The present study focuses on the development of a diagnostic system for measuring radiated power and core soft X-ray intensity emissions with the goal of detecting a broad spectrum of photon energies emitted from the central plasma region of the DEMO tokamak. The principal objective of the diagnostic apparatus is to deliver a comprehensive characterization of the radiation emitted by the plasma, with a particular focus on estimating the radiated power from the core region. This measurement is essential for determining and monitoring the power crossing the separatrix, which is a critical parameter controlling overall plasma performance. Since diagnostics rely on line-integrated measurements, the application of tomographic reconstruction techniques is necessary to extract spatially resolved information on core plasma radiation. This contribution presents the development of numerical algorithms addressing the problem of radiation tomography reconstruction. A robust and computationally efficient method is proposed for reconstructing the spatial distribution of plasma radiated power, with a view toward enabling real-time applications. The reconstruction methodology is based on a linear model formulated using a set of predefined basis functions, which define the radiation distribution within a specified plasma cross-section. In the initial stages of emissivity reconstruction in tokamak plasmas, it is typically assumed that the radiation distribution is dependent on magnetic flux surfaces. As a baseline approach, the plasma radiative properties are considered invariant along these surfaces and can thus be represented as one-dimensional profiles parameterized by the poloidal magnetic flux. Within this framework, the reconstruction method employs an approximation model utilizing three sets of basis functions: (i) polynomial splines, as well as Gaussian functions with (ii) sigma parameters and (iii) position parameters. The performance of the proposed method was evaluated using two synthetic radiated power emission phantoms, developed for the DEMO plasma scenario. The results indicate that the method is effective under the specified conditions.

The fusion energy research field presents many intricate challenges that require resolution. Many diagnostic systems employed in experiments are approaching the limits of current technology. Implementing efficient measurements requires using an appropriate set of tools to facilitate the optimal utilization of hardware. Fusion energy measurements must provide low latency processing with the capacity for future improvements and the ability to handle complex data flows efficiently. The presented work addresses these requirements and describes the implementation of a high-performance, low-latency software platform with convenient development for soft X-ray (SXR) plasma impurities emission tracing—the Asynchronous Complex Computation Platform (AC2P). This article presents the architectural design, implementation details, and performance and latency measurements based on the raw data acquired from the WEST tokamak and laboratory tests. AC2P provides the tools to develop low-latency, multi-core, multi-device complex data flow graph scale-up solutions for measuring impurities in hot plasmas. The system has been designed to operate online during experiments, calculate the energy distribution, position and occurrence time of SXR photons, monitor the data stream’s quality and archive any abnormalities for subsequent offline verification and algorithm improvement. This article presents AC2P, which operates as part of the SXR measurement system on the WEST tokamak.

This work relates to development of diagnostics for radiation power (Prad) and soft x-ray (SXR) intensity measurements in DEMO. A modular, multi-chamber, multi-channel SXR detection system based on gas electron multiplier technology in lateral configuration is currently in conceptual design phase. The high magnetic fields expected at the planned detector positions in the diagnostic ports of the tokamak must be considered in the design. The present study examines two contributions of its influence. The first one pertained to the electric field drifts of thermalized electrons. These were found to be significant, but mostly linear and mitigatable. The second contribution pertained to the impact of magnetic fields on the initial photoelectrons. This was particularly effective in the second detector chamber, which had been optimized for higher photon energies. The size and shape of the electron cloud in a working gas mixture created by primary ionizations have been evaluated as a function of x-ray energy, magnetic field strength, and angle. Moreover, a more direct analysis concerning the loss of electrons in the second chamber has been performed. In this context, the magnetic field was found to have a slightly beneficial effect on the operation of the detector, as it limited the range of ionization perpendicular to its direction and decreased the probability of a primary electron leaving the drift region. Potential design changes resulting from these findings were discussed.

Superconducting (SC) tokamak JT-60SA plays an essential role in fusion research and development by supporting and complementing the ITER project, providing directions to the DEMO design activity and fostering next generation scientists and engineers. Since the short circuit incident at the terminal joints of equilibrium field coil #1 during the integrated commissioning (IC) in March 2021, both EU and JA implementing agencies (IAs) have examined how to ensure safe operation of JT-60SA by mitigating the risk of possible discharge occurrence inside the cryostat. Based on the experience of the global Paschen tests, the IAs have established a strategy of risk mitigation measures, which is a combination of (i) reinforcement of insulation, (ii) avoiding unnecessary voltage application to the coil systems and (iii) immediate de-energization of the coils when deteriorated vacuum conditions are detected. Thanks to the considerable efforts of the Integrated Project Team members, the IC restarted in May 2023. After confirmation of the SC state of the coil systems (TF, EF and CS), the coil energization test and the plasma operation phase 1 (OP-1) started. The first plasma was successfully achieved on 23 October 2023 with a limited value of voltage and current applied to the coils. The plasma configuration control was also confirmed with low plasma current and low auxiliary heating power conditions. Based on the IO-F4E-QST collaboration, activities of JT-60SA have been shared with the IO and provided an important lesson for ITER assembly and commissioning, and will provide an outstanding contribution to fusion research at large. After OP-1, maintenance & enhancement phase 1 (M/E-1) starts from January 2024, in which in-vessel components are installed, and heating and diagnostic systems are extensively upgraded to allow a high power heating experiment planned in OP-2. In order to make the best use of JT-60SA, a newly organized JT-60SA experiment team will refine the research plan for the future high heating power operation phase.

The objective of the proposed research is to develop plasma soft X-ray (SXR) radiation imaging that includes spectral information in addition to standard SXR tomography for the purpose of studying, for example, tungsten transport and its interplay with magnetohydrodynamics (MHD) in tokamak plasmas in an ITER-relevant approach. The SXR radiation provides valuable information about both aspects, particularly when measured with high spatial and temporal resolution and when tomographic reconstructions are performed. The spectral data will facilitate the tracking of both light and high-Z impurities. This approach is pertinent to both the advancement of a detailed understanding of physics and the real-time control of plasma, thereby preventing radiative collapses. The significance of this development lies in its ability to provide three-dimensional plasma tomography, a capability that extends beyond the scope of conventional tomography. The utilization of two-dimensional imaging capabilities inherent to Gas Electron Multiplier (GEM) detectors in a toroidal view, in conjunction with the conventional poloidal tomography, allows for the acquisition of three-dimensional information, which should facilitate the study of, for instance, the interplay between impurities and MHD activities. Furthermore, this provides a valuable opportunity to investigate the azimuthal asymmetry of tokamak plasmas, a topic that has rarely been researched. The insights gained from this research could prove invaluable in understanding other toroidal magnetically confined plasmas, such as stellarators, where comprehensive three-dimensional measurements are essential. To illustrate, by attempting to gain access to anisotropic radiation triggered by magnetic reconnection or massive gas injections, such diagnostics will provide the community with enhanced experimental tools to understand runaway electrons (energy distribution and spatial localization) and magnetic reconnection (spatial localization, speed…). This work forms part of the optimization studies of a detecting unit proposed for use in such a diagnostic system, based on GEM technology. The detector is currently under development with the objective of achieving the best spatial resolution feasible with this technology (down to approximately 100 µm). The diagnostic design focuses on the monitoring of photons within the 2–15 keV range. The findings of the optimization studies conducted on the amplification stage of the detector, particularly with regard to the geometrical configuration of the GEM foils, are presented herein. The impact of hole shape and spacing in the amplifying foils on the detector parameters, including the spatial size of the avalanches and the electron gain/multiplication, has been subjected to comprehensive numerical analysis through the utilization of Degrad (v. 3.13) and Garfield++ (v. bd8abc76) software. The results obtained led to the identification of two configurations as the most optimal geometrical configurations of the amplifying foil for the three-foil GEM system for the designed detector. The first configuration comprises cylindrical holes with a diameter of 70 μm, while the second configuration comprises biconical holes with diameters of 70/50/70 μm. Both configurations had a hole spacing of 120 μm.

The mission of WEST (tungsten-W Environment in Steady-state Tokamak) is to explore long pulse operation in a full tungsten (W) environment for preparing next-step fusion devices (ITER and DEMO) with a focus on testing the ITER actively cooled W divertor in tokamak conditions. Following the successful completion of phase 1 (2016-2021), phase 2 started in December 2022 with the lower divertor made entirely of actively cooled ITER-grade tungsten mono-blocks. A boronization prior the first plasma attempt allowed for a smooth startup with the new divertor. Despite the reduced operating window due to tungsten, rapid progress has been made in long pulse operation, resulting in discharges with a pulse length of 100 s and an injected energy of around 300 MJ per discharge. Plasma startup studies were carried out with equatorial boron nitride limiters to compare them with tungsten limiters, while Ion Cyclotron Resonance Heating assisted startup was attempted. High fluence operation in attached regime, which was the main thrust of the first campaigns, already showed the progressive build up of deposits and appearance of dust, impacting the plasma operation as the plasma fluence increased. In total, the cumulated injected energy during the first campaigns reached 43 GJ and the cumulated plasma time exceeded 5 h. Demonstration of controlled X-Point Radiator regime is also reported, opening a promising route for investigating plasma exhaust and plasma-wall interaction issues in more detached regime. This paper summarises the lessons learned from the manufacturing and the first operation of the ITER-grade divertor, describing the progress achieved in optimising operation in a full W environment with a focus on long pulse operation and plasma wall interaction.

Within the 9th European Framework programme, since 2021 EUROfusion is operating five tokamaks under the auspices of a single Task Force called ‘Tokamak Exploitation’. The goal is to benefit from the complementary capabilities of each machine in a coordinated way and help in developing a scientific output scalable to future largre machines. The programme of this Task Force ensures that ASDEX Upgrade, MAST-U, TCV, WEST and JET (since 2022) work together to achieve the objectives of Missions 1 and 2 of the EUROfusion Roadmap: i) demonstrate plasma scenarios that increase the success margin of ITER and satisfy the requirements of DEMO and, ii) demonstrate an integrated approach that can handle the large power leaving ITER and DEMO plasmas. The Tokamak Exploitation task force has therefore organized experiments on these two missions with the goal to strengthen the physics and operational basis for the ITER baseline scenario and for exploiting the recent plasma exhaust enhancements in all four devices (PEX: Plasma EXhaust) for exploring the solution for handling heat and particle exhaust in ITER and develop the conceptual solutions for DEMO. The ITER Baseline scenario has been developed in a similar way in ASDEX Upgrade, TCV and JET. Key risks for ITER such as disruptions and run-aways have been also investigated in TCV, ASDEX Upgrade and JET. Experiments have explored successfully different divertor configurations (standard, super-X, snowflakes) in MAST-U and TCV and studied tungsten melting in WEST and ASDEX Upgrade. The input from the smaller devices to JET has also been proven successful to set-up novel control schemes on disruption avoidance and detachment.

This work addresses the development of diagnostics for core plasma radiated power and soft x-ray intensity measurements, which will be useful in future fusion reactors to ensure reliable plasma control (by monitoring the power loss across the separatrix) in accordance with the DEMO control requirements. For this purpose, we look into the development of such a detection system that will provide the required information via soft x-ray diagnostics. The target photon range for such a detecting system is considered to be 3–50 keV. The aspects of the development have included detailed diagnostics design, physics, engineering and integration studies, as well as an investigation into the feasibility and performance of the diagnostics and its components. The development is currently in the design phase. Nevertheless, the answer is already needed regarding the fulfillment of system requirements. In order to monitor the power crossing the separatrix, a precise estimation of the plasma radiation is needed to maintain the high-efficiency plasma. This requires strict measurement accuracy criteria, with 3% accuracy margin for the core plasma radiated power estimate and 5% noise for a single measurement of a single detector within the detector array. Here, an initial estimation of the detecting system's accuracy was provided based on an analysis of both the tomography reconstruction and detector measurement capabilities. The optimal number of lines of sight for tomography reconstruction was found for the considered plasma field of view. Additionally, the initial concept for a photon-sensitive chamber of the detecting system was developed. This allowed for the assessment of the predicted measurement accuracy of the detector for horizontal and vertical lines of sight.

A method based on the principle of x-ray tomography is a good way of assessing the parameters of the radiation emission distribution in the plasma. In this method, a set of radiation detectors is usually placed around a selected section of the plasma or in two groups of detectors arranged perpendicularly to each other in the top and side positions. Such an arrangement is intended to provide a sufficient amount of data to reconstruct the distribution of radiation emission intensities across the plasma cross section. For the plasma produced in the TJ-II stellarator, a two-dimensional (2D) imaging detector is proposed with the ability to discriminate photon energy in only one specifically selected position in the toroidal direction. The proposed diagnostics could come with advantages of a 2D toroidal camera, providing access to 3D information, and would complement standard poloidal tomography. It could be used either for better constraining of the 2D tomography in simple cases with axisymmetric SXR emissivity, for simulation validation of 3D effects in a synthetic diagnostic approach, or to attempt direct 3D tomography. The subject of this contribution is to present the idea of a 3D x-ray tomography system based on the use of a square matrix of GEM detector and the obtained preliminary results of the conducted simulations. The developed diagnostics is to contain 33 462 detection pixels associated with lines of sight. The analysis was carried out on the basis of the numerical simulations based on the GEM_MP.exe and Tomography.exe computer codes (both created at IPPLM) enabling the consideration of free-free, free-bound, and bound-bound x-ray radiation reaching each of the pixels of the GEM diagnostics (GEM_MP.exe code) and testing algorithms proposed for tomographic reconstruction of the plasma emissivity (Tomography.exe code). During calculations, real profiles of electron density and electron temperature, as well as real geometry of the measuring system were taken into account. Additionally, the influence of factors such as filters used in the detector and the efficiency of the used active medium on the quality of tomographic reconstruction was examined. The summary evaluates the proposed tomographic reconstruction method.

This work presents recent efforts in optimization of Gas Electron Multiplier (GEM) detector simulations developed so far. The mentioned triple-GEM based measurement systems were already tested at the WEST project and other devices recording soft X-ray (SXR) plasma radiation in the target range of 2-15 keV. Long term plans may envisage usage of gaseous detector based SXR diagnostics in DEMO reactor for real time plasma monitoring and control, as high neutron fluxes preclude application of semiconductor-based technologies. Conditions in fusion reactors as well as in currently operating devices necessitate simulating the interactions of high-energy photons and neutrons with the detector parts, including proper handling of primary ionization electrons paths, gas mixture fluorescence and collisions with detector materials. For this use case a full-detector simulation software was created based on the already existing interface and previous results obtained so far within the group. It combines Geant4 package for interactions with solid parts of the detector, Garfield++ for electron avalanching, Heed for X-ray interaction with gas, Gmsh and Elmer for meshing and electrostatics and introduces hybrid approach to the simulation of electron drift in different manner depending on the electron position with respect to multiplication stage. To optimize the computation time software employs precomputation algorithms in later stages of the electron cascades. The expected response profiles of the triple-GEM detector, exposed to55Fe calibration source radiation, were simulated and verified by comparing them with experimental data.

The paper presents developments and significant improvements of the soft X-ray measurement system installed at the WEST tokamak. In the introduction, a brief discussion is carried out in the scope of energy shortage, fusion energy as a remedy, and the necessity of impurities monitoring in the scope of stable and long plasma discharge. This requires high-speed and accurate measurement systems due to the intense data streams that need to be processed online. For that reason, the SXR GEM FPGA-based system was designed by the Institute of Electronic Systems of the Warsaw University of Technology, the Institute of Plasma Physics and Laser Microfusion from Warsaw, and installed at the WEST tokamak in collaboration with the Institute for Magnetic Fusion Research, Commissariat à l’Énergie Atomique. It is the second-generation system, whereas the first was installed at JET tokamak. The article describes the architecture of the designed electronic part of the system. The paper presents an entirely new approach for the data concentration module implemented in FPGA. The main premise is to select only active data and send them chronologically to the embedded computer with high throughput. It is the essential component for long-term plasma operations, about 1 min, now carried out at WEST tokamak during the C3 campaign. The paper describes the laboratory tests under the exploitation of various radiation sources and the implementation of the solution and measurements during tokamak plasmas. Previous and current data acquisition methods are compared. The results show that implementing a new local trigger has significantly improved the system performance compared to the global trigger-based acquisition. The results are approximately 17 times better in the scope of performance and more than 20 times better in terms of data compression. The described design was successfully applied during the most recent 2023 experimental campaign at the WEST tokamak.

After the problem of high-temperature plasma con fi nement, construction of diagnostics that is able to identify plasma contamination with impurities and to determine impurity distribution is another critically important issue. Solution of this problem would enable progress towards the success in controlled thermonuclear fusion. A new diagnostics, based on Gas Electron Multiplier (GEM) technology, has been recently developed for poloidal tomography focused on radiation of the metal impurities by monitoring in Soft X-Ray (SXR) region. GEM based detectors would undergo much less damage by neutrons than standard semiconductor diodes which results in better operational stability. This paper emphasizes the results of the latest examination of this type of detectors, showing in fl uence of the charging-up e ff ect on the detector performance and its physical properties for expected plasma radiation intensity. In addition, an undesired in fl uence of aging of the detector window ’ s material on the performance of the GEM detector is also shown: regular (moderate or active) usage could lead to changes of material ’ s morphology as well as its composition. This study con fi rms the importance of further research into material ’ s optimization of GEM detectors used as a base for SXR tomographic diagnostics aimed to work under di ff erent plasma radiation conditions.

Soft X-ray (SXR) radiation emitted from tokamak plasmas contains very useful information about plasma stability, shape and impurity content, all key parameters to improve plasma performance. In the deuterium-tritium phase of ITER, the high neutron fluxes, gamma and hard X-ray emission will constitute too harsh an environment to permit the use of classical semiconductor detectors. New SXR detector technologies, more robust to such environments, should thus be investigated. First GEM (Gas Electron Multiplier) measurements performed at WEST were successful and showed that both spatially and spectrally resolved calibrated data could be acquired. Strategies to reconstruct tungsten (W) impurity radiation synthetic diagnostics, modelling and real measurements based on multiple diagnostics are proposed.

The purpose of this research is to design and construct a plasma radiation imaging system for fusion devices which is focused on soft X-ray region from about 2 to 15 keV photon energy. The proposed 2D diagnostic system, as opposed to conventional 1D systems, is expected to benefit from tangential field of view and to deliver new data for toroidal phenomena observations. This contribution relates to the introductory development of such 2D system laying out details on the overall design of the detecting unit (based on GEM technology) as well as on its acquisition module. The results cover also the expected photon flux and spectra foreseen for COMPASS-U device, as a first choice for testing and verification. Considerations on working medium and internal structure of the detecting sensor are presented including electrodes configurations and collecting electrode pattern. The preliminary establishments for data acquisition system are presented as well.

WEST is an MA class superconducting, actively cooled, full tungsten (W) tokamak, designed to operate in long pulses up to 1000 s. In support of ITER operation and DEMO conceptual activities, key missions of WEST are: (i) qualification of high heat flux plasma-facing components in integrating both technological and physics aspects in relevant heat and particle exhaust conditions, particularly for the tungsten monoblocks foreseen in ITER divertor; (ii) integrated steady-state operation at high confinement, with a focus on power exhaust issues. During the phase 1 of operation (2017-2020), a set of actively cooled ITER-grade plasma facing unit prototypes was integrated into the inertially cooled W coated startup lower divertor. Up to 8.8 MW of RF power has been coupled to the plasma and divertor heat flux of up to 6 MW m(-2) were reached. Long pulse operation was started, using the upper actively cooled divertor, with a discharge of about 1 min achieved. This paper gives an overview of the results achieved in phase 1. Perspectives for phase 2, operating with the full capability of the device with the complete ITER-grade actively cooled lower divertor, are also described.

This work describes the progress of development of total core radiation power and soft X-ray (SXR) diagnostic system designed in accordance with the DEMO control requirements. Monitoring of energy loss through the separatrix is necessary for reliable plasma control. Data gathered by this system could also be helpful for studying spatial distribution of heavy impurities, MHD modes and their localization, plasma shape and position. Gas electron multiplier (GEM) technology is assessed as a base for a new radiated SXR power measurement system. The main advantages of this technology are the compactness of GEM detector, good temporal and spatial resolution, the ability to discriminate energy of incident photons and better neutron resilience than existing systems. All of these make it potentially a good candidate for SXR diagnostic system in ITER and DEMO. The scope of the study includes analysis of the feasibility of selected approaches, the design of the diagnostic system, necessary simulations and engineering considerations, and the proposal of an integration scenario. Preliminary design considerations for the GEM-sensor-based system under development have been done. Plasma radiation intensities and spectra have been simulated using data from the appropriate DEMO scenario. A concept of the photosensitive chamber has been assessed. Photoabsorption simulations with the proposed structure and parameters have been conducted and the results have been discussed.

The work describes a novel approach to the design of a fast, multichannel measurement system for plasma diagnostics [A. Wojenski et al., Fusion Eng. Des. 123, 727 (2016)]. Its main scope is to provide measurements of soft X-ray (SXR) emission during plasma phenomena at the W-Environment in Steady-state Tokamak (WEST), especially for monitoring and tracing tungsten impurities. This paper describes the vertical Gas Electron Multiplier (GEM) camera installed at the WEST [M. Chernyshova et al., J. Instrument. 10, P10022 (2015)]. The designed GEM detector readout board has more than 100 channels, resulting in high-performance requirements for the data acquisition and processing system. The novel system construction approach is that the unit works on the raw signals providing a high quality of the data, especially in the scope of pileup effect analysis. In the case of doubtful results, the source data can be easily reviewed offline. The data selection and transmission are done in Field-Programmable Gate Arrays (FPGAs) on the custom boards with the custom Peripheral Component Interconnect (PCI)-Express Gen2 switch that allows us to register signals from multiple FPGAs and then process the data by complex algorithms [G. Kasprowicz et al., J. Fusion Energy 38, 480 (2019)]. The firmware is replaceable and different working modes can be applied (some under verification): global trigger mode, high-speed data serialization, and extended signal registration. Low level optimized central processing unit software for data readout was also designed [P. Linczuk et al., J. Instrum. 14, C05001 (2019)]. The installation of the system is described due to complex system components' distribution. The first results of the successful acquisition of the plasma at the WEST are discussed. The corresponding SXR energy and topology spectra were computed. Those are the first technical measurements of the system to ensure verification of data quality.

The paper presents an optimization of a readout structure of the GEM-based detector designed for X-ray imaging for DTT tokamak in the energy range of 2–15 keV. The readout electrode of approximately 100 cm2 surface is composed of hexagonal pixels connected in a way that allows reducing the actual number of signal pixels (electronics channels). At the same time, based on time coincidence analysis, it makes possible to unambiguously identify the position of the recorded X-ray photon. For the input spectrum, the Detective Quantum Efficiency (DQE) of the detector was calculated using the Geant4 program and the spatial distributions of electron avalanches at the readout electrode were simulated using the Garfield++ program. These were conducted for a given energy range of radiation and a statistical distribution consistent with the shape of the spectrum considering the DQE of the detector. As a result, the size of a single hexagonal pixel was proposed to capture the position of the recorded radiation quanta in an optimal and effective way.

Creation and development of a new diagnostics useful for future thermonuclear reactors and helpful in studying impurity profiles, MHD modes/localization, and imaging are among urgent tasks in plasma research field. Global SXR imaging for DTT device in support of power exhaust programme and its consecutive impact for plasma core is an example of applicability of such diagnostics. This contribution presents the results of the ongoing development of the elaborated plasma X-ray imaging technology focusing on the design of the relevant structure of readout electrode. In order to achieve that, the details on the expected plasma radiation for the selected scenario for DTT machine were assessed. Then, the spatial distribution of plasma radiation intensity flux that will be reaching the detector window of the GEM based detector was simulated. Taking it into account along with the physical properties of the detector, the spatial and temporal distributions of charge cloud that will be reaching the readout plane were evaluated. The special design of the readout structure has been proposed that fulfil critical conditions originated from technological and physical constraints. The final effectiveness of the GEM based detector was evaluated proving that such detector is well suited for an effective plasma radiation imaging.

This contribution outlines the first preliminary acquisition data obtained by the GEM diagnostics on WEST. It was designed to monitor the radiation of impurities with a particular focus on the challenges of the elaborated plasma imaging technology in the area of SXR radiation. The details of the developed diagnostics and preliminary results obtained within the commissioning phase of the diagnostics at the WEST Project are provided. It is shown that both spatially and spectrally resolved calibrated data could be collected. A comparison with other WEST diagnostics manifests good qualitative agreement. Currently, the developed system records rather high energy part of the SXR radiation (above 4 keV), that nevertheless still could be useful to assess an intensification of the erosion.