Influence of twist pitch and sample length on proximity effect coupling in multifilamentary composites described in terms of a field independent, two current region model

Abstract

Magnetization and loss have been measured via vibrating sample magnetometry for a set of multifilamentary NbTi superconductive strands exhibiting a wide range of proximity effect (PE) coupling. Measurements extending over a large range of twist pitches L p and sample lengths L demonstrated that the magnetization and loss behaved similarly with respect to both parameters. For small L p ( L) values, magnetization and loss were linear with L p ( L), while for larger values a saturation was found (with either L p or L). Additionally, critical fields and critical currents for the proximity effected matrix, as well as penetration fields for the composite, were measured. Critical state models for anisotropic media were used to calculate the magnetization and penetration fields of these strands over a large range of L p values. A calculation of the transfer length and magnetization of short samples is also presented.