Kink instabilities of a field reversed ion ring with a toroidal magnetic field

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Abstract
The low frequency magnetohydrodynamic stability of axisymmetric ion rings in a current‐carrying background plasma with a toroidal magnetic field is studied. An energy principle which treats the background plasma by fluid equations and the beam by kinetic theory is employed. The major effects upon stability are the magnetohydrodynamic response of the plasma and beam, a collective reaction of the beam, and betatron resonances. It is found that, if the beam and plasma currents are roughly equal, and if the exterior region contains a cold but highly conducting plasma, there is a window of stability for kinks with safety factor q as low as 1/2. The results also explain the anomalous trapped current losses in the RECE–Christa electron ring experiment.