Summary of the international discussion meeting on radiation effects on superconductivity Page: 4 of 18
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exist In the form of a flux line lattice. There is a stiffness to the lattice,
which is represented by an effective elastic constant, which does not allow
the full pinning force of each defect to be utilized. The experimental value is
below the value found by a direct summation of the individual point
pins that clearly overestimates F . The direct summation essentially says
that a flux line can be pinned fully at every defect center. Thus, this summa-
tion completely ignores the well-known lattice nature of the flux lines.
Figure 1 is a plot of the experimentally determined specific pinning
force (F divided by the number density of defect structures) versus the calculated
maximum fluxoid-defact interaction f in Nb for various types of defects.
The predictions of a direct summation and the Labusch statistical summation
are indicated. That the experimental values lie below the direct
summation, yet above the Labusch summation, shows that the lattice nature
of the flux lines is important but over estimated by Labusch. A promising
idea being pursued that would resolve the problem invokes the use of defects
in the flux line lattice. This would retain the lattice nature of the flux
lines, but would result in increased pinning due to the enhanced flexibility
of the flux lines lattice because the defects in the lattice would lower the
elastic constants.
The effect of voids on flux pinning in Nb and V was the subject
of recent investigations. This system is especially appealing since the
size and number distribution of the voids can be controlled by the irradiation
parameters and characterized by electron microscopy. Therefore, the parameters
required for calculating the fundamental interaction are available directly.
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Brown, B. S. Summary of the international discussion meeting on radiation effects on superconductivity, article, January 1, 1977; Illinois. (https://digital.library.unt.edu/ark:/67531/metadc1074905/m1/4/: accessed July 16, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.