A Study of Pulsed Activation of Trapped Field Magnets—Part 1: Effects of Pulse Height and Creep

We report experimental results of a study of pulsed field activation of YBCO trapped field magnets (TFMs), at 77 K, in which the applied field covers an area smaller than the TFM. Data on a subset of experiments, in which pulse amplitude is varied, show the effects on trapped field distribution and creep. At low pulse height, trapped field is observed at the sample periphery, even at applied field well below
B
_C1
. At increased fields, the measured
J
is not limited to
J
_C
or zero, as in the Bean model, but varies continuously from 0 to
J
_C
, possibly as a result of averaging over the spatially varying applied field. For partial activation, creep is a function of
r
. As the critical state is approached, the spread in creep rates collapses to a single value. Full activation is obtained by a single pulse of applied field approximately 3.3 times maximum trapped field on the TFM surface.