NIFS-Repository (National Institute for Fusion Science)
Not a member yet
13159 research outputs found
Sort by
Quaternion Analysis of Transient Phenomena of Motor-Generator
Get PDFA motor-generator slowly converts low electrical power to the large rotating energy of the induction motor, which is then converted to the higher electrical power of the synchronous generator through a pulse. Such a cycle is repeated in a tokamak plasma experiment. In the transient phase at the start of the synchronous generator, high transient voltage appears in the armature windings repeatedly. Due to the repeatability, it is imperative to estimate the high voltage and control it so that the maximum voltage is kept under a tolerable value. A quaternion is a four-dimensional hypercomplex number that is good at describing three-dimensional rotation. Utilizing the quaternion capability, a three-phase motor-generator is analyzed using three-dimensional rotation. The mechanical rotation was anlyzed by the rotation quaternion. The salient pole-type rotating field can be manipulated by direct-quadrature conversion even in quaternion analysis. The rotating dynamics and electrical phenomena of a motor-generator can be analyzed by considering the quaternion power from the motor-generator and the electrical load for plasma control.journal articl
Isotope effect of transport and key physics in the isotope mixture plasmas
Get PDF0000-0002-0585-4561The isotope effect of transport and key physics in isotope mixture plasmas is reviewed. Experiment, simulation, and theory discuss isotope mass dependence on confinement, transport, and turbulence. Experimental observation shows a wide variety of isotope mass dependence, due to the complicated process of determining the plasma confinement and transport and far from the simple mass dependence predicted by the gyro-Bohm model. The isotope effect directly influences the growth rate of instability and thermal diffusivity and indirectly influences confinement and transport property through other parameters. The isotope mixing is also described as key physics of isotope mixture plasma, essential to optimize fusion power in deuterium and tritium plasma.journal articl
Perspective of Meta-Hierarchy Dynamics
Get PDF0000-0002-2459-2392The understanding of nature has been developed by separating and connecting elements in a reductive manner. For example, a spatio-temporal scale can provide us a clear picture of elemental separations. In biology, a function also gives us a useful picture to understand biological nature. Furthermore, a physical model also improves the outlook for understanding physical nature. These divided or connected elements, namely, scales, functions, and models form hierarchical structures in nature. On the other hand, fusion science explores various multi-scale and multi-physics phenomena, spreading over spatio-temporal scales from the microscopic to the macroscopic. In particular, collective motion causes structural formations not only in core plasmas but also material-facing ones. Therefore, fusion science has been an excellent subject for the application of the hierarchical approach. However, some problems have emerged with the progress of experimental and numerical research in fusion science. We often encounter phenomena that cannot be well understood by hierarchical separation. For these phenomena, beyond the conventional approaches for hierarchical systems, it is necessary to reconsider them with meta-perspectives, i.e., meta-hierarchy dynamics.journal articl
Application of container technology in LHD analysis system
Get PDFThe authors have developed AutoAna, an automatic registration system for physics data in LHD experiments. AutoAna has increased the number of data registrations and reduced the time required to complete them, making it possible to provide key data during three-minute intervals of short pulse experiments. The time reduction was achieved by running several analysis programs in parallel. However, problems arose due to this process, which could be solved by containerizing the execution environment of the analysis programs.journal articl
Fusion splicing of plastic optical fibers using a mid-IR fiber laser
Get PDFThis work demonstrated the fusion splicing of plastic optical fibers (POFs) using a 2.8 μm continuous-wave fiber laser. This mid-IR laser-based fusion splicing technique does not require the use of adhesives or any other treatments. The performance of the proposed method was investigated by assessing the optical transmission, tensile strength and bending strength values of POF specimens after fusion bonding while employing various splicing conditions. An optical transmission of 0.76 was obtained by splicing under appropriate conditions. A minimum bending radius and tensile strength of the POF samples were found to be 1.5 mm and 13.5 N, respectively.journal articl
Optimization of a fast deuterium diagnostic method based on visible energetic 3He spectroscopy for high electron density plasmas
Get PDF0000-0003-3198-042XFast ions play a crucial role in plasma heating, and their behavior in the plasma must be accurately understood. A diagnostics method based on charge exchange emission from the n = 4 − 3 transition (λ0 = 468.6 nm) of energetic 3He produced by the deuteron–deuteron reaction has been proposed as a for fast deuterons with energies in the order of MeV. The proposed method has the following advantages: No beam emission interferes with the spectra, the direction of the measuring line of sight, and the injection angle of the diagnostic beam can be freely determined. In previous studies, due to competing bremsstrahlung, it was expected that the proposed method will not be practical in the case of high electron density operation. This paper makes the proposed method available for measurement even at high electron densities by optimizing the measurement line of sight direction and the diagnostic beam incidence angle. This allows an electron density five times larger than the range of applications shown in previous studies. This result will contribute to measure of DT alpha in ITER.journal articl
Application of Digital Phase Analysis to Far-Infrared Laser Interferometer for the Large Helical Device
Get PDF0000-0002-6021-871XA digital phase analysis technique was applied to a 119-µm wavelength far-infrared (FIR) laser interferometer on the Large Helical Device (LHD). High-density plasma measurement without phase jumping was achieved, representing an improvement over measurements made using a conventional analog phase counter. Digital phase analysis became operational at a quarter of the threshold of the analog phase counter. The phase sensitivity was also improved using digital analysis because the noise level was reduced to approximately half that of the conventional analog phase counter. The improved phase sensitivity enabled measurement of small-amplitude fluctuations.journal articl
Nested invariant tori foliating a vector field and its curl: Toward MHD equilibria and steady Euler flows in toroidal domains without continuous Euclidean isometries
Get PDFORCID 0000-0002-2973-0635This paper studies the problem of finding a three-dimensional solenoidal vector field such that both the vector field and its curl are tangential to a given family of toroidal surfaces. We show that this question can be translated into the problem of determining a periodic solution with periodic derivatives of a two-dimensional linear elliptic second-order partial differential equation on each toroidal surface and prove the existence of smooth solutions. Examples of smooth solutions foliated by toroidal surfaces that are not invariant under continuous Euclidean isometries are also constructed explicitly, and they are identified as equilibria of anisotropic magnetohydrodynamics. The problem examined here represents a weaker version of a fundamental mathematical problem that arises in the context of magnetohydrodynamics and fluid mechanics concerning the existence of regular equilibrium magnetic fields and steady Euler flows in bounded domains without continuous Euclidean isometries. The existence of such configurations represents a key theoretical issue for the design of the confining magnetic field in nuclear fusion reactors known as stellarators.journal articl
Observation of Interaction between Fast Ions and Turbulence in Large Helical Device
Get PDFORCID 0000-0002-6021-871XSystematic experiments were carried out in the 23rd Large Helical Device experiment campaign to explore the interaction between fast ions and ion-scale turbulence focusing on the impact of varying the power of the neutral beam (NB) injection. During the NB heating, two distinct phases of turbulence reduction were observed. The first phase was a transient reduction of about 10 msec immediately following the initiation of the NB injection. This reduction in turbulence was noticeable even while the electron density and temperature profiles remained nearly unchanged. The second phase involved a continuous reduction that maintained a lower turbulence level throughout the duration of the NB injection. The physics mechanisms underlying these phenomena are not fully understood yet. However, it is likely that two distinct processes of turbulence stabilization, each corresponding to the transient and continuous reduction phases, are at work due to the influence of the fast ions.journal articl
Investigation of energetic ion losses induced by long-lived saturated internal mode with energetic particle diagnostics in the HL-2A tokamak
Get PDFORCID 0000-0002-7547-701XSeveral sets of energetic particle diagnostics, including a set of neutron flux monitoring systems, a solid-state neutral particle analyzer and a fast ion loss probe (FILP), have been used to investigate the energetic ion losses induced by the long-lived saturated internal mode (LLM) in the HL-2A tokamak. Clear experimental evidence for different levels of energetic ion losses induced by LLM, sawtooth and minor disruption has been observed. A numerical calculation for the evolution of neutron emissions was carried out with the FBURN code, and it shows that the neutron emission drop rate linearly increases with the LLM amplitude and no threshold perturbation amplitude exists, illustrating that the loss mechanism for LLM induced energetic ion loss is dominantly convective. In addition, measurement results of the FILP demonstrate that LLM tends to expel energetic ions with relatively low energy (keV) and high pitch angle (), and can suppress the prompt loss of energetic ions with high energy and low pitch angle to a certain degree. Furthermore, the physical process for LLM induced energetic ion loss can be explained by orbit calculations, which show that LLM induced lost energetic ions will transport from center to peripheral region first, and then get lost out of plasma. The experimental observations are successfully reproduced by calculations using the ORBIT code combined with both the NUBEAM code and the MARS-K code. The paper clearly describes the whole physical process of LLM induced energetic ion loss for the first time in the HL-2A tokamak.journal articl