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Your search keyword '"Kubo, S"' showing total 24 results
Start Over Author "Kubo, S" Journal review of scientific instruments
24 results on '"Kubo, S"'

2. W-band millimeter-wave back-scattering system for high wavenumber turbulence measurements in LHD.

Author

Tokuzawa, T., Tanaka, K., Tsujimura, T., Kubo, S., Emoto, M., Inagaki, S., Ida, K., Yoshinuma, M., Watanabe, K. Y., Tsuchiya, H., Ejiri, A., Saito, T., and Yamamoto, K.

Subjects
HETERODYNE detection, TURBULENCE, ANTENNAS (Electronics), MEASUREMENT
Abstract

A 90 GHz W-band millimeter-wave back-scattering system is designed and installed for measuring electron scale turbulence (k⊥ρs ∼ 40). A metal lens relay antenna is used for in-vessel beam focusing, and a beam diameter of less than 40 mm is achieved in the plasma core region. This antenna can be steered at an angle of 159° ± 6°, which almost covers the plasma radius. The estimated size of the scattering volume is ∼105 mm at the edge and 135 mm at the core, respectively. A 60 m corrugated waveguide is used to achieve a low transmission loss of ∼8 dB. A heterodyne detection system for millimeter-wave circuits with probing power modulation can distinguish the scattered signal from background noise. [ABSTRACT FROM AUTHOR]

Published
2021
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4. Reconstruction of high temporal resolution Thomson scattering data during a modulated electron cyclotron resonance heating using conditional averaging

Author

Kobayashi, T., primary, Ida, K., additional, Itoh, K., additional, Yoshinuma, M., additional, Moon, C., additional, Inagaki, S., additional, Yamada, I., additional, Funaba, H., additional, Yasuhara, R., additional, Tsuchiya, H., additional, Ohdachi, S., additional, Yoshimura, Y., additional, Igami, H., additional, Shimozuma, T., additional, Kubo, S., additional, and Tsujimura, T. I., additional

Published
2016
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5. Design of polarizers for a mega-watt long-pulse millimeter-wave transmission line on the large helical device

Author

Ii, T., primary, Kubo, S., additional, Shimozuma, T., additional, Kobayashi, S., additional, Okada, K., additional, Yoshimura, Y., additional, Igami, H., additional, Takahashi, H., additional, Ito, S., additional, Mizuno, Y., additional, Makino, R., additional, Kobayashi, K., additional, Goto, Y., additional, and Mutoh, T., additional

Published
2015
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9. Suppression of spurious mode oscillation in mega-watt 77-GHz gyrotron as a high quality probe beam source for the collective Thomson scattering in LHD

Author

Ogasawara, S., primary, Kubo, S., additional, Nishiura, M., additional, Tatematsu, Y., additional, Saito, T., additional, Tanaka, K., additional, Shimozuma, T., additional, Yoshimura, Y., additional, Igami, H., additional, Takahashi, H., additional, Ito, S., additional, Takita, Y., additional, Kobayashi, S., additional, Mizuno, Y., additional, Okada, K., additional, Minami, R., additional, Kariya, T., additional, and Imai, T., additional

Published
2012
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10. Collective Thomson scattering of a high power electron cyclotron resonance heating beam in LHD (invited)

Author

Kubo, S., primary, Nishiura, M., additional, Tanaka, K., additional, Shimozuma, T., additional, Yoshimura, Y., additional, Igami, H., additional, Takahash, H., additional, Mutoh, T., additional, Tamura, N., additional, Tatematsu, Y., additional, Saito, T., additional, Notake, T., additional, Korsholm, S. B., additional, Meo, F., additional, Nielsen, S. K., additional, Salewski, M., additional, and Stejner, M., additional

Published
2010
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15. The observation of nonlinear ion cyclotron wave excitation during high-harmonic fast wave heating in the large helical device

Author

Kasahara, H., primary, Seki, T., additional, Kumazawa, R., additional, Saito, K., additional, Mutoh, T., additional, Kubo, S., additional, Shimozuma, T., additional, Igami, H., additional, Yoshimura, Y., additional, Takahashi, H., additional, Yamada, I., additional, Tokuzawa, T., additional, Ohdachi, S., additional, Morita, S., additional, Nomura, G., additional, Shimpo, F., additional, Komori, A., additional, Motojima, O., additional, Oosako, T., additional, Takase, Y., additional, Zhao, Y., additional, and Kwak, J., additional

Published
2008
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16. Real time polarization monitor developed for high power electron cyclotron resonance heating and current drive experiments in large helical device

Author

Notake, T., primary, Idei, H., additional, Kubo, S., additional, Shimozuma, T., additional, Yoshimura, Y., additional, Kobayashi, S., additional, Mizuno, Y., additional, Ito, S., additional, Takita, Y., additional, Ohkubo, K., additional, Kasparek, W., additional, Watari, T., additional, and Kumazawa, R., additional

Published
2005
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20. Searching for O-X-B mode-conversion window with monitoring of stray microwave radiation in LHD.

Author

Igami, H., Kubo, S., Laqua, H. P., Nagasaki, K., Inagaki, S., Notake, T., Shimozuma, T., Yoshimura, Y., and Mutoh, T.

Subjects
*RADIATION, *MICROWAVES, *ELECTRONS, *CYCLOTRONS, *ELECTROMAGNETIC waves
Abstract

In the Large Helical Device, the stray microwave radiation is monitored by using so-called sniffer probes during electron cyclotron heating. In monitoring the stray radiation, we changed the microwave beam injection angle and search the O-X-B mode-conversion window to excite electron Bernstein waves (EBWs). When the microwave beam is injected toward the vicinity of the predicted O-X-B mode-conversion window, the electron temperature rises in the central part of overdense plasmas. In that case, the stray radiation level near the injection antenna becomes low. These results indicate that monitoring the stray radiation near the injection antenna is helpful in confirming the effectiveness of excitation of EBWs simply without precise analysis. [ABSTRACT FROM AUTHOR]

Published
2006
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21. Collective Thomson scattering diagnostic with in situ calibration system for velocity space analysis in large helical device.

Author

Nishiura M, Adachi S, Tanaka K, Kubo S, Kenmochi N, Shimozuma T, Yanai R, Saito T, Nuga H, and Seki R

Abstract

A collective Thomson scattering (CTS) diagnostic with a ±3 GHz band around a 77 GHz gyrotron probe beam was developed to measure the velocity distribution of bulk and fast ions in high-temperature plasmas. We propose a new in situ calibration method for a CTS diagnostic system combined with a raytracing code. The method is applied in two situations for electron cyclotron emission in plasmas and in a CTS diagnostic with a modulated probe beam. Experimental results highlight the importance of refraction correction in probe and receive beams. The CTS spectrum is measured with the in situ calibrated CTS receiver and responds to fast ions originating from a tangential neutral beam with an energy of 170 keV and from a perpendicular beam with an energy of 60 keV, both in the large helical device. From a velocity space analysis model, the results elucidate the measured anisotropic CTS spectrum caused by fast ions. The calibration methods and analyses demonstrated here are essential for CTS, millimeter-wave diagnostics, and electron cyclotron heating required under fusion reactor conditions.

Published
2022
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22. Development of off-axis spiral phase mirrors for generating optical vortices in a range of millimeter waves.

Author

Tsujimura TI, Goto Y, Okada K, Kobayashi S, and Kubo S

Abstract

In this paper, we report the development of off-axis spiral phase mirrors that can be used to generate optical vortices from a range of millimeter waves. An obliquely incident Gaussian beam is reflected from a spiral phase mirror and is converted into an optical vortex beam with a desired topological charge. The mirrors were fabricated by mechanical machining. The designed vortex properties of reflected waves were investigated experimentally by using a low-power test, where the designed topological charge was verified based on the interference pattern between a vortex beam and a Gaussian-like beam. The designed topological charge was also estimated by using a phase retrieval method specialized for a vortex beam. These off-axis spiral phase mirrors can be used for propagation experiments of radio frequency waves with helical wavefronts in magnetized plasma.

Published
2022
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23. Measurement of electrostatic potential fluctuation using heavy ion beam probe in large helical device.

Author

Ido T, Shimizu A, Nishiura M, Nakano H, Ohshima S, Kato S, Hamada Y, Yoshimura Y, Kubo S, Shimozuma T, Igami H, Takahashi H, Toi K, and Watanabe F

Abstract

Heavy ion beam probe (HIBP) for large helical device (LHD) has been improved to measure the potential fluctuation in high-temperature plasmas. The spatial resolution is improved to about 10 mm by controlling the focus of a probe beam. The HIBP is applied to measure the potential fluctuation in plasmas where the rotational transform is controlled by electron cyclotron current drive. The fluctuations whose frequencies change with the time constant of a few hundreds of milliseconds and that with a constant frequency are observed. The characteristics of the latter fluctuation are similar to those of the geodesic acoustic mode oscillation. The spatial profiles of the fluctuations are also obtained.

Published
2008
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24. Collective backscattering of gyrotron radiation by small-scale plasma density fluctuations in large helical device.

Author

Kharchev N, Tanaka K, Kubo S, Igami H, Batanov G, Petrov A, Sarksyan K, Skvortsova N, Azuma Y, and Tsuji-Iio S

Abstract

A version of the collective backscattering diagnostic using gyrotron radiation for small-scale turbulence is described. The diagnostic is used to measure small-scale (k(s) approximately 34 cm(-1)) plasma density fluctuations in large helical device experiments on the electron cyclotron heating of plasma with the use of 200 kW 82.7 GHz heating gyrotron. A good signal to noise ratio during plasma production phase was obtained, while contamination of stray light increased during plasma build-up phase. The effect of the stray radiation was investigated. The available quasioptical system of the heating system was utilized for this purpose.

Published
2008
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