The interaction of chorus waves with energetic electrons is investigated using test particle simulation, for two cases respectively, one (for a ducted chorus) with an assumption of parallel propagation along a dipole field line (Figure 1), and the other one (for an unducted chorus) with a more physical wave propagation in the dipole field. F or the latter case, ray tracing of many waves is used to reconstruct the spatial and temporal variation of electromagnetic field of chorus elements. Substantial differences in electron transport are found and signatures of electron precipitation pattern induced by the chorus waves are predicted.
Active experiments in space provide the opportunity to perturb the natural environment with known and controllable conditions. As such, active experiments are well-suited to studying wave-particle and wave-wave interactions. Active experiments were much more common in the 1970's and 1980's than they are today. Results from rockets, the Space Shuttle, and satellites provided important contributions to our understanding of both linear and non-linear plasma physics. New technologies provide new opportunities for using electron beams to probe the physics of the magnetosphere and, in particular, the radiation belts. In particular, newly-developed RF linear accelerator (linac) technologies can finally be adapted for space enabling much more powerful and flexible options for electron beam wave generation. Similarly, wave receivers, particle detectors, digital electronics, and high telemetry rates now allow detailed measurements of the artificially-generated waves and their effects on the local plasma environment. Specifically, full waveform capture of the 3D electric and magnetic fields allow detailed understanding of the properties of the waves including spectra, wave normal distributions, polarization, etc.
Here, we showcase an application of neural networks (NNs) to solve an inverse problem in electromagnetics. Wires are randomly distributed into an area of known dimensions. The wires are then illuminated with a monochromatic plane wave (PW) at a certain angle of incidence, and the electromagnetic (EM) field measured at a finite number of points along the perimeter of the area is then fed into a convolutional neural network (CNN) designed to predict either (i) the number of the wires or (ii) the location of the wires.
Whistler mode waves are a right-hand circularly polarized electromagnetic waves in the very low frequency (VLF) range, which can be excited and propagate in the region through the Earth's atmosphere to the magnetosphere. Typical examples of whistler mode waves include chorus, plasmaspheric hiss, lightning generated whistler (LGW), VLF waves ejected by ground transmitters. The whistler mode wave ca...
The Electron Losses and Fields Investigation (ELFIN) is a satellite mission 1 launched in 2018 consisting of two, identical 3U CubeSats in circular, polar LEO orbit at altitudes ~450 km. Onboard each spacecraft, the ELFIN prime payloads consist of energetic particle telescopes and boom-deployed fluxgate magnetometers. Each orbit, ELFIN observes energetic electrons ranging from 50 keV to 7 MeV precipitating from Earth's radiation belts, and ELFIN presents the opportunity to study such radiation belt losses in unprecedented energy resolution with multipoint observations that enable some disambiguation of spatiotemporal evolution. Furthermore, the ELFIN spacecraft are spinners, revealing for the first time details of electron pitch angle distributions within the atmospheric loss cones. In this talk, we will introduce the ELFIN mission and system and payloads. Next, we present new results from ELFIN highlighting several enlightening features of outer radiation belt precipitation, including: energy spectra of> 1 MeV precipitation events and microbursts; spatial structure and temporal evolution of precipitation bands; evidence of localized regions of enhanced precipitation, presumably from chorus wave activity just outside the plasmapause; quantification of steady “drizzle” of electrons into the atmospheric loss cones vs. enhanced, time-limited microbursts and precipitation bands; and quantification of atmospheric backscatter of precipitating electrons. All of these are new insights enabled by the unique observations made possible from the multipoint ELFIN mission.
The outer radiation belt is a highly dynamic region of the Earth's magnetosphere, with often-unpredictable variations in intensity and spatial extent. Characterization of this variable radiation environment is critical to mitigating spacecraft anomalies often caused by energetic particles. The physical processes controlling the acceleration and loss of trapped relativistic electrons in the radiation belts are complex and there are a number of competing processes that can combine to produce net enhancements or depletions of the belts. Precipitation into the atmosphere has been shown to be an important loss process for energetic particles in Earth's magnetosphere, but when, where, and how much precipitation contributes remain open questions. While radiation belt diffusion models can now reproduce observed acceleration events quite accurately, radiation belt depletion events are often less well-captured. Quantification of precipitation loss, as well as understanding of the physical mechanisms producing it, is thus critical to our understanding of the dynamics of the outer radiation belt.
This paper proposes a case study for estimating rain attenuation with rainfall data collected in Brasilia, Brazil at THz frequencies using Mie Theory and Drop Size Distribution. To address this goal, we used measured rainfall rate data for the past 18 years collected at the National Institute of Meteorology (INMET). A statistical approach that uses Monte Carlo simulation was applied to obtain a reasonable estimation of rainfall attenuation in the terahertz spectrum. To evaluate the accuracy of the method, we performed a comparison between the rain attenuation calculated by Mie Theory and ITU-R model. The estimation proposed in this work showed that the mean attenuation varies between 1.7 to 3.5 dB/km. For rain events higher than 10 mm/h, results showed that the mean attenuation varies between 8 to 18 dB/km.
Whistler mode waves in the Earth's inner magnetosphere playa key role in local energy transfer between particle populations and in larger scale processes such as scattering of trapped energetic electrons into the atmospheric loss cone. A body of recent research has focused on active experiments which generate whistler waves (e.g. via an antenna or accelerating an unstable electron beam) with the intent of influencing these processes. Accurately modeling how whistlers evolve on a global scale is an important step toward evaluating the impacts of these experimental efforts.
High energy resolution measurements of energetic (tens to hundreds of keV) electron fluxes in the Earth's inner radiation belt and slot region (below L ~ 3) have revealed the presence of drift-periodic structures named the “zebra stripes” [1].
A dual-band artificial metal grid dielectric resonator antenna (GDRA) operating at millimeter wave frequencies is presented. The embedded metal grids increase the effective permittivity of base dielectric composed of poly-methyl methacrylate (PMMA) and their I-shape allows for two unique modes. Simulation results demonstrate that the GDRA resonates at 28 and 38 GHz with 6.96 and 6.99 dBi gains, respectively. The GDRA can be tuned to operate as a lower single band, upper single band or as a dual-band antenna by adjusting the feed line dimension.
The recent years have seen a surge in interest in determining the dielectric constant of biological tissues in the microwave domain. The tissues can be classified and differentiated without radiation by using a microwave sensor. The atherosclerotic plaque of the carotid artery, which is now predominantly classified by ultrasonography and the CT scanner was not studied yet. Ultrasonography describes the level of echogenicity of the plaques, and proposes that as a representation of the plaque's composition. In this study, a microwave subwavelength resonator was employed to measure 20 carotid artery plaques and compare the results with ultrasound b-mode images. The results of the study show a correlation between the echogenicity levels and the dielectric constant of the tissues investigated. The way in which it will be evaluated in the future is how it compares to other radiological techniques.
Classical integral or integro-differential equations of the Pocklington and Hallen type, describing radiation and scattering of electromagnetic fields by thin, ideally conducting wires, are of significant practical interest and have been extensively studied. These equations follow from the boundary condition that requires a vanishing of the tangential component of the total electric field at the wire surface. The total electric field consists of both a known incident field and a scattered field that is due to a generally unknown current induced in the wire. The scattered electric field for a given point on the wire surface consists both of a “far” field at distant points significantly exceeding the wire's radius $a$, and by a “near” field due to arbitrarily nearby points. Expressions for the “near” field include a logarithmic singularity in the kernel of the associated Pocklington equation. This singularity is an important feature that makes the Pocklington equation solvable and well-posed. Thus, the Pocklington equation in its standard form can be considered as a Fredholm integral equation of the first kind with a singular kernel.
The plasmasphere is a vast torus shape region of the inner magnetosphere, filled with dense $\left(\sim 1-10^{6} \# / \text{cm}^{-3}\right)$ and cold (less than $10 \text{eV})$ ions and electrons. The outer boundary of the plasmasphere, called plasmapause, is a sharp plasma density boundary that separates closed and open drift paths for cold plasmas. Distinct plasmapause with sharp density variations are only 16% of the observed plasmapause and are preferred to occur at the post-midnight and dawnside than the duskside. Most of the plasmapause, however, is accompanied by significant density irregularities. These density irregularities are thought to play an important role in wave excitation and propagation, such as the excitation of the electromagnetic ion cyclotron (EMIC) waves and magnetosonic (MS) waves, and the propagation of EMIC wave and MS waves.
The Earth's radiation belts include electrons over a wide energy range. The dynamics of electrons can differ significantly, depending on the energy. In comparison to ~MeV energies, multi-MeV electrons are less predictable during geomagnetic storms [1], as their population can be depleted, enhanced, or remain unchanged, with nearly equal probability [2]. The depletion of electrons can be reversible (adiabatic) or irreversible, due to wave-particle interactions and loss at the outer boundary. Nonadiabatic changes can be identified by analyzing phase space density (PSD) as a function of the three adiabatic invariants. Fast-localized losses, such as interaction with electromagnetic ion cyclotron (EMIC) waves, can produce deepening PSD minima [3]. The EMIC waves are very effective in scattering multi-MeV electrons and can create sharp gradients in pitch angle distributions, although they do not resonate with nearly equatorial mirroring electrons. The depletion of electrons in a wide range of pitch angles occurs with assistance of the hiss and chorus waves [4]. However, the local minimum in PSD may be also observed due to outward radial diffusion with either subsequent refilling of the radiation belts or local acceleration. In this case, the formation of the minima will not result in continued deepening [5].
Bistatic scattering coefficients are computed for a site on a tree covered mountainside at L Band. The layer which consists of inclined trees is modeled by discrete scatterers consisting of trunks, branches, needles and leaves with varying orientations and dimensions. Due to the sloped nature of the terrain, azimuthal asymmetry occurs and this causes mixing of polarizations of the incident and scattered waves. The mean equation is solved to acquire the propagation constants inside the layer. Direct (volume) scattering is found to be the dominant scattering mechanism for the modeled layer at L band. Ground truth measurement data is used to simulate the attenuations. Further study shall be done to compare the bistatic scattering results with the ground truth measurements to be made in July 2021.
Electromagnetic ion cyclotron (EMIC) waves are transverse electromagnetic waves typically generated in the equatorial magnetosphere by anisotropic proton distributions. These waves can resonantly interact with multiple particle populations in the inner magnetosphere believed to be an important loss mechanism for both ring current ions and radiation belt electrons, as well as a cold plasma heating source. The spatiotemporal extent of wave activity is one of the key parameters used to quantify the effects of EMIC waves on magnetospheric plasma populations. However, from single-point spacecraft measurements or ground based observations alone, it is challenging to get the full picture of wave occurrence distributions. Due to a number of processes, ground and in situ observations of EMIC wave activity, specifically, its global occurrence, duration, and frequency often exhibit noticeable variations [1]. In particular, EMIC waves in the H+ frequency band are not always seen on the ground conjugately to locations of space observations [2]. In addition, ground and space EMIC wave distributions have different dependencies on local time, L shell, and geomagnetic activity, adding to the challenge of comparing measurements across these platforms [3]. Here we address this challenge by examining the relationship between EMIC wave occurrence and power on the Van Allen Probes and conjugate CARISMA ground magnetometer stations in the Canadian sector. We apply an automated wave detection algorithm to magnetometer data [4]. We present an analysis of long-term simultaneous EMIC wave observations in space and on the ground, and study wave propagation characteristics in the He+ and H+ frequency bands during different geomagnetic conditions.
High-energy electron populations within the Van Allen radiation belts are highly dynamic, and seen to increase and decrease on timescales as short as hours. One of the lingering questions about radiation belt dynamics overall is which types of plasma waves are responsible for the various changes we observe. Here, we present two studies that illuminate how ULF waves shape the boundaries and enhancements of relativistic electrons. One result, using seven years of Van Allen Probes satellite data, shows that ULF waves can create multi-MeV flux enhancements following geomagnetically active periods. Thus, ULF-driven radial diffusion can often be the dominant mechanism behind ultrarelativistic electron enhancements; although high populations of lower energies, likely produced by VLF interactions, are a necessary precondition. A second analysis, looking at decades of POES data, shows that relativistic breaches of the lower boundary of the outer belt happen in concert with elevated ULF wave power yet are not associated with particular type of solar driving. How relativistic electrons can cross this barrier and enter into the slot region and inner zone is crucial for understanding the radiation environment in this regime closest to Earth.
The NASA Artemis Program will further our understanding of Earth's moon by enabling human exploration of the lunar South Pole. This mission will require high-data-rate communications to minimize exposure of human and robotic explorers to extreme environmental effects. This requirement pushes the radio frequency higher than UHF, which would typically be used for robust surface-to-surface communications in a rugged terrain environment. To help with the design of such a communications system, the one-way propagation loss at 1.8 GHz is modeled at a candidate lunar South Pole landing site using two models: Tropospheric Electromagnetic Parabolic Equation Routine (TEMPER) and Remcom Inc.'s Wireless Insite (WI). Selenic LiDAR data of the lunar terrain is used in each model. Both models offer significant advantages over simple Line-of-Sight (LOS) coverage solutions. Each method has its advantages over the other. TEMPER captures shadowing and diffraction more accurately than WI, and WI captures scattering effects better than TEMPER. Merging the two results allows for a conservative estimate of performance, needed when designing a reliable and secure communications network on the lunar surface.
The purpose of this work is to clarify how the European Electromagnetic Compatibility Directive (EMC Directive 2014/30/EU) has been applied to a large scientific construction plant. A detailed protocol based on the Product Breakdown Structure of the installation has been devised and successfully applied to a case study: the large scale observatory based on an array of Cherenkov Telescopes.
Magnetorquers are an essential part of the Attitude Determination and Control Systems (ADCS) of space vehicles, especially cube satellites. In this paper, we compare the magnetic dipole moment, response time, weight and other important parameters of three different magnetorquers: the printed circuit board type, square loop and rod type. Hence, cube satellite designers can select their preferred design based on the available constraints.
