Energetic Ion Fluxes Research Articles

Long-lived recurrent fluxes of energetic ions from solar coronal holes

The results of studying the relative abundances and energy spectra of 4He, C, O, and Fe suprathermal ions in particle fluxes from long-lived near-equatorial coronal holes are presented. It was found that the ion energy spectra had a power or exponential form and, in a number of events, increased particle fluxes were observed in the region of ion energies (~0.2–1.5 MeV/nucleon), creating a fracture in the spectra, which may be due to additional ions accelerated beyond 1 au.

On the Formation Mechanism of Martian Dayside Ionospheric Plasma Depletion Events

AbstractPlasma Depletion Events (PDEs) are characterized by abrupt, localized reductions in ionospheric plasma density at least by an order of magnitude decrease. These events are observed over a limited range of altitudes, typically spanning a few tens of kilometers. We use Mars Atmosphere and Volatile Evolution spacecraft data to investigate the properties and possible formation mechanism of daytime PDEs, typically observed at altitudes above 250 km. We show, using two example events and statistical analysis, that the depletion events are associated with electrostatic fluctuations and increased electron temperatures. The events are further accompanied by enhanced fluxes of suprathermal electrons and light energetic ions. These are indicative of local plasma heating, possibly mediated by the electrostatic fluctuations. The heated plasma may eventually escape from the depletion region through the ambipolar diffusion.

Long-Lived Recurrent Fluxes of Energetic Ions from Coronal Holes on the Sun

Long-Lived Recurrent Fluxes of Energetic Ions from Coronal Holes on the Sun

Parametrization of Energetic Ion and Electron Fluxes in the Near‐Earth Magnetotail

AbstractThe near‐Earth plasma sheet region is the main source of energetic (tens to hundreds keV) ion and electron populations transported by convection and injections into the inner magnetosphere. Energetic ions from the plasma sheet contribute to the ring current, whereas energetic electrons contribute to the radiation belt seed population for further acceleration to relativistic energies. Near‐Earth plasma sheet energetic fluxes have been traditionally used to set boundary conditions for radiation belt and ring current models. This study provides an empirical parametrization for ∼75 keV flux intensity as a function of the geomagnetic activity index auroral electrojet and the equatorial magnetic field Bz. Such parametrization includes the dynamic magnetic field configuration in the near‐Earth plasma sheet and may be merged with empirical magnetic field models. We also provide models extending this parametrization to the [20, 300] keV of electron energy range and [75, 300] keV of ion energy range. The parametrization is developed based on THEMIS and Geostationary Operational Environmental Satellite measurements, and verified by comparison with MMS measurements in the near‐Earth plasma sheet. This parametrization incorporates meso‐scale transient flux variations associated with Bz perturbations into ring current and radiation belt simulations.

Europa's Perturbed Fields and Induced Dipole Affect Energetic Proton Depletions During Distant Alfvén Wing Flybys

AbstractWe investigate the causes of energetic proton (80–540 keV) depletions measured during the two most distant flybys of Europa by Galileo, E17 and E25A, which encountered the Alfvén wings. First, by simulating the proton flux with a Monte Carlo particle tracing code we investigate the effect of: electromagnetic field perturbations, the induced dipole, atmospheric charge exchange and plumes. Inhomogeneous fields associated with the Alfvén wings and the ionosphere strongly affect the depletions. For homogeneous fields the depletion along the trajectory is focused on a narrow pitch angle range and has no structure, whereas the depletion for perturbed (inhomogeneous) fields represents a wider and complex structure. Furthermore, also the induced dipole alters the depletion structure. The effect of plumes (density 2.5 × 1015 m−3) and charge exchange on the proton depletion is minor. Second, we compare the simulations to the proton measurements. The simulations with inhomogeneous fields describe the data qualitatively better than the homogeneous case, suggesting that indeed field perturbations are responsible for the measured losses. We attribute discrepancies between the simulations and the proton measurements to discrepancies between the simulated and real fields. We argue that simulating the fields along the trajectory is a good first step, but that ideally the energetic ion flux is reconstructed well to gain confidence in the interpretation of the simulated magnetic field. In conclusion, energetic ion observations along distant flybys through the Alfvén wings are suitable for isolating the characteristics of the global configuration of the magnetospheric interaction region of Europa (or other moons).

Simulation of Dynamic Evolution of Ring Current Ion Flux by a Lunar Base Energetic Neutral Atom (ENA) Imaging

The distribution of energetic ion flux in the ring current region, such as a meteorological cumulonimbus cloud, stores up the particle energy for a geomagnetic substorm. It is helpful to study the geomagnetic substorm mechanism by using a lunar base ENA imaging simulation of the dynamic evolution of the ring current, and establishing the corresponding relationship between key node events of the substorm. Based on the previous observation experience and our simulation results of the dynamic evolution of the ring current, we propose a macroscopic model of substorms related to the dynamic evolution of ring currents and present the possibility of confirming the causal sequence of some of those critical node events of substorms with the lunar base ENA imaging measurement. IBEX, operating in the ecliptic plane, may even give examples of the telemetry of ring current ion fluxes through ENA measurements during substorms/quiets.

Ion Energization by Turbulent Electric Fields in Fast Earthward Flows and Its Implications for the Dynamics of the Inner Magnetosphere

AbstractLarge‐amplitude electric fields (>50 mV/m) typical to bursty bulk flow (BBF) braking regions of the Earth's magnetotail can accelerate energetic electrons and ions to many times their initial thermal energies. We follow up on the Usanova and Ergun (2022), https://doi.org/10.1029/2022JA030336, study of electron energization and examine wave and plasma observations from the THEMIS satellites over four tail seasons to investigate the transfer of BBF energy to ions by turbulent electric fields. The results show that the large‐amplitude electric fields are accompanied by an ion temperature increase of ∼50% when compared to times when the turbulence is not observed. Electric field turbulence is also associated with a roughly ten‐fold increase in temperature fluctuations and a five‐fold increase in variations of energetic ion fluxes. We discuss the contribution of this turbulent energy transfer process to the dynamics of energetic ions in the magnetosphere.

The Influence of the Magnetic Field Line Curvature on Wall Erosion near the Hall Thruster Exit Plane

One of the main factors that limit the lifetime of the Hall effect Thrusters (HETs) is the erosion of the acceleration channel caused by the flux of energetic ions. The magnetic field that is curved and convex towards the anode has been widely used in HETs because of its role in reducing the divergence angle of the ion beam and the channel wall erosion. However, the mechanism of the influence of the magnetic field line curvature on the wall erosion is not clear. Therefore, in this paper, a 2D3V numerical model based on the immersed-finite-element and particle-in-cell (IFE-PIC) method is established to simulate the radial-azimuthal plane near the exit of the Hall thruster. The effect of the tilt angle of the magnetic field line on the wall sputtering erosion rate is analyzed. The results show that compared to the case with the electric field E perpendicular to the magnetic field B, the energy of the ions hitting the channel wall is smaller and the wall erosion is weaker when the magnetic field lines are convex to the anode. As the tilt angle of the magnetic field lines increases from 0° to 60°, the erosion rate is reduced by 90%. Conversely, when the magnetic field lines are convex to the exit plane of the channel, the wall erosion is much more serious compared to the case with the orthogonal electric field E and the magnetic field B. As the tilt angle of the magnetic field line changes from 0° to 60°, the erosion rate is enhanced by 171%. The results in this paper are instructive for the design and optimization of the magnetic field of the HETs.

Magnetosheath Filamentary Structures Driven by Foreshock Energetic Ions

AbstractPrevious simulation studies have revealed the formation of magnetosheath filamentary structures by foreshock energetic ions. We report Cluster and Double Star observations of three such events triggered by a foreshock bubble, a hot flow anomaly and a traveling foreshock, respectively. In each case, in association with the onset of foreshock energetic ions, the magnetosheath energetic ion fluxes have quasi‐periodic modifications. Their azimuthal and pitch angular distributions indicate that these populations flow into the magnetosheath along the magnetic field lines. As a result, filamentary plasma structures form and display as a series of ion density and pressure oscillations anticorrelated to temperature oscillations. Moreover, our statistical analyses of their properties show that filamentary structures primarily form in the magnetosheath with the magnetic field lines connecting to the quasi‐parallel bow shock and under favorable formation conditions similar to those of foreshock transients. The distributions of the angles between the filamentary structure normals and the local magnetic field directions peak at 80°–90°. The transverse sizes of those filaments are in the range of 0.2–1.6 RE. Magnetosheath filamentary structures are often associated with large‐amplitude ion density and temperature perturbations comparable to the unperturbed background levels.

Magnetic Field and Energetic Particle Flux Oscillations and High‐Frequency Waves Deep in the Inner Magnetosphere During Substorm Dipolarization: ERG Observations

AbstractUsing Exploration of energization and Radiation in Geospace (ERG or Arase) spacecraft data, we studied low‐frequency magnetic field and energetic particle flux oscillations and high‐frequency waves deep in the inner magnetosphere at a radial distance of ~4–5 during substorm dipolarization. The magnetic field oscillated alternately between dipole‐like and taillike configuration at a period of 1 min during dipolarization. When the magnetic field was dipole‐like, the parallel magnetic component of the Pi2 waves was at trough. Both energetic ion and electron fluxes with a few to tens of kiloelectronvolts enhanced out of phase, indicating that magnetosonic waves were in slow mode. Field‐aligned currents also oscillated. These observations are consistent with signatures of ballooning instability. In addition, we found that broadband waves from the Pi1 range to above the electron cyclotron frequency tended to appear intermittently in the central plasma sheet near dipole‐like configuration.

Magnetotail Dipolarizations and Ion Flux Variations During the Main Phase of Magnetic Storms

AbstractNear‐Earth tail dipolarizations are usually associated with fast plasma flows and an increase in energetic particle fluxes. Yet, the role of these dipolarizations in energetic ion flux transport toward the inner magnetosphere and in ring current (including partial ring current) development during the main phase of a geomagnetic storm is not fully understood. We investigated observations from Time History of Events and Macroscale Interactions during Substorms (THEMIS) probes A, D, and E with apogees at X ≈ −13 RE and Los Alamos National Laboratory (LANL) geosynchronous spacecraft in the midnight magnetic local time (MLT) sector (21.5–1.5 h MLT) during the main phases of storms with integrated Dst exceeding 600 nT*hr from the 2010 to 2016 THEMIS tail seasons. We selected 10 storms during which at least one of the THEMIS probes was in the midnight sector during a storm’s main phase and identified 39 dipolarization events with a Bz increase exceeding 10 nT within 500 s during these storms’ main phases. In 21 of the 39 events, an increase in the magnetic field elevation angle Θ estimated from LANL magnetospheric plasma analyzer (MPA) data was detected at geosynchronous orbit (GEO) within ±15‐min‐long time window around dipolarization onset detected by THEMIS. In only 10 of those 21 events, however, did ion fluxes at energies from 50 to 500 keV increase in three or more consecutive energy bins at LANL. Comparisons of ion spectra collected by THEMIS and LANL in these 10 events revealed a similar increase in fluxes at energies E > 20 keV. Our results indicate that a dipolarization that occupies a large portion of the nightside magnetosphere from GEO to ∼12 RE is a necessary but not sufficient condition for energetic ion flux enhancements at GEO. As suggested in previous studies, an increase in the azimuthal electric field (i.e., enhanced earthward magnetic flux transport) is most likely required for an ∼100 keV ion flux increase at GEO.

Influence of Europa’s Time‐Varying Electromagnetic Environment on Magnetospheric Ion Precipitation and Surface Weathering

AbstractWe combine the electromagnetic fields from a hybrid model with a particle‐tracing code to calculate the time‐varying spatial distribution of magnetospheric ion flux onto the surface of Jupiter’s moon Europa. The electromagnetic fields at Europa are perturbed by the sub‐alfvénic interaction of the moon’s ionosphere and induced dipole with the magnetospheric plasma. These perturbations substantially modify magnetospheric ion trajectories at all energies. We calculate spatially resolved surface flux maps of thermal and energetic ions for various distances between Europa and the center of Jupiter’s magnetospheric plasma sheet. The upstream ion distributions are constrained through in‐situ particle data from the Galileo and Juno spacecraft. These maps are then combined to obtain the average distribution of magnetospheric ion surface flux over a full synodic rotation. Our results show that the draping and pileup of the magnetic field reduce ion flux onto Europa’s trailing hemisphere by several orders of magnitude, while a significant number of the incident ions are deflected onto the leading hemisphere. Taking into account the deflection of energetic ions in the draped electromagnetic fields shifts the region of minimum energetic ion surface flux from Europa’s wakeside equator to its ramside equator. This generates an “inverted bullseye” pattern of energetic ion flux centered at the trailing apex. Despite drastic changes to the morphology of the ion surface flux when the alfvénic plasma interaction is included, we still find a strong correlation between variations of sulfuric acid concentration observed across Europa’s surface by Galileo and our modeled sulfur influx pattern.

Molecular dynamics simulation of amine groups formation during plasma processing of polystyrene surfaces

Plasma treatment and plasma polymerization processes aiming to form amine groups on polystyrene surfaces were studied in-silico with molecular dynamics simulations. The simulations were compared with two experiments, (i) plasma treatment in N2/H2 bipolar pulsed discharge and (ii) plasma polymerization in cyclopropylamine/Ar radio frequency (RF) capacitively coupled discharge. To model favorable conditions for the incorporation of primary amine groups, we assumed the plasma treatment as the flux of NH2 radicals and energetic NH3 ions, and the plasma polymerization as the flux of cyclopropylamine molecules and energetic argon ions. It is shown in both the simulation and the experiment that the polystyrene treatment by the bipolar pulsed N2/H2 plasmas with an applied voltage of about ±1 kV formed a nitrogen-rich layer of a thickness of only a few nm. The simulations also showed that, as the NH3 incident energy increases, the ratio of primary amines to the total number of N atoms on the surface decreases. It is because the energetic ion bombardment brakes up N–H bonds of primary amines, which are mostly brought to the surface by NH2 radical adsorption. Our previous experimental work on the CPA plasma polymerization showed that increased RF power invested in the plasma leads to the deposition of films with lower nitrogen content. The MD simulations showed an increase of the nitrogen content with the Ar energy and a limited impact of the energetic bombardment on the retention of primary amines. Thus, the results highlighted the importance of the gas-phase processes on the nitrogen incorporation and primary amines retention in the plasma polymers. However, the higher energy flux towards the growing film clearly decreases amount of hydrogen and increases the polymer cross-linking.

SAR arc observation during the overlap registration of an energetic plasma with a plasmapause aboard the Van Allen Probe

Stable auroral red (SAR) arcs are the consequence of interaction of the outer plasmasphere (plasmapause) with energetic ions of the ring current. In this work the event of SAR arc observation using the all-sky imager (ASI) at the Yakutsk meridian (130°E; 200°E, geom.) simultaneously with the registration of plasmapause and energetic ion fluxes aboard the Van Allen Probe B satellite at the beginning of the large magnetic storm on March 17, 2015 (St. Patrick's Day geomagnetic storm) is presented. ASI registers the intense SAR arc at the 52-59°N geomagnetic latitudes in the MLT evening sector from the observation start at ~1116 UT (1926 MLT) during the low auroral activity at IMF Bz > 0. The Probe B determines the plasmapause location in the L ~ 3–4 interval and registers the inner boundary of the H+ and O+ energetic ion fluxes at L ~2.8–3.3 near the meridian of optical observations. The DMSP- F19 satellite registers the electron temperature subauroral peaks (Te peak) at 1014 and 1155 UT in the evening MLT sector. We show that SAR arc in this event maps the overlap region of plasmasphere dusk-bulge by the energetic ions flux of the ring current after the onset of magnetic storm.

Dynamical Properties of Peak and Time‐Integrated Geomagnetic Events Inferred From Sample Entropy

AbstractWe provide a comprehensive statistical analysis of the sample entropy of peak and time‐integrated geomagnetic events in 2001–2017, considering different measures of event strength, different geomagnetic indices, and a simplified solar wind‐magnetosphere coupling function . Our investigations reveal the existence of significant correlations between the entropies of , , and , and between such entropies and event strengths, as well as good correlations between peak levels of solar wind‐magnetosphere coupling and ring current ( ) and entropies, suggesting a potential predictability of significant and events on the basis of appropriate functions of . Sensibly weaker correlations are found with entropy. We further show the presence of several significant entropy correlations between geomagnetic indices, solar wind‐magnetosphere coupling, and trapped or precipitated energetic electron and ion fluxes measured by geostationary and low Earth orbit satellites in the outer radiation belt during the same periods. Entropy correlations between and trapped or precipitated 30‐ to 80‐keV ion fluxes at low and between and trapped 40‐keV electron fluxes at geostationary orbit correspond well with ring current properties and substorm‐induced injections, respectively. Entropy correlations between and precipitation rates of energetic ion and electron fluxes demonstrate the sensibility of index entropy to both low‐energy (5–30 keV) electron injections and ring current. The stronger entropy correlation between solar wind‐magnetosphere coupling and than likely stems from the more stochastic behavior of electron injections and fast losses near geostationary orbit.

Acceleration of Energetic Ions in Corotating Interaction Region near 1.5 au: Evidence from MAVEN

Abstract The dearth of observations between 1 and 3 au limits our understanding of energetic particle acceleration processes in interplanetary space. We present first-of-their-kind observations of the energetic particle acceleration in a corotating interaction region (CIR) using data from two vantage points, 1 au (near Earth) and 1.5 au (near Mars). The CIR event of 2015 June was observed by the particle detectors aboard the Advanced Composition Explorer satellite as well as the Solar Energetic Particle (SEP) instrument aboard the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft situated near 1.5 au. We find that a CIR shock can accelerate a significant number of particles even at 1.5 au. During this event the acceleration by the shocks associated with the CIR could cause an enhancement of around two orders of magnitude in the SEP energetic ion fluxes in the ∼500 keV to 2 MeV range when the observations near 1 and 1.5 au are compared. To demonstrate the differences between SEP acceleration in CIR and other impulsive events, we show the energetic ion flux observations during an intense coronal mass ejection period in March 2015, in which case the enhanced SEP fluxes are seen even at 1 au. These observations provide evidence that CIR shock can accelerate particles in the region between Earth and Mars—that is, only within the short heliocentric distance of 0.5 au—in interplanetary space.

Update on Galactic Cosmic Ray Integral Flux Measurements in Lunar Orbit With CRaTER

AbstractWe report updated measurements of the integral fluxes of energetic protons, helium ions, and heavier ions as measured by the Cosmic Ray Telescope for the Effects of Radiation (CRaTER). CRaTER is a particle telescope that has been operating aboard the Lunar Reconnaissance Orbiter since 2009. In an earlier report, we presented the methodology used to extract linear energy transfer spectra and integral fluxes for particles with sufficient energies to fully penetrate the telescope. Results were presented for the time span from late 2009 to the end of calendar year 2014, a period that encompassed the rise of solar activity from deep solar minimum to the weak maximum of Cycle 24. Here, we update the results with data obtained from that point in time through the end of 2018, in the declining phase of Cycle 24. Fluxes obtained in the most recent data are approaching the peak levels observed in late 2009 and early 2010. The results can be used as input to models of solar modulation of galactic cosmic rays and are also relevant to human exploration of deep space.

Plasma characterization in Hall thrusters by Langmuir probes

One of the main factors that limits the Hall thruster lifetime is the degradation of surfaces exposed to plasma caused by the flux of energetic ions. Since the magnetic field shapes the plasma properties inside the thruster channel, non-standard magnetic configurations have been proposed in recent years to substantially increase the thruster lifetime. The present article reports an experimental investigation of different magnetic topologies of a Hall thruster operating on xenon and krypton. Plasma properties were measured using probes installed on the channel walls and a fast diving probe. Data are analysed by means of a Bayesian methodology. Results show that magnetic shielding correctly reduces the interaction between the plasma and the channel walls, which can result in lower erosion rates. A comparison between xenon and krypton operation showed that magnetic shielding is less effective for krypton, as the grazing line presents higher temperatures. Fast probe results also show how krypton discharges present wider acceleration regions and higher temperatures inside the channel.

Combined IR and XPS characterization of organic refractory residues obtained by ion irradiation of simple icy mixtures

Context. Multi-year laboratory experiments have demonstrated that frozen icy mixtures containing simple organic and inorganic molecules (such as H2O, N2, CH4, CO, CO2, C2H6, etc.), if exposed to a flux of energetic ions or UV photons, give rise to new more complex molecules at low temperatures (10–50 K). A fraction of the new synthesized molecules is volatile while the remaining fraction is refractory and therefore it is preserved after the warm-up of the substrate to room temperature. Moreover, a part of the refractory material is formed during the annealing to room temperature, when molecules and radicals into the processed ice become mobile and react to form non-volatile molecules. By means of similar mechanisms, complex organic materials may be formed on the icy surfaces of some objects in the outer solar system, such as trans-Neptunian objects, comets and some satellites of the giant planets: in fact the interaction with solar wind and solar flares ions, solar photons and galactic cosmic rays could produce more refractory materials, analogous to those produced in the laboratory. In some cases, the materials thus synthesized may contain functional groups considered relevant to the pre-biotic chemistry in the hypothesis that interplanetary dust particles, comets and meteoroids contributed to seed the early Earth with the building blocks of life. Aims. The aim of this work is to investigate the chemical similarities and differences between some organic residues left over after ion bombardment (200 keV H+) of different ice mixtures followed by subsequent warm up under vacuum to room temperature. Methods. Seven organic residues have been prepared in our laboratory following a procedure involving the proton irradiation of seven different icy mixtures and their warm-up to room temperature. All the organic samples were characterized by FTIR spectroscopy with measurements performed in situ, in the ultra-high vacuum condition preventing any sample degradation. Three of them were selected to be characterized by XPS spectroscopy as well. Results. Among the organic residues presented in this paper, only those containing nitrogen and carbon exhibit the multi-component band centred at 2200 cm−1. This multi-component band presents interest from the astrobiological point of view due to its attribution to nitriles (–C≡N) and isonitriles (–N≡C). Our results demonstrate that this band is present in the IR spectra of organic nitrogen residues regardless the use of oxygen-bearing species in the icy mixture. This finding is of interest since the 2200 cm−1 band has been observed in some extraterrestrial samples (micro-meteorites) collected in the Antarctica.

Electron emission from carbon velvet due to incident xenon ions

We present measurements of the ion-induced electron emission from carbon velvet. The results from carbon velvet with high aspect ratio vertical fibers (6.8 μm diameter and 2.6 mm length) show a more than 60% reduction in ion-induced electron emission for normal incident xenon ions over the entire ion incident energy investigated (i.e., 500–2000 eV) when compared to graphite. This is important for plasma-facing surfaces that are exposed to large fluxes of energetic ions, such as beam dumps and chamber walls used to control facility effects in plasma-thruster ground tests.