Physics of compact stellarators

Recent progress in the theoretical understanding and design of compact stel larators is described. Hybrid devices, which depart from canonical stellara tors by deriving benefits from the bootstrap current which flows at finite beta, comprise a class of low aspect ratio A<4 stellarators. They possess e xternal kink stability (at moderate beta) in the absence of a conducting wa ll, possible immunity to disruptions through external control of the transf orm and magnetic shear, and they achieve volume-averaged ballooning beta li mits (4%-6%) similar to those in tokamaks. In addition, bootstrap currents can reduce the effects of magnetic islands (self-healing effect) and lead t o simpler stellarator coils by reducing the required external transform. Po werful physics and coil optimization codes have been developed and integrat ed to design experiments aimed at exploring compact stellarators. The physi cs basis for designing the national compact stellarator will be discussed. [S1070-664X(99)95405-8].