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49 results on '"Igami, H."'

7. Direct observation of the non-locality of non-diffusive counter-gradient electron thermal transport during the formation of hollow electron-temperature profiles in the Large Helical Device

Author

Tsujimura, T. I., primary, Kobayashi, T., additional, Tanaka, K., additional, Ida, K., additional, Nagaoka, K., additional, Yoshinuma, M., additional, Yamada, I., additional, Funaba, H., additional, Seki, R., additional, Satake, S., additional, Kinoshita, T., additional, Tokuzawa, T., additional, Kenmochi, N., additional, Igami, H., additional, Mukai, K., additional, Goto, M., additional, and Kawamoto, Y., additional

Published
2022
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9. Isotope effects on transport in LHD

Author

Tanaka, K, primary, Nagaoka, K, additional, Ida, K, additional, Yamada, H, additional, Kobayashi, T, additional, Satake, S, additional, Nakata, M, additional, Kinoshita, T, additional, Ohtani, Y, additional, Tokuzawa, T, additional, Takahashi, H, additional, Warmer, F, additional, Mukai, K, additional, Murakami, S, additional, Sakamoto, R, additional, Nakano, H, additional, Osakabe, M, additional, Morisaki, T, additional, Nunami, M, additional, Tala, T, additional, Tsujimura, T, additional, Takemura, Y, additional, Yokoyama, M, additional, Seki, R, additional, Igami, H, additional, Yoshimura, Y, additional, Kubo, S, additional, Shimozuma, T, additional, Akiyama, T, additional, Yamada, I, additional, Yasuhara, R, additional, Funaba, H, additional, Yoshinuma, M, additional, Goto, M, additional, Oishi, T, additional, Morita, S, additional, Motojima, G, additional, Shoji, M, additional, Masuzaki, S, additional, Michael, C A, additional, and Vacheslavov, L N, additional

Published
2021
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11. First observation and interpretation of spontaneous collective radiation from fusion-born ions in a stellarator plasma.

Author

Reman, B C G, Dendy, R O, Igami, H, Akiyama, T, Salewski, M, Chapman, S C, Cook, J W S, Inagaki, S, Saito, K, Seki, R, Toida, M, Kim, M H, Thatipamula, S G, and Yun, G S

Subjects
DEUTERIUM plasma, CYLINDRICAL plasmas, ION beams, PLASMA confinement, RADIATION, THERMAL plasmas, DEUTERIUM
Abstract

During bursty MHD events, transient ion cyclotron emission (ICE) is observed from deuterium plasmas in the large helical device (LHD) heliotron-stellarator. Unusually, the frequencies of the successive ICE spectral peaks are not close to integer multiples of the local cyclotron frequency of an energetic ion population in the likely emitting region. We show that this ICE is probably driven by a subset of the fusion-born protons near their birth energy E H = 3.02 MeV. This subset has a kinetic energy component parallel to the magnetic field, m H v ∥ 2 / 2 , significantly greater than its perpendicular energy m H v ⊥ 2 / 2 , for which v ⊥ ∼ V A , the AlfvĂ©n speed. First principles computations of the collective relaxation of this proton population, within a majority thermal deuterium plasma, are carried out using a particle-in-cell approach. This captures the full gyro-orbit kinetics of all ions which, together with an electron fluid, evolve self-consistently with the electric and magnetic fields under the Maxwellâ€"Lorentz equations. The simulated ICE spectra are derived from the Fourier transform of the fields which are excited. We find substantial frequency shifts in the peaks of the simulated ICE spectra, which correspond closely to the measured ICE spectra following the resonance condition ω = k ∥ v ∥ + n Ω H for n th proton harmonic. This suggests that the transient ICE in LHD is generated by the identified subset of the fusion-born protons, relaxing under the magnetoacoustic cyclotron instability. So far as is known, this is the first report of a collective radiation signal from fusion-born ions in anon-tokamak magnetically confined plasma. Disambiguation between two or more energetic ion species that could potentially generate complex observed ICE spectra is an increasing challenge, and the results and methodology developed here will assist this. Our approach is also expected to be relevant to ICE driven by ion beams with lower parallel velocities, for example in cylindrical plasma experiments. [ABSTRACT FROM AUTHOR]

Published
2022
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13. Improved performance of electron cyclotron resonance heating by perpendicular injection in the Large Helical Device

Author

Tsujimura, T.I., primary, Yanai, R., additional, Mizuno, Y., additional, Tanaka, K., additional, Yoshimura, Y., additional, Tokuzawa, T., additional, Nishiura, M., additional, Sakamoto, R., additional, Motojima, G., additional, Kubo, S., additional, Shimozuma, T., additional, Igami, H., additional, Takahashi, H., additional, Yoshinuma, M., additional, and Ohshima, S., additional

Published
2020
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14. Long-pulse Plasma Discharges by Upgraded ECH System in the LHD

Author

Yoshimura Y., Kasahara H., Nagasaki K., Tokitani M., Ashikawa N., Ueda Y., Ito S., Kubo S., Shimozuma T., Igami H., Takahashi H., Nishiura M., Kobayashi S., Mizuno Y., Okada K., Ogasawara S., Makino R., Yamada I., Tokuzawa T., Tanaka K., Mutoh T., and Yamada H.

Subjects
Physics, QC1-999
Abstract

Until 2009, three high-power, over 1MW each, 77GHz gyrotrons have been installed and applied to the LHD experiment. In addition, a 154GHz gyrotron of 1MW was installed in 2012. The 77GHz gyrotrons suffer gradual increases of internal pressure during long-pulse operation delivering power to LHD. To mitigate the problem, quasi-steady operation by combination of on-off operations of the 77GHz gyrotrons was performed. Applying two 77GHz gyrotrons alternately with intervals of two minutes and an 84GHz gyrotron continuously, a 30 min. long-pulse discharge with the line average electron density ne_ave of 0.7×1019m−3 and the central electron temperature Te0 of 1.7keV was achieved by the time average injection power Pinj of 260kW in 2012, showing significant progress in sustained density from the former 65 min. discharge with ne_ave of 0.15×1019m−3 and Te0 of 1.7keV by Pinj of 110kW of 84GHz wave. In 2013, one of the 77GHz gyrotron was improved to furnish a sub-window to remove stray radiation inside the tube. And the new 154GHz gyrotron was applied to the long-pulse discharge experiment. Using three gyrotrons: 154, the improved and an existing 77GHz with Pinj of 340kW in total, higher temperature plasma having steep temperature gradient typical for internal transport barrier, with ne_ave of 1.1×1019m−3 and Te0 of 3.5keV was quite stably sustained for 325s.

Published
2015
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15. Experimental characterization of plasma start-up using ECRH in preparation of W7-X operation

Author

Preynas M., Aßmus D., Igami H., Kado S., Kobayashi S., Kubo S., Laqua H.P., Mutoh T., Nagasaki K., Otte M., Shimozuma T., Stange T., and Yoshimura Y.

Subjects
Physics, QC1-999
Abstract

The upcoming operation of Wendelstein 7-X (W7-X) will be supported by an Electron Cyclotron Resonance Heating (ECRH) system working at 140 GHz in second harmonic at the nominal magnetic field of 2.5T. Because the optimization of the plasma breakdown is crucial to ensure a successful plasma build-up, dedicated plasma start-up experiments were performed on three stellarator/heliotron devices: Heliotron J, LHD and WEGA. Start-up behavior and dependencies on ECRH injected power, neutral gas pressure and rotational transform were obtained in X2 heating. Plasma start-up delay time decreases with the increase in ECRH input power. However, this behavior saturates when low pre-fill neutral gas pressure conditions are met. Both the delay time and the electron density are an increasing function of the gas pressure. On Heliotron J and WEGA devices, the higher the rotational transform is, the faster the start-up and the higher the plasma density are. Analysis of the temporal evolution of the plasma start-up shows that plasma start-up on stellarators is a two-step process. In addition, off-axis heating experiments are characterized by a longer plasma start-up duration compared to on-axis heating discharges. Third harmonic in X-mode has been attempted on LHD for different neutral gas puffing settings but no plasma breakdown was achieved. This multi-machine study was useful to define ECRH start-up scenarios for W7-X.

Published
2015
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16. Development of a Millimeter-Wave Beam Position and Profile Monitor for Transmission Efficiency Improvement in an ECRH System

Author

Shimozuma T., Kobayashi S., Ito S., Ito Y., Kubo S., Yoshimura Y., Nishiura M., Igami H., Takahashi H., Mizuno Y., Okada K., and Mutoh T.

Subjects
Physics, QC1-999
Abstract

In a high power Electron Cyclotron Resonance Heating (ECRH) system, a long-distance and low-loss transmission system is required to realize effective heating of nuclear fusion-relevant plasmas. A millimeter-wave beam position and profile monitor, which can be used in a high-power, evacuated, and cooled transmission line, is proposed, designed, manufactured, and tested. The beam monitor consists of a reflector, Peltier-device array and a heat-sink. It was tested using simulated electric heater power or gyrotron output power. The data obtained from the monitor were well agreed with the heat source position and profile. The methods of data analysis and mode-content analysis of a propagating millimeter-wave in the corrugated wave-guide are proposed.

Published
2015
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17. Isotope effect in transient electron thermal transport property and its impact on the electron internal transport barrier formation in LHD

Author

Kobayashi, T., primary, Ida, K., additional, Tanaka, K., additional, Yoshinuma, M., additional, Tsujimura, T.Ii, additional, Inagaki, S., additional, Tokuzawa, T., additional, Tsuchiya, H., additional, Tamura, N., additional, Igami, H., additional, Yoshimura, Y., additional, Itoh, S.-I., additional, Itoh, K., additional, and Experiment Group, LHD, additional

Published
2020
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18. Collective Thomson scattering with 77, 154, and 300 GHz sources in LHD

Author

Nishiura, M., primary, Tanaka, K., additional, Kubo, S., additional, Saito, T., additional, Kenmochi, N., additional, Nuga, H., additional, Seki, R., additional, Shimozuma, T., additional, Yoshimura, Y., additional, Igami, H., additional, Takahashi, H., additional, Tsujimura, T.I., additional, Yanai, R., additional, and Tatematsu, Y., additional

Published
2020
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19. Isotope effects on energy, particle transport and turbulence in electron cyclotron resonant heating plasma of the Large Helical Device

Author

Tanaka, K., primary, Ohtani, Y., additional, Nakata, M., additional, Warmer, F., additional, Tsujimura, T., additional, Takemura, Y., additional, Kinoshita, T., additional, Takahashi, H., additional, Yokoyama, M., additional, Seki, R., additional, Igami, H., additional, Yoshimura, Y., additional, Kubo, S., additional, Shimozuma, T., additional, Tokuzawa, T., additional, Akiyama, T., additional, Yamada, I., additional, Yasuhara, R., additional, Funaba, H., additional, Yoshinuma, M., additional, Ida, K., additional, Goto, M., additional, Motojima, G., additional, Shoji, M., additional, Masuzaki, S., additional, Michael, C.A., additional, Vacheslavov, L.N., additional, Osakabe, M., additional, and Morisaki, T., additional

Published
2019
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21. 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

24. 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

25. Improved performance of electron cyclotron resonance heating by perpendicular injection in the Large Helical Device.

Author

Tsujimura, T.I., Yanai, R., Mizuno, Y., Tanaka, K., Yoshimura, Y., Tokuzawa, T., Nishiura, M., Sakamoto, R., Motojima, G., Kubo, S., Shimozuma, T., Igami, H., Takahashi, H., Yoshinuma, M., Ohshima, S., and Group, The LHD Experiment

Subjects
CYCLOTRON resonance, ELECTRON cyclotron resonance heating, ELECTRON density, CYCLOTRONS
Abstract

A real-time interlock system for power injection in electron cyclotron resonance heating (ECRH) was developed to be applied to Large Helical Device (LHD) plasma. This system enabled perpendicular injection, thus improving the performance of ECRH more than has ever been achieved before in LHD. Perpendicular propagation of the electron cyclotron wave at 77 GHz became more insensitive to the effect of refraction in comparison to the conventional oblique propagation. The achieved central electron temperature in the case of perpendicular injection was approximately 2 keV higher than that in the case of standard oblique injection for a central electron density of 1 × 1019 m−3 by 1 MW injection. With such improved performance of ECRH, high-density ECRH plasma of 8 × 1019 m−3 was successfully sustained after the injection of multiple hydrogen ice pellets for the first time in LHD. [ABSTRACT FROM AUTHOR]

Published
2021
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26. Extended investigations of isotope effects on ECRH plasma in LHD.

Author

Tanaka, K., Nakata, M., Ohtani, Y., Tokuzawa, T., Yamada, H., Warmer, F., Nunami, M., Satake, S., Tala, T., Tsujimura, T., Takemura, Y., Kinoshita, T., Takahashi, H., Yokoyama, M., Seki, R., Igami, H., Yoshimura, Y., Kubo, S., Shimozuma, T., and Akiyama, T.

Subjects
PLASMA turbulence, ISOTOPES, INVESTIGATIONS, ELECTRON transport, ION temperature
Abstract

Isotope effects of ECRH plasma in LHD were investigated in detail. A clear difference of transport and turbulence characteristics in H and D plasmas was found in the core region, with normalized radius ρ < 0.8 in high collisionality regime. On the other hand, differences of transport and turbulence were relatively small in low collisionality regime. Power balance analysis and neoclassical calculation showed a reduction of the anomalous contribution to electron and ion transport in D plasma compared with H plasma in the high collisionality regime. In core region, density modulation experiments also showed more reduced particle diffusion in D plasma than in H plasma, in the high collisionality regime. Ion scale turbulence was clearly reduced at ρ < 0.8 in high collisionality regime in D plasma compared with H plasma. The gyrokinetic linear analyses showed that the dominant instability ρ = 0.5 and 0.8 were ion temperature gradient mode (ITG). The linear growth rate of ITG was reduced in D plasma than in H plasma in high collisionality regime. This is due to the lower normalized ITG and density gradient. More hollowed density profile in D plasma is likely to be the key control parameter. Present analyses suggest that anomalous process play a role to make hollower density profiles in D plasma rather than neoclassical process. Electron scale turbulence were also investigated from the measurements and linear gyrokinetic simulations. [ABSTRACT FROM AUTHOR]

Published
2020
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28. Extension of the operational regime of the LHD towards a deuterium experiment

Author

Takeiri, Y., primary, Morisaki, T., additional, Osakabe, M., additional, Yokoyama, M., additional, Sakakibara, S., additional, Takahashi, H., additional, Nakamura, Y., additional, Oishi, T., additional, Motojima, G., additional, Murakami, S., additional, Ito, K., additional, Ejiri, A., additional, Imagawa, S., additional, Inagaki, S., additional, Isobe, M., additional, Kubo, S., additional, Masamune, S., additional, Mito, T., additional, Murakami, I., additional, Nagaoka, K., additional, Nagasaki, K., additional, Nishimura, K., additional, Sakamoto, M., additional, Sakamoto, R., additional, Shimozuma, T., additional, Shinohara, K., additional, Sugama, H., additional, Watanabe, K.Y., additional, Ahn, J.W., additional, Akata, N., additional, Akiyama, T., additional, Ashikawa, N., additional, Baldzuhn, J., additional, Bando, T., additional, Bernard, E., additional, Castejón, F., additional, Chikaraishi, H., additional, Emoto, M., additional, Evans, T., additional, Ezumi, N., additional, Fujii, K., additional, Funaba, H., additional, Goto, M., additional, Goto, T., additional, Gradic, D., additional, Gunsu, Y., additional, Hamaguchi, S., additional, Hasegawa, H., additional, Hayashi, Y., additional, Hidalgo, C., additional, Higashiguchi, T., additional, Hirooka, Y., additional, Hishinuma, Y., additional, Horiuchi, R., additional, Ichiguchi, K., additional, Ida, K., additional, Ido, T., additional, Igami, H., additional, Ikeda, K., additional, Ishiguro, S., additional, Ishizaki, R., additional, Ishizawa, A., additional, Ito, A., additional, Ito, Y., additional, Iwamoto, A., additional, Kamio, S., additional, Kamiya, K., additional, Kaneko, O., additional, Kanno, R., additional, Kasahara, H., additional, Kato, D., additional, Kato, T., additional, Kawahata, K., additional, Kawamura, G., additional, Kisaki, M., additional, Kitajima, S., additional, Ko, W.H., additional, Kobayashi, M., additional, Kobayashi, S., additional, Kobayashi, T., additional, Koga, K., additional, Kohyama, A., additional, Kumazawa, R., additional, Lee, J.H., additional, López-Bruna, D., additional, Makino, R., additional, Masuzaki, S., additional, Matsumoto, Y., additional, Matsuura, H., additional, Mitarai, O., additional, Miura, H., additional, Miyazawa, J., additional, Mizuguchi, N., additional, Moon, C., additional, Morita, S., additional, Moritaka, T., additional, Mukai, K., additional, Muroga, T., additional, Muto, S., additional, Mutoh, T., additional, Nagasaka, T., additional, Nagayama, Y., additional, Nakajima, N., additional, Nakanishi, H., additional, Nakano, H., additional, Nakata, M., additional, Narushima, Y., additional, Nishijima, D., additional, Nishimura, A., additional, Nishimura, S., additional, Nishitani, T., additional, Nishiura, M., additional, Nobuta, Y., additional, Noto, H., additional, Nunami, M., additional, Obana, T., additional, Ogawa, K., additional, Ohdachi, S., additional, Ohno, M., additional, Ohno, N., additional, Ohtani, H., additional, Okamoto, M., additional, Oya, Y., additional, Ozaki, T., additional, Peterson, B.J., additional, Preynas, M., additional, Sagara, S., additional, Saito, K., additional, Sakaue, H., additional, Sanpei, A., additional, Satake, S., additional, Sato, M., additional, Saze, T., additional, Schmitz, O., additional, Seki, R., additional, Seki, T., additional, Sharov, I., additional, Shimizu, A., additional, Shiratani, M., additional, Shoji, M., additional, Skinner, C., additional, Soga, R., additional, Stange, T., additional, Suzuki, C., additional, Suzuki, Y., additional, Takada, S., additional, Takahata, K., additional, Takayama, A., additional, Takayama, S., additional, Takemura, Y., additional, Takeuchi, Y., additional, Tamura, H., additional, Tamura, N., additional, Tanaka, H., additional, Tanaka, K., additional, Tanaka, M., additional, Tanaka, T., additional, Tanaka, Y., additional, Toda, S., additional, Todo, Y., additional, Toi, K., additional, Toida, M., additional, Tokitani, M., additional, Tokuzawa, T., additional, Tsuchiya, H., additional, Tsujimura, T., additional, Tsumori, K., additional, Usami, S., additional, Velasco, J.L., additional, Wang, H., additional, Watanabe, T.-H., additional, Watanabe, T., additional, Yagi, J., additional, Yajima, M., additional, Yamada, H., additional, Yamada, I., additional, Yamagishi, O., additional, Yamaguchi, N., additional, Yamamoto, Y., additional, Yanagi, N., additional, Yasuhara, R., additional, Yatsuka, E., additional, Yoshida, N., additional, Yoshinuma, M., additional, Yoshimura, S., additional, and Yoshimura, Y., additional

Published
2017
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29. Analysis of higher harmonics on bidirectional heat pulse propagation experiment in helical and tokamak plasmas

Author

Kobayashi, T., primary, Ida, K., additional, Inagaki, S., additional, Tsuchiya, H., additional, Tamura, N., additional, Choe, G.H., additional, Yun, G.S., additional, Park, H.K., additional, Ko, W.H., additional, Evans, T.E., additional, Austin, M.E., additional, Shafer, M.W., additional, Ono, M., additional, López-bruna, D., additional, Ochando, M.A., additional, Estrada, T., additional, Hidalgo, C., additional, Moon, C., additional, Igami, H., additional, Yoshimura, Y., additional, Tsujimura, T.Ii., additional, Itoh, S.-I., additional, and Itoh, K., additional

Published
2017
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31. 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

33. 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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34. Progress of long pulse discharges by ECH in LHD

Author

Yoshimura, Y., primary, Kasahara, H., additional, Tokitani, M., additional, Sakamoto, R., additional, Ueda, Y., additional, Ito, S., additional, Okada, K., additional, Kubo, S., additional, Shimozuma, T., additional, Igami, H., additional, Takahashi, H., additional, Tsujimura, T.I., additional, Makino, R., additional, Kobayashi, S., additional, Mizuno, Y., additional, Akiyama, T., additional, Ashikawa, N., additional, Masuzaki, S., additional, Motojima, G., additional, Shoji, M., additional, Suzuki, C., additional, Tanaka, H., additional, Tanaka, K., additional, Tokuzawa, T., additional, Tsuchiya, H., additional, Yamada, I., additional, Goto, Y., additional, Yamada, H., additional, Mutoh, T., additional, Komori, A., additional, and Takeiri, Y., additional

Published
2016
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35. Development and application of a ray-tracing code integrating with 3D equilibrium mapping in LHD ECH experiments

Author

Ii Tsujimura, T., primary, Kubo, S., additional, Takahashi, H., additional, Makino, R., additional, Seki, R., additional, Yoshimura, Y., additional, Igami, H., additional, Shimozuma, T., additional, Ida, K., additional, Suzuki, C., additional, Emoto, M., additional, Yokoyama, M., additional, Kobayashi, T., additional, Moon, C., additional, Nagaoka, K., additional, Osakabe, M., additional, Kobayashi, S., additional, Ito, S., additional, Mizuno, Y., additional, Okada, K., additional, Ejiri, A., additional, and Mutoh, T., additional

Published
2015
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36. Integrated discharge scenario for high-temperature helical plasma in LHD

Author

Nagaoka, K., primary, Takahashi, H., additional, Murakami, S., additional, Nakano, H., additional, Takeiri, Y., additional, Tsuchiya, H., additional, Osakabe, M., additional, Ida, K., additional, Yokoyama, M., additional, Yoshinuma, M., additional, Morita, S., additional, Goto, M., additional, Oishi, T., additional, Pablant, N., additional, Fujii, K., additional, Tanaka, K., additional, Tamura, N., additional, Nakamura, Y., additional, Du, X., additional, Ido, T., additional, Shimizu, A., additional, Kubo, S., additional, Igami, H., additional, Seki, R., additional, Suzuki, C., additional, Suzuki, Y., additional, Tsumori, K., additional, Ikeda, K., additional, Kisaki, M., additional, Yoshimura, Y., additional, Shimozuma, T., additional, Seki, T., additional, Saito, K., additional, Kasahara, H., additional, Kamio, S., additional, Mutoh, T., additional, Kaneko, O., additional, Yamada, H., additional, and Komori, A., additional

Published
2015
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37. Development of gyrotrons for fusion with power exceeding 1 MW over a wide frequency range

Author

Kariya, T., primary, Imai, T., additional, Minami, R., additional, Numakura, T., additional, Eguchi, T., additional, Kato, T., additional, Endo, Y., additional, Ichimura, M., additional, Shimozuma, T., additional, Kubo, S., additional, Takahashi, H., additional, Yoshimura, Y., additional, Igami, H., additional, Ito, S., additional, Mutoh, T., additional, Sakamoto, K., additional, Idei, H., additional, Zushi, H., additional, Nagasaki, K., additional, Sano, F., additional, Ono, M., additional, and Mitsunaka, Y., additional

Published
2015
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38. 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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43. High-power and Steady-state Operation of ICRF Heating in the Large Helical Device.

Author

Mutoh, T., Seki, T., Saito, K., Kasahara, H., Seki, R., Kamio, S., Kumazawa, R., Kubo, S., Shimozuma, T., Yoshimura, Y., Igami, H., Takahashi, H., Ii, T., Makino, R., Nagaoka, K., Nomura, G., and Shinya, T.

Subjects
ELECTRIC power, CYCLOTRON resonance, ELECTRIC impedance, ELECTRON temperature, ANTENNAS (Electronics)
Abstract

Recent progress in an ion cyclotron range of frequencies (ICRF) heating system and experiment results in a Large Helical Device (LHD) are reported. Three kinds of ICRF antenna pairs were installed in the LHD, and the operation power regimes were extended up to 4.5 MW; also, the steady-state operation was extended for more than 45 min in LHD at a MW power level. We studied ICRF heating physics in heliotron configuration using a Hand Shake type (HAS) antenna, Field Aligned Impedance Transforming (FAIT) antenna, and Poloidal Array (PA) antenna, and established the optimum minority-ion heating scenario in an LHD. The FAIT antenna having a novel impedance transformer inside the vacuum chamber could reduce the VSWR and successfully injected a higher power to plasma. We tested the PA antennas completely removing the Faraday-shield pipes to avoid breakdown and to increase the plasma coupling. The heating performance was almost the same as other antennas; however, the heating efficiency was degraded when the gap between the antenna and plasma surface was large. Using these three kinds of antennas, ICRF heating could contribute to raising the plasma beta with the second- and third-harmonic cyclotron heating mode, and also to raising the ion temperature as discharge cleaning tools. In 2014, steady-state operation plasma with a line-averaged electron density of 1.2 x 1019 m-3, ion and electron temperature of 2 keV, and plasma sustainment time of 48 min was achieved with ICH and ECH heating power of 1.2 MW for majority helium with minority hydrogen. In 2015, the higherpower steady-state operation with a heating power of up to 3 MW was tested with higher density of 3 x 1019 m-3. [ABSTRACT FROM AUTHOR]

Published
2015
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44. 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

45. High Power Heating and Steady State Operation in the Large Helical Device

Author

Mutoh*, T., Nagaoka, K., Takahashi, H., Kasahara, H., Osakabe, M., Kubo, S., Shimozuma, T., Yoshimura, Y., Tsumori, K., Seki, T., Saito, K., Igami, H., Nakano, H., Ikeda, K., Kisaki, M., Seki, R., Kamio, S., Ii, T., Nakamura, Y., Takeiri, Y., and Kaneko, O.

Abstract

Recent advances in the high power and steady state heating system and experiment results of the Large Helical Device (LHD) are reviewed in this paper. Plasma performance is extended largely through high power NBI, ECH and steady state ICRF heating devices, and improved operation techniques. The NBI of a 28 MW has extended the plasma parameter regime such as ion ITB plasmas, has a central ion temperature of more than 8 keV, and the extremely high-density plasmas ten times higher than the tokamak limit. An ECH system with seven gyrotrons (total power of 4.6MW) has been operated for pre-ionization and plasma heating. The high electron temperature regime was extended toward a higher density regime and a central electron temperature of 13.5 keV was achieved with a line-averaged electron density of ne= 1 x 1019m-3. Steady state operation plasma with ne= 1.2 x 1019m-3, ion and electron temperature of 2 keV, and plasma sustainment time of 48 min was achieved with ICH and ECH heating power of 1.2 MW for majority helium with minority hydrogen.

Published
2015
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46. Power and polarization monitor development for high power millimeter-wave.

Author

Makino, R., Kubo, S., Kobayashi, K., Kobayashi, S., Shimozuma, T., Yoshimura, Y., Igami, H., Takahashi, H., and Mutoh, T.

Subjects
MILLIMETER waves, POLARIZATION (Electricity), ELECTRIC lines, CYCLOTRON resonance, ELECTRIC fields
Abstract

A new type monitor of power and polarization states of millimeter-waves has been developed to be installed at a miter-bend, which is a part of transmission lines of millimeter-waves, for electron cyclotron resonance heating on the Large Helical Device. The monitor measures amplitudes and phase difference of the electric field of the two orthogonal polarizations which are needed for calculation of the power and polarization states of waves. The power and phase differences of two orthogonal polarizations were successfully detected simultaneously. [ABSTRACT FROM AUTHOR]

Published
2014
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47. Fast nondiffusive response of heat and turbulence pulse propagation.

Author

Kenmochi N, Ida K, Tokuzawa T, Mizuno Y, Yasuhara R, Funaba H, Uehara H, Den Hartog DJ, Yoshinuma M, Takemura Y, Igami H, and Yanai R

Abstract

The experimental findings from the Large Helical Device have demonstrated a fast, nondiffusive behavior during the propagation of heat pulses, with an observed increase in speed with reduction in their temporal width. Concurrent propagation of the temperature gradient and turbulence, in a timeframe spanning from a few milliseconds to tens of milliseconds, aligned with the avalanche model. These results indicate that the more spatiotemporally localized the heat and turbulence pulses are, the greater the deviation of the plasma from its equilibrium state, coupled with faster propagation velocity. This insight is pivotal for future fusion reactors, which necessitate the maintenance of a steady-state, non-equilibrium condition., (© 2024. The Author(s).)

Published
2024
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48. Impact of Magnetic Field Configuration on Heat Transport in Stellarators and Heliotrons.

Author

Warmer F, Tanaka K, Xanthopoulos P, Nunami M, Nakata M, Beidler CD, Bozhenkov SA, Beurskens MNA, Brunner KJ, Ford OP, Fuchert G, Funaba H, Geiger J, Gradic D, Ida K, Igami H, Kubo S, Langenberg A, Laqua HP, Lazerson S, Morisaki T, Osakabe M, Pablant N, Pasch E, Peterson B, Satake S, Seki R, Shimozuma T, Smith HM, Stange T, Stechow AV, Sugama H, Suzuki Y, Takahashi H, Tokuzawa T, Tsujimura T, Turkin Y, Wolf RC, Yamada I, Yanai R, Yasuhara R, Yokoyama M, Yoshimura Y, Yoshinuma M, Zhang D, W-X Team, and Lhd Experimental Group

Abstract

We assess the magnetic field configuration in modern fusion devices by comparing experiments with the same heating power, between a stellarator and a heliotron. The key role of turbulence is evident in the optimized stellarator, while neoclassical processes largely determine the transport in the heliotron device. Gyrokinetic simulations elucidate the underlying mechanisms promoting stronger ion scale turbulence in the stellarator. Similar plasma performances in these experiments suggests that neoclassical and turbulent transport should both be optimized in next step reactor designs.

Published
2021
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49. Photosensitized E/Z isomerization of (all-E)-lycopene aiming at practical applications.

Author

Honda M, Igami H, Kawana T, Hayashi K, Takehara M, Inoue Y, and Kitamura C

Subjects
Antioxidants chemistry, Chromatography, High Pressure Liquid, Food Handling methods, Isomerism, Lycopene, Solanum lycopersicum chemistry, Carotenoids chemistry, Photosensitizing Agents chemistry
Abstract

Photoisomerization of (all-E)-lycopene to the corresponding Z-isomers was investigated under visible to middle-infrared light irradiation in the presence of several sensitizers, including edible ones. Highly purified (all-E)-lycopene from tomato paste was isomerized to Z-isomers to the extent of 46.4-57.4% after irradiation with the sensitizers for 60 min in acetone, in which a thermodynamically stable isomer of (5Z)-lycopene was predominantly generated, whereas kinetically preferable (9Z)- and (13Z)-lycopenes were dominant without sensitizer. Examination of the time course of photoisomerization demonstrated that the highest isomerization efficiency (80.4%) was attained using erythrosine as the sensitizer under 480-600 nm light irradiation in hexane for 60 min, a protocol that successfully suppressed the degradation of lycopene. (5Z)-Lycopene, reported as a more bioavailable isomer, was again predominantly produced with erythrosine and rose bengal in each solvent.

Published
2014
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