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17 results on '"Wakatsuki, T."'

2. Results of lower hybrid wave experiments using a dielectric loaded waveguide array antenna on TST-2

Author

Wakatsuki, T., primary, Ejiri, A., additional, Shinya, T., additional, Takase, Y., additional, Furui, H., additional, Hiratsuka, J., additional, Imamura, K., additional, Inada, T., additional, Kakuda, H., additional, Kasahara, H., additional, Nagashima, Y., additional, Nakamura, K., additional, Nakanishi, A., additional, Oosako, T., additional, Saito, K., additional, Seki, T., additional, Shimpo, F., additional, Sonehara, M., additional, Togashi, H., additional, Tsuda, S., additional, Tsujii, N., additional, and Yamaguchi, T., additional

Published
2014
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3. Characteristics of a novel lower hybrid wave antenna for the TST-2 spherical tokamak

Author

Takase, Y., primary, Moeller, C. P., additional, Shinya, T., additional, Wakatsuki, T., additional, Ejiri, A., additional, Furui, H., additional, Hiratsuka, J., additional, Imamura, K., additional, Inada, T., additional, Kakuda, H., additional, Nakamura, K., additional, Nakanishi, A., additional, Oosako, T., additional, Sonehara, M., additional, Togashi, H., additional, Tsuda, S., additional, Tsujii, N., additional, and Yamaguchi, T., additional

Published
2014
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4. Characteristics of a Novel Lower Hybrid Wave Antenna for the TST-2 Spherical Tokamak.

Author

Takase, Y., Moeller, C. P., Shinya, T., Wakatsuki, T., Ejiri, A., Furui, H., Hiratsuka, J., Imamura, K., Inada, T., Kakuda, H., Nakamura, K., Nakanishi, A., Oosako, T., Sonehara, M., Togashia, H., Tsuda, S., Tsujii, N., and Yamaguchi, T.

Subjects
ANTENNA arrays, PLASMA waves, PLASMA physics, PLASMA hybrid waves, PLASMA antennas, PLASMA devices
Abstract

A new type of traveling wave antenna which excites the lower hybrid wave directly was developed. This antenna is similar to the inductively-coupled combline antenna in that only the first element of the antenna array is excited externally, and subsequent elements are excited passively by mutual coupling between adjacent elements. The main difference is that whereas the inductively-coupled combline antenna makes use of mutual inductance, the presently proposed antenna makes use of mutual capacitance. The radiating elements are located at the voltage maximum, and the electric field induced in the plasma is in the toroidal direction rather than the poloidal direction, matching the polarization of the lower hybrid wave. Optimization studies were carried out to obtain a band-pass characteristic centered around 200 MHz, and a unidirectional wavenumber spectrum with the parallel index of refraction corresponding to approximately 5. Plasma current ramp-up to 2 kA has been achieved on the TST-2 spherical tokamak with 12 kW of RF power at 200 MHz during the initial experimental period using this antenna. Further optimization studies are being performed. [ABSTRACT FROM AUTHOR]

Published
2014
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5. Development of steady-state operation using ICH in the LHD.

Author

Kasahara, H., Seki, T., Saito, K., Seki, R., Yoshimura, Y., Kubo, S., Shimozuma, T., Igami, H., Takahashi, H., Nagasaki, K., Ueda, Y., Tokitani, M., Ashikawa, N., Shoji, M., Wakatsuki, T., Kamio, S., Tsuchiya, H., Tanaka, H., Yoshimura, S., and Tamura, N.

Subjects
STEADY state conduction, CYCLOTRONS, ELECTRON cyclotron resonance heating, ELECTRIC fields, BOLOMETERS, FUSION reactor divertors, IONS, ELECTRON temperature
Abstract

doi: Long-pulse discharge with the electron density ne0 of 1 x 1019 m-3, electron temperature Te0 of 2.5 keV, discharge length tdis of 19 minutes and heating power Pinject of 1MW, is demonstrated using the HAS antenna and the PA antenna for ion cyclotron heating (ICH) and increasing in the power of electron cyclotron heating (ECH). The HAS antenna is designed to phase dipole and excite ideal fast wave with parallel electric field kept small, and low impurity generation and accumulation are achieved on the steady-state discharge by weak parasitic heating around antennas. On the long-pulse discharge, the radiation measured by bolometer is kept smaller than 20% for injection power, and the heat load to divertor is approximately 60 % with low energetic particle losses. The heat load ratio to divertor is not as a function of injection power around 1MW, and energy confinement has been kept during the steady-state discharge. [ABSTRACT FROM AUTHOR]

Published
2014
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6. Plasma Curent Start-up Experiment using Waves in the Lower Hybrid Frequency Range in TST-2

Author

Takase, Y., primary, Wakatsuki, T., additional, Ejiri, A., additional, Kakuda, H., additional, Moeller, C. P., additional, Ambo, T., additional, Hanashima, K., additional, Hiratsuka, J., additional, Kasahara, H., additional, Kumazawa, R., additional, Nagashima, Y., additional, Saito, K., additional, Sakamoto, T., additional, Seki, T., additional, Shimpo, F., additional, Shino, R., additional, Sonehara, M., additional, Watanabe, O., additional, Yamaguchi, T., additional, Phillips, Cynthia K., additional, and Wilson, James R., additional

Published
2011
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7. Plans for Lower Hybrid Current Drive Experiment using a Dielectric Loaded Waveguide Array Antenna in TST-2

Author

Wakatsuki, T., primary, Ejiri, A., additional, Kakuda, H., additional, Meneghini, O., additional, Shiraiwa, S., additional, Takase, Y., additional, Wright, J. C., additional, Ambo, T., additional, Hanashima, K., additional, Hiratsuka, J., additional, Nagashima, Y., additional, Sakamoto, T., additional, Shino, R., additional, Sonehara, M., additional, Yamaguchi, T., additional, Watanabe, O., additional, Phillips, Cynthia K., additional, and Wilson, James R., additional

Published
2011
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10. Equilibrium Analysis of EC-Sustained and RF-Sustained ST Plasmas

Author

Takase, Y., primary, Ejiri, A., additional, Nagashima, Y., additional, Watanabe, O., additional, An, B. I., additional, Hayashi, H., additional, Hanashima, K., additional, Hiratsuka, J., additional, Kakuda, H., additional, Kobayashi, H., additional, Kurashina, H., additional, Matsuzawa, H., additional, Oosako, T., additional, Sakamoto, T., additional, Wakatsuki, T., additional, Yamada, K., additional, Yamaguchi, T., additional, Bobkov, Volodymyr, additional, and Noterdaeme, Jean-Marie, additional

Published
2009
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12. Plasma Curent Start-up Experiment using Waves in the Lower Hybrid Frequency Range in TST-2.

Author

Takase, Y., Wakatsuki, T., Ejiri, A., Kakuda, H., Moeller, C. P., Ambo, T., Hanashima, K., Hiratsuka, J., Kasahara, H., Kumazawa, R., Nagashima, Y., Saito, K., Sakamoto, T., Seki, T., Shimpo, F., Shino, R., Sonehara, M., Watanabe, O., and Yamaguchi, T.

Subjects
PLASMA gases, ELECTRIC currents, RADIO frequency, ELECTRIC displacement, TOKAMAKS, PERMITTIVITY, STATISTICAL bootstrapping, ELECTRONIC excitation, ELECTRON temperature
Abstract

Noninductive plasma current (Ip) start-up experiments using RF power in the lower hybrid frequency range are being conducted on the TST-2 spherical tokamak. The lower hybrid wave (LHW) has demonstrated efficient current drive in conventional tokamaks. However, in spherical tokamak (ST) plasmas with very high dielectric constants (;[variant_greek_epsilon]∼ωpe2/Ωe2>1), accessibility of the LHW to the plasma core is severely limited. Our approach is to keep the plasma density low (such that [variant_greek_epsilon]∼1) during Ip ramp-up. Once Ip reaches a level sufficiently high for neutral beam current drive, plasma can be densified and transformed into an advanced tokamak plasma dominated by the self-driven bootstrap current. Initial plasma start-up experiments were performed on TST-2 using a combline antenna which excites a traveling fast wave. After formation of toroidal flux surfaces, RF power and vertical field were ramped up to increase Ip. Up to 12 kA of Ip has been obtained by this method. Soft X-ray measurements indicate that the electron temperature increases as Ip increases, and hard X-ray spectroscopy indicates that energetic electrons build up as Ip is ramped up. [ABSTRACT FROM AUTHOR]

Published
2011
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