Butt, Y.-L. Chiu, A. Colangeli, F. Dacquait, M. Damiano, D. Flammini, N. Fonnesu, M.R. Gilbert, et al.

ENEA, UKAEA, The University of Birmingham, CEA, University of Rome “Tor Vergata”

Non-inductive high-performance discharges on TCV on the path to steady state

S. Coda, C. Piron, I. Voitsekhovitch, M. Agostini, F. Auriemma, L. Cordaro, A. Mele, M. Podestà, S. Garavaglia, A. Jardin, et al.

Consorzio RFX, Ecole Polytechnique Fédérale de Lausanne, Istituto per la Scienza e la Tecnologia dei Plasmi, CNR, ENEA, UKAEA

An extended experimental effort is underway on the TCV tokamak to develop scenarios compatible with long-pulse operation, featuring mostly non-inductively driven current—preferably with a large fraction of bootstrap current. A closely related goal is to achieve good plasma performance, typically measured through the normalized beta β N . This work is part of a broader endeavor involving several European tokamaks, under the auspices of the Tokamak Exploitation Work Package (WPTE) of EUROfusion, and aimed in part at preparing advanced scenarios for the new JT-60SA tokamak, which is the largest such device ever operated and has these scenarios at the core of its mission. This paper reports on the encouraging progress achieved in the last campaign, featuring an extensive set of discharges sustained over multiple current relaxation times ( T pulse ≫ τ R ) with zero flux contribution from the central solenoid (CS), and approaching stationary conditions with β N ∼ 2 and ion temperature ( T i ) rising towards the same order of magnitude as the electron temperature ( T e ). Auxiliary power currently appears to be a key limitation. With increased heating being added in 2027, there is now a realistic prospect of TCV reaching a fully stationary, high- β N , fully non-inductive neutral-beam injection-heated scenario. In the process of exploring the boundaries of this scenario, the hot-electron ( T e ≫ T i ) internal-transport-barrier (ITB) regime was also revisited and temperatures of 12 keV were recorded (a record for TCV non-inductive discharges). Additionally, a fully CS-free current ramp-up, starting only 30 ms after breakdown and displaying robustly negative central magnetic shear, has also been demonstrated, with a smooth continuation into the flat-top, non-inductive, advanced-scenario phase. This scenario, which is accompanied by an electron ITB of varying strength, is also a promising step towards a possible spherical-tokamak power plant. Finally, central-solenoid-free operation in the X -point target divertor configuration has been achieved, with a view to attempting detachment in a closed divertor geometry.

The FreeGSNKE Pulse Design Tool (FPDT): a computational framework for evolutive plasma scenario and control design

Kamran Pentland, Nicola C. Amorisco, Alasdair Ross, Pedro Cavestany, Timothy Nunn, Adriano Agnello, George K Holt, Graham McArdle, Charles Vincent, James Buchanan, et al.

United Kingdom Atomic Energy Authority, STFC Hartree Centre

We present the FreeGSNKE Pulse Design Tool (FPDT), an open-source, Python-based computational framework that enables in silico testing and predictive design of tokamak plasma scenarios and control strategies. The FPDT couples the FreeGSNKE evolutive equilibrium solver with a virtual Plasma Control System (PCS) containing modular and customisable controllers. Given a set of user-defined waveforms and control parameters, the virtual PCS uses feedback and feedforward control to modulate plasma current, position, and shape, while adhering to machine safety limits on poloidal field coil currents and voltages. The resulting framework allows simulation of the controlled dynamic evolution of plasma equilibria, along with the currents in both active poloidal field coils and passive conducting structures, under the assumption of axisymmetry. The FPDT can be used to develop plasma scenarios, test control schemes, calibrate control parameters, and perform uncertainty quantification studies, thereby reducing iterative and expensive experimental testing on a physical tokamak. The FPDT is machine-agnostic and can be customised to implement different control algorithms tailored to the specific tokamak of interest. Here, we outline the overall framework and validate its performance on plasma discharges on the MAST Upgrade tokamak in the `flat-top' phase. We demonstrate excellent quantitative agreement between the FPDT simulations, the desired control waveforms, and the experimental shot data. With this extension to the FreeGSNKE open-source suite of codes we aim to encourage more reproducible and collaborative research in plasma modelling and control.

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.

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.

Towards digital twins of fusion systems

F. Jenko, J. Ball, D. Borodin, C. Bourdelle, G. Ciraolo, J.E. Cook, J.M. García-Regaña, T. Görler, M. Hoelzl, F. Imbeaux, et al.

Max Planck Institute for Plasma Physics, CEA, Ecole Polytechnique Fédérale de Lausanne (EPFL), Forschungszentrum Jülich GmbH, United Kingdom Atomic Energy Authority

Bridging the gap to next-step devices—while saving valuable time and resources—requires more than semi-empirical models, which struggle to predict plasma behavior in unexplored parameter regimes. Instead, validated simulation tools are essential, leveraging high-fidelity exascale computing and multi-fidelity models, including AI-based surrogates. To address these challenges, the ‘EUROfusion Theory and Advanced Simulation Coordination (E-TASC)’ initiative was launched in 2021. It includes 15 TSVV (Theory, Simulation, Verification, and Validation) projects supported by five Advanced Computing Hubs. This ‘team of teams’ has made substantial progress toward developing digital twins of fusion systems, with key scientific achievements to be presented in the paper. This includes the following topical areas: core performance in burning plasmas, magnetohydrodynamic transients, L–H transitions and ELM-free regimes, plasma exhaust, and plasma–wall interactions—with applications to both tokamaks and stellarators.

Axisymmetric global Alfvén eigenmodes in the TCV tokamak

M. Dreval, S.E. Sharapov, H.J.C. Oliver, M. Fitzgerald, A.N. Karpushov, A. Jansen van Vuuren, J. Poley, M. Podesta, F. Porcelli

Ecole Polytechnique Fédérale de Lausanne (EPFL), UKAEA, Kharkov Institute of Physics and Technology, Polytechnic University of Turin

Global Alfvén eigenmodes (GAEs) with toroidal mode number n = 0 (i.e. axisymmetric) have been observed in the toroidicity-induced, ellipticity-induced, and above non-circularity-induced frequency ranges in the TCV tokamak. Observation of n = 0 GAEs at multiple frequencies, caused by the periodic structure of the Alfvén continuum in frequency, demonstrates the fundamental nature of these modes. A radial splitting of the n = 0 GAEs has been predicted by linear MHD calculation. This calculation is consistent with the recently observed radial splitting of GAEs in the sub-cyclotron frequency range. Linear MHD codes were used to compute the n = 0 Alfvén continuum and the corresponding eigenmode structures. The modeling confirms that the n = 0 GAEs are located mainly below the minima of the Alfvén continuum, although some modes are observed above the continuum maxima, similar to the sub-cyclotron-frequency GAEs, for which modes above the continuum maxima have also been reported. The n = 0 GAEs have been observed in a variety of discharge types, including low- and high-density plasmas, positive- and negative-triangularity configurations, and discharges with neutral beam injection in both co-current and counter-current directions. A key factor for the appearance of n = 0 GAEs is a positive gradient in the particle energy distribution function, ∂ f /∂ E > 0 (bump-on-tail), which has been confirmed by TRANSP calculations for all discharges.

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.