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395 results on '"Nishitani T"'

1. Optimization of a fast deuterium diagnostic method based on visible energetic 3He spectroscopy for high electron density plasmas.

Author

Kimura, K., Matsuura, H., Itoh, C., Kawamoto, Y., Oishi, T., Goto, M., Ogawa, K., Nishitani, T., Isobe, M., and Osakabe, M.

Subjects
PLASMA density, ELECTRON spectroscopy, ELECTRON plasma, ELECTRON density, CHARGE exchange, PLASMA heating, DEUTERIUM
Abstract

Fast 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. [ABSTRACT FROM AUTHOR]

Published
2023
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7. Adsorption structure deteriorating negative electron affinity under the H2O environment.

Author

Kashima, M., Ishiyama, S., Sato, D., Koizumi, A., Iijima, H., Nishitani, T., Honda, Y., Amano, H., and Meguro, T.

Subjects
PHOTOCATHODES, ELECTRON affinity, INDIUM gallium nitride, IONIZED gases, SPIN polarization, ADSORPTION (Chemistry), PHOTOEMISSION
Abstract

Photocathodes with negative electron affinity (NEA) characteristics have various advantages, such as small energy spread, high spin polarization, and ultrashort pulsing. Nitride semiconductors, such as GaN and InGaN, are promising materials for NEA photocathodes because their lifetimes are longer than those of other materials. In order to further prolong the lifetime, it is important to better understand the deterioration of NEA characteristics. The adsorption of residual gases and back-bombardment by ionized residual gases shorten the lifetime. Among the adsorbed residual gases, H2O has a significant influence. However, the adsorption structures produced by the reaction with H2O are not comprehensively studied so far. In this study, we investigated adsorption structures that deteriorated the NEA characteristics by exposing InGaN and GaAs to an H2O environment and discussed the differences in their lifetimes. By comparing the temperature-programmed desorption curves with and without H2O exposure, the generation of CsOH was confirmed. The desorption of CsOH demonstrated different photoemission behaviors between InGaN and GaAs results. InGaN recovered its NEA characteristics, whereas GaAs did not. Considering the Cs desorption spectra, it is difficult for an NEA surface on InGaN to change chemically, whereas that for GaAs changes easily. The chemical reactivity of the NEA surface is different for InGaN and GaAs, which contributes to the duration of photoemission. We have attempted to prolong the lifetime of InGaN by recovering its NEA characteristics. We found that InGaN with NEA characteristics can be reused easily without thermal treatment at high temperatures. [ABSTRACT FROM AUTHOR]

Published
2022
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10. Indirect energy transfer channel between fast ions via nuclear elastic scattering observed on the large helical device.

Author

Matsuura, H., Kimura, K., Umezaki, D., Ogawa, K., Isobe, M., Kawamoto, Y., Oishi, T., Goto, M., Tamura, N., Osakabe, M., Nishitani, T., and Sugiyama, S.

Subjects
FAST ions, ELASTIC scattering, DISTRIBUTION (Probability theory), ALTERNATIVE fuels, ION beams, ENERGY transfer
Abstract

An 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. [ABSTRACT FROM AUTHOR]

Published
2022
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15. Surface photovoltage effect and its time dependence in GaAs-GaAsp superlattice studied with combination of synchrotron and laser radiation

Author

Tanaka, S., Nishitani, T., Nakanishi, T., More, S. D., Azuma, J., Takashi, K., Watanabe, O., and Kamada, M.

Subjects
Gallium arsenide -- Optical properties, Laser beams -- Analysis, Synchrotron radiation -- Analysis, Physics
Abstract

The surface photovoltage (SPV) effect and its temporal profiles in a GaAs-GaAsP superlattice (SL) are measured by core-level photoelectron spectroscopy with the combination of synchrotron radiation and laser. The findings show that the SL with high-doping surface layer is suitable for the spin-polarized electron source without the SPV effect.

Published
2004

44. Development of 275kV gas cooled type gas-insulated power transformer

Author

Kudo, A., Nishitani, T., Yoshikawa, T., and Wan, C.T.

Subjects
Electric transformers -- Design and construction, Electric insulators -- Usage, Business, Computers, Electronics, Electronics and electrical industries
Abstract

A world's first 275kV gas cooled type gas insulated power transformer with a low sound level ideal for urban area, which depends on SF6 gas alone for both insulation and cooling, was developed and has been put into commercial service since 1990 in Hong Kong. This paper presents the design philosophy, the principal technical items, the rating and the feature of 275kV 30MVA transformer, the performance test results, and the long term energization test result of the transformer.

Published
1993

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