SIZE EFFECT IN AC LOSSES OF SUPERCONDUCTING CABLES

We calculate the dependence of the transverse coupling losses in cable s, the most important contribution to ac losses in cables without cent ral insulating layer, Two effects cause differences with respect to th e infinite samples: 1) changed area of the loops between the strands, and 2) increased resistivity between them, At low frequencies, the tra nsverse losses P for finite samples of length l are well-described by the formula P/P-infinity = 1 - C(0)l(0)/l, where C-0 depends on the ra tio b/c (b-cable width, c-thickness of normal layer between strands), l(0) is the cabling length and P-infinity the losses for corresponding infinite sample, We obtain a = 1/C-0 approximate to 3 for b/c approxi mate to 10 and a approximate to 2 for b/c > 50. The same formula appli es for higher frequencies, with frequency dependent correction factor C(omega). This correction factor decreases and becomes even negative a t higher frequencies, Thus, the losses in finite samples are higher th an in the corresponding infinite cables, This effect could be therefor e called the inverse size effect, appearing above omega tau > 0.9 for b/c = 10 and omega tau > 1.53 for b/c = 50. It may explain some experi mental results where size effect was expected but not found in the los s measurements.