The performance potential of superconducting linear and planar motors

Electromagnetic motors currently used in lithography systems are pushed to their limit and it is challenging to increase acceleration without introducing additional disturbances. Superconductors could provide an improvement in magnetic flux density and/or current density compared to the permanent magnets and copper coils currently used. The improvement potential of three superconducting (SC) alternatives is analysed in this paper. The achievable magnetic flux density with SC electromagnets and SC bulk magnets is derived and the (alternating) current density in a SC coil is presented as a function of cooling power. All three are analysed for a range of cryogenic temperatures. An increase in magnetic flux density of a factor of three is computed at a temperature of 30 K and the same increase in current density is found at 50 K with equal cooling power compared to copper coils. As a result, superconductivity is expected to provide a significant improvement with respect to magnetic flux density and/or current density in a motor application.