Wavelength-shifting (WLS) materials are used in radiation detectors to convert ultraviolet photons into visible light, enabling improved photon detection in systems such as scintillators and optical diagnostics for nuclear fusion devices. However, the long-term performance of these materials under radiation is still a critical issue in high-dose environments. In this work, we investigated the radiation tolerance of three WLS compounds (TPB, NOL1, and SB2001), each deposited on reflective substrates (ESR and E-PTFE), resulting in six distinct WLS/substrate systems. The samples underwent gamma irradiation at absorbed doses of 100 kGy, 500 kGy, and 1000 kGy, as well as fast neutron (14.1 MeV) irradiation up to a fluence of 1.9 × 1013 n/cm2. Qualitative photoluminescence and reflectance measurements were performed before and after irradiation to assess changes in optical performance. Gamma exposure caused spectral broadening in several samples, particularly those with TPB and SB2001, with variations of the two metrics used to compare the performance of the materials exceeding 10% at the highest doses. Neutron-induced effects were generally weaker and did not exhibit a clear fluence dependence. Reflectance degradation was also observed, with variations depending on both the WLS material and the deposition method. These findings contribute to the understanding of WLS material stability under radiation and support their qualification for use in optical components exposed to harsh nuclear environments.

The measurement of 14 MeV neutrons in deuterium-deuterium plasmas provides insights into triton burn-up and confinement in magnetic fusion devices. At the Divertor Tokamak Test (DTT) facility, triton burn-up neutron yields will be measured by liquid scintillators and single-crystal diamond matrices, which are expected to face saturation-related issues due to low-energy neutron and gamma-ray interference. This work evaluates flux-shaping materials, such as borated polyethylene and lead, to enhance detector performance for the measurement of 14 MeV neutrons in the DTT mixed n/γ field. MCNP simulations are used to model neutron and gamma-ray transport through various material configurations and results show that a combination of a 30%-boron-loaded polyethylene slab followed by a layer of lead can effectively attenuate signals created by low-energy neutrons and gamma-rays while retaining the neutron flux above an energy threshold suitable for 14 MeV neutron measurements. Based on this, a modular configuration is proposed allowing the adjustment of material thicknesses between the different power scenarios of DTT to ensure a flat detector response. The proposed flux-shaping method allows for the insertion of different material combinations in front of each detector, which can extend its operational range by 1–3 orders of magnitude, to simultaneously cover with all three detectors the full spectrum of neutron yield scenarios anticipated at DTT.

The JET neutron camera is used to monitor a 2D profile of the neutron emission from the plasma, using 19 sightlines with plastic scintillators suited for measuring neutrons from the D + T → n + 4He (DT) reaction. This paper describes an independent, first-principles physics method for estimating the volume integrated DT neutron yield with the neutron camera. This is performed for a selection of shots from the two recent DT campaigns at JET, the DTE2 and DTE3 JET campaigns. It covers the data reduction methods from a light yield calibration of the scintillators to treatment of pile-up, which is prevalent during high yield DT experiments. Several models of the camera geometry are used to account for scattering and transmission effects in the neutron transport. The neutron yield is estimated using models of the neutron emission profile, which are fitted to measurement data. The neutron yield estimates from this method are compared to corresponding estimates from the JET fission chambers. Our estimates with the neutron camera are on average 34% and 41% higher than the fission chamber estimates for DTE2 and DTE3, respectively. The reasons for the discrepancies between the two systems are presently unknown and prompt further investigation. In this paper, we detail the methods used to reach the neutron yield estimate from the neutron camera, along with their strengths, weaknesses, and potential points of failure. This method is an evolution of an earlier work that estimated the deuterium–deuterium neutron yield using similar methods.

The Radial Neutron Camera (RNC) is an ITER diagnostic designed to measure the un-collided 14 MeV and 2.5 MeV neutrons from deuterium-tritium (DT) and deuterium-deuterium (DD) fusion reactions, through an array of detectors covering a poloidal plasma section along collimated Lines Of Sight (LOS). The Ex-Port RNC is located in the Port Cell (PC) Interspace zone, the first area outside the Vacuum Vessel, and includes several detector units, mounted inside detector boxes. On the base of reliability considerations, the Radial Neutron Camera Maintenance Plan (RNC-MP) has foreseen a hands-on maintenance task to replace detectors unit equipment in case of failure. Despite not precluding workers access, the radiation field at shutdown in the PC Interspace zone requires optimization of hands-on operations to enable the minimization of occupational radiation exposure under the ALARA (As Low As Reasonably Achievable) principle. The relevant complexity and dimensions of the Ex-Port RNC requires a maintenance evaluation method different from a physical mock-up. The Virtual Reality technology may help to create a digital mock-up for evaluating the detectors replacement operations. The paper aims to demonstrate the potentialities of such technologies, in a field where safety and worker ergonomics are primary priorities. Thanks to the virtual scenario built, the RNC-MP updated steps are evaluated, improved and finally validated. The VR simulation is as well validated via a simple physical mock-up of the detector box.

The primary purpose of the ITER Radial Neutron Camera (RNC) is the real-time control of plasma burn. It requires neutron emissivity profile reconstruction with an accuracy better than 10% and a time resolution of 10 ms. Algorithms based on the Tikhonov Regularization, Minimum Fisher Information, Maximum Entropy and Maximum Likelihood methods were compared for the 1D deconvolution of the neutron emissivity profile from RNC measurements. The reconstruction performance was evaluated using the baseline RNC architecture and two ITER DT 15 MA scenarios of inductive operation. The reconstruction was carried out assuming constant neutron emissivity on the magnetic flux surfaces: in this case, the neutron profile can be represented as a normalized poloidal magnetic flux function. The number of the used flux surfaces was about twice the number of lines of sight in the RNC. All methods (except Maximum Entropy) achieved a reconstruction accuracy better than 10%. The two Tikhonov Regularization algorithms provide in general a good reconstruction, with the second-order derivative regularization matrix giving a better accuracy than 10% in a wider range of the normalized poloidal magnetic flux (Ψ) but a higher standard deviation than the first-order derivative regularization matrix. At the same time, the Minimum Fisher Information proved to be the most stable method. The performance of these two best methods was validated with actual experimental data using the JET neutron camera measurements collected in the second deuterium-tritium campaign.

The Radial Neutron Camera is an ITER diagnostic designed to measure the un-collided 14 MeV and 2.5 MeV neutrons from deuterium-tritium (DT) and deuterium-deuterium (DD) fusion reactions, through an array of detectors covering a poloidal plasma section along collimated Lines Of Sight (LOS). It is composed by two fan-shaped collimating structures viewing the plasma radially through vertical slots in the diagnostic shielding module of ITER Equatorial Port 1: the In-Port RNC, devoted to plasma edge coverage, and the Ex-Port RNC, devoted to the plasma core coverage. This paper presents an overview of the mechanical design of the Ex-Port RNC at the Preliminary Design Review (PDR) stage. The Ex-Port RNC is located in the Port Interspace and consists of a massive shielding structure hosting the detector units and two sets of collimators lying on different toroidal planes. The Ex-Port RNC design is presented both from the point of view of functional requirements (e.g. LOS positions and angles, radiation shielding, weight limitations) and of manufacturability. Finally, the Ex-port RNC structural integrity is assessed, and its design validated against the main loads and load combinations.

The Radial Neutron Camera (RNC) is a diagnostic system located in the ITER Equatorial Port 1 (EP01) composed by two sub-systems (i.e.: in-port and ex-port RNC) probing a poloidal section of the plasma through a set of fan-shaped Lines of Sight (LOS). The RNC is designed to provide a time resolved measurement of the neutron and alpha particles source profiles and of the total neutron source strength, through the application of reconstruction techniques to the line-integrated neutron fluxes.The Ex-port sub-system is composed by 16 LOS distributed in two different toroidal planes and enclosed in a massive shielding unit, extending from the EP01 closure plate through the Port Interspace, up to the Bioshield Plug. Neutrons, generated in the plasma core, stream through dedicated optical paths hollowed out in the central EP01 diagnostic shielding module and reach the detectors units located at the end of collimating structures. Each detector unit contains one 4He gas scintillator, one plastic scintillator as well as one single Crystal Diamond (sCD) matrix.The performed nuclear analysis allowed the selection of the SWX-277Z-5 castable borated hydrogenated mix as suitable material for the RNC shielding block; moreover, the evaluation of the nuclear heating on the ex-port RNC subcomponents, provided as input for structural analyses, highlighted that the impact of the radiation streaming is negligible with respect to the environmental thermal loads.

RAMI (Reliability, Availability, Maintainability and Inspectability) assessments are mandatory part of the design process for all ITER systems to anticipate possible risks in terms of reliability and availability and support reliability growth program. A RAMI assessment performed on the ITER Radial Neutron Camera (RNC) diagnostic system is presented. The assessment is aimed at evaluating the RNC design capability to provide the neutron emissivity radial profile measurement with required reliability and availability. The RNC is composed by two collimating structures equipped with neutron flux detectors, the In-Port RNC sub-system and the Ex-Port RNC sub-system respectively. Such systems radially view different plasma locations thus enabling the emissivity profile reconstruction. Both In-Port and Ex-Port detection systems (sensors, collimators, shielding) and full acquisition system chain (front-end and back-end electronics) are considered in the analysis. The RAMI performance was assessed by means of reliability block diagrams (RBDs) with respect to required mean inherent availability for 2 years of operations fixed at 99.5% for the Ex-Port system and at 88.3 % for the In-Port system. A set of failure events for each RNC component was defined by means of a failure mode and effect analysis. The resulting unavailability conditions of the systems were then identified. Hence identified groups of events were used to feed the RBDs model definition according to reliability-wise integration of the considered components. The integrated RAMI performance of RNC systems was finally estimated. Considering the current level of design development, In-Port RNC system appears able to meet stated requirement thanks to design redundancy. Ex-Port RNC, which includes Back End Electronics for data acquisition, is still below the RAMI target and requires further design improvement.

The JET neutron camera is a well-established detector system at JET, which has 19 sightlines each equipped with a liquid scintillator. The system measures a 2D profile of the neutron emission from the plasma. A first principle physics method is used to estimate the DD neutron yield that is based on JET neutron camera measurements and is independent of other neutron measurements. This paper details the data reduction techniques, models of the neutron camera, simulations of neutron transport, and detector responses used to this end. The estimate uses a simple parameterized model of the neutron emission profile. The method makes use of the JET neutron camera's upgraded data acquisition system. It also accounts for neutron scattering near the detectors and transmission through the collimator. These components together contribute to 9% of the detected neutron rate above a 0.5 MeVee energy threshold. Despite the simplicity of the neutron emission profile model, the DD neutron yield estimate falls on average within 10% agreement with a corresponding estimate from the JET fission chambers. The method can be improved by considering more advanced neutron emission profiles. It can also be expanded to estimate the DT neutron yield with the same methodology.

Diagnostic systems in fusion environments need to satisfy stringent requirements, often involving radiation and electromagnetic shielding as well as fire protection. A conceptual design of a multilayer cabinet for the RNC (Radial Neutron Camera) diagnostic systems, located in the equatorial port (EP) #01 in ITER, with a required fire rating REI-120 (R -integrity, E -leak tightness to hot gasses and flames, I - thermal) was analyzed from the thermal insulation (I) point of view during external fire scenario (Tmax=805 celcius for 2 h). The modeling of the fire was based on the convective heat transfer represented by a HTC (heat transfer coefficient) of 35 W/m2K and radiative heat transfer with unit emissivity according to ISO-834. Focusing on the thermal criterion prescribed by the REI requirement, the objective was to demonstrate that the temperatures will remain below specified limits for at least 120 min subjected to given fire loads. The adopted strategy was to exploit an advanced microporous incombustible material - Microtherm & REG; overstitched - selected for the fire insulation and being applicable for the ITER environment. A parametric 3D model was developed and solved using the Finite Element Method (FEM) and the ANSYS code, including not only the heat conduction but internal radiation via SURF252 elements and internal convection via LINK34 elements. The relation between the thickness of fire protection and the maximum temperature after 2 h of fire was analyzed for two types of designs: with internal and external fire protection. In addition to the ideal thermal connection between the layers of the cabinet, the effects of imperfect thermal contacts were analyzed by varying the thermal conductance of CONTA174 elements. The effect of the boundary conditions: adiabatic versus specified temperature was analyzed, as well as the need for protecting the supports of the cabinet. The effect of the cabinet size at constant thickness of the walls was analyzed parametrically revealing increasing temperatures for smaller cabinets - more fire insulation needed. An analytical model used to explain the size effect relate to the competing effects of increasing heat transfer area and increasing heat capacity. The developed methodology provides an easy tool for early dimensioning of the necessary fire protection layer often needed before the start of the detailed CAD design. The necessary thickness of external protection layer for the analyzed cabinet resulted in 10 mm.

The radial neutron camera (RNC) is a key ITER diagnostic system designed to measure the uncollided 14- and 2.5-MeV neutrons from deuterium–tritium (DT) and deuterium–deuterium (DD) fusion reactions, through an array of detectors covering a full poloidal plasma section along collimated lines of sight (LoS). Its main objective is the assessment of the neutron emissivity/ $\alpha $ source profile and the total neutron source strength, providing spatially resolved measurements of several parameters needed for fusion power estimation, plasma control, and plasma physics studies. The present RNC layout is composed of two fan-shaped collimating structures viewing the plasma radially through vertical slots in the diagnostic shielding module (DSM) of ITER Equatorial Port 1 (EP01): the ex-port subsystem and the in-port one. The ex-port subsystem, devoted to the plasma core coverage, extends from the Port Interspace to the Bioshield Plug: it consists of a massive shielding unit hosting two sets of collimators lying on different toroidal planes, leading to a total of 16 interleaved LoS. The in-port system consists of a cassette, integrated inside the port plug DSM, containing two detectors per each of the six LoS looking at the plasma edges. The in-port system must guarantee the required measurement performances in critical operating conditions in terms of high radiation levels, given its proximity to the plasma neutron source. This article presents an updated neutronic analysis based on the latest design of the in-port system and port plug. It has been performed by means of the Monte Carlo MCNP code and provides nuclear loads on the in-port RNC during normal operating conditions (NOC) and inputs for the measurement performance analysis.

The general features of a He-4 gas scintillator prototype detector were characterized, as an alternative to liquid and plastic scintillators for a potential integration into the Radial Neutron Camera (RNC) in ITER. Two measurement campaigns were conducted at the Physikalisch-Technische Bundesanstalt (PTB) Ion Accelerator Facility (PIAF) in Germany using fast mono-energetic neutrons. Results from the first measurement campaign showed a light output response of the detector linear with the incident neutron energy, at least up to 14.8 MeV. A complete discrimination between neutrons and gammas was achieved by applying a 0.30 MeV threshold in terms of deposited neutron energy. The response function and the intrinsic efficiency of the detector were characterized in a second measurement campaign using collimated-beam conditions, similar to those expected in the RNC at ITER, to test the suitability of the detector in such a diagnostic system. The response function to 2.5 MeV and 14.8 MeV mono-energetic neutrons was measured and validated by Monte Carlo simulations. Some changes to the present prototype may be considered in the future to make it suitable as a neutron detector for the RNC at ITER.

Three-dimensional neutronics, activation and shutdown dose rate analyses were performed with MCNP5 Monte Carlo code, FISPACT-II inventory code and Advanced D1S dynamic tool for the design and licensing of Divertor Tokamak Test facility (DTT). Advanced shielding concepts and mitigation strategies have been studied to guarantee sufficient protection of the superconducting coils and to reduce the streaming and the neutron-induced radioactivity. The present nuclear design study provides main outcomes for the loads assessment, shielding and materials requirements and on maintenance strategy and storage of activated components.

The purpose of the ITER Radial Neutron Camera (RNC) is the measurement of the plasma neutron emissivity profile [neutrons.s(-1) m(-3)] for burn control purposes. The present RNC design consists of 22 collimated detector systems providing a set of line-integrated neutron measurements [neutrons.s(-1)m(-2)] with full coverage of the plasma poloidal cross-section; the neutron emissivity can be recovered from the line-integrated measurements by means of dedicated reconstruction techniques (1D spatial inversion, 2D tomography). The present paper focuses on the evaluation of the improvement in the RNC 2D reconstruction of the neutron emissivity obtained by using the total neutron yield value provided by an independent diagnostic as additional constraint in the tomography procedure. The analysis was performed using a tomography code based on the Minimum Fisher Regularization (MFR). A clear improvement of the neutron emissivity reconstruction has been observed when the total neutron yield constraint is considered. The improvement is seen in: extension of the spatial region in which the accuracy of the reconstruction is better than 10 %; better reconstruction of peaked emissivity profiles; and robustness against measurements noise and line of sight data loss.

The ITER Radial Neutron Camera (RNC) is a diagnostic system designed as a multichannel detection system to measure the uncollided neutron flux from the plasma, generated in the tokamak vacuum vessel, providing information on neutron emissivity profile. The RNC consists of array of cylindrical collimators located in two diagnostic structures: the ex-port system and the in-port system. The in-port system, contains the diamond detectors which need a temperature protection. Feasibility study of the efficiency of the cooling system for the In-port Detector Modules of the RNC during baking process was the main goal of thermo-hydraulic numerical modeling. The paper presents the concept of the cooling system layout and the original way of integration of numerical thermo-hydraulic analyses of the in-port detector cassette. Due to the large extent of the detector cassette it is impossible to include all relevant thermal and hydraulic effects in one global model with sufficient level of details. Thus the modelling strategy is based on the concept of three stage modelling from details to global model. The presented paper includes results of numerical calculations made with ANSYS Fluent software in order to provide the final answer, including calculation of heat loads in the detector cassette from adjacent walls during baking and normal operation conditions.

The present paper describes the architecture and the performances of a diamond detector data acquisition system based on PXIexpress (one of the standards suggested by ITER). Performances have been evaluated by feeding the digital acquisition system with pulses generated by a digital detector emulator replicating the shape and energy distribution expected for a Single Crystal Diamonds (sCD) neutron detector in deuterium-tritium plasmas.

The Divertor Tokamak Test (DTT) facility, whose design phase is currently under finalization, is an Italian project aimed to investigate alternative power exhaust solutions for DEMO. It is designed to operate with sig-nificant power loads and enough flexibility to test innovative divertor configurations, different plasma edge and bulk conditions approaching, as much as possible, those planned for DEMO. Among the neutron diagnostics, a multi-channel neutron camera, most likely equipped with the liquid scintillators NE213, is foreseen to provide spatially resolved measurements of several plasma parameters needed for fusion power estimation, plasma control and plasma physics studies. This paper presents a preliminary study performed in support of the DTT neutron camera design. A detailed MCNP model representing a 20 degrees sector of the machine integrating its main components and detectors assemblies has been developed and used for this study. Three-dimensional neutron transport simulations have been carried out by means of the MCNP Monte Carlo code coupled with the FENDL nuclear data libraries. The diagnostic design was optimized starting from the assessment of the expected detector performances obtained by using the calculated neutron fluxes and spectra and the NE213 response functions. The outcomes of this analysis provide the detectors requirements and guidelines for the development of the above-mentioned diagnostics, investigating its feasibility and suitability with the neutron emissivity foreseen for the DTT operational scenarios.

In several nuclear applications, scintillators, coupled with a photomultiplier and pulse amplifier, are used in order to detect high energy particles, i.e. neutrons and gamma rays. The different particles incident on the scintillator produce electrical pulses having different shape; moreover, the amplitude of these signals is related to the particles energy. The electrical pulses of the scintillator chain are acquired by digital systems that, generally, perform a triggered acquisition consisting of a stream of pulse windows. The aim of this study is the development of a simplified clustering algorithm able to produce reference patterns in compliance with the pattern recognition algorithm based on the matched filter technique, starting from a stream of pulses generated by particles having different energy and type. This paper contains a general description of the clustering algorithm and of the main customizations performed for the scintillator signals. In order to test in real case the efficiency, the algorithm has been applied on the data acquired during a radiation test performed at Frascati Neutron Generator for Stilbene scintillator. The results show that this algorithm works properly, deriving the centroids of the clusters representing the neutron and gamma shapes, together with their occurrences in the analysed data stream.

The ITER Radial Neutron Camera (RNC) is a multichannel detection system hosted in the Equatorial Port Plug 1 (EPP 1). It is designed to measure the uncollided neutron flux from the plasma, providing information on the neutron emissivity profile and total strength. The RNC structure consists of two sub-systems based on fan-shaped arrays of cylindrical collimators: the ex-port system, covering the plasma core with 2 sets of lines of sight lying on different toroidal planes, and the in-port system, enclosed in a dedicated cassette within the EPP1 diagnostic shielding module, for the measurement of neutrons generated in the plasma edge. Due to the harsh environment in which it has to operate, the design of the in-port RNC system is particularly critical both from the measurements point of view (low signal to noise ratio induced by the high level of scattered neutrons at the detector positions) and from the structural point of view. The paper presents the results of the neutronic analyses performed with the MCNP Monte Carlo code with the aim of optimizing the in-port RNC design in order to enhance the diagnostic measurement performance and evaluating the nuclear loads that have to be withstand by its structural elements, detectors and associated components.