Fernanda Rimini

We measured single event effects (SEEs) in 40 nm and 65 nm Static Random Access Memories (SRAMs) exposed to the D–T fusion neutron environment of the JET tokamak during the DTE-3 campaign (September–October 2023), while also characterizing the neutron spectrum seen by the devices. Using consolidated JET neutron production data, the measured SEE rates show good agreement with predictions based on the measured spectra and independently determined SRAM sensitivity parameters from thermal and monoenergetic neutron tests. These results extend the validation of our spectrum-based SEE prediction methodology, previously demonstrated in a D–D fusion neutron environment in 2021, to a D–T fusion neutron field. The novelty of this work is therefore the first experimental validation of this complete prediction approach in a D–T fusion environment, using real-time neutron spectrometry and independent device sensitivity data, rather than a new SEE model. The experiments also show that a local B ₄ C shield reduces the bit-flip rate by absorbing thermal neutrons, and we discuss the conditions under which such shielding can improve electronics reliability in tokamak and accelerator neutron environments.

In future fusion reactors, measuring the neutron production rate from deuterium–tritium (DT) fusion reactions will be crucial 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 Joint European Torus 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 machine learning methods by analyzing similar DT experiments conducted at Tokamak Fusion Test Reactor.

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 conditions 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.

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 (DT) 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 DT ITER scenario.

Since the installation of a beryllium–tungsten (Be/W) first wall on JET an intense scenario development programme has taken place to realize a high-current (3.5–4 MA) scenario, denominated JET baseline scenario, with q 95 ∼ 3 , β N ∼ 1.8 and capable of delivering high fusion performance ( P fus > 10 MW) for 5 s in the deuterium–tritium (D–T) campaigns conducted in 2021 and 2023. The JET baseline scenario was realized in D–T at 3.5 MA in 2021 (DTE2 campaign), but, despite achieving transitorily P fus ∼ 8 MW, it could not be sustained for more than 3 s. In this paper we will revisit and expand the analysis of the baseline scenario at 3.5 MA and present new results obtained in D–T at 3.0 MA in DTE3, where we were able to sustain the scenario for 5 s. We will also present recent modelling results showing how available semi-empirical and first-principles transport models can explain a variety of phenomena ranging from fusion performance, impurity transport and control of the fuelling mix. Many of these points are potentially relevant for bigger machines such as ITER. Finally, we will discuss open questions and improvements to our present modelling capabilities required to extrapolate the results to power plant devices.

The HL-3 tokamak program addresses critical challenges in developing integrated high-performance scenarios compatible with power exhaust demands for ITER and future reactors. Through systematic facility enhancements including auxiliary heating upgrades to 19.5 MW and AI-enabled control systems achieving 95.5% disruption avoidance, HL-3 finished a new round of exploration and validation for high-performance operation and power exhaust solution. Experiments at mega-ampere plasma currents demonstrated a reactor-relevant hot-ion regime with core ion temperatures exceeding 10 keV and a fusion triple product of . High normalized beta scenarios featuring internal and double transport barriers were successfully established. To address the compatibility of the plasma boundary, various small- or no-edge localized mode (ELM) regimes were achieved, including the enhanced D-alpha (EDA) H-mode, quiescent H-mode (QH-mode), and the quasi continuous exhaust (QCE) regime. Investigations into power exhaust integration highlighted the efficacy of advanced divertor configurations, specifically snowflake and tripod geometries, in significantly reducing peak heat fluxes. Active ELM control was demonstrated via resonant magnetic perturbations (RMPs), lower hybrid waves (LHW), and impurity supersonic molecular beam injection (SMBI), complemented by real-time feedback control of divertor detachment. These developments establish the fundamental physics basis and technical foundations necessary for demonstrating and extrapolating high-performance operations to ITER and next-step devices.

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 10-12keV 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 ~120keV in T-rich plasmas produces larger 14MeV 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 12MW of fusion power averaged over 5s. 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.

In recent years, an intense modeling activity has been focused on preparing and analyzing the second JET Deuterium-Tritium (D-T) experimental campaign DTE2. Among the numerous scientific outcomes of this campaign was the unique opportunity to test and validate the state of the art of modeling tools with fusion-relevant DT plasmas using the full metallic ITER-like wall in different scenarios. This work reports on the core predictive modeling of plasma density, electron, and ion temperatures (ne, Te, Ti) performed using TRANSP [1] coupled with TGLF- SAT2[2, 3] for the JET D-T baseline scenario (Ip = 3.5MA, q95 = 3, βN < 2, with pellet pacing)[4]. The sensitivity to different input parameters, as the E×B shear parameterization and the values of the kinetic quantities at the boundary of the prediction domain (ρ = 0.85) has been assessed, identifying the confidence interval of the prediction results. In particular, the dependence of the electron density profile on the particle source parameters has been studied, identifying the ionization source as the main cause for the density gradient underprediction obtained by TRANSP-TGLF, reported in [5]

The Joint European Torus (JET) Restart is a critical phase in the operation of the JET, enabling the transition of JET plant from Shutdown to experimental plasma campaigns. This paper provides a comprehensive overview divided into its two main stages. The first stage, Integrated Commissioning, encompasses the activation and synchronization of critical systems, from magnet energization to diagnostics calibration. The second stage, Plasma Commissioning, focuses on achieving reliable and sustained plasma initiation, conditioning plasma-facing components, and optimizing auxiliary heating and other systems. The paper details the sequential phases and steps of JET Restart, outlines the planning and coordination, and introduces how the commissioning procedures for Restart activities are reviewed, managed, and monitored. The paper also explores the specific commissioning activities required for deuterium–tritium experimental campaigns, highlighting the additional safety measures and operational adjustments needed for tritium handling. By documenting the JET Restart methodology and lessons learned, this paper provides valuable insights for the commissioning of next-generation fusion machines. As one of the most complex fusion facilities globally, JET’s Restart activities serve as a critical benchmark for the operational procedures of future large-scale fusion machines.

The Joint European Torus (JET) was the only tokamak capable of Deuterium-Tritium (D-T) operations in the last 30 years. The first D-T operations were in the 1990s and again in 2004. In 2020/2021/2023, JET operated a much larger D-T and pure T campaigns aimed at sustained high fusion power, requiring a much higher tritium throughput. This paper presents operational aspects of the recent Tritium Injections into the JET Tokamak. Tritium injection into the JET Tokamak involves transfer of tritium between the Active Gas Handling System (AGHS) and the Tritium Gas Injection Modules (TIMs) and Neutral Beam Injectors (NBIs), the control of TIMs, and NBI, gas inventory (pre-pulse estimate, post-pulse usage), gas limits (explosive, tritium) etc. Operations require close collaboration of staff in the JET Control Room,), AGHS, vacuum, and cryogenic groups.