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Chang Wook Shin, Suk-Kwon Kim, Dae-Sik Chang, Myungho Kim, Seok-Kwon Son, Hyung Gon Jin, Dong Won Lee, Youngmin Lee, Mu-Young Ahn
Zheng Xue, Wang Yingqiao, Wu Yi, Gu Zhengyang, Chen Xin, Li bo, Xiong Zhenming
J. Hidalgo-Salaverri, J. Gonzalez-Martin, M. Kocan, J. Ayllon-Guerola, C. Navarro, E. Agus, G. Simic, M. Garcia-Munoz, J. Rueda-Rueda, R. Marques
Veronika Korzueva, Elizaveta Kaveeva, Vladimir A Rozhansky, Nikita Shtyrkhunov, Xavier Pierre Bonnin
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.
Joerg Hobirk, Richard A Pitts, Pierre Manas, Clemente Angioni, Matthias Bernert, Dominik Brida, Guido Ciraolo, Laurent Colas, Corinne Desgranges, Ralph Dux, et al.
Understanding the performance of limiter plasmas in the ITER start-up phase is important for the whole pulse and a possible challenge if performed on tungsten, as will now be the case following the switch to a W first wall in the new 2024 ITER Baseline. Experiments were performed on ASDEX Upgrade and WEST to characterise limiter plasmas using boronizations with different degree of boron surface coverage and toroidal asymmetries. Non-boronized start-up is shown to be slow and laborious, and, on both machines, was aborted in favour of a non-homogeneous boronization, performed also in support of the ITER re- baseline to study the impact of spatially non-uniform boron coatings. This allows normal start- up and short (few 100 ms, ITER will run ≈ 10s long limiter phases) limiter phases can be run without problems. Even with a full boronization, the limiter can de-condition and long limiter plasmas of several seconds suffer from high densities and radiation. Short limiter plasmas for plasma current ramp-up remain possible. The conditioning effect on limiter plasmas is documented, but also how the start-up is affected by an ageing boronization.
G.H. Kim, Y.J. Jung, M.S. Ha, H.S. Kim, Y.G. Jeong, S.G. Han, H.K. Kim
Lidia Piron, Nicolò Ferron, Eric Fredrickson, Morten Lennholm, Alessandro Pau, Timo Ravensbergen, Olivier Sauter, Fulvio Auriemma, Matteo Baruzzo, Krassimir K. K Kirov, et al.
Consorzio RFX, Culham Centre for Fusion Energy, United Kingdom Atomic Energy Authority, Max-Planck-Institut fuer Plasmaphysik, PPPL
Among the burning plasma controllers for research fusion reactors, the dud detector will be of primary importance as it determines whether the plasma is performing well or if it is a dud. In the latter case, the discharge needs to be terminated to remain within tritium and neutron activation limits. To this scope, monitors which track the plasma performance will be integrated in the plasma control system. In this work, we present a novel dud detector that has been empirically identified based on Deuterium-Tritium campaigns carried out at JET and TFTR. This controller estimates a proxy of the neutron rate using a combination of the diamagnetic energy and the density peakedness. If the predicted neutron rate deviates from the real-time measurement, then the dud detector will trigger an alarm leading to a safe plasma termination if plasma recovery is not expected or, to actuator requests when adjustment is possible. This monitoring function can also be coupled with equilibrium solver and control-oriented models, such as RAPDENS, as proposed in the 15 MA plasma current, 5.3 T toroidal magnetic field baseline Deuterium-Tritium ITER scenario.
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.
Saeid Houshmandyar, W. L. Rowan, J. P. Ziegel, A. Ouroua
The University of Texas at Austin
The electron cyclotron emission (ECE) diagnostics suite at ITER utilizes a front-end quasi-optical (QO) system whose design is fundamentally constrained by a field-stop concept. The field-stop defines the Gaussian beam variation throughout the optical system and within the plasma, thereby setting the ECE sampling volume and spatial resolution. An in-situ hot calibration source, optimized using Gaussian beam transmission criteria, provides independent and absolute electron temperature measurements. The QO system extends beyond the front-end to include the polarization splitter unit (PSU), transmission lines, and switchyard, forming an integrated optical path to the ECE instruments. Misalignment between the front-end and PSU reduces the effective field-stop size, degrading spatial resolution and measurement fidelity. The oblique ECE view, a key feature of the ITER design, enhances sensitivity to non-thermal electron populations and complements the diagnosis of neoclassical tearing modes. Integrated QO design and plasma physics understanding are essential for reliable ITER ECE measurements.
Weikang Tang, Matthias Hoelzl, Paul Heinrich, Di Hu, F J Artola, Pascal de Marne, Mathias Dibon, Mike G Dunne, Ondřej Ficker, Peter Halldestam, et al.
Max-Planck-Institut für Plasmaphysik, ITER Organization, Beihang University, Institute of Plasma Physics Czech Academy of Sciences, CEA
Shattered pellet injection (SPI) as primary mitigation method for major disruptions in ITER has a large parameter space available for optimization including the total amount of injected material, the size of the individual pellet fragments, the material composition, and the timing of multiple injections. This flexibility needs to be exploited to simultaneously minimize thermal heat loads, electromagnetic vessel forces, and formation of relativistic electrons and their impacts on plasma facing components. In this article, we apply 3D non-linear magnetohydrodynamic modelling to SPI experiments in the ASDEX Upgrade tokamak, going beyond our previous work [Tang et al Nucl. Fusion 65 116003 (2025)] by resolving some discrepancies between simulations and experiment and carrying out direct qualitative and quantitative comparisons to experimental measurements. The key element that enables the transition is the incorporation of the parallel heat-flux limit, which is done here in a simplified form. The work increases the confidence of reproducing key processes of disruption mitigation in direct 3D non-linear simulations in view of future predictive studies for ITER.
Yashika Ghai, Donald A. Spong, Jacobo Varela, Luis Garcia
Fast and accurate prediction of energetic-particle transport driven by Alfvén eigenmode (AE) instabilities is essential for integrated modeling workflows used in the design and optimization of burning plasma fusion reactors. In this work, we develop machine-learning-based surrogate models for rapid prediction of energetic beam and alpha-particle transport fluxes, together with predictive uncertainty estimates, for an ITER steady-state scenario. Two complementary surrogate methodologies, Gaussian process (GP) regression and hierarchical neural networks (NNs), are trained using nonlinear FAR3d gyrofluid simulations of energetic-particle transport. A flux-variability analysis demonstrates that the selected plasma-state representation provides a sufficiently unique parameterization of the nonlinear transport response over most of the sampled feature space, thereby justifying the surrogate formulation. Both surrogate models reproduce the nonlinear transport fluxes with high predictive accuracy while reducing the computational cost of transport evaluation by approximately five to six orders of magnitude relative to direct nonlinear FAR3d simulations. Although the two approaches achieve comparable predictive accuracy, they exhibit distinct uncertainty characteristics: the GP provides more consistent global uncertainty estimates, whereas the NN more clearly distinguishes between different transport regimes. This work establishes a proof of concept for developing machine-learning surrogate models of energetic-particle transport that are sufficiently accurate and computationally efficient to be incorporated into future integrated modeling workflows.
E. García-Blanco, F. Tata-Ducru, D. Guerra, J.P. Martins, F. Fantini, A. Portone, I. Ricapito, R. Rotella, J. Van der Laan
Fusion for Energy, ITER Organization
Lidia Piron, Thomas Pütterich, Tomas Markovic, Olivier Sauter, Wolfgang Suttrop, Paolo Bettini, M Bonotto, Athina Kappatou, Marc Maraschek, Leonardo Pigatto, et al.
Max-Planck-Institut für Plasmaphysik, Universita degli Studi di Padova, Czech Academy of Sciences Institute of Plasma Physics, Ecole Polytechnique Federale de Lausanne, Universita di Udine
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.
Fabio Camilo de Souza, Kenneth G McClements, Alexander Philip Kofi Prokopyszyn, Antti Snicker, Alex Reyner-Vinolas, Javier Gonzalez Martin, Lucia Sanchis, Rafael Marqués Gómez
University of Seville, Culham Centre for Fusion Energy, Tokamak Energy Ltd, VTT, University of California Irvine
This paper presents simulations of alpha-particle transport in ITER driven by static 3D magnetic field perturbations in the high-performance 15 MA Q = 10 baseline scenario, specifically resonant magnetic perturbations (RMPs) arising from edge-localized mode (ELM) control coils, combined with toroidal field ripple (TFR) and effects from ferromagnetic materials. We employ the Lorentz-Orbit Code for Use in Stellarators and Tokamaks (LOCUST), which tracks fast-ion orbits under the Lorentz force and Monte Carlo collisions with the bulk plasma, taking into account the detailed geometry of ITER plasma-facing components (PFCs). LOCUST uses GPU cards to enable the high-resolution modelling required to accurately resolve power fluxes across surfaces with complex morphologies, including unprotected cooling pipes beneath the dome divertor, and the generation of reliable synthetic diagnostics for the ITER Fast Ion Loss Detector (FILD) to support its design. The simulations include a range of ELM control coil current profiles with toroidal mode number n=3. The results indicate that the total alpha-particle energy loss has a negligible impact on plasma performance, remaining below 1% of the alpha energy produced in D–T reactions. Furthermore, the power flux density on the divertor structures and the first wall remains well below design limits and is comparable to thermal and radiative loads. The simulated alpha flux on the FILD scintillator plate is well above the noise threshold and can be significantly higher than conservative estimates.
Ji-Young Jeong, Sa-Woong Kim, Jun-Sung Chang, Tae-Hwan Kwon, Duck-Hoi Kim
ITER Korea Domestic Agency, Korea Institute of Fusion Energy, ITER Organization
Andrea M Garofalo, Bart Van Compernolle, Siye Ding, Jeremy M Hanson, Christopher Thomas Holcomb, Tomas Odstrcil, Nathan Jordan Richner, Shengyu Shi, H Q Wang, Torrin Bechtel, et al.
General Atomics, Columbia University, Lawrence Livermore National Laboratory, Oak Ridge Associated Universities, Princeton Plasma Physics Laboratory
Experiments on DIII-D have demonstrated a density-confinement synergy that enables sustainment of high performance in a previously unattained parameter regime of simultaneous very high energy confinement quality (H 98y2 ≥ 1.5), very high line-average density Greenwald fraction (ƒ Gr = πa 2 <n>/I P ≥ 1.4), and high toroidal beta (β T ≥ 3%). Tokamak operation in this regime is essential for a compact steady-state FPP, as well as for Q=10 with 500 MW of fusion power in ITER at I P << 15 MA. These experiments leveraged the knowledge that, in the high-poloidal-beta (β P ) regime, impurity and density gradients can enhance turbulence stabilization caused by high α MHD (α MHD ~(dβ P )⁄dr). This was described by theoretical predictions and gyrokinetic transport simulations [M.T. Kotschenreuther et al, 2024 Nucl. Fusion, 64 076033], and later confirmed by experiments on DIII-D [S. Ding et al, 2024 Nature 629 555]. To increase both β P and β T , the new experiments increased the ideal-wall stability β N -limit by using a smaller plasma-outer wall distance and higher triangularity in the plasma cross section (top/bottom average δ~0.9), enabled by the recent “shape & volume rise” (SVR) modification to the DIII-D divertor. The higher triangularity also contributed to achieving higher ƒ Gr by enabling higher pedestal density. At high density, the pedestal is ballooning limited and exhibits small and frequent ELMs, while the divertor is near detachment even without any impurity seeding. High plasma performance was attained and sustained reproducibly, with the eventual terminations brought about by an MHD mode destabilized as the current profile slowly continued to evolve. A path to stationary fully noninductive operation might include ECH injection to reduce both core impurity accumulation and the electron collisionality, thus increasing the bootstrap current. These experiments provide the first experimental demonstration of the ƒ Gr , H 98y2 , and β T values required simultaneously for ITER Q = 10 at I P < 10 MA, pointing to practical ways to improve the energy confinement in a fusion reactor.
E. Z. Gusakov, A. Y. Popov
Ioffe Institute
The low-threshold parametric decay of an obliquely propagating ordinary wave into electron and ion Bernstein waves in a plasma with a monotonic density profile is considered. This particular scenario is critical as it provides a mechanism for direct nonlinear energy transfer from the pump beam to both the electron and ion components of the plasma, even under conditions when the ECR absorption is expected by the linear theory to be localized elsewhere. Given its practical significance for future electron cyclotron resonance heating operations on ITER, the results of the analysis are illustrated under ITER-relevant conditions. The parametric decay instability threshold power is shown to be substantially smaller than that of a single gyrotron beam.
Emanuele Sartori, Valeria Candeloro, Isabella Mario, Antonio Pimazzoni, Carlo Poggi, Gianluigi Serianni, Pierluigi Veltri, Matteo Brombin, Riccardo Casagrande, Michele Fadone, et al.
Consorzio RFX (CNR ENEA INFN University of Padova Acciaierie Venete SpA), National Institutes for Quantum and Radiological Science and Technology, ITER, National Institute for Fusion Science, Consiglio Nazionale delle Ricerche
Large plasma sources are employed in negative ion based heating neutral beam injectors for fusion applications. A review of the ITER beam source plasma properties is presented, in comparison with negative ion sources of comparable size, based on the latest experimental measurements from SPIDER and supporting numerical simulations. Spatial investigation of plasma parameters using several diagnostics, including the beam itself, retarding field energy analysers, optical emission spectroscopy, movable and fixed Langmuir probes, is key to understanding the source physics, to support the operation and improve the source performances. The influence of multiple rf-driver configuration on uniformity and the improvement flexibility it provides, as well as the implications of control parameters like filter field and plasma grid bias are examined. Similarities and differences with other giant negative ion sources are discussed to highlight the key physical processes leading to the optimal operation and viable paths for possible improvements of the ITER source design.
Paul Heinrich, Gergely Papp, Stefan Jachmich, F J Artola, Matthias Bernert, Pascal de Marne, Mathias Dibon, Ralph Dux, Thomas Eberl, Ondřej Ficker, et al.
Max-Planck-Institut für Plasmaphysik, ITER Organization, Czech Academy of Sciences - Institute of Plasma Physics, TU Wien, Commissariat `a l’ Energie Atomique (CEA)
Disruptions are a major concern for future fusion reactors based on the tokamak principle. To ensure machine protection, the thermal loads and vessel forces that arise during disruptions have to be mitigated reliably. For the ITER disruption mitigation system (DMS), the shattered pellet injection (SPI) technology has been selected. It can provide a prompt delivery of the injection material into the plasma core, with the mitigation efficiency depending on fragment size and velocity. A highly flexible SPI system was built and installed at the tokamak ASDEX Upgrade (AUG) to aid the finalization process of the ITER DMS and provide crucial input for modeling. The SPI-induced disruptions in the 2022 AUG experiments follow a typical chain of events, which are discussed in this paper: The first light (FL), main fragment arrival (MFA), plasma movement event (PME), MARFE, thermal quench (TQ)/plasma current spike (IP-spike), current quench (CQ), and vertical displacement event (VDE) phase. Depending on the injection parameters, these phases may vary significantly or some might not be present at all. In this paper, we will focus on the characterization of these disruption phases and figures of merit for the mitigation efficiency, depending on the SPI configuration. With increasing amount of assimilated neon in the plasma - primarily influenced by the neon content in the pellet but also the shattering parameters - the disruptions exhibit different behaviors. This disruption evolution seems to be a continuous process, with the most prominent feature being the changing disruption time scales and plasma current time trace shape during the CQ from convex (poorly or unmitigated) → concave (well mitigated/radiation dominated). Depending on the injection, pre-TQ durations between 15 - 0.5 ms and early CQ durations (Δt CQ 100 → 80 ) between 13.3 - 8.2 ms had been achieved at AUG.
Giulia Emma, Margherita Ugoletti, Matteo Agostini, Riccardo Agnello, Riccardo Casagrande, Isabella Mario, Roberto Pasqualotto, Antonio Pimazzoni, Carlo Poggi, Basile Pouradier-Duteil, et al.
Consorzio RFX, ISTP-CNR, Institute for Plasma Science and Technology, University of Padova, École Polytechnique Fédérale de Lausanne (EPFL), ITER Organization
The production of high energy neutral hydrogen/deuterium beams (0.87 MeV/1 MeV) with more than 90% uniformity and extremely low divergence (< 7 mrad) is highly challenging for the realization of the ITER Neutral Beam Injection system. The ITER prototype negative ion source, SPIDER, is in operation at the Neutral Beam Test Facility in Padua and it is equipped with a full set of diagnostics to study and investigate the beam properties. Among them, a system of 15 2D visible cameras, surrounding the vacuum vessel, is employed to measure the beam uniformity and divergence by detecting the light emitted from the beam-background gas interaction. In this paper, the beam divergence measured by these cameras is evaluated for the first time in the multi-beamlet configuration explored during the most recent SPIDER operation. The analysis is performed using the top-view and the side-view cameras, studying both the horizontal and vertical beam profiles through a 1D Gaussian fitting procedure, to estimate the width of the beamlet column or row aligned with the camera's lines of sight. The divergence is then retrieved from the linear fit of the width measured at different positions along the beam propagation direction. The method is here presented and applied to the experimental data acquired with an open beam segment. The dependence of the divergence on the main source and accelerator parameters, namely the RF power, the source filling pressure, and the voltage of the accelerator grids, is investigated. The results are then compared with measurements of the divergence given by the other beam diagnostics available in SPIDER, showing good agreement and validating the use of the visible camera system for the beam optics characterisation in the multi-beamlet operation.
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