Space Plasma Environments Research Articles

Shock waves in magnetized plasmas with superthermal trapped electrons.

Formation of ion-acoustic shock waves (IAShWs) and their propagation nature in a magnetized plasma in the presence of superthermal trapped electrons are investigated for the first time via the fluid dynamical approach. A magnetized plasma system, comprising of inertial ions and non-inertial electrons following κ-superthermal trapped distribution, is considered to examine the basic features (amplitude, width, phase speed, etc.) of IAShWs in such a plasma. A diffusion effect (due to the ion kinematic viscosity) is taken into account. The reductive perturbation technique is adopted to derive the modified Korteweg de-Vries Burgers’ (mKdVB) equation and the solution of mKdVB equation (derived by adopting the tangent hyperbolic method) is used to investigate the dynamical and structural characteristics (speed, amplitude, width, etc.) of IAShWs. The influence of relevant plasma (configuration) parameters (e.g., the superthermality index κ, concentration of trapped electrons, external magnetic field, and obliquity angle, etc.) on the nature of IAShWs is examined. The applications of the results in space and laboratory plasma environments, where nonthermal trapped electrons are available, are briefly discussed.

Cylindrical and spherical ion acoustic shock waves with two temperature superthermal electrons in dusty plasma

In the present study, the cylindrical/spherical ion acoustic shock waves have been investigated in unmagnetized dusty plasma consisting of positive ions, immobile dust particles and kappa distributed cold and hot electrons. A multiple scale expansion method is employed to derive Burgers equation (BE) and modified Burgers equation (MBE) by including higher order nonlinearity. The basic characeristics of the shock waves have been analyzed numerically and graphically for different physical parameters relevant to space and laboratory dusty plasma environments through 2D figures. We show that the amplitude of the wave decreases faster as one departs away from the axis of the cylinder or centre of the sphere. Such decaying behaviour continues as time progresses. Furthermore, the parametric dependence of wave properties (amplitude, width) on kappa index, density and temperature of cold and hot electrons, concentration of dust particles, thermal effects and kinematic viscosity of ions has been studied in detail and findings obtained here will be beneficial to further astrophysical investigations.

Dust-acoustic solitary waves in a self-gravitating warm opposite polarity dusty plasma

A theoretical investigation is made to study the propagation of dust-acoustic solitary waves in a general and realistic self-gravitating dusty plasma system containing positively as well as negatively charged warm dust species and nonthermally distributed ion species. The standard reductive perturbation method is employed to derive the Korteweg–de Vries equation which admits the solitary wave solution. The parametric regimes for the existence of dust-acoustic solitary waves associated with electrostatic and self-gravitational potentials are obtained. It is shown that the population of nonthermal ion species significantly modifies the basic features of the dust-acoustic solitary waves. The significant effects of ratios of mass, temperature, and number density of positively charged dust species to those of negatively charged one on the basic properties (namely, phase speed, polarity, amplitude, and width) of the dust-acoustic solitary waves are also identified. A brief comparison between electrostatic and self-gravitational solitary potential structures is also made. The implications of our results to different space and laboratory dusty plasma environments, where opposite polarity dust grains are observed, are briefly discussed.

Electrophoretically Deposited Graphene-Based Composite Coatings for Spacecraft Charging Mitigation

Spacecraft charging has been recognized as an important consideration for spacecraft design, and occurs due to interaction between hazardous space plasmas and spacecraft surface. Spacecraft can experience charging throughout operation due to high flux of incident electrons (ex. during geomagnetic sub-storm). As a result, different materials/components may experience a range of potentials which may lead to plasma-induced arcs, damaging spacecraft components. Graphene are emerging two-dimensional (2D) carbon materials with excellent physical and chemical properties, such as high conductivity, high tensile strength, high transparency, and high carrier mobility. These excellent properties make graphene potentially useful for applications in energy storage, aerospace, coatings and polymer markets and thermal protection. Substrates constituted by graphene harness the thermal and mechanical properties to create novel coatings with superior performance, hence broadening the graphene application spectrum. Of particular interest is the potential capability of graphene-based materials to provide increased protection against spacecraft charging in the space plasma environments. Furthermore, the work function of graphene can be tuned by either metal doping or functionalization, thereby facilitating autonomous or passive electron emission and increasing the electron yields and enhancing the possibility of emission through negative electron affinity. By enabling charge dissipation between the various components at modest potential differences, discharge arcing may be preventedWithin this context, Faraday Technology is developing a graphene-based composite coating with high electron yields over a wide range of incident electron energies. This approach utilizes electrophoretic deposition to deposit graphene-based coatings onto test substrates, which may maintain integrity of spacecraft by autonomous electron emission in relevant environments. Next, an electrochemical process is used to decorate the graphene surface with various low work function metals (alkali, alkaline earth, transition). This approach offered significant improvements in the electron yield (290% increase over the undecorated coating) and substantially extended the range (~9 times) of incident electron energies between crossover points as shown in Figure 1/Table 1.Acknowledgements: The financial support of DOD Air Force Contract No.: FA9453-19-P-0573 is acknowledged. Figure 1

Examining the Magnetic Geometry of Magnetic Flux Ropes from the View of Single-point Analysis

Abstract Magnetic flux ropes, characterized as magnetic field lines that wrap and rotate around a central axis, are observed ubiquitously in the space-plasma environment. Accurately examining the physical parameters (e.g., axis orientation, helical handedness, current density, curvature radius, and size) of flux ropes is essential for studying their evolution and associated dynamics. The geometric parameters of flux ropes can be resolved by a cluster of at least four spacecraft with the separation scale much smaller than the flux ropes. However, most spacecraft missions are of single-point measurements, especially for the missions on other planets (e.g., Mars, Venus, Mercury), thus, the method for investigating the flux ropes based on single-point measurements becomes particularly important. A single-point method that infers the axis orientation of flux ropes was recently developed by Rong et al. Here, we apply this method to study two flux ropes observed by the Magnetospheric Multiscale Mission (MMS), one close to the force-free field and the other close to the non-force-free field, by comparing them with the multipoint analysis of MMS. Our study demonstrates that, apart from axis orientation, the method of Rong et al. can reasonably infer the current density, curvature radius of magnetic field, and the transverse size of flux ropes. We discussed the main error sources of calculated parameters, and suggest that it is worthwhile to widely apply the method by Rong et al. to single-point spacecraft missions for the purpose of examining the geometry and dynamics of flux ropes.

Design of HCN laser based interferometer on the Space Plasma Environment Research Facility (SPERF)

A single-channel far-infrared (FIR) hydrogen cyanide (HCN) laser interferometer will be constructed aiming to provide the line integrated electron density on the Space Plasma Environment Research Facility (SPERF) . A continuous glow discharge HCN laser with a cavity length of 3 m is used as the laser source with a wavelength of 337 μm and an output power about 10 mW . The interferometer system is a Mach-Zehnder type. The temporal resolution of the system is 0.1 ms since the phase modulation is achieved by a rotating grating with a modulation frequency of 10 kHz. The beat signal is detected by AlGaN/GaN high electron mobility transistors (HEMT) detector. It has a noise equivalent power of 10 pW/Hz−1/2. Excellent port access (1500×150 mm) and high laser power would promise a profile measurement across the whole plasma section with good signal quality. The design and structure of the single-channel FIR HCN laser interferometer in SPERF is described in detail.

New method for rekindling the explosive waves in Maxwellian space plasmas

Our interest is to study the nonlinear wave phenomena in complex plasma constituents with Maxwellian electrons and ions. The main aim is to use a new method known as the (G′/G) method to exhibit the effects of dust charge fluctuations on the evolution of nonlinear waves. The coherent features of the shock and solitary waves along with the generation of high-energy waves have been amplified through the solution of the Korteweg–de Vries–Burgers equation, and the different natures of the waves were found successfully. Results are discussed graphically with the thoughtful choice of typical plasma parameters from different space plasma environments, exactly those found in cosmic dusty plasmas laden in ionospheric auroral region, radial spokes of Saturn’s rings, planetary nebulae and solar F-corona region. All conclusions are in good accordance with the actual occurrences and could be of interest to further investigations of space. Moreover, the applicability of the present method is hoped to be a great enhancement by its use as ingenious mechanism used to evaluate the soliton dynamics and Burgers shock waves.

Using Dimensionality Reduction and Clustering Techniques to Classify Space Plasma Regimes

Collisionless space plasma environments are typically characterised by distinct particle populations. Although moments of their velocity distribution functions help in distinguishing different plasma regimes, the distribution functions themselves provide more comprehensive information about the plasma state, especially at times when the distribution function includes non-thermal effects. Unlike moments, however, distribution functions are not easily characterised by a small number of parameters, making their classification more difficult to achieve. In order to perform this classification, we propose to distinguish between the different plasma regions by applying dimensionality reduction and clustering methods to electron distributions in pitch angle and energy space. We utilise four separate algorithms to achieve our plasma classifications: autoencoders, principal component analysis, mean shift, and agglomerative clustering. We test our classification algorithms by applying our scheme to data from the Cluster-PEACE instrument measured in the Earth's magnetotail. Traditionally, it is thought that the Earth's magnetotail is split into three different regions (the plasma sheet, the plasma sheet boundary layer, and the lobes), that are primarily defined by their plasma characteristics. Starting with the ECLAT database with associated classifications based on the plasma parameters, we identify 8 distinct groups of distributions, that are dependent upon significantly more complex plasma and field dynamics. By comparing the average distributions as well as the plasma and magnetic field parameters for each region, we relate several of the groups to different plasma sheet populations, and the rest we attribute to the plasma sheet boundary layer and the lobes. We find clear distinctions between each of our classified regions and the ECLAT results.

Plasma Double Layers at the Boundary Between Venus and the Solar Wind.

The solar wind is slowed, deflected, and heated as it encounters Venus's induced magnetosphere. The importance of kinetic plasma processes to these interactions has not been examined in detail, due to a lack of constraining observations. In this study, kinetic‐scale electric field structures are identified in the Venusian magnetosheath, including plasma double layers. The double layers may be driven by currents or mixing of inhomogeneous plasmas near the edge of the magnetosheath. Estimated double‐layer spatial scales are consistent with those reported at Earth. Estimated potential drops are similar to electron temperature gradients across the bow shock. Many double layers are found in few high cadence data captures, suggesting that their amplitudes are high relative to other magnetosheath plasma waves. These are the first direct observations of plasma double layers beyond near‐Earth space, supporting the idea that kinetic plasma processes are active in many space plasma environments.

Observations and Modeling of the Onset of Fast Reconnection in the Solar Transition Region

Abstract Magnetic reconnection is a fundamental plasma process that plays a critical role not only in energy release in the solar atmosphere, but also in fusion, astrophysics, and other space plasma environments. One of the challenges in explaining solar observations in which reconnection is thought to play a critical role is to account for the transition of the dynamics from a slow quasi-continuous phase to a fast and impulsive energetic burst of much shorter duration. Despite the theoretical progress in identifying mechanisms that might lead to rapid onset, a lack of observations of this transition has left models poorly constrained. High-resolution spectroscopic observations from NASA's Interface Region Imaging Spectrograph now reveal tell-tale signatures of the abrupt transition of reconnection from a slow phase to a fast, impulsive phase during UV bursts or explosive events in the Sun's atmosphere. Our observations are consistent with numerical simulations of the plasmoid instability, and provide evidence for the onset of fast reconnection mediated by plasmoids and new opportunities for remote-sensing diagnostics of reconnection mechanisms on the Sun.

Subsonic and supersonic nucleus-acoustic solitary waves in thermally degenerate multi-nucleus plasma systems

A new thermally degenerate multi-nucleus plasma system (containing thermally degenerate electron species, non-degenerate warm light nucleus species, and low dense stationary heavy nucleus species) is considered. The basic features of arbitrary amplitude subsonic and supersonic solitary waves associated with thermally degenerate pressure-driven nucleus-acoustic waves in such a plasma system are studied by the pseudo-potential approach. The effects of the stationary heavy nucleus, non- and ultra-relativistically degenerate electron degeneracies, and light nucleus temperature on such arbitrary amplitude subsonic and supersonic solitary waves are also examined. It is found that (i) the presence of the heavy nucleus and Boltzmann distributed electron species supports the existence of subsonic solitary waves and the effects of electron degeneracies and light nucleus temperature reduce the possibility for the formation of these subsonic solitary waves; (ii) the amplitude (width) of these subsonic solitary waves increases (decreases) with the increase in the number density of the heavy nucleus species; (iii) the amplitude of the supersonic solitary waves in the situation of non-relativistically degenerate electron species is much smaller than that of the ultra-relativistically degenerate electron species but is much larger than that of the Boltzmann distributed electron species; (iv) their width in the situation of non-relativistically degenerate electron species is much wider than that of the ultra-relativistically degenerate electron species; and (v) their amplitude (width) decreases (increases) with the increase in the light nucleus temperature. The applications of the results in some degenerate astrophysical plasma systems and non-degenerate space plasma environments are discussed.

An 18.3 MJ charging and discharging pulsed power supply system for the Space Plasma Environment Research Facility (SPERF). I. The overall design.

The Space Plasma Environment Research Facility (SPERF) is a new ground-based experimental device for fundamental research studies on space plasma currently under construction at Harbin Institute of Technology in China. Scientific objectives of the SPERF include studying the asymmetric reconnection dynamics relevant to the interaction between the interplanetary and magnetospheric plasmas, reproducing the inner magnetosphere to simulate the processes of trapping, acceleration, and transport of energetic charged particles restrained in a dipole magnetic field configuration, and revealing the physical mechanism of the dipolarization front in the magnetotail. The device comprises a vacuum chamber, 11 coils consisting of 18 groups of sub-coils that are independently programmablely energized, and the plasma source system to provide the magnetic field and the plasma required by the physical experiments. Thus, each of these 18 groups of sub-coils requires a separate pulsed power supply; furthermore, the 18 pulsed power supplies constitute the pulsed power supply system of the SPERF of which the total storage energy is up to 18.3 MJ, and the technical challenges have to be overcome. The power supply energizing a dipole field coil (labeled OJC coil) wired by the copper wire to provide a dipole magnetic field is the most energetic power supply (labeled OJC power supply) with a 2.42 MJ, 16.8 mF capacitor bank charged to 20 kV. The OJC power supply delivers a current with a peak of 18 kA for a rise time of ∼26.69 ms, and the duration of the current is not less than 95% of the peak over 10 ms to the OJC coil. Meanwhile, the most challenging power supply is the power supply labeled poloidal field power supply with a 5.04 mF capacitor bank charged to 20 kV, which provides the excitation current for the load coil set with the current not less than 360 kA at the typical time of 0.11 ms to produce the sufficient growth of the magnetic field that the experiments need. In this paper, the overall design of the pulsed power supply system, the design concept of the modularization, and the principle selection basis of the key components are presented. The technical details of each power supply will be demonstrated in the future.

Theory of ion holes in space and astrophysical plasmas

ABSTRACT Coherent bipolar electric field structures, ubiquitously found in various space and astrophysical plasma environments, play an important role in plasma transport and particle acceleration. Most of the studies found in the literature about them pertain to bipolar structures with positive potentials interpreted in terms of electron holes. Magnetospheric Multiscale spacecraft have recently observed a series of coherent electric field structures with negative potential in the Earth’s bow shock region, which are interpreted as ion holes. The existing theoretical models of ion holes are inadequate because they entail stringent conditions on the ratio of ion to electron temperature. This letter presents a new theory that provides a satisfactory explanation to these observations. A salient point is that this letter incorporates the electron dynamics in the theoretical formalism, which removes ambiguities associated with existing theories, thus showing that the new theory for ion holes may be widely applicable for space and astrophysical plasmas.

Growth of concomitant laser-driven collisionless and resistive electron filamentation instabilities over large spatiotemporal scales

Collective processes in plasmas often induce microinstabilities that play an important role in many space or laboratory plasma environments. Particularly notable is the Weibel-type current filamentation instability, which is believed to drive the creation of collisionless shocks in weakly magnetized astrophysical plasmas. Here, this instability class is studied through interactions of ultraintense and short laser pulses with solid foils, leading to localized generation of megaelectronvolt electrons. Proton radiographic measurements of both low- and high-resistivity targets show two distinct, superimposed electromagnetic field patterns arising from the interpenetration of the megaelectronvolt electrons and the background plasma. Particle-in-cell simulations and theoretical estimates suggest that the collisionless Weibel instability building up in the dilute expanding plasmas formed at the target surfaces causes the observed azimuthally symmetric electromagnetic filaments. For a sufficiently high resistivity of the target foil, an additional resistive instability is triggered in the bulk target, giving rise to radially elongated filaments. The data reveal the growth of both filamentation instabilities over large temporal (tens of picoseconds) and spatial (hundreds of micrometres) scales. In the interaction of ultraintense, short laser pulses with solid targets, the collisionless Weibel instability is observed. For a sufficiently high resistivity of the target, an additional resistive instability appears.

Strategies for Determining Electron Yield Material Parameters for Spacecraft Charge Modeling

AbstractAccurate modeling of spacecraft charging is essential to mitigate well‐known and all‐too‐common deleterious and costly effects on spacecraft resulting from charging induced by interactions with the space plasma environment. This paper addresses how limited availability of electron emission and transport properties of spacecraft materials—in particular, secondary electron yields—and the wide ranges measured for such properties pose a critical issue for modeling spacecraft charging. It describes a materials charging database for electron emission properties under development, which facilitates more accurate spacecraft charge modeling when used in concert with the strategies outlined herein. These data and techniques provide tools for more accurate material selection, increased confidence in charge models, and a concomitant decrease in mission risk. They also allow better customization of models in response to prolonged space environment exposure and specific mission requirements, which may evolve materials properties.

Roles of electrons and ions in formation of the current in mirror-mode structures in the terrestrial plasma sheet: Magnetospheric Multiscale observations

Abstract. Mirror-mode structures widely exist in various space plasma environments. Here, we investigate a train of mirror-mode structures in the terrestrial plasma sheet on 11 August 2017 based on the Magnetospheric Multiscale mission. We find that bipolar current densities exist in the cross section of two hole-like mirror-mode structures, referred to as magnetic dips. The bipolar current density in the magnetic dip with a size of ∼2.2 ρi (the ion gyro radius) is mainly contributed by variations of the electron velocity, which is mainly formed by the magnetic gradient–curvature drift. For another magnetic dip with a size of ∼6.6 ρi, the bipolar current density is mainly caused by an ion bipolar velocity, which can be explained by the collective behaviors of the ion drift motions. The current density inside the mirror dip contributes to the maintenance of the hole-like structure's stable. Our observations suggest that the electrons and ions play different roles in the formation of currents in magnetic dips with different sizes.

Design and Testing of the Space Floating Potential Detector

A space floating potential detector (FPD) is an instrument being developed to study the charging of spacecraft structures. It measures the floating potential that arises as the spacecraft interacts with the low Earth orbit (LEO) plasma as well as the Earth’s magnetic field. The FPD belongs to the active potential control system and consists of three functional modules. Leakage current-eliminating and zero-clearing techniques are used in the detector design to ensure the measurement of the floating potential over the long term within the range from −150 to 0 V and at a voltage resolution of less than 1 V. In order to investigate the performance of the FPD, a typical LEO space plasma environment is simulated in the laboratory. The calibrations of the FPD show that the output voltage is basically linear with the input bias voltage, and the maximum nonlinear error is less than 0.9%.

Study on the Magnetic Forces of the Dipole in the SPERF

The Space Plasma Environment Research Facility (SPERF) in Harbin, China, is a user facility dedicated to studying space plasma physics on ground. Magnetic forces are critical to the reliable operation of a magnetic system. A dipole magnet plays a central role in the system and its force conditions are extremely complicated. So, the magnetic force of the dipole magnet is studied in this article. The magnetic system is first introduced. Then, the virtual work principle is presented to evaluate the force analytically. Not dedicated to the complex analytical computation, the qualitative analysis is done based on the breaking of the symmetry of the system from the perspective of the dipole. To validate the qualitative results and solve the force precisely, the finite-element analysis in ANSYS Maxwell is performed. The force results are analyzed and regular patterns are obtained. The influence of the spatial position and the eddy current are studied. In a complex system, the dipole forces from different source magnets compete to dominate as the time proceeds. The methods for analyzing the magnetic forces can easily be extended to other electromagnetic systems.

Dust-acoustic shock waves in a plasma system with opposite polarity dust fluids and trapped ions

The propagation of dust-acoustic (DA) shock waves (SWs) is studied in a four-component dusty plasma system containing viscous dust fluids of opposite polarity, Schamel distributed ions and Boltzmann distributed electrons. The reductive perturbation method is employed to derive a modified Burgers equation which gives rise to the DA shock waves with stronger nonlinearity. The viscous force acting in the dust fluids is identified as a source of dissipation, and is responsible for the formation of the DA shock waves. The basic characteristics (viz., speed, amplitude, width) of the DA shock waves are found to be significantly modified by the combined effects of opposite polarity dust fluids and trapped ions. The applications of this investigation in different space plasma environments and laboratory devices are pinpointed.

Analytical solitary wave solution of the dust ion acoustic waves for the damped forced modified Korteweg-de Vries equation in q-nonextensive plasmas

Analytical solitary wave solution of the dust ion acoustic waves is studied due to the damped forced modified Korteweg-de Vries equation in an unmagnetized collisional dusty plasma consisting of negatively charged dust grain, positively charged ions, q-nonextensive electrons, and neutral particles in the presence of external periodic force. Using reductive perturbation technique, the damped forced modified Korteweg-de Vries equation is obtained for the dust ion acoustic waves. Momentum consevation law is used to obtain the dust ion acoustic solitary wave solutions in the framework of the damped forced modified Korteweg-de Vries equation. The effects of different physical parameters such as entropic index, dust ion collisional frequency, strength and frequency of the external periodic force, speed of the traveling wave and the parameter which is the ratio between the unperturbed densities of the dust ions and electrons are investigated on the analytical solution of the dust ion acoustic waves. It is observed that those parameters have significant effects on the structures of the damped forced dust ion acoustic solitary waves. The results of the present paper may have applications in laboratory and space plasma environments.