Electron Cyclotron Instability Research Articles

Continuous-wave operation of an electron cyclotron maser formed in a mirror magnetic trap

Among various non-linear regimes of electron cyclotron instabilities that may be driven by a strong electron cyclotron resonance (ECR) heating in open magnetic traps, the continuous generation of a quasi-monochromatic wave, characterized by a smooth release of a free energy from a system, is especially important for applications, e.g., aimed at performance optimization of ECR ion sources. We study an universal model based on the quasilinear description of plasma–wave interactions that explains the condition of a continuous-wave regime of the cyclotron instability observed experimentally including, in particular, a strong dependence on a magnetic configuration.

Critical behavior near the instability threshold of an electron cyclotron maser formed in a mirror magnetic trap.

High-power electron cyclotron resonance discharge in a laboratory open trap is frequently accompanied by growth of electron cyclotron instabilities. We study a simple universal model that explains some of the stability conditions of such plasma observed experimentally, in particular, its crucial dependence on localization of the rf power deposition zone with respect to a minimum of B. An instability threshold seems to be sensitive to particular details of electron losses in a velocity space. Comparing theoretical predictions for the threshold condition with available measurements sheds light on a structure of fast-electron losses in ongoing experiments.

Spontaneous Magnetic Fluctuations and Collisionless Regulation of Turbulence in the Earth’s Magnetotail

Abstract Among the fundamental and most challenging problems of laboratory, space, and astrophysical plasma physics is to understand the relaxation processes of nearly collisionless plasmas toward quasi-stationary states and the resultant states of electromagnetic plasma turbulence. Recently, it has been argued that solar wind plasma β and temperature anisotropy observations may be regulated by kinetic instabilities such as the ion cyclotron, mirror, electron cyclotron, and firehose instabilities; and it has been argued that magnetic fluctuation observations are consistent with the predictions of the fluctuation–dissipation theorem, even far below the kinetic instability thresholds. Here, using in situ magnetic field and plasma measurements by the THEMIS satellite mission, we show that such regulation seems to occur also in the Earth’s magnetotail plasma sheet at the ion and electron scales. Regardless of the clear differences between the solar wind and the magnetotail environments, our results indicate that spontaneous fluctuations and their collisionless regulation are fundamental features of space and astrophysical plasmas, thereby suggesting the processes is universal.

Electron mirror and cyclotron instabilities for solar wind plasma

ABSTRACT The solar wind plasma is characterized by unequal effective kinetic temperatures defined in perpendicular and parallel directions with respect to the ambient magnetic field. For electrons, the excessive perpendicular temperature anisotropy leads to quasi-parallel electromagnetic electron cyclotron (or whistler) instability and aperiodic electron-mirror instability with oblique wave vectors. The present paper carries out a direct side-by-side comparison of quasi-linear (QL) theory and particle-in-cell (PIC) simulation of combined mirror and cyclotron instabilities acting upon the initially anisotropic electron temperatures, and find that the QL theory satisfactorily encapsulates the non-linear aspect of the combined instability effects. However, a discrepancy between the present study and a previous PIC simulation result is also found, which points to the need for further investigation to resolve such an issue.

Bridging hybrid- and full-kinetic models with Landau-fluid electrons

Context. Magnetic reconnection plays a fundamental role in plasma dynamics under many different conditions, from space and astrophysical environments to laboratory devices. High-resolution in situ measurements from space missions allow naturally occurring reconnection processes to be studied in great detail. Alongside direct measurements, numerical simulations play a key role in the investigation of the fundamental physics underlying magnetic reconnection, also providing a testing ground for current models and theory. The choice of an adequate plasma model to be employed in numerical simulations, while also compromising with computational cost, is crucial for efficiently addressing the problem under study. Aims. We consider a new plasma model that includes a refined electron response within the “hybrid-kinetic framework” (fully kinetic protons and fluid electrons). The extent to which this new model can reproduce a full-kinetic description of 2D reconnection, with particular focus on its robustness during the nonlinear stage, is evaluated. Methods. We perform 2D simulations of magnetic reconnection with moderate guide field by means of three different plasma models: (i) a hybrid-Vlasov-Maxwell model with isotropic, isothermal electrons, (ii) a hybrid-Vlasov-Landau-fluid (HVLF) model where an anisotropic electron fluid is equipped with a Landau-fluid closure, and (iii) a full-kinetic model. Results. When compared to the full-kinetic case, the HVLF model effectively reproduces the main features of magnetic reconnection, as well as several aspects of the associated electron microphysics and its feedback onto proton dynamics. This includes the global evolution of magnetic reconnection and the local physics occurring within the so-called electron-diffusion region, as well as the evolution of species’ pressure anisotropy. In particular, anisotropy-driven instabilities (such as fire-hose, mirror, and cyclotron instabilities) play a relevant role in regulating electrons’ anisotropy during the nonlinear stage of magnetic reconnection. As expected, the HVLF model captures all these features, except for the electron-cyclotron instability.

Relativistic study of electromagnetic electron cyclotron instability based on trapped electrons in kappa‐Maxwellian auroral plasmas

AbstractThe presence of relativistic electrons in the Earth's magnetosphere may excite EMEC waves via resonant interaction. The understanding of EMEC waves induced by such electrons requires relativistic treatment. Therefore, we present here the investigation of EMEC waves based on relativistic trapped electrons represented by kappa‐Maxwellian distribution in auroral plasmas. The analytical expressions of real frequency and relativistic growth rate are derived. Our numerical outcomes report that relativistic approximation increases the wave growth and causes reduction in the threshold value of drift velocity of trapped electrons for instability. The wave frequency that corresponds to the maximum growth decreases as we go from nonrelativistic limit to relativistic. The maximum growth increases with the increment in plasma frequency, perpendicular thermal velocity, drift velocity of trapped electrons, and Lorentz factor γ. Moreover, the relativistic effects on maximum growth are more pronounced for smaller values of drift velocity and perpendicular thermal velocity.

Observation of electron cyclotron harmonic emissions due to electrostatic instabilities in mirror-confined plasma

The authors present observations of electromagnetic emissions near electron cyclotron harmonics from mirror-confined laboratory plasma during electron cyclotron resonance heating by microwaves, and attribute them to electron cyclotron instabilities.

Electron Temperature Anisotropy and Electron Beam Constraints from Electron Kinetic Instabilities in the Solar Wind

Abstract Electron temperature anisotropies and electron beams are nonthermal features of the observed nonequilibrium electron velocity distributions in the solar wind. In collision-poor plasmas these nonequilibrium distributions are expected to be regulated by kinetic instabilities through wave–particle interactions. This study considers electron instabilities driven by the interplay of core electron temperature anisotropies and the electron beam, and first gives a comprehensive analysis of instabilities in arbitrary directions to the background magnetic field. It clarifies the dominant parameter regime (e.g., parallel core electron plasma beta , core electron temperature anisotropy , and electron beam velocity V eb) for each kind of electron instability (e.g., the electron beam-driven electron acoustic/magnetoacoustic instability, the electron beam-driven whistler instability, the electromagnetic electron cyclotron instability, the electron mirror instability, the electron firehose instability, and the ordinary-mode instability). It finds that the electron beam can destabilize electron acoustic/magnetoacoustic waves in the low- regime, and whistler waves in the medium- and large- regime. It also finds that a new oblique fast-magnetosonic/whistler instability is driven by the electron beam with in a regime where and A ec < 1. Moreover, this study presents electromagnetic responses of each kind of electron instability. These results provide a comprehensive overview for electron instability constraints on core electron temperature anisotropies and electron beams in the solar wind.

Effects of magnetic configuration on hot electrons in a minimum-B ECR plasma

To investigate the hot electron population and the appearance of kinetic instabilities in highly charged electron cyclotron resonance ion source (ECRIS), the axially emitted bremsstrahlung spectra and microwave bursts emitted from ECRIS plasma were synchronously measured on SECRAL-II (Superconducting ECR ion source with Advanced design in Lanzhou No. II) ion source with various magnetic field configurations. The experimental results show that when the ratio of the minimum field to the resonance field (i.e. Bmin/Becr) is less than ∼0.8, the bremsstrahlung spectral temperature Ts increases linearly with the Bmin/Becr–ratio when the injection, extraction and radial mirror fields are kept constant. Above this threshold Ts saturates and the electron cyclotron instability appears simultaneously. This study has also demonstrated that Ts decreases linearly with the increase of the average gradient over the ECR surface when the on-axis gradient and hexapole field strengths are constant. In addition, it is found that Ts decreases with the increase of the gradient at the resonance zone (∇Becr on axis and <∇Becr>) at relatively low mirror ratio and is insensitive to the gradient at high mirror ratio when Bmin is constant. Compared to a recent study taken on a fully superconducting ECRIS (Benitez et al 2017 IEEE Trans. Plasma Sci. 45 1746–54), in which it was concluded that Ts is only sensitive with Bmin, this article shows different results discussing the mechanisms behind the correlation of magnetic field parameters to Ts.

2D3V kinetic simulation of Hall effect thruster, including azimuthal waves and diamagnetic effect

Axial-azimuthal (2D3V) full-kinetic PiC+MCC-model was built to simulate dynamics of Hall effect thruster discharge plasma taking into account azimuthal waves and diamagnetic effect. The transition from ignition to the steady-state regime was simulated. Calculation of discharge ignition shows a significant distortion in the shape of the magnetic field caused by high azimuthal-drift current. This effect and intensive ionization lead to the fact that full potential drop localizes in a thin non-magnetized cathode layer. In the steady-state regime, the distortion of the magnetic field is small. Plasma divides into three regions: dense anode plasma where ionization occurs; magnetic layer where ions accelerate and quasineutral cathode-side plasma (plume). The steady-state regime is subject to auto-oscillations at a gas-transit frequency (20 kHz ‘breathing modes’). Also, two types of azimuthal instabilities have been observed: gradient drift instability and electron cyclotron instability. All these instabilities lead to collisionless ‘anomalous’ electron transport across the magnetic field. Kinetic effects also were considered. It was found that the electron distribution function evolves from initial isotropic (Maxwellian) to essentially anisotropic due to electric field heating. Isotropy is partially restored inside anode plasma due to collisions.

Control of electron-cyclotron instability driven by strong ECRH in open magnetic trap

We discuss the laboratory experiment on a controlled transition from the generation of periodic bursts of electromagnetic radiation into the continuous-wave regime of a cyclotron maser formed in a magnetically confined non-equilibrium plasma (Shalashov A. G. et al., Phys. Rev. Lett., 114 (2018) 205001). The kinetic cyclotron instability of the extraordinary wave of a weakly inhomogeneous magnetized plasma is driven by the anisotropic electron population resulting from electron cyclotron plasma heating in a MHD-stable minimum-B open magnetic trap. In the present communication we focus on a theoretical model that explains the existing data and motivates further experiments.

Electron mirror instability: particle-in-cell simulations

Properties of the electron mirror instability and its competition with the usually dominant whistler (electron cyclotron) instability driven by the electron perpendicular temperature anisotropy are investigated at the linear level using a Vlasov linear solver and at the nonlinear level using a two-dimensional full particle code. The simulation results show that the linearly subdominant electron mirror instability may compete at the nonlinear level with the whistler instability and may even eventually become the dominant mode that generates robust non-propagating sub-ion-scale coherent structures in the form of magnetic peaks.

Simulation and Quasi‐Linear Theory of Whistler Anisotropy Instability

AbstractThe whistler anisotropy (or electromagnetic electron cyclotron) instability may be operative in many geomagnetic and heliospherical environments, including the radiation belt, solar wind, and the solar corona. The present investigation carries out a comparative analysis between the two‐dimensional particle‐in‐cell simulation of weakly growing whistler anisotropy instability and the velocity moment‐based two‐dimensional quasi‐linear theory under the assumption of bi‐Maxwellian electron distribution function. It is shown that the simplified quasi‐linear theory provides a qualitative agreement with the more rigorous particle‐in‐cell simulation, but some discrepancies are also found. Possible causes for the differences in either method are discussed, and future improvements on the theory are suggested. Potential applicability of the present finding in the context of the space and astrophysics is discussed.

Electromagnetic Electron Cyclotron Instability in the Solar Wind

AbstractThe abundant reports on the existence of electromagnetic high‐frequency fluctuations in space plasmas have increased the expectations that theoretical modeling may help understand their origins and implications (e.g., kinetic instabilities and dissipation). This paper presents an extended quasi‐linear approach of the electromagnetic electron cyclotron instability in conditions typical for the solar wind, where the anisotropic electrons (T⊥&gt;T∥) exhibit a dual distribution combining a bi‐Maxwellian core and bi‐Kappa halo. Involving both the core and halo populations, the instability is triggered by the cumulative effects of these components, mainly depending of their anisotropies. The instability is not very sensitive to the shape of halo distribution function conditioned in this case by the power index κ. This result seems to be a direct consequence of the low density of electron halo, which is assumed more dilute than the core component in conformity with the observations in the ecliptic. Quasi‐linear time evolutions predicted by the theory are confirmed by the particle‐in‐cell simulations, which also suggest possible explanations for the inherent differences determined by theoretical constraints. These results provide premises for an advanced methodology to characterize, realistically, the electromagnetic electron cyclotron instability and its implication in the solar wind.

Nonlinear structures and anomalous transport in partially magnetized E×B plasmas

Nonlinear dynamics of the electron-cyclotron instability driven by the electron E×B current in a crossed electric and magnetic field is studied. In the nonlinear regime, the instability proceeds by developing a large amplitude coherent wave driven by the energy input from the fundamental cyclotron resonance. Further evolution shows the formation of the long wavelength envelope akin to the modulational instability. Simultaneously, the ion density shows the development of a high-k content responsible for wave focusing and sharp peaks on the periodic cnoidal wave structure. It is shown that the anomalous electron transport (along the direction of the applied electric field) is dominated by the long wavelength part of the turbulent spectrum.

Plasma instabilities of a charge breeder ECRIS

Experimental observation of plasma instabilities in a charge breeder electron cyclotron resonance ion source (CB-ECRIS) is reported. It is demonstrated that the injection of 133Cs+ or 85Rb+ ion beam into the oxygen discharge of the CB-ECRIS can trigger electron cyclotron instabilities, which restricts the parameter space available for the optimization of the charge breeding efficiency. It is concluded that the transition from a stable to unstable plasma regime is caused by gradual accumulation and ionization of Cs/Rb and simultaneous change of the discharge parameters in 10–100 ms time scale, not by a prompt interaction between the incident ion beam and the ECRIS plasma. The instabilities lead to loss of ion confinement, which results in the sputtering of the surfaces in contact with the plasma, followed by up to an order of magnitude increase of impurity currents in the extracted ion beam.

Towards realistic characterization of the solar wind suprathermal populations and their effects

This Brief Communication presents a straightforward analytical method for estimating the effects of suprathermal particle populations present in space plasmas, based on a refined Kappa modelling of the velocity distributions which enables comparison with the thermal (core) component. If the observed distribution with suprathermal tails can be reproduced by a Kappa power-law, the core is extracted as a particular Maxwellian limit which needs to be cooler and contain a less number of particles. This approach enables study of the kinetic instabilities driven by anisotropic bi-Kappa distributions, among other applications. Thus, the electromagnetic electron cyclotron instability is found to be stimulated by the suprathermal electrons, confirming the existence of an additional free energy in these populations. Limiting to a standard Maxwellian modelling, as was and still is customary for the analysis of distributions observed in the solar wind, may therefore lead to misleading interpretations of these instabilities and other kinetic effects involving suprathermal populations.

Characteristics of heat flux and electromagnetic electron-cyclotron instabilities driven by solar wind electrons

Characteristics of heat flux and electromagnetic electron-cyclotron instabilities driven by solar wind electrons

Macroscopic quasi‐linear theory of electromagnetic electron cyclotron instability associated with core and halo solar wind electrons

AbstractSpacecraft observations made near 1 AU show that both core and halo solar wind electrons exhibit temperature anisotropies that appear to be regulated by marginal electromagnetic electron cyclotron instability condition. In the literature, the threshold conditions of this instability, operative for T⊥&gt;T∥, have been expressed as an inverse correlation between the temperature anisotropy, T⊥/T∥, and parallel beta, β∥, but such a relation was deduced on the basis of linear stability analysis combined with empirical fitting. The present paper, on the other hand, employs macroscopic quasi‐linear analysis for core‐halo two‐component model of the solar wind electrons, in order to follow the self‐consistent time history of the core and halo temperature development as well as the dynamics of magnetic field perturbation wave energy. In the present analysis, the inverse correlation for core and halo temperature anisotropy and parallel beta naturally emerges from the solutions of self‐consistent theory. The present findings indicate that the macroscopic quasi‐linear method may be useful for modeling the dynamics of solar wind electrons.

Electrostatic electron cyclotron instabilities near the upper hybrid layer due to electron ring distributions

A theoretical study is presented of the electrostatic electron cyclotron instability involving Bernstein modes in a magnetized plasma. The presence of a tenuous thermal ring distribution in a Maxwellian plasma decreases the frequency of the upper hybrid branch of the electron Bernstein mode until it merges with the nearest lower branch with a resulting instability. The instability occurs when the upper hybrid frequency is somewhat above the third, fourth, and higher electron cyclotron harmonics, and gives rise to a narrow spectrum of waves around the electron cyclotron harmonic nearest to the upper hybrid frequency. For a tenuous cold ring distribution together with a Maxwellian distribution an instability can take place also near the second electron cyclotron harmonic. Noise-free Vlasov simulations are used to assess the theoretical linear growth-rates and frequency spectra, and to study the nonlinear evolution of the instability. The relevance of the results to laboratory and ionospheric heating experiments is discussed.