Fusion for Energy

The Central Solenoid (CS) plays a crucial role in plasma current drive and control in tokamak devices such as the Divertor Tokamak Test (DTT) facility, currently under development in Frascati, Italy. High-Temperature Superconductors (HTS), and in particular REBCO tapes, are gaining increasing interest for central solenoid applications due to their superior performance in high-field regimes, offering larger operational margins compared to conventional Low-Temperature Superconductors (LTS). This work presents the design and analysis of an HTS-based pancake-wound CS for the DTT tokamak, using a SECAS or VIPER-type REBCO conductor. A parametric study was developed to get a configuration to maximize the magnetic flux swing while ensuring compliance with mechanical fatigue constraints. The design was validated through finite element electromagnetic and mechanical analyses, and it is compared to a previous layer-wound LTS CS configuration.

JT-60SA is the world's biggest operating tokamak (R = 3, a = 1.2) having achieved a plasma volume of 160m3 in 2023. As the first of a new generation of large fusion experimental machines, its commissioning represents a unique opportunity to gain invaluable operational experience. The magnets form the backbone of any tokamak, and the superconducting magnet systems of JT-60SA play a critical role in allowing long pulse operation, essential for studying plasma behaviour in conditions relevant to reactor operation. The novel design of the NbTi Toroidal Field (TF) magnet, providing the main confinement field for the plasma, allows its 18 coils (each 7.5m high) to expand radially when energized within their Outer Intercoil Structures, which in turn provide lateral support. The 100-tonne Nb3Sn Central Solenoid (CS) is key to driving current in the plasma while the six NbTi Equilibrium Field (EF) coils, up to 12m in diameter, shape and control it. The TF magnet was successfully operated at its full 2.25 Ton-axis field in 2021, and in October 2023 all the magnets could be operated together to produce the first tokamak plasma. While individual components - such as a coils, power supplies or cryoplants - can be thoroughly tested in isolation, many critical aspects of their interaction can only be assessed during integrated commissioning, where all systems are operated together. This paper provides an overview of the magnet system integrated commissioning process and highlights key lessons learned, particularly regarding insulation integrity, Paschen testing, applied voltages, power circuit design, and quench detection.

Abstract The ITER Wide Angle Viewing System (WAVS) relies on in-vessel metallic first mirrors (FM) to transport optical signals from the plasma to out-of-vessel diagnostics. Under the conditions of ITER, energetic plasma particles induce sputtering of plasma-facing components, and the resulting sputtered material can re-deposit on these mirrors, resulting in reflectivity degradation. In-situ plasma removal using radio-frequency (RF) capacitively coupled plasma discharges is one of the proposed methods to mitigate this issue. Experiments were conducted in a 3 T homogeneous magnetic field using a medical magnetic resonance imaging (MRI) system at the University Hospital of Basel. The WAVS First Mirror Unit consists of two mirror electrodes (M1 and M2), one or both of which can be powered with RF, while the remaining surfaces act as grounded areas. Systematic measurements of the self-bias voltage were performed for varying discharge conditions, including gas species (argon and helium), pressure (0.1–10 Pa) and mirror capacitance, as well as the angle θ between the mirror surface and magnetic field. The results revealed a strong dependence of the self-bias on the grounded-to-powered area ratio A g / A p , which is affected by the magnetic confinement. Erosion and deposition patterns were examined in cases where one or both mirrors were powered. Erosion occurred primarily where a powered mirror faces a grounded surface, whereas overlapping discharges in the dual-powered case resulted in low ion kinetic energy and preferential net deposition at the overlapping area. These observations were supported by one-dimensional simulations of plasma potential evolution under representative conditions. These results provide critical insight into RF plasma behaviour in fully magnetised, geometrically asymmetric discharges and support the development of robust in-situ cleaning strategies for ITER optical diagnostics.

Asthma affects over 339 million people worldwide, contributing substantially to morbidity, reduced quality of life, and premature mortality. Air pollution is a major risk factor, but stationary monitors lack the resolution to capture individual exposure. This study aimed to (i) evaluate the feasibility of integrating personalized air quality monitoring with digital health tools in patients with moderate-to-severe asthma; (ii) explore preliminary associations between pollutant exposures and respiratory outcomes; and (iii) characterize interrelations among symptoms, spirometry, wearable-derived physiology, and inhaler use. Thirteen adults with moderate-to-severe asthma participated in a six-month observational study using a digital monitoring ecosystem. This combined wearable sensors for physiological and air quality data, daily symptom reporting via smartphone, and spirometry assessments. Outdoor pollution data were obtained from the nearest fixed-site monitoring station. Personal sensors revealed highly variable exposures that diverged from ambient measurements, particularly for nitrogen dioxide, which showed greater variability and more frequent exceedances of World Health Organization thresholds. Self-reported symptoms and inhaler use were strongly correlated. However, no consistent associations were observed between pollution exposure and health outcomes, including symptoms or spirometry results, even when time-lagged effects were considered. These findings highlight the limitations of relying on ambient stations to assess exposure in asthma research and underscore the importance of individualized monitoring. Combining wearable pollution sensors with continuous symptom tracking and remote lung function testing is feasible and patient-centered. This integrative approach may inform precision medicine strategies and improve individualized asthma management.

Abstract The ITER Neutral Beam Test Facility (NBTF), called PRIMA (Padova Research on ITER Megavolt Accelerator), is hosted in Padova, Italy and includes the MITICA experiment – a full-scale prototype of the ITER heating neutral beam injector (HNB). The large cryopump is intended to absorb the gas used to neutralize the high energy beams of the MITICA experiment. The cryopump is cooled by a dedicated cryoplant based on a Helial LF refrigerator by Air Liquide Advanced Technologies. The plant delivers up to 800 W of cooling power at 4.5 K. A specifically designed Auxiliary Cold Box (ACB) is capable to provide a He flow of 220 g/s at 81 K & 40 g/s at 4.6 K to the thermal shields and the cryosorption panels respectively. This cryoplant has a high grade of versatility needed to cope with the highly variable heat loads as well as with the different modes of operation. This paper presents the design of the cryoplant and highlights the various stages of the installation, commissioning and final acceptance tests.