On the operational ideal magnetohydrodynamic b limit in sawtoothing discharges

Magnetohydrodynamic stability calculations of the n = 1 kink mode for equilibria with increasing b and values of the axis safety factor q0 > 1 and q0 < 1 show that for q0 < 1 there is a transition in both the unstable mode structure and the growth rate to a more virulent instability at approximately the b limit obtained with q0 > 1. This provides justification for the usual computational procedure of optimizing b by taking q0 > 1 and applying it to predict the b limit of sawtoothing discharges.