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Design Concept of Supercritical CO2 Gas Cooled Divertors in FFHR Series Fusion Reactors
Get PDFIn the FFHR power reactor equipped with a supercritical CO2 gas turbine power generation system, an divertor cooling system is connected to this power generation system [S. Ishiyama et al., Prog. Nucl. Energy 50, No.12-6, 325 (2008) [1]]. In this paper, for the purpose of developing a diverter by supercritical CO2 gas cooling that can cope with a neutron heavy irradiation environment with a heat load of 15 MW/m2 or more, CFD heat transfer flow analysis was carried out for performance evaluation and its design optimization by a structural analysis models of a supercritical CO2 gas cooled divertors. As a result, in the supercritical CO2 gas cooled tungsten mono-block divertors (50 × 50 mm × 5 channel × 5,000 mL) with a flow path length of 5 m or less, the engineering designable range of these advanced diverters having the same cooling performance as the water cooling divertor was clarified, and its practicality is extremely high from the feature that the structural model has an extremely low risk during operation as compared with the water cooled divertor.journal articl
An alternative expression for ad hoc field collision model
Get PDF0000-0003-3554-0675An alternative form of ad hoc collision model to the Fokker–Planck field collision operator is proposed. The model is so constructed that the results of exact Fokker–Planck field collision, applied to the low-order Legendre and associated Laguerre polynomials, are used to impose self-adjointness first and then collisional conservation laws. The model is shown to be actually identical to the conventional ad hoc model in the l = 0 and 1 parts in Legendre polynomial expansion in an isothermal case, while it is not limited to extend to the higher order, in contrast to the conventional ad hoc model, in which the collisional conservation laws are imposed primarily, using the exact test collision form of the Fokker–Planck operator. Furthermore, it is discussed that the proposed model is identified to the lowest order in an expansion of formal Hirshman–Sigmar operator, while there is a difference between the formal and conventional Hirshman–Sigmar operators. Numerical examples demonstrate that the proposed model can yield comparable results to those by the exact Fokker–Planck and conventional Hirshman–Sigmar operators.journal articl
Joint meeting of 9th Asia Pacific-Transport Working Group (APTWG) & EU-US Transport Task Force (TTF) workshop
Get PDF0000-0002-0585-4561This conference report summarizes the contributions to, and discussions at the joint meeting of the 9th Asia Pacific-Transport Working Group (APTWG) & EU-US Transport Task Force (TTF) workshop held online, hosted by Kyushu University, Japan, during 6–9 July 2021. The topics of the meeting were organized under five main topics: (1) isotope effect on transport and physics on isotope mixture plasma, (2) turbulence spreading and coupling in core-edge-SOL, (3) interplay between magnetohydrodynamic topology/instability and turbulent transport, (4) interaction between energetic particle driven instability and transport, (5) model reduction and experiments for validation.journal articl
Development of static magnetic refrigeration system using multiple high-temperature superconducting coils
Get PDFIt is expected to build a sustainable social system that uses “hydrogen” as a fuel to generate electricity without emitting CO2. To realize this, technology for storing a large amount of hydrogen is indispensable, and storage as liquid hydrogen is ideal. However, the efficiency of the cooling device in the temperature range around 20 K required for long-term storage with liquid hydrogen is low, and the equipment is huge and expensive, so it has not been established as a widely used technology. Magnetic refrigeration is expected to be a highly efficient refrigerator in the temperature range of around 20 K because it can realize an ideal refrigeration cycle. However, in magnetic refrigeration, it is necessary to give a magnetic field change to the magneto caloric material (MCM). Further, in order to perform cooling with a large capacity and extremely low temperature by magnetic refrigeration, the magnetic field strength of a permanent magnet is insufficient, and it is indispensable to use a superconducting coil capable of generating a strong magnetic field with low power consumption. This study aims to develop a static magnetic refrigeration system using multiple high-temperature superconducting coils. By utilizing the energy storage characteristics of the superconducting coil, we are considering a magnetic refrigeration system that can repeatedly generate magnetic field changes to save energy without the need for large amounts of energy to be taken in and out of the outside. We report on the technical feasibility of a static magnetic refrigeration system using HTS coils. The power consumption including the AC loss of two superconducting coils, which is the basic configuration of the static magnetic refrigeration system, is calculated, and the efficiency is estimated as a ratio to the assumed refrigeration capacity of the MCM.journal articl
大型核融合試験施設におけるメガワットミリ波ジャイロトロン発振器周辺の電磁環境調査
Get PDF0000-0001-9941-1958将来のエネルギー源として開発が進められている磁場閉じ込め方式の核融合研究では，高温プラズマの生成や制御，プラズマ加熱及び計測のために大電力高周波発振機器が利用されている．本論文では，核融合科学研究所の大型ヘリカル装置で使用されているメガワットミリ波ジャイロトロン発振器(周波数: 77 GHz，最大出力: 1～1.5 MW/2秒)を対象とし，作業従事者の安全管理を目的に，ホーンアンテナを用いて機器周辺での電磁環境を定点調査した．その結果，77 GHz発振器からおよそ30 m離れた場所で観測された漏洩電界の周波数は，77 GHzが最も強く，そこから数GHz離れた両側の周波数領域にも微弱なスプリアススペクトルが確認された．また，同じ場所で，数十秒から数百秒の発振運転に伴う漏洩電界(最大実効値: 数V/m)が観測された．電界の漏洩箇所は，ジャイロトロン発振器を構成する接地電位の電子ビームコレクターと，その他の部位とを電気的に絶縁するために具備された窒化ケイ素製絶縁部と推定された．本研究により，大型核融合試験施設におけるメガワットジャイロトロン発振器周辺のミリ波帯での漏洩電界の実態を初めて明らかにした．journal articl
Direct fast heating efficiency of a counter-imploded core plasma employing a laser for fast ignition experiments (LFEX)
Get PDFFast heating efficiency when a pre-imploded core is directly heated with an ultraintense laser (heating laser) was investigated. 'Direct heating' means that a heating laser hits a pre-imploded core without applying either a laser guiding cone or an external field. The efficiency, η, is defined as the increase in the internal core energy divided by the energy of the heating laser. Six beams (output of 1.6 kJ) from the GEKKO XII (GXII) green laser system at the Institute of Laser Engineering (ILE), Osaka University were applied to implode a spherical deuterated polystyrene (CD) shell target to form a dense core. The DD-reacted protons and the core x-ray emissions showed a core density of 2.8 ± 0.7 g cm−3, or 2.6 times the solid density. Furthermore, DD-reacted thermal neutrons were utilized to estimate the core temperature between 600 and 750 eV. Thereafter, the core was directly heated by a laser for fast-ignition experiments (LFEX, an extremely energetic ultrashort pulse laser) at ILE with its axis lying along or perpendicular to the GXII bundle axis, respectively. The former and latter laser configurations were termed 'axial' and 'transverse modes', respectively. The η was estimated from three independent methods: (1) the core x-ray emission, (2) the thermal neutron yield, and (3) the runaway hot electron spectra. For the axial mode, 0.8%< η <2.1% at low power (low LFEX energy) and 0.4%< η <2.5% at high power (high LFEX energy). For the transverse mode, 2.6%< η <7% at low power and 1.5%< η <7.7% at high power. Their efficiencies were compared with that in the uniform implosion mode using 12 GXII beams, 6% < η <12%, which appeared near to the η for the transverse mode, except that the error bar is very large.journal articl
Validation of the plasma-wall interaction simulation code ERO2.0 by the analysis of tungsten migration in the open divertor region in the Large Helical Device
Get PDF0000-0003-0655-7347Tungsten migration in the open divertor region in the Large Helical Device is analyzed for validating the three-dimensional plasma-wall interaction simulation code ERO2.0. The ERO2.0 simulation reproduced the measurement of localized tungsten migration from a tungsten-coated divertor plate installed in the inboard side of the torus. The simulation also explained the measurement of the high tungsten areal density in the private side on a carbon divertor plate, next to the tungsten-coated divertor plate, by the tungsten prompt redeposition in plasma discharges for a low magnetic field strength in a counterclockwise toroidal direction. However, the simulation disagreed with the measurement of low tungsten areal density on the plasma-wetted areas on the carbon divertor plates, which indicated that the actual erosion rate of the redeposited tungsten should be much higher than that used in the ERO2.0 code.journal articl
Improved prediction scheme for ion heat turbulent transport
Get PDF0000-0002-2459-2392A novel scheme to predict the turbulent transport of ion heat of magnetic confined plasmas is developed by combining mathematical optimization techniques employed in data analysis approaches and first-principle gyrokinetic simulations. Gyrokinetic simulation, as a first-principle approach, is a reliable way to predict turbulent transport. However, in terms of the flux-matching [Candy et al., Phys. Plasmas 16, 060704 (2009)], quantitative transport estimates by gyrokinetic simulations incur extremely heavy computational costs. In order to reduce the costs of quantitative transport prediction based on the gyrokinetic simulations, we develop a scheme with the aid of a reduced transport model. In the scheme, optimization techniques are applied to find relevant input parameters for nonlinear gyrokinetic simulations, which should be performed to obtain relevant transport fluxes and to optimize the reduced transport model for a target plasma. The developed scheme can reduce the numbers of the gyrokinetic simulations to perform the quantitative estimate of the turbulent transport levels and plasma profiles. Utilizing the scheme, the predictions for the turbulent transport can be realized by performing the first-principle simulations once for each radial position.journal articl
LEVELS OF ATMOSPHERIC TRITIUM IN THE SITE OF FUSION TEST FACILITY
Get PDF0000-0001-9941-1958In the deuterium plasma experiment using Large Helical Device at the National Institute for Fusion Science (NIFS), a small amount of tritium is produced by the D–D fusion reaction. Then, a part of produced tritium is discharged into the environment via a stack. Thus, the atmospheric tritium in the site of NIFS has been monitored before starting the deuterium plasma experiment. The atmospheric tritium concentrations at NIFS were indicated to be background levels in Japan. To investigate the impact of tritium discharged from the stack, the correlation between the atmospheric tritium concentration and the tritium concentration observed in the stack was evaluated, and no significant correlation was found. In addition, the atmospheric tritium concentration at NIFS ranged within the background levels in Japan. Therefore, the impact of discharged tritium from the stack would be negligible in the environment at NIFS.journal articl