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Erratum: “Estimation of the Tritium Yields in Deuterium Fusion Plasmas Considering the Fast-Ion Velocity Distribution Function” [Plasma Fusion Res. 17, 2402023 (2022)]
Full text linkORCID 0000-0003-3293-488Xjournal articl
Mid-infrared refractometer based on side-polished indium fluoride fiber for monitoring relative humidity
Full text linkThis work developed a fiber-optic refractometer taking advantage of the anomalous dispersion by water as an approach to monitoring relative humidity. The sensor part of this device was fabricated by mechanical polishing of an indium fluoride fiber capable of transmitting mid-infrared radiation. This sensor was found to respond to variations in relative humidity as a consequence of rapid changes in the external refractive index related to the condensation of water on the exposed fiber. Clear signal variations were also obtained in response to exposure to human breath when using a sampling rate of 10 Hz.journal articl
Solution space and effective model for turbulent transport of helical plasmas
No full textORCID 0000-0002-2459-2392We discuss an effective transport model of magnetized turbulenthelical plasma based on the solution space of first-principle gyrokinetic simulations. If the time evolution of dynamical systems can be regarded as solution trajectories in theoretical phase space, physical phenomena in the saturated stable phase are realized in the solution space formed by these trajectories in the long time limit. Similar properties are found not only in dynamical systems but also in general physical systems with renormalization group flows (Wilson and Kogut 1974 Phys. Rep. C12 75). Therefore, if the solutions effectively form a finite dimensional solution space, the physical system can generally be represented in reduced form. Here, we try to apply this discussion to develop a transport model of turbulent plasma in first-principle gyrokinetic simulations. Based on the solution space due to the trajectory of the simulations with a certain functional form (Fujii and Nunami 2022 Plasma Fusion Res. 17 2403030), we discuss the effective structure of the objective function to represent the transport model. By evaluating the structure with fitting errors of the objective function in the model parameter space, we can determine a plausible functional form. This paper discusses a methodology for constructing such an effective transport model for helical plasmas.journal articl
Water window soft X-ray spectra of Ce- to Gd-like Bi ions in an electron beam ion trap
No full textThe water window emission lines (20–40 Å) of highly charged bismuth (Bi) ions in laser produced plasmas are useful as light sources for biological microscopy of living cells. However, broad distributions of charge states and overlapping of transition arrays in the laser produced high density plasmas make precise line identification difficult. In this paper, we identified strong emission lines in the water window range from Bi ions decomposing to each charge state with a compact electron beam ion trap (CoBIT). To this end, we constructed a collisional radiative model accounting for detail atomic processes of the Bi ions interacting with mono-energetic electron beams. Each transition array observed in the experimental spectra was carefully identified with the present calculations. Distributions of the observed peaks show distinct features depending on charge state abundance in the CoBIT. We found that line emissions mediated via meta-stable excited states play an important role.journal articl
Energy exchange between electrons and ions driven by ITG–TEM turbulence
No full textIn this study, the energy exchange between electrons and ions in trapped-electron-mode (TEM) and mixed ion temperature gradient (ITG)–TEM turbulence is investigated using gyrokinetic simulations. The energy exchange in TEM turbulence is primarily composed of the cooling of electrons associated with perpendicular ∇B-curvature drift and the heating of ions moving parallel to magnetic field lines. TEM turbulence facilitates energy transfer from electrons to ions, which is opposite to the direction observed in ITG turbulence. In mixed ITG–TEM turbulence, the relative magnitudes of parallel heating and perpendicular cooling for each species determine the overall direction and magnitude of energy exchange. From the viewpoint of entropy balance, it is further confirmed that energy flows from the species with larger entropy production, caused by particle and heat fluxes, to the other species in ITG–TEM turbulence. The predictability of turbulent energy exchange in ITG–TEM turbulence by the quasilinear model is examined. In addition, an alternative method based on the correlation between energy flux and energy exchange is developed, and its validity is demonstrated.journal articl
Three-dimensional flow velocity determination using laser-induced fluorescence method with asymmetric optical vortex beams
Full text linkORCID 0000-0003-3627-6060Laser-induced fluorescence (LIF) Doppler spectroscopy using an optical vortex beam with an asymmetric intensity distribution, referred to as aOVLIF, is proposed as a new method to measure plasma flow velocity. LIF spectra were calculated numerically using typical laboratory low-temperature plasma parameters, and it was revealed that an ion flow across the beam produces a frequency shift of the spectra. This method also has the capability of temperature measurements. The propagation effects of asymmetric optical vortex beams are discussed assuming an actual experiment, and it is found that the sensitivity to the transverse flow velocity is approximately unchanged. The aOVLIF method, which exploits the inhomogeneous phase structure of optical vortices, can be applied to the determination of three-dimensional velocity vectors and promises to enhance the usefulness of conventional LIF spectroscopy using plane waves.journal articl
Femtosecond vector vortex laser ablation in tungsten: chiral nano-micro texturing and structuring
Full text linkORCID 0009-0004-5354-3030We demonstrate laser-induced periodic surface structure (LIPSS) formation on tungsten with femtosecond vector vortex laser ablation for the first time, and investigate the properties of vector vortex LIPSS by contrasting its properties with Gaussian beam irradiation, and provide some demonstrations of complex microstructuring. The annular intensity profile of vector vortex beams allows LIPSS formation over wider energy range than Gaussian beams. Also, we demonstrate 2 and 3-dimensional chiral texturing and structuring by femtosecond vector vortex laser ablation. Vector vortex beam laser processing, which enables the fabrication of controllable complex structures, will open the door to innovative applications of tungsten.journal articl
Application of two-dimensional temperature response functions for reconstruction of divertor heat flux profile in commercial fusion reactors
Full text linkORCID 0009-0005-6662-7935To keep the tritium breeding rate TBR > 1 and to meet the high heat load and neutron shielding requirements for the first wall and divertor in fusion demonstration (DEMO) reactors, the number of port plugs and other openings must be limited. To accomplish this, it is necessary to develop alternatives to the use of infrared (IR) hermography to determine the peak heat flux and the heat flux profile onto divertor targets. A divertor tile equipped with multiple temperature monitoring channels can be used to reproduce the temperature profile. To avoid the high temperatures and high neutron flux environment in a DEMO, the monitoring positions can be set well away from the irradiated surface. However, the spatial resolution of this method is lower than that provided by IR thermography. In the present work, we apply twodimensional temperature response functions and the corresponding heat conduction model to temperature data obtained from a divertor tile surface in the large helical device to study the effects of the spatial resolution of the monitored temperature profile on the reconstructed heat flux profile. The findings provide information that will be useful in defining a method for embedding thermocouples into the divertor tiles of future DEMO reactors.journal articl
Suppression of "Edge MHD Instability of LHD" by External RMP
Full text linkWe experimentally investigate the effect of external resonant magnetic perturbation (RMP) on "Edge MHD instability", which is observed in a discharge with relatively low magnetic Reynolds number and middle beta in the Large Helical Device (LHD) and leads to minor collapse (rapid degradation of volum-averaged beta value by 10%). When the external RMP is small, the instability is continuously observed in a discharge, and the fluctuation amplitude decreases a little with the increment of the RMP. When the RMP is large enough, the appearance of the instability becomes intermittent, and the fluctuation amplitude rapidly decreases with the increment of the RMP. Moreover, the confinement performance degraded by the instability also recovers when the intermittent instability appears.datase
The initial measurement of a compact D–T neutron spectrometer based on a single-crystal chemical vapor deposition diamond stack for fusion plasma diagnostic
Full text linkORCID 0000-0002-2771-6979For developing and characterizing a novel compact D–T neutron spectrometer based on a single-crystal chemical vapor deposition diamond stack for plasma diagnostics toward future D–T fusion reactors, the initial measurement was performed using the accelerator-based D–T neutron sources OKTAVIAN at Osaka University. This neutron spectrometer was designed for the detection of 3–17 MeV neutrons and operated in the proton recoil telescope configuration by installing a polyethylene converter in front of the diamond stack. The measured neutron energy spectra were obtained by summing the energy of the recoil protons deposited in the diamond stack after the coincidence of the recoil protons identified by the time coincidence analysis. The neutron energy peaks measured by the compact D–T neutron spectrometer were almost in agreement with those obtained by the Monte Carlo N-Particle transport (MCNP) simulation. The energy resolution of the compact D–T neutron spectrometer was emulated to be about 4%–5% in D–T neutron measurement. In future work, the design of the compact D–T neutron spectrometer would be optimized to measure the fusion neutron for plasma diagnostics.journal articl