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Experimental study of the stability and dynamics of a two-dimensional ideal vortex under external strain

Published online by Cambridge University Press:  01 June 2018

N. C. Hurst Open the ORCID record for N. C. Hurst [Opens in a new window] ,
J. R. Danielson ,
D. H. E. Dubin  and
C. M. Surko
N. C. Hurst*
Affiliation:
Department of Physics, University of California – San Diego, La Jolla, CA 92093, USA
J. R. Danielson
Affiliation:
Department of Physics, University of California – San Diego, La Jolla, CA 92093, USA
D. H. E. Dubin
Affiliation:
Department of Physics, University of California – San Diego, La Jolla, CA 92093, USA
C. M. Surko
Affiliation:
Department of Physics, University of California – San Diego, La Jolla, CA 92093, USA
*
†Email address for correspondence: [email protected]
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Abstract

The dynamics of two-dimensional (2-D) ideal fluid vortices is studied experimentally in the presence of an irrotational strain flow. Laboratory experiments are conducted using strongly magnetized pure electron plasmas, a technique which is made possible by the isomorphism between the drift–Poisson equations describing plasma dynamics transverse to the field and the 2-D Euler equations describing an ideal fluid. The electron plasma system provides an excellent opportunity to study the dynamics of a 2-D Euler fluid due to weak dissipation and weak 3-D effects, simple diagnosis and precise control. The plasma confinement apparatus used here was designed specifically to study vortex dynamics under the influence of external flow by applying boundary conditions in two dimensions. Additionally, vortex-in-cell simulations are carried out to complement the experimental results and to extend the parameter range of the studies. It is shown that the global dynamics of a quasi-flat vorticity profile is in good quantitative agreement with the theory of a piecewise-constant elliptical patch of vorticity, including the equilibria, dynamical orbits and stability properties. Deviations from the elliptical patch theory are observed for non-flat vorticity profiles; they include inviscid damping of the orbits and modified stability limits. The dependence of these phenomena on the flatness of the initial profile is discussed. The relationship of these results to other theoretical, numerical and experimental studies is also discussed.

JFM classification

Nonlinear Dynamical Systems: Low-dimensional models MHD and Electrohydrodynamics: Plasmas Vortex Flows: Vortex dynamics
Type
JFM Papers
Information
Journal of Fluid Mechanics , Volume 848 , 10 August 2018 , pp. 256 - 287
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Copyright
© 2018 Cambridge University Press 

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