Optimum design of superconducting magnet coil for a micro SMES unit

The paper outlines a systematic procedure for the design of a solenoidal coil to obtain maximum stored energy for a given length of normal conductor and superconductor. In case of normal conductor, it would suffice if we design the coil to obtain maximum inductance. For superconducting coil, it is essential to maximize (1/2Li/sup 2/) as a whole since the value of allowable current depends on flux density which in turn is linked with L. This results in the design of a coil, whose inductance is much lower than the maximum possible value and has relatively large diameter as compared to its length and radial thickness. Since such a coil requires a cryostat of unusually large neck, one may choose a sub-optimal design based on commercially available drum type cryostat for transportable micro SMES units. The paper concludes with the dimensions of a solenoidal coil for optimum and sub-optimum designs using superconducting (Nb-Ti) wire of 8 km length and 1 mm diameter.