Ambient Plasma Environment Research Articles

Empirical Modeling of the Global Distribution of Magnetosonic Waves with Ambient Plasma Environment using Van Allen Probes

It is suggested that magnetosonic waves (also known as equatorial noise) can scatter radiation belt electrons in the Earth’s magnetosphere. Therefore, it is important to understand the global distribution of these waves between the proton cyclotron frequency and the lower hybrid resonance frequency. In this study, we developed an empirical model for estimating the global distribution of magnetosonic wave amplitudes and wave normal angles. The model is based on the entire mission period (approximately 2012–2019) of observations of Van Allen Probes A and B as a function of the distance from the Earth (denoted by L*), magnetic local time (MLT), magnetic latitude (λ), and geomagnetic activity (denoted by the Kp index). In previous studies the wave distribution inside and outside the plasmasphere were separately investigated and modeled. Our model, on the other hand, identifies the wave distribution along with the ambient plasma environment—defined by the ratio of the plasma frequency (fpe) to the electron cyclotron frequency (fce)—without separately determining the wave distribution according to the plasmapause location. The model results show that, as Kp increases, the dayside wave amplitude in the equatorial region intensifies. It thereby propagates the intense region towards the wider MLT and inward to L* < 4. In contrast, the fpe/fce ratio decreases with increasing Kp for all regions. Nevertheless, the decreasing aspect differs between regions above and below L* = 4. This finding implies that the particle energy and pitch angle that magnetosonic waves can effectively scatter vary depending on the locations and geomagnetic activity. Our model agrees with the statistically observed wave distribution and ambient plasma environment with a coefficient of determination of > 0.9. The model is valid in all MLTs, 2 ≤ L* < 6, |λ| < 20°, and Kp ≤ 6.

Distribution and variability of plasma perturbations observed by ARTEMIS near the Moon in the terrestrial magnetotail

The lunar environment while in the Earth’s magnetosphere represents a unique plasma regime, in which we can directly detect the Moon’s effects on the ambient plasma environment. To a much greater degree than in the solar wind, the presence of the Moon and its exosphere perturb the ambient plasma environment. We identified and analyzed a variety of different effects of this interaction. We mapped four different interaction signatures and analyzed the solar and solar wind parameters during their occurrence. Confirming previous work, we found that the lunar events investigated in this paper tend to occur above the lunar dayside surface. In addition, we found that magnetospheric activity indices are higher during the categorized lunar events. This suggests that when the terrestrial magnetosphere is more active, as a result of solar wind activity, the terrestrial magnetospheric plasma and electromagnetic fields interact with lunar plasma to create the observed perturbations.

Holistic numerical calibration of the iMESA electrostatic analyzer.

A drifted Maxwellian velocity distribution is the most common model used to interpret the data from low-energy charged-particle instruments onboard spacecraft that are used to investigate the ambient plasma environment in the low Earth orbit (LEO). An original method is presented for determining the flow parameters (density, temperature, and flow energy) of such a distribution from the output of the integrated miniaturized electrostatic analyzer, which has been successfully flown on several LEO missions. Rather than attempting to deconvolve from the on-orbit data the analyzer's response to an ideal, monoenergetic input, numerical simulation is used to predict and parameterize the response of the device to an input distribution that includes an isotropic, non-zero temperature, yielding a straightforward method for extracting the flow parameters from the spacecraft data. The method is computationally simple enough to be incorporated into a robust algorithm suitable for rapid batch processing or real-time analysis of data.

Low‐Resource Technique for Measurement of H+ and O+ in the Terrestrial Magnetosphere

AbstractMeasurement of O+ in the Earth's magnetosphere is important for monitoring and understanding the initiation and evolution of geomagnetic activity. During active times, O+ can be the most abundant ion in the magnetosphere. Furthermore, because O+ and H+ damage exposed spacecraft materials through different processes, measurement and prediction of O+ and H+ fluxes is critical for understanding cumulative damage effects to these materials resulting from the ambient plasma environment of a spacecraft. We describe a simple technique for quantitative, in situ measurement of O+ and H+ fluxes using ultrathin foils. This technique is a low‐resource addition to a standard electrostatic energy‐per‐charge analyzer followed by an array of detectors. H+ and O+ abundances up to a few tens of keV can be determined by comparison of counts in detectors having no ultrathin foil at the detector aperture, in which both H+ and O+ are detected, and adjacent detectors having a foil over the aperture of the appropriate thickness to stop the transmission of O+ but through which H+ can transit. We describe three techniques for implementing this method enabling differentiation of O+ and H+ in an instrument package significantly simpler than traditional mass spectrometers.

Solar Wind Plasma Interaction with Asteroid 16 Psyche: Implication for Formation Theories

AbstractThe asteroid 16 Psyche is a primitive metal‐rich asteroid that has not yet been visited by spacecraft. Based on remote observations, Psyche is most likely composed of iron and nickel metal; however, the history of its formation and solidification is still unknown. If Psyche is a remnant core of a differentiated planetesimal exposed by collisions, it opens a unique window toward understanding the cores of the terrestrial bodies, including the Earth and Mercury. If not, it is perhaps a reaccreted rubble pile that has never melted. In the former case, Psyche may have a remanent, dipolar magnetic field; in the latter case, Psyche may have no intrinsic field, but nevertheless would be a conductive object in the solar wind. We use Advanced Modeling Infrastructure in Space Simulation (AMITIS), a three‐dimensional GPU‐based hybrid model of plasma that self‐consistently couples the interior electromagnetic response of Psyche (i.e., magnetic diffusion) to its ambient plasma environment in order to quantify the different interactions under these two cases. The model results provide estimates for the electromagnetic environment of Psyche, showing that the magnetized case and the conductive case present very different signatures in the solar wind. These results have implications for an accurate interpretation of magnetic field observations by NASA's Discovery mission (Psyche mission) to the asteroid 16 Psyche.

Potential of Earth Orbiting Spacecraft Influenced by Meteoroid Hypervelocity Impacts

Detection of hypervelocity impacts on a spacecraft body using electric field instruments has been established as a new method for monitoring of dust grains in our solar system. Voyager, WIND, Cassini, and STEREO spacecraft have shown that this technique can be a complementary method to conventional dust detectors. This approach uses fast short time changes in the spacecraft potential generated by hypervelocity dust impacts, which can be detected by monopole electric field instruments as a pulse in the measured electric field. The shape and the duration of the pulse strongly depend on parameters of the ambient plasma environment. This fact is very important for Earth orbiting spacecraft crossing various regions of the Earth’s magnetosphere where the concentration and the temperature of plasma particles change significantly. We present the numerical simulations of spacecraft charging focused on changes in the spacecraft potential generated by dust impacts in various locations of the Earth’s magnetosphere. We show that identical dust impacts generate significantly larger pulses in regions with lower electron density. We discuss the influence of the photoelectron distribution for dust impact detections showing that a small amount of energetic photoelectrons significantly increases the potential of the spacecraft body and the pulse duration. We also show that the active spacecraft potential control (ASPOC) instrument onboard the cluster spacecraft strongly reduces the amplitude and the duration of the pulse resulting in difficulties of dust detection when ASPOC is ON. Simulation of dust impacts is compared with pulses detected by the Earth orbiting cluster spacecraft in the last part of Section III .

SPECTRAL STRUCTURES AND THEIR GENERATION MECHANISMS FOR SOLAR RADIO TYPE-I BURSTS

The fine spectral structures of solar radio type-I bursts were observed by the solar radio telescope AMATERAS. The spectral characteristics, such as the peak flux, duration, and bandwidth, of the individual burst elements were satisfactorily detected by the highly resolved spectral data of AMATEAS with the burst detection algorithm that is improved in this study. The peak flux of the type-I bursts followed a power-law distribution with a spectral index of 2.9-3.3, whereas their duration and bandwidth were distributed more exponentially. There were almost no correlations between the peak flux, duration, and bandwidth. That means there were no similarity shapes in the burst spectral structures. We defined the growth rate of a burst as the ratio between its peak flux and duration. There was a strong correlation between the growth rate and peak flux. These results suggest that the free energy of type-I bursts that is originally generated by non-thermal electrons is modulated in the subsequent stages of the generation of non-thermal electrons, such as plasma wave generation, radio wave emissions, and propagation. The variation of the time scale of the growth rate is significantly larger than that of the coronal environments. These results can be explained by the situation that the source region may have the inhomogeneity of an ambient plasma environment, such as the boundary of open and closed field lines, and the superposition of entire emitted bursts was observed by the spectrometer.

Three-dimensional, two-species magnetohydrodynamic studies of the early time behaviors of the Combined Release and Radiation Effects Satellite G2 barium release

We present a three-dimensional, two-species (Ba+ and H+) MHD model to study the early time behaviors of a barium release at about 1 RE like Combined Release and Radiation Effects Satellite G2, with emphasis placed on the three-dimensional evolution of the barium cloud and its effects on the ambient plasma environment. We find that the perturbations caused by the cloud are the combined results of the initial injection, the radial expansion, and the diamagnetic effect and propagate as fast MHD waves in the magnetosphere. In return, the transverse expansion and the cross-B motion of barium ions are constrained by the magnetic force, which lead to a field-aligned striation of ions and the decoupling of these ions from the neutrals. Our simulation shows the formation and collapse of the diamagnetic cavity in the barium cloud. The estimated time scale for the cavity evolution might be much shorter if photoionization time scale and field aligned expansion of barium ions are considered. In addition, our two species MHD simulation also finds the snowplow effect resulting from the momentum coupling between barium ions and background H+, which creates density hole and bumps in the background H+ when barium ions expanding along the magnetic field lines.

On the signature of positively charged dust particles on plasma irregularities in the mesosphere

Recent rocket payloads have studied the properties of aerosol particles within the ambient plasma environment in the polar mesopause region and measured the signature of the positively charged particles with number densities of (2000cm−3) for particles of 0.5–1nm in radius. The measurement of significant numbers of positively charged aerosol particles is unexpected from the standard theory of aerosol charging in plasma. Nucleation on the cluster ions is one of the most probable hypotheses for the positive charge on the smallest particles. This work attempts to study the correlation and anti-correlation of fluctuations in the electron and ion densities in the background plasma by adopting the proposed hypothesis of positive dust particle formation. The utility being that it may provide a test for determining the presence of positive dust particles. The results of the model described show good agreement with observed rocket data. As an application, the model is also applied to investigate the electron irregularity behavior during radiowave heating assuming the presence of positive dust particles. It is shown that the positive dust produces important changes in the behavior during Polar Mesospheric Summer Echo PMSE heating experiments that can be described by the fluctuation correlation and anti-correlation properties.

Fine scale structures of pulsating auroras in the early recovery phase of substorm using ground‐based EMCCD camera

We have carried out ground‐based observations, optimized to temporal and spatial characteristics of pulsating auroras (PAs) in the micro/meso scale, using an electron multiplying charge coupled device (EMCCD) camera with a wide field of view corresponding to 100 × 100 km at an altitude of 110 km and a high sampling rate up to 100 frames per second. We focus on transient PAs propagating southward around 1100 UT, in the early recovery phase of the substorm, on 4th March 2011. Three independent patches (PA1–3) each with different periods between 4 and 7 s were observed, which means that the periodicity was not explained by the electron bounce motion and strongly depended on local plasma conditions in the magnetosphere or in the ionosphere. One more insight is that only PA1 had also a sharp peak of modulations around 1.5 Hz, with a narrow frequency width of 0.30 Hz, and the strong modulations existed as a small spot in the center of PA1. We have also conducted cross spectrum analysis and have obtained coherence and phase distributions for auroral variations between 0.1 and 3.0 Hz. The results indicated that low frequency variations from 0.2 to 0.5 Hz inside PA1–3 propagated as a collective motion in well‐defined directions. The estimated horizontal propagation velocities ranged from 50 to 120 km/s at the auroral altitude. The velocities are almost consistent with the Alfven speed at the magnetic equator, which suggests that compressional waves have an effect on PA via modulations of the ambient plasma environment.

The implications of the H2variability in Titan's exosphere

[1] We present in this paper an investigation of the distribution of H2 in Titan's exosphere, based on the measurements made with the Ion Neutral Mass Spectrometer (INMS) onboard Cassini during 32 encounters with the satellite. The observed H2 density in Titan's exosphere shows significant variance from flyby to flyby. However, no appreciable trend with geophysical or solar conditions can be identified. A data-model comparison is made in the framework of the Chamberlain approach, taking into account two ideal cases. First, we assume that the observed variability is spatial. In this case, the damping of exobase perturbations when propagating into the exosphere is a diagnostic of the spatial scale of the perturbations. We find that for all reasonable choices of this spatial scale, the model predicts significantly more damping than implied by the INMS data. Second, we assume that at any given time, the physical conditions in Titan's upper atmosphere and exosphere are globally uniform, but these conditions evolve with time, indicating that the observed variability is temporal. In such a case, the observations can be interpreted as a result of exobase perturbations on timescales in the range of ∼103–106 s. The time-varying H2 exosphere of Titan essentially reflects the varying structure and energy deposition in the upper atmosphere of the satellite, which are ultimately determined by the variations in either the solar EUV/UV radiation or the level of magnetospheric particle precipitation. However, we do not expect the considerable variability observed for Titan's H2 exosphere to be induced by the varying solar inputs into Titan's atmosphere. Instead, we postulate that such a variability is more likely to be associated with Titan's varying plasma environment. Comparisons between different categories of Titan flybys tentatively reveal that the H2 exosphere tends to be more energetic and more expanded, and H2 molecules tend to escape more rapidly, with increasing levels of electron precipitation from the ambient plasma environment.

Importance of Surface Conditions for Spacecraft Charging

Abstract : Spacecraft charging is determined by the ambient plasma environment and the surface properties. Whereas the ambient plasma environment is measured in-situ and in real time, the surface property data rely on measurements conducted previously in the laboratory and empirical formulae derived from the laboratory measurements. This note addresses the importance of surface conditions in determining the spacecraft surface potentials. For example, the surface smoothness, thickness, surface composition, and surface contamination are important factors that govern the current balance at equilibrium and the onset of spacecraft charging. These parameters of surface conditions can also greatly influence the accuracy of model calculations of the spacecraft potential. We will provide supporting data to illustrate the main points and to make the case. For spacecraft design, it is inadequate to look up published tables of the coefficients for a given type of surface material. It is necessary to measure the secondary electron coefficient, for example, of an actual piece of the material, because the thickness, smoothness, and surface composition, etc. do matter. In the harsh space environment, surface conditions can also change gradually as a result of the unceasing bombardment by the incoming electrons and ions. All these factors pose uncertainty to spacecraft charging.

The ECOMA 2007 campaign: rocket observations and numerical modelling of aerosol particle charging and plasma depletion in a PMSE/NLC layer

Abstract. The ECOMA series of rocket payloads use a set of aerosol particle, plasma, and optical instruments to study the properties of aerosol particles and their interaction with the ambient plasma environment in the polar mesopause region. In August 2007 the ECOMA-3 payload was launched into a region with Polar Mesosphere Summer Echoes (PMSE) and noctilucent clouds (NLC). An electron depletion was detected in a broad region between 83 and 88 km, coincident with enhanced density of negatively charged aerosol particles. We also find evidence for positive ion depletion in the same region. Charge neutrality requires that a population of positively charged particles smaller than 2 nm and with a density of at least 2×108 m−3 must also have been present in the layer, undetected by the instruments. A numerical model for the charging of aerosol particles and their interaction with the ambient plasma is used to analyse the results, showing that high aerosol particle densities are required in order to explain the observed ion density depletion. The model also shows that a very high photoionisation rate is required for the particles smaller than 2 nm to become positively charged, indicating that these may have a lower work function than pure water ice.

Evaluation of Electric Field Probe Onboard Spacecraft Using a 3D Full PIC Simulation

A three-dimensional electrostatic full Particle-In-Cell code has been developed to analyze spacecraft-plasma interactions quantitatively. The code is expected to achieve highly accurate computation because it has no robust algorithm. We adopted the code to evaluate the electric field measurement onboard spacecraft, especially under low-density ambient plasma environment with photoelectron emission. In this paper, first, fundamental functions for computation of the electric field were validated in Low Earth Orbit and Geosynchronous Orbit environments by comparing with the thin-sheath limit theory and the thick-sheath limit theory, respectively. Second, the floating potential of a spacecraft model with photoelectron emission in Geosynchronous Orbit was computed to examine the effects of photoelectron emission to the electric potential around the spacecraft. The dependence of the floating potential on the photoelectron temperature was shown in the simulation.

Ground-Based Experiment of Electric Breakdown of Spacecraft Surface Insulator in an Ambient Plasma Environment

In the future, LEO spacecraft will be larger and higher powered. Because of the balance of the leakage currents through the ambient space plasma, their main conductive body will have a higher negative potential without plasma contactor operation. When the spacecraft operates with a higher voltage, more intensive arcing is suspected to occur on the surface. In this study, a ground-based experiment was carried out to understand the arcing phenomenon and to examine the influences of the ambient space plasma on the arcing process. Simulating plasmas were generated by electron-cyclotron-resonance discharge. When arcing occurred on negatively biased anodized-aluminum-sample (AAS) plates in the plasma environment, the time variations in the arc current and bias voltage were measured. The arc-spot diameter was also measured. The single-arcing characteristics showed that both the peak arc current and the total charge emitted by arcing increased with the initial-charging voltage and neutral-particle number density. The diameter of the arc spot increased with the initial-charging voltage although it was almost constant regardless of the neutral-particle density. The repetitive-arcing characteristics showed that the arc rate gradually increased with the arcing number. Lots of overlapping arc spot were observed after 1000 arcings, and its number increased with the arcing number. The influences of the initial-charging energy on arcing characteristics were also examined by widely changing the capacitance and the initial-charging voltage. The arc-spot diameter intensively increased with the initial-charging energy, and the fitting line could be evaluated. Accordingly, a high-voltage operation of the LEO spacecraft might bring a drastic degradation of AAS by arcing, depending on the ambient plasma conditions and spacecraft capacitance

Three-Dimensional Numerical Simulation of Field-Emission-Electric-Propulsion Neutralization

A three-dimensional full-particle-simulation model is developed for simulation of a e eld-emission-electricpropulsion (FEEP) thruster operation in an ambient plasma. Simulations are performed with ion-to-electron massratios close to actual values (mi/me =80,000)to resolve the basic characteristics of thepropellant ionsemitted from a FEEP thruster and their neutralization in an ambient plasma environment or by a thermionic neutralizer. The slit geometry allows a FEEP emitter to transmit reasonable values of emission current, even when no neutralization mechanism is present. However, to neutralize the FEEP beam, one must either operate the FEEP in an ambient plasma with a density comparable with the density of the FEEP beam ions and/or place a neutralizer at a location sufe cientlyfarfrom theFEEP emitter.Becausetheelectrice eldfrom theexposed high-voltageaccelerator dominates the neighboring region of FEEP thrusters, a neutralizer placed on the spacecraft surface beside the FEEP emitter will not provide effective neutralization.

Time evolution of ion contaminant clouds at geosynchronous orbit

The exploitation of geosynchronous orbit will bring with it perturbations of the ambient plasma environment by man‐made effluents. In this paper, the creation, ionization, and subsequent transport of an artificially produced contaminant cloud in the immediate vicinity of a spacecraft at geosynchronous orbit will be examined. The theory predicts the probability of observing xenon from the SCATHA (P78‐2) SC4 xenon beam experiment by GEOS II. Estimates will also be presented for the ionization cloud expected from projected systems such as large space stations (air leakage) or a solar power satellite (argon thrusters).