Fusion Energy Research Articles

Nonlinear excitation of energetic particle driven geodesic acoustic mode by Alfvén instability in ASDEX-Upgrade tokamak

Abstract Recently, the coexistence of multiple energetic particle driven instabilities was observed in experiments on the ASDEX-Upgrade tokamak[P. Lauber et al., EX 1-1, 27th IAEA Fusion Energy Conference, 22-27 October 2018, Gandhinagar, India]. A hybrid simulation using the MEGA code was performed to investigate the properties of those instabilities. The basic mode properties obtained in the simulations, such as mode frequencies, mode numbers, and inward energetic particle (EP) redistribution, are in good agreement with the experiments. It is found that the energetic particle driven geodesic acoustic mode (EGAM) is initially stable, then zonal flow gradually occurs with the growth of the Alfvén instability, and finally, the EGAM is nonlinearly excited and the amplitude exceeds the Alfvén instability. The dependence of EGAM properties on EP pressure and pitch angle distribution is analyzed. The EGAM amplitude increases with EP pressure. The nonlinearly excited EGAM is a high-frequency branch that appears even under the condition of a slowing-down EP distribution. The resonant particles are also analyzed, but the dominant resonant particles of the EGAM in the linear growth phase are not found because the EGAM does not grow in the linear regime. In the phase space of pitch angle variable Λ and energy E, it is found that initially the Alfvén instability is excited by EPs with poloidal frequency 70 kHz, then, after the saturation of the Alfvén instability, the resonance region moves towards lower energy and touches the EGAM resonance line, and finally, EGAM is excited by the particles with poloidal frequency 50 kHz. This process is a kind of resonance overlap.

Highest fusion performance without harmful edge energy bursts in tokamak

The path of tokamak fusion and International thermonuclear experimental reactor (ITER) is maintaining high-performance plasma to produce sufficient fusion power. This effort is hindered by the transient energy burst arising from the instabilities at the boundary of plasmas. Conventional 3D magnetic perturbations used to suppress these instabilities often degrade fusion performance and increase the risk of other instabilities. This study presents an innovative 3D field optimization approach that leverages machine learning and real-time adaptability to overcome these challenges. Implemented in the DIII-D and KSTAR tokamaks, this method has consistently achieved reactor-relevant core confinement and the highest fusion performance without triggering damaging bursts. This is enabled by advances in the physics understanding of self-organized transport in the plasma edge and machine learning techniques to optimize the 3D field spectrum. The success of automated, real-time adaptive control of such complex systems paves the way for maximizing fusion efficiency in ITER and beyond while minimizing damage to device components.

An Improved Voltage Control Method for EAST Fast Control Power Supply

The Experimental Advanced Superconducting Tokamak (EAST) fast control power supply (FCPS) is an important device for controlling the vertical displacement of plasma during the nuclear fusion power generation process, adopting a multiple H-bridge invertor branch parallel operation structure to output total current. At the beginning of each shot of plasma discharge, FCPS works in open-loop voltage control mode (VCM) or closed-loop current control mode (CCM) determined by the plasma control system to output current for exciting the load coil, to achieve plasma vertical displacement control. VCM has the characteristics of fast dynamic response speed but poor consistency of branch current and insufficient branch current control accuracy and stability because of open-loop control. CCM has the characteristics of high branch current control accuracy but poor dynamic response and robustness because of control delay and control parameters determined based on engineering experience. To achieve fast and robust control, an improved voltage control method (IVCM) is proposed by combining the advantages of VCM and CCM. In the beginning of establishing the output current, FCPS operates in VCM, and rapid establishment of the output current is ensured. After the output current rapidly increases to the critical value, closed-loop current control is added to VCM to ensure the accuracy of output current control. In closed-loop current control, linear super-twisting sliding mode control is designed to achieve fast and robust control, ensuring good consistency and fast dynamic response performance of each branch current. Simulations and experiments verify that the designed IVCM has better compatibility characteristics in output current stability, control accuracy, and consistency of each branch current compared to VCM.

Legal Issues of Fusion Technologies

Abstract A comprehensive regulatory framework for fusion must consider the unique characteristics and challenges of fusion technology, including safety, environmental protection, waste management, export/import control, and nuclear liability. The International Atomic Energy Agency (IAEA) has established safety standards and guidelines related to fusion, but more needs to be done to address the gaps in the existing legal frameworks. The article emphasizes the need for clear and predictable regulations to provide confidence for investors and promote the research, development, and deployment of this promising technology. Although significant progress has been made in recent years, commercial fusion power is still likely many years away from being a reality, but a legal framework is essential for its eventual success.

Development of pulsed plasma operation scenario and required conditions in JA DEMO

Abstract We have developed the pulsed plasma operation scenarios for JA DEMO, a design concept of the steady-state tokamak demonstration reactor, to clarify controls of the current profile and power required for the operation. We compare the scenarios when injecting electron cyclotron waves only and both neutral beam and electron cyclotron waves for external heating and current drive. We demonstrate current profile control that maintains the minimum value of the safety factor above one and avoids creating the local minima in the safety factor profile and power control by argon seeding that maintains the fusion power constant at the desired value and reduces the heat load on the divertor, performing long-time integrated modelling simulations. We clarify the conditions of the heating and current drive system and impurity injection system required for such control. The dependence of power control on argon anomalous transport coefficients is investigated. We have the prospect of maintaining the fusion power of 1 GW for more than two hours, i.e., obtaining the required plasma performance determined using a systems code.

Ion–surface interactions in plasma-facing material design

A multi-scale simulation framework for ion–solid interactions in plasma-exposed materials provides crucial insight into advancing fusion energy and space electric propulsion. Leveraging binary-collision approximation (BCA) simulations, the framework uniquely predicts sputter yields and analyzes material transport within volumetrically complex materials. This approach, grounded in the validated BCA code TRI3DYN, addresses key limitations in existing models by accurately capturing ion–solid interaction physics. A case study is presented, highlighting the framework’s ability to replicate experimental sputter yield results, underscoring its reliability and potential for designing durable materials in harsh plasma environments. Insights into sputtering transport phenomenology mark a significant advancement in material optimization for improved resilience in plasma-facing applications.

360-Degree Tri-Modal Scanning: Engineering a Modular Multi-Sensor Platform for Semantic Enrichment of BIM Models

Abstract. Point clouds, image data, and corresponding processing algorithms are intensively investigated to create and enrich Building Information Models (BIM) with as-is information and maintain their value across the building lifecycle. Point clouds can be captured using LiDAR and enriched with color information from images. Complementary to such dual-sensor systems, thermography captures the infrared light spectrum, giving insight into the temperature distribution on an object’s surface and allowing a diagnosis of the as-is energetic health of buildings beyond what humans can see. Although the three sensor modes are commonly used in pair-wise combinations, only a few systems leveraging the power of tri-modal sensor fusion have been proposed. This paper introduces a sensor system comprising LiDAR, RGB, and a radiometric thermal infrared sensor that can capture a 360-degree range through bi-axial rotation. The resulting tri-modal data is fused to a thermo-color point cloud from which temperature values are derived for a standard indoor building setting. Qualitative data analysis shows the potential for unlocking further object semantics in a state-of-the-art Scan-to-BIM pipeline. Furthermore, an outlook is provided on the cross-modal usage of semantic segmentation for automatic, accurate temperature calculations.

Improved structure and enhanced properties of detonation sprayed W coating via hot isostatic pressing

Tungsten has garnered significant attention for its superior performance as a plasma-facing material in tokamak devices. However, its hardness and high ductile-to-brittle transition temperature present challenges for its application in plasma-facing components. To address these issues, this study employs the detonation spraying (DS) technique to prepare tungsten coatings on a TZM alloy substrate and further optimizes their properties through hot isostatic pressing (HIP) treatment. Advanced characterization techniques were utilized to conduct a detailed microstructural and compositional analysis of the coatings. The results indicated that the HIP treatment significantly reduced the porosity of the coatings, improving their density and overall quality. Additionally, HIP treatment led to a decrease in internal stress, a reduction in dislocations, and the grain growth within the coatings. The study also discussed how the HIP process improved the microstructure of the DS tungsten coatings through these mechanisms, thereby enhancing the coatings' thermodynamic properties. Mechanical property tests revealed that the coatings treated with HIP exhibited higher bonding strength and lower hardness, attributed to the increase in grain size and the reduction in dislocation density within the coatings. Thermal property tests demonstrated that the HIP-treated coatings possessed higher thermal diffusivity and specific heat capacity in the temperature range of 100 to 500 °C. Furthermore, the performance of the coatings under transient high heat flux conditions was significantly improved after the HIP treatment, showing better resistance to the thermal shock and cracking. These findings are of great importance for understanding the performance enhancement of DS tungsten coatings in nuclear fusion reactor applications via HIP, especially as candidate materials for the first wall of tokamak devices.

Bremsstrahlung power conversion for fusion power and propulsion in space

Centrifugally confined Direct Fusion Drive propulsion has the capability of greatly advancing humanity’s ability to traverse and explore the solar system. p-11B is a promising fusion fuel to use in such a system because the reaction is aneutronic. However, a large amount of bremsstrahlung radiation is produced and must be converted into electricity to power the electric field used to help confine the fusion plasma. This work details an idealized analytical model to determine the viability of using a thermionic energy converter for this purpose. The model finds a maximum power density of 105W/m2 with a Carnot efficiency of 30%. The required electric and magnetic fields to produce net positive fusion power are >350MV/m and ∼30T respectively. This data is then used to discuss the feasibility of using p-11B as a fusion fuel for Direct Fusion Drive.

Fusion plasma turbulence research beyond the burning plasma era: perspectives on transport model validation in fusion and fission

In fusion, the validation of turbulent transport models is undertaken with the goals of making basic physics discoveries as well as for development of new predictive models to improve the operation and enhance the performance of existing and future fusion reactors. A fusion industry is just beginning to emerge globally. Like fission, validation in fusion energy research is a vibrant research area, but unlike fusion, a fission industry exists. The fission power industry motivates validation efforts, often performed at universities with small-scale experiments and advanced models and simulations developed in-house. Because fission research spans basic physics and applications, and addresses near-term and long-term industry interests, validation is thriving. This perspective article describes the validation of turbulent transport models in both fusion research and fission research, draws parallels between the validation methods and techniques used in two areas of the fields, and presents an outlook for thriving university fusion and fission research programs underpinned by a virtual cycle of basic and applied research that supports industry needs as well as tackling intellectual grand challenges.

Benefits of the Super-X divertor configuration for scenario integration on MAST Upgrade

The integration of good core and edge/pedestal confinement with strong dissipation of heat and particles in the divertors is a significant challenge for the development of fusion energy. Alternative divertor configurations offer potential advantages by broadening the operational space where a device can operate with detached divertors and acceptable power exhaust. First results from MAST Upgrade are presented from high confinement mode experiments with outer divertors in the Super-X divertor configuration, showing that the outer divertors naturally detach when the Super-X is formed with no discernible impact on the plasma core and pedestal. These initial findings confirm predicted benefits of the Super-X configuration in terms of facilitating scenario integration.

Tritium transport modelling in Europe: Current status, multi-physics integration and proposal of material property data

The capability to predict tritium retention and permeation by accurate and reliable tritium transport models for the breeding blanket design development is one of the most relevant objectives of the European Test Blanket Module (TBM) Programme. This also represents a key aspect for the development and licensing of next-future fusion systems and power plants, including the European DEMO. Tritium analyses can be performed using either system-level models to calculate global blanket and the related ancillary system performances or detailed 3D models for spatially limited areas and critical regions: the choice between these two modelling approaches depend on the objective of each analyse. When looking at the accuracy of tritium transport simulations, two main aspects have to be considered: the first one is the completeness of the description of the physical phenomena participating to the tritium transport dynamics; the second one is the reliability of the tritium transport material property values used in the simulation activities.In this context, this paper has the objective to carry out a critical analysis on the status of the integration of the most relevant multi-physics elements, providing recommendations on the approach to follow, with a particular focus on the system-level codes. Moreover, a set of data and correlations on tritium transport materials properties is proposed as a first step towards a material property database to be shared within the breeding blanket community.

Optimization of pellet design parameters to achieve deep fueling depth in EAST plasma with PAM code

Abstract Deep pellet fueling depth is necessary to achieve a high-density high confinement operation and to conduct some pellet-related researches in current devices, such as trigger of internal transport barrier, and to achieve high fusion power and tritium burn-up fraction in future fusion devices. The newly developed PAM code which can make a fast evaluation on pellet ablation and deposition is applied to optimize injection parameters to achieve deep pellet fueling. Systematic scans on pellet injection parameters including pellet injection position, injection angle, size and speed are performed for optimization purpose, while at the same time demonstrating flexibility and time efficiency of the PAM code. Dependences of the pellet fueling depth on these injection parameters are revealed by simulation results and analyzed. Simulation results indicate that pellet penetration contributes more to the deep pellet deposition than the ∇B-induced plasmoid drifts in low temperature plasmas, while deep pellet fueling in reactor relevant high temperature plasmas has to rely on plasmoid drifts. Though a shallow penetration is expected in high temperature plasmas, the ∇B-induced plasmoid drift is expected to be larger than that in relatively low temperature plasmas.

Numerical Approach for Investigating the Influence of Various Flow and Fluid Parameters on the Performance of a Cryogenic Two-Phase Flow Meter

Despite the intricacy, inline metering of two-phase flow has a significant impact in multitudinous applications, including nuclear fusion reactors, particle accelerators, and other systems that use cryogenic fluids. In this regard, a new concept for two-phase flow metering has been developed using model fluids. However, the geometric configurations of the channels and fluid properties are pivotal in ensuring accurate flow rate measurement. In this study, numerical analysis are performed to investigate the influence of channel width, number of channels, and gravitational field on the performance of the flow meter. The liquid height extracted from the volume fraction contour using an image processing tool has been used for calculating the mass flow rate of the liquid. The measured flow rate has been compared with the theoretical data, and it shows acceptable correspondence within ±6%. The investigations suggest that the increase in channel width governs the slope development. The appropriate width of the channel has been found to be ranging between 1mm and 3mm for the selected flow conditions and configurations. It is found that as the number of channels is increased from 10 to 20, the flow rate range that the system can measure within ±5% error has increased from 250g/s to 450g/s. The analysis broadened the reliability of the supposition and, therefore, provided a sturdy base for developing a cryogenic two-phase flow meter.

Secondary phases characterization by SANS and XAS of an ODS ferritic steel after thermal aging at 873 K

An ODS steel with nominal composition Fe–14Cr–2W–0.4Ti-0.3Y2O3 (wt.%) was produced by mechanical alloying, compacted by hot isostatic pressing (HIP) followed by hot cross rolling (HCR). To check the effects of thermal aging at relevant temperatures of operation of fusion power plants, the alloy was thermally aged at 873 K for 2000 h. In this work, small-angle neutron scattering (SANS) and X-ray absorption spectroscopy (XAS) techniques are used for the advanced characterization of secondary phases and the oxide nanoparticle dispersion. SANS results show that the oxide nanoparticles remain stable after the thermal aging treatment. Composition of the oxide nanoparticles was identified as Y2TiO5 or Y2Ti2O7 by SANS, while non-stoichiometry was found by XAS analysis. Laves phase precipitation after the thermal aging treatment is further confirmed by SANS, from the magnetic anisotropic contribution to the scattering intensity associated to this metallic phase, and by XANES.

Analysis Framework for Nuclear Heating Effects on HTS-Based Conductors in Fusion Power Plants

Analysis Framework for Nuclear Heating Effects on HTS-Based Conductors in Fusion Power Plants

Reducing the user burden when running MELCOR for accident analysis for a tokamak

MELCOR is a software tool for accident analysis with a long history in the fission sector. A model has been developed for use in MELCOR, using proposed layouts of EU DEMO and assumptions based on current design choices, to facilitate safety design and development for fusion power plants.There seems however to be a misconception that MELCOR is difficult to run and that the tasks must be executed sequentially. Accident analysis also requires reruns of multiple slightly different scripts. We have streamlined the running of MELCOR tasks to allow simultaneous execution on a computing cluster. The input decks are version controlled within UKAEA's internal GitLab repository, and shell scripts wrap the separate MELCOR invocations, embed specific job parameters, and keep separate the inputs and outputs of multiple separate instances.We illustrate the streamlined running using two examples: a matrix representing potential responses to an incident by different valves, and a parameter sweep across a range of response times for a single valve. The new technique is shown to be a much faster method of carrying out sensitivity studies and allowing further investigations into specific areas of concern in more detail.

SITUACIÓN ACTUAL, DESAFÍOS Y PERSPECTIVAS DE LA FUSIÓN NUCLEAR CONTROLADA: LA TECNOLOGÍA

This article objectively discusses the potential of development of nuclear fusion as a profitable energy source for the society of the future. After a brief exposition treating the physical foundations on which nuclear fusion is based – that are known for a century -, attention is drawn to the formidable difficulties that have been encountered when trying its practical implementation in a controlled device, and to the different proposals for reactors which have been conceived with the aim of overcoming them and demonstrate its scientific-technical feasibility. Information is provided regarding the most relevant (public and private) projects that are currently being developed in this field, which exhibits a situation characterized by the strong irruption of private initiative in recent years, and by diversification in terms of concepts and reactor designs, without it being clear at the moment which solution will prevail in the commercial stage, or whether the path to that goal will be completed by several models that will coexist. It is estimated that, in the most optimistic case and thanks to the impetus given by private initiative, the first commercial fusion energy plants could be available in the 2040s, making it plausible that public-private collaboration mechanisms will proliferate. The enormous advantages that this resource would bring to society are pointed, taking account of its virtues as a clean, safe, almost unlimited and cheap energy. This article will be continued by another devoted to exploring the economic viability of fusion technology, assuming the high level of uncertainty associated with both the vagueness of the details in the design and operation of the plants, as well as the lack of knowledge in the energy environment, economic and social in the coming years. Keywords: energy sources, energy prospective, energy technology, controlled nuclear fusion, energy economics, decarbonization.

Evaluation of the operational curve for heat storage technology using n-octacosane/low-density as a binding material

Heat storage technology has a critical role for a number of applications involving renewable thermal energy (such as solar water heater). The application of wax (n-octacosane/OCT) as a medium for storing heat brings many positive influences for the system. However, the operational curve is undesirable for the OCT-based energy storage, which makes it necessary to use a binding material. The present work employed LD-class polymer (LDPE) and linear-LDPE as binding materials for OCT. The mixture is prepared through mechanical hot stirring, which comes into two categories: SOCT1 (OCT/LD) and SOCT2 (OCT/LLD). The assessment through the calorimetry method shows an increment in transition temperature for SOCT with a value of 2.1 °C and 5.5 °C. This contributes to the variation of fusion energy for solid-liquid change for both materials, which amounted to 132.05 J/g (SOCT1) and 113.4 J/g (SOCT2). Another assessment related to its chemical and structural phase demonstrates that SOCT has an identical structure to OCT, indicating that SOCT is mixed physically. At the operational level, SOCT is more optimal than OCT according to the indicator related to charge and discharge duration for energy exchange. SOCT1 demonstrates a short plateau line as the indication of a steady transition between 65.4–67.9 °C, while SOCT2 indicates the average heating rate, which is higher than for single OCT. The heat releasing curve for SOCT1 varies at a lower value between 1.92 °C/min and 0.77 °C/min, while SOCT2 has the lowest variation, which is only 0.17 °C/min. Moreover, the self-insulation for SOCT2 has the lowest rate, which is only 0.3 °C/min. The evaluation and analysis from this work show that SOCT is reliable to increase the operational curve of OCT and can be implemented for thermal systems

Combining Chemical Vapor Deposition and Spark Plasma Sintering for the Production of Tungsten Fiber‐Reinforced Tungsten (Hybrid – Wf/W)

Successful upscaling of tungsten fiber‐reinforced tungsten composites (Wf/W) on industrial level could represent an important milestone for future nuclear fusion reactors. The primary objective of these materials is to enhance the durability and operational lifespans of critical components. Developing mature manufacturing approaches remains a challenge, highlighting the need for innovative solutions. This study evaluates the feasibility of merging chemical vapor deposition (CVD) with spark plasma sintering (SPS) for producing such composites. This analysis indicates that combining CVD‐W sealed tungsten fabrics with SPS requires additional manufacturing steps or the utilization of tungsten powders for effective sintering. The process is currently only suitable for simple textile structures utilizing single filaments, mitigating one of the main advantages of CVD. Configurations such as radially braided yarns are currently less compatible to the high stress levels during SPS. A key outcome of this work is the introduction of a thin secondary CVD‐W interface into the composite design, substantially improving the stability of the yttria‐interface and effectively shielding the W‐fibers from potential matrix interactions. This innovation reduces issues such as carbon embrittlement and allows the potential integration of tungsten fibers into different matrix materials such as ceramics, broadening the potential application range of tungsten fiber‐reinforcements.