NIFS-Repository (National Institute for Fusion Science)
Not a member yet
13159 research outputs found
Sort by
Microstructural evolution of two-way cold rolled 12Cr ODS steel under 1073–1373 K annealing
Get PDFORCID 0000-0001-5706-0221Microstructural evolution and hardness variations of cold rolled 12Cr ODS steel with 60%–90% thickness reductions after 1073–1373 K annealing were systematically studied by electron backscatter diffraction technique, transmission electron microscopy, and Vickers hardness measurements. Recovery took place with heating up to 1273 K in specimens with 60% thickness reduction accompanying with gradual hardness decrease, and followed by recrystallization at 1373 K with an evident hardness reduction. By contrast, regarding specimens with 75% and 90% thickness reductions, recrystallization was observed at 1273 K which is 100 K lower than that of 60% thickness reduction, and 400 K lower than that of as-fabricated specimen without further cold rolling, indicating that a higher thickness reduction stimulated the onset of recrystallization at a lower temperature. Furthermore, partial recrystallization was characterized at 1073 K and 1173 K in the specimen with 90% thickness reduction, which produced equiaxed grain bands along the final rolling direction with none/lower density of oxide particles, and full recrystallization occurred at 1273 K and above, forming coarse elongated grains with high density of oxide particles and a smaller fraction of equiaxed grains. These bimodal grains were probably ascribed to heterogeneous distribution of oxide particles in the matrix, which were partially dissolved during cold rolling process, and re-precipitated after the thermal annealing.journal articl
Suppression method of COVID-19 infection by isolation time control based on the SIR model and the analogy of nuclear fusion research
Get PDFdepartmental bulletin pape
Observation of clump structure in transported particle orbit using an upgraded neutral particle analyzer during TAE burst in LHD
Get PDF0000-0003-0755-2433Toroidal Alfvén eigenmode (TAE) bursts are often observed in relatively low-magnetic-field experiments in the Large Helical Device (LHD) with tangential nuclear beam injection. During TAE bursts, hole-clump pairs in real space were observed in previous studies. In order to observe the behavior of the energetic particles during TAE bursts in more detail, a tangential E-parallel-B-type neutral particle analyzer (E||B-NPA) was upgraded to improve the time resolution up to 100 kilo samples per second by updating its measurement electronic circuits. Using this high time resolution E||B-NPA, the clump formations are clearly observed in real space. In order to analyze the observed particles with high time resolution, the conditional averaging technique is used. The lost energetic particles with 150 keV were initially observed just before the TAE burst, and the energy decreases faster than the classical slowing down time. The energetic particles transported by the TAE burst were detected with energy slowing down time of 6–8 ms for more than 6 ms after the TAE burst had finished. According to the orbit trace code Lorentz orbit (LORBIT) calculation, the particle pitch angle and radial location (ρ = r/a99) of the energetic particles resonating with the TAE mode frequency are increased by 5° and 0.2, respectively, during TAE bursts. These results are consistent with the observed downward frequency chirping of the magnetic fluctuation. By comparing the energy of the detected particles by E||B-NPA and the corresponding frequency of the magnetic fluctuation, the pitch angles of the resonant particles are considered to be 15°–25° at 150 keV before they are transported by the TAE burst. The frequency chirping of the magnetic fluctuation shows good agreement with the observed clump structure by considering the pitch angle of the resonant particles.journal articl
Observation of line emissions from Ni-like W46 + ions in wavelength range of 7–8 Å in the Large Helical Device
Get PDF0000-0002-1171-8603Tungsten W46+ lines were successfully observed in the extreme ultraviolet (EUV) wavelength range of 7 ∼ 8 Å in the Large Helical Device (LHD). Tungsten ions are distributed in the neutral beam injection (NBI) heated LHD plasma by injecting a pellet consisting of a small piece of tungsten metal wire enclosed by a carbon tube. While the electron temperature has a sudden drop due to the pellet injection, it can be recovered by applying electron cyclotron heating (ECH) together with continuous NBI heating. It is found that a W46+ line at 7.93 Å is emitted when the central electron temperature ranges around 3.4 keV with relatively high intensity and is isolated from other intrinsic impurity lines. The 7.93 Å line consists of two lines of forbidden transitions which are blended with each other; an electric quadrupole (E2) transition at 7.928 Å and a magnetic octupole (M3) transition at 7.938 Å. Observation of W46+ lines in the stellarator experiments is reported for the first time in the present study while the lines have been already observed in several tokamak experiments. The electron temperature dependence of the emission intensity of the 7.93 Å line agreed well with that of the fractional abundance of W46+ ions calculated using the ionization and recombination rate coefficients available in the ADAS database under the assumption of the collisional ionization equilibrium. The 7.93 Å line observed in this study will be used as tools for further spectroscopic researches, such as the measurements of spatial profile of W46+ ions using a space-resolved EUV spectrometer developed in LHD.journal articl
Non-contact and real-time measurement of heart rate and heart rate variability using microwave reflectometry
Get PDF0000-0002-9298-5585In this paper, we present noncontact and noninvasive vital signal detection using a microwave reflectometer. Elimination of noise components due to random movement of human subjects has been the biggest issue for microwave measurement. Appropriate filtering, amplitude control of the reflectometer signal, and cross correlation among multiple reflectometers together with new algorithms have enabled motion artifact elimination, signal peak detection, and data processing for various parameters related to heart rate (HR) and heart rate variability (HRV). We focus here on the real time measurements of instantaneous HR and HRV for practical use. The evaluation by microwave reflectometry is completely noninvasive and feasible even through clothing, which is extremely effective for health maintenance in daily life as well as for preventing sudden death related to, for example, coronary heart disease and ventricular arrhythmia.journal articl
Real-time control of the deposition location of ECRH in the LHD
Get PDF0000-0002-2983-5920A real-time control system for the deposition location of electron cyclotron resonance heating (ECRH) has been newly developed and applied to experiments on the Large Helical Device (LHD). Appropriate settings for a steerable launcher for ECRH were obtained by evaluating the deposition location and the absorption power for various electron density profiles using a ray-tracing code. The real-time deposition location control system adjusts launcher settings to improve the first-pass absorption of the refracted electron cyclotron wave, based on the ray-tracing calculations. The control system was designed to use a fast field programmable gate array (FPGA). The FPGA processes in real time the calculation of characteristic parameters regarding the density profile and the calculation of target positions requested for rotation control of a steering mirror of the launcher. The real-time deposition location control during ECRH discharges on the LHD functioned successfully in maintaining the absorption power higher than that without the control, which resulted from the deposition location maintained in the plasma core region.journal articl
Modeling of the ECCD injection effect on the Heliotron J and LHD plasma stability
Get PDF0000-0002-6114-0539The aim of the study is to analyze the stability of the energetic particle modes (EPM) and Alfven Eigenmodes (AE) in Helitron J and LHD plasma if the electron cyclotron current drive (ECCD) is applied. The analysis is performed using the code FAR3d that solves the reduced MHD equations describing the linear evolution of the poloidal flux and the toroidal component of the vorticity in a full 3D system, coupled with equations of density and parallel velocity moments for the energetic particle (EP) species, including the effect of the acoustic modes. The Landau damping and resonant destabilization effects are added via the closure relation. The simulation results show that the n=1 EPM and n=2 global AE (GAE) in Heliotron J plasma can be stabilized if the magnetic shear is enhanced at the plasma periphery by an increase (co-ECCD injection) or decrease (ctr-ECCD injection) of the rotational transform at the magnetic axis (-ι0). In the ctr-ECCD simulations, the EPM/AE growth rate decreases only below a given-ι0, similar to the ECCD intensity threshold observed in the experiments. In addition, ctr-ECCD simulations show an enhancement of the continuum damping. The simulations of the LHD discharges with ctr-ECCD injection indicate the stabilization of the n=1 EPM, n=2 toroidal AE (TAE) and n=3 TAE, caused by an enhancement of the continuum damping in the inner plasma leading to a higher EP β threshold with respect to the co- and no-ECCD simulations.journal articl
Correcting for non-periodic behaviour in perturbative experiments: application to heat pulse propagation and modulated gas-puff experiments
Get PDF0000-0001-6574-3823This paper introduces a recent innovation in dealing with non-periodic behavior often referred to as transients in perturbative experiments. These transients can be the result from the unforced response due to the initial condition and other slow trends in the measurement data and are a source of error when performing and interpreting Fourier spectra. Fourier analysis is particularly relevant in system identification used to build feedback controllers and the analysis of various pulsed experiments such as heat pulse propagation studies. The basic idea behind the methodology is that transients are continuous complex-valued smooth functions in the Fourier domain which can be estimated from the Fourier data. Then, these smooth functions can be subtracted from the data such that only periodic components are retained. The merit of the approach is shown in two experimental examples, i.e. heat pulse propagation (core transport analysis) and radiation front movement due to gas puffing in the divertor. The examples show that the quality of the data is significantly improved such that it allows for new interpretation of the results even for non-ideal measurements.journal articl
External RMP effect on locked-mode-like instability in helical plasmas
Get PDF0000-0003-3754-897XThe slowing-down mechanism of the locked-mode-like instabilities with and without an island structure is investigated through the effects of an external RMP (resonant magnetic perturbation) on the instabilities. For both instabilities, the slowing-down duration decreases with the increase in the external RMP, and the RMP dependence is consistent with the braking model of the j × B force due to the interaction between the instabilities and the external RMP. Moreover, the relationship between the amplitude and the frequency of both locked-mode-like instabilities during the slowing down is consistent with the force balance model between the j × B force due to the external RMP and a viscous force. These results suggest that the slowing down of both locked-mode-like instabilities with finite external RMP occurs due to the j × B force driven by the external RMP.journal articl
Electron temperature profile collapse induced by double-odd-parity MHD mode in the Large Helical Device
Get PDF0000-0001-5669-19370000-0003-3754-897X0000-0001-7618-63050000-0002-0585-4561In this paper, we report new results of a beam switching experiment aiming at a reversed magnetic shear profile formation for the study of an MHD-mode-induced profile collapse event. A transient MHD mode, whose oscillation frequency chirps down, is observed. The electron temperature profile collapse is induced by the mode activity, leading to the flattening of the central electron temperature profile. The radial mode structure is the double-oddparity at the beginning, but it transits to the even-parity in its final stage. The central electron temperature profile recovers after the radial mode structure changes to the even-parity, even though the mode itself does not disappear.journal articl