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1,907 results on '"Ohshima S"'

1. Efficient multi-keV X-ray generation from high-contrast laser plasma interaction

Author

Zhang Z., Nishimura H., Nishikino M., Sunahara A., Johzaki T., Cai H.B., Kawachi T., Pirozhkov A.S., Sagisaka A., Orimo S., Ogura K., Yogo A., Okano Y., Ohshima S., Fujioka S., Kiriyama H., Kondo K., Shimomura T., and Kanazawa S.

Subjects
Physics, QC1-999
Abstract

Kα line emission from Mo was experimentally and theoretically studied using clean, ultrahigh-intensity femtosecond laser pulses. The absolute yields of Kα x-rays at 17 keV from Mo were measured as a function of the laser pulse contrast ratio and irradiation intensity. Significantly enhanced Kα yields were obtained by employing high contrast ratio at optimum irradiance. Conversion efficiencies of 4.28 × 10−5/sr, the highest values obtained to date, was demonstrated with contrast ratios in the range of 10−10 to 10−11.

Published
2013
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2. Impact of multifold magnetic structure on spectroscopy analysis in Heliotron J based on EMC3‐EIRENE simulation

Author

Cai, F., primary, Kado, S., additional, Kawamura, G., additional, Feng, C., additional, Matoike, R., additional, Miyashita, A., additional, Ohshima, S., additional, Minami, T., additional, Inagaki, S., additional, Kin, F., additional, Kobayashi, S., additional, Ishizawa, A., additional, Nakamura, Y., additional, Okada, H., additional, Konoshima, S., additional, Mizuuchi, T., additional, Feng, Y., additional, Frerichs, H., additional, and Nagasaki, K., additional

Published
2024
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3. Development of the poloidal Charge eXchange Recombination Spectroscopy system in Heliotron J

Author

Lu, X. X., Kobayashi, S., Harada, T., Tanohira, S., Ida, K., Nishimura, S., Narushima, Y., Yu, D. L., Zang, L., Nagasaki, K., Kado, S., Okada, H., Minami, T., Ohshima, S., Yamamoto, S., Yonemura, Y., Haji, N., Watanabe, S., Okazaki, H., Kanazawa, T., Adulsiriswad, P., Ishizawa, A., Nakamura, Y., Konoshima, S., and Mizuuchi, T.

Subjects
Physics - Plasma Physics, 82D10 (Primary), 76Xxx (Secondary)
Abstract

A Charge eXchange Recombination Spectroscopy (CXRS) system designed to measure the poloidal rotation velocity is developed in Heliotron J. The poloidal CXRS system measures the carbon emission line (C VI, n=8-7, 529.05nm) and the Doppler shift of the emission line provides the information of plasma rotation velocity. A high throughput photographic-lens monochromator (F/2.8) with 0.73nm/mm dispersion is adopted to achieve high rotation velocity and temporal resolution. Since two heating neutral beams from two tangential injectors (NBI) are used as the diagnostic beams, a wide observation range (0.26 < 0.06) at peripheral region (r/a>0.6). The system design and the calibration method are presented. The initial results of poloidal rotation measurement show an electron diamagnetic rotation in an NBI heated plasma, while an ion diamagnetic rotation is observed when ECH is additionally applied. The evaluated radial electric field profile shows a positive Er at plasma core region in the ECH+NBI plasma, and a negative Er in the NBI heated plasma., Comment: With 20 pages, 10 figures

Published
2018

6. Effects of the resonance modification by electron cyclotron current drive on the linear and nonlinear dynamics of energetic particle driven magnetohydrodynamics modes in Heliotron J

Author

Adulsiriswad, P., primary, Todo, Y., additional, Yamamoto, S., additional, Kado, S., additional, Kobayashi, S., additional, Ohshima, S., additional, Okada, H., additional, Minami, T., additional, Nakamura, Y., additional, Ishizawa, A., additional, Konoshima, S., additional, Mizuuchi, T., additional, and Nagasaki, K., additional

Published
2023
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9. Characterization of a retroreflector array for 320-GHz interferometer system in Heliotron J

Author

Zhang, P., primary, Ohshima, S., additional, Zhao, H., additional, Kobayashi, S., additional, Kado, S., additional, Minami, T., additional, Kin, F., additional, Miyashita, A., additional, Iwata, A., additional, Kondo, Y., additional, Qiu, D., additional, Wang, C., additional, Luo, M., additional, Konoshima, S., additional, Inagaki, S., additional, Okada, H., additional, Mizuuchi, T., additional, and Nagasaki, K., additional

Published
2023
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10. NON-RESONANT MICROWAVE DISCHARGE START-UP IN HELIOTRON J

Author

Kovtun, Y., Nagasaki, K., Kobayashi, S., Minami, T., Kado, S., Ohshima, S., Nakamura, Y., Ishizawa, A., Konoshima, S., Mizuuchi, T., Okada, H., Laqua, H., Stange, T., and https://orcid.org/0000-0003-4154-1455

Abstract

The non-resonant microwave discharge in strong magnetic fields was investigated in Heliotron J under the condition, ωce/ωMW > 1 (ωce and ωMW are the angular electron cyclotron frequency and the angular microwave frequency, respectively). Following the production of a non-resonant microwave discharge plasma, it undergoes several phases in sequence: breakdown and formation of pre-ionized plasma, increase in linear and nonlinear phases of plasma density, and quasi-stationary stage. Several modes of non-resonant microwave discharge were investigated. In the power-scanning mode in non-resonant microwave discharge, a higher plasma density than that in the constant-power mode is achieved. The maximum average density achieved in the experiments is substantially greater than the critical density for O-wave (ordinary waves) 7.45 ⸱1016 m -3 and can reach the value of 2.5⸱10 18 m -3. .

Published
2023

12. Simple test for high Jc and low Rs superconducting thin films

Author

Sundaresan, A., Tanaka, Y., Iyo, A., Kusunoki, M., and Ohshima, S.

Subjects
Condensed Matter - Superconductivity
Abstract

A simple method, fishing high-Tc superconductor thin films out of liquid nitrogen bath by a permanent magnet (field > Hc1) due to the effect of high flux pinning, has been suggested to identify films having high critical current density (Jc > 106 A/cm2 at 77 K) and thus a low microwave surface resistance (Rs). We have demonstrated that a Nd-Fe-B magnet, having a maximum field of ~ 0.5 T, could fish out Tl-1223 superconducting thin films on LSAT substrate with a thickness of ~ 5000 Angstrong having Jc > 1 MA/cm2 (at 77 K) whereas it could not fish out other films with Jc < 0.1 MA/cm2 at 77 K. The fished out films exhibit Rs values 237 - 245 ((at 77 K and 10 GHz, which is lower than that (Rs = 317 (() of the best YBCO film at the same temperature and frequency. On the other hand, the non-fishable films show very high Rs values. This method is a very simple tool to test for high Jc and good microwave properties of superconducting films of large area which otherwise require a special and expensive tool., Comment: 5 pages including 2 figures, to be published as Rapid Commun. in Supercond. Sci. Technol

Published
2003
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15. Experimental studies of zonal flow and field in compact helical system plasma

Author

Fujisawa, A, Itoh, K, Shimizu, A, Nakano, H, Ohshima, S, Iguchi, H, Matsuoka, K, Okamura, S, Minami, T, Yoshimura, Y, Nagaoka, K, Ida, K, Toi, K, Takahashi, C, Kojima, M, Nishimura, S, Isobe, M, Suzuki, C, Akiyama, T, Ido, T, Nagashima, Y, Itoh, SI, and Diamond, PH

Subjects
Fluids & Plasmas, Atomic, Molecular, Nuclear, Particle and Plasma Physics, Astronomical and Space Sciences, Classical Physics, Atomic, Molecular, Nuclear, Particle and Plasma Physics
Abstract

The experimental studies on zonal flows and turbulence have been carried out in Compact Helical System [K. Matsuoka, S. Kubo, M. Hosokawa, 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. © 2008 American Institute of Physics.

Published
2008

17. Experimental progress on zonal flow physics in toroidal plasmas

Author

Fujisawa, A, Ido, T, Shimizu, A, Okamura, S, Matsuoka, K, Iguchi, H, Hamada, Y, Nakano, H, Ohshima, S, Itoh, K, Hoshino, K, Shinohara, K, Miura, Y, Nagashima, Y, Itoh, S-I, Shats, M, Xia, H, Dong, JQ, Yan, LW, Zhao, KJ, Conway, GD, Stroth, U, Melnikov, AV, Eliseev, LG, Lysenko, SE, Perfilov, SV, Hidalgo, C, Tynan, GR, Holland, C, Diamond, PH, McKee, GR, Fonck, RJ, Gupta, DK, and Schoch, PM

Subjects
Atomic, Molecular, Nuclear, Particle and Plasma Physics, Fluids & Plasmas
Abstract

The present status of experiments on zonal flows in magnetic confinement experiments is examined. The innovative use of traditional and modern diagnostics has revealed unambiguously the existence of zonal flows, their spatio-temporal characteristics, their relationship to turbulence and their effects on confinement. In particular, a number of observations have been accumulated on the oscillatory branch of zonal flows, named geodesic acoustic modes, suggesting the necessity for theories to give their proper description. In addition to these basic properties of zonal flows, several new methods have elucidated the processes of zonal flow generation from turbulence. Further investigation of the relationship between zonal flows and confinement is strongly encouraged as cross-device activity including low temperature, toroidal and linear devices. © 2007 IAEA.

Published
2007

18. Experimental Evidence of a Zonal Magnetic Field in a Toroidal Plasma

Author

Fujisawa, A, Itoh, K, Shimizu, A, Nakano, H, Ohshima, S, Iguchi, H, Matsuoka, K, Okamura, S, Minami, T, Yoshimura, Y, Nagaoka, K, Ida, K, Toi, K, Takahashi, C, Kojima, M, Nishimura, S, Isobe, M, Suzuki, C, Akiyama, T, Nagashima, Y, Itoh, S-I, and Diamond, PH

Subjects
Mathematical Sciences, Physical Sciences, Engineering, General Physics
Abstract

A zonal magnetic field is found in a toroidal plasma. The magnetic field has a symmetric bandlike structure, which is uniform in the toroidal and poloidal directions and varies radially with a finite wavelength of mesoscale, which is analogous to zonal flows. A time-dependent bicoherence analysis reveals that the magnetic field should be generated by the background plasma turbulence. The discovery is classified as a new kind of phenomenon of structured magnetic field generation, giving insight into phenomena such as dipole field generation in rotational planets.

Published
2007

21. Development and initial results of 320 GHz interferometer system in Heliotron J

Author

Zhang, P., primary, Ohshima, S., additional, Zhao, H., additional, Deng, C., additional, Kobayashi, S., additional, Kado, S., additional, Minami, T., additional, Matoike, R., additional, Miyashita, A., additional, Iwata, A., additional, Kondo, Y., additional, Qiu, D., additional, Wang, C., additional, Luo, M., additional, Konoshima, S., additional, Inagaki, S., additional, Okada, H., additional, Mizuuchi, T., additional, and Nagasaki, K., additional

Published
2022
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22. Measurement of Pa α line from pellet ablation cloud in Heliotron J

Author

Iwata, A., primary, Kado, S., additional, Murakumo, M., additional, Shikama, T., additional, Motojima, G., additional, Mori, A., additional, Feng, C., additional, Okada, H., additional, Minami, T., additional, Ohshima, S., additional, Kobayashi, S., additional, Ishizawa, A., additional, Nakamura, Y., additional, Konoshima, S., additional, Mizuuchi, T., additional, and Nagasaki, K., additional

Published
2022
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24. Development of dual X-mode Doppler reflectometry system in Heliotron J

Author

Kondo, Y., primary, Ohshima, S., additional, Kuwahara, D., additional, Inoshita, K., additional, Fukuda, T., additional, Minami, T., additional, Kado, S., additional, Kobayashi, S., additional, Konoshima, S., additional, Mizuuchi, T., additional, Okada, H., additional, Tomita, T., additional, and Nagasaki, K., additional

Published
2022
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26. Gas fueling effect on plasma profile in Heliotron J

Author

Mizuuchi, T., Lee, H.Y., Mukai, K., Yamamoto, K., Kobayashi, S., Okada, H., Yamamoto, S., Ohshima, S., Zang, L., Nagasaki, K., Minami, T., Kagawa, T., Minami, T.Y., Mizuno, K., Wada, Y., Arai, S., Yashiro, H., Watada, H., Hashimoto, K., Kenmochi, N., Nagae, Y., Sha, M., Nakamura, Y.I., Kasajima, K., Nishino, N., Hosoi, K., Nakashima, Y., Nakamura, Y., Konoshima, S., and Sano, F.

Published
2013
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41. Numerical investigation into the peripheral energetic-particle-driven MHD modes in Heliotron J with free boundary hybrid simulation

Author

Adulsiriswad, P., primary, Todo, Y., additional, Kado, S., additional, Yamamoto, S., additional, Kobayashi, S., additional, Ohshima, S., additional, Okada, H., additional, Minami, T., additional, Nakamura, Y., additional, Ishizawa, A., additional, Konoshima, S., additional, Mizuuchi, T., additional, and Nagasaki, K., additional

Published
2021
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42. Measurement of Paα line from pellet ablation cloud in Heliotron J.

Author

Iwata, A., Kado, S., Murakumo, M., Shikama, T., Motojima, G., Mori, A., Feng, C., Okada, H., Minami, T., Ohshima, S., Kobayashi, S., Ishizawa, A., Nakamura, Y., Konoshima, S., Mizuuchi, T., and Nagasaki, K.

Subjects
SPECTRAL line broadening, DETECTION limit, ELECTRON density
Abstract

The Paα line (1875.13 nm) in the near-infrared (NIR) region was evaluated to apply Stark broadening of the line spectrum to the electron density measurement of the small-pellet ablation cloud in Heliotron J, a medium-sized helical-axis heliotron device. Paα is three-to-four times broader than the visible Hβ line (486.13 nm) for the same electron density. Using a portable NIR spectrometer, preliminary proof-of-concept experiments determined the marginal density, below which the broadening was undetectable. The lower detection density limit can be decreased using a narrower entrance slit or a denser grating. [ABSTRACT FROM AUTHOR]

Published
2022
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