Possible explanation for trapped field enhancement on REBaCuO bulk by modified multi-pulse technique with stepwise cooling (MMPSC)

The time evolutions of the local fields BL(t) have been measured on the surface of the superconducting bulk disk magnetized by a two-stage pulse-field magnetizing technique, called a modified multi-pulse technique combined with stepwise cooling (MMPSC), and the magnetic flux movement and the flux trapping have been investigated. The optimum concaved (“M-shaped”) trapped field profile, which is a necessary condition at the first stage to enhance the final trapped field BT, makes a larger magnetic gradient (dB/dx  ) at the bulk periphery in the ascending stage of the applied magnetic pulse at the second stage due to the large viscous force FvFv. The magnetic fluxes, which stay at the bulk periphery, start to flow to the center of the bulk, after the applied pulse field reaches a maximum, at which the flux velocity vv is nearly zero and then FvFv decrease. As a result, a large number of the magnetic fluxes are trapped at the bulk center. The effect of the “M-shaped” profile at the first stage in MMPSC on the enhancement of BT is discussed.