NIFS-Repository (National Institute for Fusion Science)
Not a member yet
13159 research outputs found
Sort by
Users′ perspective on D-Li neutron sources (A-FNS and IFMIF-DONES) for DEMO and beyond
Get PDFA-FNS and IFMIF-DONES neutron source program in Japan and in the EU, respectively, are advancing targeting on the start of operation in ∼2030. These facilities will play a central function in realizing DEMO. This paper will discuss the role of the materials scientists, as the users, in A-FNS and IFMIF-DONES programs in order to encourage them to enhance their commitment to the programs. The past collaborations by the materials scientists and the designers in the IFMIF project are introduced first. Then the roles of the neutron sources in the DEMO-roadmap are discussed, for which materials scientists are requested to take leadership. This paper also emphasizes the need for development of advanced materials and for obtaining fundamental understanding on fusion neutron radiation effects by application of the neutron sources.journal articl
Regression Approach for Acquiring a Quantitative Guidance toward Updating the Deuterium-Deuterium Fusion Neutron Emission Rate in the Large Helical Device
Get PDF0000-0003-4555-1837A regression approach has been adopted to acquire a quantitative guidance for updating the total neutron emission rate (Sn) in the Large Helical Device (LHD) with employing the externally controllable parameters such as heating power and plasma density. A deduced regression expression is worthwhile to understand for the contribution of an individual parameter during high Sn discharges, and then to be exploited in the experiment planning to update the record Sn value in LHD in the coming campaigns. It was found that Sn in high Sn discharges in LHD is expressed as Sn = 1014.25 × ne_avg0.52 × PN-NB0.69 × PP-NB0.37, where ne_avg, PN-NB, and PP-NB represent the line-averaged electron density [1019 m−3] and the injection power of negative and positive ions based neutral beam injection [MW], respectively. This expression shows that, among three parameters, PN-NB is essential for achieving high Sn in this employed high Sn discharge database.journal articl
Neutronics Assessment of a Compact D-D Neutron Generator as a Neutron Source for the Neutron Calibration in Magnetic Confinement Fusion Devices
Get PDF0000-0003-2254-3164Neutronics aspects of a compact D-D neutron generator as a neutron source for the neutron calibration in magnetic confinement fusion devices are assessed by the MCNP calculation. The neutron emission distribution of the compact D-D neutron generator has a large anisotropy not only due to the scattering with the neutron generator body but also due to the intrinsic anisotropy of the differential cross-section of the d(d,n)3He reaction. The angular neutron distribution at the target of the compact D-D neutron generator is calculated with the PHITS code where the slowing down on the accelerated deuterons in the target material is considered. The calibration experiments are simulated by using the MCNP-6 code for the ITER neutron flux monitor (NFM) to be installed in the equatorial port. The detection efficiency of NFM is calculated for a D-D plasma neutron source, an idealistic D-D neutron source, a 252Cf neutron source and the compact neutron generator. It is found that the detection efficiency of NFM for the compact neutron generator is approximately 50% larger than that for the idealistic D-D neutron source. The discrepancy is improved to be 25% by the intention of the target 20 cm from the body of the compact neutron generator.journal articl
Simulation of Alfvén eigenmodes destabilized by energetic electrons in tokamak plasmas
Get PDF0000-0002-8678-8075Alfvén eigenmodes (AEs) driven by energetic electrons were investigated via hybrid simulations of an MHD fluid interacting with energetic electrons. The investigation focused on AEs with the toroidal number n = 4. Both energetic electrons with centrally peaked beta profile and off-axis peaked profile are considered. For the centrally peaked energetic electron beta profile case, a toroidal Alfvén eigenmode (TAE) propagating in the electron diamagnetic drift direction is found. The mode is mainly driven by deeply trapped energetic electrons. It is also found that a few passing energetic electrons spatially localized around rational surfaces can resonate with the mode. For the off-axis peaked energetic electron beta profile case, an AE propagating in the ion diamagnetic drift direction is found when a with weak magnetic shear is adopted. The destabilized mode is an elliptical-Alfvén-eigenmode-type (EAE-type) mode which has a spatial profile peaking at the rational surface and a frequency close to the second Alfvén frequency gap. It is found that passing energetic electrons and barely trapped energetic electrons are responsible for this EAE-type mode destabilization. The saturation levels are compared for a TAE with the same linear growth rate among energetic electron driven mode and energetic ion driven mode with isotropic and anisotropic velocity space distributions. The saturation level of TAE driven by trapped energetic electrons is comparable to that driven by energetic electrons with isotropic velocity space distribution where the contribution of trapped particles is dominant. It is found that the trapped energetic ion driven TAE has a larger saturation level than the passing energetic ion driven TAE, which indicates the difference in particle trapping by the TAE between trapped and passing energetic ions.journal articl
Exhaust behavior of tritium from the large helical device in the first deuterium plasma experiment
Get PDFThe tritium exhaust behavior from the Large Helical Device (LHD) was observed in the first deuterium plasma experimental campaign. Tritium in the exhaust gas was monitored at the conducted by use of the ionization chamber and water bubbler system with the discrimination of chemical forms. The observation results indicated that (i) tritium on the surface of the first wall and divertor tiles as plasma facing components was released by the hydrogen isotope exchange reaction of the glow discharge cleaning operation and the diffusion-limited process was suggested in the tritium release behavior from the bulk, (ii) the amount of tritium release from the LHD vacuum vessel was about one-third of the produced tritium and the mostly produced tritium was still retained at the end of plasma experimental campaign, (iii) the ratio of exhausted tritium from the LHD vacuum vessel was larger than that in the case of JT-60U based on the carbon materials as the plasma-facing components. It indicated that the tritium inventory would be reduced and controlled by the kind of plasma-facing materials.journal articl
Initial operation results of exhaust detritiation system using a polymer membrane
Get PDFAn exhaust detritiation system using commercially available hollow fiber-type polyimide membrane modules, a PM system, was installed and applied for tritium recovery in the vacuum vessel purge gas of a large fusion test device. The PM system is operated annually and there were no serious malfunctions after starting the operation for approximately 2.5 y. The continuous recovery of tritiated water without the heating operation and the switching of valves as well as the regeneration operation of molecular sieves, was demonstrated. The tritium in the process gas was successfully recovered by the PM system even though the average tritium concentration at the inlet of the PM system was less than the order of 10−3 Bq/cm3. The detritiation factor and tritium recovery ratio were greater than 103 and 0.97, respectively. The tritium concentration at the outlet of the PM system was maintained in the order of 10−6 Bq/cm3 irrespective of the tritium concentration at the inlet of the PM system. Thus, the operating data indicates that the PM system has a potentially higher detritiation factor than DF = 103.The exhaust detritiation system using a polymer membrane was operated for 2.5 y.There were no serious malfunctions after starting the operation.The operating data indicates that the system has a potentially higher detritiation factor than DF = 103.journal articl
Progress of statistical modelling of thermal transport of fusion plasmas
Get PDF0000-0001-8856-1483Progress of statistical modelling of thermal transport of fusion plasmas based on (2–4 a) a transport analysis database is described. Statistically induced ion and electron thermal diffusivities are checked with an actual discharge which had not been included in the database. Usefulness of this statistical approach is explained in terms of (1) extracting important parameters through the application of information criterion, and (2) making possible for discussing exponents of regression expression and then implying the thermal transport property. The statistical approach reported in this paper could provide a new insight for thermal transport modelling for fusion plasmas, complementing conventional global scalings on the energy confinement time.journal articl
Evaluation of abrupt energy transfer among turbulent plasma structures using singular value decomposition
Get PDF0000-0001-6835-1569A method to quantify the energy transfer among turbulent structures using singular value decomposition (SVD) is presented. We apply the method to numerical turbulence data obtained from a global plasma simulation using the Hasegawa–Wakatani fluid model, in which the Kelvin–Helmholtz instability plays a dominant role. Using the SVD method, the electrostatic potential is decomposed into a background potential deformation, a zonal flow, a coherent mode and an intermittent structure. Thus there are four key structures, as distinct from the three found in conventional theory. The kinetic energy of each structure is evaluated, and the limit cycle among them is obtained. In the limit cycle, an abrupt change of the background is found to be synchronised with the period of the zonal flow. The energy transfer function of each turbulence structure, which is defined on the basis of a vorticity equation, is evaluated. This then provides physical understanding of how the limit cycle is sustained by dynamical changes in the energy transfer among structures over the its period. In addition, it is shown that the abrupt deformation of the background is caused by the non-linear self-coupling of the intermittent structure.journal articl
The systematic investigation of energetic-particle-driven geodesic acoustic mode channeling using MEGA code
Get PDF0000-0002-9819-7483Energetic-particle-driven geodesic acoustic modes (EGAMs) channeling in the Large Helical Device (LHD) plasmas are systematically investigated for the first time using MEGA code. MEGA is a hybrid simulation code for energetic particles interacting with a magnetohydrodynamic (MHD) fluid. In the present work, both the energetic particles and the bulk ions are described kinetically. The EGAM profiles in the three-dimensional form is illustrated. Then, EGAM channeling behaviors are analyzed under different conditions. During the EGAM activities without frequency chirping, EGAM channeling occurs in the linear growth
stage but terminates in the decay stage after the saturation. During the EGAM activities with frequency chirping, EGAM channeling occurs continuously. Also, low-frequency EGAM makes the energy transfer efficiency (Eion/EEP) higher, and this is confirmed by changing the energetic particle pressure, energetic particle beam velocity, and energetic particle pitch angle. Moreover, higher bulk ion temperature makes the energy transfer efficiency higher. In addition, under a
certain condition, the energy transfer efficiency in the deuterium plasma is lower than that in the hydrogen plasma.journal articl
Hybrid simulation of NBI fast-ion losses due to the Alfvén eigenmode bursts in the Large Helical Device and the comparison with the fast-ion loss detector measurements
Get PDF0000-0002-5364-805XThe multiphase simulations are conducted with the kinetic-magnetohydrodynamics hybrid code MEGA to investigate the spatial and the velocity distributions of lost fast ions due to the Alfvén eigenmode (AE) bursts in the Large Helical Device plasmas. It is found that fast ions are lost along the divertor region with helical symmetry both before and during the AE burst except for the promptly lost particles. On the other hand, several peaks are present in the spatial distribution of lost fast ions along the divertor region. These peaks along the divertor region can be attributed to the deviation of the fast-ion orbits from the magnetic surfaces due to the grad-B and the curvature drifts. For comparison with the velocity distribution of lost fast ions measured by the fast-ion loss detector (FILD), the ‘numerical FILD’ which solves the Newton–Lorentz equation is constructed in the MEGA code. The velocity distribution of lost fast ions detected by the numerical FILD during AE burst is in good qualitative agreement with the experimental FILD measurements. During the AE burst, fast ions with high energy (100–180 keV) are detected by the numerical FILD, while co-going fast ions lost to the divertor region are the particles with energy lower than 50 keV.journal articl