A New Direct Magnetic Method for Determining ${\rm J}_{\rm C}$ in Bulk Superconductors From Magnetic Field Diffusion Measurements

The knowing the critical current density J
_C
is important to calculate AC losses in superconducting applications. Usually can be obtained from magnetization measurements or electric measurements based on global quantities as the magnetic flux or the voltage. In this paper a quick and direct magnetic method for determining J
_C
is proposed. It is based on direct measurements of local magnetic field in the gap between two bulk HTS pellets. Field penetration measurements were carried out on HTS pellets at 77 K by applying increasing axial magnetic fields with a quasi constant sweep rate. This determination of J
_C
is theoretically based on Bean model. J
_C
is deduced from the complete penetration magnetic field B
_P
. B
_P
is deduced from the delay T
_P
between the applied magnetic field B
_a
(t)and the magnetic field at the center between the two pellets B
₀
(t). Numerical calculations allow deducing J
_C
more precisely from theoretical calculations and measurements. The numerical calculations are made with the power law E = E
_C
(J/J
_C
)
ⁿ
. For the determination of J
_C
the influence of the gap due to Hall probe sensor and the applied magnetic field rise rate are taken into account. The influence of thermal is also studied.