Kinematic dynamos surrounded by a stationary conductor

We investigate kinematic dynamos in cylinders and spheres surrounded by an insulator. The flow volume is divided into an inner region, in which the co nducting fluid is in motion, and an outer region enclosing the inner one, i n which the conductor is at rest. The dependence of the critical magnetic R eynolds number on the thickness of the outer conducting shell is discussed as well as implications for the design of experimental dynamos. [S1063-651X (99)04309-3].