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Improvement of thermal conductivity by adding tungsten and/or copper wire in F82H
Get PDF0000-0002-6814-4874The F82H, which is one of reduced activation ferritic/martensitic steels, is a strong candidate structure material for fusion reactor because of its satisfactory mechanical property and high swelling resistance in the operating temperature range. One disadvantage of F82H would be its low thermal conductivity as a structural material for divertor. In this study, we have fabricated several F82H-based composite materials by the spark plasma sintering to improve its thermal conductivity by adding tungsten and/or copper wires. F82H-20 vol.% W and F82H-10 vol.% W-10 vol.% Cu composites included reaction layers at the interface between tungsten wire and F82H matrix, resulting in the decrease in ductility and tensile strength because of the formation of tungsten carbide. On the other hand, F82H-20 vol.% Cu composite, sintered for 120 min at 1000°C, included no reaction layers and showed the highest thermal conductivity with a high relative density. Furthermore, it showed a great tensile property, which is comparable to that of the original F82H.journal articl
Observation of Arc Trails with Significant Damage due to Glow Discharge Wall Conditioning in the Large Helical Device
Get PDF0000-0001-6090-5010We report the observation of arcing damage on the diagnostic shutter during the glow discharge wall conditioning in LHD. The diagnostic system has no experience of plasma discharge produced by electron or ion cyclotron resonance heating or neutral beam injection. The arc trails were observed on the aluminum surface but not on the stainless steel although both materials were exposed to the glow discharge with the same duration. The difference in work functions between two materials may be a cause to divide the conditions of arcing ignition.journal articl
Simulation study of energetic-particle driven off-axis fishbone instabilities in tokamak plasmas
Get PDF0000-0003-3116-3569Kinetic-magnetohydrodynamic hybrid simulations were performed to investigate the linear growth and the nonlinear evolution of off-axis fishbone mode (OFM) destabilized by trapped energetic ions in tokamak plasmas. The spatial profile of OFM is mainly composed of m/n = 2/1 mode inside the q = 2 magnetic flux surface while the m/n = 3/1 mode is predominant outside the q = 2 surface, where m and n are the poloidal and toroidal mode numbers, respectively, and q is the safety factor. The spatial profile of the OFM is a strongly shearing shape on the poloidal plane, suggesting the nonperturbative effect of the interaction with energetic ions. The frequency of the OFM in the linear growth phase is in good agreement with the precession drift frequency of trapped energetic ions, and the frequency chirps down in the nonlinear phase. Two types of resonance conditions between trapped energetic ions and OFM are found. For the first type of resonance, the precession drift frequency matches the OFM frequency, while for the second type, the sum of the precession drift frequency and the bounce frequency matches the OFM frequency. The first type of resonance is the primary resonance for the destabilization of OFM. The resonance frequency which is defined based on precession drift frequency and bounce frequency of the nonlinear orbit for each resonant particle is analyzed to understand the frequency chirping. The resonance frequency of the particles that transfer energy to the OFM chirps down, which may result in the chirping down of the OFM frequency. A detailed analysis of the energetic ion distribution function in phase space shows that the gradient of the distribution function along the E' = const. line drives or stabilizes the instability, where E' is a combination of energy and toroidal canonical momentum and conserved during the wave–particle interaction. The distribution function is flattened along the E' = const. line in the nonlinear phase leading to the saturation of the instability.journal articl
Measurement of Anisotropic Electron Velocity Distribution Function in LHD by Polarization Spectroscopy
Get PDF0000-0002-9160-682XPolarization of the hydrogen Lyman-α line is detected in the Large Helical Device. It is the first observation of a polarized atomic emission line in magnetically confined fusion plasma devices. With the help of an atomic model simulation, the anisotropy in the electron velocity distribution function (EVDF) in terms of T∥/T⊥ is evaluated, where T∥ and T⊥ represent the electron temperature in the parallel and perpendicular directions regarding the magnetic field, respectively. The results show that T∥/T⊥ has a tendency to decrease and deviate from unity with decreasing electron-electron collision frequency, which qualitatively agrees with an intuitive understanding of the anisotropic EVDF in the plasma boundary.journal articl
Method for estimating the frequency-wavenumber resolved power spectrum density using the maximum entropy method for limited spatial points
Get PDF0000-0001-6835-15690000-0001-5669-19370000-0002-0585-45610000-0003-1804-2308A combination of the Fourier transform and the maximum entropy method for estimating the frequency-wavenumber resolved power spectrum density is proposed. After illustrating the physical insight of the maximum entropy method by using synthetic test data, capability of the proposed method is tested using numerical simulation data. The method is also applied to experimental data obtained by the beam emission spectroscopy in the Large Helical Device. All of those examinations show that the proposed method provides more plausible results than conventional methods when the available spatial points are limited.journal articl
The Eulerian variational formulation of the gyrokinetic system in general spatial coordinates
Get PDF0000-0001-5444-1758The Eulerian variational formulation of the gyrokinetic system with electrostatic turbulence is presented in general spatial coordinates by extending our previous work [H. Sugama et al., Phys. Plasmas 25, 102506 (2018)]. The invariance of the Lagrangian of the system under an arbitrary spatial coordinate transformation is used to derive the local momentum balance equation satisfied by the gyrocenter distribution functions and the turbulent potential, which are given as solutions of the governing equations. In the symmetric background magnetic field, the derived local momentum balance equation gives rise to the local momentum conservation law in the direction of symmetry. This derivation is in contrast to the conventional method using the spatial translation in which the asymmetric canonical pressure tensor generally enters the momentum balance equation. In the present study, the variation of the Lagrangian density with respect to the metric tensor is taken to directly obtain the symmetric pressure tensor, which includes the effect of turbulence on the momentum transport. In addition, it is shown in this work how the momentum balance is modified when the collision and/or external source terms are added to the gyrokinetic equation. The results obtained here are considered useful for global gyrokinetic simulations investigating both neoclassical and turbulent transport processes even in general non-axisymmetric toroidal systems.journal articl
Magnetohydrodynamic hybrid simulation model with kinetic thermal ions and energetic particles
Get PDF0000-0001-9323-8285A new kinetic-magnetohydrodynamic hybrid simulation model where the gyrokinetic particle-in-cell simulation is applied to both thermal ions and energetic particles is presented. Toroidal Alfvén eigenmodes (TAEs) destabilized by energetic ions in tokamak plasmas are simulated with the new simulation model. Energy channeling from energetic ions to thermal ions through Alfvén eigenmodes (AEs) is demonstrated by the simulation. The distribution function fluctuations and the resonance condition are analyzed for both thermal ions and energetic ions. The strong energy transfer between the particles and the AE and the strong particle transport occur when the following conditions are satisfied at the resonance location in phase space: (1) the poloidal resonance number is close to the poloidal mode number of the AE, (2) the AE has a substantial amplitude, (3) the distribution function has a substantial gradient along the line, where is a conserved variable for the wave-particle interaction. While the distribution function fluctuations for energetic ions are consistent with the resonance condition with the TAEs, the distribution function fluctuations for thermal ions do not satisfy the resonance condition when the bulk plasma beta is 1%. This indicates that the resonance does not play an important role in the interaction between thermal ions and the TAE for the relatively low bulk plasma temperature. On the other hand, when the bulk plasma beta is 4%, the resonance between thermal ions and the TAEs become important leading to Landau damping.journal articl
電力変動監視によるマルウェア検出方法
Get PDF核融合炉などの大規模プラントでは，制御システムのセキュリティ確保が重要な研究課題である．この課題に対して従来の研究では，主に市販の情報デバイスを標的にした既知のマルウェアをソフトウェアで検知し，駆除を試みるのが一般的である．本研究ではサーバー攻撃の検知を侵入したマルウェア自身が使用する消費電力の監視により行い，その電力変動の有意差を持って早期検知を試みるものである．journal articl
Conceptual Design of HFIR Irradiation Experiment for Material Compatibility Study on Liquid Sn Divertor
Get PDFLiquid Sn is one of the promising coolants for liquid surface divertor concept of fusion reactors. However, the compatibility between liquid Sn and structural materials is an important issue that has to be addressed, because liquid Sn is extremely corrosive to steels at high temperatures. The corrosion may be mitigated when a protective Al2O3 layer is formed on the surface of alumina forming steels. However, the effect of neutron irradiation on the integrity of protective layer is not made clear so far. Japan and US joint research project “FRONTIER” started in 2019 to investigate the material compatibility under neutron irradiation. The purpose of the present study is to develop the conceptual design of the irradiation test capsule which enables material compatibility tests for the alumina forming steels - liquid metal systems under neutron irradiation in the High Flux Isotope Reactor at Oak Ridge National Laboratory, TN, USA. The three dimensional drawing of capsule structure was then developed. The validity of the material selections for the capsule design was investigated by means of corrosion tests of SiC, Si3N4, Ti, and Mo in liquid Sn at 773 K for 262 hr.journal articl
Isotope effect of rovibrational distribution of hydrogen molecules desorbed from amorphous carbon
Get PDF0000-0002-0593-8810When the hydrogen isotope atom is injected into the amorphous carbon with the incident energies Ein of 20, 50, and 80 eV, we obtain the following physical quantities of hydrogen isotope atoms/molecules emitted from the amorphous carbon using molecular dynamics and heat conduction hybrid simulation. The physical quantities are the time evolution of the emission rate, the depth distribution of the original location of the hydrogen emitted from the target, the polar angular dependence, and the translational, rotational, and vibrational energy distributions. In addition, the approximate analysis yields the emission distributions at the vibrational (v) and rotational (J) levels. Using these distributions, we evaluate the rotational temperature Trot for v = 0 and small J states. From the above, it is found that molecules with higher rotational levels J tend to be emitted as Ein increases or as the mass of hydrogen isotope increases. Moreover, the isotope effect appears in the mass dependence of Trot.journal articl