The trapped field properties during pulsed-field magnetization (PFM) have been investigated numerically using three different assumptions relating to the Jc(B, T) characteristics (Jirsa, Kim and Bean models) and compared with experimental results. The trapped field properties using the Jirsa model with the so-called 'peak effect', in which a realistic Jc(B, T) is assumed, rather than the Kim model, result in a more realistic numerical simulation. The trapped field properties using a Kim model with a monotonically decreasing Jc(B) also show similar results to those using the Jirsa model. The trapped field properties using a Bean model, for which Jc is independent of magnetic field, are not necessarily enhanced because of a larger temperature rise. The numerical results suggest it is necessary to fabricate REBaCuO bulks with Jc(B, T) characteristics with moderate magnetic field and temperature dependences to enhance the trapped field by PFM.
In this paper, the trapped field properties of GdBaCuO disk bulk superconductors of various diameters during pulsed-field magnetization (PFM) using an identical split coil at 65 K have been investigated both experimentally and numerically. The maximum trapped field, BT max , of the 43 mm bulk was larger than that of the 30 mm bulk. However, BT max of the 65 mm bulk was smaller than that of the 43 mm bulk and the trapped field profile exhibited a distorted "C-shaped" profile. Using the numerical simulation, these results for the 65 mm bulk can be explained by an inhomogeneous temperature profile and the larger generated heat, Q, due to the lower cooling power of the refrigerator compared to the generated heat. The important issues to achieve higher and homogeneous trapped fields are discussed when using splitcoil PFM for larger bulks.
We have performed numerical simulations of the electromagnetic hoop stress, σθ
, in a REBaCuO disk bulk reinforced by a metal ring during pulsed-field magnetization (PFM) using a solenoid coil, in which the superconducting characteristics of the bulk material were assumed to have realistic J
c-B-T ones. The compressive and tensile σθ
stresses were applied in the bulk during the ascending and descending stages of PFM, respectively. The time and position dependences of the mechanical stresses were estimated. The possibility of mechanical fracture due to these hoop stresses and the effect of the metal ring reinforcement were discussed.
We have performed numerical simulations of the electromagnetic, thermal and mechanical properties of a REBaCuO ring-shaped bulk with various reinforcement structures during pulsed-field magnetization (PFM). Compressive and tensile electromagnetic stresses,
σ
θ
mag
, are developed in the ring-shaped bulk during the ascending and descending stages of PFM, respectively. These stresses increase at lower operating temperatures and for higher applied pulsed fields. In order to reduce these stresses, the ring-shaped bulk was fully encapsulated by outer and inner ring with upper and lower plates made by Al alloy. In particular, this reinforcement structure can achieve the lowest electromagnetic compressive stress, which corresponds to about 54% of that for a conventional ring reinforcement structure, and the electromagnetic tensile stress was also reduced. We also compared the simulation results of the electromagnetic stresses for the ring-shaped bulk to those for a disk-shaped bulk.
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