Reconnection dynamics for quantized vortices

PHYSICA D-NONLINEAR PHENOMENA

卷:239

Article; Proceedings Paper

Paoletti, M. S.^1,2  Fisher, Michael E.³  Lathrop, D. P.^1,2,3,4 

[1] Univ Maryland, Dept Phys, College Pk, MD 20742 USA

[2] Univ Maryland, Inst Res Elect & Appl Phys, College Pk, MD 20742 USA

[3] Univ Maryland, Inst Phys Sci & Technol, College Pk, MD 20742 USA

[4] Univ Maryland, Dept Geol, College Pk, MD 20742 USA

关键词: Reconnection;    Turbulence;    Quantum turbulence;    Flow visualization;   

DOI  :  10.1016/j.physd.2009.03.006

来源: Elsevier

【 摘 要 】

By analyzing trajectories of solid hydrogen tracers in superfluid He-4, we identify tens of thousands of individual reconnection events between quantized vortices. We characterize the dynamics by the minimum separation distance delta(t) between the two reconnecting vortices both before and after the events. Applying dimensional arguments, this separation has been predicted to behave asymptotically as delta(t) approximate to A (kappa vertical bar t - t(0)vertical bar)(1/2), where kappa = h/m is the quantum of circulation. The major finding of the experiments and their analysis is strong support for this asymptotic form with kappa as the dominant controlling feature, although there are significant event to event fluctuations. At the three-parameter level the dynamics may be about equally well-fit by two modified expressions: (a) an arbitrary power-law expression of the form delta(t) = B vertical bar t - t(0)vertical bar(alpha) and (b) a correction-factor expression delta(t) = A (kappa vertical bar t - t(0)vertical bar)(1/2) (1 + C vertical bar t - t(0)vertical bar). The measured frequency distribution of alpha is peaked at the predicted value alpha = 0.5, although the half-height values are alpha = 0.35 and 0.80 and there is marked variation in all fitted quantities. Accepting (b) the amplitude A has mean values of 1.24 +/- 0.01 and half height values of 0.8 and 1.6 while the c distribution is peaked close to c = 0 with a half-height range of -0.9 s(-1) to 1.5 s(-1). In light of possible physical interpretations we regard the correction-factor expression (b), which attributes the observed deviations from the predicted asymptotic form to fluctuations in the local environment and in boundary conditions, as best describing our experimental data. The observed dynamics appear statistically time-reversible, which suggests that an effective equilibrium has been established in quantum turbulence on the time scales (<= 0.25 s) investigated. We discuss the impact of reconnection on velocity statistics in quantum turbulence and, as regards classical turbulence, we argue that forms analogous to (b) could well provide an alternative interpretation of the observed deviations from Kolmogorov scaling exponents of the longitudinal structure functions. (C) 2009 Elsevier B.V. All rights reserved.

【 授权许可】

Free