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Observation of wall stabilization and active control of low-n magnetohydrodynamic instabilities in a tokamak (1996)

Ivers, T. H. ; Eisner, E. ; Garofalo, A. ; [et al.]

[S.l.] : American Institute of Physics (AIP)

Physics of Plasmas 3 (1996), S. 1926-1934

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ISSN: 1089-7674

Source: AIP Digital Archive

Topics: Physics

Notes: The High Beta Tokamak-Extended Pulse (HBT-EP) experiment [J. Fusion Energy 12, 303 (1993)] combines an internal, movable conducting wall with a high-power, modular saddle coil system to provide passive and active control of long wavelength magnetohydrodynamic (MHD) instabilities. Systematic adjustment of the radial position, b, of the conducting wall elements in relation to the surface of the plasma (minor radius a) resulted in the suppression of β-limiting disruptions for discharges in which b/a〈1.2 and a positive plasma current ramp was maintained. Conducting wall stabilization of kink instabilities was observed in discharges with strong current ramps and in plasmas with β values near the Troyon stability boundary. The frequency of slowly growing modes that persisted in wall-stabilized discharges was controlled by applying oscillating m=2, n=1 resonant magnetic perturbations. A compact, single-phase saddle coil system permitted modulation of the rotation velocity of internal m/n=2/1 instabilities by a factor of 2. © 1996 American Institute of Physics.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.871988

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Initial high beta operation of the HBT-EP Tokamak (1993)

Sankar, M. K. Vijaya ; Eisner, E. ; Garofalo, A. ; [et al.]

Springer

Journal of fusion energy 12 (1993), S. 303-310

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ISSN: 1572-9591

Keywords: High beta operation ; HBT-EP tokamak

Source: Springer Online Journal Archives 1860-2000

Topics: Energy, Environment Protection, Nuclear Power Engineering

Notes: Abstract HBT-EP is a new research tokamak designed and built to investigate passive and active feedback techniques to control MHD instabilities. In particular, HBT-EP will be able to test techniques to control fast MHD instabilities occurring at high Troyon-normalized beta, βN ≡ βBa/Ip [Tm/MA], since it is equipped with a thick, close-fitting, and adjustable conducting shell. The major goals of the initial operation of HBT-EP have been the achievement of high beta operation (βN ∼ 3) using only ohmic heating and the observation of MHD instabilities. By using a unique fast startup technique, we have successfully achieved these goals. A variety of MHD phenomena were observed during the high beta operation of HBT-EP. At modest beta (βN ≤ 2), discharges have been maintained for more than 10 msec, and these discharges exhibit saturated resistive instabilities. When βN approaches 3, major disruptions occur preceded by oscillating, growing precursors. During start-up, one or more minor disruptions are usually observed. A 1-D transport code has been used to simulate the evolution of the current profile, and these early minor instabilities are predicted to be double tearing modes. The simulation also reproduces the observed high beta operation when saturated neo-Alcator energy confinement scaling is assumed.