Nb3Sn conductors for 12 tesla toroidal field coils

Several advanced multifilamentary Nb3Sn conductors were examined for various modes of cooling for the 12 Tesla ETF application. Of these, a pancake-wound 15,000 Ampere flat cable of triplets of large strands in a perforated stainless steel channel was selected as the preferred candidate. This cable will be cold-end cryostable in a pool-boiling environment with a maximum heat transfer from the unoccluded strand surface of 0.24 Watts/cm2. The construction of the conductor and coil is relatively simple, offering potential economies in quality assurance and production costs.