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2000
A model is developed to analyze the stabilization of the resistive wall mode (RWM) by plasma rotation. Central to the model is a cylindrical plasma that is ideal magnetohydrodynamic unstable in the absence of a wall, and possesses an internal resonance [J. M. Finn, Phys. Plasmas 2 , 198 (1995)]. This system is then a qualitative model for the actua…
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1999
The possibility of stabilizing ideal magnetohydrodynamical (MHD) instabilities by resistive walls and slow plasma rotation (rotation frequencies comparable to resistive tearing growth rates) was proposed recently by Finn [Phys. Plasmas 2 , 3782 (1995)] on the basis of cylindrical theory. In the present paper we analyze toroidal effects (pressure gr…
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1999
A uniform compressible plasma with a uniform flow along the magnetic field in the presence of a resistive wall is shown to be subject to two instabilities. For the first instability, the flow velocity is required to exceed the Alfve´n speed, whereas for the second it need only exceed the sound speed. For a sufficiently high ion temperature, ion La…
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1998
Theoretical and experimental work on the vertical position control system on the COMPASS-D tokamak is described. An analog proportional 1 derivative (P 1 D) system is currently used, and two important sources of disturbance are observed in the system. One source is 600-Hz noise from thyristor power supplies, and the other is impulselike disturbance…
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1997
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1996
Advanced Tokamak Concepts [C. Kessel, J. Manickam, G. Rewoldt, and W. M. Tang, Phys. Rev. Lett. 72 , 1212 (1994)] have been designed assuming that the ‘‘Resistive Wall Mode’’ (RWM) is stable. It has recently been shown that the RWM can be stabilized by a combination of strong uniform plasma rotation and visco-resistive dissipation. In this …
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1996
This paper reports on the ideal magnetohydrodynamic (MHD) stability of tokamak field profiles that have a non-monotonic safety factor q ( r ). An analytic criterion is obtained for these ‘‘inverse shear’’ profiles by expanding in inverse aspect ratio and assuming that the minimum in q is slightly less than the m / n value of the mode under …
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1991
The question of the influence of nonaxisymmetric field perturbations on tokamaks is investigated. Recent experiments in the COMPASS-C tokamak [in Proceedings of the 15th Symposium on Fusion Technology, Utrecht (North-Holland, Amsterdam, 1989), Vol. 1, p. 3611 with externally applied helical fields reveal that magnetic islands do not appear until th…
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1989
Magnetic feedback control has been used in the DITE tokamak to substantially reduce saturated m = 2, n = 1 instabilities in both Ohmic discharges and discharges with lower-hybrid current drive (LHCD). Feedback has been used for the first time to significantly increase the disruptive density limit in a tokamak. LHCD on DITE stabilizes the sawtooth i…
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