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Study on photoluminescence properties of Er2O3 materials as irradiation damage and temperature sensors
Full text linkPhotoluminescence (PL) properties of Er2O3 specimens were examined by using visible lasers (532 nm and 635 nm) and a UV LED light source (365 nm) to investigate the applicability for irradiation damage monitoring of materials in fusion reactors. Both in the laser induced and UV light induced PL spectra, green (510–590 nm) and red (630–725 nm) luminescence was observed. In the spectrum measurements on specimens with different crystallinities, it was confirmed that an intensity of the red luminescence weakened significantly compared with that of the green luminescence in an Er2O3 specimen with a lower crystallinity. The results indicate that the PL measurements of Er2O3 materials could be applicable for the irradiation damage monitoring in fusion reactors. The luminescence property of ion beam irradiated Er2O3 showed that information of irradiation damages could be kept up to ∼ 300 ℃ and almost recovered at 700 ℃. Based on the obtained luminescence properties, positions in a fusion reactor where Er2O3 materials could be used as irradiation damage sensors are proposed. Changes in PL spectra at high temperatures up to ∼ 400 ℃ indicate the possibility that the Er2O3 materials might be applicable also for temperature monitoring of in-vessel components during reactor maintenance periods.journal articl
Experimental study of the effect of geodesic curvature on turbulent transport in magnetically confined plasma
Full text linkORCID 0009-0009-5097-6566An experimental study has demonstrated the impact of the geodesic curvature of the magnetic field line on turbulent ion-heat transport in magnetically confined plasma using the large helical device. Statistical analyses with corrected Akaike Information Criterion and multiple regression have revealed that the geodesic curvature indicates a dominant contribution to the ion-heat transport. Geodesic curvature dependence of the zonal-flow effect is evaluated by using a gyrokinetic-simulation-based reduced model. Then, the analysis implies a significant enhancement of the zonal-flow effect with a small geodesic curvature. These two independent analyses indicated the possibility of external zonal-flow control with the geodesic curvature of the magnetic field.journal articl
High power Er:YAP laser at 2.92 μm based on incoherent beam combining
Full text linkWe report on a high-power Er3+-doped yttrium aluminum perovskite (Er:YAP) laser system run by incoherent beam combining at RT. A stable continuous-wave (CW) laser beam at 2.92 μm with an average power of 8.2 W is generated. To the best of our knowledge, this is the highest average power achieved from CW Er3+-doped solid-state lasers above 2.9 μm. No power saturation is observed, indicating that the output power can be further scaled up. Moreover, the experimental results show that the beam quality is maintained during the beam combining process.journal articl
Effect of nanosecond laser irradiation on tungsten grain structure
Full text linkORCID 0000-0001-9867-4051The laser-induced grain structure of pure tungsten was evaluated using a nanosecond Q-switched Nd:YAG laser. The grain structure, crystal orientation, and grain boundary angular distribution were analyzed through electron backscatter diffraction analysis, both before and after laser processing. The mechanical properties of pure tungsten after laser processing were also measured. The results obtained indicate that laser processing-induced recrystallization can offer micro-nano surface treatment of materials without compromising the mechanical properties.journal articl
Simulation of a scintillator-based fast ion loss detector for steady-state operation in Wendelstein 7-X (invited)
Full text linkORCID 0000-0002-2552-0411journal articl
Electron-scale turbulence characteristics with varying electron temperature gradient in LHD
Full text linkORCID 0000-0002-9172-7381Electron-scale turbulence, whose wavelength is the electron Larmor radius, is thought to have the potential to cause stiffness in an electron temperature gradient and degrade the confinement of future burning plasma in which the electron heating by alpha particles is dominant. The dependence of electron-scale turbulence and electron heat flux on the electron temperature inverse gradient length Rax/LTe , were investigated. The electron temperature gradient was successfully varied in the range of −3 < Rax/LTe < 12 by controlling the injection power of on/off-axis electron cyclotron heating. The results show a significant increase in the electron-scale turbulence with increasing Rax/LTe , especially in conditions where Electron Temperature Gradient (ETG) instability is linearly unstable, suggesting the presence of ETG turbulence at high Rax/LTe . The electron heat flux also increases steeply with increasing Rax/LTe . In addition, the electron-scale turbulence is observed even at Rax/LTe∼ 0, which is stable in linear GKV calculations. Finding the cause of this phenomenon is an interesting task
for the future.journal articl
Emission of high rovibrational hydrogen molecules under detached plasma conditions by recycling on the tungsten wall
Full text linkIt is well known that the rate coefficient of molecular-assisted recombination (MAR) varies by several orders of magnitude depending on the rovibrational states of the hydrogen molecules. A molecular dynamics simulation is performed to estimate the rovibrational states of recycled hydrogen molecules at the divertor in the JA-DEMO reactor under detached plasma conditions. The simulation results reveal that molecules in high rovibrational states are released even with low incident energy, which will be the dominant condition under detached plasma conditions. Molecules generated in this way can strongly affect the formation of the detached plasma via a molecular assisted-process such as MAR.journal articl
Initial results of hard X-ray spectroscopy by LaBr (Ce) detector for runaway electron study in Thailand Tokamak-1
No full textThailand Tokamak-1 (TT-1) successfully achieved its first plasma operation in early 2023. Understanding the behavior of high-energy runaway electrons (RE) during plasma discharges is crucial in TT-1 due to the potential risk of significant damage to in-vessel components. To study the RE behavior and analyze its characteristics, the LaBr(Ce) detector was employed for measuring hard X-ray emissions in TT-1. In this study, we first characterized the LaBr(Ce) detector in the laboratory and then performed hard X-ray spectroscopy in TT-1. Calibration sources, including 133Ba, 137Cs, 22Na, and 60Co, with energies up to 1.33 MeV, were used in the laboratory. The detector was calibrated using biased high voltage of -1000 V. It was found to have an energy resolution of approximately 6.2% at an energy of 0.662 MeV. After calibration, the detector was installed at TT-1 to measure hard X-ray. We analyze the hard X-ray emission from discharge #2183 during a selected time interval. It is found that the high-energy hard X-ray emissions reach up to approximately 500 keV. Assuming a simple Maxwellian distribution of the RE population, their temperature is estimated to be 224±4 keV. These findings confirm the presence of high-energy runaway electrons during TT-1’s plasma discharges. However, to accurately derive the runaway electron energy spectrum from the hard X-ray energy spectrum, the unfolding technique is required. In future work, we plan to apply the unfolding method, conduct numerical simulations on the physics of runaway electrons, and employ Monte Carlo simulations on the hard X-ray emissions.journal articl
Impacts of the large fusion test facility on tritium in environmental water and natural radiation levels
No full textORCID 0000-0001-9941-1958In the progress of nuclear fusion development, environmental radiation monitoring in the vicinity of the facility would be an important issue. At the National Institute of Fusion Science (NIFS), the deuterium plasma experiment, which produces tritium and neutrons using d-d fusion reactions, was conducted from 2017 to 2022. Environmental radiation and tritium in environmental water were monitored before and during the deuterium plasma experiment for public acceptance. As a result, there was no significant change in the observed dose rate and tritium concentration in the rainwater, and no statistically significant difference was identified in the statistical analysis of the data observed before and during the deuterium plasma experiment. Therefore, the environmental impact of the deuterium plasma experiments at NIFS is considered to be negligible.journal articl
Asymmetry in particle load on divertor tiles in different magnetic field configurations of LHD
Full text linkORCID 0000-0002-9974-2359The asymmetry of plasma-particle load on divertor tiles at helically symmetrical positions has been investigated in the Large Helical Device (LHD). The asymmetry reverses when the toroidal magnetic field direction changes, suggesting that particle drifts cause the asymmetry. This study conducted proton orbit tracing calculations under a vacuum condition to investigate the effects of grad-B drift and curvature drift on the asymmetry. The calculations were performed for the major radius of the magnetic axis, Rax, at 3.75 m and 3.6 m configurations. The results showed that due to the effects of grad-B drift and curvature drift, a similar asymmetry to the experimentally observed one appeared in the number of protons reaching the divertor tiles. The degree of asymmetry (DOA), representing the ratio of protons reaching the symmetrical divertor tiles, increased with higher proton energy and was smaller for the Rax = 3.75 m configuration than the Rax = 3.6 m one. An analysis of the experimental data for these magnetic field configurations revealed a consistent asymmetry between the Rax = 3.75 m and the Rax = 3.6 m configuration. It was also found that the asymmetry increased with higher electron temperature and was smaller in the Rax = 3.75 m configuration than in the Rax = 3.6 m one, which was consistent with the calculations. On the other hand, the experiments showed that the DOA saturated, which was not reproduced in the calculations.journal articl