NIFS-Repository (National Institute for Fusion Science)
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Plasma Wall Interaction of New Type of Divertor Heat Removal Component in LHD Fabricated by Advanced Multi-Step Brazing (AMSB)
Get PDFORCID 0000-0002-3744-2481A novel method, called Advanced Multi-Step Brazing, was developed to fabricate a new type of divertor heat removal component with W armor and an oxide-dispersion-strengthened copper (GlidCop®) heat sink in the initial phase of our work. Later, a new type of divertor heat removal component, which has a rectangular-shaped cooling channel with a V-shaped staggered-rib structure in the GlidCop heat sink, was developed. This new component showed an extremely high heat removal capability during a ~30 MW/m2 steady-state heat loading condition in our previous work. In this work, the new component was installed in the divertor strike position of the Large Helical Device and exposed to neutral beam injection–heated plasma discharges with 1180 shots (~8000 s) in total. Though submillimeter-scale damage, such as unipolar arc trails and microscale cracks, was identified on the W surface, the extremely high heat removal capability did not show any sign of degradation over the experimental period. On the other hand, remarkable sputtering erosion and redeposition phenomena, due to the strong influx of the divertor plasma, was confirmed on the W armor.journal articl
First measurements of p11B fusion in a magnetically confined plasma
Get PDF0000-0001-6697-7891Proton-boron (p11B) fusion is an attractive potential energy source but technically challenging to implement. Developing techniques to realize its potential requires first developing the experimental capability to produce p11B fusion in the magnetically-confined, thermonuclear plasma environment. Here we report clear experimental measurements supported by simulation of p11B fusion with high-energy neutral beams and boron powder injection in a high-temperature fusion plasma (the Large Helical Device) that have resulted in diagnostically significant levels of alpha particle emission. The injection of boron powder into the plasma edge results in boron accumulation in the core. Three 2 MW, 160 kV hydrogen neutral beam injectors create a large population of well-confined, high -energy protons to react with the boron plasma. The fusion products, MeV alpha particles, are measured with a custom designed particle detector which gives a fusion rate in very good relative agreement with calculations of the global rate. This is the first such realization of p11B fusion in a magnetically confined plasma.journal articl
The design of a slit ICRF antenna in EU-DEMO
Get PDF0000-0001-6075-1146Although ICRF heating has achieved the high heating efficiency necessary to achieve high-performance plasmas, it has not overcome the reliability and economic problems associated with the antenna structure inside the vacuum vessel in fusion reactors. We suggested a slit ICRF antenna that uses the blanket surface as a transmission line to solve these problems. With a single slit ICRF antenna with a width of 3 m and a height of 15 cm, the electric field strength to the magnetic field direction was successfully suppressed to 5 kV/cm when 20 MW of power radiation was achieved from the single slit. The slit ICRF antenna had a bending angle in the electromagnetic wave transmission path to prevent direct neutron impact on the first wall and a vacuum gate from rapidly preventing water or air leakage accidents. The slit ICRF antenna has a simple structure that allows heating at high power density while minimizing blanket volume reduction.journal articl
Investigation of the Magnetic Field Configuration for Magnetic Surface Measurements in the CFQS Quasi-Axisymmetric Stellarator
Get PDF0000-0003-0655-7347It has been found that magnetic surfaces in the CFQS quasi-axisymmetric stellarator in a standard magnetic configuration are robust against error fields caused by misalignments of the modular coils. While this property is advantageous for preserving the magnetic field line structures for the plasma confinement as designed, it prevents the detection of the misalignments of the coils by magnetic surface measurements. Thus, a magnetic configuration specialized in measuring magnetic surfaces to detect the error fields is proposed. Calculations by tracing magnetic field lines reveal that the magnetic surfaces in the specialized magnetic configuration are sensitive to the error fields compared to those in the standard magnetic configuration. Additionally, the calculations demonstrate that a weighted electric current on some modular coils can make the magnetic surfaces more sensitive to the error fields, which enables the magnetic surface measurements to detect smaller misalignments of the modular coils in the CFQS.journal articl
High accuracy interatomic potential model for binary collision approximation and its application into sputtering yield estimation for amorphous carbon
No full textAlthough binary collision approximation (BCA) and molecular dynamics (MD) are well used for plasma-material interaction simulation, the atomic collision in the energy above 10 eV is often out of scope in general potential model for MD. For BCA, the Ziegler–Biersack–Littmark (ZBL) potential has been often employed for high energy collision. In the present work, as one of modernizations of BCA, more accurate potential model for high energy collision, which is named ReGenerated ZBL (ReGZ) potential, was proposed. The function from of the ReGZ potential was analytically derived from the spherical electron density of an independent atom. To evaluate the potential, sputtering yield and reflection coefficient were compared between the BCA simulations using the ReGZ potential and the ZBL potential. In addition, by also improving the surface binding energy by density functional theory, the sputtering yield using the ReGZ potential becomes consistent with existing results.journal articl
Data-driven modal analysis of nonlinear quantities in turbulent plasmas using multi-field singular value decomposition
Get PDF0000-0001-5695-5699Nonlinear dynamics in the two-dimensional multi-component plasma turbulence described by the Hasegawa–Wakatani equation is investigated by using a data-driven modal analysis with the singular value decomposition (SVD). The conventional SVD is extended to 'multi-field SVD' which can decompose multiple turbulence fields simultaneously by a single set of orthonormal basis functions without imposing a priori scale separations. Then, in addition to the mode amplitude labeled by the singular value, the information on the phase relations in the nonlinear quantities such as a transport flux or a triad energy transfer is extracted in the mode space. Through applications to the two-dimensional plasma turbulence, it is revealed that the multi-field SVD can extract the dominant spatial structures for the turbulent transport and the nonlinear energy transfer, preserving the multi-scale nature of the original turbulent fields. It is also demonstrated that one can reduce the dimensionality or information using the multi-field SVD through comparisons with the conventional Fourier decomposition.journal articl
Research Plan of Complex Global Simulation Unit
Get PDFORCID 0000-0001-9323-8285Global simulation, which takes into account the interactions between multiple hierarchies, is expected to be realized not only in the field of nuclear fusion research but also in other academic fields. However, such a complex global simulation is difficult to realize because the temporal and spatial scales of the microscopic hierarchy and those of the entire system are generally extremely different. The aim of the Complex Global Simulation Unit at the National Institute for Fusion Science is to develop simulation methods to address the abovementioned issue and to promote simulation research. This unit aims to develop 1) a global simulation of the whole magnetically-confined fusion plasma, including the core and peripheral plasma, based on the kinetic-magnetohydrodynamic hybrid simulation coupled with the gyrokinetic Poisson equation, and 2) a methodology with broad applicability for enabling simulations that closely reproduce real-world phenomena, transcending the strong limitations imposed by the capacity and capability of supercomputers. In addition, the unit aims to develop a method for coupling a particle-in-cell simulation and a global analysis of plasma waves. Furthermore, it aims to develop a multiphase (solid, liquid, gas, and plasma) simulation method for pellet injection into fusion plasmas.journal articl
Ultrahigh-Flux Concerting Materials
Get PDFORCID 0000-0002-5000-1269The purpose of the research unit UlCoMat (Ultrahigh-flux Concerting Materials) is creation of novel materials for advanced engineering systems, such as fusion and fission reactors, aerospace craft, rockets and chemical plants, based on understanding and control of the metastable phase and the self-organization induced in materials under extreme conditions. The UlCoMat will accelerate a paradigm shift from stable and resistant materials to metastable but adaptive ones. It focuses also on the science of life to seek long-life materials and a precise estimation of their existence for the development of robust engineering systems using the minimum materials compatible with economical and safety requirements.journal articl
A Study on Laser Processing of Tungsten-Rhenium Alloys for Divertor Development
Get PDFTungsten-rhenium alloys are more attractive due to their excellent characteristics, such as high ductility and improved mechanical properties. They can be expected to become some of the candidate materials for the next-generation of nuclear fusion reactors. We have successfully achieved crack-free laser processing in high-doped tungsten-rhenium alloys using a nanosecond Q-switched Nd:YAG laser system. In addition, the connection between the number of cracks and grain size on different rhenium doping concentrations is also characterized.journal articl