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Indirect energy transfer channel between fast ions via nuclear elastic scattering observed on the large helical device
Get PDF0000-0002-7498-4191An energy transfer phenomenon between energetic ions, which cannot be explained only considering the Coulomb scattering process, was observed on a large helical device (LHD). This phenomenon often occurs in fusion reactivity enhancement and fast-ion slowing-down process that can be observed as a delay in the decay time of the D(d,n)3He neutron generation rate. The transferred energy required to induce such a reactivity enhancement or delay in the fast-ion slowing-down time (neutron decay time) was examined based on the Boltzmann−Fokker−Planck analysis in which a discrete energy transfer process, called nuclear elastic scattering (NES), is included. It was shown that even though the cross section of the NES is smaller than that of the Coulomb scattering, enough knock-on population appears in the energetic region in ion distribution function to induce the observable NES effects; thus, enough energy is transferred from beam ions to fast component of bulk ion distribution function indirectly and the transferred energy per unit time via NES is comparable to the Coulomb scattering rate. This study analytically demonstrates that the observed phenomena on LHD can be explained smoothly by considering the alternative indirect energy transfer channel between energetic ions, which can be comparable with the one via Coulomb scattering.journal articl
Energy Transfer of the Gross-Pitaevskii Turbulence in Weak-Wave-Turbulence and Strong-Turbulence Ranges
Get PDF0000-0002-5366-0403Numerical simulations of quantum fluid turbulence obeying the Gross-Pitaevskii equation are performed with the simulation sizes as large as the weak-wave-turbulence and the strong-turbulence wavenumber ranges coexist in one simulation. The energy cascade is observed within the simulated wavenumber range. The spectrum F(k) in the weak-wave-turbulence range agrees with the k−1 scaling without logarithmic correction suggested by a closure approximation (Yoshida and Arimitsu in J Phys A Math Theor 46(33):335501, 2013) and the slope of F(k) in the strong-turbulence range is steeper than that suggested in the same closure approximation. The energy flow from the interaction energy to the kinetic energy during the cascade is also observed.journal articl
Deformation and fracture behaviour, and thermal stability of ODS-Cu/ODS-Cu and SUS/ODS-Cu joints fabricated by advanced brazing technique
Get PDF0000-0002-3744-2481A joint of oxide dispersion strengthened copper alloy (ODS-Cu; GlidCop®), i.e., GlidCop®/GlidCop® joint and a joint of stainless steel (SUS) and GlidCop®, i.e., SUS/GlidCop® joint were prepared by using the advanced brazing technique (ABT). Deformation and fracture behavior, and thermal stability of these joints were investigated by means of three-point bending test, scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDS). Firstly, in the case of the GlidCop®/GlidCop® joint, plastic deformation occurred predominantly in the diffusion layer with lower hardness. The fracture proceeded approximately at the center of the diffusion layer. In the case of the SUS/GlidCop® joint, on the other hand, plastic deformation occurred widely in the bulks, GlidCop® and SUS near the interfaces between the bulk and the bonding layer. The fracture proceeded mainly along the interface between the bonding layer and the bulk GlidCop®, and substantially along the interface between the bonding layer and the bulk SUS. Secondly, influences of 2nd-step heat on the GlidCop®/GlidCop® and SUS/GlidCop® joints were examined from viewpoints of microstructure and mechanical strength. Almost no obvious changes in the width of the diffusion layer (GlidCop®/GlidCop® joint) or the bonding layer (SUS/GlidCop® joint), and in the element distribution in these layers after the 2nd-step heat were recognized. In addition, any obvious changes in the shape of stress-strain curve and yield strength were not recognized for both joints.journal articl
Overview of coordinated spherical tokamak research in Japan
Get PDF0000-0002-4846-5267Spherical tokamak (ST) research in Japan has produced many innovative results: (i) plasma start-up to Ip > 70 kA was achieved by electron cyclotron wave (ECW) with N∥ = 0.75, while electron heating to Te > 500 eV was achieved with N∥ = 0.26 on QUEST. (ii) The radiofrequency (RF)-induced transport model was combined with the x-ray emission model, and extended magnetohydrodynamics equilibrium with kinetic electrons was developed to interpret fast-electron-dominated lower hybrid wave sustained plasmas on TST-2. (iii) Density as high as 30 times the cutoff density was achieved by electron Berstein wave current drive combined with electron beam injection on LATE. (iv) Multiple plasmoids formed by tearing instability in the elongated current sheet were observed, and flux closure and ion heating by plasmoid-mediated fast magnetic reconnection were observed on HIST. (v) Optimization of ECW-assisted inductive start-up with a vertical field with positive decay index was performed on TST-2. (vi) Stabilization of the vertical displacement event by a set of upper and lower helical field coils was demonstrated on TOKASTAR-2. (vii) A 6 h discharge was achieved by cool-down of the center stack cover on QUEST, where the plasma duration limit was consistent with the wall saturation time estimated by modeling. (viii) Extension of ion heating by plasma merging was achieved on TS-3U, TS-4U, UTST, MAST, and ST40.journal articl
Inward diffusion driven by low frequency fluctuations in self-organizing magnetospheric plasma
Get PDFORCID 0000-0003-1088-8237The new findings for dynamic process of inward diffusion in the magnetospheric plasma are reported on the Ring Trap 1 (RT-1) experiment: (i) the evolution of local density profile in the self-organized process has been analyzed by the newly developed tomographic reconstruction applying a deep learning method; (ii) the impact of neutral-gas injection excites low-frequency fluctuations, which continues until the peaked density profile recovers. The fluctuations have magnetic components (suggesting the high-beta effect) which have two different frequencies and propagation directions. The phase velocities are of the order of magnetization drifts, and both the velocities and the intensities increase in proportion to the electron density. The self-regulating mechanism of density profile works most apparently in the naturally made confinement system, magnetosphere, which teaches the basic physics of long-lived structures underlying every stationary confinement scheme.journal articl
Direct Measurement of the Millimeter Wave Phase Singularity with Helical Wavefront using Heterodyne Detection System at Two Spatial Points
Get PDF0000-0001-6636-8500In this paper, we measured the one-dimensional phase and polarization structure of a millimeter-wave with a helical wavefront (vortex beam) using a simultaneous heterodyne detection system at two spatial points. This is a novel approach, and it provides us with the relative phase of the vortex beam. We measured the phase discontinuity of the vortex beam by scanning the one-dimensional path where an antenna passes through the optical axis. It was found that relative phases gradually increase or decrease when the antenna does not pass through the optical axis. Additionally, we measured polarization parameters, which were indefinite near the optical axis. In other words, the optical axis of the vortex beam is a singular point about the phase.journal articl
Simulation of Decay of Shielding Currents in ITER-TF Joint Samples
Get PDF0000-0003-1454-8117As a qualification test of ITER-TF coils, each joint sample was tested prior to manufacture of each TF coil. Eleven joint samples were tested by a conductor test facility with a 9 T split coil. The joint sample comprised two short TF conductors that had twin-box joint terminals at both ends. The lower joint is a testing part that is a full-size joint of the TF coil. Hall probes were attached on the lower joint box to measure the field induced by shielding currents. In order to simulate the shielding currents, an equivalent current circuit has been considered. The main loop of the shielding currents is the current flow in two conductors with crossing the jointed plane twice. The other two loops are the current loops inside superconducting cables in the two conductors. The resistance of the latter loops is given by twice the value of an average contact resistance between the superconducting strands. The calculated results are in good accordance with the experimental data, with an assumption that the overall joint resistance is decreased at low current. This phenomenon can be explained by the existence of a few strands contacting the joint box with extremely low joint resistances.journal articl
Abundance ratio of multiple velocity distribution components in a single negative ion beamlet produced by a cesium-seeded negative ion source
Get PDF0000-0003-1516-0288Well focused negative ion beams are required for neutral beam injection systems for heating and current drive in magnetically confined fusion plasma experiments. The control of a single negative ion beamlet divergence is a significant challenge with the use of a cesium-seeded negative ion source, where negative ions are mainly produced by conversion of hydrogen or deuterium atoms on a cesiated surface of a plasma grid. The single negative ion beamlet was found to be made by three-Gaussian components in our previous work. The origins of such multiple components are considered to be related to dynamics in the ion source and extraction processes of negative ions. This work has demonstrated a measurement of the abundance ratio of the three components (41%, 40%, and 19%) based on a full picture of their transverse velocity distributions, which is a powerful technique to investigate the origins of individual components and will contribute to improve the divergence of negative ion beamlet.journal articl
Identification of electrostatic microinstability maps in quasi-axisymmetric stellarator
Get PDF0000-0003-4179-943XMicroinstabilities such as ion temperature gradient (ITG) mode and trapped electron mode (TEM) in quasi-axisymmetric (QA) stellarator are investigated by using gyrokinetic Vlasov simulations, where the QA configuration of Chinese first quasi-axisymmetric stellarator is utilized. Extensive parameter scans with respect to the density and temperature gradients for the zero beta cases identify the microinstability maps that indicate the transition boundary among ITG and TEM. It is found that, in particular for the modes with the ion-gyroradius scale, a relatively more stabilized regime appears along the transition boundary of ITG–TEM. Such a valley-like stability structure is not observed in the other cases with the sub-ion-gyroradius-scale. A stabilization effect attributed to the hollow density profile is also demonstrated.journal articl
Conceptual Design of Plasma Vacuum Vessel for Fusion DEMO Considering Integration of Core Components
Get PDFA fusion DEMO will be designed as a long-term D-T reaction machine, and it will provide electricity to the grid. The core components of the fusion DEMO such as superconducting TF coils and vacuum vessel sectors become larger and heavier than those of ITER. The difficulties of manufacturing and handling increase significantly. Therefore, the conceptual design of the plasma vacuum vessel and its leg are carried out based on the consideration of assembly and disassembly processes of the core components. When the global density of the device is assumed to be same as the ITER, the total weight of the fusion DEMO would be about 77,500 tons and one TF coil weigh wound be about 1,200 tons. To carry out the easy works for assembling and disassembling, demountable superconducting TF coils are proposed which will be made of high temperature superconducting tapes so that the enough workspace can be secured. The weld joint of the vacuum vessel with a double wall structure is investigated, and the support leg is designed considering the three-dimensional displacement and the integration processes.journal articl