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Technical Paper

Overview of Recent Progress in the GAMMA 10 Tandem Mirror

T. Cho Plasma Research Center, University of Tsukuba, Ibaraki, Japan.

H. Higaki Plasma Research Center, University of Tsukuba, Ibaraki, Japan.

M. Hirata Plasma Research Center, University of Tsukuba, Ibaraki, Japan.

H. Hojo Plasma Research Center, University of Tsukuba, Ibaraki, Japan.

M. Ichimura Plasma Research Center, University of Tsukuba, Ibaraki, Japan.

K. Ishii Plasma Research Center, University of Tsukuba, Ibaraki, Japan.

K. Islam Plasma Research Center, University of Tsukuba, Ibaraki, Japan.

A. Itakura Plasma Research Center, University of Tsukuba, Ibaraki, Japan.

I. Katanuma Plasma Research Center, University of Tsukuba, Ibaraki, Japan.

J. Kohagura Plasma Research Center, University of Tsukuba, Ibaraki, Japan.

R. Minami Plasma Research Center, University of Tsukuba, Ibaraki, Japan.

Y. Nakashima Plasma Research Center, University of Tsukuba, Ibaraki, Japan.

T. Numakura Plasma Research Center, University of Tsukuba, Ibaraki, Japan.

T. Saito Plasma Research Center, University of Tsukuba, Ibaraki, Japan.

Y. Tatematsu Plasma Research Center, University of Tsukuba, Ibaraki, Japan.

M. Yoshikawa Plasma Research Center, University of Tsukuba, Ibaraki, Japan.

O. Watanabe Plasma Research Center, University of Tsukuba, Ibaraki, Japan.

Y. Kubota Plasma Research Center, University of Tsukuba, Ibaraki, Japan.

T. Kobayashi Plasma Research Center, University of Tsukuba, Ibaraki, Japan.

Y. Yamaguchi Plasma Research Center, University of Tsukuba, Ibaraki, Japan.

H. Saimaru Plasma Research Center, University of Tsukuba, Ibaraki, Japan.

Y. Higashizono Plasma Research Center, University of Tsukuba, Ibaraki, Japan.

Y. Miyata Plasma Research Center, University of Tsukuba, Ibaraki, Japan.

S. Kiminami Plasma Research Center, University of Tsukuba, Ibaraki, Japan.

K. Shimizu Plasma Research Center, University of Tsukuba, Ibaraki, Japan.

M. Itou Plasma Research Center, University of Tsukuba, Ibaraki, Japan.

T. Ikuno Plasma Research Center, University of Tsukuba, Ibaraki, Japan.

A. Mase Art, Science and Technology Center for Cooperative Research, Kyushu University, Japan

Y. Yasaka Department of Electrical and Electronics Engineering, Kobe University, Japan

K. Sakamoto Naka Fusion Research Establishment, Japan Atomic Energy Agency, Japan

M. Yoshida Naka Fusion Research Establishment, Japan Atomic Energy Agency, Japan

A. Kojima Naka Fusion Research Establishment, Japan Atomic Energy Agency, Japan

K. Ogura Graduate School of Science and Technology, Niigata University, Japan

N. Nishino Graduated School of Engineering, Hiroshima University, Japan

W. Horton Institute for Fusion Studies, The University of Texas at Austin, USA

T. Kariya Toshiba Electron Tubes and Devices Co. Ltd., Tochigi, Japan

T. Imai Plasma Research Center, University of Tsukuba, Ibaraki, Japan.

V.P. Pastukhov Russian Research Center “Kurchatov Institute”, Moscow, Russia Kurchatov Institute, Russia

S. Miyoshi Plasma Research Center, University of Tsukuba, Ibaraki, Japan.

& GAMMA10 Group show all

Abstract

(1) Four-time progress in ion-confining potentials Φ_c to 3.0 kV in comparison to Φ_c attained 1992-2002 is achieved in the hot-ion mode (T_i=several keV). A scaling of Φ_c, which favorably increases with plug electron-cyclotron heating (ECH) powers (P_PECH), is obtained. (2) The advance in Φ_c leads to a finding of remarkable effects of radially sheared electric fields (dE_r/d_r) on turbulence suppression and transverse-loss reduction. (3) A weak decrease in Φ_c with increasing n_c to ˜10¹⁹ m^-3 with the recovery of Φ_c with increasing P_PECH is obtained. (4) The first achievement of active control and formation of an internal transport barrier (ITB) has been carried out with the improvement of transverse energy confinement. Off-axis ECH in an axisymmetric barrier mirror produces a cylindrical layer with energetic electrons, which flow through the central cell and into the end region. The layer, which produces a localized bumped ambipolar potential Φ_c, generates a strong E_r shear and peaked vorticity with the direction reversal of Er_r × B sheared flow near the Φ_c peak. Intermittent vortex-like turbulent structures near the layer are suppressed in the central cell. This results in T_e and T_i rises surrounded by the layer. The phenomena are analogous to those in tokamaks with ITB. (5) Preliminary central ECH (170 kW, 20 ms) in a standard tandem-mirror operation raises T_e0 from 70 to 300 eV together with T_{i[perpendicular]0} from 4.5 to 6.1 keV, and T_i//0 from 0.5 to 1.2 keV with τ_p0=95 ms for Φ_c (=1.4 kV) trapped ions. The on-axis particle to energy confining ratio of τ_p0/τ_E0 is observed to be 1.7 for Φ_c trapped ions (consistent with Pastukhov’s theory) and 2.4 for central mirror-trapped ions with 240-kW plug ECH and 90-kW ICH (η_ICH˜0.3; nl_c=4.5×10¹⁷ m^-2). (6) Recently, a 200 kW central ECH with 430 kW plug ECH produces stable central-cell plasmas (T_e=600 eV and T_i=6.6 keV) with azimuthal E_r×B sheared flow. However, in the absence of the shear flow, hot plasmas migrate unstably towards vacuum wall with plasma degradation.

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Overview of Recent Progress in the GAMMA 10 Tandem Mirror

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Overview of Recent Progress in the GAMMA 10 Tandem Mirror

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