Plasma current start-up experiments using a dielectric-loaded waveguide array antenna in the TST-2 spherical tokamak

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

doi:10.1088/0029-5515/54/9/093014

Plasma current start-up experiments using a dielectric-loaded waveguide array antenna in the TST-2 spherical tokamak

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

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14 Citations (Scopus)

Abstract

Plasma current start-up and ramp-up using the lower hybrid wave (LHW) were investigated on the TST-2 spherical tokamak. The LHW was launched by a dielectric-loaded waveguide array (grill) antenna. The antenna-plasma coupling of this antenna deteriorates as the input power exceeds several kW. This deterioration is believed to be caused by the density depletion due to the ponderomotive force. This conjecture was confirmed by the measurement of density reduction and the result of a non-linear full wave numerical calculation based on the finite element method (FEM). The plasma current was started and ramped up to 10 kA using this antenna. The ability of this grill antenna to excite the LHW with different n_∥ = ck_∥/ω was used to identify the most favourable n_∥ spectrum for plasma current ramp-up. It was found that effective current drive can be achieved by the LHW with n_∥ less than 6. However, even in this case, the energetic electrons which account for a large fraction of the driven current, are lost rapidly because the poloidal field generated by this level of plasma current is not sufficient to confine high energy electrons.

Original language	English
Article number	093014
Journal	Nuclear Fusion
Volume	54
Issue number	9
DOIs	https://doi.org/10.1088/0029-5515/54/9/093014
Publication status	Published - Aug 19 2014

All Science Journal Classification (ASJC) codes

Nuclear and High Energy Physics
Condensed Matter Physics

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10.1088/0029-5515/54/9/093014

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Wakatsuki, T., Ejiri, A., Shinya, T., Takase, Y., Furui, H., Hiratsuka, J., Imamura, K., Inada, T., Kakuda, H., Kasahara, H., Nagashima, Y., Nakamura, K., Nakanishi, A., Oosako, T., Saito, K., Seki, T., Sonehara, M., Togashi, H., Tsuda, S., ... Yamaguchi, T. (2014). Plasma current start-up experiments using a dielectric-loaded waveguide array antenna in the TST-2 spherical tokamak. Nuclear Fusion, 54(9), Article 093014. https://doi.org/10.1088/0029-5515/54/9/093014

Wakatsuki, T, Ejiri, A, Shinya, T, Takase, Y, Furui, H, Hiratsuka, J, Imamura, K, Inada, T, Kakuda, H, Kasahara, H, Nagashima, Y, Nakamura, K, Nakanishi, A, Oosako, T, Saito, K, Seki, T, Sonehara, M, Togashi, H, Tsuda, S, Tsujii, N & Yamaguchi, T 2014, 'Plasma current start-up experiments using a dielectric-loaded waveguide array antenna in the TST-2 spherical tokamak', Nuclear Fusion, vol. 54, no. 9, 093014. https://doi.org/10.1088/0029-5515/54/9/093014

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title = "Plasma current start-up experiments using a dielectric-loaded waveguide array antenna in the TST-2 spherical tokamak",

abstract = "Plasma current start-up and ramp-up using the lower hybrid wave (LHW) were investigated on the TST-2 spherical tokamak. The LHW was launched by a dielectric-loaded waveguide array (grill) antenna. The antenna-plasma coupling of this antenna deteriorates as the input power exceeds several kW. This deterioration is believed to be caused by the density depletion due to the ponderomotive force. This conjecture was confirmed by the measurement of density reduction and the result of a non-linear full wave numerical calculation based on the finite element method (FEM). The plasma current was started and ramped up to 10 kA using this antenna. The ability of this grill antenna to excite the LHW with different n∥ = ck∥/ω was used to identify the most favourable n∥ spectrum for plasma current ramp-up. It was found that effective current drive can be achieved by the LHW with n∥ less than 6. However, even in this case, the energetic electrons which account for a large fraction of the driven current, are lost rapidly because the poloidal field generated by this level of plasma current is not sufficient to confine high energy electrons.",

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

note = "Funding Information: This work is supported by JSPS Grant-in-Aid for Scientific Research (S) 21226021 and Grant-in-Aid for JSPS fellows, and by NIFS Collaboration Research program NIFS12KNWR001. Publisher Copyright: {\textcopyright} 2014 IAEA, Vienna.",

year = "2014",

month = aug,

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doi = "10.1088/0029-5515/54/9/093014",

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T1 - Plasma current start-up experiments using a dielectric-loaded waveguide array antenna in the TST-2 spherical tokamak

AU - Wakatsuki, T.

AU - Ejiri, A.

AU - Shinya, T.

AU - Takase, Y.

AU - Furui, H.

AU - Hiratsuka, J.

AU - Imamura, K.

AU - Inada, T.

AU - Kakuda, H.

AU - Kasahara, H.

AU - Nagashima, Y.

AU - Nakamura, K.

AU - Nakanishi, A.

AU - Oosako, T.

AU - Saito, K.

AU - Seki, T.

AU - Sonehara, M.

AU - Togashi, H.

AU - Tsuda, S.

AU - Tsujii, N.

AU - Yamaguchi, T.

N1 - Funding Information: This work is supported by JSPS Grant-in-Aid for Scientific Research (S) 21226021 and Grant-in-Aid for JSPS fellows, and by NIFS Collaboration Research program NIFS12KNWR001. Publisher Copyright: © 2014 IAEA, Vienna.

PY - 2014/8/19

Y1 - 2014/8/19

N2 - Plasma current start-up and ramp-up using the lower hybrid wave (LHW) were investigated on the TST-2 spherical tokamak. The LHW was launched by a dielectric-loaded waveguide array (grill) antenna. The antenna-plasma coupling of this antenna deteriorates as the input power exceeds several kW. This deterioration is believed to be caused by the density depletion due to the ponderomotive force. This conjecture was confirmed by the measurement of density reduction and the result of a non-linear full wave numerical calculation based on the finite element method (FEM). The plasma current was started and ramped up to 10 kA using this antenna. The ability of this grill antenna to excite the LHW with different n∥ = ck∥/ω was used to identify the most favourable n∥ spectrum for plasma current ramp-up. It was found that effective current drive can be achieved by the LHW with n∥ less than 6. However, even in this case, the energetic electrons which account for a large fraction of the driven current, are lost rapidly because the poloidal field generated by this level of plasma current is not sufficient to confine high energy electrons.

AB - Plasma current start-up and ramp-up using the lower hybrid wave (LHW) were investigated on the TST-2 spherical tokamak. The LHW was launched by a dielectric-loaded waveguide array (grill) antenna. The antenna-plasma coupling of this antenna deteriorates as the input power exceeds several kW. This deterioration is believed to be caused by the density depletion due to the ponderomotive force. This conjecture was confirmed by the measurement of density reduction and the result of a non-linear full wave numerical calculation based on the finite element method (FEM). The plasma current was started and ramped up to 10 kA using this antenna. The ability of this grill antenna to excite the LHW with different n∥ = ck∥/ω was used to identify the most favourable n∥ spectrum for plasma current ramp-up. It was found that effective current drive can be achieved by the LHW with n∥ less than 6. However, even in this case, the energetic electrons which account for a large fraction of the driven current, are lost rapidly because the poloidal field generated by this level of plasma current is not sufficient to confine high energy electrons.

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SN - 0029-5515

VL - 54

JO - Nuclear Fusion

JF - Nuclear Fusion

IS - 9

M1 - 093014

ER -

Plasma current start-up experiments using a dielectric-loaded waveguide array antenna in the TST-2 spherical tokamak

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