Nonuniform Plasma Research Articles

Solitary structures in an inhomogeneous plasma with pseudo-potential approach

The set of nonlinear partial differential equations for the coupled ion acoustic and drift waves is reduced to the KdV equation, which is finally transformed into the form of energy integral equation of a pseudo particle in small amplitude limit. It is pointed out that this approach is convenient for choosing appropriate plasma parameters and numerically obtaining drift solitary wave profiles as compared to the solution of the KdV equation, particularly, in non-uniform plasmas. Electrons are assumed to follow the Kappa distribution function. It is found that the solitons amplitude decreases corresponding to steeper density and temperature gradients because of the restriction on the validity of local approximation. Deviation of electrons from thermal equilibrium distribution is supportive for the formation of electrostatic solitary structures by the coupled nonlinear ion acoustic and drift waves. The estimates of the width of the solitons formed by these coupled nonlinear electrostatic waves in the F-region ionosphere are found to be a few meters in agreement with the satellite observations.

Linear and Nonlinear Coupling of Electrostatic Drift and Acoustic Perturbations in a Nonuniform Bi-Ion Plasma with Non-Maxwellian Electrons

Linear and nonlinear coupling of drift and ion acoustic waves are studied in a nonuniform magnetized plasma comprising of Oxygen and Hydrogen ions with nonthermal distribution of electrons. It has been observed that different ratios of ion number densities and kappa and Cairns distributed electrons significantly modify the linear dispersion characteristics of coupled drift-ion acoustic waves. In the nonlinear regime, KdV (for pure drift waves) and KP (for coupled drift-ion acoustic waves) like equations have been derived to study the nonlinear evolution of drift solitary waves in one and two dimensions. The dependence of drift solitary structures on different ratios of ion number densities and nonthermal distribution of electrons has also been explored in detail. It has been found that the ratio of the diamagnetic drift velocity to the velocity of the nonlinear structure determines the existence regimes for the drift solitary waves. The present investigation may be beneficial to understand the formation of solitons in the ionospheric F-region.

Analytic model for electromagnetic fields in the bubble regime of plasma wakefield in non-uniform plasmas

Based on a model of plasma wakefield in the strongly nonlinear (bubble) regime, we develop a lowest-order perturbation theory for the components of electromagnetic fields inside and outside the bubble using the assumption of small thickness of the electron sheath on the boundary of the bubble. Unlike previous models, we derive simple explicit expressions for the components of electromagnetic fields not only in the vicinity of the center of the bubble, but in the whole volume of the bubble (including the areas of driving or accelerated bunches) as well as outside it. Moreover, we apply the results to the case of radially non-uniform plasma and, in particular, to plasma with a hollow channel. The obtained results are verified with 3D particle-in-cell simulations which show a good correspondence to our model.

Gestational Diabetes and Subsequent Risk of Albuminuria in Later Life Among US Women

Local dispersion relations for resistive drift mode in a nonuniform magnetize plasma are derived for thermal and non-thermal distribution of electrons. The coupled mode equations are obtained by using Braginskii's transport equations for ions and electrons with thermal as well as non-thermal (Cairns and kappa) distribution for electrons. The dispersion relations are then analyzed both analytically as well as numerically for all distributions. It is found that growth rate is highest for Maxwellian, Intermediate for kappa and lowest for Cairns distribution. It has been found that increasing values of Γ (which estimate population of non-thermal electrons) for Cairn distributed electrons are able to stabilize the mode. Furthermore, increasing the values of κ (which is spectral index) for the kappa distributed electrons have destabilizing effects on the mode. The result might be useful in the interpretation of electromagnetic fluctuations in nonuniform magneto-plasma in which resistivity is a key element in calculation of drift instabilities in the presence of thermal or nonthermal electron distributions, such systems are extensively observed in laboratory as well as space plasma.

Effect of a dielectric layer on plasma uniformity in high frequency electronegative capacitive discharges

The authors use a fast 2D axisymmetric fluid-analytical code to study the effect of adding a dielectric layer over the wafer electrode of a high frequency capacitively coupled plasma (CCP) reactor. At higher frequencies and larger areas, the wavelengths of the radially propagating surface waves in the plasma can become significantly shorter than the reactor dimensions, leading to center-high plasma nonuniformities. These wavelengths increase with increasing sheath widths, suggesting that a method to suppress wave effects in a high frequency CCP is to increase the effective sheath width by adding a dielectric layer over the wafer electrode. The authors conducted simulations with and without a dielectric layer and found that the dielectric layer improved plasma uniformity. The authors also studied the effect of adding a thin conducting or resistive silicon wafer above the dielectric layer and found that a conducting silicon wafer shorts out the fields and shields the discharge from the dielectric layer, while the resistive silicon wafer allows the fields to pass through to the dielectric layer.

Propagation of short pulses in a non-uniform gas-jet induced plasma

A formalism describing the propagation of short duration (sub-picosecond) Gaussian pulses in a preformed axially non-uniform collisionless plasma has been established; a plasma inhomogeneity consistent with the gas jet induced plasma as super-Gaussian (flat-top) profile has been considered herein. In order to specify the pulse dynamics using nonlinear Schrödinger wave equation (NLSE) in paraxial regime, a set of coupled equations characterizing the transverse focusing (in space) and temporal compression (in time) of the laser pulse has been derived, and further solved numerically to investigate the propagation characteristics of the pulse as it advances through gas jet induced plasma. The effect of plasma inhomogeneity parameters on the characteristic features of the pulse propagation have been analysed and illustrated graphically. The focusing and axial intensity of the propagating pulse is observed to be sensitive to the plasma profile (gas jet parameters), and the focusing length can be tuned up to desired extent by suitable choice of the inhomogeneity parameters.

Second-order dissipative hydrodynamics for plasma with chiral asymmetry and vorticity

By making use of the chiral kinetic theory in the relaxation-time approximation, we derive an Israel-Stewart type formulation of the hydrodynamic equations for a chiral relativistic plasma made of neutral particles (e.g., neutrinos). The effects of chiral asymmetry are captured by including an additional continuity equation for the axial charge, as well as the leading-order quantum corrections due to the spin of particles. In a formulation of the chiral kinetic theory used, we introduce a symmetric form of the energy-momentum tensor that is suitable for the description of a weakly nonuniform chiral plasma. By construction, the energy and momentum are conserved to the same leading order in the Planck constant as the kinetic equation itself. By making use of such a chiral kinetic theory and the Chapman-Enskog approach, we obtain a set of second-order dissipative hydrodynamic equations. The effects of the fluid vorticity and velocity fluctuations on the dispersion relations of chiral vortical waves are analyzed.

Conductivity tensor for anisotropic plasma in gyrokinetic theory

It has been argued that oblique firehose and mirror instabilities are important candidates for the regulation of temperature anisotropy in solar wind. To quantify the role of anisotropy driven instabilities, global kinetic simulations of the solar wind would be extremely useful. However, due to long time scales involved, such simulations are prohibitively expensive. Gyrokinetic theory and simulations have proven to be valuable tools for the study of low frequency phenomena in nonuniform plasmas; however, there are discrepancies between the anisotropy driven instabilities appearing in the gyrokinetic theory and those of a fully kinetic one. We present a derivation of the conductivity tensor based on the arbitrary frequency gyrokinetics and show that relaxing the condition ω/Ω≪1, where ω is the wave frequency, and the Ω is the cyclotron frequency, eliminates these discrepancies, while preserving the advantages of the gyorkinetic theory for global kinetic simulations.

Effect of degeneracy temperature on drift solitary structures in a nonuniform degenerate plasma

Linear and nonlinear propagation of quantum drift ion acoustic waves have been studied in a spatially inhomogeneous degenerate quantum plasma taking into account the effect of electron trapping. The linear dispersion relation has been derived in this regard in a 2D quantum magnetoplasma with trapped electrons and a significant amendment in the linear propagation characteristics of the wave under consideration has been observed due to the degeneracy temperature. The drift ion solitary structures have been investigated in 1D and 2D by employing the drift approximation. We obtained the compressive drift solitary structures which are analyzed numerically for the parameters, such as degeneracy temperature, typically found in white dwarfs.

Absorption of electromagnetic waves by a moving non-uniform plasma

The absorption coefficient of electromagnetic waves by a moving non-uniform plasma slab is investigated theoretically. Two cases of movement are considered: (1) the plasma slab moves parallel to the interface and (2) the plasma slab moves perpendicular to the interface. In both the cases, the influences of six typical plasma parameters on the absorption coefficient are discussed in detail by analyzing the relativistic model. It has been obtained that the absorption coefficient is strongly affected by the velocity of the moving plasma. Various interesting features concerning the variation of the absorption coefficient are obtained, which are very important for applications in space exploration.

Nonlinear relativistic plasma resonance: Renormalization group approach

An analytical solution to the nonlinear set of equations describing the electron dynamics and electric field structure in the vicinity of the critical density in a nonuniform plasma is constructed using the renormalization group approach with allowance for relativistic effects of electron motion. It is demonstrated that the obtained solution describes two regimes of plasma oscillations in the vicinity of the plasma resonance— stationary and nonstationary. For the stationary regime, the spatiotemporal and spectral characteristics of the resonantly enhanced electric field are investigated in detail and the effect of the relativistic nonlinearity on the spatial localization of the energy of the plasma relativistic field is considered. The applicability limits of the obtained solution, which are determined by the conditions of plasma wave breaking in the vicinity of the resonance, are established and analyzed in detail for typical laser and plasma parameters. The applicability limits of the earlier developed nonrelativistic theories are refined.

Effect of dust size distribution on ion-acoustic solitons in dusty plasmas with different dust grains

Theoretical studies are carried out for ion acoustic solitons in multicomponent nonuniform plasma considering the dust size distribution. The Korteweg−de Vries equation for ion acoustic solitons is given by using the reductive perturbation technique. Two special dust size distributions are considered. The dependences of the width and amplitude of solitons on dust size parameters are shown. It is found that the properties of a solitary wave depend on the shape of the size distribution function of dust grains.

Fast magnetic field penetration into low resistivity plasma

Penetration of a magnetic field into plasma that is faster than resistive diffusion can be induced by the Hall electric field in a non-uniform plasma. This mechanism explained successfully the measured velocity of the magnetic field penetration into pulsed plasmas. Major related issues have not yet been resolved. Such is the theoretically predicted, but so far not verified experimentally, high magnetic energy dissipation, as well as the correlation between the directions of the density gradient and of the field penetration.

Propagation of Electromagnetic Waves on a Relativistically Moving Nonuniform Plasma

The propagation properties of electromagnetic wave (EMW) in a moving nonuniform plasma are first introduced in this study. The incident frequency and the angle of incidence of the EMW in a moving plasma are discussed in detail by analyzing the relativistic model. It has been obtained that both of them are strongly affected by the moving speed. By utilizing Wentzel–Kramers–Brillouin approximation method in a moving plasma, the nonuniform plasma density of a parabolic profile is taken as an example to make analyses about these six parameters of plasma in this study. Results indicate that the influences of these five parameters on the EMW attenuation are the same whether the plasma is stationary or moving except for the angle of incidence. Furthermore, only the angle of incidence has the ability to determine the critical speed of the maximum attenuation.

Modeling and simulations on the propagation characteristics of electromagnetic waves in sub-atmospheric pressure plasma slab

Sub-atmospheric pressure plasma slabs exhibit the feature of relatively high plasma number density and high collisional frequency between electrons and neutral gases, as well as similar thickness to the electromagnetic (EM) wavelength in communication bands. The propagation characteristics of EM waves in sub-atmospheric pressure plasma slabs are attracting much attention of the researchers due to their applications in the plasma antenna, the blackout effect during reentry, wave energy injection in the plasma, etc. In this paper, a numerical model with a one-dimensional assumption has been established and therefore, it is used for the investigations of the propagation characteristics of the EM waves in plasma slabs. In this model, the EM waves propagating in both sub-wavelength plasma slabs and plasmas with thicker slabs can be studied simultaneously, which is superior to the model with geometrical optics approximation. The influence of EM wave frequencies and collisional frequencies on the amplitude of the transmitted EM waves is discussed in typical plasma profiles. The results will be significant for deep understanding of the propagation behaviors of the EM waves in sub-atmospheric pressure nonuniform plasma slabs, as well as the applications of the interactions between EM waves and the sub-atmospheric pressure plasmas.

Effect of standing wave on the uniformity of a low magnetic field helicon plasma

Helicon wave discharge has higher coupling efficiency than capactively coupled and inductively coupled discharge in low static magnetic field. In the wave sustained mode, a large volume and large area plasma can be produced at lower pressure by using comparable discharge power, and thus it expands the helicon wave plasma applications in material surface modification, thin film deposition, dry etching and thruster usage. However, the application of helicon wave source still faces challenges, such as the controversial power coupling mechanism, operation stability and the plasma distribution uniformity in the experiment. The wave mode existing in bounded helicon wave plasma column generally consists of helicon and Trivelpiece-Gould (TG) components, and their mode transitions and different transverse wave field distribution regions, and the propagating characteristic of the helicon wave are directly related to the power coupling and plasma density distribution in the source region, then affect the uniformity of material processing and film deposition in the diffusion chamber. In this paper, the plasma azimuthal non-uniformity, with using Doubble Saddle antenna, 100 G static magnetic field in helicon wave plasma source, is studied by electrical characteristic (power-current) curve, intensified charge coupled device (ICCD) image and magnetic probe measurements. The electrical characteristic curve indicates two discharge stages with different effective resistances. Meanwhile, in the second stage, the higher effective resistance would result in higher coupling efficiency and higher plasma density. But the ICCD image demonstrates the azimuthal non-uniformity of plasma, indicating that the main heating points at the diagonal edge are linked to the stationary transverse electrical field line pattern of azimuthal mode number m=+1 helicon wave, and the magnetic probe is used to measure the helicon wave magnetic field Bz component along the quartz source tube axially. The magnetic probe results show that the standing wave appearing below the antenna even though in the upper region of the antenna is characteristic of the traveling wave. Furthermore, at the plasma boundary, the standing wave can be coupled to the TG wave, and not like travelling wave it has no angular rotation of the electric field and may cause the non-uniform coupling between the helicon and TG components. The TG wave then has azimuthal non-uniform electron heating. Therefore, the standing helicon wave below the antenna is the key factor to the plasma non-uniformity problem. Changing the propagating characteristics of the helicon wave further in the plasma column will be of positive significance for optimizing the discharge efficiency of the plasma source and controlling the plasma distribution uniformity, stability and other operations as well.

A miniature, low‐power scientific fluxgate magnetometer: A stepping‐stone to cube‐satellite constellation missions

AbstractDifficulty in making low noise magnetic measurements is a significant challenge to the use of cube‐satellite (CubeSat) platforms for scientific constellation class missions to study the magnetosphere. Sufficient resolution is required to resolve three‐dimensional spatiotemporal structures of the magnetic field variations accompanying both waves and current systems of the nonuniform plasmas controlling dynamic magnetosphere‐ionosphere coupling. This paper describes the design, validation, and test of a flight‐ready, miniature, low‐mass, low‐power, and low‐magnetic noise boom‐mounted fluxgate magnetometer for CubeSat applications. The miniature instrument achieves a magnetic noise floor of 150–200 pT/√Hz at 1 Hz, consumes 400 mW of power, has a mass of 121 g (sensor and boom), stows on the hull, and deploys on a 60 cm boom from a three‐unit CubeSat reducing the noise from the onboard reaction wheel to less than 1.5 nT at the sensor. The instrument's capabilities will be demonstrated and validated in space in late 2016 following the launch of the University of Alberta Ex‐Alta 1 CubeSat, part of the QB50 constellation mission. We illustrate the potential scientific returns and utility of using a CubeSats carrying such fluxgate magnetometers to constitute a magnetospheric constellation using example data from the low‐Earth orbit European Space Agency Swarm mission. Swarm data reveal significant changes in the spatiotemporal characteristics of the magnetic fields in the coupled magnetosphere‐ionosphere system, even when the spacecraft are separated by only approximately 10 s along track and approximately 1.4° in longitude.

Research on the FDTD Method of Electromagnetic Wave Scattering Characteristics in Time-Varying and Spatially Nonuniform Plasma Sheath

3-D time-varying and spatially nonuniform plasma is applied using the finite-difference time-domain algorithm in investigating the effects of electromagnetic (EM) wave scattering in the plasma sheath. The plasma sheath is stratified in space, and three types of electron density in time-varying forms are assumed. The characteristics of different time-varying forms are analyzed using radar cross section (RCS). In addition, the effects of RCS change with time at ${S}$ - and ${L}$ -bands are investigated using electron density as the time variable. In the condition of time-varying and spatially nonuniform plasma sheath, the attenuation of EM wave is affected by different time-varying regularities of electron density ( $n_{e}$ ). The RCS varying with time is related to the change rate of $n_{e}$ .

An iterative method to include spatial dispersion for waves in nonuniform plasmas using wavelet decomposition

A novel method for solving wave equations with spatial dispersion is presented, suitable for applications to ion cyclotron resonance heating. The method splits the wave operator into a dispersive and a non-dispersive part. The latter can be inverted with e.g. finite element methods. The spatial dispersion is evaluated using a wavelet representation of the dielectric kernel and added by means of iteration. The method has been successfully tested on a low frequency kinetic Alfven wave with second order Larmor radius effects in a nonuniform plasma slab.

Motion Magnification in Coronal Seismology

We introduce a new method for the investigation of low-amplitude transverse oscillations of solar plasma non-uniformities, such as coronal loops, individual strands in coronal arcades, jets, prominence fibrils, polar plumes, and other contrast features, observed with imaging instruments. The method is based on the two-dimensional dual tree complex wavelet transform (DT$\mathbb{C}$WT). It allows us to magnify transverse, in the plane-of-the-sky, quasi-periodic motions of contrast features in image sequences. The tests performed on the artificial data cubes imitating exponentially decaying, multi-periodic and frequency-modulated kink oscillations of coronal loops showed the effectiveness, reliability and robustness of this technique. The algorithm was found to give linear scaling of the magnified amplitudes with the original amplitudes provided they are sufficiently small. Also, the magnification is independent of the oscillation period in a broad range of the periods. The application of this technique to SDO/AIA EUV data cubes of a non-flaring active region allowed for the improved detection of low-amplitude decay-less oscillations in the majority of loops.