Multiresolution analysis of the two-dimensional free decaying turbulence in a pure electron plasma

Bettega, G.; Pozzoli, R.; Romé, M.

doi:10.1088/1367-2630/11/5/053006

Cited by 10 publications

(15 citation statements)

References 30 publications

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“…Two different initial conditions are considered. The reference case is a flat annular density (vorticity) distribution (Peurrung & Fajans 1993 a ; Bettega, Pozzoli & Romé 2009 b ; Rodgers et al. 2009) where denotes the Heaviside step function, and and are the inner and outer radius of the annulus, respectively.…”

Section: Numerical Simulationsmentioning

confidence: 99%

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Spectral analysis of forced turbulence in a non-neutral plasma

2017

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The paper investigates the dynamics of magnetized non-neutral (electron) plasmas subjected to external electric field perturbations. A two-dimensional (2-D) particle-in-cell code is effectively exploited to model this system with a special attention to the role that non-axisymmetric, multipolar radio frequency (RF) drives applied to the cylindrical (circular) boundary play on the insurgence of azimuthal instabilities and the subsequent formation of coherent structures preventing the relaxation to a fully developed turbulent state, when the RF fields are chosen in the frequency range of the low-order fluid modes themselves. The isomorphism of such system with a 2-D inviscid incompressible fluid offers an insight into the details of forced 2-D fluid turbulence. The choice of different initial density (i.e. fluid vorticity) distributions allows for a selection of conditions where different levels of turbulence and intermittency are expected and a range of final states is achieved. Integral and spectral quantities of interest are computed along the flow using a multiresolution analysis based on a wavelet decomposition of both enstrophy and energy 2-D maps. The analysis of a variety of cases shows that the qualitative features of turbulent relaxation are similar in conditions of both free and forced evolution; at the same time, fine details of the flow beyond the self-similarity turbulence properties are highlighted in particular in the formation of structures and their timing, where the influence of the initial conditions and the effect of the external forcing can be distinguished.

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Section: Numerical Simulationsmentioning

confidence: 99%

“…Both kinds of density distribution are typically used in experiments on pure electron plasmas confined in Penning–Malmberg traps (Malmberg & deGrassie 1975; Kriesel & Driscoll 1998; Peurrung & Fajans 1993 a ; Bettega et al. 2009 b ; Rodgers et al. 2009).…”

Section: Numerical Simulationsmentioning

confidence: 99%

Spectral analysis of forced turbulence in a non-neutral plasma

2017

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“…Annular and Archimedean spiral density distributions are considered. Both kinds of density distribution are typically used in experiments on pure electron plasmas confined in Penning-Malmberg traps [64,65,25,1,66]. The density and the area covered by the initial electron distribution (and therefore the total number of particles) is the same in all simulations.…”

Section: Numerical Simulationsmentioning

confidence: 99%

“…One of the characteristic features of 2D fluid turbulence is intermittency, i.e., the presence of field (here, vorticity) activity localized in both physical and spectral space. A suitable tool for its analysis is the wavelet decomposition [72,73,65,74]. Namely, in contrast to Fourier analysis wavelets have well localized basis functions both in physical and wavenumber space, allowing for the identification of local and non-stationary features of the flow.…”

Section: Influence Of Initial Conditions and Drivesmentioning

confidence: 99%

“…Each density (vorticity) distribution saved during a numerical run is decomposed into coefficients that contain coarse and fine details at increasing resolution. These wavelet coefficients are then separated into coherent and incoherent parts using a suitable iterative method [75,65]. At each step of the iteration, the coefficients are divided into two classes, depending on whether their modulus is larger or smaller than a given threshold.…”

Section: Influence Of Initial Conditions and Drivesmentioning

confidence: 99%

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Coherent structures and turbulence evolution in magnetized non-neutral plasmas

Romé

Chen²,

Maero

2018

AIP Conference Proceedings

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The evolution of turbulence of a magnetized pure electron plasma confined in a Penning-Malmberg trap is investigated by means of a two-dimensional particle-in-cell numerical code. The transverse plasma dynamics is studied both in the case of free evolution and under the influence of non-axisymmetric, multipolar radio-frequency drives applied on the circular conducting boundary. In the latter case the radio-frequency fields are chosen in the frequency range of the low-order azimuthal (diocotron) modes of the plasma in order to investigate their effect on the insurgence of azimuthal instabilities and the formation and evolution of coherent structures, possibly preventing the relaxation to a fully-developed turbulent state. Different initial density distributions (rings and spirals) are considered, so that evolutions characterized by different levels of turbulence and intermittency are obtained. The time evolution of integral and spectral quantities of interest are computed using a multiresolution analysis based on a wavelet decomposition of density maps. Qualitative features of turbulent relaxation are found to be similar in conditions of both free and forced evolution, but the analysis allows one to highlight fine details of the flow beyond the self-similarity turbulence properties, so that the influence of the initial conditions and the effect of the external forcing can be distinguished. In particular, the presence of small inhomogeneities in the initial density configuration turns out to lead to quite different final states, especially in the presence of competing unstable diocotron modes characterized by similar growth rates.

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