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Quenches of formvar - coated NbTi/Cu caused by step input in power

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4 Author(s)
Li-He Lin ; Zhejiang University, China ; Chuang, C. ; Kim, Y. ; Frederking, T.H.K.

We have investigated the stability of the composite Nb48Ti/Cu coated with a formvar layer (30 μm thick). Starting from thermal equilibrium in the superfluid liquid He II range below the lambda temperature (T = Tλ), the composite temperature is found to rise first monotonically with time t, upon onset of energy dissipation. However, restricted stability is visible as a relative temperature maximum (Tmax) of the composite at the time tmax, followed by a relative minimum in T at tmin. These coated composite phenomena are similar to stability conditions of bare composites in the same "conductor-in-box " geometry employed. However at a specified power the times tmaxand tminare shifted in comparison to the bare composite. Diagnosis is based on power-time functions whose tangents are characterized by power law exponents (m) . The m-values found are re - presentative of strong, localized solid - coolant interaction, of a caloric condition, or of locally turbulent fluid motion. In the range covered by the present transients, stability is available by creation of entropy - rich buffer domains of fluid, below the superconducting transition temperature, between He II and the heated composite. The latter is quench - protected in an intermediate power range.

Published in:

Magnetics, IEEE Transactions on  (Volume:19 ,  Issue: 3 )