The AC losses of a rolling-assisted-biaxially-textured-substrate (RABiTS™) processed
YBa2Cu3O7−δ
(YBCO) coated conductor (Goyal et al 1996 Appl. Supercond. 4 403–27) with Ni-alloy
substrate and Cu stabilizer were measured at 77 K by both calorimetric (CM) and
electromagnetic (EM) methods. In the CM method, improvements in the measurement
were observed when a Cernox temperature sensor was used to measure the temperature rise
on the sample instead of a differential thermocouple. The effect of heat transferred from
current leads was taken into account to improve the accuracy of the CM results. In the EM
method, the magnetization losses of the sample in a perpendicular applied field were
measured by an in-plane pick-up coil. The calculation of the calibration factor
C
of the pick-up coil is discussed. Good agreement between AC loss results obtained
from the CM and EM methods confirmed the validity of our measurements and
calculations.
When a coil or a winding is made, the superconducting tapes must be bent to different
curvatures. Bending of high temperature superconducting (HTS) tapes can result in
degradation of the critical current density and thus increase the AC losses of the tapes.
Therefore, the effects of bending strain on the critical current and AC loss should be
considered in the design of high temperature superconducting apparatus. In this paper, the
dependence of critical current and AC loss on the bending diameter of the superconductor
tape was experimentally investigated. The diameters of the curved tape were varied from
110 to 36 mm. AC loss measurements were taken at 77 K, 50 Hz. Analysis of the bending
strain effects on the critical current and AC loss are presented. An expression describing
the dependence of AC losses on bending strain is proposed by modifying Norris’ formula.
The experimental results are presented and compared with the calculated values.
A versatile experimental facility was designed and set up to measure transport ac losses, magnetization ac losses, and total ac losses in high-temperature superconductors at variable temperatures. Several sets of measurements were carried out in the temperature range of 35 K to 100 K. Sample temperature during the measurements could be controlled within 0.5 K of set temperature. Temperature dependence of transport losses reflects variation of critical current density of the tapes with temperature. Temperature dependence of magnetization losses exhibits an interesting behavior with a peak, whose position shifts to lower temperatures as the magnetic field is increased. Experimental data of ac losses at various temperatures are compared with those calculated using numerical methods. Generally, the simulated results reproduce well the experimental data.
Fluorination of Pb-doped HgBa 2 Ca 2 Cu 3 O (Hg-1223) system was investigated. Structural and magnetic measurements reveal that fluorine addition promotes the phase formation, optimize the charge carrier concentration, and enhance flux pinning. We report an increase in both the transition temperature and the critical current density through controlled fluorine incorporation. Even a possible change in the pinning mechanism in this technologically important system is suggested.
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