Design studies on electronics and data acquisition of a real time diamond spectrometer for the SPARC neutron camera.

The design of a compact 2 × 2 diamond matrix with independent and redundant pixels optimized for the spectrometric neutron camera of the SPARC tokamak is presented in this article. Such a matrix overcomes the constraints in dynamic range posed by the size of a single diamond sensor while keeping the ability to perform energy spectral analysis, marking a significant advancement in tokamak neutron diagnostics. A charge pre-amplifier based on radio frequency amplifiers based on InGaP technology transistors, offering up to 2 GHz bandwidth with high robustness against radiation, has been developed.

Overview of the early campaign diagnostics for the SPARC tokamak (invited).

The SPARC tokamak is a high-field, Bt0 ∼12 T, medium-sized, R0 = 1.85 m, tokamak that is presently under construction in Devens, MA, led by Commonwealth Fusion Systems. It will be used to de-risk the high-field tokamak path to a fusion power plant and demonstrate the commercial viability of fusion energy.

Development of a multi-layer high-efficiency GEM-based neutron detector for spallation sources.

Neutron detection is nowadays mostly based on He gas detectors, but its shortage and the continuous upgrades of the neutron facilities require new devices to perform experiments with maximum performances. This work presents a new detector based on the Gas Electron Multiplier (GEM) combined with several boron layers. This detector combines the features of GEM technology with the properties of boron as a neutron converter and the device is produced to sustain high neutron fluxes with high detection efficiency.

Overview of the neutron diagnostic systems for the SPARC tokamak.

Neutron measurement is the primary tool in the SPARC tokamak for fusion power (Pfus) monitoring, research on the physics of burning plasmas, validation of the neutronics simulation workflows, and providing feedback for machine protection. A demanding target uncertainty (10% for Pfus) and coverage of a wide dynamic range (>8 orders of magnitude going up to 5 × 1019 n/s), coupled with a fast-track timeline for design and deployment, make the development of the SPARC neutron diagnostics challenging. Four subsystems are under design that exploit the high flux of direct DT and DD plasma neutrons emanating from a shielded opening in a midplane diagnostic port.

Ion optical design of the magnetic proton recoil neutron spectrometer for the SPARC tokamak.

A magnetic proton recoil (MPR) neutron spectrometer is being designed for SPARC, a high magnetic field (BT = 12 T), compact (R0 = 1.85 m, a = 0.57 m) tokamak currently under construction in Devens, MA, USA.

Learning from each other: Cross-cutting diagnostic development activities between magnetic and inertial confinement fusion (invited).

Inertial Confinement Fusion and Magnetic Confinement Fusion (ICF and MCF) follow different paths toward goals that are largely common. In this paper, the claim is made that progress can be accelerated by learning from each other across the two fields. Examples of successful cross-community knowledge transfer are presented that highlight the gains from working together, specifically in the areas of high-resolution x-ray imaging spectroscopy and neutron spectrometry.

Development of fast 2.5 MeV neutron detectors for high-intensity stray magnetic field environments.

Several small to medium-scale magnetic confinement fusion devices operate using deuterium as fuel. These low neutron rate (108-1010 n/s) devices rely on 2.45 MeV neutron measurements to validate physical models and to assess their performance.

Measurement of the Gamma-Ray-to-Neutron Branching Ratio for the Deuterium-Tritium Reaction in Magnetic Confinement Fusion Plasmas.

At present, magnetic confinement fusion devices rely solely on absolute neutron counting as a direct way of measuring fusion power. Absolute counting of deuterium-tritium gamma rays could provide the secondary neutron-independent technique required for the validation of scientific results and as a licensing tool for future power plants. However, this approach necessitates an accurate determination of the gamma-ray-to-neutron branching ratio.

Development of a measuring technique based on JET second D-T campaign (DTE2) experience for assessing fusion power at ITER during D-T operation using the radial gamma-ray spectrometer.

The ITER Radial Gamma-Ray Spectrometer (RGRS) consists of three gamma-ray detectors observing the plasma through three collimated, coplanar, radial lines of sight (LoS). The system was initially designed to monitor the runaway electron emission and the alpha-particle density profile [Nocente et al., Nucl.

Design solutions for the hodoscope of the magnetic proton recoil neutron spectrometer of the SPARC tokamak.

A new 14 MeV neutron spectrometer utilizing the magnetic proton recoil (MPR) technique is under development for the SPARC tokamak. This instrument measures neutrons by converting them into protons, whose momenta are subsequently analyzed using a series of magnets before detection by an array of scintillators known as the hodoscope. In this work, we explore various solutions for the hodoscope detectors through laboratory tests with radioactive sources and simulations.

COSMONAUT: A COmpact spectrometer for measurements of neutrons at the ASDEX upgrade tokamak.

A COmpact Spectrometer for Measurements Of Neutrons at the ASDEX Upgrade Tokamak (COSMONAUT) has been developed for spectroscopy measurements of the 2.45 MeV neutron emission from deuterium plasmas at the ASDEX Upgrade. The instrument is based on a CLYC-7 inorganic scintillator, whereby the detection of fusion neutrons occurs via their interaction with 35Cl nuclei in the detector crystal, leading to a peak in the detector response function and providing excellent neutron/gamma-ray discrimination capabilities.

Sensitized Triplet-Triplet Annihilation in Nanostructured Polymeric Scintillators Allows for Pulse Shape Discrimination.

Scintillating materials emit light when exposed to ionizing radiation or particles and are used for the detection of nuclear threats, medical imaging, high-energy physics, and other usages. For some of these applications, it is vital to distinguish neutrons and charged particles from γ-rays. This is achievable by pulse shape discrimination (PSD), a time-gated technique, which exploits that the scintillation kinetics can depend on the nature of the incident radiation.

Conceptual design of a GEM (gas electron multiplier) based gas Cherenkov detector for measurement of 17 MeV gamma rays from T(D, γ)He in magnetic confinement fusion plasmas.

The only method for assessing the fusion power throughput of a deuterium-tritium (DT) reactor presently relies on determining the absolute number of 14 MeV neutrons produced in the DT plasma. An independent method, developed and investigated during the recent DT campaign at the Joint European Torus, is based on the absolute counting of 17 MeV gamma rays produced by the competing T(D, γ)He reaction that features a very weak branching ratio (about 3-6 × 10) when compared to the main T(D, n)He reaction. The state-of-the-art spectrometer used for gamma-ray measurements in magnetic confinement fusion plasmas is LaBr(Ce) scintillator detectors, although they require significant neutron shielding to extract a relatively weak gamma-ray signal from a much more abundant neutron field.

Upgrades to the gamma ray imager on DIII-D enabling access to high flux hard x-ray measurements during the runaway electron plateau phase (invited).

The Gamma Ray Imager (GRI) is a pinhole camera providing 2D imaging of MeV hard x-ray (HXR) bremsstrahlung emission from runaway electrons (REs) over the poloidal cross section of the DIII-D tokamak. We report a series of upgrades to the GRI expanding the access to RE scenarios from the diagnosis of a trace amount of REs to high flux HXR measurements during the RE plateau phase. We present the implementation of novel gamma ray detectors based on LYSO and YAP crystals coupled to multi-pixel photon counters, enabling a count rate in excess of 1 MHz.

A high-resolution neutron spectroscopic camera for the SPARC tokamak based on the Jet European Torus deuterium-tritium experience.

Dedicated nuclear diagnostics have been designed, developed, and built within EUROFUSION enhancement programs in the last ten years for installation at the Joint European Torus and capable of operation in high power Deuterium-Tritium (DT) plasmas. The recent DT Experiment campaign, called DTE2, has been successfully carried out in the second half of 2021 and provides a unique opportunity to evaluate the performance of the new nuclear diagnostics and for an understanding of their behavior in the record high 14 MeV neutron yields (up to 4.7 × 10 n/s) and total number of neutrons (up to 2 × 10 n) achieved on a tokamak.

Simulations of neutral beam injection and ion cyclotron resonance heating synergy in high power EAST scenarios.

The EAST plasmas heated with deuterium neutral beam injection and ion cyclotron resonance heating (ICRH) have been simulated by the TRANSP code. The analysis has been conducted using the full wave solver TORIC5, the radio frequency (RF)-kick operator, and NUBEAM to model the RF heating effects on fast ion velocity distribution. In this work, we present several simulated results compared with experiments for high power EAST scenarios, indicating that the interactions between ICRH and fast ions can significantly accelerate fast ions, which are confirmed by the increased neutron yield and broadened neutron emission spectrum measurements.

Fusion product measurements by nuclear diagnostics in the Joint European Torus deuterium-tritium 2 campaign (invited).

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.

A new dedicated signal processing system for gamma-ray spectrometers in high power deuterium-tritium plasma scenarios in tokamaks.

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 10 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.

Role of neutron attenuators for gamma-ray measurements in deuterium-tritium magnetic confinement plasmas.

The Joint European Torus (JET) is the only tokamak in the world able to operate in Deuterium-Tritium (DT) plasmas. A successful DT experimental campaign, the DTE2, has recently been carried out, providing unique opportunities for studying both physics and technological aspects. In particular, it allowed us to investigate and benchmark the solutions adopted to attenuate the significant 14 MeV neutron flux, needed to enable high-resolution gamma-ray spectroscopy measurements on a tokamak.

Novel compact hard x-ray spectrometer with MCps counting rate capabilities for runaway electron measurements on DIII-D.

A novel compact spectrometer optimized for the measurement of hard x rays generated by runaway electrons is presented. The detector is designed to be installed in the fan-shaped collimator of the gamma-ray imager diagnostic at the DIII-D tokamak. The spectrometer is based on a 1 × 1 cm cerium doped yttrium aluminum perovskite scintillator crystal coupled with a silicon photomultiplier.

Neutron emission and fast ion simulation for high performance long pulses at EAST.

Neutron emission spectroscopy and neutron yield measurements are important for high neutral beam injection (NBI) power heating at the Experimental Advanced Superconducting Tokamak (EAST). The neutron yields mainly depend on the deposition from NBI to the deuterium plasmas in the EAST. We have recently used TRANSP with time dependent diagnostic results to simulate the transport process of 30 s long pulse deuterium plasma discharges in the EAST, obtaining the time dependent fast ion distribution, neutron emission spectrum, and total neutron emission rate.

A new tangential gamma-ray spectrometer for fast ion measurements in deuterium and deuterium-tritium plasmas of the Joint European Torus.

A new tangential gamma-ray spectrometer has been developed for fast ion measurements in deuterium and deuterium-tritium plasmas of the Joint European Torus (JET). The instrument is based on a LaBr crystal with a photo-multiplier tube and replaces a pre-existing bismuth germanate detector, providing enhanced energy resolution and a counting rate capability in the MHz range. The line of sight is equipped with a LiH attenuator, which reduces the background due to 14 MeV neutron interactions with the crystal by more than two orders of magnitude and enables the observation of gamma-ray emission from confined α particles in JET deuterium-tritium plasmas.

A compact stilbene crystal neutron spectrometer for NBI-heated plasma neutron diagnostics at EAST.

Stilbene crystal detectors are widely used as fast neutron measurement tools based on recoil proton detection, such as liquid scintillators. A compact stilbene crystal neutron spectrometer (CSCNS) has been installed at the Experimental Advanced Superconducting Tokamak (EAST) to obtain information on fuel ions produced in the plasma core because of its merits of good n/γ discrimination capability, high detection efficiency, and fast response. For the first time, CSCNS has been used for neutron emission spectroscopy measurements in EAST plasmas with neutral beam injection (NBI) heating.

Design and optimization of an advanced time-of-flight neutron spectrometer for deuterium plasmas of the large helical device.

A time-of-flight neutron spectrometer based on the Time-Of-Flight Enhanced Diagnostic (TOFED) concept has been designed and is under development for the Large Helical Device (LHD). It will be the first advanced neutron spectrometer to measure the 2.45 MeV D-D neutrons (DDNs) from helical/stellarator plasmas.