NIFS-Repository (National Institute for Fusion Science)
Not a member yet
13159 research outputs found
Sort by
Improvement of Ic degradation of HTS Conductor (FAIR Conductor) and FAIR Coil Structure for Fusion Device
Get PDF0000-0002-1705-9039As a high-temperature superconducting (HTS) conductor with a large current capacity applicable to a nuclear fusion experimental device, REBCO (REBa 2 CuO y ) tapes and high-purity aluminum sheets are alternately laminated, placed in a groove of an aluminum alloy jacket having a circular cross section, and the lid is friction-stir welded. To make the current distribution and mechanical characteristics uniform, the conductor is twisted at the end of the manufacturing process. In the early prototype conductor, when the I c was measured in liquid nitrogen under self-magnetic field conditions, I c degradations were observed from the beginning, and the characteristic difference between the two prototype samples under the same manufacturing conditions were large. Furthermore, I c degradation was progressed by repeating the thermal cycle from room temperature to liquid nitrogen temperature. This I c degradation did not occur uniformly in the longitudinal direction of the conductor but was caused by local I c degradation occurring at multiple locations. If the conductor was not manufactured uniformly in the longitudinal direction, the difference in thermal shrinkage between the REBCO tape and the aluminum alloy jacket caused local stress concentration in the REBCO tape and buckling occurred. Element experiments to explain this mechanism were conducted to clarify the conditions under which I c degradation due to buckling occurs. Then prototype conductors were tested with improved manufacturing methods, and as a result, I c degradation could be suppressed to 20% or less. We have achieved the prospect of producing a conductor with uniform characteristics in the longitudinal direction.journal articl
Precession drift reversal and rapid transport of trapped energetic particles due to an energetic particle driven instability in the Large Helical Device
Get PDF0000-0001-8626-2770Energetic particle transport by a magnetohydrodynamic (MHD) instability driven by helically trapped energetic particles is studied for a high-performance Large Helical Device plasma with kinetic-MHD hybrid simulations. It is observed in the simulation that an MHD mode with poloidal/toroidal mode numbers ????/????=2/1
driven by helically trapped energetic particles causes a significant redistribution of perpendicular energetic particle pressure profile. The frequency of the MHD mode decreases rapidly at the saturation of the instability and changes sign, which indicates a reversal of the mode propagation direction. It is found that the helically trapped energetic particles interacting strongly with the MHD mode change the precession drift direction at the same time as the reversal of the MHD mode propagation direction. The helically trapped energetic particles with the precession drift reversal are transported rapidly in the radially outward direction before the original precession drift direction is recovered. The precession drift reversal and the outward transport are caused by interaction with the electric field of the MHD mode. The vast majority of trapped energetic particles which interact strongly with the MHD mode experience precession drift reversal, leading to a significant redistribution of the perpendicular energetic particle pressure profile.
Numerical computations were performed on the Plasma Simulator (NEC SX-Aurora TSUBASA) of NIFS with the support and under the auspices of the NIFS Collaboration Research program (No. NIFS20KNST169), the JFRS-1 of the International Fusion Energy Research Centre, and the Supercomputer Fugaku of the RIKEN Center for Computational Science (Project ID: hp210178). This work was supported by MEXT as Program for Promoting Research studies on the Supercomputer Fugaku (Exploration of burning plasma confinement physics).journal articl
Estimation of tritium inventory in exhaust detritiation system for fusion test device in the initial tritium recovery operation
Get PDF0000-0001-9941-1958As one of the radiation safety issues at nuclear fusion facilities, the development of the tritium handling technique is indispensable. A small amount of tritium is produced by the deuterium plasma experiment in a large fusion test device and is exhausted from the vacuum vessel. From the viewpoint of radiation safety and public acceptance, tritium in the exhaust gas could be recovered by the exhaust detritiation system (EDS). Most of the tritium recovered by EDS is stored in the wastewater tanks as tritiated water. Then they are fractionated into the wastewater containers for delivery to the Japan Radioisotope Association once a year. However, some of the tritiated water would have remained in EDS. The residual tritium would be the issue of the dismantlement of EDS in the future. Thus, the amount of residual tritium in EDS was estimated in the initial tritium recovery operation. Since most of the wastewater containing tritium remains in the storage tanks, the residual wastewater was the main tritium inventory. Also, the tritium in the molecular sieve used in EDS was estimated to be less than 0.1 GBq. Thus, the decontamination of molecular sieves would be preferred when dismantling the EDS.journal articl
Q-band high-performance notch filters at 56 and 77 GHz notches for versatile fusion plasma diagnostics
Get PDF0000-0003-2410-7550A six-pole Q-band waveguide filter with a notch frequency above the Q-band has been developed for plasma diagnostics. The previous paper [Nishiura et al., J. Instrum. 10, C12014 (2015)] reported that the notch frequency exists within the standard band. In this study, the newly required notch filter extends the function, which prevents a thorny wave from being mixed into an instrument beyond the standard bandwidth of the waveguide. The mode control technique for cavities realizes a deep and sharp filter shape for Q-band notch filters with 56 and 77 GHz notches, respectively. The former filter has an attenuation more than 50 dB at 56.05 GHz and a bandwidth of 1.1 GHz at −3 dB. The latter filter has an attenuation more than 55 dB at 76.95 GHz and a bandwidth of 1.6 GHz at −3 dB. The electron cyclotron emission imaging and the electron cyclotron emission (ECE) diagnostics for the Q-band implemented a pair of the fabricated filters and demonstrated the ECE measurement successfully in the intense stray radiation from a 56 GHz gyrotron.journal articl
Implementation of synthetic fast-ion loss detector and imaging heavy ion beam probe diagnostics in the 3D hybrid kinetic-MHD code MEGA
Get PDF0000-0002-8455-1090A synthetic fast-ion loss (FIL) detector and an imaging Heavy Ion Beam Probe (i-HIBP) have been implemented in the 3D hybrid kinetic-magnetohydrodynamic code MEGA. First synthetic measurements from these two diagnostics have been obtained for neutral beam injection-driven Alfvén Eigenmode (AE) simulated with MEGA. The synthetic FILs show a strong correlation with the AE amplitude. This correlation is observed in the phase-space, represented in coordinates (Pϕ, E), being toroidal canonical momentum and energy, respectively. FILs and the energy exchange diagrams of the confined population are connected with lines of constant E′, a linear combination of E and Pϕ. First i-HIBP synthetic signals also have been computed for the simulated AE, showing displacements in the strike line of the order of ∼1 mm, above the expected resolution in the i-HIBP scintillator of ∼100 μm.journal articl
Effect of nuclear elastic scattering on the D(d,n)3He fusion reactivity induced by energetic protons observed in the large helical device
Get PDF0000-0002-7498-4191The enhancement of the fusion reaction rate coefficient induced by energetic protons, which is
one of the typical nuclear elastic scattering (NES) effects, was observed in the large helical
device (LHD) located at the National Institute for Fusion Science. An intense high purity
hydrogen beam (the atomic ratio of the contained deuterium was less than 1 ppm) with
∼170 keV-energy and ∼10 MW-power was injected into a deuterium plasma with the electron
temperature ∼9 keV and density ∼1019 m−3. After the hydrogen beam injection, the neutron
generation rate by the D(d,n)3He fusion reaction immediately increased, and an increment of
over one order of magnitude was observed, even though there was no meaningful ion
temperature variation. The reasons for the increment in the neutron generation rate are
discussed with reference to the Boltzmann–Fokker–Planck analysis along with LHD
experimental data. It is concluded that the increment was induced by the production of
energetic deuterons due to the NES of energetic protons.journal articl
Divertor heat load distribution measurements with infrared thermography in the LHD helical divertor
Get PDF0000-0001-6090-5010We evaluated the two dimensional (2D) distribution of the divertor heat flux in LHD. The Infrared (IR) thermography was performed to measure the surface temperature at a divertor plate. The 3D heat conduction equation was solved using the finite element method (FEM) by taking into account the practical divertor geometry including the heat sink behind the graphite tile and the cooling system. The FEM analysis successfully reconstructs heat load distribution from the measured temperature pattern. Significant difference was found between the temperature and the heat load patterns. The FEM analysis shows that the highest heat deposition is observed at the strike line with 5–10 MWm−2 of ∼ 10 mm width in NBI heated discharge. In addition to the strike line there is also found the lower heat deposition region of ∼ 1 MW m−2 with wide channel width ∼ 30 mm. The detailed heat transport analysis inside the divertor components shows that the heat transport process is different between the strike line and the other region due to the heat channel width and to the divertor component structure. The comparison between the heat flux obtained by the thermography and that by the Langmuir probes shows reasonable agreement, except that the peak value of the heat load is higher in the IR thermography than in the Langmuir probe. By relaxing the assumption that electron temperature, Te, equal to be ion temperature, Ti, in the sheath model for the Langmuir probe analysis, the agreement becomes better for the case with Ti > Te.journal articl
Novel features of the helical volumetric neutron source FFHR-b2
Get PDF0000-0002-7901-6077The compact helical fusion reactor FFHR-b2 is a multipurpose HElical Volumetric Neutron Source available as the component test facility to test the divertor and blanket systems. In the latest design, three new technologies of the high-temperature superconducting conductor, the ceramic pebble divertor, and the cartridge-type blanket are adopted. Tin-based functional liquid metals (FLMs) including lithium are considered as the working fluid for the blanket. The FLMs have multi functions of low vapor pressure, low density, low melting point, low corrosiveness, high tritium breeding ratio, and so on. The target construction cost of the FFHR-b2 has been set to 200 billion JPY. The main target of FFHR-b2 is to demonstrate the fusion gain larger than one. To achieve this in a relatively small device, the tangential neutral beam injection (NBI) heating with a moderate energy of 80 keV is adopted for the FFHR-b2. The beam-plasma fusion with 5 MW of NBI heating can produce a fusion power of 5 MW that is larger than the absorbed power of 3 MW.journal articl
Ro-vibrational population distribution in the ground state of hydrogen isotopologues in LHD peripheral plasmas deduced from emission spectroscopy
Get PDFWide wavelength range with high-resolution emission spectroscopy was applied to LHD peripheral plasmas. All measured Fulcher-a band Q-branches spectra (600–630 nm) were measured with a single shot exposure time of 100–200 ms for all investigated discharges. Ro-vibrational populations up to v = 2 and N = 11 for H2 and up to v = 3 and N = 14 for D2 in the 3p3Πu state were estimated, where v and N are vibrational and rotational quantum numbers, respectively. It was found that the rotational population of every vibrational state follows two-temperature Boltzmann distribution. From the calculation with a coronal model, ro-vibrational populations distribution up to such high N quantum numbers in the ground state are deduced.journal articl
Simulation study of helium bubble coalescence in tungsten at various temperatures relevant to fusion conditions
Get PDFMolecular dynamics (MD) methods are used to study nanosized helium (He) bubble coalescence process in tungsten (W) at various temperatures relevant to fusion conditions, on an atomistic scale. Bubble coalescence in W is observed at a higher temperature and He/V ratio, while the calculated internal bubble pressure due to virial stress increases with the increase in the He/V ratio; bubble coalescence is significantly dependent on the bubble distance. In these MD simulations, coalescence occurs, only when the surface distance between the two bubbles is equal to 1a0, where a0 denotes the lattice constant and is approximately 0.317 nm at 2100 K. On the other hand, a bubble diameter between 1a0 and 3a0 may have relatively limited effect on the coalescence, although larger-sized bubbles may have higher migration energy. Local stress profile calculated indicates that initial bubbles can interact with each other, which may enhance the He atoms diffusion between bubbles and their coalescence. Physical contact at the initial stage of coalescence may occur between two nearby bubbles accompanied by W lattice distortion because of the limited displacement of W atoms near the bubbles and rapid migration of He atoms within the two bubbles. These results are beneficial for understanding the evolution of He bubbles in bulk W.journal articl