Transport optimization and mhd stability of a small aspect ratio toroidal hybrid stellarator

A class of small aspect ratio(A)stellarators is found that does not rely on quasisymmetrization to achieve good confinement. These systems depart from canonical stellarators by allowing a small net plasma current. An optimization procedure with bounce-averaged omnigeneity and other desirable physical properties as target criteria is described and applied to show the existence of a compact plasma device having A ≲ 3, highβ(ratio of thermal energy to magnetic field energy), and low plasma current. The added design flexibility afforded by the plasma current leads to an attractive low-A hybrid device which is stable to magnetohydrodynamic ballooning modes for(β)<6%.