Stability of a finite β, l =2 stellarator

The stability of an infinitely long, high β, l = 2 stellarator is investigated. The calculation is carried out by using the new scyllac expansion in the sharp boundary ideal magnetohydrodynamic model. It is found that for any given size l = 2 field and mode number m, an infinite but discrete set of wavenumbers k exist for which the plasma is unstable to all β; that is, the critical β equals zero. These modes can be described as long wavelength interchanges. Thus, with regard to sharp boundary stability, l = 2 is less desirable than l = 1 for the basic scyllac field, and in addition does not offer any particular advantage over l = 0 as a sideband field required for toroidal equilibrium in the l = 1 configuration. configuration.