Interpretation of complex patterns observed in the electron-cyclotron instability of a mirror confined plasma produced by an ECR discharge

Shalashov, A. G.; Golubev, S. V.; Gospodchikov, E. D.; Mansfeld, D. A.; Viktorov, M. E.

doi:10.1088/0741-3335/54/8/085023

Cited by 21 publications

(19 citation statements)

References 27 publications

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“…1, maximum detuning ω ce /ω ≈ 1.32 is observed at the initial phase of the instability development just after the first broadband pulse. This indicates that Used model is discussed in [38,41]; modeling is performed for the following initial conditions relevant to the experimental shot shown in fig. 1:…”

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confidence: 99%

Observation of quasi-periodic frequency sweeping in electron cyclotron emission of nonequilibrium mirror-confined plasma

Viktorov¹,

Shalashov²,

Mansfeld³

et al. 2016

EPL

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-Chirping frequency patterns have been observed in the electron cyclotron emission from strongly nonequilibrium plasma confined in a table-top mirror magnetic trap. Such patterns are typical for the formation of nonlinear phase space structures in a proximity of the wave-particle resonances of a kinetically unstable plasma, also known as the "holes and clumps" mechanism. Our data provides the first experimental evidence for acting of this mechanism in the electron cyclotron frequency domain.Introduction. -Resonant interaction of electromagnetic waves and charged particles plays an important role in the dynamics of magnetoactive plasma confined in space and laboratory magnetic traps. One of the most intriguing manifestations of such interaction is emission of broadband radiation with regular variations of dynamical spectra, e.g. quasi-periodic bursts with a frequency sweeping, resulting from the development of kinetic plasma instabilities. Such events are common features of experimental plasmas. Kinetic instabilities are caused by the presence of positive gradients in the velocity distribution of resonant particles, whose formation is universal for both space and laboratory plasma. In space magnetic traps, the sources of free energy are formed due to different acceleration mechanisms of particles, such as betatron acceleration, plasma-wave turbulence and magnetic reconnection. Under laboratory conditions, the energetic particles with an anisotropic velocity distribution can be formed due to the features of plasma heating, when the energy of the external source is embedded in a specific region of the phase space, such as provided by resonant cyclotron heating or neutral beam injection in magnetic fusion experiment. Spatial gradients can also result in instabilities of waves for which the diffusion in real space is coupled to the diffusion in velocity space due to conservation of invariants of particle motion in inhomogeneous systems energy; this type of instability is exploited in the so-called alpha channeling proposals [1,2]. As a rule, plasma confined in laboratory traps consists of at least two components, one

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confidence: 99%

Observation of quasi-periodic frequency sweeping in electron cyclotron emission of nonequilibrium mirror-confined plasma

Viktorov¹,

Shalashov²,

Mansfeld³

et al. 2016

EPL

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“…In all cases, the cyclotron-maser instability is presumed to be driven by an electron horseshoe or modified horseshoe-ring distribution. Scaled laboratory experiments have demonstrated the potential for such horseshoe distributions to generate narrowband cyclotron-maser emission at GHz frequencies over distances of a few meters [21][22][23][24][25].Although the generation mechanism is well established, there remain important questions with regard to how the radiation may propagate within the parent auroral density cavity and ultimately escape [26]. Cairns et al [27] have demonstrated how the radiation, generated just below the electron cyclotron frequency, may successfully couple onto the upper branch of the plasma dispersion relation and escape.…”

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confidence: 99%

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Backward Wave Cyclotron-Maser Emission in the Auroral Magnetosphere

et al. 2014

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In this Letter, we present theory and particle-in-cell simulations describing cyclotron radio emission from Earth's auroral region and similar phenomena in other astrophysical environments. In particular, we find that the radiation, generated by a down-going electron horseshoe distribution is due to a backwardwave cyclotron-maser emission process. The backward wave nature of the radiation contributes to upward refraction of the radiation that is also enhanced by a density inhomogeneity. We also show that the radiation is preferentially amplified along the auroral oval rather than transversely. The results are in agreement with recent Cluster observations. DOI: 10.1103/PhysRevLett.113.155002 PACS numbers: 94.05.Dd, 94.30.Aa, 96.12.Wx, 98.62.Nx The electron cyclotron-maser instability plays a significant role in the generation of highly nonthermal, polarized radio emission from the auroral region of planets and stars having a dipolelike magnetic field [1,2]. More recently, this radiation model has been extended to a variety of astrophysical environments including Blazar jets, collisionless shocks, and brown dwarfs [3][4][5][6][7]. Planetary auroral radio emission has been a topic of interest for many years with several mechanisms having been proposed [8][9][10][11][12][13][14][15]. As the dispersion relation describing the electromagnetic wave growth only depends on the factor by which the magnetic field increases and on the ratio of plasma and cyclotron frequencies, the mechanism can scale effectively over many orders of magnitude both in wavelength and spatial scale. Blazar jets, in particular, represent a prime example of this scalability [3]. Generated perpendicular to the accretion disk of super massive black holes, they can extend over many thousands of light years and have been observed to generate highly nonthermal radio emission at frequencies in the hundreds of GHz range. It has been suggested that small scale magnetic mirrors or convergent flux tubes may be formed within the jet via hydrodynamic instabilities or shocks, providing the means of generating the required electron velocity distribution Bing2003, Begel2005. In Earth's auroral region, observations by the Viking spacecraft [11,16] and the Fast Auroral Snapshot (FAST) satellite [14] led to the suggestion that the free energy source for AKR is a population of downward accelerated electrons having a large perpendicular velocity produced by a combination of parallel accelerating electric fields and converging magnetic field lines. The electron distribution takes the form of a horseshoe or crescent shape due to the first adiabatic invariance as the electrons move into the stronger magnetic field. The FAST satellite [13,14,17] clearly demonstrates a strong correlation between the electromagnetic wave emission and the occurrence of the horseshoe distribution [13].Further observations by FAST of localized double-layer structures within the auroral density cavity have combined our understanding of auroral particle acceleration with the auroral kilome...

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“…The instability is triggered by the stored electron energy accumulated 16 into the anisotropic EED with v ? ) v k (with respect to the confining magnetic field) and a (local) positive slope of the EED, i.e., df ðEÞ dE > 0.…”

Section: Introductionmentioning

confidence: 99%

Influence of axial mirror ratios on the kinetic instability threshold in electron cyclotron resonance ion source plasma

et al. 2022

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Electron Cyclotron Resonance (ECR) ion source plasmas are prone to kinetic instabilities. The onset of the instabilities manifests as emission of microwaves, bursts of electrons expelled from the plasma volume, and the collapse of the extracted highly charged ion (HCI) currents. Consequently, the instabilities limit the HCI performance of ECR ion sources by limiting the parameter space available for ion source optimization. Previous studies have shown that the transition from stable to unstable plasma regime is strongly influenced by the magnetic field structure, especially the minimum field value inside the magnetic trap (B min ). This work focuses to study the role of the magnetic confinement on the onset of the kinetic instabilities by probing the influence of the injection and extraction mirror field variation on the instability threshold. The experiments have been performed with a room-temperature 14.5 GHz ECR ion source with an axially movable middle coil that provides flexible control over the axial field profile and especially the B min , which was used to quantify the variation in the instability threshold. The experimental results show that variation of the extraction field B ext , which defines the weakest magnetic mirror, correlates systematically with the variation of the instability threshold; decreasing the B ext allows higher threshold B min . The result demonstrates the importance of electron confinement and losses on the plasma stability. The connection between the weakest mirror field and the onset of instabilities is discussed taking into account the variation of magnetic field gradient and resonance plasma volume.

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Interpretation of complex patterns observed in the electron-cyclotron instability of a mirror confined plasma produced by an ECR discharge

Cited by 21 publications

References 27 publications

Observation of quasi-periodic frequency sweeping in electron cyclotron emission of nonequilibrium mirror-confined plasma

Observation of quasi-periodic frequency sweeping in electron cyclotron emission of nonequilibrium mirror-confined plasma

Backward Wave Cyclotron-Maser Emission in the Auroral Magnetosphere

Influence of axial mirror ratios on the kinetic instability threshold in electron cyclotron resonance ion source plasma

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