NIFS-Repository (National Institute for Fusion Science)
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Multi-hole coupling power monitor with tapered sub-waveguide for dual-frequency high-power gyrotron
Get PDFORCID 0000-0002-4501-1956In magnetically confined fusion plasmas, a gyrotron is an essential auxiliary heating device for generating and sustaining plasma through electron cyclotron resonance heating owing to its ability to generate high-power microwaves. Microwaves emitted from a gyrotron are often transmitted through waveguides, and the transmitted power is monitored by a power monitor with a multi-hole directional coupler at the miter bend of the transmission line. Recently, a high-power dual-frequency gyrotron has been installed and operated in the Large Helical Device. A power monitor with good sensitivity to multiple frequencies is required to monitor the power transmission of the different frequencies at the same transmission line. In order to realize the power monitor, which can couple with the multiple-frequency microwaves, we focused on a sub-waveguide shape in the power monitor and investigated the influence of the tapered sub-waveguide by conducting electromagnetic simulations using a simple model. We also performed the high-power test using a power monitor with a tapered sub-waveguide. The experimental result was different from the simulation, but enough receiving power was obtained at both 116 and 154 GHz.journal articl
Simulation study of interaction between energetic particles and magnetohydrodynamic modes in the JT-60SA inductive scenario with a flat q≈1 profile
Get PDFORCID 0000-0001-7332-037XInteractions between energetic particles (EPs), an internal kink mode, and other magnetohydrodynamic (MHD) instabilities in the inductive scenario of JT-60SA (scenario #2) are simulated with MEGA, a global EP–MHD hybrid code. For this scenario, it was predicted by TOPICS, an integrated transport code that the internal kink mode can be unstable and the sawtooth relaxation results in a flat safety factor (q) profile with q ≈ 1 for r/a ⩽ 0.6. In this equilibrium, it is found in the simulation results that the stability of the internal kink mode depends strongly on the bulk plasma pressure gradient (∇Pb). In the n = 1 simulations where the toroidal mode number is restricted to n = 0 and 1, the pressure-driven internal kink mode is dominant. In the presence of co-passing EPs generated by the negative-ion-based neutral beam (NB), these EPs transfer energy to the internal kink mode; however, the EP driving rate (γh) is much lower than the driving rate from the bulk plasma pressure gradient (γP). The mode’s frequency is less than 1 kHz because the toroidal orbit frequency (ωϕ) and poloidal orbit frequency (ωθ) of the co-passing EPs are approximately equal within the q = 1 surfaces. This mode affects the EP and bulk plasma pressure redistributions. The feasibility of stabilizing the internal kink mode using trapped EPs is also investigated. It is found that the trapped EPs with energy 85 keV generated by the positive-ion-based NBs cannot stabilize the internal kink mode. Stabilization is observed when the injection energy is greater than 500 keV. In the multi-n simulations, where n ⩽ 8 modes are retained, the most unstable modes are high n interchange loidal number m = n whose linear growth rates exceed that of the pressure-drivenjournal articl
Characterization of Liquid Scintillator-Based CNES for Deuterium–Deuterium Neutron Emission Spectroscopy in the LHD
Get PDFORCID 0000-0002-0160-0468The compact neutron emission spectrometers (CNESs) based on conventional liquid (EJ-301) scintillation detectors were characterized in this work. The CNESs were employed for deuterium–deuterium neutron emission spectroscopy in the Large Helical Device (LHD). Prior to the installation, the EJ-301 scintillation detectors were characterized at the Fast Neutron Laboratory (FNL) of Tohoku University. In order to discriminate the neutron and γ -ray signals, the charge comparison method was used. The neutron energy spectrum was successfully unfolded from the measured recoil proton energy spectrum of the EJ-301 scintillation detector using the derivative unfolding technique. The detector’s energy resolution was examined. In the LHD, EJ-301-based CNESs with both tangential and perpendicular line-of-sight were employed for characterization. Furthermore, the characterization of the CNES was performed in the deuterium–deuterium experiment campaign. The operational capabilities of CNESs in the LHD were examined. Deuterium–deuterium neutron emission spectroscopy in various approaches of neutral beam (NB)-heated plasmas was conducted using CNES. Because of the high energy of the injected fast ions from tangential NB injection, an investigation of the Doppler effect on deuterium–deuterium neutron energy was conducted. The upper and lower shifted deuterium–deuterium neutron energies were observed when the fast ions moved toward and away from the tangential CNES, respectively. As expected, no notable energy shift was observed from fast ions injected by the perpendicular NB injection. Additionally, the 5-D orbit following code DELTA5D, which takes into account Larmor motion effects and the detector’s energy resolution, was utilized to compute the expected deuterium–deuterium neutron energy spectrum that would be measured by the CNES. There was a concurrence between the calculations and experimental results.journal articl
フッ素樹脂コーティングによる予冷時間短縮 ―液体窒素による急冷実験―
Get PDFORCID 0000-0002-5682-3343While fluoropolymer coatings are effective in reducing the pre-cooling time, quenching experiments have revealed that the formation of cracks in the coating during cooling enables a significant reduction in the pre-cooling time. The cracks affected the boiling heat transfer characteristics and accelerated the transition from film boiling to transition boiling during cooling. The high heat fluxes of subsequent transition and nucleate boiling contributed to the shorter pre-cooling time. The room temperature curable fluoropolymer coating is expected to have a wide range of applications because the coating is easy to apply and can be applied to narrow or curved surfaces such as the inside of pipes and tanks.journal articl
Global gyrokinetic simulations of electrostatic microturbulent transport in LHD stellarator with boron impurity
Get PDFGlobal gyrokinetic simulations of electrostatic microturbulent transport for discharge # 166256 of the Large Helical Device stellarator in the presence of boron impurity show the co-existence of the ion temperature gradient (ITG) turbulence and trapped electron mode (TEM) turbulence before and during boron powder injection. ITG turbulence dominates in the core, whereas TEM dominates near the edge, consistent with the experimental observations. Linear TEM frequency increases from kHz to kHz during boron injection, and ITG frequency decreases from kHz to kHz, consistent with the experiments. The poloidal wave number spectrum is broad for both ITG (0–0.5 mm−1) and TEM (0–0.25 mm−1). The nonlinear simulations with boron impurity show a reduction in the heat conductivity compared to the case without boron. The comparison of the nonlinear transport before and during boron injection shows that the ion heat transport is substantially reduced in the region where the TEM is dominant. However, the average electron heat transport throughout the radial domain and the average ion heat transport in the region where the ITG is dominant are similar. The simulations with boron show the effective heat conductivity values qualitatively agree with the estimate obtained from the experiment.journal articl
Bonding of Tungsten and Graphite Using Spark Plasma Sintering for Divertor Component in LHD
Get PDFThe manufacturing of tungsten (W) - graphite bonded divertor components for the Large Helical Device (LHD) has been investigated. The spark plasma sintering method was used to bond W and graphite with titanium (Ti) interlayer. Small specimens were fabricated to investigate the bonding strength and to diagnose the bonding interface. The granular structure was formed in the grooved area on the graphite surface. It was suggested that this granular structure had affected the bonding strength.journal articl
Feasibility study of neutral beam injection in Thailand Tokamak-1
Get PDF0000-0002-0160-0468Thailand Institute of Nuclear Technology (TINT) is developing Thailand- 1 (TT-1) from a former device HT-6 M of China. The first hydrogen plasma will be initiated in 2023. To investigate high-β plasma and physics related to fast ions, TT-1 will be equipped with auxiliary heating systems. In this work, a feasibility study for installing a neutral beam injection (NBI) heating system in TT-1 is carried out. This work is motivated to characterize beam ion's orbits in different injection angles and to explore a condition suitable in terms of higher heating efficiency. In this work, we assume that a hydrogen beam will be launched into the TT-1 plasma with an acceleration voltage of 20 kV. The orbit simulations using the gyromotion following code LORBIT are performed in various magnetic field equilibria, i.e., different plasma current (Ip), toroidal magnetic field strength (Bt), and the magnetic axis (Rax). Furthermore, beam ions are injected in different directions, i.e., tangential co-injection and tangential counter-injection. In the case of co-injection, beam ion loss is not significant, by about 6%, whereas beam ion loss fraction is evaluated to be 26–34% in the case of counter-injection. Also, it is found that the number of lost beam ions is significantly affected by changing Ip and Rax. The results obtained in this work will directly support the experiment plan for the high-performance plasmas, design of the fast-ion diagnostic system, and systematic understanding of beam ion's confinement property and beam-ion-driven magnetohydrodynamic (MHD) instabilities in TT-1.journal articl
Numerical Investigations on Superconducting Linear Acceleration System by Using Finite Element Method: Influence of Magnet Current on Pellet Velocity
Get PDF0000-0001-9924-9241The performance of a superconducting linear accelerator (SLA) system for pellet injection in fuel nuclear fusion reactors was investigated numerically. To this end, a numerical code using the finite element method was developed to analyze the shielding current density and dynamic motion of the high-temperature superconducting thin film of the SLA system. The computational results showed that applying an exponential current to the electromagnet, significantly improved the acceleration performance. It was concluded that SLA systems of the order of several hundred meters, and with realistic acceleration distances using the proposed currents can be designed.journal articl