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Development of a heated liquid Sn flowing system and preliminary results of wettability improvement by inter-metallic layer
Get PDFORCID 0000-0002-9230-2334A new gas-driven liquid metal (Sn) flow device named Gas-driven Liquid-metal Flow test device (GaLF) was established. The device is a pilot device for a linear plasma device that irradiates flowing liquid metal (LM) free-surface. The flow rate of Sn controlled by the inlet gas rate was evaluated by comparison with the weight change of the downstream Sn tank. A new method to achieve better wettability against liquid Sn by forming an intermetallic layer was suggested and tested in GaLF. The treated stainless steel showed better wettability enough to achieve a good free surface flow for plasma-surface interaction studies.journal articl
Laboratory Transition-rate Measurement of the Coronal Intercombination Line of Ar xv by Time-resolved Laser Spectroscopy
Get PDFORCID 0000-0002-4088-239XThe extreme-ultraviolet emission line (424 Å) of the intercombination 1s22s21S0–1s22s2p3P1 transition of Ar xv can potentially characterize the electron temperature of astrophysical plasma. Various theoretical studies have investigated the intercombination transition rate, which is essential for the plasma diagnostics; however, experimental difficulties have prevented its measurement. We present here measurement of the lifetime of the 3P1 excited state of Ar xv, providing the experimental value of the intercombination transition rate. Employing time-resolved plasma-assisted laser spectroscopy, a method we recently demonstrated, enables us to measure this submicrosecond lifetime. The experimental result exhibits a 25%–43% higher transition rate than theoretical predictions.journal articl
Effect of Ball Diameter on Mechanical Alloying Process for the Production of Dispersion Strengthened Tungsten
Get PDFORCID 0000-0001-9016-2318Tungsten is candidate material for plasma facing armor. In our initial study, to improve the plasma facing tungsten on fusion divertor, a new oxide dispersion strengthened tungsten (ODS-W) has been developed using by REDOX (oxidation-reduction reaction) process between W and TiC, including titanium oxide as strengthening nano-particles in matrix, fabricated by mechanical alloying (MA)-hot isostatic pressing (HIP), which can inhibit the decrease of mechanical property even after recrystallization occurs. Our past studies showed that the condition of MA process affects the mechanical and the thermal properties of the products. In the present study, the optimal ball size to be used in the MA process of preparing ODS-W has been proposed by investigation of the relationship between different ball sizes and the MA effect, focusing the optimization of manufacturing process for DS-W. The evolutions of the lattice constant and microstructure were shown to indicate the progress of mechanical alloying. The effect of the ball size was interpreted as that of collision energy delivered by the weight of MA balls.journal articl
Research of turbulent transport due to dissipative trapped electron mode in tokamak plasmas
Get PDFORCID 0000-0002-0712-8811The purpose of this article is to study turbulent transport for laboratory plasmas in toroidal devices by gyrokinetic analyses. Linear analysis is performed to clarify the dominant mode for tokamak plasmas. The dissipative trapped electron mode (d-TEM) and the ion temperature gradient (ITG) mode are predicted using the Sugama collision model operator [Sugama et al., Phys. Plasmas 16, 112503 (2009)]. Nonlinear gyrokinetic analysis is used to quantify turbulent transport. The nonlinear simulation results show the levels of particle and energy transport, where the d-TEM and ITG mode are unstable. The effect of zonal flows is studied by the linear and nonlinear simulation results. The results of the analysis are compared when two types of model collision operator, which are the Sugama and Lenard–Bernstein [Phys. Rev. 112, 1456 (1958)] collision model operators, are used. In this study, the simulation results using the Sugama collision operator show a stronger effect of the zonal flows on the turbulent transport than those using the Lenard–Bernstein collision operator, as predicted by the linear simulation result such as the zonal flow decay time.journal articl
Deuterium and helium desorption/retention properties of low-activation vanadium alloys possible for reuse in a short time in fusion reactors
Get PDFORCID 0000-0002-9950-2419Low-activation vanadium (V) alloys are alternative to the reduced-activation ferritic/martensitic steels due to their high-temperature strength, superior irradiation properties and non-magnetic characteristics. To make the reusage of the alloys possible in a short time in fusion reactors, new design concepts of V alloy have been suggested in National Institute for Fusion Science. In the present study, the deuterium and helium retention/desorption behaviors of the new designed V alloys were investigated.
A major desorption peak of D2 appeared at 600–750 K for the irradiation at room temperature. This peak would be originated from D atom in a binding state in the alloy. In the case of the irradiation at 773 K, a new peak appeared around 820 K only for the alloy with low purity and high Ti content. Discussion with results of EELS analysis suggests that the desorption around 820 K were originated form D trapped by the precipitates. Other V alloy samples used in the present study showed low D retention for the case of the 773 K irradiation.
The helium desorption which was originated from the blisters appeared at the high temperature region. The amounts of these desorption for the alloy with high Ti content was large, compared with the case of low Ti content.datase
Co-deposited layers on gap surfaces of bulk tungsten divertor tiles in JET ITER-like wall: Directional effects and nanostructures
Get PDFORCID 0000-0002-3744-2481Co-deposited layers on surfaces of bulk tungsten divertor tiles (W lamellae) from the first campaign of JET with the ITER-Like Wall (JET-ILW, 2011–2012) were examined by means of a cross-sectional transmission electron microscope observation. The focus was on geometrical effects in impurity deposition, mainly beryllium (Be), on surfaces located in the poloidal gap separating adjacent lamellae. The study was carried out on the sides (gap surfaces) of two W lamellae from Stack C (located on the outboard part of the horizontal section of the lower divertor), from the region most exposed to the plasma (lamella C23) and in the magnetic shadow of the upstream divertor module (lamella C3). The tile manufacturing process (cold rolling) left shallow grooves, i.e. structures classified as convex (hill) and concave (valley) regions. These regions are decisive for the deposition structure. The main results were: (i) two kinds of impurity deposition features, “homogeneous” and “directional”, have been distinguished; (ii) the directional ones were characterized by nanoscale inclined vertical stripes in the deposition layer; (iii) homogeneous deposition without directional features were in the valley region. The results clearly indicate the impact of the surface finish, even in the tile gaps, on the qualitative and quantitative aspects of deposition.journal articl
Data-volume reduction of optical vortex laser absorption spectroscopy by coarse-graining using a quadrant photodiode
Get PDFORCID 0000-0002-1583-3094We developed optical vortex laser absorption spectroscopy (OVLAS) to measure the transverse flow velocity relative to the probe beam. In our previous OVLAS setups, a camera is used in the measurement system. This approach constrained the time resolution by image data transfer time and required large computational resources due to the considerable amount of image data. In this paper, we discuss the coarse-graining of OVLAS as a method to improve time resolution and reduce computational resources achieved by replacing the camera with a quadrant photodiode (QPD). Measurement image data obtained from a camera was numerically coarse-grained to evaluate the feasibility of measurements using a QPD. Subsequently, the transverse flow velocity was measured by QPD. Measured transverse flow velocity had a mean absolute percentage error of 18%, confirming the practical validity of coarse-graining OVLAS. The data volume required to determine the flow velocity was reduced to 1/120 from the original OVLAS.journal articl
Collisional-Radiative modeling of unresolved transition array spectra near 200 Å from W17+-W25+ emissions for diagnostics of ITER edge plasma
Get PDFORCID 0009-0008-3408-9337Tungsten (W) is one of the major impurities in ITER and future DEMO reactors. However,
diagnosing the ion density, temperature, and spatial distribution of tungsten ions in intermediate charge states, such as W8+-W27+, is difficult because of the lack of spectral line data. In this study, we observed a tungsten Unresolved Transition Array (UTA) spectrum, which has a pseudo-continuum structure, around W20+ in the Extreme Ultraviolet wavelength region in the Large Helical Device (LHD). We conducted Collisional-Radiative (CR) modeling for W17+-W25+. Two pseudo-continuum peaks corresponding to 5 s-5p transition and transition between doubly excited states of 5 s2-5s5p, are strongly emitted around 200 Å for each ion. The synthesized spectrum of W17+-W25+ ions reproduced the observed LHD spectrum near 200 Å. From the electron temperature dependence of the UTA spectral shape, the UTA shifted toward longer wavelength region with several pseudo-continuum peaks appearing for ions in lower charge states, with decreasing electron temperature from 0.4 keV to 0.2 keV. This result qualitatively explained the observed time evolution of the spectrum.journal articl
Numerical Simulations of Hall MHD Turbulence with Magnetization
Get PDFDirect numerical simulations (DNS) and large eddy simulations (LES) of homogeneous Hall magnetohydrodynamic (MHD) simulations are carried out to verify the properties of a sub-grid-scale (SGS) model which has been developed for LES recently. LES with the new SGS model reproduces one-dimensional spectra of DNS. It is also shown that the probability density functions (PDFs) of the current density components of DNS and LES in the grid-scale coincide with each other by an appropriate normalization. We verify by this numerical study that our improved SGS model is applicable to homogeneous Hall MHD turbulence. We also find that the difference in the deviation of the current density components is smaller in the MHD-scale of LES than in that of DNS. These results provide a new insight to study the spectral anisotropy of turbulence, especially in relation to the sub-ion-scale.journal articl
Measurement of DNA length on video of fluorescence microscope by pix2pix trained by molecular dynamics simulation
Get PDF0000-0002-0593-8810For the automatic measurement of DNA length in the video captured by fluorescence microscope, image processing method using pix2pix is developed. To increase the accuracy of the measurement in low-resolution video, a method of inputting multiple time-series frames to pix2pix are proposed. To generate the training data, molecular dynamics simulation is employed to prepare dummy video. The trained pix2pix by multiple frames input can generate more accurate images in a scene of DNA breakage than the pix2pix trained by single frame input.journal articl