Erik Gallo

The SPARC tokamak aims to demonstrate net fusion power gain in tokamaks (Q-fus > 1). To measure neutron emission, a neutron spectrometer based on the magnetic proton recoil technique is being developed. This diagnostic operates by converting collimated neutrons into recoil protons through elastic scattering on a polyethylene target. The recoiled protons are then separated based on their momentum by a magnetic field and subsequently detected by a hodoscope composed of plastic scintillation detectors coupled to photomultiplier tubes. This allows neutron energies in the 2–20 MeV range to be discriminated, though only neutrons in a narrower energy window (±25% around the selected central energy) can be measured. The instrument will contribute to the determination of the total fusion power and provide information on plasma parameters such as ion temperature and the presence of non-thermal fuel ions. In this study, the design rationale of the hodoscope is presented and the main instrumental effects that govern proton collection are characterized. The hodoscope is divided into three regions with different channel widths, depths, and lengths, jointly optimized to satisfy three coupled physical requirements: sufficient energy resolution at the 14.1 MeV DT peak, full proton containment up to 18.75 MeV, and limitation of the background through minimization of the detector volume. Three correction factors are evaluated through dedicated simulations: the vertical signal loss due to protons falling outside the scintillator rod length, the cross-talk between adjacent channels, and the background contribution per channel. A correction scheme combining all three factors is presented.

In nuclear fusion reactors, deuterium and tritium are fused together. Most reactions produce a 4He ion and a 14 MeV neutron, while about 2 × 10−5 of them produce a 5He ion and a gamma photon. One of the most important measurements from a fusion reactor is the total fusion power, which can be measured using the 14 MeV neutrons or the gamma-rays. Using both provides two independent measurements, which is valuable for researchers and regulators. Facilities such as JET use scintillators such as LaBr3 to measure gamma-ray emission, but such detectors could struggle with background on high-power reactors such as SPARC and ITER. We propose that a magnetic electron recoil gamma-ray spectrometer (MERGS) can make gamma-ray measurements in these high-background environments. MERGS will consist of a foil that converts photons to electrons via Compton scattering, a magnetic electron-optic system that focuses and disperses the electron beam, and a detector array that counts the electrons and uses their positions to infer their energy. A conceptual design framework of MERGS is presented, along with three numerically optimized electron-optic geometries for three different resolution requirements. Simulations are presented showing that each presented design can meet its requirements. This shows that MERGS can measure the gamma-ray emission spectrum more effectively than scintillators for a variety of price points, enabling improved measurements of fusion power as well as the study of fast ion physics via other nuclear reactions.

Silicon carbide (SiC) detectors are promising candidates for neutron diagnostics in fusion environments, where instruments must endure intense neutron and gamma fluxes, high temperatures, and restricted accessibility. Partial depletion operation enables online control of detector efficiency by varying the applied bias voltage, thereby tuning the response to adapt to the widely changing neutron fluxes expected in future tokamak experiments. In this work, the functionality of two 4H-SiC detectors with different thicknesses (100 μm and 250 μm) is investigated under partial depletion conditions. Measurements are performed with 2.5 MeV and 14 MeV neutrons produced at the Frascati Neutron Generator and benchmarked against Geant4 simulations. Results show that detector efficiency can be predictably controlled within a factor of five without degrading energy resolution. Full depletion in the 100 μm device was reached at lower voltages than expected, possibly due to doping variations or irradiation effects. These findings confirm the potential of partial depletion as a tool for real-time tuning of SiC detector response, with significant implications for neutron diagnostics in future fusion reactors.

The gamma rays emitted by the T(D,γ)5He fusion reaction have been measured at the FNG neutron irradiation facility in ENEA-Frascati by using a large 3”x3” LaBr3 scintillator crystal. Since the gamma ray emission probability by the DT reaction is 10-5 lower with respect to the main fusion reaction channel T(D,n)4He a neutron attenuator is needed. In this paper we present the design of a neutron attenuator based on a combination of different materials. The neutron attenuator performances have been studied with a series of MCNP simulations benchmarked with an experiment performed with a 137Cs gamma ray source. The analysis of the experimental results shows a gamma component in the region of interest that is compatible with the T(D,γ)5He reaction. Although the results obtained at FNG indicate that the gamma rays emitted by the T(D,γ)5He can be measured with the present set-up, they also show that an improvement of the experimental set-up is needed. An analysis of the background induced by the scattered neutrons is provided and improvements to the neutron attenuator are proposed.

This study investigates the electrical performance of two 4H-SiC p⁺-i-n⁻ diodes, based on lightly doped epitaxial layers, representative of high-voltage and neutron-detector structures. Each design was implemented in multiple nominally identical devices and characterized over the temperature range 298–623 K, with particular attention to the influence of p⁺ layer fabrication, n-type epitaxial layer thickness, and doping concentration. One diode features an ion-implanted p⁺ layer on a 250 µm thick n-type epitaxial layer, while the other employs an epitaxially grown p⁺ layer on a 100 µm thick n-type epitaxial layer. A comparison of reverse-bias Current–Voltage (I–V) and Capacitance–Voltage (C–V) characteristics indicates that, although both designs exhibit high-quality epitaxial 4H-SiC material, devices with an implanted p⁺ anode tend to show a more pronounced temperature-dependence and degradation of selected electrical parameters in reverse bias than those with an epitaxial p⁺ anode, while forward I–V in the range 298–623 K remains broadly similar for both designs. These observations suggest that anode fabrication and epitaxial design may jointly influence thermal stability, recombination mechanisms, and overall electrical performance, offering guidance for the optimization of 4H-SiC-based power and neutron-detector devices for high-temperature and harsh environments.

The development of high-field, large-bore magnets based on High-Temperature Superconductors (HTS) is a strategic challenge with impact across high-energy physics, fusion energy, and other scientific and societal applications. In particular, the target decay and capture solenoid for the Muon Collider and the central solenoid of next-generation fusion devices both demand solenoids capable of producing a 20 T peak field in a bore larger than 1 m, at 20 K, with stored energy exceeding 300 MJ (single coil). Such performance is well beyond present state-of-the-art, requiring a dedicated programme to validate conductor technologies, magnet architectures, and protection strategies. This paper presents the results of a feasibility study originated from discussions between CERN and Eni on a common solenoid concept serving as technology validation for both high-energy physics experiments and magnetic-confinement fusion devices such as tokamaks. The main result of the study, which brought together universities and research centers, is a “20@20” model coil concept. We report here the rationale for the selection of the target performance of the “20@20” model coil, and the highlights of the study, which was instrumental to identify high priority developments required towards its realization.

Hydrogen isotope permeation through structural alloys represents a critical challenge for tritium management in fusion systems. In this work, the performance of a 1 μm thick Al₂O₃ coating deposited by Pulsed Laser Deposition (PLD) on AISI 316L stainless steel is quantitatively assessed under fusion-relevant conditions.Permeation experiments were conducted using deuterium between 400°C and 500°C and at upstream partial pressures of 100–500 Pa. A matched pristine–coated dataset enables a direct evaluation of the permeation reduction factor (PRF), yielding values between 8.6 × 10² and 2.5 × 10³, corresponding to a systematic reduction of approximately three orders of magnitude.A resistance-in-series formulation shows that the coating resistance dominates transport in all investigated conditions (Rc ≫ Rs), confirming that the film acts as a functional barrier rather than a marginal surface modification. Factorial statistical analysis of ln(PRF) indicates that pressure exerts a stronger degrading effect on barrier performance than temperature within the explored domain, while a complementary multi-level model confirms the robustness of this trend.Response surface models for permeation flux and PRF provide continuous engineering maps over temperature–pressure space. In parallel, Monte Carlo inference of the pressure exponent in ln(J)–ln(p) space reveals a transition from near bulk-controlled transport in pristine AISI 316L to surface/film-controlled behaviour in coated samples, indicating that the PLD coating fundamentally alters the rate-controlling mechanism.The proposed framework provides a transferable, uncertainty-aware methodology for the quantitative assessment of permeation barriers and supports the potential of PLD-deposited Al₂O₃ as an effective tritium permeation barrier under fusion-relevant conditions.