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19 results on '"WATANABE, Kiyomasa Y."'

1. Experimental observation of response to Resonant Magnetic Perturbation and its hysteresis in LHD

Author

NARUSHIMA, Yoshiro, SAKAKIBARA, Satoru, OHDACHI, Satoshi, SUZUKI, Yasuhiro, WATANABE, Kiyomasa Y., NISHIMURA, Shin, SATAKE, Shinsuke, HUANG, B, FURUKAWA, Masaru, TAKEMURA, Yuki, IDA, Katsumi, YOSHINUMA, Mikiro, YAMADA, Ichihiro, the, LHD experimental group, NARUSHIMA, Yoshiro, SAKAKIBARA, Satoru, OHDACHI, Satoshi, SUZUKI, Yasuhiro, WATANABE, Kiyomasa Y., NISHIMURA, Shin, SATAKE, Shinsuke, HUANG, B, FURUKAWA, Masaru, TAKEMURA, Yuki, IDA, Katsumi, YOSHINUMA, Mikiro, YAMADA, Ichihiro, and the, LHD experimental group

Abstract

The magnetic island in the large helical device (LHD) shows the dynamic behaviour of the healing/growth transition withthe hysteretic behaviour. The thresholds of plasma beta and poloidal flow for island healing are larger than that for growth.The threshold of resonant magnetic perturbation (RMP) for healing is smaller than that for growth. Furthermore, thresholds of the amplitude of RMP depend on the magnetic axis position Rax in the LHD. The RMP threshold increases as the magnetic axis position Rax increases. The poloidal viscosity may be considered as a candidate to explain the experimental observation from the viewpoint of the relationship between the electromagnetic torque and the viscous torque., source:https://iopscience.iop.org/article/10.1088/0029-5515/55/7/073004

Published
2021

2. Developments of frequency comb microwave reflectometer for the interchange mode observations in LHD plasma

Author

Soga, R., TOKUZAWA, Tokihiko, WATANABE, Kiyomasa Y., TANAKA, Kenji, YAMADA, Ichihiro, INAGAKI, Shigeru, KASUYA, Naohiro, Soga, R., TOKUZAWA, Tokihiko, WATANABE, Kiyomasa Y., TANAKA, Kenji, YAMADA, Ichihiro, INAGAKI, Shigeru, and KASUYA, Naohiro

Abstract

We have upgraded the multi-channel microwave reflectometer system which uses a frequency comb as a source and measure the distribution of the density fluctuation caused by magneto-hydro dynamics instability. The previous multi-channel system was composed of the Ka-band, and the U-band system has been developed. Currently, the U-band system has eight frequency channels, which are 43.0, 45.0, 47.0, 49.0, 51.0, 53.0, 55.0, and 57.0 GHz, in U-band. Before the installation to the Large Helical Device (LHD), several tests for understanding the system characteristics, which are the phase responsibility, the linearity of output signal, and others, have been carried out. The in situ calibration in LHD has been done for the cross reference. In the neutral beam injected plasma experiments, we can observe the density fluctuation of the interchange mode and obtain the radial distribution of fluctuation amplitude., source:Citation R. Soga et al 2016 JINST 11 C02009, source:https://doi.org/10.1088/1748-0221/11/02/C02009

Published
2021

3. Linear MHD analyses of locked-mode-like instabilities in LHD

Author

Okamoto, M., Tomita, H., WATANABE, Kiyomasa Y., SATO, Masahiko, TAKEMURA, Yuki, SAKAKIBARA, Satoru, IDA, Katsumi, YOSHINUMA, Mikiro, LHD, Experiment Group, Okamoto, M., Tomita, H., WATANABE, Kiyomasa Y., SATO, Masahiko, TAKEMURA, Yuki, SAKAKIBARA, Satoru, IDA, Katsumi, YOSHINUMA, Mikiro, and LHD, Experiment Group

Abstract

To investigate the driving mechanism of the locked-mode-like instability observed in the large helical device, we reconstruct the magnetohydrodynamic (MHD) equilibria consistent with the measurement and identify a dominant MHD instability in the precursor phase based on linear MHD analyses. From the dependence of the linear growth rate on the magnetic Reynolds number, the radial mode structure of the electrostatic potential fluctuation and other indices, the ideal interchange mode is found to be dominant. Moreover, it is found that the Mercier parameter, DI, becomes much larger than 0.3 during the phase, while the precursor has constant frequency and fluctuation amplitude. Therefore, DI ≫ 0.3 is a good index of the on-set condition of the minor collapse itself. It is also found that the achievement of DI ≫ 0.3 is due to the movement of the resonant surface to the inner plasma region, which corresponds to the larger pressure gradient region., source:Citation M. Okamoto et al 2021 Nucl. Fusion 61 046005, source:https://doi.org/10.1088/1741-4326/abd7ba

Published
2021

4. Experimental observation of response to Resonant Magnetic Perturbation and its hysteresis in LHD

Author

NARUSHIMA, Yoshiro, SAKAKIBARA, Satoru, OHDACHI, Satoshi, SUZUKI, Yasuhiro, WATANABE, Kiyomasa Y., NISHIMURA, Shin, SATAKE, Shinsuke, HUANG, B, FURUKAWA, Masaru, TAKEMURA, Yuki, IDA, Katsumi, YOSHINUMA, Mikiro, YAMADA, Ichihiro, and the, LHD experimental group

Subjects
Physics, Nuclear and High Energy Physics, helical plasma, Condensed matter physics, business.industry, Plasma, Condensed Matter Physics, Magnetic field, Viscosity, Hysteresis, Large Helical Device, Optics, Amplitude, Beta (plasma physics), plasma respnse, Torque, business, magnetic island
Abstract

The magnetic island in the large helical device (LHD) shows the dynamic behaviour of the healing/growth transition with the hysteretic behaviour. The thresholds of plasma beta and poloidal flow for island healing are larger than that for growth. The threshold of resonant magnetic perturbation (RMP) for healing is smaller than that for growth. Furthermore, thresholds of the amplitude of RMP depend on the magnetic axis position Rax in the LHD. The RMP threshold increases as the magnetic axis position Rax increases. The poloidal viscosity may be considered as a candidate to explain the experimental observation from the viewpoint of the relationship between the electromagnetic torque and the viscous torque.

Published
2015
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5. Relationships between the Prediction of Linear MHD Stability Criteria and the Experiment in LHD

Author

WATANABE, Kiyomasa Y., NARUSHIMA, Yoshiro, SAKAKIBARA, Satoru, OHDACHI, Satoshi, TOI, Kazuo, COOPER, Antony W., NAKAJIMA, Noriyoshi, NARIHARA, Kazumichi, TANAKA, Kenji, LHD, Experimental Group, Kiyomasa Y., WATANABE, Yoshiro, NARUSHIMA, Satoru, SAKAKIBARA, Satoshi, OHDACHI, Kazuo, TOI, Antony W., COOPER, Noriyoshi, NAKAJIMA, Kazumichi, NARIHARA, Kenji, TANAKA, and experimental group, LHD

Subjects
Physics::Plasma Physics, Physics::Space Physics, MHD stability, heliotron, beta limit
Abstract

We analyze the relationship between the experimentally observed pressure gradients at resonant rational surfaces and the theoretically predicted ideal magnetohydrodynamics (MHD) unstable region of global modes in the large helical device (LHD). According to the stability analysis of the ideal MHD modes with a low toroidal mode number, we find that the ideal MHD mode gives a constraint on the operational regime of the pressure gradients in the core. In the edge, a clear saturation of the pressure gradients due to the ideal MHD instability has not been observed up to the high beta regime around 3% as the volume-averaged toridal beta value, where global ideal MHD modes are predictedto be unstable.

Published
2004

8. Physics of Heliotron J Confinement

Author

SANO, Fumimichi, primary, MIZUUCHI, Tohru, additional, NAGASAKI, Kazunobu, additional, HANATANI, Kiyoshi, additional, OKADA, Hiroyuki, additional, NAKAMURA, Yuji, additional, MINAMI, Takashi, additional, KOBAYASHI, Shinji, additional, YAMAMOTO, Satoshi, additional, KONOSHIMA, Shigeru, additional, OHSHIMA, Shinsuke, additional, TAKEUCHI, Masaki, additional, IJIRI, Yoshiyuki, additional, YAGUCHI, Keiji, additional, SENJU, Tohru, additional, SHIBANO, Masashi, additional, TOHSHI, Kiyoshi, additional, SAKAMOTO, Kinzou, additional, MATSUYAMA, Akinobu, additional, MUKAI, Kiyofumi, additional, MINAMI, Keishi, additional, KISHI, Shintarou, additional, LEE, Hyunyong, additional, TAKABATAKE, Yu, additional, YASHIRO, Hiroaki, additional, YAMAMOTO, Kento, additional, NOMURA, Kohta, additional, SUWA, Masashige, additional, YOSHINO, Hayao, additional, MURAKAMI, Sadayoshi, additional, MUTOH, Takashi, additional, TAKEIRI, Yasuhiko, additional, NAGAOKA, Kenichi, additional, OKAMURA, Shoichi, additional, WATANABE, Kiyomasa Y., additional, YOKOYAMA, Masayuki, additional, SUZUKI, Yasuhiro, additional, YOSHIMURA, Yasuo, additional, NISHIMURA, Shin, additional, TAMURA, Naoki, additional, SAKAKIBARA, Satoru, additional, MOTOJIMA, Gen, additional, NISHINO, Nobuhiro, additional, FUKUDA, Takeshi, additional, NAKASHIMA, Yousuke, additional, FENG, Zhen, additional, YANG, Qingwei, additional, FERNÁNDEZ, Angela, additional, CAPPA, Alvaro, additional, TRIBALDOS, Victor, additional, BLACKWELL, Boyd D., additional, and CHECHKIN, Viktor V., additional

Published
2010
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11. Effect of Rotational Transform and Magnetic Shear on Confinement of Stellarators

Author

ASCASÍBAR, Enrique, primary, LÓPEZ-BRUNA, Daniel, additional, CASTEJÓN, Francisco, additional, VARGAS, Víctor I., additional, TRIBALDOS, Víctor, additional, MAASSBERG, Henning, additional, BEIDLER, Craig D., additional, BRAKEL, Rudolf, additional, DINKLAGE, Andreas, additional, GEIGER, Joachim, additional, HARRIS, Jeffrey H., additional, KUS, Andreas, additional, MIZUUCHI, Tohru, additional, MURAKAMI, Sadayoshi, additional, OKAMURA, Shoichi, additional, PREUSS, Roland, additional, SANO, Fumimichi, additional, STROTH, Ulrich, additional, SUZUKI, Yasuhiro, additional, TALMADGE, Joseph, additional, TURKIN, Yuri, additional, WATANABE, Kiyomasa Y., additional, YAMADA, Hiroshi, additional, and YOKOYAMA, Masayuki, additional

Published
2008
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12. Magnetohydrodynamic Stability of Free-Boundary Quasi-Axisymmetric Stellarator Equilibria with Finite Bootstrap Current

Author

Cooper, Wilfred Anthony, primary, Margalet, Sergi Ferrando i, additional, Allfrey, Simon J., additional, Kißlinger, Johann, additional, Wobig, Horst F. G., additional, Narushima, Yoshiro, additional, Okamura, Shoichi, additional, Suzuki, Chihiro, additional, Watanabe, Kiyomasa Y., additional, Yamazaki, Kozo, additional, and Isaev, Maxim Yu., additional

Published
2004
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18. Progress of High-Beta Experiments in Stellarator/Heliotron

Author

Watanabe, Kiyomasa Y., Weller, Arthur, Sakakibara, Satoru, Narushima, Yoshiro, Ohdachi, Satoshi, Narihara, Kazumichi, Tanaka, Kenji, Ida, Katsumi, Toi, Kazuo, Yamada, Hiroshi, Suzuki, Yasuhiro, and Kaneko, Osamu

Abstract

AbstractRecently, dramatic progress has been achieved in the study of helical systems with high-beta experiments. Discharges with more than 3% beta plasmas have been achieved in Large Helical Device (LHD) and Wendelstein 7-AS (W7-AS). Although magnetohydrodynamic (MHD) instabilities affect local pressure gradients, the global transport property does not seem to limit the achieved beta value in either device. We summarize the LHD high-beta properties in MHD stability, equilibrium, and transport, and we show the relationship between the experimentally achieved parameters and theoretical predictions. We contrast the LHD results with the W7-AS high-beta properties. In both devices, stationary discharges in the definitely MHD unstable region have not been observed. We mention the key issue for achievement of the beta values >5%.

Published
2004
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19. Drift stabilization of ballooning modes in a high-$\langle \beta \rangle$ LHD configuration

Author

Brocher, Lucie, Cooper, W. Anthony, Graves, Jonathan P., Cooper, Guy A., Narushima, Yoshiro, and Watanabe, Kiyomasa Y.

Subjects
Physics::Plasma Physics, High Energy Physics::Lattice, diamagnetic drifts, LHD, energetic particles, ballooning
Abstract

Ideal MHD yields at best inconclusive predictions about the stability of the LHD heliotron for $\langle \beta \rangle \geq 3\%$. We investigate the impact of the drift stabilization of ballooning modes for the inward shifted LHD configuration (vacuum magnetic axis $R_0 \sim 3.5m $). The background equilibrium is considered anisotropic in which the neutral beam ions contribute about $1/4$ fraction of the total diamagnetic beta, $\langle \beta_{dia} \rangle$. A drift corrected ballooning mode equation obtained from the linearized gyrokinetic equation is expanded assuming that the hot particle drifts are much larger than the mode frequency. The fast particle pressure gradients contribute weakly to both the instability drive and the diamagnetic drift stabilization (which is dominated by the thermal ion diamagnetic drifts) for $\langle \beta_{dia} \in [0,4.8] \%$. In the single fluid limit (diamagnetic drifts ignored), the thermal pressure gradients drive ballooning modes in a broad region encompassing the outer $60-90 \%$ of the plasma volume at $\langle \beta_{dia} \rangle \approx 4.8 \%$. To stabilize these modes, we find that diamagnetic drift corrections must be invoked (mainly due to the thermal ions). The energetic ion diamagnetic drifts play a role only for low wave number values, $k_{\alpha}\leq 8$. It has been verified that the fast particle drift ordering imposed by the model is amply satisfied for on-axis hot particle to thermal density $N_{h0}/N_{i0} \approx 1\%$ even at high $\langle \beta_{dia} \rangle$.

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