Recent Publications

Sep 25

Impact of magnetic drift configuration on the edge radial electric field in the TCV tokamak

S. Rienäcker, L. Vermare, P. Hennequin, C. Honoré, B. Labit, S. Coda, L. Frassinetti, B. Vincent, O. Panico, Y. Wang, et al.

arXiv (physics.plasm-ph)·Sep 25, 2026Plasma & Confinement

The edge radial electric ($E_r$) in the Tokamak à Configuration Variable (TCV) is compared in matched L-mode discharges with opposite ion magnetic drift directions (favorable versus unfavorable $B \! \times \! \nabla B$ configurations). As previously reported on the WEST and AUG tokamaks, the $E_r$ profile---measured by Doppler backscattering (DBS)---exhibits a "well" just inside the separatrix in the favorable drift case, which is absent or less pronounced in the unfavorable counterpart. This observation holds over a broad range of plasma conditions, notably also in Ohmic discharges with nearly identical edge density and temperature profiles. Density fluctuation characteristics inferred from DBS are not drastically different: Under Ohmic heating, edge fluctuation levels tend to be higher in the favorable configuration, while radial correlation lengths are similar. The edge $E_r$ difference appears uncorrelated with carbon toroidal rotation behavior. Reducing density, or increasing auxiliary heating power tends to accentuate the edge $E_r$ disparity. Plasma current has little impact on both favorable and unfavorable $E_r$ profiles---in contrast to results from WEST. Approaching the L-H transition via auxiliary heating, edge $E_r \times B$ shear and pressure grow more readily in the favorable configuration, and DBS fluctuation levels are reduced relative to the unfavorable case. Overall, our results confirm that the edge $E_r$ sensitivity to magnetic drift configuration is a robust, multi-machine phenomenon, with a plausible connection to confinement level and H-mode access.

Swiss Federal Institute of Technology Lausanne

Sep 24

Comprehensive full-f drift-kinetic and delta-f gyrokinetic simulations of a linear plasma device based on the gyro-moment approach

Jacob Emil Mencke, Paolo Ricci, Luca Da Silva

Journal of Plasma Physics·Sep 24, 2026AI, Modeling & Simulation

First of a kind comprehensive full-f drift-kinetic (DK) and delta δ $\delta$ -f gyrokinetic (GK) turbulent simulations are carried out in a linear plasma device. We self-consistently derive an electrostatic model including large-scale slowly varying DK-ordered fields coupled to small-scale rapidly fluctuating GK-ordered fields. By relying on the critical balance ordering, we show that the electrons are described by a drift-reduced Braginskii model while we rely on a Hermite–Laguerre spectral expansion for describing both the DK and GK parts of the ion distribution function. Global simulations are carried out using the parameters of the linear device LAPD, showing that the DK part of the ion distribution function is approximately a bi-Maxwellian. It is observed that the GK fields do not affect the DK fields at the physical LAPD collisionality. Only when the collisionality is reduced and the source term is amplified for the GK fluctuations, an amplification of small-scale turbulent structures is observed. The findings are supported by linear results that show that the simulations are dominated by turbulent fluctuations that are Kelvin–Helmholtz driven. Additionally, a GK Kelvin–Helmholtz-like mode is observed in the low-GK-collisionality regime which can nonlinearly drive small-scale structures.

Swiss Federal Institute of Technology Lausanne

Sep 23

Applications of a novel model-based real-time observer for electron density profile control experiments in TCV

Francesco Pastore, Olivier Sauter, Federico Felici, Daniela Kropáčková, Alessandro Balestri, Cristian Galperti, Ondrej Kudlacek, Kenneth Lee, Adriano Mele, Alessandro Pau, et al.

Nuclear Fusion·Sep 23, 2026Plasma & ConfinementControl & DiagnosticsAI, Modeling & Simulation

Real-time estimation and control of the electron plasma density profile is fundamental for monitoring and regulating particle confinement, fusion power, heating efficiency, exhaust performance, impurity concentration, and proximity to the density limit [1] in present and future tokamaks. This work presents the experimental applications of a multi-rate electron density observer [2] based on RAPDENS [3], integrated into the TCV Plasma Control System, to control the density profile in a range of plasma scenarios relevant to future fusion power plants. Three main experimental contributions are reported. First, the observer enables control of the line-averaged electron density within the last-closed flux surface (NEL LCFS ) in ohmic, nitrogen-seeded plasmas with alternative divertor geometries, decoupling upstream density from Scrape-Off Layer pickup in the interferometer signal – a limitation of the traditional control scheme. Second, local control of the central electron density below the ECH cutoff is demonstrated in L-mode plasmas with mixed ECH and NBI heating, where auxiliary-heating-induced profile peaking is treated as a disturbance to the control task. Real-time estimation and adjustment of the electron pinch velocity-to-diffusivity ratio ν/D improves the spatial accuracy of the profile reconstruction, especially in the core region. The underlying turbulent transport in this scenario is characterised via linear and non-linear gyrokinetic simulations with GENE, confirming quantitatively a TEM-dominated pumpout regime during ECH, which affects the amount of gas flux needed to sustain the target density reference. Last, simultaneous control of the edge-normalised density fraction and toroidal beta is demonstrated in high-performance H-mode plasmas (β N ≈ 2.15, f GW ≈ 0.80), yielding reproducible scenarios with a device-agnostic density metric and robust handling of interferometer fringe jumps.

Google·ITER Organization·Swiss Federal Institute of Technology Lausanne·Max Planck Institute for Plasma Physics

Sep 21

Extension of the RAPDENS Control-Oriented Model with a Scrape-Off Layer Particle Balance Model for ASDEX Upgrade and ITER

Daniela Kropáčková, Francesco Pastore, Ondrej Kudlacek, Timo Ravensbergen, Olivier Sauter, Guillermo Suarez-Lopez, Andrei Pshenov, Emiliano Fable, Davide Silvagni, Maximilian Reisner

Nuclear Fusion·Sep 21, 2026Plasma & ConfinementControl & DiagnosticsAI, Modeling & Simulation

The plasma density is a key parameter in tokamak operation, as it influences plasma performance and stability. Hence, accurate real-time estimation and control are essential. Real-time estimation of the plasma electron density profile can be maintained even in the presence of corrupted or unavailable diagnostics by employing model-based electron density observers. This work extends one of these observers, RAPDENS [1], by incorporating a heuristic scrape-off layer model capable of predicting the separatrix electron density, thereby building upon previous work that implemented a non-zero boundary condition at the separatrix [2]. Implementations for both ASDEX Upgrade (AUG) and ITER are presented. For AUG, the RAPDENS adaptation is tested using offline Extended Kalman Filter simulations of existing AUG discharges. These simulations show that RAPDENS is capable of providing a reasonable reconstruction of the electron density profile, supporting its future real-time implementation and routine use at AUG. For ITER, the implementation is based on and compared against results of a high-fidelity simulation performed with JINTRAC, the integrated modeling suite, for a start of research operation ramp-up scenario, concluding that the improved version of RAPDENS can be used for ITER density controller design.

Swiss Federal Institute of Technology Lausanne·Max Planck Institute for Plasma Physics·ITER Organization·United Kingdom Atomic Energy Authority

Sep 16

Helicon wave propagation, plasma generation and interaction with low-frequency waves in toroidal magnetic configurations

Simon P. H. Vincent, Mounir Alfazzaa, Patrick Quigley, Cyrille Sepulchre, Philippe Guittienne, Rémy Jacquier, Marcelo Baquero-Ruiz, Ivo Furno

arXiv (physics.plasm-ph)·Sep 16, 2026

Helicon waves are widely used for efficient plasma production in low-temperature devices and have recently attracted attention as a candidate for current drive in fusion plasmas. Yet experimental investigations of helicon waves in toroidal geometries, and of their interaction with plasma dynamics, remain extremely limited. In this work, we present, to our knowledge, the first detailed experimental characterization of helicon waves in a toroidal configuration. A birdcage resonant antenna operating at 13.56 MHz is used to launch helicon waves in the toroidal basic plasma physics device TORPEX, either into a pre-existing magnetron-generated plasma, or as the plasma source. Measurements are performed in pure toroidal and simple magnetized torus magnetic configurations, for both argon and hydrogen plasmas. Three-axis magnetic probe measurements enable clear identification of a dominant m=+1 helicon mode over our parameter space. The helicon amplitude is found to scale linearly with the antenna power, and decreases with the confining magnetic field amplitude. As the antenna power is increased the helicon amplitude exhibits a saturation, correlated with enhanced low-frequency fluctuations and turbulent transport. In addition, a strong interaction between helicon waves and low-frequency density fluctuations is observed, revealing a non-linear coupling between RF waves and plasma turbulence. These results provide the first detailed experimental characterization of helicon waves in a toroidal low-temperature plasma device and establish TORPEX as a unique testbed for studying toroidal helicon wave physics under controlled and well-diagnosed conditions.

Swiss Federal Institute of Technology Lausanne

Sep 15

Negative triangularity studies in view of DTT operations

Paola Mantica, Lorenzo Aucone, Alessandro Balestri, Alberto Mariani, Roberto Ambrosino, Justin Ball, A. Castaldo, Stefano Coda, Tim Happel, Joerg Hobirk, et al.

Plasma Physics and Controlled Fusion·Sep 15, 2026Plasma & ConfinementAI, Modeling & Simulation

This paper summarizes experimental and modelling work carried out across the last 5 years on Negative Triangularity (NT) scenarios in view of future DTT operations. The shapes foreseen for DTT have been tested experimentally on TCV and ASDEX Upgrade (AUG). Integrated modelling using ASTRA/TGLF and local gyrokinetic simulations using GENE have been performed on the experimental results and to predict DTT scenarios. Experiments and modelling find a stronger beneficial effect of NT in TCV than in AUG. DTT predictions are more in line with AUG results. Various mechanisms to explain this difference have been examined and are discussed. In all devices, the NT scenarios provide a viable ELM-free alternative to Positive Triangularity ELMy H-modes, with central values of pressure comparable or even higher.

Max Planck Institute for Plasma Physics·University of Milano-Bicocca·National Research Council·Swiss Federal Institute of Technology Lausanne

On energy conservation laws in the drift-reduced Braginskii model

Sergio García Herreros, Brenno de Lucca, Davide Mancini, Zeno Tecchiolli, Micol Bassanini, Paolo Ricci, Louis Stenger, Christian Theiler

arXiv (physics.plasm-ph)·Sep 15, 2026Plasma & ConfinementAI, Modeling & Simulation

A revision of the drift-reduced Braginskii model is presented, focusing on its practical implementation in numerical codes, and systematically analyzing the effect of several commonly-used approximations on energy conservation. As a practical example, the effect of the approximations is quantified in the GBS code. By dropping the most important approximations and related energy sinks, the simulation shows increased transport levels and a target heat flux with closer agreement to experimental observations.

Swiss Federal Institute of Technology Lausanne

Sep 14

Two-length spatial correlation function of turbulence in TCV

Olivier Panico, Pascale Hennequin, Sascha Rienäcker, Oleg Krutkin, Benoit Labit, Yanick Sarazin, the TCV team

arXiv (physics.plasm-ph)·Sep 14, 2026Plasma & ConfinementControl & Diagnostics

Spatial correlation functions of density fluctuations are measured in the Tokamak à Configuration Variable (TCV) using a dual-channel Doppler backscattering (DBS) diagnostic. In certain cases, the spatial correlation function exhibits two characteristic length scales. By analogy with nonlinear reduced simulations, the presence of two correlation lengths may be indicative of avalanche-like transport. The correlation functions obtained from DBS are compared with those from short-pulse reflectometry measurements and show reasonable agreement. Both short- and long-range correlations are measured in the same plasma geometry for different heating powers. Short-scale correlation lengths are found to be on the order of 3-5 Larmor radii, while large-scale correlations extend over approximately 5-15 Larmor radii. The correlations are found to decrease towards the very edge of electron cyclotron heated discharges, coinciding with a narrow Er well.

Ecole Polytechnique·Swiss Federal Institute of Technology Lausanne

Sep 2

Real-time tomography-based Bayesian inference from TCV bolometry data

Daniele Hamm, Christian Theiler, Luke Michael Simons, Basil P Duval, Umar Ahmed Sheikh

Nuclear Fusion·Sep 2, 2026Plasma & ConfinementControl & DiagnosticsAI, Modeling & Simulation

Radiated power information is crucial to diagnose and optimize the performance of fusion plasmas. Traditionally, at the TCV tokamak, radiated power analysis has only ever been possible following plasma discharge termination. However, recently, TCV bolometer data have become available in real-time. This offers the opportunity of integrating the radiated power information into the TCV plasma control system. In this work, we propose a novel real-time tomography-based Bayesian technique allowing estimation of the power radiated from user-defined regions of interest in the plasma. The real-time estimates are obtained as computationally cheap linear combinations of bolometer measurements, using pre-computed coefficients that are optimized for the specific discharge planned. This method is not, thus, trained on a set of synthetic or tomographically reconstructed emissivity profiles. We detail the derivation of the technique and show its equivalence to traditional tomographic estimates under suitable conditions. We then demonstrate that this technique enables accurate real-time estimation of the total, core, divertor and main chamber radiated power, by its application to a representative and heterogeneous set of TCV discharges. Finally, we discuss the robustness of the technique to faulty detectors, showing that simple precautions allow safe handling of many common issues. The computational routines implementing the described technique are provided as open-source code.

Swiss Federal Institute of Technology Lausanne

Aug 26

Effect of electron cyclotron waves on plasma with runaway electrons

Pavel Aleynikov, Alexander Franklin Battey, Carlos Paz-Soldan, Eric Matthias Hollmann, Andrey Lvovskiy, Claudio Marini, Daisuke Shiraki, Charles Lasnier

Nuclear Fusion·Aug 26, 2026Plasma & ConfinementControl & DiagnosticsHeating & Current Drive

Runaway electrons generated during tokamak disruptions are a major concern for the safe operation of future fusion devices. The interaction of runaway electrons with waves has been proposed as a potential mechanism for their mitigation. This study investigates the effect of electron-cyclotron (EC) waves on post-disruption plasmas containing runaway electrons (REs). O- and X-mode EC waves are routinely used for plasma heating and current drive. However, these modes do not interact directly with relativistic electrons and cannot be injected into plasmas with densities exceeding their respective cutoff densities. In contrast, the internal slow X-mode (sX) can resonate with relativistic electrons and may therefore provide a pathway for their mitigation. We report DIII-D experiments designed to access the internal slow X-mode through O--sX conversion during post-disruption RE plateaus. ECH increased the background-plasma density, doubled the loop voltage, and strongly enhanced the RE synchrotron signal, demonstrating substantial ECH--plasma coupling and increased effective dissipation of the RE channel. Although ECH produced a pronounced response consistent with enhanced RE dissipation, we could not isolate conclusive evidence of resonant sX--RE interaction. Strong heating, ionization, and impurity-redistribution effects appear to dominate the response and may mask a direct wave--particle signature. Nevertheless, the results demonstrate the potential of ECH for RE control through background-plasma modification, with O--sX access offering an additional possibility of direct resonant interaction.

General Atomics·Swiss Federal Institute of Technology Lausanne·Max Planck Institute for Plasma Physics

Fast-ion enhanced modeling of neoclassical tearing modes at NSTX and DIII-D

James Yang, Eric Fredrickson, John W Berkery, Robert John La Haye, Mario Podesta

Plasma Physics and Controlled Fusion·Aug 26, 2026Plasma & ConfinementAI, Modeling & Simulation

A new framework for the solution of modified Rutherford equation including fast ions is successfully applied to interpret the tearing mode stability of two discharges NSTX #134020 and DIII-D #135861. The simulated island width growth rates are in better agreement with the measured island growth rate when the fast ions are included. While constants are multiplied to the polarization current contribution terms for NSTX #134020, no constants are necessary to match the simulated and measured island width growth rates for DIII-D #135861. The estimated island frequencies appear to provide an explanation of the different constants used in the two discharges. The gradient scale lengths suggest that the fast ion contribution can become significant in plasmas with flat thermal ion density profile and steep fast ion density profile.

Princeton Plasma Physics Laboratory·General Atomics·Swiss Federal Institute of Technology Lausanne

Aug 25

An Inverse Grad-Shafranov Neural Network Approach to Tokamak Magnetic Control

Allen M. Wang, Adriano Mele, Cosmas Heiß, Cristian Galperti, Zander Keith, Alessandro Pau, Antoine Merle, Olivier Sauter, Daniel Gonzalez Castiñeiras, Francesco Carpanese, et al.

arXiv (physics.plasm-ph)·Aug 25, 2026Plasma & ConfinementControl & DiagnosticsAI, Modeling & Simulation

A new approach to tokamak magnetic control enabling high-precision plasma shaping and novel real-time adaptability is experimentally demonstrated on the Tokamak a Configuration Variable (TCV). The method is motivated by the insight that, under appropriate assumptions, a real-time inverse Grad-Shafranov solver approximates an optimal control policy for plasma boundary regulation. Building on this, a control architecture is developed in which classical controllers enforce operational constraints while a fast surrogate model provides a real-time inverse mapping from the desired plasma boundary to Poloidal Field Coil currents. Experimental results on TCV demonstrate improved plasma shaping with respect to the standard discharge preparation procedure --- albeit without explicit real-time shape feedback --- while enabling flexible response to asynchronous events. It is shown that a single network provides satisfactory performance across a range of plasma magnetic configurations. Real-time adaptivity is demonstrated in simulation, and partially in experiment, through adaptive strike point motion and early termination in response to a real-time trigger. These results suggest a viable path toward magnetic control architectures that reduce reliance on dense diagnostic coverage while maintaining high-accuracy plasma shaping, with potential relevance for future fusion power plant operation.

Fusionality·EUROfusion·Massachusetts Institute of Technology·Swiss Federal Institute of Technology Lausanne·Commonwealth Fusion Systems

Physics Attention Transformer Surrogate for Rapid Vertical Instability Growth Rate Prediction: Alcator C-Mod to SPARC

Arunav Kumar, Cesar Clauser, Theodore Golfinopoulos, Cristina Rea, Francesco Capersene, Dan Boyer, SPARC Team, Alcator C-Mod Team

arXiv (physics.plasm-ph)·Aug 25, 2026Plasma & ConfinementControl & DiagnosticsAI, Modeling & Simulation

In this work, we investigate rapid prediction of the dominant $n{=}0$ vertical instability growth rate in C-Mod and SPARC equilibria, where nonrigid free boundary response models are too slow for control cycle use. Using a Physics Attention Transformer trained on MEQ-FGE-L labels, we predict both the scalar growth rate and the associated two dimensional perturbed toroidal current density. We find mean absolute errors of 5.4~s$^{-1}$ on held out C-Mod equilibria and 12.7~s$^{-1}$ on synthetic SPARC cases, with spatial eigenfunction errors near 5\%. We also compared PAT with operator based ML models : FNO2D and DeepONet, where we found PAT predicts a much lower normalised growth rate error and improved spatial reconstruction. These results indicate that PAT can reproduce MEQ-FGE-L outputs at control relevant latency and could support future studies of growth rate headroom monitoring and proximity aware shape control.

Massachusetts Institute of Technology·Swiss Federal Institute of Technology Lausanne·Commonwealth Fusion Systems

Non-dimensional confinement scaling in similar negative triangularity plasmas on the DIII-D and TCV tokamaks

Alessandro Marinoni, Colin Chrystal, Stefano Coda, Reinart Coosemans, Claudio Marini, Mario Podesta, Olivier Sauter, Matteo Agostini, Max E Austin, Emily A Belli, et al.

Nuclear Fusion·Aug 25, 2026Plasma & Confinement

Similarity experiments were performed on the DIII-D and TCV tokamaks to explore the scaling of energy confinement in negative triangularity plasmas using non-dimensional variables. Near up-down symmetric plasmas with large top-bottom averaged negative triangularity were created in a lower single null configuration, with the shape of the separatrix being closely matched between the two devices. The normalized energy confinement is found to weakly improve at increasing collisionality and, between the two devices, shows a machine size scaling behavior between Bohm and gyro-Bohm. Engineering scaling on a large DIII-D dataset is in agreement with the non-dimensional experiment.

Consorzio RFX·General Atomics·Swiss Federal Institute of Technology Lausanne·University of California San Diego

Aug 24

Beam optics and stripping losses in a full-scale ITER negative ion source: multibeamlet analysis by beam emission spectroscopy

Riccardo Agnello, Marco Barbisan, Roberto Pasqualotto, Antonio Pimazzoni, Emanuele Sartori, Barbara Zaniol, Edgard Zuin

Plasma Physics and Controlled Fusion·Aug 24, 2026Control & DiagnosticsHeating & Current Drive

In this work, Beam Emission Spectroscopy (BES) is applied to the investigation of beam divergence and stripping losses in the full-scale ITER negative ion source prototype SPIDER, operating in multibeamlet configuration. A semi-analytical model is developed to simulate the emission spectra produced by overlapping beamlets, accounting for realistic beamlet divergence, aiming, and beam composition along the accelerator and drift regions. The comparison between synthetic and experimental spectra shows that the Doppler broadening measured in multibeamlet operation cannot be interpreted solely in terms of single-beamlet divergence, but results from the combined effects of beamlet overlap, residual magnetic deflections, electrostatic repulsion, and halo contributions. Using beamlet parameters independently obtained from calorimetric diagnostics, the model reproduces a significant fraction of the experimentally measured divergence. Moreover, the possibility of displacing a line-of-sight allows the detection of variations in the populations of particles with different divergences, namely the core and halo components, across the beam. As a phenomenological characterization, stripping losses are systematically quantified over a wide range of operational parameters, showing an approximately linear increase with source pressure and values consistent with previous single-beamlet studies. These results demonstrate the capability of BES, combined with multibeamlet modelling, to support beam optimization and performance assessment in ITER-relevant negative ion sources.

Swiss Federal Institute of Technology Lausanne·National Research Council

Aug 21

Challenges of Locked Mode Avoidance in the Low-ν* ITER Baseline Scenario Plasmas in ASDEX Upgrade

Lidia Piron, Thomas Pütterich, Tomas Markovic, Olivier Sauter, Wolfgang Suttrop, Paolo Bettini, M Bonotto, Athina Kappatou, Marc Maraschek, Leonardo Pigatto, et al.

Plasma Physics and Controlled Fusion·Aug 21, 2026Plasma & ConfinementControl & DiagnosticsAI, Modeling & Simulation

In AUG, the requirement to explore the low-ν* regime within the same ITER baseline scenario parameters, i.e. a Greenwald fraction of ~0.85, q₉₅ ≈ 3, βN ≈ 1.8, and H98 ≈ 1, has been addressed by inducing density pump-out through n=2 magnetic field perturbations. This approach required additionally relaxing the high-δ plasma shape to δ ≈ 0.1 to enable sufficiently strong density pump-out. However, at low density also the generation of locked modes was observed which deteriorates the plasma performance. Several strategies were therefore tested, including model-based error field correction combined with different heating schemes, as well as a core–edge decoupling metric derived from the GPEC code. Nevertheless, these attempts were unsuccessful, largely because the gap between the onset of density pump-out and the excitation of the core mode is very small.

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

Aug 19

High-power TCV scenario for conventional and alternative divertor studies

K. Lee, C. Theiler, M. Carpita, M. Zurita, P. Sintre, O. Février, F. Pastore, H. Reimerdes, K. Verhaegh, M. Winkel, et al.

arXiv (physics.plasm-ph)·Aug 19, 2026Plasma & Confinement

Alternative divertor configurations (ADCs) must be evaluated under boundary plasma conditions approaching reactor-level values to be considered a reliable, physics-based solution for tokamak power exhaust. Most ADC experiments performed to date were at relatively low exhaust power. This work presents a high-power scenario on the TCV tokamak enabling the study of a wide variety of divertor magnetic shapes under an expanded SOL and power exhaust parameter space. The scenario is characterized by high power levels of electron cyclotron resonance heating ($2.5\,\text{MW}$ fully absorbed in a $\sim1\,\text{m}^{3}$ plasma) at high plasma current (edge safety factor $q_{95}\approx 2.5$), and low upstream separatrix densities ($n_{e,\text{u}}\approx1\times10^{19}\,\text{m}^{-3}$, Greenwald fraction $f_{\text{G}}\approx 0.1$). Stationary parallel heat fluxes up to $100\,\text{MW m}^{-2}$ are measured at the divertor target, an order of magnitude above previous TCV power exhaust studies. The obtained SOL collisionality and Lengyel detachment scaling metric lie within range of values expected in future reactors (SPARC, ITER, ARC).

Swiss Federal Institute of Technology Lausanne·Max Planck Institute for Plasma Physics·Dutch Institute for Fundamental Energy Research

Aug 18

ELM suppression and confinement in negativetriangularity with stronger shaping in ASDEXUpgrade

Branka Vanovac, Joerg Hobirk, Andrew Oakleigh Nelson, Olivier Sauter, Mike G Dunne, Michael Faitsch, Thomas Pütterich, Rainer Fischer, Dirk Stieglitz, Erika Strumberger, et al.

Nuclear Fusion·Aug 18, 2026Plasma & ConfinementAI, Modeling & Simulation

Recent experiments conducted during the 2025 campaign in ASDEX Upgrade have pushed the limits of negative triangularity shaping, achieving top triangularity values of δ top ∼-0.55 while keeping bottom triangularity around 0 in diverted plasmas. Guided by ideal-MHD stability calculations using the linear MHD BALOO solver and supported by TCV results, these experiments have demonstrated a transition to an edge that is more stable against peeling-ballooning modes, leading to ELM-free plasmas. Those ELM-free plasmas also exhibit a dithering behavior similar to limit-cycle oscillations. Linear MHD modeling showed that the achieved shapes remained marginal with respect to the second stability region for ballooning modes suggesting that with minor further shaping, a robust NT edge could be achieved. The associated energy confinement is generally reduced, with clear signs of strong power degradation. In addition, a high fraction of fast-ion energy is observed, particularly in high-power/low-density discharges. An approximately 15% improvement in normalized energy confinement is obtained when seeding nitrogen. As this effect comes from the edge, it highlights a path towards pedestal tailoring for further confinement optimization and supporting negative triangularity as a potentially viable reactor- relevant operational scenario in full-metal-wall devices.

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

Aug 17

The status and design challenges of the heating and current drive systems for DTT

Gustavo Granucci, Silvio Ceccuzzi, Afra Romano, Andrea Murari, Gian Luca Ravera, Piero Agostinetti, Sofia Bertolami, Falk Braunmüller, Alessandro Bruschi, Daniele Busi, et al.

Nuclear Fusion·Aug 17, 2026Plasma & ConfinementHeating & Current DriveFusion Plant Engineering

This paper reports the main design keys and the challenging issues of the Heating and Current Drive System (HCD) of the Divert Tokamak Test (DTT) facility that is under construction at ENEA site in Frascati with the aim to perform studies on the power exhaust in a flexible and easily modifiable environment. The selected HCD systems for DTT are those with the most consolidated technology and expected to be relevant for the future reactor. The status of each system is reported, both in terms of design and procurement, which are well advanced for the system required in the first phase of the DTT exploitation: electron and ion cyclotron resonant heating. The third system is neutral beam injector, based on negative ion acceleration, which will be installed in DTT in a second phase, after the first five years of operation. The full heating power will be reached with the doubling of the radiofrequency power to reach the 45 MW at plasma needed to test the divertor with a power density at reactor level.

National Research Council·Swiss Federal Institute of Technology Lausanne·Italian National Agency for New Technologies, Energy, and Sustainable Economic Development·Consorzio RFX

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