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A Mesh-Generation Scheme for the Large Helical Device Based on the Structure of Magnetic-Field Lines
Get PDFWe report herein an automated scheme for generating a mesh based on a structure of magnetic-field lines. For all angles in the toroidal subdomain, the mesh generated by this scheme must not contain broken tetragons. To satisfy this requirement, we propose herein a first method to detect broken elements and a second method to automatically modify the broken elements. We use the proposed mesh-generation scheme with magnetic-field data acquired on the magnetic axis of the Large Helical Device at Rax = 3.75 m. The results show that broken elements are detected by the first method, and the second method transforms broken elements into regular elements.journal articl
Three-Dimensional Electromagnetic Field Calculation for Microwave Holography
Get PDF0000-0002-5008-7285The lens-less technique of microwave holography is expected to provide information of three-dimensional structures of plasma with a wide field of view. From the complex amplitudes of waves, which are observed on a single planar array of antennas, we will be able to obtain an imaging of the three-dimensional object. With a geometry of back-scattering observation, the feasibility is examined with a numerical tool of electromagnetic analysis on dielectric objects. With respect to the variety of the dielectric constant and shape of object, it is shown that useful information can be acquired in regarding the complex amplitude distribution at planar detector.journal articl
Impact of Magnetic Field Configuration on Heat Transport in Stellarators and Heliotrons
Get PDF0000-0001-9585-5201We assess the magnetic field configuration in modern fusion devices by comparing experiments with the same heating power, between a stellarator and a heliotron. The key role of turbulence is evident in the optimized stellarator, while neoclassical processes largely determine the transport in the heliotron device. Gyrokinetic simulations elucidate the underlying mechanisms promoting stronger ion scale turbulence in the stellarator. Similar plasma performances in these experiments suggests that neoclassical and turbulent transport should both be optimized in next step reactor designs.journal articl
Measurement of polarization in Lyman-α line caused by anisotropic electron collisions in LHD plasma
Get PDF0000-0002-4668-4087Polarization in the Lyman-α line caused by anisotropic electron collisions has been investigated in the Large Helical Device (LHD). High-sensitivity polarization-resolved measurements of the Lyman-α line from edge LHD plasma have been carried out. To obtain spectra of linearly polarized light at all angles a high-reflectivity mirror, a polarization analyzer, and a half-waveplate have been additionally installed into an existing VUV spectrometer system. These optical components have been designed and developed by the CLASP (Chromospheric Lyman-Alpha Spectro-Polarimeter) [R Kano et al. ApJL, 839(1):L10, 2017] team. The present measurement has been made during an electron cyclotron heated discharge. Intensity of the Lyman-α line integrated over line profile has been obtained and plotted as a function of time to generate temporal profile of line. The profile shows that intensity of light varies in synchronization with the angle of the observed linearly polarized light, which clearly indicates that the line is polarized. By performing least-squares fitting on the temporal profile, the magnitude of polarization degree has been evaluated to be 0.033 ± 0.004. In addition, phase analysis of the measured intensity variation has been carried out. From this analysis it has been found that the observed polarization in Lyman-α can be attributed to the anisotropic electron velocity distribution function (EVDF) at the inboard side of LHD plasma. The preliminary results of a simulation model code suggest that the value of polarization degree is negative and electron temperature in the perpendicular direction to the magnetic field is higher compared to electron temperature in the parallel direction. Therefore, the final value of polarization degree in Lyman-α is -0.033 ± 0.004.journal articl
情報セキュリティ対策としての検疫認証システムの構築と評価
No full text0000-0001-5888-8901核融合科学研究所のキャンパス情報ネットワークは，検疫認証システムが導入されており，端末を接続する場合は，事前に端末情報の認証システムへの登録と一定のセキュリティ要件を求める検疫システムの承認の2つの要件を満たすことが必要である．端末情報を登録するため認証システムの登録者になるためには情報セキュリティ講習会を毎年度受講することが必要である．この情報セキュリティ講習会は，検疫認証システムの前システムとなる「事前MACアドレス登録によるDHCPサービス」開始時から実施している．一方，共同研究者など来訪者への利便性を高めるために登録が不要なゲストネットワークを提供している．ここでは核融合科学研究所の情報セキュリティ対策の一環として実施している検疫認証システムと情報セキュリティ講習会について，導入の経緯とその機能，所員からの評価を含めた実施状況などについて述べるjournal articl
First experiments on plasma production using field-aligned ICRF fast wave antennas in the large helical device
Get PDF0000-0003-0755-2433The results of the first experimental series to produce a plasma using the ion cyclotron range of frequency (ICRF) in the large helical device (LHD) within the minority scenario developed at Uragan-2M (U-2M) are presented. The motivation of this study is to provide plasma creation in conditions when an electron cyclotron resonance heating start-up is not possible, and in this way widen the operational frame of helical machines. The major constraint of the experiments is the low RF power to reduce the possibility of arcing. No dangerous voltage increase at the radio-frequency (RF) system elements and no arcing has been detected. As a result, a low plasma density is obtained and the antenna-plasma coupling is not optimal. However, such plasmas are sufficient to be used as targets for further neutral beam injection (NBI) heating. This will open possibilities to explore new regimes of operation at LHD and Wendelstein 7-X (W7-X) stellarator. The successful RF plasma production in LHD in this experimental series stimulates the planning of further studies of ICRF plasma production aimed at increasing plasma density and temperature within the ICRF minority scenario as well as investigating the plasma prolongation by NBI heating.journal articl
Characterization of isotope effect on ion internal transport barrier and its parameter dependence in the Large Helical Device
Get PDF0000-0001-5669-1937In this paper, the background physics of the isotope effects in the ion internal transport barrier (ITB) are discussed in detail. An heuristic criterion for the ITB strength is defined based on the nonlinear dependence of the ion thermal diffusivity on the local ion temperature in the L-mode phase. Comparing deuterium plasmas and hydrogen plasmas, two isotope effects on the ion ITB are clarified: stronger ITBs formed in the deuterium plasmas and an ITB concomitant edge confinement degradation in the hydrogen plasmas. Principal component analysis reveals that the ion ITB becomes strong when a high input power normalized by the line averaged electron density is applied and electron density profile is peaked. A gyrokinetic simulation suggests that the ITB profile is determined by the ion temperature gradient driven turbulence, while the way the profile saturates in L-mode plasmas is unknown. In the electron density turbulence behavior, a branch transition is observed, where the increasing trend in turbulence amplitude against the ITB strength is flipped to a decreasing trend across the ITB formation. The radial electric field structure is measured by the charge exchange recombination spectroscopy system. It is found that the radial electric field shear plays a minor role in determining the ITB strength.journal articl
Visualization of plasma shape in the LHD-type helical fusion reactor, FFHR, by a deep learning technique
Get PDFA magnetic field is used to confine the plasma to achieve controlled fusion. Therefore, since the movement of the plasma follows magnetic field lines, a plurality of magnetic field lines is calculated from electromagnetic field simulation results in a fusion reactor. Because of the complicated distribution of magnetic field lines in three-dimensional (3D) space, existing analysis measures which are mostly based on two-dimensional poloidal plasma cross-sections are unsatisfactory for domain experts. To solve this problem, we propose a technique for reconstructing a regular scalar field from the magnetic field lines. First, on poloidal plasma cross-sections, intersection points of magnetic field lines are used to make annotations of learning the plasma shape. Then, a deep neural network is built to approximate the scalar field that represents the probability of the existence of magnetic field lines. Consequently, a 3D model of plasma shape has managed to be constructed by applying the marching cubes method. The effectiveness of the proposed method is demonstrated by comparing it with the conventional method and domain experts’ reviews.journal articl
Acceleration Techniques for Linear-System Solver in Shielding Current Analysis of Cracked HTS Film
Get PDF0000-0002-4027-6576Two types of acceleration techniques, H-matrix arithmetics and an H-matrix-based variable preconditioning (VP), as well as their combination are applied to a linear-system solver in the shielding current analysis of a cracked high-temperature superconducting film. Although the combination seems to be the most effective of three types of the acceleration techniques, the results of computations show that, from the standpoint of the acceleration performance, neither the H-matrix-based VP nor the combination is superior to H-matrix arithmetics. The reason for this unexpected result is explained from the standpoint of operation counts.journal articl
Hot Electron and Ion Spectra in Axial and Transverse Laser Irradiation in the GXII-LFEX Direct Fast Ignition Experiment
Get PDFAn electron spectrometer was used to measure the electron and ion spectra in two different irradiations of implosion laser to the deuterated spherical shell targets at the direct fast ignition experiments on the Gekko-LFEX facility. In the transverse irradiation against the LFEX laser axis, the low effective hot electron temperature (Teff) and huge neutron yield (Ny) could be obtained although high Teff and low Ny could be observed in the axial irradiation. In the transverse irradiation, the efficient core heating could be obtained because the laser-plasma interaction position is close to the core and the diffusive/ion drag heating may be effective.journal articl