A new deuterium-tritium experimental, DTE2, campaign has been conducted at the Joint European Torus (JET) between August 2021 and late December 2021. Motivated by significant enhancements in the past decade at JET, such as the ITER-like wall and enhanced auxiliary heating power, the campaign achieved a new fusion energy world record and performed a broad range of fundamental experiments to inform ITER physics scenarios and operations. New capabilities in the area of fusion product measurements by nuclear diagnostics were available as a result of a decade long enhancement program. These have been tested for the first time in DTE2 and a concise overview is provided here. Confined alpha particle measurements by gamma-ray spectroscopy were successfully demonstrated, albeit with limitations at neutron rates higher than some 1017 n/s. High resolution neutron spectroscopy measurements with the magnetic proton recoil instrument were complemented by novel data from a set of synthetic diamond detectors, which enabled studies of the supra-thermal contributions to the neutron emission. In the area of escaping fast ion diagnostics, a lost fast ion detector and a set of Faraday cups made it possible to determine information on the velocity space and poloidal distribution of the lost alpha particles for the first time. This extensive set of data provides unique information for fundamental physics studies and validation of the numerical models, which are key to inform the physics and scenarios of ITER.

The most performant deuterium-tritium (DT) plasma discharges realized by the Joint European Torus (JET) tokamak in the recent DT campaign have produced neutron yields on the order of 1018 n/s. At such high neutron yields, gamma-ray spectroscopy measurements with scintillators are challenging as events from the neutron-induced background often dominate over the signal, leading to a significant fraction of pileup events and instability of the photodetector gain along with the consequent degradation of the reconstructed spectrum. Here, we describe the solutions adopted for the tangential lanthanum bromide spectrometer installed at JET. A data acquisition system with free streaming mode digitization capabilities for the entire duration of the discharge has been used to solve dead-time related issues and a data reconstruction code with pileup recovery and photodetector gain drift restoration has been implemented for off-line analysis of the data. This work focuses on the acquired data storage and parsing, with a detailed explanation of the pileup recovery and gain drift restoration algorithms.

Discussion ongoing with IPP, regarding possible collaboration on future joint experiments on BUG and ELISE, in particular integrating additional diagnostics (e.g. emittance scanner).

The full size ITER NBI ion source SPIDER has recently produced the first neutrons generated by Deuterium-Deuterium beam-target fusion reactions (2.45 MeV) with Caesium (Cs) seeding in the ion source. A principle aim of SPIDER regarding the negative ion beam is to achieve better than 90% uniformity at low beam divergence. In Deuterium operation, the neutron diagnostic can provide an additional measurement of the beam uniformity by comparing the neutron flux measured in a spatially resolved manner with a 2D matrix of scintillators. The diagnostic consists of an array of plastic, crystal, and liquid scintillators capable of neutrongamma discrimination and a single NaI crystal gamma-ray spectrometer. Since the previous SPIDER deuterium campaign, performed without Cs, the scintillator setup has been re-arranged and upgraded, with the addition of three more detectors and the installation of an LED control and monitoring system. In this work, the new experimental setup of the neutron diagnostic is presented and the results of the two campaigns (with and without Cs) are compared. Despite some technical limitations, the system has successfully measured the first Cs enhanced D-D neutrons and working challenges of the diagnostics have been identified and targeted for improvement.

The future DEMO tokamak will be equipped with a suite of diagnostics which will operate as sensors to monitor and control the position and operation parameters of DT plasmas. Among the suite of sensors, an integrated neutron and gamma-ray diagnostic system is also studied to verify its capability and performance in detecting possible DEMO plasma position variations and contribute to the feedback system in maintaining DEMO DT plasma in stable conditions. This work describes the progress of the conceptual study of the gamma-ray diagnostic for DEMO reactor performed during the first Work-Package contract 2015-2020. The reaction of interest for this Gamma-Ray Spectrometer Instrument (GRSI) consists of D(T, ?)5He with the emission of 16.63 MeV ? rays. Due to DEMO tokamak design constraints, the gamma and neutron diagnostics are integrated, both featuring multi-line of sight (camera type), viewing DEMO plasma radially with vertical (12) and horizontal (13) viewing lines to diagnose the ? and neutron emission from the DT plasma poloidal section. The GRSI design is based on the investigation of the reaction cross sections, on the calculations performed with GENESIS and MCNP simulation codes and on the physics and geometry constrains of the integrated instrument. GRSI features long collimators which diameters are constrained by the neutron flux at the neutron detectors of the Radial Neutron Camera (RNC) system placed in front, which are key to control DEMO DT plasma position. For these reasons, only few GRSI parameters can be independently selected to optimize its performance. Among these, the choice of the collimator diameters at the back side of the neutron detector box up to the GRSI detector, the use of LiH neutron attenuators in front of the GRSI detectors, the GRSI detector material and shielding. The GRSI detector is based on commercial LaBr3(Ce) inorganic scintillating crystal coupled with a photomultiplier tube or a silicon photomultiplier. They are designed to operate at high count rate although GRSI geometry constraints severely impact on this feature. The GRSI can also provide an independent assessment of DEMO DT fusion power and T burning.

MITICA is an experiment located at Consorzio RFX which aims to create a prototype for Iter's Neutral Beam Injector (NBI). Since its design features an unprecedented potential gradient (1 MV) there is an interest in researching means to prevent discharges in vacuum, which might prove fatal to the structure of the machine. In this context, High Voltage Padova Test Facility (HVPTF) is an experimental device with the aim of studying the processes leading to such undesirable discharges. HVPTF features a vacuum chamber containing two electrodes which can achieve an HV difference up to 800 kV. Both the vacuum (pressure, gas composition) and the electrodes (shape, distance) can be controlled in order to produce different conditions. Supplied voltage, current and pressure are monitored, as well as the bremsstrahlung hard X-rays produced by the free charges accelerated by the HV interacting with the electrodes. The aim of this work is to show X-ray spectroscopy to be a promising monitoring mechanism, allowing for various insights in the physics of discharges. This contribution details the scintillators used to collect data (one LYSO and one LaBr), the development of the analyzing software, the resolution of issues like pile-up discrimination and time calibration, and some of first results obtained from the data acquired during the period between 2019 and 2022. Future perspectives will be also drawn, in particular related to the recent installation of a new Gas Electron Multiplier (GEM) detector on HVPTF.

Two of the most important reactions in a fusion plasma are the D(d,n)3He (DD) and T(d,n)4He (DT) reactions. Both these reactions produce neutrons, and if a neutron spectrometer is used to resolve the emitted neutrons in energy it is therefore possible to infer various features of the energy distribution of the D and T fuel ions. Furthermore, if the neutron spectrum is measured along several different sightlines, it is possible to resolve the fuel ions spatially and/or in pitch as well. A common application of neutron spectroscopy is the study MeV-range fast ions, which typically result in distinct high-energy tails in the neutron spectrum. The DD and DT reaction cross sections exhibit different dependences on the reactant energies. Hence, the neutron spectra of DD and DT neutrons is sensitive to different regions of the fast-ion velocity-space. In this contribution, we examine this velocity-space sensitivity in detail, by means of previously determined velocity-space weight functions. By multiplying the weight functions with various trial distributions representative of radio-frequency (RF) accelerated ions at the JET tokamak, we obtain explicit maps of how much different regions of the fast-ion velocity-space is expected to contribute to the measured neutron spectrum. For JET-relevant distributions of RF-accelerated deuterons, we find that the average energy of fast ions contributing to the DD signal is about 50-100 percent higher than the average energies of the ions contributing to the DT signal. DD spectroscopy can therefore probe the most energetic part of an RF-accelerated ion distribution (MeV-range ions), while DT spectroscopy is mostly sensitive to more intermediate energies (200-500 keV). The implications of these results for the interpretation and comparison of recent DD and DT neutron spectroscopy results at JET is discussed.

The JET 2019-2020 scientific and technological programme exploited the results of years of concerted scientific and engineering work, including the ITER-like wall (ILW: Be wall and W divertor) installed in 2010, improved diagnostic capabilities now fully available, a major neutral beam injection upgrade providing record power in 2019-2020, and tested the technical and procedural preparation for safe operation with tritium. Research along three complementary axes yielded a wealth of new results. Firstly, the JET plasma programme delivered scenarios suitable for high fusion power and alpha particle (?) physics in the coming D-T campaign (DTE2), with record sustained neutron rates, as well as plasmas for clarifying the impact of isotope mass on plasma core, edge and plasma-wall interactions, and for ITER pre-fusion power operation. The efficacy of the newly installed shattered pellet injector for mitigating disruption forces and runaway electrons was demonstrated. Secondly, research on the consequences of long-term exposure to JET-ILWplasma was completed, with emphasis on wall damage and fuel retention, and with analyses of wall materials and dust particles that will help validate assumptions and codes for design and operation of ITER and DEMO. Thirdly, the nuclear technology programme aiming to deliver maximum technological return from operations in D, T and D-T benefited from the highest D-D neutron yield in years, securing results for validating radiation transport and activation codes, and nuclear data for ITER.

Alfvén eigenmode (AE) instabilities driven by alpha-particles have been observed in D-3He fusion experiments on the Joint European Torus (JET) with the ITER-like wall. For the efficient generation of fusion alpha-particles from D-3He fusion reaction, the three-ion radio frequency scenario was used to accelerate the neutral beam injection 100 keV deuterons to higher energies in the core of mixed D-3He plasmas at high concentrations of 3He. A large variety of fast-ion driven magnetohydrodynamic modes were observed, including the elliptical Alfvén eigenmodes (EAEs) with mode numbers n = -1 and axisymmetric modes with n = 0 in the frequency range of EAEs. The simultaneous observation of these modes indicates the presence of rather strong alpha-particle population in the plasma with a 'bump-on-tail' shaped velocity distribution. Linear stability analysis and Fokker-Planck calculations support the observations. Experimental evidence of the AEs excitation by fusion-born alpha-particles in the D-3He plasma is provided by neutron and gamma-ray diagnostics as well as fast-ion loss measurements. We discuss an experimental proposal for the planned full-scale D-T plasma experiments on JET based on the physics insights gained from these experiments.

Two of the most important reactions in a fusion plasma are the D(d,n)3He (DD) and T(d,n)4He (DT) reactions. Both these reactions produce neutrons, and if a neutron spectrometer is used to resolve the emitted neutrons in energy it is therefore possible to infer various features of the energy distribution of the D and T fuel ions. Furthermore, if the neutron spectrum is measured along several different sightlines, it is possible to resolve the fuel ions spatially and/or in pitch as well. A common application of neutron spectroscopy is the study MeV-range fast ions, which typically result in distinct high-energy tails in the neutron spectrum. The DD and DT reaction cross sections exhibit different dependences on the reactant energies. Hence, the neutron spectra of DD and DT neutrons is sensitive to different regions of the fast-ion velocity-space. In this contribution, we examine this velocity-space sensitivity in detail, by means of previously determined velocity-space weight functions. By multiplying the weight functions with various trial distributions representative of radio-frequency (RF) accelerated ions at the JET tokamak, we obtain explicit maps of how much different regions of the fast-ion velocity-space is expected to contribute to the measured neutron spectrum. For JET-relevant distributions of RF-accelerated deuterons, we find that the average energy of fast ions contributing to the DD signal is about 50-100 percent higher than the average energies of the ions contributing to the DT signal. DD spectroscopy can therefore probe the most energetic part of an RF-accelerated ion distribution (MeV-range ions), while DT spectroscopy is mostly sensitive to more intermediate energies (200-500 keV). The implications of these results for the interpretation and comparison of recent DD and DT neutron spectroscopy results at JET is discussed.

Nuclear fusion research is one of the most prominent fields set to revolutionize the energy market in the medium-long term period. Recent scientific achievements, such as the ones obtained at JET [1] and NIF [2], have renewed public and private interest in this topic, sparking the creation of numerous new projects and reactor concepts. Nuclear diagnostics are an essential tool to assess any deuterium-tritium machine performance. Absolute neutron counting is the gold standard technique to measure fusion power. Neutron emission spectroscopy grants access to the fuel ion physics providing information on the fuel ion temperature and energy distribution, the fuel ion ratio and the thermal to non-thermal neutron fraction. Gamma-ray and hard X-ray spectroscopy are the most direct way to obtain information on the fast particle energy distribution and their interaction with the plasma. Fusion nuclear diagnostics need to be carefully designed to operate in extreme cenarios, both in terms of operational capabilities (energy range, energy resolution, counting rate potential, etc.) and in terms of robustness in the harsh environment of a nuclear reactor. In this work, we present the state of the art for nuclear measurements in fusion experiments and we discuss possible solutions for the next-generation reactors.

SPIDER, the full size ITER NBI ion source, aims to prove the ITER requirements in terms of the ion source performance, a beam uniformity better than 90% and a low beam divergence. The SPIDER experiment can operate in deuterium, thus producing beam-target D-D fusion neutron emissions. These emissions can be used to evaluate the beam uniformity as well as machine parameter dependence, since the neutron flux is proportional to the beam power. To this end, a new neutron diagnostic array, consisting of a mix of seven crystal, plastic, and liquid scintillators, has been installed externally on the beam dump side of the vessel. Six of them are capable of neutron/gamma discrimination and are positioned to study the beam uniformity and allow parametric comparisons. A NaI scintillator-based gamma detector allows for the energy spectra reconstruction of incident gamma rays without neutron interference. In this work, the scintillator array's capability and arrangement, together with first results achieved during the deuterium campaigns performed in SPIDER, are presented and discussed.

Using capabilities of the gamma-ray spectrometry, fusion born alpha-particles were studied in recent D-3He plasma experiments on JET. A substantial population of the alpha-particles was generated in the 3He-rich plasma due to the 3He(D, p)4He reaction. Fast deuterium ions of the neutral beam injection (NBI) heating were accelerated to MeV energies with three-ion scenario D-(DNBI)-3He using radio frequency waves in the ion cyclotron range of frequencies (ICRF). A high reaction rate allowed to measure the alpha-particle production rate and their spatial distribution in the plasma by detecting 16.7-MeV gamma-rays from the 3He(D, y)5 Li reaction, which is a weak branch of 3He(D, p)4He reaction. A branching ratio of gamma-ray transitions to the ground and the first excited states of 5Li was obtained. Due to the beryllium is a main impurity of JET plasmas, intensive gamma-rays from the Be-9(D, ny) 10B, Be-9(D, py) 10Be and Be-9(a, ny) C-12 reactions were observed. Exploitation of the reaction cross-sections and the Doppler shape analysis (DSA) of gamma-lines in the recorded spectra provided the possibility to reconstruct distribution functions of the confined D-ions and the fusion-born alpha-particles.

The inaugural deuterium acceleration campaign in the SPIDER negative ion source facility in Padua has recently taken place. The first neutrons generated by deuterium-deuterium beam-target fusion reactions (2.45 MeV) have been recorded, occurring from the collision of accelerated deuterium with deuterium absorbed by the calorimeter of SPIDER. A neutron detector based on a novel EJ276 plastic scintillator has been employed to successfully measure the neutron flux, which shows strong agreement with the extracted current of the acceleration grid. We have performed neutron-gamma pulse shape discrimination with the EJ276 device at SPIDER combined with direct spectroscopic comparisons of the D-D neutrons with data from the Frascati neutron generator (241AmB quasi-monoenergetic 2.5 MeV). Despite the low statistics produced in this first campaign, both pulse shape discrimination and spectral analysis of the fusion neutrons was viable. The success of these first measurements has led to the installation of an array of 6 new scintillators to be used for further physical studies in future campaigns.

The forthcoming JET DT campaign represents a unique possibility for validating the suite of neutron diagnostics of a DT burning plasma. In particular, issues such as operation at high 14 MeV neutron flux, availability, long term stability, remote control will be important. This work will present the state of the art of the 14 MeV neutron diagnostics systems of JET, with special emphasis on the major enhancements that have been carried out in the last ten years. The plasma parameters that can be provided by the entire suite of neutron diagnostics will be presented: i) time resolved 14 MeV neutron emissivity/fusion power (by absolute neutron flux monitoring); ii) the neutron spatial emissivity (neutron camera); iii) information on the fuel ion distribution (high resolution neutron spectrometers). Finally, the benefit for ITER and DEMO of experience acquired at JET will be discussed.

Neutron emission spectroscopy is an established diagnostic for thermonuclear plasmas. The best proven technique is based on time of flight measurements, as they provide superior performance, but are also rather demanding in terms of machine interface requirements. The recent development of novel compact neutron spectrometers with good n/? discrimination capability made it possible to? discrimination capability made it possible to perform neutron spectroscopy measurements also in machines where there is limited space for a large installation, which is often the case of medium-sized tokamaks. In order to improve the suite of neutron diagnostics at the ASDEX Upgrade tokamak, a C7LYC based detector optimized for 2.5 MeV neutrons spectroscopy has been recently developed. The instrument, named COSMONAUT (COmpact Spectrometer for Measurements Of Neutrons at the ASDEX Upgrade Tokamak) was developed to measure the 2.5 MeV neutron spectrum from deuterium plasmas at the tokamak ASDEX Upgrade and is based on a former prototype detector developed for EAST. In this contribution, we present calculations of synthetic neutron spectra that may be measured in deuterium plasmas heated by neutral beam injection at the ASDEX Upgrade tokamak. These calculations are obtained by simulating the beam slowing down distribution paired with neutron production and transport to the detector position. Simulation results are then used to assess COSMONAUT detection capability.

Various private investors have recently shown their interest into nuclear fusion as a source of clean energy. One of the most challenging project is SPARC, a DT tokamak under development by Commonwealth Fusion Systems in collaboration with the Massachusetts Institute of Technology and contribution from investors among which the Italian ENI. The SPARC [1] tokamak is at present under design and has the main features of being superconducting, of compact size (major radius ~1.9 m, minor radius ~0.6 m) with very high magnetic field (toroidal field>12 T). External heating to achieve these plasma conditions will be provided by ICRH. Despite being of compact size, SPARC aims to reach the conditions of a burning plasma with a fusion gain Q~2 and Pfus~55 MW in the most conservative extrapolations, and Q>10, Pfus~140 MW in the most favorable one, with high power density (Pfusion/Vplasma~7 MWm-3) relevant for fusion power plants. This will open up the possibility to study the alpha particle physics and their of interactions with high-frequency MHD modes. In this work, starting from the last two decade experience on JET, we will present a preliminary study of the nuclear (neutron and gamma ray) diagnostics that could be installed on SPARC. Focus will be given to the alpha particle diagnostic capabilities offered by gamma ray diagnostic and to the assessment of the effectiveness of ICRH heating scheme with high resolution neutron and gamma ray spectroscopy.