ITER Requirements Research Articles

Summary of caesium evaporation and deposition during SPIDER first campaign

SPIDER (Source for the Production of Ions of Deuterium Extracted from a Radio frequency plasma) is currently in a major shutdown period dedicated to the upgrade of several components in order to enhance its performances and guarantee their agreement with the ITER requirements. During this phase, an in-depth inspection of the beam source components is fundamental to understand SPIDER behaviour during the previous experimental campaigns, and in particular caesium evaporation inside the source by means of Cs ovens. Caesium evaporation and its deposition on the plasma grid (PG) is fundamental to minimize the work function of PG surface causing an increased generation of negative ions and a reduction of the electron density in front of the PG, which means less co-extracted electrons. This work presents the analysis of the caesium ovens performances and of their status after removal. Inductively Coupled Plasma Mass Spectrometry (ICP-MS) analyses were carried out on samples of plasma source walls, and the experimental data was compared to the results obtained from other investigations: numerical models for the caesium evaporation and deposition, chemical surface analyses (performed in strategical locations of the source walls and extraction grid), and Laser Absorption Spectroscopy (LAS) measurements. The non-uniformity of Cs distribution has been taken into account since it has repercussions on negative ion extraction efficiency and uniformity.

A hybrid physics/data-driven logic to detect, classify, and predict anomalies and disruptions in tokamak plasmas

Disruptions are abrupt collapses of the configuration that have afflicted all tokamaks ever operated. Reliable observers are a prerequisite to the definition and the deployment of any realistic strategy of countermeasures to avoid or mitigate disruptions. Lacking first principle models of the dynamics leading to disruptions, in the past decades empirical predictors have been extensively studied and some were even installed in JET real time network. Having been conceived as engineering tools, they were often very abstract. In this work, physics and data-driven methodologies are combined to identify the main macroscopic precursors of disruptions: magnetic instabilities, abnormal kinetic profiles and radiation patterns. Machine learning predictors utilising these observers can not only detect and classify these anomalies but also determine their probability of occurrence and estimate the time remaining before their onset. These tools have been applied to a database of about two thousand JET discharges with various isotopic compositions including DT, in conditions simulating in all respects real time deployment. Their performance would meet ITER requirements, and they are expected to be easily transferrable to larger devices, because they rely only on normalised quantities, form factors, and physical/empirical scaling laws.

3D radiated power analysis of JET SPI discharges using the Emis3D forward modeling tool

Precise values for radiated energy in tokamak disruption experiments are needed to validate disruption mitigation techniques for burning plasma tokamaks like ITER and SPARC. Control room analysis of radiated power (P rad) on JET assumes axisymmetry, since fitting 3D radiation structures with limited bolometry coverage is an under-determined problem. In mitigated disruptions, radiation is toroidally asymmetric and 3D, due to fast-growing 3D MHD modes and localized impurity sources. To address this problem, Emis3D adopts a physics motivated forward modeling (‘guess and check’) approach, comparing experimental bolometry data to synthetic data from user-defined radiation structures. Synthetic structures are observed with the Cherab modeling framework and a best fit chosen using a reduced χ 2 statistic. 2D tomographic inversion models are tested, as well as helical flux tubes and 3D MHD simulated structures from JOREK. Two nominally identical pure neon shattered pellet injection (SPI) mitigated discharges in JET are analyzed. 2D tomographic inversions with added toroidal freedom are the best fits in the thermal quench (TQ) and current quench (CQ). In the pre-TQ, 2D reconstructions are statistically the best fits, but are likely over-optimized and do not capture the 3D radiation structure seen in fast camera images. The next-best pre-TQ fits are helical structures that extend towards the high-field side, consistent with an impurity flow under the magnetic nozzle effect also observed in JOREK simulations. Whole-disruption radiated fractions of 0.98+0.03/ −0.29 and 1.01+0.02/−0.17 are found, suggesting that the stored energy may have been fully mitigated by each SPI, although mitigation efficiencies well below ITER and SPARC requirements for high energy pulses are still within the large uncertainties. Emis3D is also used to validate JOREK SPI simulations, and confirms improvements in matching experiment from changes to impurity modeling. Time-dependent toroidal peaking factors are calculated and discussed.

Analysis of the Barriers to Smart City Development Using DEMATEL

This study analyzes the barriers to developing smart cities (SCs) using the decision-making trial and evaluation laboratory (DEMATEL) approach. The primary objective is to identify, classify, and assess the main barriers hindering the progress of SCs. Through an extensive literature review, twelve main barriers were identified. The DEMATEL approach models and analyzes the relationships among these barriers based on expert input. The results reveal that technical problems, a lack of infrastructure, and high costs are classified as cause barriers. Security and privacy concerns and the absence of coordinated planning are classified as effect barriers. This study emphasizes the need for established criteria and iterative development requirements. Although the influence of knowledge and skills gaps and a lack of awareness is less significant, these aspects still require attention. The findings suggest that a comprehensive approach focusing on technical solutions, infrastructure development, strategic planning, and cybersecurity measures can effectively overcome barriers. Regular evaluation of barrier dynamics is crucial for implementing adaptive measures. The results provide decision-makers with a valuable model to address the challenges and foster the efforts of SC stakeholders.

An iterative approach for model-based requirements engineering in large collaborative projects: A detailed experience report

In this paper, we report on our 7 years of practical experience designing, developing, deploying, using, and evolving an iterative Model-based Requirements Engineering (MBRE) approach and language in the context of five large European collaborative projects providing complex software-intensive solutions. Based on significant data sets collected both during project execution and via surveys realized afterward, we demonstrate that such a model-based approach can bring interesting benefits in terms of scalability (e.g., a large number of handled requirements), heterogeneity (e.g., partners with different types of RE background), adaptability and extensibility (e.g., to various project's needs), traceability (e.g., from the requirements to the software components), automation (e.g., documentation generation), consistency and quality (e.g., central model), and usefulness or usability (e.g., actual deployment and practical use). Along the way, we illustrate the application of our MBRE approach and language with concrete elements from these several European collaborative projects. More broadly, we discuss the general benefits and current limitations of using such a model-based approach and corresponding language, as well as the related lessons we learned during these past years.

Analysis of Al-generated Music Applications in Primary Schools under the STEAM Education System

As a refinement of STEM (science, technology, engineering, and mathematics), STEAM (science, technology, engineering, arts, and mathematics) is considered a more comprehensive and practical pedagogy. However, in China’s educational environment, without the combination of test-oriented content, such methodology is hard to apply and popularize. Therefore, how to integrate more STEAM elements into the classroom while still meeting the assessment objectives of the exams needs to be considered further. Besides, to meet the iterative requirement of STEAM design, integrating advanced technology elements, especially Al, is an unavoidable trend. With a focus on music in the arts section of STEAM, our research is mainly intended to discuss the validity and practicality of using AI to generate songs that can help both Chinese primary school teachers to make innovations in class content and students to memorize certain knowledge points. Drawing on findings in the previous literature on STEAM education concerning AI music, the impact of nursery rhymes, and related AI platforms, this study collects knowledge points that are appropriate for primary school students and produces AI-generated songs. Then we discuss how these songs can be integrated into the STEAM system. The study assumes that AI-generated knowledge memory songs are actionable and have a good potential for further development. These songs could have a significant positive impact on primary school students’ knowledge memory and also stimulate teachers’ interest in adapting more technology elements in their teaching to make teaching more creative.

China's progress on hot helium leak test of ITER shield blocks

China Domestic Agency (DA) will provide ITER with 220 shield blocks (SB) which are important, large, and actively water-cooled components in ITER vacuum vessel, their leakage rate shall not exceed 2.69×10−10Pa·m3/s in hot helium leak tests (HHLT) at 250±20 °C. The HHLT work started with developing a HHLT facility and manufacturing a SB full-scale prototype (FSP). The result showed the FSP could satisfy ITER's requirement at 235 °C. H2 outgassing from stainless steel surfaces is the main factor that impacts both the background leakage rate and sensitivity of the testing system in hot testing cases. Hydrogen-removal measures were taken to improve the facility performance, and a new facility was built. A better facility performance came out at 250 °C rather than 235 °C, the background leakage rate decreased by one order of magnitude while the system sensitivity increased by two orders of magnitude. The background is at 10−10 Pa.m3/s and 10−9 Pa.m3/s level at room temperature (RT) and 250 °C, respectively, while the system sensitivity is at 10−12 Pa.m3/s and 10−11 Pa.m3/s level at the two temperatures. With the two facilities, series HHLTs have been carried out on 50 SBs covering two types, with all results complying with ITER requirements.

Summary report of the 4th IAEA Technical Meeting on Fusion Data Processing, Validation and Analysis (FDPVA)

The objective of the Fourth Technical Meeting on Fusion Data Processing, Validation and Analysis was to provide a platform during which a set of topics relevant to fusion data processing, validation and analysis are discussed with the view of extrapolating needs to next step fusion devices such as ITER. The validation and analysis of experimental data obtained from diagnostics used to characterize fusion plasmas are crucial for a knowledge-based understanding of the physical processes governing the dynamics of these plasmas. This paper presents the recent progress and achievements in the domain of plasma diagnostics and synthetic diagnostics data analysis (including image processing, regression analysis, inverse problems, deep learning, machine learning, big data and physics-based models for control) reported at the meeting. The progress in these areas highlight trends observed in current major fusion confinement devices. A special focus is dedicated on data analysis requirements for ITER and DEMO with a particular attention paid to artificial intelligence for automatization and improving reliability of control processes.

SPIDER, the Negative Ion Source Prototype for ITER: Overview of Operations and Cesium Injection

An overview of the recent operations and the main results of cesium injection in the Source for the Production of Ions of Deuterium Extracted from Rf plasma (SPIDER) negative ion source are described in this contribution. In experiments without cesium injection, all SPIDER plants were tested to verify the basic expectations on the operational parameters (e.g., electron cooling effectiveness of magnetic filter field) and to determine its operational region. For beam properties, it was shown that the current density varies across the beam in the vertical direction. In preliminary cesium experiments, the expected increase of negative ion current and simultaneous decrease of co-extracted electrons were found, along with the influence of the control parameters (polarization of the plasma electrodes, magnetic filter field) on the SPIDER beam uniformity in the horizontal and vertical directions. It was shown that non-Gaussian tails can be identified in the angular distribution on the plane perpendicular to the beam propagation direction. Stray particles, nonhomogeneous beam and large divergence might result in unexpected heat and particle loads over ITER neutral beam injector (NBI) accelerator grids; it is the goal of SPIDER to assess and possibly to identify suitable methods for controlling these beam features. A major shutdown, planned for late 2021, to solve the issues identified during the operation and to carry out scheduled modifications, is outlined. Such improvements are expected to allow SPIDER to pursue the ITER requirements in terms of negative ion current, electron-to-ion ratio, and beam duration.

Assessment of the Structural Vibration Effect on Plasma Current Measurement Using a Fiber Optic Current Sensor in ITER.

In this paper, we assess the effect of cryostat bridge vibrations on the plasma current measurement accuracy when using a fiber optic current sensor (FOCS) in ITER. The impact of vibrations on the light polarization state was first experimentally investigated using a miniaturized mock-up which represented a relevant part of the ITER FOCS structure. The set-up was then numerically simulated using the Jones matrix approach. Equivalent vibration matrices obtained from the experiment were used in the simulations to determine the effect of the vibrations on the FOCS accuracy. It is demonstrated that although the vibrations imply some changes in the polarization state, this effect can be strongly reduced when a proper low-birefringent spun optical fiber is used. The ITER requirement regarding the plasma current measurement accuracy can therefore be fulfilled.

A multilevel block preconditioner for the HDG trace system applied to incompressible resistive MHD

We present a scalable block preconditioning strategy for the trace system arising from the high-order hybridized discontinuous Galerkin (HDG) discretization of incompressible resistive magnetohydrodynamics (MHD). We construct the block preconditioner with a least squares commutator (BFBT) approximation for the inverse of the Schur complement that segregates out the pressure unknowns of the trace system. The remaining velocity, magnetic field, and Lagrange multiplier unknowns form a coupled nodal unknown block for which a system algebraic multigrid (AMG) is used to approximate the inverse. The complexity of the MHD equations together with the algebraic nature of the statically condensed HDG trace system makes the choice of smoother in the system AMG part critical for the convergence and performance of the block preconditioner. Our numerical experiments show GMRES preconditioned by ILU(0) of overlap zero as a smoother inside system AMG performs best in terms of robustness, time per nonlinear iteration and memory requirements. With several transient test cases in 2D and 3D including the island coalescence problem at high Lundquist number we demonstrate the robustness and parallel scalability of the block preconditioner. Additionally for the upper block a preliminary study of an alternate nodal block system solver based on a multilevel approximate nested dissection is presented. On a 2D island coalescence problem the multilevel approximate nested dissection preconditioner shows better scalability with respect to mesh refinement than the system AMG, but is relatively less robust with respect to Lundquist number scaling. In the Appendix B, we rigorously show: (1) the uniqueness of the solution of the nonlinear MHD system for small time, (2) the convergence of the Picard iterations for each backward Euler step, and (3) the convergence of the entire time stepping procedure.

Testing of the ITER Central Solenoid Modules

The ITER Central Solenoid is under fabrication by the U.S. ITER organization and its subcontractors. U.S. ITER will supply seven modules to ITER IO, six of which will be assembled in a stack that forms the ITER Central Solenoid. The first modules that were built by GA at their facility, went into high voltage testing, including Paschen testing in the vacuum, and then they were tested at 4.5 K and up to 40 kA to demonstrate compliance of the coil with the ITER requirements. In this article, we present the Test Plan and results of the central solenoid (CS) module’s performance, especially at the full current. We measured critical temperatures in several pancakes, we measured ac losses, joint resistance, and hydraulic characteristics of the coils. We also measured displacements of the coil height and hoop strain of the CS module (CSM) to verify the structural mechanical characteristics of the coil along with the cooldown shrinkage of the coil. We studied the performance of the cowound quench detectors and confirmed their effectiveness in the suppression of inductive noise. This information is necessary for verification of the stack behavior of CS in ITER operation. The test results and preliminary analyses are presented, compared to expectations, and discussed.

Evaluation of Mass Production Results of Cryogenic Structural Stainless Steels for ITER Toroidal Field Coils

The National Institutes for Quantum Science and Technology (QST) has been developing new cryogenic structural materials, such as JJ1 stainless, and nitrogen-enhanced 316L stainless, known as 316LN, since the 1980s for increased tensile strength to comply with the ITER requirements. QST has also developed prediction curves for yield stress and tensile strength at temperatures from room temperature to 4 K based on the actual properties of these materials at room temperature to reduce the number of tensile tests conducted at 4 K, which are costly. After material trials and qualifications, the manufacture of material candidates began in earnest from 2012. In total, over 2400 materials (over 5000 tonne) were manufactured by six fabricators until manufacturing was completed successfully in 2020. The material properties of each material candidate were evaluated by QST and added into a database registry. Sampling tests, e.g., tensile tests were conducted at 4 K and 77 K. The correlations between the mechanical and material properties were evaluated to optimize material specifications of future superconducting magnets. The accuracy of QST's prediction curves was also confirmed. This paper summarizes the evaluation of the material properties and the prediction accuracy of mass-produced materials for the ITER toroidal field coil cases.

Development of the NPA based diagnostic complex in ITER

The NPA based diagnostic complex in ITER consists of four diagnostics: the neutral particle analyzers, the diamond neutral particle spectrometer, the gamma-ray spectrometer, and the neutron spectrometer. The diagnostics are located in equatorial port #11 and share the same vacuum channel. The present paper considers the physical basis of the diagnostic complex and its measurement capabilities in ITER. In addition, the design of the complex and the engineering solutions implemented to meet the ITER requirements are described.

Quantitative analysis of hydrogen isotopes in hydrogen storage material using laser-induced breakdown spectroscopy

• The scanning-coaxial LIBS system is set up for in-situ measurements in fusion reactors. • Titanium foil with different hydrogen and deuterium contents is prepared and determined. • Hydrogen isotopes are analyzed quantitatively using the internal standard method (ISM) and the calibration free method (CF-LIBS). • The single sample correction calibration free method (SSCCF) is applied to improve the accuracy. The accurate determination of hydrogen isotopes in materials is always a challenge for laser-induced breakdown spectroscopy (LIBS). In this study, the content of hydrogen isotopes in hydrogen storage materials is quantitatively analyzed by LIBS using the internal standard method (ISM) and the calibration-free method (CF-LIBS), respectively. Based on the self-built LIBS system, the concentrations of hydrogen and deuterium in titanium hydride with various stoichiometric ratios are quantitatively analyzed. The local thermodynamic equilibrium (LTE) conditions of the plasma are evaluated by the calculation results of the plasma temperature and density: the plasma temperatures are 16000 ± 1000 K calculated by Boltzmann diagram of titanium, and the plasma electron densities are about 10 22 m −3 calculated by the H α line of spectra. Through integral intensity correction, the correlation coefficient of the calibration curves of hydrogen and deuterium is successfully increased by 3% in the internal standard method; The single sample correction is used in CF-LIBS to improve the accuracy of the measurement of hydrogen isotopes in titanium hydride, and the calibration results demonstrate that the average absolute errors are 8.3% and 3.2% for hydrogen and deuterium. We also compare the calculated contents of hydrogen isotopes in titanium hydride by integral intensity correction internal standard method (IICIS) and single sample correction calibration-free method (SSCCF). The SSCCF increases the accuracy of the hydrogen isotope contents compared with CF-LIBS in the range of 20 to 55 at.%. The results are not as precise as the IICIS but meet the ITER requirements in a way. The results provide a valuable reference for the precise measurement of hydrogen isotope content in materials for applications in hydrogen energy, nuclear energy, and nuclear technology.

Study of beamlets extracted from a multi-aperture and five-stage acceleration system.

A beam optics study using the ITER-relevant high intense negative ion beams, such as 1MeV, 200 A/m2, has been performed experimentally and analytically using a multi-aperture and five-stage accelerator. Initially, multi-beamlets generated from this accelerator were deflected in various directions due to the magnetic field and space charge repulsion between beams and showed various divergences. These had limited the pulse length and the beam energy. Compensation methods of the beamlet deflections have worked effectively and contributed to achieving the ITER requirement, the divergence angle of <7 mrad, and the deflection angle of <1 mrad for 1MeV beam. The beam pulse has been gradually extended from 1 to 100s and is now going to a longer pulse based on these results. One of the remaining issues is to understand and suppress peripheral components of the beam, namely, the halo, and to reduce the local heat loads observed around the aperture edge. This halo component has been successfully distinguished from the beam core by using a newly developed beam emittance measurement system for high intense beams. By combining this measured beam emittance and the beam simulation, it was clarified for the first time that the halo components are generated in an area of 1mm width from the aperture edge.

Progress in ITER ECE diagnostic design and integration

The ITER electron cyclotron emission (ECE) diagnostic system has primary roles in providing measurements of the core electron temperature profile and the electron temperature fluctuation associated with the neoclassical tearing modes. The ITER ECE system includes a radial and oblique line-of-sight. Four 43-meter long low-loss transmission lines (TLs) are designed to transmit millimeter wave power in the frequency range of 70–1000 GHz in both X- and O-mode polarization from the port plug to the ECE instrumentation room in the diagnostic building. The measurement instrumentation includes two Fourier transform spectrometer (FTS) systems and two radiometer systems. The Indian Domestic Agency (IN-DA) and United States Domestic Agency share the responsibility. The IN-DA scope excluding instrumentation and control has passed its preliminary design review and is progressing towards the final design review (FDR). In parallel, the diagnostic integration in different areas is ongoing. Several captive components for the TLs have passed FDR and will be manufactured for installation in the tokamak building soon. A peer review meeting has been held on the prototype hot calibration source, and its integration and new thermal analysis in the diagnostic shield module are continuing. A prototype TL is being tested. A prototype polarizing Martin-Puplett type FTS, operating in the frequency range 70–1000 GHz, features an in-vacuo fast scanning mechanism and a cryo-cooled dual-channel THz detector system. Its performance has been assessed in detail against ITER requirements.

Preliminary parametric analysis of the first neutrons measured with a scintillator array at SPIDER

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.

High Power Density Beam Measurement of a Single Beamlet Multi-Grid Prototype H- Negative Ion Accelerator

Beam optics of the ITER prototype accelerator with 88 mm acceleration gap length has been examined through H- beam acceleration tests at the ITER target beam perveance. The beam optics has been examined for beam energies up to 790 keV under the ITER target perveance. The total grid heat load was successfully reduced to 10 %, which was lower than the allowable value of 15 %. The beam emittance of the ITER perveance has been measured for the first time by using newly developed emittance measurement system consisting of carbon-fiber-composite (CFC) plate with pin-holes. The emittance of 790 keV H- beam shows the divergence angle of the beam core is satisfied with the ITER requirement of <7 mrad. Measurement at the beam periphery was made possible by modifying the pin-hole size of pepper-pot apertures, and the observed divergent components were 20 mrad. The ratio of the diverged beam became lower with the increase of the beam energy. This result contributes the design of the ITER accelerator and the beam line components.

Integration of ITER diagnostic ports at the Budker institute

The paper presents results of the design development of the diagnostic equatorial and upper ports by RF DA (Russian Federation Domestic Agency) and results of the preparation of the production and assembly areas. The ports are being developed at the Budker Institute of Nuclear Physics of the Siberian Branch of the Russian Academy of Sciences (BINP) in good coordination with the ITER Central Team with the task of standardizing ports. Studies of boron carbide ceramics were conducted to prove that they meet the requirements of ITER. The preparation of port-plug production and the construction of the assembly hall at the BINP are described.