Ion-Induced Instability of Diocotron Modes in Electron Plasmas Modelling Curvature-Driven Flute Modes

Kabant︠s︡ev, A. A.; Driscoll, C. F.

doi:10.13182/fst07-a1324

Cited by 18 publications

(9 citation statements)

References 14 publications

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“…In Penning or Penning double well traps, the ion-resonant mode has a finite growth rate at essentially any neutral pressure, and the mode grows steadily until the plasma disperses [20,25]. In CNT and in full toroidal traps non-neutral plasmas are stable for low ion fractions n i =n e < 0:1 [8,15].…”

mentioning

confidence: 99%

Observations of an Ion-Driven Instability in Non-Neutral Plasmas Confined on Magnetic Surfaces

et al. 2008

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The first detailed experimental study of an instability driven by the presence of a finite ion fraction in an electron-rich non-neutral plasma confined on magnetic surfaces is presented. The instability has a poloidal mode number m=1, implying that the parallel force balance of the electron fluid is broken and that the instability involves rotation of the entire plasma, equivalent to ion-resonant instabilities in Penning traps and toroidal field traps. The mode appears when the ion density exceeds approximately 10% of the electron density. The measured frequency decreases with increasing magnetic field strength, and increases with increasing radial electric field, showing that the instability is linked to the E x B flow of the electron plasma. The frequency does not, however, scale exactly with E/B, and it depends on the ion species that is introduced, implying that the instability consists of interacting perturbations of ions and electrons.

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mentioning

confidence: 99%

Observations of an Ion-Driven Instability in Non-Neutral Plasmas Confined on Magnetic Surfaces

et al. 2008

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“…For many years, it was thought that these instabilities are driven by the different drift rotation frequencies caused by inertial effects (mass difference). However, in past experiments [2,7] we have shown that an ion contamination of pure electron plasmas leads to the ion-induced diocotron (IID) instability, determined by the differences in z-bounce-averaged for electrons and ions with different z-bounce regions (as in "nested" or double-well traps configuration). Quite often, an ion fraction is continuously produced in warm(ish) electron plasma experiments, and special arrangements need to be made to prevent those ions from being trapped.…”

Section: Ion-induced Instability Of Diocotron Modesmentioning

confidence: 99%

“…where (see [2]). Figure 2 shows the measured growth rate of the IID instability as a linear function of the background pressure.…”

Section: Ion-induced Instability Of Diocotron Modesmentioning

confidence: 99%

Mitigation of drift instabilities by a small radial flux of charged particles through the landau-resonant layer

Kabant︠s︡ev¹,

Driscoll²

2016

AIP Conference Proceedings

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Experiments and theory on electron columns have characterized a novel algebraic damping of diocotron-like modes, caused by a small flux of halo particles through the resonant layer [1]. The damping rate is proportional to the flux. We have also investigated the diocotron instability which occurs when a small fraction of ions is transiting the electron plasma [2]. Dissimilar bounce-averaged E B drift dynamics of the ions and electrons polarizes the diocotron mode density perturbations, developing instability analogous to the classical flute instability. The exponential growth rate is proportional to the fractional neutralization and to the phase separation between electrons and ions in the wave perturbation. Here, we have shown that the flux-driven algebraic damping eliminates the ion-induced exponential instability of diocotron-like modes. Physically, the electric field from the resonant particles in the low-density halo acts back on the dense plasma core, causing E B drift motion of the core back down toward the trap axis, resulting in a damping of the mode.

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“…The primary cause for such contamination (either planned or inadvertent) in most electron plasma trap experiments is the process of ionization of the neutral background gas in the trap by the electrons. A brief history of analytical modelling 1,[4][5][6][7][8] , numerical analysis 9 , and experiments [10][11][12][13][14][15][16][17] performed to understand this destabilization process can be found in Sec I of Reference 3 3 . Of the theoretical models for the ion resonance instability, the one developed by Davidson and Uhm 5 aptly describes the collisionless dynamics of the instability in the present set of numerical experiments performed with an initially cold, partially neutralized electron cloud in cylindrical confinement.…”

Section: Introductionmentioning

confidence: 99%

Influence of electron-neutral elastic collisions on the instability of an ion-contaminated cylindrical electron cloud: 2D3V PIC-with-MCC simulations

Sengupta

Ganesh

2016

Physics of Plasmas

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This paper is a simulation based investigation of the effect of elastic collisions and effectively elastic-like excitation collisions between electrons and background neutrals on the dynamics of a cylindrically trapped electron cloud that also has an ion contaminant mixed in it. A cross section of the trapped non neutral cloud composed of electrons mixed uniformly with a fractional population of ions is loaded on a 2D PIC grid with the plasma in a state of unstable equilibrium due to differential rotation between the electron and the ion component. The electrons are also loaded with an axial velocity component, v z that mimics their bouncing motion between the electrostatic end plugs of a Penning-Malmberg trap. This v z loading facilitates 3D elastic and excitation collisions of the electrons with background neutrals under a MCC scheme. In the present set of numerical experiments, the electrons do not ionize the neutrals. This helps in separating out only the effect of non-ionizing collisions of electrons on the dynamics of the cloud. Simulations reveal that these non-ionizing collisions indirectly influence the ensuing collisionless ion resonance instability of the contaminated electron cloud by a feedback process. The collisional relaxation reduces the average density of the electron cloud and thereby increases the fractional density of the ions mixed in it. The dynamically changing electron density and fractional density of ions feed back on the ongoing ion-resonance (two-stream) instability between the two components of the nonneutral cloud and produce deviations in the paths of progression of the instability that are uncorrelated at different background gas pressures. Effects of the collisions on the instability are evident from alteration in the growth rate and energetics of the instability caused by the presence of background neutrals as compared to a vacuum background. Further in order to understand if the non-ionizing collisions can independently be a cause of destabilization of an electron cloud, a second set of numerical experiments were performed with pure electron plasmas making non-ionizing collisions with different densities of background neutrals. These experiments reveal that the nature of potential energy extraction from the electron cloud by the non-ionizing collisions is not similar to the potential energy extraction of other destabilizing processes e.g. a resistive wall instability. This difference in the energy extraction process renders these non-ionizing collisions incapable of independently triggering an instability of the cloud.

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Ion-Induced Instability of Diocotron Modes in Electron Plasmas Modelling Curvature-Driven Flute Modes

Cited by 18 publications

References 14 publications

Observations of an Ion-Driven Instability in Non-Neutral Plasmas Confined on Magnetic Surfaces

Observations of an Ion-Driven Instability in Non-Neutral Plasmas Confined on Magnetic Surfaces

Mitigation of drift instabilities by a small radial flux of charged particles through the landau-resonant layer

Influence of electron-neutral elastic collisions on the instability of an ion-contaminated cylindrical electron cloud: 2D3V PIC-with-MCC simulations

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