Plasma Wake Research Articles

Dynamical Complexity and Multistability in a Novel Lunar Wake Plasma System

Dynamical complexity and multistability of electrostatic waves are investigated in a four-component homogeneous and magnetized lunar wake plasma constituting of beam electrons, heavier ions (alpha particles, He++), protons, and suprathermal electrons. The unperturbed dynamical system of the considered lunar wake plasma supports nonlinear and supernonlinear trajectories which correspond to nonlinear and supernonlinear electrostatic waves. On the contrary, the perturbed dynamical system of lunar wake plasma shows different types of coexisting attractors including periodic, quasiperiodic, and chaotic, investigated by phase plots and Lyapunov exponents. To confirm chaotic and nonchaotic dynamics in the perturbed lunar wake plasma, 0−1 chaos test is performed. Furthermore, a weighted recurrence-based entropy is implemented to investigate the dynamical complexity of the system. Numerical results show existence of chaos with variation of complexity in the perturbed dynamics.

Generation of ultrafast electron bunch trains via trapping into multiple periods of plasma wakefields

We demonstrate a novel approach to the generation of femtosecond electron bunch trains via laser-driven wakefield acceleration. We use two independent high-intensity laser pulses, a drive, and an injector, each creating their own plasma wakes. The interaction of the laser pulses and their wakes results in a periodic injection of free electrons in the drive plasma wake via several mechanisms, including ponderomotive drift, wake-wake interference, and pre-acceleration of electrons directly by strong laser fields. Electron trains were generated with up to four quasi-monoenergetic bunches, each separated in time by a plasma period. The time profile of the generated trains is deduced from an analysis of beam loading and confirmed using 2D particle-in-cell simulations.

Ultracold ions wake in dusty plasmas

Motivated by the recent experimental realization of ultracold dusty plasma (2019 Sci. Rep. 9 3261), we present the results of particle-in-cell simulation with Monte-Carlo-collisions for wake behind a dust particle due to focusing of ions at superfluid helium temperature (∼2 K). Dynamical screening (wakefield) defines structural and dynamical properties of charged dust particles in plasmas such as phase transition, crystal formation, vibration modes (waves) etc. Here, we delineate in detail the dependence of wake strength on the streaming velocity of ions and on the ion-neutral charge exchange collision frequency (neutrals density) in the ultracold dusty plasma. Lowering the temperature to ultracold level leads to a wake pattern behind a dust particle that completely differs from the wake at normal conditions. For wide range of parameters, most remarkable features of the wakefield are (i) the formation of wake pattern with two maxima split in transverse to ion flow direction in the downstream area, (ii) pronounced inverse V shape of the wakefield closely resembling the wake in quark-gluon plasma and dense quantum plasma (warm dense matter), and (iii) the inter-dust attraction region in transverse direction. The latter shows that molecule-like interaction between dust particles is realized in ultracold dusty plasmas. These observations show a fundamental difference of ultracold dusty plasma physics from well studied complex plasmas at normal conditions.

Linear analysis of electrostatic waves in the lunar wake plasma

Propagation characteristics of electrostatic electron and ion cyclotron waves, ion- and electron- acoustic waves in a four-component magnetized plasma comprising of protons, doubly charged Helium ions, beam electrons and superthermal electrons following a kappa distribution are presented. The model supports 12 plasma modes: two electron cyclotron (modes 1 and 12), two electron acoustic (modes 2 and 11), two fast ion acoustic (modes 3 and 10), two slow ion acoustic (modes 4 and 9), two proton cyclotron (modes 5 and 8) and two Helium cyclotron (modes 6 and 7). At parallel propagation, with increase in electron beam speed, mode 11 first merges with slow ion acoustic mode 4 and then with fast ion acoustic mode 3 and drives them unstable. For oblique propagation and without the electron streaming, coupling of various plasma modes occurs and it weakens with increase in the angle of propagation. Further, for oblique propagation with finite electron beam velocity, merging as well as coupling of various plasma modes are observed. Growth rates as well as wave numbers of the excited slow and fast ion acoustic modes are much smaller in magnetized plasma than in an unmagnetized one. The results are relevant to observations of electrostatic waves in the lunar wake.

Physical Effects of the Lipetsk Meteoroid: 3

Comprehensive modeling studies of the processes induced in all geospheres by the passage and explosion of the meteoroid near the city of Lipetsk (Russia) on June 21, 2018, have been conducted. Magnetic, electric, electromagnetic, ionospheric, and seismic effects, as well as the effects of acoustic-gravity waves have been estimated. The magnetic effect of turbulence has been shown to be insignificant. The magnetic effect of the ionospheric currents and the current in the wake of the meteoroid could be substantial (~1 nT). Under the action of an external electric field, a transient current pulse with the strength of current up to 104 A could occur. The electrostatic effect could be accompanied by the accumulation of an electric charge of 1 mC producing the electric field intensity of 0.01–1 MV/m. The flow of the electric current in the wake of the meteoroid could result in the generation of an electromagnetic pulse in the 40–80 kHz band with the electric field intensity of 1–10 V/m. The electromagnetic effect of infrasound has been determined to be significant (1–10 V/m and 1–10 nT). The absorption of the shock wave at ionospheric dynamo region altitudes (100–150 km) could generate secondary atmospheric gravity waves with the 0.1–1 relative amplitude. The passage of the meteoroid acted to produce a plasma wake and noticeable disturbance not only in the lower but also in the upper atmosphere in the range of no less than 1000 km. The possibility of occurrence of the electrophonic effect, the generation of the ion and magnetic sound by infrasound, and the generation of gradient-drift and drift-dissipative instabilities are discussed. A conclusion is drawn that magnetic, electric, and electromagnetic effects dealt with in this paper significantly fill in the gaps in the theory of physical effects produced by meteoroids in the Earth–atmosphere–ionosphere–magnetosphere system. The magnitudes of magnetic, electric, electromagnetic, ionospheric, and acoustic effects were significant. The magnitude of the earthquake caused by the meteoroid explosion did not exceeded 1.7. The mean rate of the fall of celestial bodies similar to the Lipetsk meteoroid is equal to 0.68 yr–1.

Coherent terahertz emission from a plasma layer due to linear conversion of laser wakefields on pre-modulated ion density

In this paper, electromagnetic emission at the plasma frequency produced by a short laser pulse in a finite-size plasma layer with a longitudinal density modulation is studied using both analytical theory and particle-in-cell simulations. The radiation mechanism suggests that a laser pulse excites a long-lived plasma wake which, in the presence of ion density modulation with the appropriate period, generates a superluminal satellite capable of matching in phase with vacuum electromagnetic waves. It is found that such a mechanism can be used for generating tunable narrow-band (5%) multi-mJ terahertz pulses with high efficiency (>0.3%) due to ability of superluminal plasma oscillations at the cut-off frequency to diffuse through a plasma that is several times wider than the radiation wavelength.

Proof-of-Principle Experiment for Nanoparticle-Assisted Laser Wakefield Electron Acceleration

In the present work, we demonstrate for the first time a proof-of-principle experiment for nanoparticle-assisted laser wakefield acceleration. The nanoparticles, generated through laser ablation of aluminium, were introduced into the plasma and used to trigger the injection of electrons into the nonlinear plasma wake excited by a high power femtosecond laser. In this experiment, a significant enhancement of the electron beam energy, energy spread and divergence is obtained compared with the case when electrons are self-injected. The best quality electron bunches presented peak energy up to 338 MeV with a relative energy spread of 4.7% and vertical divergence of 5.9 mrad. This method can be further improved by adding an aerodynamic lens system, for instance, which would control the nanoparticle size, density, material and injection position thus allowing accurate control of the laser wakefield accelerator.

Low Earth Orbit Plasma Wake Shaping and Applications to On-Orbit Proximity Operations

A parametric investigation of plasma wake geometry is conducted to determine the applicability of Coulomb actuation to resident space objects (RSOs) in low earth orbit (LEO). The use of Coulomb forces could provide a touchless means to achieve the relative position and attitude adjustments between close-proximity objects on orbit. Theoretical models developed for techniques in the geosynchronous earth orbit (GEO) regime indicate that Coulomb actuation could facilitate on-orbit proximity operations in a highly fuel- and power-efficient manner. In LEO, however, only the plasma parameters in the wakes behind orbiting objects are a promising region for Coulomb actuation applications. These physical phenomena investigated by the charging hazards and wake studies (CHAWS), space experiments with particle accelerators (SEPAC), and other on-orbit experiments exhibit substantially decreased plasma density relative to the surroundings. This investigation considers the wake which forms behind objects of various potentials and cross-sectional areas, particularly focusing on methods of enhancing the wake with negligible changes in the objects' area, and therefore their mass. Experimental results are presented and compared with previous theoretical, numerical, and experimental works. The size of a wake formed by an uncharged object is shown to depend on its cross-sectional area. However, the same object charged to a positive potential generates a substantially larger wake. Additional experimental results indicate that a positively charged, sparse structure with similar dimensions, but significantly less cross-sectional area forms a wake similar to the previous, solid object charged to the same level. This indicates that a large wake can be generated without significantly increasing the mass or area-dependent perturbations such as the drag and the solar radiation pressure. These results increase the applicability of Coulomb actuation in LEO by enhancing the region in which the technique is feasible.

Plasma Wake Simulation for Charged Space Platforms: Fully Kinetic PIC Versus Hybrid PIC

A comparative study using both electrostatic hybrid particle-in-cell (PIC) and fully kinetic PIC simulations is carried out to study collisionless, mesothermal plasma flow over large, negatively charged plates. The surface potential considered covers plasma wakes under the “quasi-neutral,” the thin sheath, and the “thick sheath” regimes. It is shown that both approaches produce qualitatively similar plasma wake features. The hybrid-PIC approach is accurate in the sheath region around the plate and in the expansion fan region. The full-PIC simulations also confirm the presence of the embedded sheath in the wake generated by a charged plate. However, the hybrid-PIC model is quantitatively inaccurate in the deep wake region where the electrons are nonequilibrium. It is also found that, for high-voltage plates, the ratio of the ram side ion current collection to the backside one scales linearly with the logarithm of the surface potential.

Multineedle Langmuir Probe Operation and Acute Probe Current Susceptibility to Spacecraft Potential

NorSat-1 was launched on July 14, 2017 as a satellite carrying, among other instruments, the multineedle Langmuir probe (m-NLP), an instrument which, on NorSat-1, is capable of measuring the ionospheric plasma electron density with the high sampling frequency of 1000 Hz. The m-NLP instrument operates by analyzing the current–voltage diagram resulting from the measurements from each individual probe. In principle, the m-NLP operation methodology should be insensitive to spacecraft charging. However, this is not always the case. In this paper, we present an overview of the instrument response to passes into and out of eclipse. When the satellite exits eclipse, we observe a collapse in the collected probe currents. This acute drop is unaccounted for by the theoretical operation of the instrument. We present a statistical analysis of the phenomenon based on several months of NorSat-1 data, and we suggest a plausible reason for the observed drop in the current, namely, spacecraft charging, by solar cell arrays upon eclipse exit. We briefly discuss how satellite orientation and plasma wake affect the current drop. With this paper, we address Langmuir probe current susceptibility to spacecraft potential.

Similarity of magnetized plasma wake channels behind relativistic laser pulses with different wavelengths

Using particle-in-cell simulations of relativistic laser plasma wakes in the presence of an external magnetic field, we demonstrate that there exists a parameter window where the dynamics of the magnetized wake channel are largely independent of the laser wavelength λlas. One condition for this manifestation of “limited similarity” is that the electron density ne is highly subcritical, so that the plasma does not affect the laser. The freedom to choose a convenient laser wavelength can be useful in experiments and simulations. In simulations, an up-scaled wavelength (and, thus, a coarser mesh and larger time steps) reduces the computational effort, while limited similarity ensures that the overall structure and evolutionary phases of the wake channel are preserved. In our demonstrative example, we begin with a terrawatt⋅picosecond pulse from a CO2 laser with λlas=10μm, whose field reaches a relativistic amplitude at the center of a sub-millimeter-sized focal spot. The laser is shot into a sparse deuterium gas ( ne∼1013cm−3) in the presence of a tesla-scale magnetic field. Limited similarity is demonstrated in 2D for 4μm≤λlas≤40μm and is expected to extend to shorter wavelengths. Assuming that this limited similarity also holds in 3D, increasing the wavelength to 40μm enables us to simulate the after-glow dynamics of the wake channel all the way into the nanosecond regime.

Steady‐State Solution of a Solar Wind‐Generated Electron Cloud in a Lunar Crater

AbstractWe formulate an analytic description of a steady‐state electron cloud and affiliated surface charge, formed in the plasma wake generated as the solar wind flows horizontally over a lunar crater. The solution is complementary to the well‐known self‐similar plasma expansion formulation, which breaks down at the plasma wake front and thus fails to capture a substantial region of the crater interior. The present model establishes a theoretical basis for existing simulation results, which suggest that the cavity formed below the wake front is populated mainly by electrons, resulting in a substantial negative surface charge. The electrostatic potential throughout this subwake region is determined by solving Poisson's equation for a Maxwellian electron cloud, bounded above by the self‐similar plasma expansion front and below by the electrostatically charged surface.

Properties of Electron Phase Space Holes in the Lunar Plasma Environment

AbstractThe spatial distribution and amplitudes of electron phase space holes observed in the plasma environment near Earth's Moon are presented. When the Moon is in the solar wind, the overwhelming majority of holes in its vicinity occur in its wake, and we attribute them to an instability caused by distortion of the electron distribution by the wake, as predicted by theory. Approximately 30% of these wake holes are statistically correlated with observed magnetic discontinuities nearby, which implies that external effects can influence and trigger these wake instabilities, yet the wake is the determining factor. When the Moon is deep in the Earth's magnetotail, and no detectable lunar wake is present, the hole occurrence is greatly reduced and is distributed approximately homogeneously about the Moon, implicating a different production mechanism. Near the boundary of the magnetotail, homogeneously occurring holes are more frequent, showing that other instabilities associated with the magnetopause region are also active. These results demonstrate ways in which the Earth's Moon is a unique plasma physics laboratory where plasma wake physics and electron instabilities can be studied in detail.

Mapping the Lunar Wake Potential Structure With ARTEMIS Data.

The refilling of the lunar wake is relatively well explained by the theory of 1-D plasma expansion into a vacuum; however, the field-aligned wake potential is not a directly measured quantity, and thus, a statistical analysis of wake potentials at high altitudes has not been previously performed. In this study, we obtain the wake potential by comparing the field-aligned electron distributions inside and outside of the lunar wake measured by the two probes of the Acceleration, Reconnection, Turbulence, and Electrodynamics of Moon's Interaction with the Sun (ARTEMIS) mission. The derived potentials from ARTEMIS data vary with solar wind electron temperature and bulk flow velocity as the theory predicts. We also expand the 1-D plasma theory to 2-D in the plane of the interplanetary magnetic field and the solar wind velocity to examine how a tilted interplanetary magnetic field affects the wake potential structure. As the expansion time for the two sides of the wake differs, a wake potential asymmetry is developed in our model. This asymmetry is confirmed by the data-derived wake potentials. Moreover, ambipolar electric fields are obtained from both the modeled and data-derived wake potentials and show good agreement. Lastly, we examine the effects of the solar wind strahl-electron population on the wake potential structure, which appears to cause a net potential difference across the lunar shadow. This may imply that the disturbance of the wake plasma expansion extends farther outside the wake than previous plasma-expansion theories have predicted.

Transverse beam dynamics in a plasma density ramp

An electron beam experiences chromatic emittance growth in a plasma-based accelerator if it is not matched to the focusing force in the plasma wake. A ramped plasma density profile at the entrance and exit of the plasma source can control the focusing of the beam into and out of the plasma accelerator, limiting emittance growth. Here, we present a comprehensive, analytic theory to describe the transverse beam dynamics and emittance growth in a nearly arbitrary plasma ramp profile. For a given incoming beam, this theory can be used to determine the length of the ramp required to correctly focus the electron beam, the optimal location of the beam's vacuum focus, and the chromatic emittance growth in the ramp. In addition, the theory can be used to determine the effect that errors in the beam focusing and plasma profile have on the emittance of the beam. We illustrate two example ramps to demonstrate the theory: one that provides very fast focusing for beam matching, and one that is robust to errors in the plasma density profile.

Acceleration of electrons in the interaction of a subterawatt laser pulse with a nonuniform plasma

We consider the effect of nonlinear self-focusing and self-modulation processes on the acceleration of electrons in the interaction of a subterawatt femtosecond laser pulse with a gas jet plasma. A three-dimensional particle-in-cell (3D PIC) simulation of the interaction of laser radiation with a low-density nonuniform plasma shows that laser pulse self-focusing that arises when the critical power of relativistic self-focusing determined by the local concentration of plasma electrons exceeds the pulse power results in efficient generation of a plasma wave. Due to a decrease in the phase velocity of the wake plasma wave generated via self-modulation of the laser pulse, electrons are trapped into the accelerating phase of the plasma wave and are accelerated to energies of ∼10 MeV. It is demonstrated that under the conditions for limiting the electrons’ acceleration region by the length of their dephasing, quasi-monoenergetic electron bunches with a characteristic energy of ∼9 MeV can be produced. The effective temperature of the accelerated electrons and their angular distribution, obtained by 3D PIC simulation, are in good agreement with those determined in the experiment.

Assessment of electron thermodynamic and fluid approximations for collisionless plasma expansion into a wake

A commonly used assumption for modeling electrons in the collisionless plasma expansion into a wake is that the electrons are an ideal gas following a thermodynamic process governed by the polytropic law. The validity and accuracy of this assumption are assessed through a direct comparison between hybrid particle-in-cell (PIC) and fully kinetic PIC simulations. The electron thermal energy transfer along with the expansion process is analyzed. It is shown that a collisionless plasma wake can be divided into a fluid-like expansion region and a kinetic expansion region based on the local equilibrium degree of the electrons. In the fluid-like expansion region, the electrons are near equilibrium and almost isothermal, and the accuracy of hybrid PIC in that region can be improved by properly tuning the polytropic coefficient. In the kinetic expansion region, the electrons are strongly nonequilibrium, and the accuracy of hybrid PIC is always poor. Consequently, a fluid model with a polytropic thermodynamic law for electrons is meaningless in that region.

Establishment of a Wideband Radar Scattering Center Model of a Plasma Sheath

A reentry object covered by a plasma sheath will produce two reflective signals in a radar echo, which seriously affects the detection of the reentry object by radar and results in positioning error and even tracking loss. On the basis of the scattering center model and the non-uniform plasma stratification model, the present paper establishes a radar scattering model of a reentry object covered by a plasma sheath. The model effectively retains the plasma distribution and electromagnetic wave propagation characteristics of the plasma sheath. Analysis of the signal components of radar echoes in an example shows to some extent that the non-mirror reflection signal is not generated by the plasma wake.

2-D-Particle-in-Cell Simulation of Laser Wakefield in an Inhomogeneous Plasma

We performed the 2-D particle-in-cell simulation of the laser wakefield in an inhomogeneous plasma to study the dependence of the speed of the wakes to the electron density of the background plasma to search the condition of “accelerating flying mirror”. Acceleration of the plasma wakes is not observed in the simulations with the parameters that we have tested.

Effect of laser pulse self-focusing on plasma wave generation in the interaction of subterawatt laser pulse with a plasma jet

The wake plasma waves generated by high intensity laser pulses are of interest for acceleration of electrons to high energies. The aim of this work is to study the effect of self-focusing of a laser pulse on the plasma wakefields generation. Calculations were performed using the three-dimensional particle-in-cell method. When the laser pulse in the process of propagation in inhomogeneous plasma reaches the region where the pulse power exceeds a critical value for self-focusing, the laser pulse is self-focused and a steepening of the leading edge of the pulse increases. These processes lead to self-modulation instability and generation of a wake plasma wave.