Recent Publications

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.

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).

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.

Max Planck Institute for Plasma Physics, Massachusetts Institute of Technology, Columbia University, Ecole Polytechnique Federale de Lausanne

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.

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

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

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

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

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.

General Atomics, Ecole Polytechnique Federale de Lausanne, Columbia University, University of California San Diego, Consorzio RFX

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.

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

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

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.

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

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

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

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

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.

Ecole Polytechnique Fédérale de Lausanne (EPFL), ITER Organization, Eindhoven University of Technology

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.

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

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

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

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

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

Ecole Polytechnique Fédérale de Lausanne (EPFL), Kharkov Institute of Physics and Technology, Max-Planck-Institut für Plasmaphysik, Culham Centre for Fusion Energy (CCFE)

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.

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.

EPFL, CEA, Consorzio RFX, Institute of Plasma Physics, Nanyang Technological University

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.

Axisymmetric global Alfvén eigenmodes in the TCV tokamak

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

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

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