Journal of Fusion Energy最新文献

At the National Institute of Fusion Science (NIFS), the deuterium plasma experiment was conducted using the large helical device (LHD) from 2017 to 2022 for the high performance of the plasma experiment. Through this experiment, a small amount of tritium was produced by D-D fusion reaction and released to the atmospheric environment through the stack. To understand the impact of tritium on the environment, environmental tritium monitoring was conducted before, during, and after the experiment for public acceptance and in accordance with local governments. From this monitoring, no impacts were observed on monthly precipitation and pine needle samples at the NIFS site. As the result of a comprehensive assessment combined with atmosphere and environmental water monitoring, it was concluded that the impact of discharged tritium from the stack of LHD to the surrounding environment would be none and/or negligibly small.

The Impurity Powder Dropper (IPD) is a device capable of injecting controlled amounts of sub-millimetre powder into the plasma under the action of gravity. In 2019 the IPD was first installed on the Large Helical Device (LHD) in Japan, with the aim of improving the plasma performances through real time boronization and assessing the compatibility of this technique with steady state operation. Extensive series of experiments have been performed using the IPD, focused on the improvement of the plasma performance via low-Z powder injection and the understanding of the underlying physical phenomena. In this article, we review the experiments that took place in the period 2019-2024. The main results include the demonstration of the improvement of the wall conditions (reduction of intrinsic impurity content, wall recycling) both on a shot-to-shot basis and in real time. Furthermore, a reduced-turbulence improved confinement regime has been observed coincident with powder injection, resulting in an increase of the plasma temperature of the order of 25%, with enhancements that can reach up to 50% for ion temperature.

Energetic particles (EP) generated by the neutral beam injectors (NBI) in Large Helical Device (LHD) destabilize Alfvén Eigenmodes (AE) and energetic particle modes (EPM), leading to a reduction of the device performance. In particular, AE/EPM induce EP losses before thermalization that causes a lower plasma heating efficiency and damages to plasma facing components. Pressure gradient driven modes (PGDM) as interchange and ballooning modes also hamper the capability of LHD to confine the thermal plasma, limiting the maximum thermal plasma β of the discharge. The present study summarizes AE/EPM and PGDM characterization and optimization analysis performed in LHD plasma using the gyro-fluid code FAR3d. The linear and saturation phase of AE/EPM and PGDM leading to the destabilization of MHD burst, energetic-ion-driven resistive interchange mode (EIC) burst, internal collapse and saw-tooth like events are discussed. Optimization trends with respect to the NBI operation regime, magnetic field configuration, thermal plasma properties, external actuators and multiple EP populations effects are explored, comparing experiment and simulation data. Improved operation scenarios are identified and confirmed in dedicated experiments thanks to the minimization or avoidance of AE/EPM and PGDM along the discharge.

Pegasus III uses hollow-cathode arc plasma sources inside an injector assemblies to create electron beams to study tokamak plasma initiation via local helicity injection. These injector assemblies are exposed to intense power and particle fluxes from plasma material interactions that cause damage to injector components, limiting the injector lifetime. New injectors require surface conditioning to operate without sourcing current from the electrode surfaces and damaging the electrodes. Initial studies comparing surfaces of new molybdenum injector components to those at the end of their lifetime have been performed and found that significant melting is observed on electrode components most directly exposed to the injected plasma, while components exposed to the main chamber plasma show evidence of blistering.

As fusion energy technologies approach demonstration and commercial deployment, understanding public perspectives on future fusion facilities will be critical for achieving social license. In a departure from the ‘decide-announce-defend’ approach typically used to site energy infrastructure, we develop a participatory design methodology for collaboratively designing fusion energy facilities with prospective host communities. We present here our findings from a participatory design workshop that brought together 22 community participants and 34 engineering students. Analysis of the textual and visual data from this workshop shows a range of design values and decision-making criteria with ‘integrity’ and ‘respect’ ranking highest among values and ‘economic benefits’ and ‘environmental protection/safety’ ranking highest among decision-making criteria. Salient design themes that emerge across the facility concepts include connecting the history and legacy of the community to the design of the facility, respect for nature, care for workers, transparency and access to the facility, and health and safety of the host community. Participants reported predominantly positive sentiments, expressing joy and surprise as the workshop progressed from learning about fusion to designing the hypothetical facility. Our findings suggest that carrying out participatory design in the early stages of technology development can invite and make concrete perspectives on public hopes and concerns, improve understanding of, and curiosity about, an emerging technology, build toward social license and inform context-specific development of future fusion energy facilities. Drawing on our findings and design process, we propose a prototype playbook for participatory design that will be developed further in future research. We recommend that fusion development teams (1) consider using participatory design approaches at multiple junctures throughout the fusion technology or facility development process, (2) build capacity to carry out such participatory engagements and (3) design standardized but adaptable technologies and facilities. We invite fusion technology developers to use and adapt our playbook for their own projects.

Graphical Abstract

A study of aneutronic fusion, which refers to fusion reactions that do not produce neutrons, has been conducted on the Large Helical Device (LHD). For the D–³He study, feasibility investigations of detecting charged fusion products have been performed. High-energy neutral beams, lost proton detectors, and gamma-ray detectors were planned for installation to validate the D–³He fusion reactions. Numerical calculations show that the expected D–³He fusion rate is 2.7 × 10¹⁶ s^-1 with most of the protons being lost immediately from the plasma. For the p–¹¹B study, the total alpha particle emission rate was estimated to be 10¹⁴ s^-1, and the loss points of alpha particle distribution were calculated. Based on these numerical simulations, we installed an alpha particle detector on a manipulator and positioned it at the bottom of the LHD. The time evolution of the alpha particle detection rate, measured by the detector, was found to be consistent with the predictions from the numerical simulations, demonstrating the first successful observation of the p–¹¹B reaction in a magnetic confinement system.

Thomson scattering diagnostic systems are widely used to measure the local electron temperature and density of plasmas, which are one of the most important plasma parameters. The Large Helical Device (LHD) Thomson scattering system was designed and developed from 1991 to 1998, and has been in operation without any major problem since the LHD second experiment campaign in 1998. The LHD Thomson scattering system measures the pseudo-continuous time evolution of electron temperature and density profiles at 144 spatial points along the LHD major radius. The LHD Thomson scattering system can measure electron temperature and density spatially from the inner boundary to the outer boundary, and temporally from the birth to the destruction of LHD plasmas. The performance is still one of the best in the world. In this paper, we discuss improvements and newly obtained results of this system with emphasis on the results from 2010 to 2024.

To study microscale turbulence, two non-invasive scattering instruments that use electromagnetic waves in the microwave to millimeter-wave range have been installed at the Large Helical Device. One instrument is a Doppler reflectometer, which is suitable for observing turbulence with relatively low wavenumbers. Three circuit systems were constructed for this instrument. The Doppler reflectometer allows a very large number of spatial points (more than 30) to be observed simultaneously in the radial direction and toroidal correlation analysis to be conducted. The other instrument is a two-frequency millimeter-wave scattering system, which was developed to observe turbulence at relatively high wavenumbers. This scattering system has multiple antennas in a vacuum vessel. It can be used to study turbulence anisotropy or, in combination with the Doppler reflectometer, the response of turbulence at various scales.

Against the backdrop of the accelerated advancement of the International Thermonuclear Experimental Reactor project, the Central Solenoid Model Coil (CSMC) of the China Fusion Engineering Test Reactor (CFETR) plays a pivotal role in achieving efficient plasma confinement and control. During the assembly of CSMC, inevitable assembly errors can disrupt both the central symmetry around the central axis and the planar symmetry with respect to the mid-plane of the Nb₃Sn and NbTi coils. This symmetry disruption leads to the generation of substantial asymmetric radial and axial offset electromagnetic forces within the Nb₃Sn and NbTi coils, which potentially jeopardize the preload stability and structural integrity of supporting components. To systematically investigate the stability of CSMC under the influence of assembly errors, this study first established a calculation model based on electromagnetic field theory for three typical assembly error scenarios, followed by the computation of corresponding offset electromagnetic forces. Second, the linear instability analysis method was utilized to determine the instability modes of CSMC under different offset electromagnetic force conditions. Finally, an extreme offset state was selected for nonlinear instability analysis to quantify the critical load triggering instability. The research results indicate that, under extreme assembly errors, preload rods emerge as the weakest structural components susceptible to instability. Notably, the critical instability load demonstrates an 8.3-fold margin over the combined operational loads. This study offers critical data references for optimizing the assembly precision and conducting safety margin evaluations in CSMC operation.

Fast-ion transport driven by Alfvén eigenmodes (AEs) is one critical issue facing fast-ion confinement in magnetic fusion device. In the DIII-D tokamak experiment, stiff transport of fast-ions increased with increasing neutral beam (NB) injection power when the amplitudes of multiple interacting AEs exceeded a certain threshold. These experiment results are supported by simulation studies that predict monotonically degrading fast-ion confinement and profile stiffness with increasing beam power. To investigate the universality of the fast-ion profile stiffness dependence on AE amplitude, an experiment was performed at the Large Helical Device (LHD) to scan the injection current of the NB and vary the AE amplitude. Under the experimental conditions, the AE amplitude increased linearly with NB injection power. The red shifted FIDA intensity between 663 and 665 nm, corresponding to the energy range of 98–166 keV in the ctr-direction, was used for estimating the radial profile of the fast-ion density. Evidence suggests stiffening of the fast-ion profile and degraded confinement, corroborated by a reduced neutron emission rate compared to simulations. This is consistent with the experimentally observed reduction in the expected neutron emission rate. We have demonstrated that under AE-prone confinement conditions, even if the fast-ion source increases due to NB injection, they experience enhanced transport by AEs and do not increase in density.