Abstract: A motor comprised of stator and rotor and formed of an even number of magnetic poles on both is disclosed. In the gap between the stator and rotor, a rotating shield having a window therein controllably interrupts and controllably permits coupling across the gap between poles of the rotor and stator. In the preferred embodiment, the shield is rotated at the same speed as the rotor in the opposite direction. The shield is made of superconducting material and the motor is operated at superconducting temperatures to position the shield in the gap to interrupt magnetic coupling.