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 23

Calibration of cross-field transport models in SOLPS-ITER on the TCV-X21 case

Stefano Carli, Reinart Coosemans, Claudia Colandrea, Wouter Dekeyser

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

Cross-field turbulent transport remains one of the largest uncertainties in edge plasma simulations and is commonly approximated through empirical transport coefficients. In this work, we calibrate and assess several cross-field transport models implemented in SOLPS-ITER using measurements from the TCV-X21 reference case. The considered models range from conventional constant-diffusivity descriptions to the self-consistent k-model, in which anomalous diffusivities evolve along with plasma conditions. Model parameters are estimated through gradient-based optimization by minimizing discrepancies between simulated and experimental upstream and divertor profiles in forward field configuration. The calibration results show that increasing the number of free parameters substantially improves agreement with the calibration dataset. However, these more flexible models exhibit poor predictive capability when applied to the reversed field configuration, indicating overfitting. In contrast, the simplest constant-diffusivity model provides the best overall predictive performance while requiring only a small number of calibrated parameters. The k-model achieves a calibration quality comparable to the constant-diffusivity model and reproduces the experimental profiles with similar accuracy, while simultaneously providing a physics-based description of the spatial variation of anomalous transport. Predictions for a density scan reveal differences that are not apparent near the calibration point. The k-model predicts increasing transport levels around the separatrix with increasing density, leading to broader upstream profiles and an earlier onset of divertor rollover compared to the constant-diffusivity model. The presented framework provides a systematic and efficient route for model calibration in SOLPS-ITER, and a set of calibrated k-model parameters to be employed in future studies.

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 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

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 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

Parameter optimization of the reduced-order scrape-off-layer model DIV1D using Markov-Chain Monte Carlo sampling

Roel Rik Maria Hazelhof, Gijs Lukas Derks, Clemens Verhoosel, Stefan Dasbach, David vander Mijnsbrugge, Sven Wiesen

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

Accurate and efficient modeling of scrape-off layer (SOL) dynamics is essential for controlling divertor detachment in future fusion reactors. The reduced-order SOL model DIV1D provides a fast alternative to high-fidelity codes such as SOLPS-ITER, but it contains fitting parameters that are traditionally tuned manually and with limited knowledge about their posterior distribution. This paper introduces a Bayesian framework employing Markov Chain Monte Carlo (MCMC) sampling to fit DIV1D to mapped SOLPS-ITER solutions. The framework quantifies parameter uncertainties through posterior likelihood distributions, revealing parameter correlations and multi-modal behavior. A Sobol sensitivity analysis, extended with a novel adaptive formulation, provides additional insight into parameter influence and interactions. Application to SOLPS-ITER simulations of TCV shows improved fits compared to the benchmark parameter set, while results across a SOLPS-ITER density ramp on TCV highlight systematic trends and parameter correlations, suggesting the potential of density-dependent adaptive fitting. Extension of the method to SOLPS-ITER simulations of AUG demonstrates its robustness and adaptability. Overall, the Bayesian MCMC framework reduces manual workload and enables reproducible and interpretable parameter estimation, leading to improved reduced-order SOL modeling capabilities.

Dutch Institute for Fundamental Energy Research·Forschungszentrum Jülich

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 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 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 13

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.

Plasma Physics and Controlled Fusion·Aug 13, 2026Plasma & ConfinementAI, Modeling & Simulation

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.

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

Aug 4

Synthetic Diagnostic Modeling for Plasma Tomography: Geometry Matrix Computation Methods and Impact of Model Accuracy

D. Hamm, G. Partesotti, C. Theiler, U. Sheikh

arXiv (physics.plasm-ph)·Aug 4, 2026Plasma & ConfinementControl & DiagnosticsAI, Modeling & Simulation

Tomographic emissivity reconstruction from plasma diagnostics data relies on a synthetic model mapping the plasma emissivity to the measured signals. The model, referred to as a geometry matrix in the plasma imaging community, is often built using the line-of-sight (LoS) approximation. This approximation neglects the finite width of the detector viewing beams and can therefore introduce systematic errors. Physically correct volume-of-sight (VoS) models remove this inaccuracy by accounting for the full 3D extent of the viewing beams. Their adoption, however, is sometimes hindered by the difficulty of independently validating them. We present an intuitive and easily inspectable voxel-to-detector (V2D) approach for computing physically accurate VoS geometry matrices, based on discretizing the tokamak vessel into voxels and estimating the contribution of each voxel to the measurements of each detector. We apply the V2D approach to the soft X-ray (SXR) and bolometry systems of the TCV tokamak. Through phantom-based studies on physically realistic emissivity profiles, we quantify the improvement in reconstruction quality obtained by using VoS rather than LoS models. We find that the VoS model yields overall better accuracy and precision; however, interestingly, the simpler LoS model does not introduce a significant systematic bias in the estimated total, core, divertor and main chamber radiated powers. We further compare the V2D geometry matrix with an independent ray-tracing implementation, finding excellent agreement that validates both approaches for routine use at TCV. All routines developed in this work are made openly available.

Jul 17

Kinetic equilibrium prediction at TCV using RAPTOR and FBT

C.E. Contré, A. Merle, O. Sauter, S. Van Mulders, R. Coosemans, G. Durr-Legoupil-Nicoud, F. Felici, O. Février, C. Heiss, B. Labit, et al.

Nuclear Fusion·Jul 17, 2026Plasma & ConfinementControl & DiagnosticsAI, Modeling & Simulation

We present results from a new Kinetic-Equilibrium Prediction workflow and shot preparation for full Tokamak à Configuration Variable (TCV) discharges, by coupling predict-first RAPTOR transport simulations with FBT inverse equilibrium calculations. RAPTOR is a 1.5D transport code which has been extensively used for plasma shot optimization and real-time modeling. We show that rapid pre-shot simulations can be performed directly using information from the pulse schedule across a wide range of plasma shapes and scenarios, given an estimate of the confinement quality factor H 98 ( y , 2 ) and line-averaged density. The resulting p ′ and T T ′ profiles are then provided to the pre-shot equilibrium computation performed by FBT—a static free-boundary solver routinely used at TCV—achieving convergence between the two codes in a few iterations. Finally, we show that this coupling, when integrated into the TCV shot preparation, improves the evaluation of the coil currents needed to match the target plasma shape; in particular providing an accurate estimate of critical quantities such as the internal inductance l i and normalized pressure β N , giving more realistic information to tokamak operators about the expected pulse behavior and enabling them to adjust the plan correspondingly.

Swiss Federal Institute of Technology Lausanne·ITER Organization

Jul 16

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.

Nuclear Fusion·Jul 16, 2026Plasma & ConfinementHeating & Current Drive

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.

Consorzio RFX·Swiss Federal Institute of Technology Lausanne·Italian National Agency for New Technologies, Energy, and Sustainable Economic Development·United Kingdom Atomic Energy Authority

Jul 14

First observations of ion cyclotron emission in the TCV tokamak

A. Jansen van Vuuren, M.B. Dreval, R. Ochoukov, S.E. Sharapov, B.P. Duval, H. Elaian, L. Simons, C. Paraskevopoulos, A.N. Karpushov

Nuclear Fusion·Jul 14, 2026Plasma & ConfinementControl & DiagnosticsHeating & Current Drive

The first observations of ion cyclotron emission (ICE) in the Tokamak à Configuration Variable (TCV) tokamak are reported. The measured ICE frequency closely follows the deuterium ion cyclotron frequency at the magnetic axis, with temporal variations consistent with equilibrium evolution and associated shifts of the magnetic axis. Core ICE is observed primarily during phases with combined electron cyclotron resonance heating (ECRH) and neutral beam injection (NBI). In most discharges the second harmonic dominates, while in others higher harmonics (third or fourth) are observed. Fine spectral structure, including branch splitting and frequency chirping, is frequently detected, together with additional modes consistent with emission at cyclotron harmonics from regions closer to the plasma edge. Core ICE is observed during both co-current and counter-current NBI. The frequency offset of core ICE relative to the ion cyclotron harmonic at the magnetic axis reverses sign between co- and counter-current injection, and this behavior is confirmed in discharges with reversed plasma current. The observed frequency shifts are qualitatively consistent with Doppler-shifted cyclotron resonance arguments.

Kharkiv Institute of Physics and Technology·Max Planck Institute for Plasma Physics·Swiss Federal Institute of Technology Lausanne·Culham Centre for Fusion Energy

Jul 13

Impact of triangularity on power sharing and boundary turbulence in TCV double-null L-mode plasmas

D. Moiraf, N. Fedorczak, G. Ciraolo, O. Février, M. Ugoletti, S. Coda, R. Ducker, G. Durr-Legoupil-Nicoud, S. Gorno, M. La Matina, et al.

Nuclear Fusion·Jul 13, 2026Plasma & ConfinementControl & Diagnostics

We present a systematic experimental study of triangularity effects on power sharing, scrape-Off layer (SOL) transport, and boundary turbulence in double-null (DN) L-mode plasmas in TCV. We show that triangularity ( δ ) strongly influences inner/outer power sharing between divertor targets. In high- δ DN plasmas ( δ = 0.58 ), only 13 % of the exhaust power reaches the inner targets, while in low- δ DN ( δ = 0.17 ) this fraction rises to 28 % . In lower single-null plasmas, the inner target power fraction increases from 33 % ( δ = 0.58 ) to 48 % ( δ = 0.17 ). Comparisons with analytic models show that the observed power-sharing trends are qualitatively reproduced, and further suggest not only a reduction of poloidally ballooned radial transport, but also enhanced cross-field transport through the high-field side. While Thomson scattering measurements show no clear δ -dependence of midplane decay lengths, embedded Langmuir probes in the lower divertor shows a ∼ 59 % broadening of λ q ∥ between δ = 0.17 and δ = 0.58 . Finally, edge turbulence exhibit a 30 % reduction in fluctuation levels at low δ . On a smaller scale, blob structures are 35 % smaller in radial extent and with 43 % lower amplitude with regard to the background values in low- δ DN compared to high- δ , in agreement with recent GBS simulations and supporting the correlation between plasma shaping, turbulence characteristics, and power sharing dynamics.

Consorzio RFX

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

Nuclear Fusion·Jul 13, 2026Plasma & ConfinementAI, Modeling & Simulation

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.

Kharkiv Institute of Physics and Technology·Swiss Federal Institute of Technology Lausanne·Polytechnic University of Turin·United Kingdom Atomic Energy Authority