Ion Drag Research Articles

Analysis of the Steady State Available Energy Budget in the High‐Latitude Lower Thermosphere

AbstractWe evaluate the budgets of available energy (AE) production, transport, and loss under steady state forcing of the high‐latitude lower thermosphere during the southern summer time for weak or strong southward interplanetary magnetic field (IMF, Bz = −2.0 or −10.0 nT), using the National Center for Atmospheric Research Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model. The AE below 150‐km altitude is partitioned into commensurable reservoirs of kinetic energy (KE) and available potential energy (APE). KE density is larger than APE density above 123 km, but they are comparable below 123 km. Whereas Pedersen ion drag generates strong winds and KE, vertical winds and adiabatic cooling above 123 km tend to offset temperature perturbations caused by Joule heating, thereby reducing APE. Below 123 km Hall ion drag and associated vertical motions are important for creating temperature perturbations and APE. With increasingly negative IMF Bz values APE density intensifies more significantly than KE density above about 123 km, while KE density intensifies more significantly than APE density below. KE is generated primarily where the ion‐drag force associated with plasma convection accelerates the neutral gas and is destroyed primarily where the ion‐drag force opposes the wind. APE is generated primarily where Joule heat is deposited in regions of elevated temperatures and destroyed where the heat is deposited in regions of reduced temperatures. Ion drag is generally more important than Joule heating for generating AE for steady‐state conditions, but the relative contribution of the ion‐drag forcing compared with heating decreases with descending altitude. AE generation by Joule heating intensifies more significantly than generation by ion drag with increasingly negative IMF Bz values. Transport of AE by horizontal and vertical winds is a significant component of the AE budget. Conversion of APE to KE, and of KE to APE, constitutes an important part of their budgets.

Subauroral Neutral Wind Driving and Its Feedback to SAPS During the 17 March 2013 Geomagnetic Storm

AbstractSubauroral Polarization Streams (SAPS) are associated with closure of region 2 field‐aligned current (R2 FAC) through the low conductivity region. Although SAPS have often been studied from a magnetosphere‐ionosphere coupling perspective, recent observations suggest strong interaction also exists between SAPS and the thermosphere. Our study focuses on thermospheric wind driving and its impact on SAPS and R2 FAC during the 17 March 2013 geomagnetic storm using both observations and the physics‐based Rice Convection Model‐Coupled Thermosphere, Ionosphere, Plasmasphere, electrodynamics (RCM‐CTIPe) model that self‐consistently couples the magnetosphere‐ionosphere‐thermosphere system. Defense Meteorological Satellite Program (DMSP)‐18 and Gravity Field and Steady‐State Ocean Circulation Explorer (GOCE) satellite observations show that, as the storm progresses, sunward ion flows intensify and expand equatorward and are accompanied by strengthening of subauroral neutral winds with some delay. Our model successfully reproduces time evolution and overall structure of the sunward ion drift and neutral wind. A force term analysis is performed to investigate the momentum transfer to the neutrals from the ions. Contrary to previous studies showing that Coriolis force is the main driver of neutrals during storm time, we find that the ion drag is the largest force driving westward neutral wind in the SAPS region where the ion density is low in the trough region. Furthermore, simulations with and without the neutral wind dynamo effect are compared to quantify the effect of the neutral to plasma flow. The comparison shows that the self‐consistent active ionosphere thermosphere coupling increases the R2 FAC and the westward ion drift equatorward of the SAPS region by 20% and 40% by the flywheel effect, respectively.

Effect of Background Gas Pressure on Macroparticles in Cathodic Arc Plasma Deposition

The 1-D stationary fluid model combined with orbital motion limited theory is presented to describe the charging of macroparticle (MP) in a cathodic vacuum arcs operating in a reactive gas. The effect of the background gas pressure on MPs is analyzed from the viewpoint of MP dynamics. The main forces acting on an MP as well as the charging of MP in the interelectrode region of the discharge are studied. The ion drag force decreases with the gas pressure, while the neutral drag force increases. MP potential is calculated taking account the dependence of the plasma parameters on the background gas pressure. The electrostatic reflection of MP increases with the background pressure as a consequence of the increased negative potential of MP. As a result, MP can be confined in the plasma due to the force balance.

Dust vortices in a direct current glow discharge plasma: a delicate balance between ion drag and Coulomb force

Dust vortices with a void at the centre are reported in this paper. The role of the spatial variation of the plasma potential in the rotation of dust particles is studied in a parallel plate glow discharge plasma. Probe measurements reveal the existence of a local potential minimum in the region of formation of the dust vortex. The minimum in the potential well attracts positively charged ions, while it repels the negatively charged dust particles. Dust rotation is caused by the interplay of the two oppositely directed ion drag and Coulomb forces. The balance between these two forces is found to play a major role in the radial confinement of the dust particles above the cathode surface. Evolution of the dust vortex is studied by increasing the discharge current from 15 to 20 mA. The local minimum of the potential profile is found to coincide with the location of the dust vortex for both values of discharge currents. Additionally, it is found that the size of the dust vortex as well as the void at the centre increases with the discharge current.

A sixth-order numerical method for a strongly nonlinear singular boundary value problem governing electrohydrodynamic flow in a circular cylindrical conduit

This paper is concerned with the nonlinear singular boundary value problems for the electrohydrodynamic flow of a fluid in an ion drag configuration in a circular cylindrical conduit. The nonlinearity confronted in this problem is in the form of rational function. We develop a sixth-order numerical method based on sextic B-spline basis functions to obtain a more accurate result for such problem. The velocity field emerging in the electrohydrodynamic flow is computed. Further, the effects of the strength of nonlinearity and the Hartmann electric number on the velocity field are studied. The computational results reveal that nondimensional velocity at the centre line of the conduit increases with increasing Hartmann electric number and decreases with the increasing strength of nonlinearity. Error analysis of the sextic B-spline interpolation is supplemented.

Self-Rotation of Dust Particles in Induction-Type RF Discharge

Self-rotation (rotation about the center of mass) of dust particles in a magnetic field has been investigated. The angular velocity of self-rotation in a dust trap produced by an rf discharge has been measured for the first time. It has been discovered that the angular velocity is independent of magnetic induction up to 700 G in spite of the action of ion drag. In addition, the dependence of self-rotation velocity on gas pressure in the discharge when the particles are in the dust trap and on power deposited into the discharge has been measured for the first time. Experimental data correlate well with the developed model of dust particle self-rotation, which appears to maintain the stationary charge of the dust particle.

Density‐Temperature Synchrony in the Hydrostatic Thermosphere

AbstractThe paper presents a detailed analysis of the density‐temperature (ρ‐T) synchrony in the thermosphere using a hydrostatic general circulation model. The numerical models in general offer not only great potential for forecasting the transient response of the thermosphere but also are excellent tools for understanding the driving mechanisms of various thermospheric trends and features. This study investigates and isolates the dependency of the ρ‐T synchrony on the season, altitude, space weather, high‐latitude electrodynamics, and the lower atmospheric tidal spectrum. The results demonstrate that the previously reported ρ‐T synchrony begins around 300‐km (350‐km) altitude at the equator (high latitudes). The effect of the lower atmospheric tidal spectrum on the ρ‐T synchrony patterns seems to be only marginal and more noticeable during the equinox months. The study demonstrates that the ρ‐T phase lag is larger in the high latitudes of the summer hemisphere and evolves through the day and is attributable to ion drag and temperature fluctuations via soft particle precipitation. The study provides physical insights into how the winds contribute to the ρ‐T synchrony. In addition, the results show that geomagnetic activity contributes significantly to the ρ‐T synchrony; the underlying mechanism may be related to temperature enhancements in the high latitudes via Joule heating and associated nonlinear interactions. While the ρ‐T phase lags attributable to different solar activity levels are modest, the solar heating is the primary source that maintains the ρ‐T synchrony in the low/middle latitudes via upward propagating thermal tides.

Регистрация собственного вращения пылевых частиц в условиях ВЧ разряда индукционного типа

AbstractSelf-rotation (rotation about the center of mass) of dust particles in a magnetic field has been investigated. The angular velocity of self-rotation in a dust trap produced by an rf discharge has been measured for the first time. It has been discovered that the angular velocity is independent of magnetic induction up to 700 G in spite of the action of ion drag. In addition, the dependence of self-rotation velocity on gas pressure in the discharge when the particles are in the dust trap and on power deposited into the discharge has been measured for the first time. Experimental data correlate well with the developed model of dust particle self-rotation, which appears to maintain the stationary charge of the dust particle.

Dust remobilization from rough planar surfaces in tokamak steady-state plasmas

The ability of tungsten (W) dust to be remobilized from rough tokamak plasma-facing surfaces is investigated in this study. Atomic Force Microscopy is used to evaluate the adhesion force distribution between W spheroids of ∼1−10 µm radius and a rough W substrate. Our results confirm that the Rabinovich model describes reasonably well the mean adhesion force in tokamak-relevant surface roughness regimes. The external (electric and ion drag) forces are estimated as well using a simplified sheath model. The results reveal that micron-size dust can be resuspended by attainable electric fields in tokamak conditions.

Complex plasma research on the International Space Station

Complex plasmas are plasmas containing solid particles typically in the micrometer range. These microparticles are highly charged and become an additional, dominating component of the plasma. Complex plasmas are model systems to study strong coupling phenomena in classical condensed matter. They offer the unique opportunity to go beyond the limits of continuous media down to the fundamental length scale of classical systems—the interparticle distance—and thus to investigate all relevant dynamic and structural processes using the fully resolved motion of individual particles, from the onset of cooperative phenomena to large strongly coupled systems. Unlike ‘regular’ plasma species the charged microparticles are strongly affected by gravity. An electric field in the sheath or a temperature gradient are usually employed to compensate for gravity, which provides favorable conditions to study two-dimensional or stressed three-dimensional (3D) systems on ground. However, in order to perform precision measurements with large isotropic 3D systems in the bulk plasma, microgravity conditions are absolutely necessary. Since 2001, this research under microgravity conditions has continuously been performed on board the International Space Station ISS within the Russian/German(European) Plasmakristall(PK)-Program. In the long-term research laboratories PKE-Nefedov (2001–2005), PK-3 Plus (2006–2013) and PK-4 (2014-ongoing), fundamental processes in liquid or crystalline complex plasmas as well as basic complex plasma issues were addressed. Highlights are: refinement of the theories of particle charging and ion drag, electrorheological plasmas, lane formation and phase separation in binary mixtures, crystallization and melting, wave propagation, shear flow and transition to turbulent motion. In this review, we will address results from microgravity research and discuss the perspectives for future studies.

A new iterative algorithm for a strongly nonlinear singular boundary value problem

Recently, Mastroberardino (2011) proposed a homotopy analysis method (HAM) for solving a nonlinear singular boundary value problem (SBVP) governing electrohydrodynamic flow (EHF) of a fluid in an ion drag configuration in a circular cylindrical conduit. The nonlinearity confronted in this problem is in the form of rational function. The HAM (Mastroberardino, 2011) produces a series solution to the problem, but requires a large number of iterations for obtaining a reasonable analytical approximation. In this paper, we propose a new iterative technique, namely the discrete optimized homotopy analysis method (DOHAM), based on a domain decomposition approach and an optimized HAM for solving the same problem. Convergence of the new method is carried out. The uniqueness of solution of the problem is established. Computational results reveal that our method provides better results as compared to some existing iterative methods. The velocity field of electrohydrodynamic flow of a fluid is computed. The influence of the strength of non-linearity and the Hartmann electric number on the velocity profile is investigated.

Effect of ion drag on Jean's instability in dusty plasma

The effect of ion drag on the Jeans instability of the dust in the plasma background is examined. It is shown that the ion drag force significantly enhances the Jeans instability and the gravitational collapse of the dust. If the drag force exceeds a critical value, the length scale threshold on Jeans instability is removed and the arbitrary small condensation of dust may occur. The relevance of these results to the planetesimal formation in molecular clouds is briefly discussed.

Structural transition of vortices to nonlinear regimes in a dusty plasma

The structural transition of a steady state dust flow from linear to nonlinear regimes is analyzed using a two-dimensional hydrodynamic model for the dust fluid confined in an axisymmetric toroidal system along with an unbounded streaming plasma. Numerical solutions of the employed hydrodynamical model not only confirms the analytical structure of the driven dust vortex flow in the linear limit as reported in the previous analysis but also shows how the dust vortices are strongly affected by the nonlinear convective transport of the flow at the higher Reynolds number (Re) regime. Effects of various system parameters including external driving field and the Reynolds number are investigated within the linear to nonlinear transition regime 0.001 ≤ Re < 50. In agreement with relevant experimental observations, the steady flow structure which is symmetric around the center in the linear regime begins to turn asymmetric in the nonlinear regime. The structure of the steady dust flow is found to be influenced mainly by the dissipation scales due to kinematic viscosity, ion drag, and neutral collision in the nonlinear regime, whereas, in the linear regime, it is mainly controlled by the external driving field and the confining boundaries.

Direct-Current Glow Discharge Dusty Plasma in Magnetic Fields up to 3000 G

A glow discharge dusty plasma in a magnetic trap in which the current channel narrows is obtained in moderate magnetic fields up to 3000 G. The results of initial experiments are reported. The formation of stable dusty plasma structures rotating at record-high angular velocities up to 15 rad/s is observed. The dependence of the angular velocity on the strength of the applied magnetic field is measured experimentally. We interpret it quantitatively on the basis of the ion drag force.

Dynamics of nanodust particles emitted from elongated initial orbits

Context. Because of high charge-to-mass ratio, the nanodust dynamics near the Sun is determined by interplay between the gravity and the electromagnetic forces. Depending on the point where it was created, a nanodust particle can either be trapped in a non-Keplerian orbit, or escape away from the Sun, reaching large velocity. The main source of nanodust is collisional fragmentation of larger dust grains, moving in approximately circular orbits inside the circumsolar dust cloud. Nanodust can also be released from cometary bodies, with highly elongated orbits. Aims. We use numerical simulations and theoretical models to study the dynamics of nanodust particles released from the parent bodies moving in elongated orbits around the Sun. We attempt to find out whether these particles can contribute to the trapped nanodust population. Methods. We use two methods: the motion of nanodust is described either by numerical solutions of full equations of motion, or by a two-dimensional (heliocentric distance vs. radial velocity) model based on the guiding-center approximation. Three models of the solar wind are employed, with different velocity profiles. Poynting–Robertson and the ion drag are included. Results. We find that the nanodust emitted from highly eccentric orbits with large aphelium distance, like those of sungrazing comets, is unlikely to be trapped. Some nanodust particles emitted from the inbound branch of such orbits can approach the Sun to within much shorter distances than the perihelium of the parent body. Unless destroyed by sublimation or other processes, these particles ultimately escape away from the Sun. Nanodust from highly eccentric orbits can be trapped if the orbits are contained within the boundary of the trapping region (for orbits close to ecliptic plane, within ~0.16 AU from the Sun). Particles that avoid trapping escape to large distances, gaining velocities comparable to that of the solar wind.

Mesoscale F Region Neutral Winds Associated With Quasi‐steady and Transient Nightside Auroral Forms

AbstractHigh‐latitude neutral winds often circulate in a two‐cell pattern as driven by large‐scale auroral forcing. However, auroral forcing also occurs in various types of mesoscale forms (i.e., tens to hundreds of kilometers in space and a few to tens of minutes in time) and contains more energy input over mesoscale than large scale. A question arises as to whether and how winds respond to the mesoscale forcing. We characterize F region winds associated with various types of auroral forms using scanning Doppler imagers, auroral imagers, and radars. The auroras examined include a quasi‐steady east‐west elongated arc, a quasi‐steady Harang aurora, transient streamers, and a transient substorm westward traveling surge. We find that winds exhibit distinct spatial structures, appearing as channels, vortices, and reversals. Such structures are consistent with the structures of the plasma flows associated with the auroras. Winds exhibit a temporal evolution very similar to the plasma flows and reach maximum perturbations only <~20 min after the flows. The above results suggest that the thermosphere is closely coupled to the ionosphere/magnetosphere through the ion drag force. The <~20‐min time scale can be partially explained by the strong ionization effect associated with the auroras and partially by the fact that the wind perturbations do not approach the flow perturbations but halt at ~20% possibly due to momentum forces other than the ion drag.

IPIM Modeling of the Ionospheric F2 Layer Depletion at High Latitudes During a High‐Speed Stream Event

AbstractOur aim is to understand the effect of high‐speed stream events on the high‐latitude ionosphere and more specifically the decrease of the foF2 frequency during the entire day following the impact. First, we have selected one summertime event, for which a large data set was available: Super Dual Auroral Radar Network (SuperDARN) and European Incoherent SCATter (EISCAT) radars, Tromsø and Sodankylä ionosondes, and the CHAllenging Minisatellite Payload (CHAMP) satellite. We modeled with the IPIM model (IRAP Plasmasphere Ionosphere Model) the dynamics of the ionosphere at Tromsø and Sodankylä using inputs derived from the data. The simulations nicely match the measurements made by the EISCAT radar and the ionosondes, and we showed that the decrease of foF2 is associated with a transition from F2 to F1 layer resulting from a decrease of neutral atomic oxygen concentration. Modeling showed that electrodynamics can explain short‐term behavior on the scale of a few hours, but long‐term behavior on the scale of a few days results from the perturbation induced in the atmosphere. Enhancement of convection is responsible for a sharp increase of the ion temperature by Joule heating, leading through chemistry to an immediate reduction of the F2 layer. Then, ion drag on neutrals is responsible for a rapid heating and expansion of the thermosphere. This expansion affects atomic oxygen through nonthermal upward flow, which results in a decrease of its concentration and amplifies the decrease of [O]/[N2] ratio. This thermospheric change explains long‐term extinction of the F2 layer.

Summer Noontime hmF2 Long‐Term Trends Inferred From foF1 and foF2 Ionosonde Observations in Europe

AbstractA new method to retrieve hmF2 and vertical plasma drift W from foF1 and foF2 ionosonde observations has been proposed and applied at five European stations for June noontime conditions over the (1958–2017) period. Linear long‐term trends were estimated using the retrieved hmF2 and W variations. It has been shown that negative and statistically significant hmF2 trends manifest a pronounced latitudinal dependence: the largest (~2.7 km per decade) is at lower‐latitude station Rome, while the smallest (< 1 km per decade) is at high‐latitude station Sodankylä. It was shown that hmF2 trends are due to vertical plasma drifts that manifest similar latitudinal dependence: the largest (~1 m/s per decade) is at Rome and the smallest (~0.3 m/s per decade) is at Sodankylä. Vertical plasma drift converted to the meridional northward thermospheric wind manifests an average increase of (11.6 ± 3.0) m/s over the period of ~60 years. This may be related to a decrease in ion drag due to negative trends in the ionospheric F1 and F2 regions. An additional factor is a decrease in auroral heating related to long‐term decrease in solar and geomagnetic activity observed for June months over the analyzed period.

Dissipative solitary wave at the interface of a binary complex plasma

The propagation of a dissipative solitary wave across an interface is studied in a binary complex plasma. The experiments were performed under microgravity conditions in the PK-3 Plus Laboratory on board the International Space Station using microparticles with diameters of 1.55 μm and 2.55 μm immersed in a low-temperature plasma. The solitary wave was excited at the edge of a particle-free region and propagated from the sub-cloud of small particles into that of big particles. The interfacial effect was observed by measuring the deceleration of particles in the wave crest. The results are compared with a Langevin dynamics simulation, where the waves were excited by a gentle push on the edge of the sub-cloud of small particles. Reflection of the wave at the interface is induced by increasing the strength of the push. By tuning the ion drag force exerted on big particles in the simulation, the effective width of the interface is adjusted. We show that the strength of reflection increases with narrower interfaces.

Responses of Lower Thermospheric Temperature to the 2013 St. Patrick's Day Geomagnetic Storm

AbstractThe altitude‐ and latitude‐dependent responses of neutral temperature in the lower thermosphere to the 2013 St. Patrick's Day geomagnetic storm have been studied using neutral temperature measurements from the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument onboard the TIMED satellite and the Solar Occultation For Ice Experiment (SOFIE) instrument onboard the AIM satellite. Both SABER and SOFIE observations revealed that both temperature increase (having peaks of ~15–25 K) and decrease (having peak of ~15 K), which were associated with the storm, occurred in the two hemispheres. The magnitudes of temperature variations changed with latitude, altitude, and the phase of the storm. The peaks of the temperature increase occurred 0.5–1.5 days later than the peak of the AE index, depending on latitude and height. Global circulation changes initiated due to heating and ion drag in the auroral region are likely responsible for the temperature increases or decreases in the lower thermosphere.