NIFS-Repository (National Institute for Fusion Science)
Not a member yet
13159 research outputs found
Sort by
Overview of tritium retention in divertor tiles and dust particles from the JET tokamak with the ITER-like wall
Get PDFDivertor tiles after Joint European Torus-ITER like wall (JET-ILW) campaigns and dust collected after JET-C and JET-ILW operation were examined by a set of complementary techniques (full combustion and radiography) to determine the total, specific and areal tritium activities, poloidal tritium distribution in the divertor and the presence of that isotope in individual dust particles. In the divertor tiles, the majority of tritium is detected in the surface region and, the areal activities in the ILW divertor are in the 0.5–12 kBq cm−2 range. The activity in the ILW dust is associated mainly with the presence of carbon particles being a legacy from the JET-C operation. The total tritium activities show significant differences between the JET operation with ILW and the earlier phase with the carbon wall (JET-C) indicating that tritium retention has been significantly decreased in the operation with ILW.journal articl
Effect of discreteness and misalignment on magnetic field and charged particle confinement in CFQS quasi-axisymmetric stellarator
Get PDF0000-0002-5601-7106The Chinese first quasi-axisymmetric stellarator (CFQS), which will be the first quasi-axisymmetric (QA) stellarator in the world, is now under construction. The primary task of the CFQS project is to realize a QA configuration and to examine its physical properties. Based on this task, two important issues were investigated in this work in order to estimate the robustness of the CFQS design from a physical perspective. One was the toroidal field (TF) ripple due to the discreteness of modular coils (MCs) which could potentially degrade the charged particle confinement in the CFQS configuration. The other was a possible MC misalignment in the assembly that would affect the magnetic field and charged particle confinement in the CFQS. Moreover, since the stellarator symmetry might be broken by the MC misalignment, such a case was also investigated in this work. By performing a magnetic field line tracing and charged particle orbit tracing calculation, it was found that the TF ripple does not affect the confinement property significantly and the magnetohydrodynamics equilibrium was robust against possible MC misalignments. These results are helpful in defining the reasonable tolerance of assembly accuracy.journal articl
Alfvén mode induced particle loss in LHD
Get PDF0000-0002-4239-2685Losses of beam ions due to Alfvén modes are simulated for discharges in the Large Helical Device at Toki, Japan, using a guiding center code. High frequency beam particle resonances are found for the equilibria for passing particles, providing locations for the destablization of Alfvén modes observed in the device. Losses due to even small modes due to these resonances are significant.journal articl
Residual magnetic field induced by superconducting magnets of Large Helical Device
Get PDF0000-0003-1454-8117The residual magnetic field was measured to investigate its source for the Large Helical Device, the superconducting magnet system of which consists of two Helical Coils (HCs), two Inner Vertical (IV) coils, two Inner Shaping (IS) coils, and two Outer Vertical (OV) coils. NbTi cable-in-conduit conductors were adopted for the IV, IS, and OV coils. Firstly, Hall probes were installed at five periodic positions on the mid-plane of the inner cylinder of the cryostat. Since the residual field was changed by around 0.1 mT at all the positions during the warm-up of the superconducting coils, a major part of the residual field had to be induced by magnetization of the coils. In the next campaign (cool-down, plasma experiment, and warm-up), the Hall probes were moved to the five different vertical positions in order to measure the distribution of the residual field. Calculation of the residual field has been carried out under the assumption that NbTi filaments in each conductor are magnetized in the same direction as the field at the center of the conductor during excitation. From comparison between the measured and calculated values, we conclude that the residual field from the coils that had been excited to high currents should be reduced by around 35%, due to the self-field in strands in the conductor. The best fitted critical current densities of the IV and IS coils are 1.31 and 2.81 × 1010 A/m2, respectively, which are consistent with the field dependence obtained from the magnetization curve of each strand.journal articl
EUV/VUV Spectroscopy for the Study of Carbon Impurity Transport in Hydrogen and Deuterium Plasmas in the Edge Stochastic Magnetic Field Layer of Large Helical Device
Get PDF0000-0002-1171-8603The ergodic layer in the Large Helical Device (LHD) consists of stochastic magnetic fields exhibiting a three-dimensional structure that is intrinsically formed by helical coils. Spectroscopic diagnostics was employed in the extreme ultraviolet (EUV) and vacuum ultraviolet (VUV) wavelength ranges to investigate emission lines of carbon impurities in both hydrogen (H) and deuterium (D) plasmas, aiming to elucidate the impact of distinct bulk ions on impurity generation and transport in the edge plasmas of the LHD. The emission intensity of carbon CIII, CIV, CV, and CVI lines is significantly higher in the D plasma compared to the H plasma, indicating a greater sputtering rate of carbon materials in the D plasma, resulting in a higher quantity of carbon impurities originating from the divertor plates. A Doppler profile measurement of the second order of CIV line emission (1548.20 × 2 Å) was attempted using a 3 m normal-incidence VUV spectrometer in the edge plasma at a horizontally elongated plasma position. The flow velocity reaches its maximum value close to the outermost region of the ergodic layer, and the observed flow direction aligns with the friction force in the parallel momentum balance. The flow velocity increases with the electron density in H plasmas, suggesting that the friction force becomes more dominant in the force balance at higher density regimes. This leads to an increase in the impurity flow, which can contribute to the impurity screening. In contrast, the flow velocity in the D plasma is smaller than that in the H plasma. The difference in flow values between D and H plasmas, when the friction force term dominates in the momentum balance, could be attributed to the mass dependence of the thermal velocity of the bulk ions.journal articl
Investigating the Effect of Coil Length, Alignment Errors and Cooling Down on a Superconducting Magnet With Active Shielding for Rotating Gantry
Get PDFORCID 0000-0002-1989-867XA superconducting magnet with active shielding has been proposed for use in a heavy-ion beam rotating gantry in order to decrease weight. The magnet consists of two types of coils, dipole and active shielding coils, both of which are wound using Nb-Ti wires. In this study, three-dimensional coil configurations were designed, based on coil cross-sections designed in a previous study. Using the coil configurations, the magnetic field distribution in the longitudinal and radial directions of the coil and its peak magnetic field were calculated. The results indicated that the effect of the coil end section on magnetic field distributions became greater as the coil length becomes shorter. Also, the difference of the coil length has no impact on the peak field. In addition, the influence of coil alignment errors on the electromagnetic (EM) force, and that of cooling-down on coil deformation were investigated, using a coil cross-sectional model. As a result, EM forces caused by alignment errors of several mm in the shielding coil were negligible, compared to EM forces generated in the coil under a rated operation. Also, the maximum deformation of the coil cross-section was a few millimeters when the coil was cooled from 300 K to 5 K.journal articl
Shigeru Mori and Kazuhisa Mori, brothers devoted their lives to the new energy developments
Get PDF森茂、森一久兄弟は広島の御典医の家系の家に生まれ、戦時中兄茂は東京帝国大学理学部物理学科宮本研究室に、弟一久は京都帝国大学理学部物理学科湯川研究室にそれぞれ在籍して東京、京都にいた。広島に原爆が投下されたとき爆心地に近い自宅兼診療所は倒壊するだけでなく、両親を始め、長兄夫婦と姪の一家 5名が原爆の犠牲となった。日本各地の中核都市で空襲が激しくなり、家族のことを心配していた茂・一久兄弟が相談し、交代して広島に行くことになっていて、たまたま広島に行っていた一久が被爆し、自らも原爆症に苦しみながらも九死に一生を得て健康を取り戻した。
一家が原爆の犠牲となったにもかかわらず、戦後自由な時代を迎え、森兄弟の生涯は原子カエネルギーの利用と未来の核融合エネルギー開発という何れも核エネルギーの利用・開発に生涯をかけたようにみえる。しかも並大抵のものではなく、ゆるぎない信念を持って開発にあたっていたように感じる。この冊子は両氏の足跡を辿りながら、氏らが後進に伝えたかったであろうことを筆者らの主観を交えて纏めたものである。Brothers of Shigeru and Kazuhisa were born in Hiroshima, Japan in Mori’s family known as medical doctor “gotten-i”. In the middle of World War II, Sigeru was studying physics at Univ. of Tokyo, and Kazuhisa was also studying physics at Kyoto-Univ. Since regional central cities were exposed to the aerial attack one by one, Shigeru and Kazuhisa had discussed going and staying in Hiroshima to take care of their old parents. When the atomic bomb was dropped in Hiroshima, their home and clinical house collapsed, and five persons in their family, including parents, an elder brother couple, and their daughter were killed. Kazuhisa staying in Hiroshima at that time was also trapped by the crushed house and exposed to high radiation caused by the atomic bomb, but barely he escaped death and recovered.
Regardless of the tragedy of their family, Mori brothers, Shigeru engaged in the research and development of nuclear fusion research, and Kazuhisa to the utilization of atomic energy by the power plant, both devoted their lives to the peaceful use of atomic energy. The authors are impressed by their firm confidence in their approaches and their mind of responsibility.
Tracing what they had thought and done through the archives documents and through direct communication, the authors wish to convey their message without prejudice to the next generation of researchers, engineers, and leaders of this country.research repor
Development of sweeping detector phase contrast imaging in Large Helical Device
No full textORCID 0000-0002-6021-871XPhase contrast imaging (PCI) has been used for the turbulence profile measurement in Large Helical Devices; however, it does not have sufficient spatial resolution owing to the small number of two-dimensional (2D) detector elements. Therefore, in this study, we limited the measurement target to steady-state plasmas and conduct a pseudo multichanneling of a 2D detector array by sweeping using a one-dimensional detector. This new system is called SD-PCI. SD-PCI needs two detectors, one is one-dimensional detector and the other is single channel detector. By selecting suitable detector and imaging magnification for target turbulence or device characteristics, SD-PCI demonstrates the potential capability and enhancements. The wavenumber spectra comparison from the correlation calculations of the simultaneous measurement of the actual plasma with conventional 2D-PCI and proposed SD-PCI shows that SD-PCI is as effective as 2D-PCI in spectral broadening. The simplicity of the proposed system is expected to be applicable to various devices. In this paper, the SD-PCI system was explained along with the initial results of the 2D wavenumber spectrum calculation, which was necessary for obtaining turbulence profile.journal articl
Improved Variable-Reduction Method and Its Variant for Solving Asymmetric EFG-Type Saddle-Point Problem
Get PDF0000-0002-4027-6576If a boundary-value problem is discretized with the extended Element-Free Galerkin (EFG) method, an asymmetric EFG-type Saddle-Point (EFG-SP) problem is obtained. Although the improved Variable-Reduction Method (iVRM) was originally developed as a solver for symmetric EFG-SP problems, it is extended so as to be applicable to asymmetric EFG-SP problems. As a result, not only the Asymmetric-version iVRM (AiVRM) but also its variant AiVRM2 is developed. A numerical code is developed for solving an asymmetric EFG-SP problem with the AiVRM/AiVRM2 and, by means of the code, performances of the two methods are investigated numerically. Consequently, it is found that, especially for a large-scale asymmetric EFG-SP problem, both the AiVRM and the AiVRM2 are more effective than the preconditioned Krylov subspace method.journal articl
Prospect for Experimental Investigation of Phase-Space Turbulence in Magnetically Confined Fusion Plasmas
Get PDF0000-0001-5669-1937In this paper the prospect of experimental investigation of phase-space turbulence in magnetically confined fusion plasmas is assessed, motivated by a theoretical suggestion of its potential role in turbulent anomalous transport conundrums. Three experimental approaches regarding (i) fusion plasma experiment, (ii) basic plasma experiment, and (iii) simulation data analysis are considered, accounting for challenges and expected outcomes. Platforms for experiments ranging from high-temperature fusion plasmas to low-temperature linear plasmas, are overviewed. Interdisciplinary interests regarding phase-space turbulence in magnetosphere plasmas and laser wake-field acceleration are also discussed.journal articl