超伝導体における磁束ピンニング[2]

－ピンニング損失－

抄録

It seems to be believed that the critical current density is the essential factor which determines the pinning loss as described by the critical state model. However, this is not ture: the pinning loss is the essential factor which determines the critical current density in the dynamic pinning theory. The pinning loss of power is defined as an additional viscous loss of power due to the velocity fluctuation of the fluxons caused by pinning interactions. It is shown that the high velocity due to the unstable flux motion, which occurs when the fluxon drops in and jumps out of the pinning potential well, brings about the pinning loss power density that depends only on the pinning force density. This suggests that the flux motion is nearly reversible with extremely-low-loss power density deviating from the prediction of the critical state model if the flux motion is restricted within pinning potential wells. Such phenomenon is actually observed in multifilamentary wires with very-finr superconducting filaments thinner than the pinning correlation length.