Stabilization and saturation of the ideal tilt mode in a driven annular field-reversed configuration
- Departments of Physics and Aeronautics and Astronautics, University of Washington, Seattle, Washington 98195 (United States)
The coaxial slow source (CSS) is a device that was designed as a means of forming annular field-reversed configurations (AFRCs) for magnetic fusion on relatively slow (50--100 [mu]s) time scales. Such configurations are predicted to be ideally unstable to magnetohydrodynamic tilting modes in which one-half of the torus shifts in the positive axial direction and the other half in the negative direction. These instabilities have been observed to grow and saturate at finite amplitude in the CSS as formation progresses. Stable operating regimes of fill pressure/loop voltage space have also been found. The relatively cold temperature ([similar to]2 eV) of the plasma gives rise to a high classical resistivity, placing the Lundquist number (ratio of resistive to Alfven time scales) between 0.5 and 10.0. It is proposed that resistivity, along with other dissipation mechanisms such as viscosity and ion--neutral friction, are responsible for the observed stability. Experiments were performed to explore these stability issues. A nonlinear, dynamical systems stability model that accounts for the effects of inductive current drive and dissipation has also been developed, and shows some agreement with the experimental results. The findings of this study are significant for two reasons: (1) It is one of the few clear observations of tilting modes in a FRC-like geometry; and (2) it provides an experimental study of ideally unstable modes in a configuration that does not escape the low Lundquist number regime, finding that the configuration appears stable below a Lundquist number of 0.5.
- DOE Contract Number:
- FG06-87ER53243
- OSTI ID:
- 6576736
- Journal Information:
- Physics of Plasmas; (United States), Vol. 2:3; ISSN 1070-664X
- Country of Publication:
- United States
- Language:
- English
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REVERSE-FIELD PINCH
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PLASMA INSTABILITY
PLASMA MACROINSTABILITIES
THERMONUCLEAR DEVICES
700340* - Plasma Waves
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