Publications (5)3.91 Total impact
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Article: Double electron capture process in - collisions inferred from spectroscopic measurements in plasmas
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ABSTRACT: Pulsed gas was injected into a carbon doped helium plasma in TPD-II to investigate electron capture processes. Anomalous enhancement in C II line intensities was observed and considered to be due to the double electron capture in - collisions. The rate coefficient was estimated to be (, and a spectral distribution of C II lines, which relates to population densities of product ions, was also measured. Based on these results, C II spectral distributions in the JIPP T-IIU tokamak were observed to assess the influence of the double electron capture in collisions on the edge plasma. A new spectroscopic procedure showed that this process is one of the dominant processes in the edge plasma.Journal of Physics D Applied Physics 12/1998; 31(20):2789. · 2.54 Impact Factor -
Article: Development of an imaging vacuum‐ultraviolet monochromator in the normal incidence region
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ABSTRACT: An imaging vacuum‐ultraviolet monochromator has been developed to provide the space‐resolved impurity line emissions from magnetically confined plasmas. With minor modifications of a commercial normal incidence monochromator, a pinhole entrance slit and a microchannel plate detector displaced away from the exit slit, the instrument performs two‐dimensional spectroscopic observations in the wavelength range from 400 to 2000 Å. Ray tracing has been performed to understand the spatial imaging properties in the practical geometric configuration. The measured spatial resolution is about 0.5 and 1 mrad in dispersion and vertical plane, respectively, with the entrance slit of 0.1 mm width and height. The results of the testing experiments and the measurements carried out on the JIPP T‐IIU tokamak plasma are presented and discussed. © 1996 American Institute of Physics.Review of Scientific Instruments 12/1996; · 1.37 Impact Factor -
Article: Studies of Perturbative Plasma Transport, Ice Pellet Ablation and Sawtooth Phenomena in the JIPP T-IIU Tokamak
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ABSTRACT: "ln the JIPP T-IIU tokamak edge cooling imposed by positive biasing of an inserted electrode and injection of a small ice pellet induces an alrnost instantaneous increase in the electron temperature near the center. Rapid current ramp-up increases electron temperature at the edge. Thus produced hot front quickly propagates toward the center, although the toroidal current density increased by the ramp-up is still confined in the edge region of r/a geq 0.7. Rapid current ramp-up also induces a small but sudden drop of the central electron temperature which takes place at much earlier time than the current penetration. The results from cold pulse and current ramp-up experiments suggest nonlocal electron heat transport. A long helical shape (""tail"") of ablation light is observed when an ice pellet is injected on-axis(horizontal) and slightly upward or downward off-axis. The direction of the tail is found to be closely related to plasma rotation. Plasma potential and density profile are widely controlled by changing the injection angle of a pellet and pellet size. Radial profiles of particle diffusion coefficient and inward convection velocity are derived from time evolution of density profiles realized by the pellet injection. Rapid potential change is observed during sawtooth crash by a heavy ion beam probe (HIBP). This potential change is caused by combination between arnbipolar electric field and rapid MHD motion across the magnetic field. However, poloidal magnetic flux near the sawtooth inversion radius measured by HIBP hardly changes at the crash. A multichannel motional stark effect polarimeter has revealed that the safety factor at the plasma center becomes well below unity, i.e., 0.7-0.8 during sawtoothing phase. These results suggest a partial reconnection takes place at the sawtooth crash." -
Article: Density Fluctuation in JIPP T-IIU Tokamak Plasmas Measured by a Heavy Ion Beam Probe
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ABSTRACT: Multiple and small sample-volume measurements of the density turbulence and potential profile measurement in tokamak plasmas were conducted by a heavy ion beam probe. The obtained wavenumber/frequency spectrum S(k,omega) shows that the cross-section of NBI heated plasmas is divided into three regions of different turbulence characteristics. Outside the reversal layer of poloidal propagation direction of density turbulence, a low-frequency and low-wavenumber mode with ion diamagnetic drift direction dominates. The region encircled by the reversal layer is divided into two parts at nearly perpendicular NBI heating, the region where the propagation velocity is near the E_r/B_t poloidal rotation velocity and the bad-curvature region of very small wavenumber and high propagation velocity. The region of high propagation velocity, found in NBI plasmas, disappears in ohmic plasmas. In addition, a small component which propagates in the ion diamagnetic drift direction is observed in NBI plasmas. -
Article: Potential Turbulence in Tokamak Plasmas
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ABSTRACT: Microscopic potential turbulence in tokamak plasmas are investigated by a multi-sample-volume heavy ion beam probe. The wavenumber/frequency spectra S(k,omega) of the plasmas potential fluctuation as well as density fluctuation are obtained for the first time. The instantaneous turbulence-driven particle flux, calculated from potential and density turbulence has oscillations of which amplitude is about 100 times larger than the steady-state outwards flux, showing sporadic behaviours. We also observed large-scale coherent potential oscillations with the frequency around 10-40 kHz.
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1998
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The Graduate University for Advanced Studies
Toki, Gifu-ken, Japan
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