Trapped Electron Population Research Articles

Global gyrokinetic study of density gradient driven instability in tokamaks: the ubiquitous mode

The ubiquitous mode is investigated in the linear regime for the first time using a global gyrokinetic model. These modes are driven by the density gradient in trapped electron population but with mode frequency in the ion diamagnetic drift direction, in contrast to the conventional trapped electron mode. The dispersion relation is calculated along with the global mode structure. The ubiquitous mode is quite global although appears at a shorter wavelength ( 12ky2ρi2>1 ). We show that the main driving mechanism is the density gradient and the temperature gradient has only a modest effect; the mode can persist at higher temperature gradient scenarios making it another possible channel of anomalous transport. The magnetic shear reduces the growth of the mode; while the electron to ion temperature ratio has a nonmonotonic effect on the mode growth rate—growth rate increases initially for the ubiquitous branch of the mode and decreases afterwards as the conventional trapped electron mode starts dominating. The role of safety factor and toroidicity is also analyzed. Finally, a mixing length-based estimation of transport is presented.

Chorus wave power at the strong diffusion limit overcomes electron losses due to strong diffusion

Earth’s radiation belts consist of high-energy charged particles trapped by Earth’s magnetic field. Strong pitch angle diffusion of electrons caused by wave-particle interaction in Earth’s radiation belts has primarily been considered as a loss process, as trapped electrons are rapidly diffused into the loss cone and lost to the atmosphere. However, the wave power necessary to produce strong diffusion should also produce rapid energy diffusion, and has not been considered in this context. Here we provide evidence of strong diffusion using satellite data. We use two-dimensional Fokker-Planck simulations of electron diffusion in pitch angle and energy to show that scaling up chorus wave power to the strong diffusion limit produces rapid acceleration of electrons, sufficient to outweigh the losses due to strong diffusion. The rate of losses saturates at the strong diffusion limit, whilst the rate of acceleration does not. This leads to the surprising result of an increase, not a decrease in the trapped electron population during strong diffusion due to chorus waves as expected when treating strong diffusion as a loss process. Our results suggest there is a tipping point in chorus wave power between net loss and net acceleration that global radiation belt models need to capture to better forecast hazardous radiation levels that damage satellites.

Excited state lifetime of electron trapping centres in alkali feldspars

The development of the infrared photoluminescence (IRPL) signal enables the direct non-destructive probing of the trapped electron population in feldspars. Whilst IRPL offers new perspectives for luminescence dating, it also enables detailed, site-selective measurements of the dosimetric defects emitting IRPL at 880 nm (IRPL880) and 955 nm (IRPL955), allowing improved understanding of luminescence phenomena in feldspars.We perform time-resolved IRPL measurements to investigate the excited state lifetimes of IRPL880 and IRPL955 electron trapping centres in chemically and structurally different feldspars. We analyse the time-resolved off-time data with three exponentially decaying components. The contribution of the fast component (τ1) fitted to the IRPL880 data is minor and its lifetime is consistent with the switch off time of the 830 nm excitation laser. The two longer lifetimes (τ2 and τ3) dominate the IRPL880 and IRPL955 signals. The τ2 values range from 2 μs to 6 μs for IRPL880 and from 2 μs to 7 μs for IRPL955, whereas τ3 ranges from 7 μs to 25 μs for IRPL880 and from 8 μs to 22 μs for IRPL955, with an average cluster value of ∼20 μs. We observe a weak decreasing trend in τ3 lifetime with decreasing K-feldspar content. Systematic thermal depletion of the trapped electron population results in decreasing τ2 lifetimes with increasing preheat temperature, but a negligible change in τ3. We suggest that time-resolved-IRPL lifetimes not only reflect the exited state lifetime of the electron trapping centre, affected by excited-to-ground state transition as well as tunnelling, but also a direct recombination from the band-tail states. The long excited-state lifetime of the order of 20 ∼ μs (the average cluster value) allows for tunnelling induced recombination from the excited state, which is supported by the fact that reported lifetimes for time-resolved-IRSL (infra-red stimulated luminescence) are shorter than those of time-resolved-IRPL.

Cationic surface polarization centers on ionic carbon nitride for efficient solar-driven H2O2 production and pollutant abatement

Solar-driven H2O2 production and emerging organic pollutants (EOPs) elimination are of great significance from the perspective of environmental sustainability. The efficiency of the photocatalytic reaction system is the key challenge to be addressed. In this work, the strategy of constructing surface ionic local polarization centers to enhance the exciton dissociation of the polymeric photocatalytic is demonstrated. Selected bipyridinium cation (TMAP) is complexed on a K+-incorporated carbon nitride (CNK) framework, and the combination of local polarization centers both on the surface (bipyridinium cation) and bulk (K+ cation) contributes to a superior photocatalytic H2O2 production performance, affording a remarkable H2O2 generation rate of 46.8 µmol h−1 mg−1 and a high apparent quantum yield (AQY) value of 77.5% under irradiation of 405 nm photons. As substantiated experimentally by steady state/transient spectroscopy techniques, the surface local polarization centers increase the population of the long-lived trapped electrons, and thereby promote the interfacial charge transfer process for chemical conversion reaction. The strategy is potentially applicable to the design of a wide range of efficient solar-to-chemical conversion systems.

Different Behaviors of Outer Radiation Belt keV and MeV Electrons During Two Sequential Geomagnetic Storms

AbstractElectron flux dropout is an extraordinary phenomenon in the outer radiation belt, which is characterized by a drastic depletion in trapped electron populations over a broad range of energies, pitch angles, and L‐shells. Using data from multiple satellites, we study a 5‐day dropout of MeV electrons and a several‐hour dropout of keV electrons in geostationary Earth orbit (GEO) during two sequential geomagnetic storms. Outward radial diffusion caused real loss of MeV electrons, while asymmetric and depressed magnetic fields led to adiabatic variations in keV electron fluxes. In addition to time scale differences, low‐energy keV, medium‐energy keV and high‐energy MeV electron fluxes behaved differently, involving an increasing trend, an initial decreasing trend followed by an increasing trend, and a decreasing trend, respectively, as observed by Radiation Belt Storm Probes (RBSPs) and low‐altitude satellites during the first storm. Substorm injections accompanied by inward radial diffusion initially produced an enhanced flux of electrons with energies up to ∼100 keV. Chorus waves generated in morning side of magnetosphere were responsible for scattering part of this seed population into the atmosphere. In turn, these enhanced but short‐lived chorus waves accelerated lower‐energy keV electrons to achieve a moderate energy level of hundreds of keV within one day. Additionally, the initial slow outward radial diffusion was associated with MeV electron loss, and there was insufficient time for acceleration by chorus waves, so only MeV electrons could maintain long‐term dropout. Competition between energy‐ and L‐shell‐dependent acceleration and loss mechanisms caused different keV and MeV electron behaviors.

Charge Carrier Dynamics in Colloidally Synthesized Monolayer MoX2 Nanosheets

Transition metal dichalcogenides (TMDs) are nanostructured semiconductors with prospects in optoelectronics and photocatalysis. Several bottom-up procedures to synthesize such materials have been developed yielding colloidal transition metal dichalcogenides (c-TMDs). Where such methods initially yielded multilayered sheets with indirect band gaps, recently, also the formation of monolayered c-TMDs became possible. Despite these advances, no clear picture on the charge carrier dynamics in monolayer c-TMDs exists to date. Here, we show through broadband and multiresonant pump-probe spectroscopy, that the carrier dynamics in monolayer c-TMDs are dominated by a fast electron trapping mechanism, universal to both MoS2 and MoSe2, contrasting hole-dominated trapping in their multilayered counterparts. Through a detailed hyperspectral fitting procedure, sizable exciton red shifts are found and assigned to static shifts originating from both interactions with the trapped electron population and lattice heating. Our results pave the way to optimizing monolayer c-TMDs via passivation of predominantly the electron-trap sites.

ORFEES – a radio spectrograph for the study of solar radio bursts and space weather applications

Radio bursts are sensitive tracers of non-thermal electron populations in the solar corona. They are produced by electron beams and shock waves propagating through the corona and the heliosphere, and by trapped electron populations in coronal mass ejections (CMEs) and in quiescent active regions. Combining space-borne and ground-based radio spectrographs allows one to track disturbances between the low corona, near or at the sites of particle acceleration, and the spacecraft. Radio observations are, therefore, a significant tool in probing the solar origin of heliospheric disturbances, which is a central research topic as witnessed by the Parker Solar Probe and Solar Orbiter missions. The full scientific return of these projects needs vigorous ground-based support, which at radio wavelengths covers altitudes up to about a solar radius above the photosphere. Besides research in solar and heliospheric physics, monitoring solar radio bursts also supports space weather services. On occasion, radio bursts can themselves be a space weather hazard. The Nançay radio astronomy station in central France has a long tradition of monitoring radio emission at decimetre-to-meter wavelengths. This article describes the radio spectrograph ORFEES (Observations Radiospectrographiques pour FEDOME et l’Etude des Eruptions Solaires). It observes the whole-Sun flux density between 144 and 1004 MHz, pertaining to regions between the low corona and about half a solar radius above the photosphere. ORFEES results from a partnership between Observatoire de Paris and the French Air Force, which operates the experimental space weather service FEDOME. The primary use of the instrument at the Paris Observatory is astrophysical observation. Low-resolution data with rapid availability are presently produced for the French Air Force. Similar information can be made available to a broader range of space weather service providers. This article gives an overview of the instrument design and access to the data and shows a few illustrative observations.

How whistler mode hiss waves and the plasmasphere drive the quiet decay of radiation belts electrons following a geomagnetic storm

We show how an extended period of quiet solar wind conditions contributes to a quiet state of the plasmasphere that expands up to L ∼ 5.5, which creates the perfect conditions for wave-particle interactions between the radiation belt electrons and whistler-mode hiss waves. The correlation between the hiss waves and the plasma density is direct with hiss wave power increasing with plasma density, while it was generally assumed that these quantities can be specified independently. Whistler-mode hiss waves pitch angle diffuse and ultimately scatter freshly injected electrons into the atmosphere until the slot region is formed between the inner and outer belt and the outer belt is drastically reduced. In this study, we use and combine Van Allen Probes observations and Fokker-Planck numerical simulations. The Fokker-Planck model uses consistent event-driven pitch angle diffusion coefficients from whistler-mode hiss waves. Observations and simulations allow us to reach a global understanding of the variations in the trapped electron population with time, space, energy, and pitch angle that is based on the existing theory of quasi-linear wave-particle interactions. We show, for instance, the outer belt is pitch-angle homogeneous, which is explained by the event-driven diffusion coefficients that are roughly constant for equatorial pitch angle α 0∼<60°, E>100 keV, 3.5<L<Lpp∼6. The impact of this work is to bring an improved understanding of the belt evolution based on the integration of high quality and highly temporally and spatially resolved measurements that are integrated in modern computations. We also propose the event-driven method as an accurate method (within ×2) to predict the electron flux decay after storms.

Magnetic Field Variations and Dynamics of the Outer Electron Radiation Belt of the Earth’s Magnetosphere in February 2014

The paper presents the results of a comparative analysis of the dynamics of relativistic electron fluxes of the Earth’s outer radiation belt and correspondent ring current and magnetospheric magnetic field variations for February 15–22, 2014, based on experimental data obtained in the radiation belt core aboard Van Allen Probes satellites and in geostationary orbit aboard the GOES-15 satellite. The A2000 paraboloid model of the magnetosphere is used to calculate the contributions of main magnetospheric current systems to the Dst variation. The influence of external factors—solar wind and interplanetary magnetic field—is considered. Comparison of the dynamics of electron fluxes in different orbits and the geomagnetic field variations for February 15‒22, 2014 indicate that the main mechanisms of the evolution of outer electron radiation belt are global processes: (i) outward and inward shifts of the trapped electron population inside the Earth’s magnetosphere due to large-scale variations of the magnetospheric magnetic field during geomagnetic disturbances and (ii) ExB drift of electrons from the magnetotail under the influence of electric and magnetic fields. Local particle acceleration is auxiliary process in the dynamics of radiation belts. The southward orientation of the interplanetary magnetic field is the necessary condition for an increase in the intensity of electron fluxes of the Earth’s outer radiation belt, while the function (–BzVsw) is the key external factor.

The Storm Time Development of Source Electrons and Chorus Wave Activity During CME‐ and CIR‐Driven Storms

AbstractWhistler mode chorus waves influence the dynamics of the Earth's radiation belts and the inner magnetosphere through gyroresonant wave particle interactions. Chorus waves are generated by anisotropic hot electrons from a few to tens of keV, called source electrons, which have increased access from the nightside plasma sheet to the inner magnetosphere during geomagnetic storms. The primary drivers of geomagnetic storms are coronal mass ejections (CMEs) and corotating interaction regions (CIRs). Through differences in their characteristic physical parameters, they can each impact the nightside plasma sheet differently. Using Van Allen Probes observations, we have conducted a superposed epoch analysis of chorus wave activity and source electron development across all local times between L = 2–6 during 25 CME‐ and 35 CIR‐driven storms. The superposed epoch analysis shows that chorus wave power follows the storm phase‐dependent access of the source electron population. Chorus waves and source electrons are observed on the dawnside during the main phase, when open drift path access via eastward convective drift from the plasma sheet is enhanced. During the recovery phase, chorus waves and source electrons are observed at all magnetic local times with low intensities, exemplifying the formation of a weak symmetric, trapped electron population. A linear theory approximation for wave growth from source electron observations shows that increased wave growth follows the enhanced source electrons during each storm phase. CME and CIR storms display similar behavior and levels of average wave power; however, chorus wave activity reaches lower L‐shells during CME storms on average.

Optical dating in a new light: A direct, non-destructive probe of trapped electrons

Optical dating has revolutionized our understanding of Global climate change, Earth surface processes, and human evolution and dispersal over the last ~500 ka. Optical dating is based on an anti-Stokes photon emission generated by electron-hole recombination within quartz or feldspar; it relies, by default, on destructive read-out of the stored chronometric information. We present here a fundamentally new method of optical read-out of the trapped electron population in feldspar. The new signal termed as Infra-Red Photo-Luminescence (IRPL) is a Stokes emission (~1.30 eV) derived from NIR excitation (~1.40 eV) on samples previously exposed to ionizing radiation. Low temperature (7–295 K) spectroscopic and time-resolved investigations suggest that IRPL is generated from excited-to-ground state relaxation within the principal (dosimetry) trap. Since IRPL can be induced even in traps remote from recombination centers, it is likely to contain a stable (non-fading), steady-state component. While IRPL is a powerful tool to understand details of the electron-trapping center, it provides a novel, alternative approach to trapped-charge dating based on direct, non-destructive probing of chronometric information. The possibility of repeated readout of IRPL from individual traps will open opportunities for dating at sub-micron spatial resolution, thus, marking a step change in the optical dating technology.

Trapped Electrons at the Amorphous Solid Water/Vacuum Interface as Possible Reactants in a Water Splitting Reaction

The dynamics and energetics of electrons in water impacts diverse fields, from electrochemistry to astrochemistry. In the present experiments, long-lived, low-energy, electronic states are observed at the amorphous solid water (ASW)/vacuum interface with decay times on the order of seconds, orders of magnitude longer than solvated electron states observed in the ASW bulk. The formation, relaxation, and reactivity of these trapped electrons were investigated using two-photon photoemission of >15 bilayers of amorphous D2O adsorbed on the Cu(111) surface. The decay time of the trapped electron signal is approximately 16 s. This extraordinarily long lifetime allows for a reaction between trapped electrons and the ASW surface, producing hydroxide anions and molecular hydrogen at the interface. This reaction is observed by a decrease of the trapped electron population and a concomitant increase of the work function during ultraviolet light exposure. The low-energy electron reactivity at the ASW/vacuum interface...

Simulation study of overtaking of ion-acoustic solitons in the fully kinetic regime

The overtaking collisions of ion-acoustic solitons in the presence of trapping effects of electrons are studied based on a fully kinetic simulation approach. The method is able to provide all the kinetic details of the process alongside the fluid-level quantities self consistently. Solitons are produced naturally by utilizing the chain formation phenomenon, and then are arranged in a new simulation box to test the different scenarios of overtaking collisions. Three achievements are reported here. First, simulations prove the long-time life span of the ion-acoustic solitons in the presence of trapping effect of electrons (kinetic effects), which serves as the benchmark of the simulation code. Second, their stability against overtaking mutual collisions is established by creating collisions between solitons with different number and shapes of trapped electrons, i.e., different trapping parameter. Finally, details of solitons during collisions for both ions and electrons are provided on both fluid and kinetic levels. These results show that on the kinetic level, trapped electron population accompanying each of the solitons are exchanged between the solitons during the collision. Furthermore, the behavior of electron holes accompanying solitons contradicts the theory about the electron holes interaction developed based on kinetic theory. They also show behaviors much different from other electron holes witnessed in processes such as nonlinear Landau damping (Bernstein-Greene-Kruskal -BGK- modes) or beam-plasma interaction (like two-beam instability).

Electron holes in the outer radiation belt: Characteristics and their role in electron energization

AbstractVan Allen Probes have detected electron holes (EHs) around injection fronts in the outer radiation belt. Presumably generated near equator, EHs propagate to higher latitudes potentially resulting in energization of electrons trapped within EHs. This process has been recently shown to provide electrons with energies up to several tens of keV and requires EH propagation up to rather high latitudes. We have analyzed more than 100 EHs observed around a particular injection to determine their kinetic structure and potential energy sources supporting the energization of trapped electrons. EHs propagate with velocities from 1000 to 20,000 km/s (a few times larger than the thermal velocity of the coldest background electron population). The parallel scale of observed EHs is from 0.3 to 3 km that is of the order of hundred Debye lengths. The perpendicular to parallel scale ratio is larger than one in a qualitative agreement with the theoretical scaling relation. The amplitudes of EH electrostatic potentials are generally below 100 V. We determine the properties of the electron population trapped within EHs by making use of the Bernstein‐Green‐Kruskal analysis and via analysis of EH magnetic field signatures. The density of the trapped electron population is on average 20% of the background electron density. The perpendicular temperature of the trapped population is on average 300 eV and is larger for faster EHs. We show that energy losses of untrapped electrons scattered by EHs in the inhomogeneous background magnetic field may balance the energization of trapped electrons.

Ion gyroradius effects on particle trapping in kinetic Alfvén waves along auroral field lines

AbstractIn this study, a 2‐D self‐consistent hybrid gyrofluid‐kinetic electron model is used to investigate Alfvén wave propagation along dipolar magnetic field lines for a range of ion to electron temperature ratios. The focus of the investigation is on understanding the role of these effects on electron trapping in kinetic Alfvén waves sourced in the plasma sheet and the role of this trapping in contributing to the overall electron energization at the ionosphere. This work also builds on our previous effort by considering a similar system in the limit of fixed initial parallel current, rather than fixed initial perpendicular electric field. It is found that the effects of particle trapping are strongest in the cold ion limit and the kinetic Alfvén wave is able to carry trapped electrons a large distance along the field line yielding a relatively large net energization of the trapped electron population as the phase speed of the wave is increased. However, as the ion temperature is increased, the ability of the kinetic Alfvén wave to carry and energize trapped electrons is reduced by more significant wave energy dispersion perpendicular to the ambient magnetic field which reduces the amplitude of the wave. This reduction of wave amplitude in turn reduces both the parallel current and the extent of the high‐energy tails evident in the energized electron populations at the ionospheric boundary (which may serve to explain the limited extent of the broadband electron energization seen in observations). Even in the cold ion limit, trapping effects in kinetic Alfvén waves lead to only modest electron energization for the parameters considered (on the order of tens of eV) and the primary energization of electrons to keV levels coincides with the arrival of the wave at the ionospheric boundary.

A new ionospheric electron precipitation module coupled with RAM‐SCB within the geospace general circulation model

AbstractElectron precipitation down to the atmosphere due to wave‐particle scattering in the magnetosphere contributes significantly to the auroral ionospheric conductivity. In order to obtain the auroral conductivity in global MHD models that are incapable of capturing kinetic physics in the magnetosphere, MHD parameters are often used to estimate electron precipitation flux for the conductivity calculation. Such an MHD approach, however, lacks self‐consistency in representing the magnetosphere‐ionosphere coupling processes. In this study we improve the coupling processes in global models with a more physical method. We calculate the physics‐based electron precipitation from the ring current and map it to the ionospheric altitude for solving the ionospheric electrodynamics. In particular, we use the BATS‐R‐US (Block Adaptive Tree Scheme‐Roe type‐Upstream) MHD model coupled with the kinetic ring current model RAM‐SCB (Ring current‐Atmosphere interaction Model with Self‐Consistent Magnetic field (B)) that solves pitch angle‐dependent electron distribution functions, to study the global circulation dynamics during the 25–26 January 2013 storm event. Since the electron precipitation loss is mostly governed by wave‐particle resonant scattering in the magnetosphere, we further investigate two loss methods of specifying electron precipitation loss associated with wave‐particle interactions: (1) using pitch angle diffusion coefficients Dαα(E,α) determined from the quasi‐linear theory, with wave spectral and plasma density obtained from statistical observations (named as “diffusion coefficient method”) and (2) using electron lifetimes τ(E) independent on pitch angles inferred from the above diffusion coefficients (named as “lifetime method”). We found that both loss methods demonstrate similar temporal evolution of the trapped ring current electrons, indicating that the impact of using different kinds of loss rates is small on the trapped electron population. However, for the precipitated electrons, the lifetime method hardly captures any precipitation in the large L shell (i.e., 4 &lt; L &lt; 6.5) region, while the diffusion coefficient method produces much better agreement with NOAA/POES measurements, including the spatial distribution and temporal evolution of electron precipitation in the region from the premidnight through the dawn to the dayside. Further comparisons of the precipitation energy flux to DMSP observations indicates that the new physics‐based precipitation approach using diffusion coefficients for the ring current electron loss can explain the diffuse electron precipitation in the dawn sector, such as the enhanced precipitation flux at auroral latitudes and flux drop near the subauroral latitudes, but the traditional MHD approach largely overestimates the precipitation flux at lower latitudes.

MESSENGER observations of solar energetic electrons within Mercury's magnetosphere

AbstractDuring solar energetic particle (SEP) events, the inner heliosphere is bathed in MeV electrons. Through magnetic reconnection, these relativistic electrons can enter the magnetosphere of Mercury, nearly instantaneously filling the regions of open field lines with precipitating particles. With energies sufficient to penetrate solid aluminum shielding more than 1 mm thick, these electrons were observable by a number of sensors on the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft. Because of its thin shielding, frequent sampling, and continuous temporal coverage, the Fast Imaging Plasma Spectrometer provided by far the most sensitive measurements of MeV electrons of all MESSENGER sensors. Sharp changes in energetic electron flux coincided with topological boundaries in the magnetosphere, including the magnetopause, polar cap, and central plasma sheet. Precipitating electrons with fluxes equal to ~40% of their corresponding upstream levels were measured over the entire polar cap, demonstrating that electron space weathering of Mercury's surface is not limited to the cusp region. We use these distinct precipitation signatures acquired over 33 orbits during 11 SEP events to map the full extent of Mercury's northern polar cap. We confirm a highly asymmetric polar cap, for which the dayside and nightside boundary latitudes range over ~50–70°N and ~30–60°N, respectively. These latitudinal ranges are consistent with average models of Mercury's magnetic field but exhibit a large variability indicative of active dayside and nightside magnetic reconnection processes. Finally, we observed enhanced electron fluxes within the central plasma sheet. Although these particles cannot form a stable ring current around the planet, their motion results in an apparent trapped electron population at low latitudes in the magnetotail.

Electron vortex magnetic holes: A nonlinear coherent plasma structure

We report the properties of a novel type of sub-proton scale magnetic hole found in two dimensional particle-in-cell simulations of decaying turbulence with a guide field. The simulations were performed with a realistic value for ion to electron mass ratio. These structures, electron vortex magnetic holes (EVMHs), have circular cross-section. The magnetic field depression is associated with a diamagnetic azimuthal current provided by a population of trapped electrons in petal-like orbits. The trapped electron population provides a mean azimuthal velocity and since trapping preferentially selects high pitch angles, a perpendicular temperature anisotropy. The structures arise out of initial perturbations in the course of the turbulent evolution of the plasma, and are stable over at least 100 electron gyroperiods. We have verified the model for the EVMH by carrying out test particle and PIC simulations of isolated structures in a uniform plasma. It is found that (quasi-)stable structures can be formed provided that there is some initial perpendicular temperature anisotropy at the structure location. The properties of these structures (scale size, trapped population, etc.) are able to explain the observed properties of magnetic holes in the terrestrial plasma sheet. EVMHs may also contribute to turbulence properties, such as intermittency, at short scale lengths in other astrophysical plasmas.

Enhanced loss of magnetic-mirror-trapped fast electrons by a shear Alfvén wave

Laboratory observations of enhanced loss of magnetic mirror trapped fast electrons irradiated by a shear Alfvén Wave (SAW) are reported. The experiment is performed in the quiescent after-glow plasma in the Large Plasma Device [Gekelman et al., Rev. Sci. Instrum. 62(12), 2875–2883 (1991)]. A trapped energetic electron population (&amp;gt;100 keV) is generated in a magnetic mirror section (mirror ratio ≈ 2, length = 3.5 m) by an X-mode high power microwave pulse, and forms a hot electron ring due to the grad-B and curvature drift. SAWs of arbitrary polarization are launched externally by a Rotating Magnetic Field source (δB/B0 ≈ 0.1%, λ∥ ≈ 9 m). Irradiated by a right-handed circularly polarized SAW, the loss of electrons, in both the radial and the axial direction of the mirror field, is significantly enhanced and is modulated at fAlfvén. The periodical loss continues even after the termination of the SAW. Experimental observations suggest that a spatial distortion of the ring is formed in the SAW field and creates a collective mode of the hot electron population that degrades its confinement and leads to electron loss from the magnetic mirror. The results could have implications on techniques of radiation belt remediation.

Nascap-2k Self-Consistent Simulations of a VLF Plasma Antenna

We simulate the plasma response through tens of cycles of the Demonstration and Science Experiments (DSX) kilovolt near-square-wave very low frequency (VLF) (0.1-50 kHz) antenna in Medium Earth Orbit plasma with Nascap-2k. DSX is an Air Force Research Laboratory experiment that will explore the physics of electromagnetic wave injection from space transmitters, wave propagation, and wave-particle interactions in the magnetosphere. DSX will transmit and receive VLF waves and quantify their effect on the trapped electron populations in the magnetosphere. In these preflight calculations, the plasma is modeled with a hybrid particle-in-cell (PIC) approach with PIC ions and fluid barometric electron densities. The plasma response, collected ion currents, and chassis floating potential are computed self-consistently with a near-square-wave bias applied to the antennas. Particle injection and splitting are used to replenish the plasma depleted at the boundary, represent the thermal distribution, and maintain appropriately sized macroparticles. Therefore, limitation of current due to the thermal distribution of ions and the resulting angular momentum barrier is included. Above the ion plasma frequency, the plasma current lags the voltage by about 10, while below the ion plasma frequency, the current leads the voltage by about 7 . The volume ion current shows periodic launch of blocks of energetic ions radially outward.