Inviscid damping of an elliptical vortex subject to an external strain flow

被引:3
作者
Wongwaitayakornkul, P. [1 ]
Danielson, J. R. [1 ]
Hurst, N. C. [2 ]
Dubin, D. H. E. [1 ]
Surko, C. M. [1 ]
机构
[1] Univ Calif, Phys Dept, San Diego, CA 92093 USA
[2] Univ Wisconsin, Phys Dept, Madison, WI 53706 USA
关键词
DYNAMICS; INSTABILITY; TRANSPORT; VORTICES; BEHAVIOR; NEPTUNE;
D O I
10.1063/5.0086227
中图分类号
O35 [流体力学]; O53 [等离子体物理学];
学科分类号
070204 ; 080103 ; 080704 ;
摘要
Inviscid spatial Landau damping is studied experimentally for the case of oscillatory motion of a two-dimensional vortex about its elliptical equilibrium in the presence of an applied strain flow. The experiments are performed using electron plasmas in a Penning-Malmberg trap. They exploit the isomorphism between the two-dimensional Euler equations for an ideal fluid and the drift-Poisson equations for the plasma, where plasma density is the analog of vorticity. Perturbed elliptical vortex states are created using E x B strain flows, which are generated by applying voltages to electrodes surrounding the plasma. Measurements of spatial Landau damping (also called critical-layer damping) are in agreement with previous studies in the absence of an applied strain, where the damping is due to a resonance between the local fluid motion and the vortex oscillations. Interestingly, the damping rate does not change significantly over a wide range of applied strain rates. This can be accurately predicted from the initial vorticity profile, even though the resonant frequency is reduced substantially due to the applied strain. For higher amplitude perturbations, nonlinear trapping oscillations also exhibit behavior similar to the strain-free case. In principle, higher-order effects of the applied strain, such as separatrix crossing of peripheral vorticity and interactions with harmonics of the fundamental resonance, are expected to change the damping rate. However, this occurs only for conditions that are not realized in the experiments described here. Vortex-in-cell simulations are used to investigate the possible roles of these effects. Published under an exclusive license by AIP Publishing.
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页数:11
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