PPPL-3368 is available in <a href="PPPL-3368.pdf">pdf</a> or 
<a href="PPPL-3368.ps">postscript</a> formats.
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<b>Vertical Stability in a Current-carrying Stellarator</b>

<p>G.Y. Fu</p>

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<b>Date of PPPL Report:</b> October 19, 1999</p>

<b>Submitted to:</b> Physics of Plasmas</p>

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An analytic stability criterion is derived for the vertical mode in a large aspect ratio stellarator. The effects of vacuum magnetic field generated by helical coils are shown to be stabilizing due to enhancement of field line bending energy. For wall at infinite distance from the plasma, the amount of external poloidal flux needed for stabilization is given by <I>f</I> = <FONT FACE = "SYMBOL">  (k<sup>2</sup> - k)/(k<sup>2</sup> + 1) </FONT> where <FONT FACE = "SYMBOL"> k </FONT> is the axisymmetric elongation and <I>f</I> is the ratio of vacuum rotational transform to the total transform.
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