DC and AC Shielding Properties of Bulk High-Tc Superconducting Tubes

Abstract

Abstract-We have studied numerically and experimentally the magnetic flux penetration in highsuperconducting tube subjected to a uniform magnetic field parallel to its long axis. This study is carried in view of designing low-frequency magnetic shields by exploiting the diamagnetic properties of high-superconducting ceramics. We have measured the field attenuation for applied magnetic fields in the frequency range 5 mHz-0.1 Hz by Hall probe measurements and at audio frequencies using a sensing coil. A simple 1D analysis using the Kim critical state model was found to be able to reproduce the experimental data satisfactorily. We have also determined the phase shift between the internal and the applied field both experimentally and numerically. Finally, we have studied the sweep rate dependence of the magnetic shielding properties, using data recorded either at several constant sweep rates d d or at several AC fields of various amplitudes and frequencies. Both methods agree with each other and lead to a -value of the n law equal to 40 at 77 K.

Magnetic shielding properties of a superconducting hollow cylinder containing slits: modelling and experiment

“…First, the limiting field in the transverse configuration B lim is ≈ 18 mT, which corresponds to the best values reported so far for superconducting magnetic shieding at the liquid nitrogen temperature [9,11,[12][13][14][15]. Second, the average critical current density J c = 350 A/cm² corresponds to the self field ~ 20 mT at the surface of the cylinder.…”

“…For θ = 0° (i.e. H ⊥ slits), the distribution of J z exhibits an eye-shape structure which is similar to that found in an infinite cylinder without any slit [15,27]. This is an anticipated result since the shielding currents in the median plane are always perpendicular to the applied field, i.e.…”

“…They can be used either at liquid nitrogen temperature (77 K) -at which magnetic shielding occurs up to a few tens of mT -or at low temperature (10 K and below) where shielding of magnetic fields in excess of 1 tesla was demonstrated recently [8,9]. Several materials are candidates for efficient magnetic screens, including MgB 2 [8,10], YBa 2 Cu 3 O 7 [3,11] or Bi-based compounds [12][13][14][15]. The basic shape for studying magnetic shielding is a hollow cylinder of typically of 2-5 cm diameter and 5-20 cm height.…”

“…The axial configuration is the simplest to consider. When the aspect ratio (height / diameter) of the cylinder is large enough (let say > 3), valuable information can be obtained from a one-dimensional analysis (1D) based on the Bean model [22,23], possibly with a field-dependent critical current density J c [21,24]. For short cylinders, finite size effects need to be considered and a 2D model should be used in order to account for the two mechanisms of field penetration, i.e.…”

Use of second generation coated conductors for efficient shielding of dc magnetic fields

“…4 Until recently, HTS shields have been made out of bulk materials. 5,[8][9][10] The significant progress in manufacturing the second generation ͑2G͒ coated conductors 11,12 has opened a possibility that they can be used as a material for magnetic screens. A recent study 13 reported the use of YBCO coated conductors to attenuate ac magnetic fields at low frequencies ͑10-100 Hz͒.…”