Optimization of SMES solenoids with regard to their stray fields

Solenoidal SMES (Superconducting Magnetic Energy Storage) usually suffer form their remarkable stray field. A certain arrangement was devised that should reduce the extension of the far ranging stray field. Hence, a second solenoid was placed outside the SMES device with a current flowing in the opposite direction compared to the inner coil. Configurations with both coils in a single plane were regarded only. As an important factor the minimum energy to be stored was given. In a first step calculation, methods have been found that reveal data for the minimum geometrical dimensions of the SMES device in an analytical way. It was shown that the stray field, compared to a single coil arrangement could be reduced remarkably. Evolution strategies and a conjugate gradient method were used to improve the quality of the above solution