Cryostatic influence of formvar coatings on sizing of the stabilizer in superconductive NbTi-Cu: Conductor bundle effects

In continuation of single-conductor studies, quench onset data of quasi-steady operation are reported for a formvar-coated composite (Nb48Ti/Cu) in bundle geometry (conductor thickness ≈ 0.2 cm, approximately square cross section). Overall thermal conductances of the heater simulation technique applied are of the order 0.1 W/(cm²K), comparable to single-specimen results, around 4 K and below the lambda transition in agreement with model predictions. Considerable deterioration however occurs below 3 K and down to the lambda temperature during operation in near-saturated He I. Consequences for magnets of intermediate energy density are discussed with emphasis on the modifications necessitated by coatings.