Recent Publications

Sep 25

On the relationship between the H-mode separatrix density and engineering parameters across multiple tokamaks: physics-based models, regression, and extrapolations to next-step devices

Davide Silvagni, Ondřej Grover, Adriano Stagni, Jerry W Hughes, Marco Andrés Miller, Bartosz Lomanowski, L. Balbinot, Guido Ciraolo, Wouter Dekeyser, Michael G Dunne, et al.

Nuclear Fusion·Sep 25, 2026Plasma & ConfinementAI, Modeling & Simulation

The electron density at the separatrix (n e,sep ) plays a central role in balancing energy confinement, detachment achievement, and ELM suppression in tokamaks, thereby influencing core-edge integration. To study what determines this key parameter, a database of H-mode separatrix density measurements from the Alcator C-Mod, ASDEX Upgrade, and JET tokamaks has been assembled using a consistent analysis method across all devices. This dataset is used to assess the validity of a physics-based predictive model and to derive a regression scaling expression for n e,sep , both requiring only engineering parameters as input. The theory-based expression is obtained by coupling two-point model equations with simple geometrical relations, and successfully reproduces experimental measurements across all three devices, with the exception of a common multiplicative constant. The regression confirms similar parameter dependencies, revealing a positive dependence on divertor neutral pressure and the ratio of the power entering the scrape-off layer to the major radius, a negative dependence on the toroidal magnetic field and minor radius, and no significant dependence on the plasma current. Both the resulting scaling and theory-based expressions predict n e,sep within a factor of 1.5 across the three machines, and provide projections to next-step devices (ITER, SPARC, DTT, JT-60SA and COMPASS-U) that are in agreement with available SOLPS simulations.

Consorzio RFX·Max Planck Institute for Plasma Physics·Culham Centre for Fusion Energy·Massachusetts Institute of Technology·Oak Ridge National Laboratory

Sep 23

Alfvénic high-frequency oscillations at the pedestal of JET plasmas

Leonor Roque, Paulo Rodrigues, Emilia R. Solano, JET contributors, The Eurofusion Tokamak Exploitation Team

arXiv (physics.plasm-ph)·Sep 23, 2026Plasma & ConfinementControl & DiagnosticsAI, Modeling & Simulation

Long-lived ($\sim 10$ s) high-frequency oscillations (HFOs, $50-450$ kHz) near the plasma edge have been reported and experimentally described in L-H transition studies at JET and AUG. In this work, we show that these HFOs are a general phenomenon observed in various plasma scenarios and compositions (H$^1$, D, D-He$^3$, D-T) under different heating schemes, including pure Ohmic, ICRH and NBI. We demonstrate that dominant axisymmetric ($n=0$) HFOs are Global Alfvén eigenmodes (GAEs) tied to the shear-Alfvén continuum (SAC) minima arising at the plasma edge due to the sharp decrease of the density and increase of the safety factor. This hypothesis is corroborated by the remarkable agreement found between the measured frequencies of HFOs and the SAC minima computed by the ideal MHD code CSMISH for a comprehensive set of JET pulses. This result, along with the fact that HFOs are observed over long time windows and across a variety of plasma scenarios, makes them convenient MHD constraints for accurate equilibrium reconstruction near the edge. In view of this pragmatic application, we derive a first-order analytic expression for the two lowest coupled branches of the $n=0$ SAC, disclosing their dependence (and, consequently, that of the HFOs) on the plasma density, safety factor, and elongation profiles. In addition, we discuss the nature of $n\neq 0$ HFOs observed along with the dominant $n=0$ HFOs.

Sep 15

Improved n=1 empirical error field penetration threshold scaling with Ohmic and L-mode conventional tokamak plasma discharges

Evan Maxwell Bursch, Jong-Kyu Park, Nikolas C. Logan, Feiyue Mao, Nengchao Wang, Carl Friedrich Benedikt Zimmermann, Richard J Buttery, Carlos Paz-Soldan, Matthew Pharr, Lidia Piron, et al.

Plasma Physics and Controlled Fusion·Sep 15, 2026Plasma & ConfinementFusion Plant Engineering

This paper presents an updated n=1 error field penetration threshold scaling, which increases fit quality compared to previous error field scaling laws, is produced from an expanded database, and exhibits reduced uncertainty in projections to future tokamaks. It improves confidence in tokamak engineering tolerances, which are a significant driver of cost and time constraints on device construction. We add J-TEXT data, new JET data, and create the scaling using only conventional tokamak Ohmic and L-mode experiments. Since H-mode plasmas are more resilient to error field penetration, this scaling predicts what is likely the most dangerous regime of error field penetration for new tokamak designs. These decisions improve confidence in the error field penetration threshold scaling and its application in the construction and design decisions of any future conventional tokamak or fusion pilot plant.

Huazhong University of Science and Technology ·General Atomics

Sep 14

A new model for runaway electron transport in chaotic magnetic geometries

Daniel Janosi, Anikó Horváth, Hannes Bergström, Matthias Hölzl, Gergely Papp, Gábor Veres, Gergo I Pokol, György Károlyi

Plasma Physics and Controlled Fusion·Sep 14, 2026Plasma & ConfinementAI, Modeling & Simulation

The transport of runaway electrons (RE) in chaotic 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.

Max Planck Institute for Plasma Physics

Sep 9

JET neutron emissivity reconstruction using the Minimum Fisher Information method for 1 ms temporal resolution

Katarzyna Mikszuta-Michalik, Daniele Marocco, Basilio Esposito, Marco Riva, Gianluca Pucella

Plasma Physics and Controlled Fusion·Sep 9, 2026Plasma & ConfinementControl & DiagnosticsAI, Modeling & Simulation

A tomography code based on the Minimum Fisher Regularisation method with a geometry description based on the field of view has been applied to reconstruct the neutron emissivity profiles from measurements performed in 2021 during the second JET deuterium-tritium campaign (DTE2). The Neutron Profile Monitor Upgrade installed at JET offers a unique opportunity for investigating the neutron emissivity in a full poloidal cross-section with unprecedented time resolution (~1 ms), thanks to the availability of digital data reprocessing and the high neutron emission that enables milisecond line-integrated raw data with low statistical error. Measurements of 14.1 MeV neutrons provided by the Bicron BC418 plastic scintillators installed in the JET neutron camera have been used.The analysis focuses on the effect of sawtooth crashes on the neutron emission profiles. Tomography results were compared with 1D reconstructions using two different methods and 10 ms time resolution. The use of the neutron camera data sampled at 1 ms enables the observation of hollowing of the neutron emissivity profiles during the sawtooth crash and their subsequent flattening.

Italian National Agency for New Technologies, Energy, and Sustainable Economic Development·Institute of Plasma Physics and Laser Microfusion

Sep 4

Neutron measurements with VERDI detectors in the long term irradiation station at JET tokamak during Deuterium-Tritium operation

Ion Evangelos Evangelos Stamatelatos, Marilia Savva, Theodora Vasilopoulou, K Mergia, S Messoloras, Steven Bradnam, Chantal Shand, Lee William Packer, Zamir Ghani, Paola Batistoni, et al.

Plasma Physics and Controlled Fusion·Sep 4, 2026Control & DiagnosticsBlankets & Neutronics

The VERDI detector is a passive neutron detector using the multi-foil activation technique to measure neutron fluence in extreme fusion conditions. It features a low-activation capsule that contains a defined concentration of metallic elements. The robustness of the detector is ensured by the capsule material, while neutron detection relies on activation of the metallic elements. Post-irradiation gamma spectrometry combined with computational unfolding enables reconstruction of the neutron fluence and energy spectrum. This study reviews the development of the VERDI detector and reports the first deployment of VERDI detectors in an operational Deuterium-Tritium (D-T) fusion environment in the Long-Term Irradiation Station (LTIS) of JET tokamak during the DTE2 campaign, featuring a neutron spectrum representative of future fusion devices such as ITER and DEMO. The results provide benchmarks for validating neutronic simulations and nuclear data, supporting the design optimization and safety assessment of future fusion power plants.

Italian National Agency for New Technologies, Energy, and Sustainable Economic Development·Demokritos·United Kingdom Atomic Energy Authority

Sep 1

Investigation of impurity behaviour in three-ion ICRF scenarios in H-D and D-T plasmas at JET

Agata Chomiczewska, Yevgen Kazakov, Wojciech Gromelski, Irena Ivanova-Stanik, Agnieszka Jardin, Axel Jardin, Ewa Kowalska-Strzęciwilk, Kerry Lawson, Evie Litherland-Smith, Andy Meigs, et al.

Nuclear Fusion·Sep 1, 2026Plasma & ConfinementControl & DiagnosticsHeating & Current Drive

This study investigates impurity behaviour during ion cyclotron resonance heating (ICRF) experiments, focusing on the application of two different three-ion heating schemes in H-D and D-T plasmas at JET. In the D-(³He)-H scenario, the phasing of the ICRF antenna straps was varied to modify the launched parallel wave number k||, enabling a systematic study of its effect on fast-ion generation, plasma dynamics and impurity transport. The results indicate dependence of impurity behaviour on antenna phasing, particularly for the nickel (Ni) in the main plasmas and for the beryllium (Be) source. Analysis of sawtooth oscillations using the symmetrised dot pattern method reveals correlations between sawtooth frequency and crash intensity, the applied ICRF power and antenna phasing. The lowest impurity levels are obtained with +90° antenna phasing, corresponding to maximised fast-ion generation. A comparative study of impurity behaviour in D-T plasmas is also presented for the three-ion T-(⁹Be)-D and hydrogen minority heating scenarios. The three-ion scheme produces the largest increases in ion temperature Ti, while hydrogen minority heating yields higher electron temperatures Te and slightly reduced impurity levels. These results suggest that impurity behaviour in three-ion ICRF scenarios depends on the chosen heating optimisation (fast-ion generation versus ion heating) and can be further controlled through appropriate selection of ICRF antenna phasing.

Ecole Royale Militaire-Koninklijke Militaire School·United Kingdom Atomic Energy Authority·Institute of Plasma Physics and Laser Microfusion

Aug 27

Impurity modelling and transport coefficient reconstruction in tokamak core plasmas

Yoon Seong Han, Junhyeok Yoon, Inwoo Song, Junghoo Hwang, H.H. Lee, Si-Woo Yoon, Jaemin Kwon, Wonho Choe

Plasma Physics and Controlled Fusion·Aug 27, 2026Plasma & ConfinementControl & DiagnosticsAI, Modeling & Simulation

The developed KAIST impurity modelling (KIM) code analyzes impurity transport in the poloidal cross-section of tokamak plasma in both prediction and reconstruction modes. The prediction mode utilizes a numerical solution of the one-dimensional radial continuity equation to simulate impurity transport based on the given plasma parameters and extends the resulting radial impurity density distribution to a two-dimensional poloidal distribution by incorporating centrifugal-force-driven asymmetry. Synthetic diagnostic data, such as radiation power distribution and spectral emissions, are generated using atomic databases for direct comparison with experimental measurements. In reconstruction mode, the code reconstructs the impurity transport coefficient profiles from the experimentally obtained impurity density evolution over time, to overcome the limitations of forward-modelling-based transport coefficient inference. The developed reconstruction algorithm is based on numerical impurity flux calculations and Bayesian techniques and was validated using six phantom impurity transport coefficient profiles from the KSTAR, JET, and ASDEX-U tokamaks. The reconstruction accuracy evaluated using the R 2 value, demonstrated good agreement (R 2 > 0.87) between the reconstructed and phantom profiles in the core regions (r/a < 0.8), even in the presence of 5% random noise. The code was applied to a stationary KSTAR H-mode discharge to demonstrate its capability in analysing experimental W transport. The reconstructed transport coefficients were compared with neoclassical predictions to assess their physical validity. The results show that the total diffusion coefficient follows a radial trend similar to the neoclassical prediction but at a higher level consistent with the expectation of turbulent transport enhancement. This trend confirms that the KIM code yields physically reasonable transport coefficients from experimental data. This study details the theoretical framework, numerical validation, and experimental efficacy of the KIM code in advancing impurity transport research.

Analysis of neutron single event effect experiment on electronics during JET DTE-3 campaigns

Martin Felix Dentan, Soilihi Moindjie, Matteo Cecchetto, Jean-Luc Autran, Ruben Garcia Alia, Richard Naish, John Waterhouse, Alan R Horton, Xavier L Litaudon, Fernanda Rimini, et al.

Plasma Physics and Controlled Fusion·Aug 27, 2026Control & DiagnosticsBlankets & Neutronics

We measured SEEs in 40 nm and 65 nm SRAMs exposed to the D–T fusion neutron environment of the JET tokamak during the DTE-3 campaign (September–October 2023), while also characterizing the neutron spectrum seen by the devices. Using consolidated JET neutron production data, the measured SEE rates show good agreement with predictions based on the measured spectra and independently determined SRAM sensitivity parameters from thermal and monoenergetic neutron tests. These results extend the validation of our spectrum-based SEE prediction methodology, previously demonstrated in a D–D fusion neutron environment in 2021, to a D–T fusion neutron field. The novelty of this work is therefore the first experimental validation of this complete prediction approach in a D–T fusion environment, using real-time neutron spectrometry and independent device sensitivity data, rather than a new SEE model. The experiments also show that a local B₄C shield reduces the bit-flip rate by absorbing thermal neutrons, and we discuss the conditions under which such shielding can improve electronics reliability in tokamak and accelerator neutron environments.

French Alternative Energies and Atomic Energy Commission·Italian National Agency for New Technologies, Energy, and Sustainable Economic Development·United Kingdom Atomic Energy Authority

Aug 25

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.

Plasma Physics and Controlled Fusion·Aug 25, 2026Plasma & ConfinementControl & Diagnostics

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.

United Kingdom Atomic Energy Authority·Max Planck Institute for Plasma Physics·Culham Centre for Fusion Energy·Consorzio RFX·Princeton Plasma Physics Laboratory

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.

Plasma Physics and Controlled Fusion·Aug 25, 2026Plasma & ConfinementControl & DiagnosticsFusion Plant Engineering

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.

University of Sevilla·Fusion for Energy·Consorzio RFX·Centre for Energy, Environmental and Technological Research

Aug 24

Impact of nitrogen injection on L-H transitions in JET with Be/W wall

Costanza F Maggi, Clarisse Bourdelle, Ephrem Delabie, Mathias Brix, Pedro Carvalho, Francis J Casson, Alex V Chankin, Nicholas Hawkes, Evie Litherland-Smith, Sheena Menmuir, et al.

Plasma Physics and Controlled Fusion·Aug 24, 2026Plasma & Confinement

L-H transition experiments in JET with Be/W wall (JET-ILW), with N2 injection into the divertor region, have revealed that the H-mode power threshold, PL-H, increases with nitrogen injection rate in the high-density branch and modifies the density at which the power threshold is minimum, ne,min. PL-H values approaching those obtained in JET with C wall are achieved for a sizeable increase in nitrogen concentration. At a given density in the high density branch of PL-H, both the total loss power (Ploss) as well as the power crossing the separatrix (Psep) at the L-H transition increase by a factor ~ 1.5 at high N2 levels. At a given line averaged density, while the edge density is similar in plasmas with and without N2 injection, the edge temperature at the L-H transition is higher in pulses with high nitrogen seeding levels and a larger shear of the edge radial electric field Er is measured. At low N concentrations, little change in PL-H is observed. Qualitative agreement is reported with Zeff impact on L-mode edge turbulence drive [1]. The enhanced L-mode edge turbulence drive with N2 seeding at higher Zeff implies that a higher PL-H is expected as, indeed, measured in experiment. It is assumed that the mean equilibrium Er×B shear is a key player for reduction of L-mode edge turbulence, leading to the L-H transition. In this framework, the L-H transition observations in JET-Be/W + N2 are interpreted by an increase in L-mode edge plasma turbulence with increased N concentration and the need for a larger stabilizing ErxB shear, thus higher Psep, to trigger the L-H transition. For future fusion reactors with scenarios with extrinsic low-Z impurity seeding for divertor heat load mitigation, our results suggest the need to predict Psep for H-mode access taking into account not only the high radiation fractions from the bulk plasma, but also the impact of low Z impurity concentration on Ploss and Psep at the L-H transition.

Max Planck Institute for Plasma Physics·United Kingdom Atomic Energy Authority·Oak Ridge National Laboratory

Aug 21

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.

Plasma Physics and Controlled Fusion·Aug 21, 2026Plasma & ConfinementMaterials & Plasma-Facing ComponentsAI, Modeling & Simulation

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.

Institute of Plasma Physics and Laser Microfusion·National Research Council·Culham Centre for Fusion Energy·United Kingdom Atomic Energy Authority

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.

Nuclear Fusion·Aug 21, 2026Plasma & ConfinementControl & DiagnosticsMaterials & Plasma-Facing Components

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.

Culham Centre for Fusion Energy·Forschungszentrum Jülich·Consorzio RFX·Centre for Energy, Environmental and Technological Research

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.

Plasma Physics and Controlled Fusion·Aug 21, 2026Materials & Plasma-Facing ComponentsBlankets & NeutronicsAI, Modeling & Simulation

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.

French Alternative Energies and Atomic Energy Commission·Culham Centre for Fusion Energy·United Kingdom Atomic Energy Authority·Institute of Plasma Physics and Laser Microfusion

Aug 19

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

Nuclear Fusion·Aug 19, 2026Plasma & ConfinementAI, Modeling & Simulation

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.

Aug 14

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.

Nuclear Fusion·Aug 14, 2026Plasma & Confinement

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.

Culham Centre for Fusion Energy·Max Planck Institute for Plasma Physics·Swiss Federal Institute of Technology Lausanne·Czech Academy of Sciences

Aug 11

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.

Nuclear Fusion·Aug 11, 2026Plasma & ConfinementControl & DiagnosticsAI, Modeling & Simulation

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.

Max Planck Institute for Plasma Physics·Consorzio RFX·Swiss Federal Institute of Technology Lausanne

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.

Nuclear Fusion·Aug 11, 2026Plasma & ConfinementMaterials & Plasma-Facing ComponentsAI, Modeling & Simulation

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.

Forschungszentrum Jülich·Consorzio RFX·United Kingdom Atomic Energy Authority·Institute of Plasma Physics and Laser Microfusion

Aug 7

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.

Nuclear Fusion·Aug 7, 2026Plasma & Confinement

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.

General Atomics·Max Planck Institute for Plasma Physics·Chinese Academy of Sciences