Quadrupole Stabilization of then=2Rotational Instability of a Field-Reversed Theta-Pinch Plasma

The $n=2\mathrm{}$ rotational instability is the most dangerous gross instability in a field-reversed theta pinch. It is demonstrated for the first time that the instability is completely suppressed by superposing a quadrupole field which is much smaller than the axial confinement field at the separatrix. The experimental threshold intensity of the field for stabilization is about 2.5 times less than that predicted by theoretical stability analysis.