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    11598 research outputs found

    Raman and Rayleigh Calibrations of the LHD YAG Thomson Scattering

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    We have carried out absolute calibrations of the LHD YAG Thomson scattering system by using Raman scattering and Rayleigh scattering in order to verify the applicability of Rayleigh calibration in the LHD Thomson scattering, and make a comparative study of Raman and Rayleigh calibrations. In the LHD Thomson scattering device, Rayleigh calibration is expected to give more reliable calibration factors. For the Rayleigh calibration, additional Rayleigh channel was installed into 20 polychromators. The other 124 polychromators without Rayleigh channel were calibrated by only Raman scattering. In the Raman calibration, pure gaseous nitrogen was introduced into the LHD vacuum vessel whereas the Rayleigh calibration was made by using air as target gas. The calibration factors obtained from the Raman and Rayleigh calibrations show good agreements. Uncertainties in the calibration factors obtained from the Raman and Rayleigh calibrations are discussed

    Tangential SX Imaging for Visualization of Fluctuations in Toroidal Plasmas

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    When the ratio of the plasma pressure to the magnetic pressure increases, Various kinds of instabilities evolve. Among them, magnetohydrodynamic instabilities, by which the plasma is deformed macroscopically, are in concern. Non-linear evolution of them is fairly complicated and two-dimensional structure of them is the key to understanding the phenomena. Tangentially viewing SX camera is promising diagnostics for 2D visualization, because most of the perturbations tend to have the equal phase along the field lines, the tangential view, which is almost parallel to the field lines, give a good opportunity to resolve the structure. Issues in this kind of camera are discussed. Improved system using multi-layer mirror is also described

    Experimental studies of zonal flow and field in compact helical system plasma

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    The experimental studies on zonal flows and turbulence have been carried out in Compact Helical System [K. Matsuoka, S. Kubo, M. Hosokawa et al., in Plasma Physics and Controlled Nuclear Fusion Research, Proc. 12th Int. Conf., Nice, 1988 (International Atomic Energy Agency, Vienna, 1989, Vol. 2, p. 411] using twin heavy ion beam probes. The paper presents the experimental observations of stationary zonal flow, nonlinear couplings between zonal flow and turbulence, and the role of zonal flow in the improved confinement, together with the recent discovery of zonal magnetic field. The presented experimental results strongly support the new paradigm that the plasma transport should be considered as a system of drift wave and zonal flows, and provides the first direct evidence for turbulence dynamo that the structured magnetic field can be really generated by turbulence

    Formation of wave-front pattern accompanied by current-driven electrostatic ion-cyclotron instabilities

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    Formation of a wave-front pattern accompanied by an electrostatic ion-cyclotron instability driven by electrons drifting along a magnetic field is investigated by two-and-half dimensional particle simulations. A clear spatial wave-front pattern appears as the ion cyclotron wave grows due to the instability. When the electron stream is uniform in the system, an obliquely intersected stripe wave-front pattern is formed. When the stream has a bell-shaped pattern across the magnetic field, a V-shaped stripe wave-front pattern appears. The wave fronts have small angles with the magnetic field lines and propagate from the high-stream region to the low-stream region

    原子分子データベースの構築と利用 3.原子分子データベースの構築

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    原子分子データベースを構成する原子分子データが,どのような研究によって生産されているのか原子物理学の理論研究や実験研究の紹介と,理論や実験で得られたデータをどのように評価して,データベースとして構築していくのかについて紹介する.原子分子物理学研究の例として,電子衝突過程断面積と,重粒子衝突過程断 面積について述べる

    Design and fabrication of module coil as an R&D program for Large Helical Device

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    A twisted solenoid coil (TOKI-MC) has been designed and fabricated in order to study the mechanical properties of the Large Helical Device (LHD). One of the most important R&D items of the LHD is the mechanical behavior of the helical coils under a large electromagnetic force. The TOKI-MC was wound obliquely on the 3D-machined elliptical bobbin with a maximum torsional rate of 36deg/m at the innermost conductor. The maximum field in the coil is 7.7 T with an operating current of 20 kA, an average current density of 40 A/mm^2, and a stored energy of 11 MJ. The TOKI-MC can simulate the electromagnetic force, conductor torsional rate, magnetic field, operating current, and current density of the LHD superconducting helical coils. The design and test results of the conductor and the design and fabrication of the coil are describe

    Charge exchange spectroscopy by Fabry-Pérot spectrometer in W7-AS

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    Charge exchange spectroscopy using a Fabry?P?rot spectrometer has been developed to study the dynamic of ion temperature and radial electric field in plasmas. A charge coupled device detecter with 80×80 pixels was used to gain the spectral resolution of the charge exchange spectroscopy system. This Fabry?P?rot charge exchange spectroscopy system has been applied to measure the ion temperature using the charge exchange line of carbon impurity with a time resolution of 5 ms for high density quasisteady discharges in W7-AS. The cold component due to the charge exchange reaction between the carbon impurity and thermal neutrals is subtracted from the change emission with the beam modulatio

    Reduction of Turbulent Transport with Zonal Flows Enhanced in Helical Systems

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    Gyrokinetic Vlasov simulations of the ion temperature gradient turbulence are performed in order to investigate effects of helical magnetic configurations on turbulent transport and zonal flows. The obtained results confirm the theoretical prediction that helical configurations optimized for reducing neoclassical ripple transport can simultaneously reduce the turbulent transport with enhancing zonal-flow generation. Stationary zonal-flow structures accompanied with transport reduction are clearly identified by the simulation for the neoclassically optimized helical geometry. The generation of the stationary zonal flow explains a physical mechanism for causing the confinement improvement observed in the inward-shifted plasma in the Large Helical Device [O. Motojima et al., Nucl. Fusion 43, 1674 (2003)]

    Short wavelength far infrared laser polarimeter with silicon photoelastic modulators

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    A short wavelength far infrared laser whose wavelength lambda is about 50 mu m is preferable for a polarimeter and an interferometer for high density operations in the Large Helical Device (LHD) and on future large fusion devices such as ITER. This is because the beam bending effect (propto lambda^2) in a plasma, which causes fringe jump errors, is small and the Faraday and the Cotton?Mouton effects are moderate.We have developed a polarimeter with highly resistive silicon photoelastic modulators (PEMs) for the CH_3OD laser (lambda =57.2 and 47.7 mu m) . We performed bench tests of the polarimeter with a dual PEM and demonstrated the feasibility for the polarimeter. Good linearity between actual and evaluated polarization angles is achieved with an angular resolution of 0.05° and a temporal resolution of 1 ms. The baseline drift of the polarization angle is about 0.1° for 1000 s


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