Two-Layer Solenoids for Superconductive Magnetic Energy Storage (SMES)

A new two-layer SMES solenoid design is presented as a possible replacement for earlier low aspect ratio single-layer Wisconsin SMES designs. The two-layer low aspect ratio design maintains most of the advantages and simplicities of the single layer design with several added benefits: lower current, smaller conductors at 200 kA which replace 800 kA conductors; more accessible and easier mounted conductors in two vertical layers, one inside and the other outside a solenoidal axial structure wall; improved conductor mechanical support due to the tapering together of the axial structure at the top and bottom to bring the end turns of inner and outer layers closer together; and an improved flexibility for force and field optimization for a thicker wall two-layer solenoid. Advantages for both double and single-layer coils are: compatible thermal-mechanical mounting on bedrock trench walls to contain expanding forces; rippled structure and conductor to reduce cooldown and magnetic loading stresses; open mounting in 1.8 K pool helium for good cooling; round conductor continuous assembly without joints; convenient design to short all turns in parallel for emergency discharge; and relatively low voltages for such large storage inductors. The key features of system stress analyses and system conductor stabilities for the new two-layer design will be described.