Cold Homogeneous Plasma Research Articles

Theory of wakefields excited by an off-axis drive bunch in a plasma–dielectric waveguide

A linear theory of wakefield excitation by a drive electron bunch in a plasma–dielectric accelerating structure has been constructed for the case of off-axis bunch injection. The structure under investigation is a round dielectric-loaded metal waveguide with a channel for charged particles, filled with homogeneous cold plasma. The developed theory was used to investigate the spatial distribution of the bunch-excited transverse wakefield components, which act on the drive electron bunch. The numerical simulations using the particle-in-cell method have confirmed the predictions of the linear theory in terms of transverse drive bunch dynamics. The numerical analysis has shown stable drive bunch transport through the plasma–dielectric accelerating structure compared with the corresponding dielectric-loaded structure.

Effect of ion motion on breaking of longitudinal relativistically strong plasma waves: Khachatryan mode revisited

The effect of ion motion on the spatiotemporal evolution of a relativistically strong space charge wave is studied using a 1D fluid simulation code. In our simulation, these waves are excited in the wake of a rigid electron beam propagating through a cold homogeneous plasma with a speed close to the speed of light. It is observed that the excited wave is a mode as described by Khachatryan [Phys. Rev. E 58, 7799–7804 (1998)] whose profile gradually sharpens and the wave eventually breaks after several plasma periods exhibiting explosive behavior. It is found that breaking occurs at amplitudes, which is far below the breaking limit analytically derived by Khachatryan [Phys. Rev. E 58, 7799–7804 (1998)]. This phenomenon of wave breaking, at amplitudes well below the breaking limit, is understood in terms of phase mixing of the excited wave. It is further found that the phase mixing time (wave breaking time) inversely scales with the energy density of the wave.

Light deflection by squashed Kaluza-Klein black holes in a plasma medium

We study motions of photons in an unmagnetized cold homogeneous plasma medium in the five-dimensional charged static squashed Kaluza-Klein black hole spacetime. In this case, a photon behaves as a massive particle in a four-dimensional spherically symmetric spacetime. We consider the light deflection by the squashed Kaluza-Klein black hole surrounded by the plasma in a weak-field limit. We derive corrections of the deflection angle to general relativity, which are related to the size of the extra dimension, the charge of the black hole and the ratio between the plasma and the photon frequencies.

Excitation of upper‐hybrid plasma wake wave by a low‐frequency extraordinary electromagnetic wave

AbstractThe excitation of upper‐hybrid wake electrostatic wave by interaction of an extraordinary Gaussian wave propagating perpendicular to the external magnetic field in a cold homogeneous plasma is investigated using magnetohydrodynamics theory. The plasma oscillations can be excited due to the charge separation appeared by the ponderomotive force of the electromagnetic wave whose frequency is considered in the lower pass band. By obtaining the equation governing the plasma wake, the dependency of the wake amplitude on the physical parameters is studied. It is observed that larger wake oscillation takes place when the pulse length is approximately close to 3λp/π and the X‐wave frequency is greater than ωp, which means that the phase velocity is less than the speed of light in vacuum (vp < c).

Effect of transverse beam size on the wakefields and driver beam dynamics in plasma wakefield acceleration schemes

In this paper, wakefields driven by a relativistic electron beam in a cold homogeneous plasma are studied using 2D fluid simulation techniques. It has been shown that in the limit when the transverse size of a rigid beam is greater than the longitudinal extension, the wake wave acquires a purely electrostatic form, and the simulation results show a good agreement with the 1D results given by Bera et al. [Phys. Plasmas 22, 073109 (2015)]. In the other limit when the transverse dimensions are equal to or smaller than the longitudinal extension, the wake waves are electromagnetic in nature, and 2D effects play a crucial role. Furthermore, a linear theoretical analysis of 2D wakefields for a rigid bi-parabolic beam has also been carried out and compared with the simulations. It has also been shown that the transformer ratio, which is a key parameter that measures the efficiency in the process of acceleration, becomes higher for a 2D system (i.e., for a beam having a smaller transverse extension compared to the longitudinal length) than the 1D system (i.e., for a beam having a larger transverse extension compared to the longitudinal length). Furthermore, including the self-consistent evolution of the driver beam in the simulation, we have seen that the beam propagating inside the plasma undergoes transverse pinching, which occurs much earlier than the longitudinal modification. Due to the presence of transverse dimensions in the system, the 1D rigidity limit given by Tsiklauri [Phys. Plasmas 25, 032114 (2018)] gets modified. We have also demonstrated the modified rigidity limit for the driver beam in a 2D beam–plasma system.

Higher order corrections to deflection angle of massive particles and light rays in plasma media for stationary spacetimes using the Gauss-Bonnet theorem

The purpose of this article is twofold. First, we extend the results presented in [Gabriel Crisnejo and Emanuel Gallo, Phys.Rev.D 97, 124016 (2018)] to stationary spacetimes. Specifically, we show that the Gauss-Bonnet theorem can be applied to describe the deflection angle of light rays in plasma media in stationary spacetimes. Second, by using a correspondence between the motion of light rays in a cold non magnetized plasma and relativistic test massive particles we show that this technique is not only powerful to obtain the leading order behavior of the deflection angle of massive/massless particles in the weak field regime but also to obtain higher order corrections. We particularize it to a Kerr background where we compute the deflection angle for test massive particles and light rays propagating in a non homogeneous cold plasma by including third order corrections in the mass and spin parameters of the black hole.

Nonlinear dynamics of relativistically intense cylindrical and spherical plasma waves

Spatio-temporal evolution and breaking of relativistically intense cylindrical and spherical space charge oscillations in a homogeneous cold plasma are studied analytically and numerically using the Dawson Sheet Model [J. M. Dawson, Phys. Rev. 113, 383 (1959)]. It is found that cylindrical and spherical space charge oscillations break via the process of phase mixing at an arbitrarily small amplitude due to anharmonicity introduced by geometry and relativistic mass variation effects. A general expression for phase mixing time (wave breaking time) has been derived and it is shown that for both cases, it scales inversely with the cube of the initial wave amplitude. Finally, this analytically obtained scaling is verified by using a numerical code based on the Dawson Sheet Model.

Study and optimization on the scattering characteristic of two-dimensional metal airfoil covered with plasma using ADE-FDTD

The bistatic radar cross section (RCS) of airfoil covered with cold homogeneous plasma is studied using 2-D auxiliary differential equation finite-difference time-domain (ADE-FDTD) method. The bistatic RCS of conductive cylinder, conductive cylinder covered with plasma and conductive airfoil are calculated and the results are compared with those of available literature to validate the accuracy of the algorithm. The influence of different parameters such as incident frequency, plasma frequency, collision frequency and plasma thickness on the airfoil's bistatic RCS are researched. The calculations demonstrate that the influence mechanisms of plasma frequency and collision frequency are more complicated, so they are chosen as variables to optimize the bistatic RCS of airfoil. RCS at every bistatic angle has various levels of attenuation under different choices of plasma frequency and collision frequency. The backscattering stealth effect is prominent with a reduction of 30dB. At last, the radar scattering characteristics of bending aerofoil is analyzed, which indicates that plasma coat can further reduce the airfoil's RCS in certain angles.

Phase mixing of relativistically intense longitudinal wave packets in a cold plasma

Phase mixing of relativistically intense longitudinal wave packets in a cold homogeneous unmagnetized plasma has been studied analytically and numerically using the Dawson Sheet Model. A general expression for phase mixing time (ωptmix) as a function of amplitude of the wave packet (δ) and width of the spectrum (Δk/k) has been derived. It is found that the phase mixing time crucially depends on the relative magnitude of amplitude “δ” and the spectral width “Δk/k”. For Δk/k≤2ωp2δ2/c2k2, ωptmix scales with δ as ∼1/δ5, whereas for Δk/k>2ωp2δ2/c2k2, ωptmix scales with δ as ∼1/δ3, where ωp is the non-relativistic plasma frequency and c is the speed of light in vacuum. We have also verified the above theoretical scalings using numerical simulations based on the Dawson Sheet Model.

Fluid simulation of relativistic electron beam driven wakefield in a cold plasma

Excitation of wakefield in a cold homogeneous plasma, driven by an ultra-relativistic electron beam is studied in one dimension using fluid simulation techniques. For a homogeneous rigid beam having density (nb) less than or equal to half the plasma density (n0), simulation results are found to be in good agreement with the analytical work of Rosenzweig [Phys. Rev. Lett. 58, 555 (1987)]. Here, Rosenzweig's work has been analytically extended to regimes where the ratio of beam density to plasma density is greater than half and results have been verified using simulation. Further in contrast to Rosenzweig's work, if the beam is allowed to evolve in a self-consistent manner, several interesting features are observed in simulation viz. splitting of the beam into beam-lets (for lb > λp) and compression of the beam (for lb < λp), lb and λp, respectively, being the initial beam length and plasma wavelength.

The Brush‐Shape Device Used to Generate Atmospheric and Homogeneous Plasmas for Biomedical Applications

AbstractThe brush‐shape device mainly consisting of the well‐aligned and microns‐thick hollow quartz fibers can be used to generate an atmospheric and homogeneous cold plasma jet for biomedical applications. Addition of a trace amount of O2 into the feed gas greatly altered the electrical properties of the plasma jet, thus had an obvious effect on the sterilization efficiency. The uniformity of the brush‐shape plasma jet along its transverse direction was well consistent with the uniform distribution of sterilization efficiency. The atmospheric He plasma jet containing 1% O2 may kill all the Candida albicans cells with a population of 105 spores within an exposure time of 180 s. Analysis indicates that both O radicals and charged species can be an important contributor in this plasma inactivation. magnified image

Wave breaking phenomenon of lower-hybrid oscillations induced by a background inhomogeneous magnetic field

In a fluid description, we study space-time evolution of lower hybrid modes in a cold quasi-neutral homogeneous plasma in presence of a background inhomogeneous magnetic field. Within a linear analysis, a dispersion relation with inhomogeneous magnetic field shows “phase mixing” of such oscillations. A manifestation of “phase mixing” is shown in “mode coupling.” By using Lagrangian variables, an exact solution is presented in parametric form of this nonlinear time dependent problem. It is demonstrated that initially excited lower hybrid modes always break via phase mixing phenomenon in presence of an inhomogeneous magnetic field. Breaking of such oscillations is revealed by the appearance of spikes in the plasma density profile.

Residual Bernstein-Greene-Kruskal-like waves after one-dimensional electron wave breaking in a cold plasma

A one-dimensional particle in cell simulation of large amplitude plasma oscillations is carried out to explore the physics beyond wave breaking in a cold homogeneous unmagnetized plasma. It is shown that after wave breaking, all energy of the plasma oscillation does not end up as random kinetic energy of particles, but some fraction, which is decided by Coffey's wave breaking limit in warm plasma, always remains with two oppositely propagating coherent Bernstein-Greene-Kruskal like modes with supporting trapped particle distributions. The randomized energy distribution of untrapped particles is found to be characteristically non-Maxwellian with a preponderance of energetic particles.

Breaking of upper hybrid oscillations in the presence of an inhomogeneous magnetic field

We present space-time evolution of large-amplitude upper hybrid modes in a cold homogeneous plasma in the presence of an inhomogeneous magnetic field. Using the method of Lagrange variables, an exact space-time-dependent solution is obtained in parametric form. It is found that the magnetic field inhomogeneity causes various nonlinearly excited modes to couple, resulting in phase mixing and eventual breaking of the initially excited mode. The occurrence of wave breaking is seen by the appearance of spikes in the density profile. These results will be of relevance to laboratory and space plasma situations in which the external magnetic field is inhomogeneous.

Phase mixing/wave breaking studies of large amplitude oscillations in a cold homogeneous unmagnetized plasma

The subject of phase mixing/wave breaking serves as a useful paradigm to illustrate the physics of many plasma-based phenomena in the laboratory and astrophysical situations where nonlinear oscillations/waves are excited. Phase mixing leads to wave breaking and occurs whenever the characteristic frequency acquires a spatial dependence. In this paper, we review our investigations done in the area of phase mixing/wave breaking of large amplitude oscillation and waves in cold homogeneous unmagnetized plasma.

Nonlinear evolution of an arbitrary density perturbation in a cold homogeneous unmagnetized plasma

An exact and general analytical solution describing the nonlinear evolution of a large amplitude plasma oscillation initiated by an arbitrary density perturbation which can be expressed as a Fourier series in x is found. This general solution is first used to reproduce the earlier results of R. C. Davidson and P. P. Schram [Nucl. Fusion 8, 183 (1968)] and J. M. Dawson [Phys. Rev. 113, 383 (1959)] using appropriate initial conditions and later applied to derive the space time evolution for a square wave and a triangular wave. It is found that the addition of a second harmonic increases the wave breaking limit of the fundamental mode. Analytical results pertaining to this two mode case have been verified using one-dimensional particle-in-cell simulation.

Phase mixing of relativistically intense waves in a cold homogeneous plasma

We report on spatiotemporal evolution of relativistically intense longitudinal electron plasma waves in a cold homogeneous plasma, using the physically appealing Dawson sheet model. Calculations presented here in the weakly relativistic limit clearly show that under very general initial conditions, a relativistic wave will always phase mix and eventually break at arbitrarily low amplitudes, in a time scale omegapetaumix approximately {3/64(omegape2delta3/c2k2)|Deltak/k|(|1+Deltak/k|)](1+1|1+Deltak/k|)}(-1). We have verified this scaling with respect to amplitude of perturbation delta and width of the spectrum (Deltakk) using numerical simulations. This result may be of relevance to ultrashort, ultraintense laser pulse-plasma interaction experiments where relativistically intense waves are excited.

Radiation from a small spheroidal antenna with plasma shell

We construct and study an analytical solution of the boundary-value problem for the radiation field of a small spheroidal antenna located in free space and surrounded by a thin shell of cold homogeneous isotropic plasma. Conditions for a resonant increase in the field in free space as a function of the plasma-shell thickness with the variation in the spheroidal-antenna shape are studied. It is shown that the plasma shell has the largest effect on the radiation field of a strongly prolate spheroidal antenna.

Interaction of electromagnetic waves with a radially bounded electron beam

The resonant interaction of a narrow electron beam spiraling in a cold homogeneous magnetized plasma with electromagnetic cylindrical waves is considered. The conclusions derived in recent papers about the formation, in the presence of effective electromagnetic energy dissipation out of the radially bounded beam, of dynamically stable and longtime living bunches of resonant electrons in the developed stage of their nonlinear interaction with the waves are discussed in this paper for more general physical cases and for wider ranges of characteristic parameters. General analytical formulas for the excited electromagnetic fields, the radiated electromagnetic power flux and the linear growth rate as well as relevant numerical simulations results are presented.

Correction to “Properties of lower hybrid solitary structures: A comparison between space observations, a laboratory experiment, and the cold homogeneous plasma dispersion relation”

[1] In the paper “Properties of lower hybrid solitary structures: A comparison between space observations, a laboratory experiment, and the cold homogeneous plasma dispersion relation” by P. W. Schuck, J. W. Bonnell, and J. L. Pinçon, (Journal of Geophysical Research, 109, A01310, doi:10.1029/2002JA009673, 2004), there are several typographical errors. In four places, the symbol ψ should be replaced with ϕ. The paragraphs with the corrected sentences are reproduced below. [2] [41] The term “electrostatic” seems to be a point of general confusion and contention in space physics. The electrostatic approximation “lies simply in the replacement of the vector electric field by the potential gradient E = −∇ϕ” [Stix 1992, p. 54]. The electrostatic field associated with a wave is longitudinal or along the direction of k, e.g., EL = −∇ϕ. The electromagnetic field associated with a wave is transverse or perpendicular to the direction of k, e.g., ET = −∂tA where A is the vector potential in the Coulomb gauge (∇ · A = 0). Throughout this discussion the terms longitudinal and transverse will be used to describe the orientation of E respect to k, and the terms perpendicular and parallel will be used to describe the orientation of E with respect to the background applied magnetic field B0 = B0. [3] [43] The electrostatic approximation is analogous to the familiar quasineutral approximation in plasma physics. The quasineutral approximation assumes that the densities of the ions and electrons are equal everywhere to lowest order (ni = ne). This does not mean that the electric field is zero. However, this assumption does mean that the Poisson equation cannot be used to determine the electric field. Once the electric field is determined by · J = 0, the charge separation can be estimated from Poisson's equation. Similarly, the electrostatic approximation assumes that E = −∇ϕ + (ET/EL). This approximation presumes that the electric field is predominantly longitudinal and curl free to lowest order. This does not imply that the magnetic fluctuation associated with the electrostatic wave is zero. However, this does imply that Faraday's law ∂tB = −∇ × E cannot be used to determine the magnetic fluctuation B. Once the current of the electrostatic wave is determined, the associated magnetic fluctuation may be estimated from Ampere's law ∇ × B ≈ μ0(J + ε0 ∂tEL) where J = JL + JT is an implicit function of EL with ∇ · JT = 0 and ∇ × JL = 0. (Note that the constraint ∇ · (J + ε0 ∂tEL) = 0 does not imply that J + ε0 ∂tEL = 0 i.e., JT ≠ 0 with the JL + ε0 ∂tEL = 0 (longitudinal components canceling).) Subsequently, ∇ × E may then be estimated from Faraday's law ∇ × E = −∂tB. The magnetic field associated with an “electrostatic” wave may be generally estimated from Ampere's law [Stix, 1992, p. 78]. However, experimentally the noise levels and sensitivity of the detector determine whether the magnetic fields associated with “electrostatic” waves are observable.