Tearing mode stability of elongated field‐reversed plasmas without toroidal field

The marginal stability of long thin field‐reversed plasmas to axisymmetric tearing modes is examined. It is found that stability improves greatly as flux is excluded from the plasma. Such naturally occurring states may account for the lack of tearing mode activity in many experiments. Consideration is also given as to whether, in three dimensions, the tearing mode is an instability or a condition for the breakdown of equilibrium. An example is given that demonstrates that it is an instability. Idealized analytic results and more realistic numerical results are presented.