Plasma Wave Phenomena Research Articles

New aspects on plasma wave and instability phenomena in basic-plasma experiments

AbstractOur basic-plasma experiments relating to fusion-oriented and space plasmas have yielded deep and unique insight into wave and instability physics in ordinary electron-ion and unusual pair-particle plasmas. Here recent results on flow shears, polarization reversal and pair-ions are presented in the way that light is shed on the underlying physics.

Demonstratsiya nelineinykh volnovykh yavlenii v plazme laboratornoi modeli ionosferno-magnitosfernogo dakta plotnosti

Demonstratsiya nelineinykh volnovykh yavlenii v plazme laboratornoi modeli ionosferno-magnitosfernogo dakta plotnosti

Nonlinear electrostatic modes in astrophysical plasmas with charged dust distributions

Context. Most theoretical investigations of wave phenomena in dusty plasmas have treated charged dust as additional heavy negative ions in standard multispecies models. Many dusty plasma experiments use monodisperse grains, but charged (and neutral) grains in space environments come in a whole range of sizes and compositions, hence in masses and charges. Dust density distributions having a power-law decay with size are often observed in planetary rings. Aims. There is a need to investigate larger solitary structures, since wave descriptions involving charged dust distributions have usually been limited to linear or weakly nonlinear modes. Methods. Sagdeev pseudopotential methods describe large-amplitude solitary waves in a co-moving reference frame and are adapted to include dust distributions, using mass and charge, or alternatively size, as additional variables. Observed power-law distributions lead to descriptions involving hypergeometric functions. Results. Lower limits for possible solitary wave velocities follow from requiring that the Sagdeev pseudopotentials have a local maximum for the undisturbed conditions, whereas upper limits come from ensuring that dust densities remain real. Nonlinear amplitudes increase with solitary wave velocities and relative electron temperature. Under similar plasma conditions, dust size distributions admit slower solitary wave solutions, with correspondingly smaller amplitudes than given by monodisperse dust models. For typical planetary ring conditions, the difference can be quite appreciable.

Plasma wave measurements with STEREO S/WAVES: Calibration, potential model, and preliminary results

The S/WAVES experiments on the two STEREO spacecraft measure waves, both in situ plasma waves and remotely generated waves such as Type II and Type III solar bursts. A part of the experiment is aimed at understanding the generation of electromagnetic waves from electrostatic Langmuir waves. For this, rapid measurements of plasma density, sufficiently rapid to be on the time scale of Langmuir wave fluctuations, are deemed necessary. Measurements of the potential of the antennas relative to the spacecraft can supply these rapid measurements. The antennas were not provided with a bias current, and so this unbiased technique has not been used previously. However, the cylindrical antennas of S/WAVES respond to temperature as well as the density of the ambient plasma, giving five quantities, ne, Te, and 3 components of E, to be determined from the three measurements of antenna potential. The work presented here discusses the analysis and interpretation of these measurements from the early part of the mission, when there were frequent observations of foreshock Langmuir waves to use for calibration. A model of the photoemission‐plasma equilibrium has been constructed, using these and other measurements. It is shown that the response to one or a few of the five quantities may be negligible, depending on the phenomenon observed, so that useful measurements are obtained of the others. Application to observation and analysis of various plasma wave phenomena will be discussed.

Ion-temperature-gradient-driven modes in bi-ion magnetoplasma

The toroidal ion-temperature-gradient (ITG)-driven electrostatic drift waves are investigated for bi-ion plasmas with equilibrium density, temperature and magnetic field gradients. Using Braginskii's transport equations for the ions and Boltzmann distributed electrons, the mode coupling equations are derived. New ITG-driven modes are shown to exist. The results of the present study should be helpful to understand several wave phenomena in space and tokamak plasmas.

Nature of magnetic fluctuations in Saturn's middle magnetosphere

The saturnian magnetosphere contains a rich array of plasma wave and MHD wave phenomena. These waves are fed by mass loading in the region of the E ring starting with Enceladus at 3.9 Saturn radii (Rs). In this paper we examine the nature of these waves in what we term to be the middle magnetosphere from just outside the mass loading at Enceladus to just inside the region of the magnetodisk, roughly 5 Rs to 15 Rs. In the inner part of this region are ion‐cyclotron waves near the water group gyrofrequency associated with mass loading of the magnetosphere by the E ring neutral torus that produces a ring beam of water group ions in velocity space. At about 5.5 Rs, isolated flux tubes are seen that appear to be convecting outward containing cooler plasma. This is a region of high levels of compressional noise. The compressional fluctuations associated with isolated flux tubes never completely disappear but their amplitude diminishes with distance. Weak mirror mode waves are present even at 5 Rs. Those waves grow with increasing radial distance, become dominant, and then the ion cyclotron waves weaken. While both instabilities grow from the same pressure anisotropy, the mirror mode dominance at large distances may be due to the fact that the ion cyclotron waves propagate out of the wave growth region, while the mirror mode waves remain in it and convect with the plasma. Finally, around 12 Rs the magnetosphere switches to be turbulent, more strongly in the transverse component than in the compressional component.

Introduction

The Sun's magnetic field is responsible for many spectacularly dynamic and intricate phenomena, such as the 11 year solar activity cycle, the hot and tenuous outer atmosphere called the solar corona, and the continuously expanding stream of solar particles known as the solar wind.Recently, there has been an enormous increase in our understanding of the role of solar magnetism in producing the observed complex atmosphere of the Sun. One such advance has occurred in the detection, by several different high-resolution space instruments on-board the Solar and Heliospheric Observatory and Transition Region and Coronal Explorer satellites, of magnetic waves and oscillations in the solar corona. The new subjects of solar atmospheric and coronal seismology are undergoing rapid development. The aim of this Scientific Discussion Meeting was to address the progress made through observational, theoretical and numerical studies of wave phenomena in the magnetic solar plasma. Major theoretical and observational advances were reported by a wide range of international scientists and pioneers in this field, followed by lively discussions and poster sessions on the many intriguing questions raised by the new results. Theoretical and observational aspects of magnetohydrodynamic waves and oscillations in general, and how these wave phenomena differ in various regions of the Sun, including sunspots, the transient lower atmosphere and the corona (in magnetic loops, plumes and prominences), were addressed through invited review papers and selected poster presentations. The results of these deliberations are collected together in this volume.

Planetary foreshock radio emissions

The electron foreshock regions upstream of Earth's bow shock and upstream of traveling interplanetary shocks are known to be propitious sites for a variety of energetic particle and plasma wave phenomena, including radio emissions. A quantitative theoretical model has been developed for radio emissions associated with the terrestrial foreshock and for type II radio bursts associated with interplanetary shocks. Here, we generalize this model and apply it to other planetary foreshocks. We present predictions for the levels of planetary foreshock radio emissions and compare these with observations by past and present space missions. One key result is that Mercury can be a strong source of foreshock radio emissions, and this prediction may be testable with the anticipated BepiColombo space mission. Although the terrestrial foreshock radio emissions are the most detectable with existing instruments, our results predict that they are the second strongest in absolute terms, following the Jovian foreshock emissions. Indeed, we predict that the radio instrument on board Ulysses should have detected Jovian foreshock radio emissions, and we suggest that there is some evidence in the data to support this. We also suggest that Cassini was potentially capable of detecting foreshock emissions from Venus during its gravity‐assist flybys and may possibly be capable of detecting foreshock emissions from Saturn under favorable solar wind conditions.

Effect of ion-temperature gradients on the formation of drift-Alfvén vortices in electron-positron-ion magnetoplasma with equilibrium flows

A set of coupled nonlinear equations which governs the dynamics of low-frequency electromagnetic waves in a nonuniform electron-positron-ion magnetoplasma with non-zero ion-temper-ature-gradients is derived and solved analytically under various approximations. In the linear limit, a local dispersion relation has been derived and analyzed in several interesting limiting cases. On the other hand, a quasi-stationary solution of the mode coupling equations in the absence of collisions can be represented in the form of dipolar and vortex-chain solutions. The results of the present investigation should be useful to understand the wave phenomena in laboratory and astrophysical plasmas.

Parametric Variations of Dromion Solutions in Auroral Plasmas

Dromions are exact nonlinear solutions of a large class of two-dimensional (2-D) partial differential equations and may be considered as an extension of the familiar soliton solutions to the 2-D space. They have stable localized structures with an exponential decay in both space dimensions and are characterized by time-dependent boundary conditions. While solitons have been used extensively to model coherent wave phenomena in plasmas, dromions have received little attention in terms of application to experimental observations. In a recent paper, we have shown that the nonlinear evolution of a 2-D electron acoustic wave in auroral plasma may lead to dromion solutions whose shape and size can be consistent with those of monopolar and bipolar pulses observed by the high resolution measurements of POLAR and FAST satellites. The previous theoretical analysis is extended to examine the time evolution of the dromion solution, study its stability, and discuss its boundary conditions in the context of auroral plasmas. The effect of different parameters on the shape and size of the dromion solutions is also estimated.

Alpha: A large-area plasma helicon array

Helicon sources are extremely efficient in creating high density, current free plasma discharges. However, these sources typically have a small cross-sectional area and are unsuitable for studies that require a large diameter plasma. We report the construction of a plasma facility that overcomes this limitation by using multiple helicon sources in a close-packed array. A large-area plasma helicon array (Alpha) is a 4 m long, 50 cm diam device that uses seven helicon sources to generate a large diameter rf plasma. The facility is designed to study basic plasma wave phenomena in a high-density, current-free plasma. The helicon array can operate in one of two modes, creating either seven distinct plasma columns or an integrated uniform large diameter plasma column. Details of the facility specifications, construction, and initial plasma parameters of the multihelicon source are reported.

Localized Multi-Dimensional Coherent Structures in Space and Laboratory Plasmas

The study of multi-dimensional localized structures has recently attracted a lot of attention due to their potential applications in nonlinear optical media and as a higher dimensional generalization of solitonic studies. Dromions are one such class of nonlinear structures that occur as exact solutions of a large class of two and three dimensional partial differential equations. They have localized structures with an exponential decay in all space dimensions and are driven by time dependent boundary conditions. While solitons have been used extensively to model coherent wave phenomena in plasmas, dromion solutions are not so well known in the plasma community and have received scant attention. We provide a brief introductory review of dromion solutions and discuss their potential application as a paradigm for modeling the rich variety of multi-dimensional coherent pulse structures observed in space and laboratory plasmas.

Sudden commencements related plasma waves observed by the Akebono satellite in the polar region and inside the plasmasphere region

Plasma wave phenomena associated with sudden commencements (SC) are analyzed using the database of the Akebono satellite observations that have been carried out for more than 13 years since March 1989. All the 719 data sets simultaneously observed in the periods of SC events show that plasma waves are enhanced with one‐to‐one correspondence to SCs in entire regions of the polar cap, auroral zone, and plasmasphere within a response time of ±90 s. In the middle latitude and equatorial regions of the plasmasphere, intensification and frequency shift of electromagnetic whistler mode, LHR waves, and ion cyclotron harmonic waves are found. The electric field variations in this region also show clear response to the onset of SCs with the amplitude of 0.2–30 mV/m. The variations are observed in the nightside as well as dayside sectors, and no clear dependence of magnetic latitude, local time, and L shell is found. On the other hand, electrostatic whistler mode waves and electromagnetic ion cyclotron waves which show broadband spectra are generated in the high‐latitude region. Spectra of low‐energy particles observed simultaneously with the enhancement of these plasma waves show that electron fluxes are enhanced in all of pitch angle bins of the low‐energy particle detector onboard the Akebono satellite. Near the cusp region, the ion fluxes are more enhanced in the upward direction than in the downward direction along the magnetic field lines. In about half of the cases of the high‐latitude events, sudden appearance and intensification of AKR are also found after the onsets of SC. The delay time between the onsets of SC and AKR enhancement shows several minutes with the average time of 5.7 min. Time differences between the onsets of SC measured at Kakioka Magnetic Observatory and plasma wave enhancements observed by the Akebono satellite show positive correlation with possible delay time according to the propagation route of SC disturbances. Propagation character of SC disturbances shows two group signatures: one group takes a route which crosses the geomagnetic equator region with an average speed of 389.5 km/s. The speed is almost consistent with plasmaspheric fast‐mode MHD wave velocity. The other group takes a route which starts from the dayside cusp region. In the second case, the SC disturbances propagate through the polar ionosphere region from the dayside to the nightside sectors with an average speed of 47 km/s in the XGSM coordinate corresponding to the ionospheric fast‐mode MHD wave velocity.

Electrostatic instabilities and nonlinear structures of low-frequency waves in nonuniform electron–positron–ion plasmas with shear flow

It is found that the low-frequency ion acoustic and electrostatic drift waves can become unstable in uniform electron–ion and electron–positron–ion plasmas due to the ion shear flow. In a collisional plasma a drift-dissipative instability can also take place. In the presence of collisions the temporal behavior of nonlinear drift-dissipative mode can be represented in the form of well-known Lorenz and Stenflo type equations that admit chaotic trajectories. On the other hand, a quasi-stationary solution of the mode coupling equations can be represented in the form of monopolar vortex. The results of the present investigation can be helpful in understanding electrostatic turbulence and wave phenomena in laboratory and astrophysical plasmas.

On the performance of a cylindrical dipole antenna in diagnostics of wave phenomena in space plasma

There is a pronounced, permanent, variable frequency banded enhancement in high frequency spectra recorded in the ionospheric electron plasma on APEX and CORONAS-I. Spectral characteristics of this banded structure in diverse geophysical regions are discussed. The local plasma density derived with independent techniques is crucial for the interpretation of the banded enhancement. The quasi-simultaneous local plasma density is derived from the antenna impedance measurement, artificial electron beam induced spectra and topside sounder data. Equivalent circuit simulations of wave and impedance measurements reveal spectral signatures of cold plasma density, which match both types of data recorded under stationary conditions. The major spectral characteristics of the banded enhancement are also consistent with equivalent circuit simulations. The data and simulations suggest that the upper hybrid band may be misinterpreted as a circuit resonance. Circuit resonance can be neatly controlled to provide very low interference technique to monitor the density of cold plasma. Circuit resonance monitoring, if properly coupled with impedance measurements and electron beam injection may be a very useful low interference tool for diagnostics of highly structured plasmas like those in the auroral region.

Self-Organized and Chaotic States in Dust-Contaminated Electron-Positron Magnetoplasma with Equilibrium Flows

Nonlinear equations governing the dynamics of low-frequency (in comparison with electron gyro-frequency) electrostatic disturbances in a nonuniform resistive dust-contaminated electron-positron magnetoplasma with equilibrium sheard flow are derived. In the linear limit, a local dispersion relation has been derived and analyzed. On the other hand, in the nonlinear case, the temporal behavior of the nonlinear system can be represented in the form of a 5 × 5 matrix, which is a generalization of Lorenz-Stenflo equations admitting chaotic trajectories. We have also presented a linear stability analysis of a generalized Lorenz-Stenflo system of equations under different approximations. It is also shown that for small magnetic shear and for a nondissipative plasma, a quasi-stationary solution of the mode coupling equations can be represented in the form of counter-rotating vortices. These results would be helpful to understand plasma turbulence and wave phenomena which have frequently been observed in several laboratory and astrophysical plasma systems.

Nonlinear Structures in Solar System Plasmas

The magnetosphere and the heliosphere constitute a magnificent laboratory for plasma wave phenomena, some of which have been studied in situ by ingenious spacecraft instrumentation, on board satellites probing interplanetary space as well as planetary and cometary environments. In several of these missions nonlinear structures have been observed. On the theoretical side, there are well known paradigms for nonlinear waves and solitons, like the different versions of the Korteweg-de Vries or nonlinear Schrödinger equations in multi-ion plasmas. We give a brief overview of how some of the more recent observations can be connected to the archetypical mathematical descriptions, in particular for magnetospheric boundary layer waves, nonlinear Alfvén waves in interplanetary space and solitary waves in cometary plasmas.

First results from the Cluster wideband plasma wave investigation

Abstract. In this report we present the first results from the Cluster wideband plasma wave investigation. The four Cluster spacecraft were successfully placed in closely spaced, high-inclination eccentric orbits around the Earth during two separate launches in July – August 2000. Each spacecraft includes a wideband plasma wave instrument designed to provide high-resolution electric and magnetic field wave-forms via both stored data and direct downlinks to the NASA Deep Space Network. Results are presented for three commonly occurring magnetospheric plasma wave phenomena: (1) whistlers, (2) chorus, and (3) auroral kilometric radiation. Lightning-generated whistlers are frequently observed when the spacecraft is inside the plasmasphere. Usually the same whistler can be detected by all spacecraft, indicating that the whistler wave packet extends over a spatial dimension at least as large as the separation distances transverse to the magnetic field, which during these observations were a few hundred km. This is what would be expected for nonducted whistler propagation. No case has been found in which a strong whistler was detected at one spacecraft, with no signal at the other spacecraft, which would indicate ducted propagation. Whistler-mode chorus emissions are also observed in the inner region of the magnetosphere. In contrast to lightning-generated whistlers, the individual chorus elements seldom show a one-to-one correspondence between the spacecraft, indicating that a typical chorus wave packet has dimensions transverse to the magnetic field of only a few hundred km or less. In one case where a good one-to-one correspondence existed, significant frequency variations were observed between the spacecraft, indicating that the frequency of the wave packet may be evolving as the wave propagates. Auroral kilometric radiation, which is an intense radio emission generated along the auroral field lines, is frequently observed over the polar regions. The frequency-time structure of this radiation usually shows a very good one-to-one correspondence between the various spacecraft. By using the microsecond timing available at the NASA Deep Space Net-work, very-long-baseline radio astronomy techniques have been used to determine the source of the auroral kilometric radiation. One event analyzed using this technique shows a very good correspondence between the inferred source location, which is assumed to be at the electron cyclotron frequency, and a bright spot in the aurora along the magnetic field line through the source.Key words. Ionosphere (wave-particle interactions; wave propagation) – Magnetospheric physics (plasma waves and instabilities; instruments and techniques)

The plasma wave environment of Europa

The Galileo spacecraft has executed nine close flybys of Jupiter's moon Europa for which plasma wave observations were obtained. This paper presents an analysis of the observations from these flybys taking into consideration the variable geometry of the trajectories in an attempt to characterize the general plasma-wave environment associated with the interaction of the Jovian magnetosphere with the moon. A wide variety of plasma-wave phenomena are found to be associated with this interaction. While there are apparently temporal variations which complicate the analysis, a crude model of the distribution of these phenomena around Europa is derived. Primarily on the upstream side of Europa, and working inward to the moon, electron–cyclotron harmonics are first observed, followed by a region within about two Europa radii of the moon with whistler-mode hiss or chorus, and culminating in a region closest to the moon where a band at the upper hybrid resonance frequency is sometimes enhanced over its ambient intensity. The wake region is approximately two Europa radii across and comprises a broadband, highly variable, and bursty electrostatic phenomenon. Upon closer inspection, these bursty emissions appear as solitary structures similar to those in Earth s auroral zone and plasma sheet boundary layer. In addition to the survey of wave phenomena in the vicinity of Europa, we provide density profiles derived primarily from the upper hybrid resonance frequency which is readily apparent throughout most of each of the flybys. Finally, we suggest that the whistler mode, electron cyclotron harmonic, and upper hybrid resonance emissions are driven by some combination of factors including variations in the magnetic field near Europa and the loss and production of plasma at Europa as a result of the interaction of the Jovian magnetosphere with the moon. By analogy with studies of the ion and electron holes and broadband electrostatic noise at Earth and Jupiter, we argue that the electrostatic solitary structures in the wake are associated with currents and beams coupling Europa to Jupiter's ionosphere.

Chaotic behavior of ion-temperature-gradient driven drift-dissipative modes

A new set of nonlinear mode coupling equations for finite amplitude low-frequency electromagnetic waves has been derived for nonuniform, resistive, magnetized electron-ion plasma with sheared flows. At equilibrium, the plasma is assumed to have density, ion-temperature, magnetic field, and velocity gradients. The temporal behavior of the nonlinear mode coupling equations is found to be governed by eight coupled equations, which are the generalization of the Lorenz and Stenflo equations, admitting chaotic trajectories. The linear stability of the generalized Lorenz–Stenflo system of equations is also presented under different approximations. The results of the present investigation should be helpful in understanding the wave phenomena in space and tokamak plasmas.