The movie shows the initial penetration of a flux front into a sample with an intermediate density of intermediate strength pinning sites. We add vortices at a constant rate to an unpinned region at the left edge of the sample, creating a gradient in vortex density that drives the vortices into the pinned region. Circles represent vortices, and lines are drawn tracing the path each vortex follows through the sample.
The randomly placed parabolic pins in this sample are at a density of np = 1.92 (Pinning site density) and are all of strength fp = 1.0 (Pinning site strength) The pinning sites are strong enough to trap vortices for a long period of time, but it is possible for a vortex to be pushed out of a pinning site by vortices entering the sample behind it. Although the pinning density is too high to permit a vortex to cross the entire sample without hitting a pinning site, some paths through the sample intersect fewer pinning sites than others, and these paths are favored by the vortices. Temporarily pinned vortices serve to repel the other vortices moving through the sample, and help guide the vortices into the paths of easiest flow.
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Created by: Cynthia Olson and Jared Groth
Last modified: 12/18/96