Are Vacuum Bubbles a Cause of Major Disruptions in Tokamaks?

The maximum amplitude of the $m=2\mathrm{}$ tearing mode in tokamaks is found to increase rapidly with rising safety factor at the magnetic axis, $q\left(0\right)\mathrm{}$. The resulting large magnetic islands encompass virtually the entire plasma cross section for $1.5\lesssim q\left(0\right)\mathrm{}\lesssim 1.8$ and are shown to be related to the vacuum bubbles formed during the saturation of the ideal $m=2\mathrm{}$ kink mode. On the basis of these results, a mechanism for major distruptions is proposed along with a possible method for their elimination.