Alternating current losses in stacked Bi2Sr2Ca2Cu3O10/Ag tapes in perpendicular magnetic fields

Abstract

Alternating current losses in stacks of powder-in-tube-processed Bi2Sr2Ca2Cu3O10/Ag tapes were measured in perpendicular magnetic fields and compared with calculated hysteresis losses based on the critical-state model. Four main factors had to be taken into account for the calculations of the losses: (1) the inclusion of the area of the Ag sheath in determining the critical-current densities of the stacks, (2) the zero-applied-field critical currents Ic⊥(0) with truly perpendicular fields only, not the standard self-field critical current IcS(0), and (3) the field-dependent critical current Ic(H), e.g., the Kim’s model, and (4) the subtraction of the frequency-dependent losses at very high fields. With these considerations, the agreement between the calculated and the measured values of the losses is excellent for fields beyond the full-penetration fields. However, these factors did not totally account for the low-field losses.

Magnetic properties of arrays of superconducting strips in a perpendicular field

“…This effect has been experimentally found in several works. 28,29,60,61 Actually, the cause of the disagreement between theoretical predictions and experiments in these works is that they used models for single strips or disks, which yielded narrow peaks. Our model allows for the explanation of this effect.…”

Theoretical AC susceptibility of superconducting multifilamentary tapes in a perpendicular field

“…In the low limit the matrix behaves as an -array with a filament thickness equal to the sum of the thicknesses of all the strips, since when the strips in the same column are in contact with each other and behave as a whole. This effect has already been predicted for and -stacks of single strips [7], [9] and experiementally observed for stacks of multifilamentary tapes [8], [22].…”

“…Since flux compression is lower when the strips became more penetrated, the corresponding enhancement of is reduced, resulting in a widening of the peak. The widening of the peak, as compared with the theoretical predictions for a slab in the critical state model or a strip, has been experimentally observed for real tapes [8], [22], [23]. Furthermore, the peak widening for isolated strips results in a crossover of the curves for isolated and interconnected strips, so that for low AC fields is higher for isolated strips but lower for high AC fields.…”

AC loss evaluation of an HTS insert for high field magnet cooled by cryocoolers

“…In order to estimate the parallel-field loss Q // in the k-th turn, the SC layer of coated conductor could be considered as an infinite slab with the thickness d of SC layer because d is much smaller than the tape width 2a. On the other hand, the magnetic interactions between turns [10][11][12][13][14] have to be taken into account for estimation of the perpendicular-field loss Q \ . It has been well known that there are three theoretical expressions to estimate AC losses in SC strips exposed to a cyclic external magnetic field perpendicular to the broad faces [18][19][20][21][22][23].…”

“…The proposed expression to estimate the AC losses in the HTS inserts for 32-T magnet is also applicable for the case where the radial component of a local magnetic field applied to every part of the windings in solenoid coils is larger than the full penetration field, but such a situation could not be realized for an HTS insert constituting a high field magnet with relatively tall height. If the local magnetic field becomes less than the full penetration field, it has been well known that the magnetic interactions between SC wires strongly affect the AC loss properties, for example, in NbTi multifilamentary wires [7][8][9], BSCCO tapes [10,11] and coated conductors [12][13][14]. In this paper, AC losses in an HTS insert coil designed for one of high field magnets [15] are numerically evaluated.…”