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19 results on '"Igami, H."'

1. Measurement of stray millimeter-wave radiation from a 70-GHz ECH/ECCD system in Heliotron J

Author

Nagasaki, K., Watanabe, S., Sakamoto, K., Isayama, Akihiko, Okada, H., Minami, T., Kado, S., Kobayashi, S., Yamamoto, S., Ohshima, S., Konoshima, S., Mizuuchi, T., Nakamura, Y., Ishizawa, A., Kubo, S., Igami, H., Weir, G., and Marushchenko, N.

Subjects
Physics::Plasma Physics, Physics::Space Physics, Astrophysics::Instrumentation and Methods for Astrophysics
Abstract

Stray millimeter-wave radiation from a 70-GHz electron cyclotron heating and current drive (ECH/ECCD) system has been measured in the Heliotron J helical device. Two rotatable diode detectors located at the out- board side ports are used to pick up the stray radiation: one is installed at the ECH launcher port and the other is installed at a toroidal angle of 135 deg far from the ECH launcher port. Both detectors are rotated to measure the polarization of the stray radiation. The results show that at the toroidal position far from the ECH launcher, the polarization is not fully randomized before plasma breakdown, whereas the polarization is uniform after a quasi- stationary plasma is generated. The polarization near the ECH launcher is not uniform even in a quasi-stationary plasma. Plasma experiments scanning the electron density indicate that the EC power absorption estimated from the stray radiation at the toroidal position far from the ECH launcher is correlated with the single-pass ab- sorption rate calculated by the TRAVIS ray-tracing code. These results indicate that the diagnostic using a simple diode detector can be used as a real-time monitor of EC power absorption only when the plasma with finite density is produced and the detector is placed far from the ECH launcher port.

Published
2019

4. Correcting for non-periodic behaviour in perturbative experiments: application to heat pulse propagation and modulated gas-puff experiments

Author

van Berkel, M., van Kampen, R.J. R., Vandersteen, G., Kobayashi, T., Ravensbergen, T., Igami, H., Lammers, J.T., Oosterwegel, G., Galperti, C., Felici, F., de Baar, M.R., Group, LHDExperiment, team, TCV, Control Systems Technology, Group Heemels, Applied Physics and Science Education, Science and Technology of Nuclear Fusion, and Electricity

Subjects
perturbative experiments, Radiation, 01 natural sciences, gas puff, 010305 fluids & plasmas, power, symbols.namesake, Quality (physics), 0103 physical sciences, Initial value problem, electron transport, 010306 general physics, Physics, Divertor, System identification, local polynomial method, Mechanics, Condensed Matter Physics, Fourier analysis, Core (optical fiber), Fourier transform, Nuclear Energy and Engineering, transport, detachment, symbols, identification, systems
Abstract

This paper introduces a recent innovation in dealing with non-periodic behavior often referred to as transients in perturbative experiments. These transients can be the result from the unforced response due to the initial condition and other slow trends in the measurement data and are a source of error when performing and interpreting Fourier spectra. Fourier analysis is particularly relevant in system identification used to build feedback controllers and the analysis of various pulsed experiments such as heat pulse propagation studies. The basic idea behind the methodology is that transients are continuous complex-valued smooth functions in the Fourier domain which can be estimated from the Fourier data. Then, these smooth functions can be subtracted from the data such that only periodic components are retained. The merit of the approach is shown in two experimental examples, i.e. heat pulse propagation (core transport analysis) and radiation front movement due to gas puffing in the divertor. The examples show that the quality of the data is significantly improved such that it allows for new interpretation of the results even for non-ideal measurements.

Published
2020

6. New evidence and impact of electron transport non-linearities based on new perturbative inter-modulation analysis

Author

van Berkel, M., Kobayashi, T., Igami, H., Vandersteen, G., Hogeweij, G.M. D., Tanaka, K., Tamura, N., Zwart, H.J., Kubo, S., Ito, S., Tsuchiya, H., de Baar, M.R., Group, LHDExperiment, Electricity, Supporting clinical sciences, Medical Imaging, Control Systems Technology, and Dynamics and Control

Subjects
Physics, higher harmonic analysis, perturbative experiments, Nuclear and High Energy Physics, Volterra series, Electron, Condensed Matter Physics, 01 natural sciences, Transfer function, Electron cyclotron resonance, 010305 fluids & plasmas, Computational physics, Large Helical Device, Nuclear magnetic resonance, Quadratic equation, Amplitude, Modulation, 0103 physical sciences, distributed non-linearities, stellarators, 010306 general physics, electron thermal transport
Abstract

A new methodology to analyze non-linear components in perturbative transport experiments is introduced. The methodology has been experimentally validated in the Large Helical Device for the electron heat transport channel. Electron cyclotron resonance heating with different modulation frequencies by two gyrotrons has been used to directly quantify the amplitude of the non-linear component at the inter-modulation frequencies. The measurements show significant quadratic non-linear contributions and also the absence of cubic and higher order components. The non-linear component is analyzed using the Volterra series, which is the non-linear generalization of transfer functions. This allows us to study the radial distribution of the non-linearity of the plasma and to reconstruct linear profiles where the measurements were not distorted by non-linearities. The reconstructed linear profiles are significantly different from the measured profiles, demonstrating the significant impact that non-linearity can have.

Published
2017

8. Flow damping due to stochastization of the magnetic field

Author

Ida, K., Yoshinuma, M., Tsuchiya, H., Kobayashi, T., Suzuki, C., Yokoyama, M., Shimizu, A., Nagaoka, K., Inagaki, S., Itoh, K., Akiyama, T., Goto, M., Goto, T., Hasuo, M., Hidalgo, C., Ichiguchi, K., Ishizawa, A., Jakubowski, M., Kamiya, K., Kasahara, H., Kawamura, G., Pablant, N., Kato, D., Kobayashi, M., Morita, S., Mukai, K., Murakami, I., Murakami, S., Narushima, Y., Nunami, M., Ohdach, S., Ohno, N., Sakakibara, S., Osakabe, M., Seki, T., Shimozuma, T., Shoji, M., Sudo, S., Tanaka, K., Tokuzawa, T., Todo, Y., Wang, H., Fujita, T., Yamada, H., Takeiri, Y., Mutoh, T., Imagawa, S., Mito, T., Nagayama, Y., Watanabe, K. Y., Ashikawa, N., Chikaraishi, H., Ejiri, A., Hamaguchi, S., Furukawa, M., Igami, H., Isobe, M., Masuzaki, S., Morisaki, T., Motojima, G., Nagasaki, K., Nakano, H., Oya, Y., Yamamoto, T., Suzuki, Y., Sakamoto, R., Sakamoto, M., Sanpei, A., Takahashi, H., Tokitani, M., Ueda, Y., Yoshimura, Y., Yamamoto, S., Nishimura, K., Idei, H., Sugama, H., Isayama, A., Kitajima, S., Masamune, S., Shinohara, K., Bawankar, P. S., Bernard, E., Von Berkel, M., Funaba, H., Nishimura, S., Huang, X. L., Ii, T., Ido, T., Ikeda, K., Kamio, S., Kumazawa, R., Moon, C., Muto, S., Miyazawa, J., Ming, T., Ogawa, K., Nakamura, Y., Ozaki, T., Oishi, T., Ohno, M., Pandya, S., Seki, R., Sano, R., Saito, K., Sakaue, H., Emoto, M., Takemura, Y., Tsumori, K., Tamura, N., Tanaka, H., Toi, K., Wieland, B., Yamada, I., Yasuhara, R., Zhang, H., Kaneko, O., Evans, T., Komori, A., Dinklage, A., Du, X., and Fujii, K.

Subjects
Physics::Fluid Dynamics, Physical sciences, Physics::Plasma Physics, Fluids and plasma physics, food and beverages, sense organs, equipment and supplies, human activities
Abstract

The driving and damping mechanism of plasma flow is an important issue because flow shear has a significant impact on turbulence in a plasma, which determines the transport in the magnetized plasma. Here we report clear evidence of the flow damping due to stochastization of the magnetic field. Abrupt damping of the toroidal flow associated with a transition from a nested magnetic flux surface to a stochastic magnetic field is observed when the magnetic shear at the rational surface decreases to 0.5 in the large helical device. This flow damping and resulting profile flattening are much stronger than expected from the Rechester-Rosenbluth model. The toroidal flow shear shows a linear decay, while the ion temperature gradient shows an exponential decay. This observation suggests that the flow damping is due to the change in the non-diffusive term of momentum transport.

Published
2015

9. Overview of transport and MHD stability study: focusing on the impact of magnetic field topology in the Large Helical Device

Author

Ida, K., Nagaoka, K., Inagaki, S., Kasahara, H., Evans, T., Yoshinuma, M., Kamiya, K., Ohdach, S., Osakabe, M., Kobayashi, M., Sudo, S., Itoh, K., Akiyama, T., Emoto, M., Dinklage, A., Du, X., Fujii, K., Goto, M., Goto, T., Hasuo, M., Hidalgo, C., Ichiguchi, K., Ishizawa, A., Jakubowski, M., Kawamura, G., Kato, D., Morita, S., Mukai, K., Murakami, I., Murakami, S., Narushima, Y., Nunami, M., Ohno, N., Pablant, N., Sakakibara, S., Seki, T., Shimozuma, T., Shoji, M., Tanaka, K., Tokuzawa, T., Todo, Y., Wang, H., Yokoyama, M., Yamada, H., Takeiri, Y., Mutoh, T., Imagawa, S., Mito, T., Nagayama, Y., Watanabe, K.Y., Ashikawa, N., Chikaraishi, H., Ejiri, A., Furukawa, M., Fujita, T., Hamaguchi, S., Igami, H., Isobe, M., Masuzaki, S., Morisaki, T., Motojima, G., Nagasaki, K., Nakano, H., Oya, Y., Suzuki, C., Suzuki, Y., Sakamoto, R., Sakamoto, M., Sanpei, A., Takahashi, H., Tsuchiya, H., Tokitani, M., Ueda, Y., Yoshimura, Y., Yamamoto, S., Nishimura, K., Sugama, H., Yamamoto, T., Idei, H., Isayama, A., Kitajima, S., Masamune, S., Shinohara, K., Bawankar, P.S., Bernard, E., von Berkel, M., Funaba, H., Huang, X.L., Ii, T., Ido, T., Ikeda, K., Kamio, S., Kumazawa, R., Kobayashi, T., Moon, C., Muto, S., Miyazawa, J., Ming, T., Nakamura, Y., Nishimura, S., Ogawa, K., Ozaki, T., Oishi, T., Ohno, M., Pandya, S., Shimizu, A., Seki, R., Sano, R., Saito, K., Sakaue, H., Takemura, Y., Tsumori, K., Tamura, N., Tanaka, H., Toi, K., Wieland, B., Yamada, I., Yasuhara, R., Zhang, H., Kaneko, O., Komori, A., and Collaborators

Subjects
Nuclear and High Energy Physics, Electron density, topology, Materials science, Plasma, Electron, Condensed Matter Physics, Topology, 7. Clean energy, 01 natural sciences, 010305 fluids & plasmas, Ion, Magnetic field, Momentum, Large Helical Device, transport, 0103 physical sciences, Atomic physics, Magnetohydrodynamics, 010306 general physics, helical
Abstract

The progress in the understanding of the physics and the concurrent parameter extension in the large helical device since the last IAEA-FEC, in 2012 (Kaneko O et al 2013 Nucl. Fusion 53 095024), is reviewed. Plasma with high ion and electron temperatures (Ti(0) ~ Te(0) ~ 6 keV) with simultaneous ion and electron internal transport barriers is obtained by controlling recycling and heating deposition. A sign flip of the nondiffusive term of impurity/momentum transport (residual stress and convection flow) is observed, which is associated with the formation of a transport barrier. The impact of the topology of three-dimensional magnetic fields (stochastic magnetic fields and magnetic islands) on heat momentum, particle/impurity transport and magnetohydrodynamic stability is also discussed. In the steady state operation, a 48 min discharge with a line-averaged electron density of 1 × 1019 m−3 and with high electron and ion temperatures (Ti(0) ~ Te(0) ~ 2 keV), resulting in 3.36 GJ of input energy, is achieved.

Published
2015

10. Recent progress in Large Helical Device experiments

Author

Komori, A., Morisaki, T., Mutoh, T., Sakakibara, S., Takeiri, Y., Kumazawa, R., Kubo, S., Ida, K., Morita, S., Narihara, K., Shimozuma, T., Tanaka, K., Watanabe, K., Yamada, H., Yoshinuma, M., Akiyama, T., Ashikawa, N., Beidler, C., Emoto, M., Fujita, T., Funaba, H., Goncharov, P., Goto, M., Ido, T., Ikeda, K., Inagaki, S., Isayama, A., Isobe, M., Igami, H., Ishii, K., Itoh, K., Kaneko, O., Kawahata, K., Kawazome, H., Kobuchi, T., Masuzaki, S., Matsuoka, K., Minami, T., Miyazawa, J., Murakami, S., Muto, S., Nagayama, Y., Nakamura, Y., Nakanishi, H., Narushima, Y., Nishimura, K., Nishiura, M., Nishizawa, A., Noda, N., Notake, T., Ohdachi, S., Oka, Y., Okajima, S., Osakabe, M., Ohyabu, N., Ozaki, T., Peterson, B., Sagara, A., Saito, K., Sakamoto, M., Sakamoto, R., Sakamoto, Y., Sasao, M., Sato, K., Seki, T., Shoji, M., Sudo, S., Takeuchi, N., Takenaga, H., Tamura, N., Toi, K., Tokuzawa, T., Torii, Y., Tsumori, K., Uda, T., Watari, T., Yamada, I., Yokoyama, M., Yoshimura, Y., Motojima, O., and LHD Experimental Group

Published
2006

14. Extension of operation regimes and investigation of three-dimensional currentless plasmas in the Large Helical Device

Author

Kaneko, O., Yamada, H., Inagaki, S., Jakubowski, M., Kajita, S., Kitajima, S., Koga, K., Morisaki, T., Morita, S., Mutoh, T., Sakakibara, S., Suzuki, Y., Takahashi, H., Tanaka, K., Toi, K., Yoshimura, Y., Akiyama, T., Asahi, Y., Ashikawa, N., Chikaraishi, H., Cooper, A., Darrow, D. S., Drapiko, E., Drewelow, P., Du, X., Ejiri, A., Emoto, M., Evans, T., Ezumi, N., Fujii, K., Fukuda, T., Funaba, H., Furukawa, M., Gates, D. A., Goto, M., Goto, T., Guttenfelder, W., Hamaguchi, S., Hasuo, M., Hino, T., Hirooka, Y., Ichiguchi, K., Ida, K., Idei, H., Ido, T., Igami, H., Ikeda, K., Imagawa, S., Imai, T., Isobe, M., Itagaki, M., Ito, T., Itoh, K., Itoh, S., Iwamoto, A., Kamiya, K., Kariya, T., Kasahara, H., Kasuya, N., Kato, D., Kato, T., Kawahata, K., Koike, F., Kubo, S., Kumazawa, R., Kuwahara, D., Lazerson, S., Lee, H., Masuzaki, S., Matsuoka, S., Matsuura, H., Matsuyama, A., Michael, C., Mikkelsen, D., Mitarai, O., Mito, T., Miyazawa, J., Motojima, G., Mukai, K., Murakami, A., Murakami, I., Murakami, S., Muroga, T., Muto, S., Nagaoka, K., Nagasaki, K., Nagayama, Y., Nakajima, N., Nakamura, H., Nakamura, Y., Nakanishi, H., Nakano, H., Nakano, T., Narihara, K., Narushima, Y., Nishimura, K., Nishimura, S., Nishiura, M., Nunami, Y. M., Obana, T., Ogawa, K., Ohdachi, S., Ohno, N., Ohyabu, N., Oishi, T., Okamoto, M., Okamoto, A., Osakabe, M., Oya, Y., Ozaki, T., Pablant, N., Peterson, B. J., Sagara, A., Saito, K., Sakamoto, R., Sakaue, H., Sasao, M., Sato, K., Sato, M., Sawada, K., Seki, R., Seki, T., Sergeev, V., Sharapov, S., Sharov, I., Shimizu, A., Shimozuma, T., Shiratani, M., Shoji, M., Sudo, S., Sugama, H., Suzuki, C., Takahata, K., Takeiri, Y., Takemura, Y., Takeuchi, M., Tamura, H., Tamura, N., Tanaka, H., Tanaka, T., Tingfeng, M., Todo, Y., Tokitani, M., Tokunaga, K., Tokuzawa, T., Tsuchiya, H., Tsumori, K., Ueda, Y., Vyacheslavov, L., Watanabe, K. Y., Watanabe, T., Watanabe, T. H., Wieland, B., Yamada, I., Yamada, S., Yamamoto, S., Yanagi, N., Yasuhara, R., Yokoyama, M., Yoshida, N., Yoshimura, S., Yoshinaga, T., Yoshinuma, M., and Komori, A.

Subjects
Physics::Plasma Physics
Abstract

The progress of physical understanding as well as parameter improvement of net-current-free helical plasma is reported for the Large Helical Device since the last Fusion Energy Conference in Daejeon in 2010. The second low-energy neutral beam line was installed, and the central ion temperature has exceeded 7 keV, which was obtained by carbon pellet injection. Transport analysis of the high-T-i plasmas shows that the ion-thermal conductivity and viscosity decreased after the pellet injection although the improvement does not last long. The effort has been focused on the optimization of plasma edge conditions to extend the operation regime towards higher ion temperature and more stable high density and high beta. For this purpose a portion of the open helical divertors are being modified to the baffle-structured closed ones aimed at active control of the edge plasma. It is compared with the open case that the neutral pressure in the closed helical divertor increased by ten times as predicted by modelling. Studies of physics in a three-dimensional geometry are highlighted in the topics related to the response to a resonant magnetic perturbation at the plasma periphery such as edge-localized-mode mitigation and divertor detachment. Novel approaches of non-local and non-diffusive transport have also been advanced.

16. Impact of local magnetic shear and Te/Ti ratio on confinement properties in toroidal confinement systems

Author

Takeshi Fukuda, Tamura, N., Ida, K., Tanaka, K., Yoshinuma, M., Kobuchi, T., Watanabe, K. Y., Funaba, H., Igami, H., Itoh, K., Ido, T., Inagaki, S., Oishi, T., Kato, T., Kado, S., Kubo, S., Goto, M., Sakamoto, R., Satake, S., Shimizu, A., Shimozuma, T., Suzuki, C., Sudo, S., Takeiri, Y., Toi, K., Tokuzawa, T., Nakano, H., Narihara, K., Nishimura, S., Notake, T., Muto, S., Morita, S., Liu, Y., Yamada, H., Yamada, I., Yokoyama, M., Kawahata, K., and Komori, A.

18. Recent progress in large helical device experiments

Author

Komori, A., Morisaki, T., Mutoh, T., Sakakibara, S., Takeiri, Y., Kumazawa, R., Kubo, S., Ida, K., Morita, S., Narihara, K., Shimozuma, T., Tanaka, K., Watanabe, K. Y., Yamada, H., Yoshinuma, M., Akiyama, T., Ashikawa, N., Emoto, M., Funaba, H., Goto, M., Ido, T., Ikeda, K., Inagaki, S., Isobe, M., Igami, H., Itoh, K., Kaneko, O., Kawahata, K., Kobuchi, T., Masuzaki, S., Matsuoka, K., Minami, T., Miyazawa, J., Muto, S., Nagayama, Y., Nakamura, Y., Nakanishi, H., Narushima, Y., Nishimura, K., Nishiura, M., Nishizawa, A., Noda, N., Ohdachi, S., Oka, Y., Osakabe, M., Ohyabu, N., Ozaki, T., Peterson, B. J., Sagara, A., Saito, K., Ryuichi Sakamoto, Sato, K., Seki, T., Shoji, M., Sudo, S., Tamura, N., Toi, K., Tokuzawa, T., Tsumori, K., Uda, T., Watari, T., Yamada, I., Yokoyama, M., Yoshimura, Y., Motojima, O., Beidler, C. D., Fujita, T., Isayama, A., Sakamoto, Y., Takenaga, H., Goncharov, P., Ishii, K., Sakamoto, M., Kawazome, H., Torii, Y., Murakami, S., Notake, T., Takeuchi, N., Okajima, S., Sasao, M., and Exp Group, L. H. D.

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