Recent Publications

Identifying non-performing or Dud Plasmas for Burning Plasma Control: Insights from JET and TFTR Deuterium-Tritium Campaigns

Lidia Piron, Nicolò Ferron, Eric Fredrickson, Morten Lennholm, Alessandro Pau, Timo Ravensbergen, Olivier Sauter, Fulvio Auriemma, Matteo Baruzzo, Krassimir K. K Kirov, et al.

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.

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.

Consorzio RFX, Consiglio Nazionale delle Ricerche, ENEA Agenzia Nazionale per Le Nuove Tecnologie l'Energia e lo Sviluppo Economico Sostenibile, EniProgetti SpA, Ecole Polytechnique Federale de Lausanne

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.

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.

Beam optics analysis by visible cameras applied to the multi-beamlet configuration in the ITER NBI prototype source

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.

First wall particle fluxes and Be erosion in high-performance JET-ITER baseline plasmas

Eduardo de la Cal, Carine Giroud, Henri Aaron Kumpulainen, Juri Romazanov, Itziar Balboa, Scott Alan Silburn, Pedro Carvalho, Juuso Karhunen, Beth Thomas, Alex Tookey, et al.

Culham Centre for Fusion Energy, VTT, Consorzio RFX, Forschungszentrum Juelich GmbH, Centro de Investigaciones Energeticas Medioambientales y Tecnologicas

In next step large fusion devices with a tungsten (W) first wall such as ITER, impurity control will be a challenge to avoid strong core radiation from highly ionized metals. Here we analyse the deuterium (D) fluxes impacting on the beryllium (Be) first wall limiters and the resulting surface erosion in high-performance neon (Ne) seeded ITER-baseline plasmas with up to 35 MW heating power in JET tokamak. Visible cameras are used to quantify the fluxes using the spectroscopic S/XB method at the regions of strongest plasma-wall interaction: the Outer Midplane (OMP) and the Upper Dump Plates (UDP). We first describe how Ne seeding, which significantly improves core plasma performance and power exhaust control, modifies the plasma flux dynamics and ELM properties at the walls. It is then shown, that the global Be erosion by sputtering is not significantly affected by Ne seeding. This is because the time-averaged fluxes are dominated by the inter-ELM phase, where the main erosion precursor is deduced to be D+. Furthermore, we observe a beneficial strong decrease of the fluxes at the OMP when slightly increasing the Separatrix-limiter clearance, indicating short far scrape-off layer (SOL) decay lengths. We also describe, how the fluxes change with average plasma density and toroidal magnetic field and plasma current. Regarding the fluxes at the UDP, we show the critical effect of the magnetic topology at the top of the chamber. The formation of a secondary Separatrix in this region enhances the parallel plasma fluxes to the UDP, which eventually becomes the main plasma-wall interaction area. Finally, we compare the experimentally estimated Be effective sputtering yields at the OMP for the inter- and intra-ELM phases with the values calculated using the SDTrim code to infer information on the mean ion impinging energies Ei and to show that the main global erosion precursor is D+. The obtained Ei values are in the range or at least compatible with those expected for the plasmas analysed: approximately 30 eV for the inter- and 1 keV for the intra-ELM periods respectively.

Machine learning aided neutron yield for dud detection based on JET and TFTR Deuterium-Tritium plasmas

Lidia Piron, Alessandro Pau, Nicolò Ferron, Eric Fredrickson, Olivier Sauter, Matteo Baruzzo, Clive D Challis, Remi Dumont, Dirk Van Eester, Michael Fitzgerald, et al.

Culham Science Centre, Consorzio RFX, Ecole Polytechnique Federale de Lausanna, Laboratory for Plasma Physics, Max-Plank-Institut für Plasma Physik

as it indicates fusion performance. To optimize Tritium consumption and limit neutron activation, a support function included in the plasma control system called a dud detector will trigger an alarm if the plasma fails to achieve expected fusion performance. This function has been developed and routinely employed at JET during DT campaigns. This study presents machine-learning methods based on a surrogate model of the neutron rate, which can be used as an advanced dud detector. In preparation for DT operations in BEST, HL-3, ITER, and SPARC, we investigate the portability and inherent limitations of these ML methods by analysing similar DT experiments conducted at TFTR.

Diagnostics for large tokamaks: from JET to JT-60SA 1

Carlo Sozzi, A Jokinen, G Phillips, K Tanaka, Juan Ayllon-Guerola, Andrea Belpane, Attila Buzás, Santiago Cabrera, mario - cavinato, Daniel Carralero, et al.

Fusion for Energy, Consorzio RFX, Hungarian Academy of Sciences Centre for Energy Research, Centro de Investigaciones Energeticas Medioambientales y Tecnologicas, Consiglio Nazionale delle Ricerche

The main scientific purpose of JT-60SA is complementing ITER in the preparation of the operation of a DEMOnstration fusion reactor, in particular investigating the conditions for a controllable high beta steady-state regime able to optimize the fusion gain. In order to accomplish this task, a sequence of operation and machine enhancement periods in the next few years are planned to reach the target performance of the machine before a transition to a full tungsten wall. EUROfusion and Fusion for Energy are jointly contributing to the enhancement plan of JT-60SA, in particular, for what concerns the present contribution, to provide JT-60SA with state-of-art diagnostics in support of its scientific and technical objectives. This paper reports the status of the projects being implemented in view of the next scientific campaigns or under consideration through the various stages from feasibility to detailed design.

Integrated core-SOL modelling of JET baseline plasmas in D/D-T/T: impact of ELMs and isotopic composition on Tungsten sputtering

Rachele Cicioni, Luca Garzotti, Lidia Piron, Vito Konrad Zotta, Vassili Parail, Agata Chomiczewska, Domenico Frigione, Alexander Huber, Florian Koechl, Henri Aaron Kumpulainen, et al.

University of Padova, United Kingdom Atomic Energy Authority, Consorzio RFX, Institute of Plasma Physics and Laser Microfusion, Institute of Fusion Energy and Nuclear Waste Management-Plasma Physics, Forschungszentrum Jülich GmbH

The JET DTE2 experimental campaign revealed an isotopic dependence in the baseline scenario, where the target stationary conditions achieved in deuterium plasmas could not be maintained in tritium and deuterium-tritium mixtures. This loss of stationarity was associated with a gradual increase in plasma density, reduced ELM activity, and rising core radiation. This work investigates whether isotope-dependent tungsten sputtering contributes to the loss of stationarity observed in JET DTE2 baseline plasmas. The analysis focuses on the tungsten sputtering source and on tungsten transport during inter- and intra-ELM phases, as a function of the isotopic species of the main plasma. The study is carried out using the integrated core-edge-SOL framework COCONUT/JINTRAC, which was used to evolve the plasma self-consistently across the entire domain. The simulations show a clear isotopic dependence of the tungsten sputtering source, which increases with the mass of the main plasma ion and reaches the highest levels in tritium plasmas. Despite the enhanced tungsten source, most of the sputtered tungsten remains confined to the SOL, and no substantial net increase of the tungsten content is observed in the plasma core over the ELM time window. Pedestal onditions affect tungsten transport across the separatrix and the transient tungsten response during the ELM cycle. The results also indicate that ELM dynamics, in particular the ELM frequency, can modify the transient tungsten content in the core. Overall, the simulations suggest that isotope composition and ELM activity affect the tungsten sputtering source and its short-time redistribution, but that ELM-induced sputtering alone does not explain the loss of stationarity observed experimentally.

Conceptual design of the Halo Machine

V.V. Yanovskiy, M. Alessio, G. Becatti, E. Cattaruzza, R. Cavazzana, E. Martines, B. Momo, R. Paccagnella, D. Tskhakaya, F. Villone, et al.

Consorzio RFX, Institute of Plasma Physics of the CAS, Università Ca’ Foscari Venezia, Università di Pisa, Università di Milano-Bicocca

In 1996, when the danger of sideways forces was first recognised, the operational window of the JET tokamak was significantly restricted. Limits were placed on the maximum magnetic field and plasma current to prevent excessive stresses on the vacuum vessel. Despite three decades of research, predictions for the sideways force on the ITER wall remain highly uncertain, ranging from 2 to 60 MN with the upper estimate exceeding the design value of 48 MN, which would result in operational restrictions (operation with I p < 15 MA potentially affecting ITER’s ultimate fusion performance). To address this issue, the ITPA community launched the dedicated joint experiment MDC-25 in 2018. While substantial progress has been made, recent findings highlight the need for complementary studies on a specialised linear device to investigate plasma–wall currents, key contributors to sideways forces. Here, we propose the first linear device specifically designed to investigate plasma–wall interactions in the presence of kink modes, with the aim of resolving uncertainties related to plasma–wall currents and associated sideways forces. It is expected that the findings obtained with the new device will guide the design of vacuum vessels and plasma facing components for future tokamaks.

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.

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.

Comparative analysis between particle tracing model and thermographic data for a MeV class beam for fusion application

Antonio Pimazzoni, Piero Agostinetti, Giuseppe Chitarin, Giulia Emma, Mieko Kashiwagi, Kisaki Masashi, Nicolo Marconato, Isabella Mario, Basile Pouradier-Duteil, Beatrice Segalini, et al.

Università degli Studi di Padova, Consiglio Nazionale delle Ricerche, Consorzio RFX, ENEA, INFN

For the ITER experimental fusion reactor up to 3 heating neutral beams (HNBs) are foreseen. Each HNB will generate 1280 individual beamlets of H-/D- ions which will be accelerated up to 870 keV/1 MeV, neutralized and focused into the tokamak plasma, to provide up to 16.5 MW of heating power. To this purpose, divergence and aiming of each beamlet are required to be ≤7 mrad and within ± 2 mrad, respectively. An accurate compensation is thus essential, both for the magnetic deflection induced by the magnets embedded in the extraction grid (necessary to immediately deflect the co-accelerated electrons) and for the Coulomb repulsion among the beamlets. The Asymmetric Deflection Compensation Magnets (ADCM), the solution developed for the full-scale ITER HNB prototype called MITICA, was recently tested, for the first time on a MeV class beam, at the MegaVolt Test Facility (MTF) at QST (Naka, Japan). In these experiments, a MITICA-like extraction grid was built and installed on MTF. In this work, the beam pattern measured on a calorimeter made of unidirectional carbon fiber composite (1D-CFC) is compared with the predictions from simulations by the numerical code IBSimu, in order to develop methodologies and identify limitations for its application for MITICA exploitation and improvements. The model accuracy varied with experimental conditions; in all the cases however the proposed methodology proved very valuable in providing trends and dependencies.

Numerical investigation of the impact of conductivity modelling in fluid simulations of RF drivers for giant negative ion sources

Iacopo Regoli, Roman Zagorski, Isabella Mario, Antonio Pimazzoni, Emanuele Sartori, Alastair Shepherd, Valeria Candeloro, Edgard Zuin, Gianluigi Serianni

Consorzio RFX, University of Pisa, National Centre for Nuclear Research, University of Padova, Culham Centre for Fusion Energy

Numerical investigations of surface negative ion production in the giant NBI source SPIDER

Iacopo Regoli, Roman Zagórski, Daniel López-Bruna, Isabella Mario, Antonio Pimazzoni, Emanuele Sartori, Alastair Shepherd, Gianluigi Serianni

Consorzio RFX, University of Pisa, National Centre for Nuclear Research, Centro de Investigaciones Energéticas Medioambientales y Tecnològicas, University of Padova

Heating D ions to optimal D–T fusion energies in JET-ILW

E. Lerche, M. Maslov, P.H. Jacquet, I. Monakhov, D. King, D. Keeling, C.D. Challis, D. Van Eester, P. Mantica, C. Maggi, et al.

Culham Campus, ERM/KMS, Institute of Plasma Science and Technology, IRFM, Consorzio RFX ISTP-CNR

In JET-ILW, beam-target reactions contribute to a large fraction of the fusion power generated in deuterium–tritium (D–T) plasmas, with core ion temperatures of 10–12 keV and large neutral-beam injection (NBI) power. Previous modelling done in preparation for the recent D–T campaigns in JET have shown that injecting D beam ions with energies of ∼120 keV in T–rich plasmas produces larger 14 MeV fusion yield than in 50:50 D:T plasmas, but such scenario had never been tested in past D–T experiments. In addition, the simulations showed that fundamental ion cyclotron resonance heating (ICRH) of the D ions can significantly boost the net fusion reactivity, since both the D-bulk ions and the fast D-beam ions are accelerated to energy ranges that are optimal for the D–T reactions to take place. In the last JET D–T campaigns (DTE2 and DTE3), dedicated experiments confirmed—for the first time—the improved fusion performance of T-rich plasmas with high D-NBI power and highlighted the key impact of fundamental D ICRH on the fusion performance. This new scenario led to the world-wide D–T fusion energy record ever achieved in a fusion device and allowed to sustain more than 12 MW of fusion power averaged over 5 s. The main results of these unprecedented experiments will be presented and the NBI + ICRF physics responsible for the high fusion performance achieved will be highlighted through numerical modelling.