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Dynamics of pinned quantized vortices in superfluid He in a microelectromechanical oscillator
We numerically studied the vortex dynamics at zero temperature in superfluid
He confined between two parallel rough solid boundaries, one of which
oscillates in a shear mode. This study was motivated by the experimental work
by Barquist which employed a microelectromechanical systems (MEMS)
oscillator operating in superfluid He at a near-zero temperature. Their
experiments suggest that the motion of the MEMS oscillator is damped by
quantized vortices. In our study, we postulated that this damping effect was
closely associated with vortex pinning phenomena and developed pinning models.
Our primary objective is to understand the vortex dynamics in the presence of
pinning and to provide insight into the experimental observations regarding the
damping mechanism. We confirmed that Kelvin waves were excited in the pinned
vortices when the oscillation frequency of the solid boundary matched with the
mode frequency of the Kelvin wave. Additionally, we examined the formation and
evolution of vortex tangles between the boundaries. The vortex tangle was
suppressed in the presence of pinning, while the absence of pinning allowed to
form well developed vortex tangle resulting in turbulence. Finally, by
evaluating the tension of pinned vortices we extracted the damping force acting
on the solid boundaries.Comment: 11 pages + supplement, 17 figure
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