Electrostatic diagnostics of nanosecond pulsed electron beams in a Malmberg–Penning trap

Paroli, B.; Bettega, G.; Maero, G.; Romé, M.; Norgia, M.; Pesatori, Alessandro; Svelto, C.

doi:10.1063/1.3455200

Cited by 7 publications

(9 citation statements)

References 14 publications

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“…Recently, a few modifications have been introduced in the device to adapt it to other experiments. 23,24 In particular, the spiral thermocathode placed at one end of the trap had to be removed, but a novel plasma production mechanism has been devised: 25 a sinusoidal drive V G of few volts and frequency in the megahertz range is applied on two opposite sectors of the S4 electrode. The free electrons present in the device are heated up to an energy sufficient to ionize the background gas even in the typical UHV conditions ͑the pressure is not artificially raised to favor the ionization discharge͒.…”

Section: Methodsmentioning

confidence: 99%

Stabilizing effect of a nonresonant radio frequency drive on the m=1 diocotron instability

et al. 2011

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It has been experimentally shown that the rotation radius of a non-neutral plasma column around the longitudinal axis of a Malmberg-Penning trap experiences a growth in amplitude ͑m = 1 diocotron instability͒, leading to the loss of the plasma on the surface of the confining electrodes. A new stabilization mechanism has been investigated with the help of systematic experiments in the ELTRAP ͑ELectron TRAP͒ device where a high-frequency, low-amplitude drive has been applied on an azimuthally sectored electrode. An effective confining force is created, which reduces the offset of the column from the center. This interpretation and its theoretical analysis show a qualitative agreement with the experimental findings, where a net confinement effect is present for a wide range of drive amplitudes and frequencies.

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Section: Methodsmentioning

confidence: 99%

Stabilizing effect of a nonresonant radio frequency drive on the m=1 diocotron instability

et al. 2011

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“…2009 b ; Paroli et al. 2010 a ). A 2-D orthogonal wavelet-based multiresolution analysis is adopted here.…”

Section: Wavelet Analysismentioning

confidence: 99%

“…A suitable analysis tool for studying the intermittency features of turbulence, i.e. the presence of field (vorticity) activity localized in both physical and spectral space, is wavelet decomposition (Farge 1992;Mallat 1999;Bettega et al 2009b;Paroli et al 2010a). A 2-D orthogonal wavelet-based multiresolution analysis is adopted here.…”

Section: Wavelet Analysismentioning

confidence: 99%

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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“…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%

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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Electrostatic diagnostics of nanosecond pulsed electron beams in a Malmberg–Penning trap

Cited by 7 publications

References 14 publications

Stabilizing effect of a nonresonant radio frequency drive on the m=1 diocotron instability

Stabilizing effect of a nonresonant radio frequency drive on the m=1 diocotron instability

Spectral analysis of forced turbulence in a non-neutral plasma

Coherent structures and turbulence evolution in magnetized non-neutral plasmas

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