Electron Density In Region Research Articles

A simple model of solenoidal inductively coupled plasma sources considering finite size

This paper proposes an updated transformer model for solenoidal inductively coupled plasma sources that can be applied even in low electron density regions. The proposed model can handle plasma in a finite geometry where the electric fields propagating from each boundary overlap, employing a simple analytic expression of the electric field, a one-dimensional (1D) sine hyperbolic function. Based on this field expression, all circuit elements of the transformer model that depend on the electron density, namely, plasma resistance, magnetic inductance, and mutual inductance, can now be obtained. Comparison of absorbed power as well as the circuit elements calculated using the proposed model, named here as the 1D transformer model, shows good agreement with the electromagnetic model, which is known for being quite accurate for cold plasma not only in high but also in low electron density regions. Results also indicate that the 1D transformer model is not limited to a specific setup but rather can be applied in a wide range of discharge conditions.

Stimulated Brillouin scattering of backward stimulated Raman scattering

The rescattering of backward stimulated Raman scattering (BSRS) by stimulated Brillouin scattering (SBS) is found in the high electron density region by relativistic Vlasov-Maxwell simulation and particle-in-cell (PIC) simulation, where the BSRS is in the regime of absolute instability and dominates in all the scatterings. Both one dimension (1D) Vlasov simulation and two dimension (2D) PIC simulation have been given to verify that there exists SBS of BSRS in the regime of absolute instability for BSRS. The SBS of BSRS will be even stronger than forward stimulated Raman scattering (FSRS) and SBS in regime of absolute instability for BSRS. Thus, besides Langmuir decay instability and laser energy absorption, the SBS of BSRS is also an important saturation mechanism of BSRS in high electron density region.

Experimental response of the divertor particle flux to internal transport barrier dynamics in EAST high-βN discharges

Experiments in EAST have concentrated on studying the internal transport barrier (ITB) regime in high normalized beta () discharges, where the study of the compatibility between ITB dynamics and divertor plasmas is an important step for future steady-state and high-performance plasma operations. In this work, the characteristics of the divertor particle flux and their responses to ITB dynamics have been studied in high- discharges. In order to describe the characteristics, the ITB duration is divided into two phases: phase I (i.e. ITB formation) and phase II (i.e. ITB degradation), according to the variation of plasma stored energy. In phase I, the particle flux near the inner strike point (SP) is continuously enhanced during the inter-edge-localized mode (ELM) phase in both the lower single-null and upper single-null configurations. The total particle flux in the scrape-off layer (SOL) region reveals a similar trend with an increase of the flux near the SP. However, in the private flux region (PFR) the total particle flux shows a reduction. Meanwhile, a movement of the SP away from the divertor corner is also observed during the ITB formation. In phase II, the particle flux near the inner SP, the total particle flux in the inner SOL and PFR region recover to their initial level before ITB formation, respectively. Additionally, the particle decay length is obviously reduced in phase I and then gradually enhanced in phase II. The continuous variation of the particle flux at the inner divertor target is in accordance with a compression of the magnetic flux surfaces due to ITB formation, which increases the gradient of electron density in the edge region. It is indicative that the ITB has a feasible impact on the behavior of divertor plasmas by means of increasing the Shafranov shift during the inter-ELM phase.

Assimilating VLF Transmitter Observations With an LETKF for Spatial Estimates of the ${D}$ -Region Ionosphere

The ${D}$ -region ionosphere plays an important role in coupling the neutral atmosphere to denser ionospheric plasma above. Practically, it impacts long-range radio communications between extremely low frequencies (ELFs), where communications are enabled by the layer, and high frequencies (HFs), which are attenuated by the layer. A combination of its altitude and extremely low electron density means that it is difficult to make measurements of the region using typical ionospheric remote sensing techniques, and our knowledge of the ${D}$ -region is limited as a result. This article presents the development of an ensemble Kalman filter method to spatially map ${D}$ -region electron density profiles over the continental United States using an array of very low frequency (VLF) radio transmitters and receivers. Data assimilation has previously been used to estimate higher altitude regions of the ionosphere, but its application to VLF radio measurements and the ${D}$ -region is new. The technique has several favorable features, including statistical confidence measures with every estimate, the ability to localize the influence of measurements, inclusion of physically realistic spatial correlations, relatively fast convergence, and the ability to add observations to the estimate as they become available. We describe the filter and present results for day, night, and terminator ionospheres using simulated data. We also present a study on the robustness of the filter when initialized with a prior that is far from the true ionosphere. The method shows promise for application to real data in the near future, especially for estimating the characteristics of large-scale features in the ${D}$ -region.

Effects of cathode operating parameters on the ignition voltage threshold of Hall thrusters

Changing the operating parameters of a cathode affects the ignition process of a Hall thruster mainly by changing the micro-plasma parameters emitted by the cathode at the moment of ignition. However, the micro-plasma parameter that dominates this effect is not clear. Therefore, the ignition voltage thresholds with different cathode operating parameters were first measured. Then, to better understand how these operating parameters affect the ignition voltage threshold of a Hall thruster, the two-dimensional distribution characteristics of the electron density, electron temperature, and plasma potential in the cathode plume region were measured using a Langmuir probe. The results showed that increasing both the keeper current and mass flow rate of the cathode causes an increase in the electron density emitted by the cathode and a decrease in the electron temperature. It was also found that increasing the cathode mass flow rate has a more pronounced effect than increasing the keeper current. Furthermore, when both the mass flow rate and keeper current of the hollow cathode are increased, the ignition voltage threshold of the Hall thruster decreases significantly. This is mainly because of a significant increase in the electron density resulting from the increases in the mass flow rate and keeper current.

On the determination of stopping cross-sections in ion scattering in solids and deviations from standard models

When atomic particles traverse solids they suffer energy losses due to elastic scattering from nuclei and excitation of electron–hole pairs. These are referred to as nuclear and electronic stoppings respectively. In this paper we discuss methods of determining energy losses and ‘stopping’ cross-sections in ion transmission through thin films, as well as in large angle and grazing backscattering from surfaces. This is done on the basis of deterministic simulations of ion scattering by following ion trajectories as they pass through the solid and sample regions of different electron densities depending on the distance from atomic nuclei. The ab initio calculated electron densities in the crystal are used to determine the stopping power, as predicted by the free electron gas model, and including a threshold value for d electron excitation. We discuss some aspects that are not included in standard descriptions based on the use of free electron models and averaged effective electron densities. In this context, we point out the possibility of inelastic processes involving inner-shell excitations, and briefly summarise main findings.

Probing the location of the unpaired electron in spin-orbit changing collisions of NO with Ar.

Understanding the molecular forces that drive a reaction or scattering process lies at the heart of molecular dynamics. Here, we present a combined experimental and theoretical study of the spin-orbit changing scattering dynamics of oriented NO molecules with Ar atoms. Using our crossed molecular beam apparatus, we have recorded velocity-map ion images and extracted differential and integral cross sections of the scattering process in the side-on geometry. We observe an overall preference for collisions close to the N atom in the spin-orbit changing manifold, which is a direct consequence of the location of the unpaired electron on the potential energy surface. In addition, a prominent forward scattered feature is observed for intermediate, even rotational transitions when the atom approaches the molecule from the O-end. The appearance of this peak originates from an attractive well on the A' potential energy surface, which efficiently directs high impact parameter trajectories towards the region of high unpaired electron density near the N-end of the molecule. The ability to orient molecules prior to collision, both experimentally and theoretically, allows us to sample different regions of the potential energy surface(s) and unveil the associated collision pathways.

VLF Remote Sensing of the D Region Ionosphere Using Neural Networks

AbstractNarrowband very low frequency (VLF) remote sensing has proven to be a useful tool for characterizing the ionosphere's D region (60‐ to 90‐km altitude) electron density. This work expands upon single transmitter‐receiver pair electron density profile inference methods to create a more generalized narrowband VLF remote sensing method that concurrently resolves a two‐parameter electron density profile for an arbitrary number of transmitter‐receiver pairs. A target function is constructed to take in a single time step of narrowband amplitude and phase observations from an arbitrary number of transmitter and receiver combinations and return the inferred average waveguide parameters along all paths. The target function is approximated using an artificial neural network (ANN). Synthetic training data are generated using the U.S. Navy's Long‐Wavelength Propagation Capability program, which is then used to train the ANN. Performance of the ANN with real‐world data is measured in two ways. First, ANN inferred average waveguide parameters are compared to a variety of previously published narrowband VLF remote sensing experiments. Second, ANN inferred average waveguide parameters are used in Long‐Wavelength Propagation Capability to predict narrowband VLF amplitude and carrier phase at a receiver that was withheld when performing the average waveguide parameter inference. Results show the approximated target function performs well in capturing temporal and spatial characteristics of the D region.

Research on small-scale structures of ice particle density and electron density in the mesopause region

Abstract. The formation of ice particle density irregularities with a meter scale in the mesopause region is explored in this paper by developing a growth and motion model of ice particles based on the motion equation of a variable mass object. The growth of particles by water vapor adsorption and the action of gravity and the neutral drag force on particles are considered in the model. The evolution of the radius, velocity, and number density of ice particles is then investigated by solving the growth and motion model numerically. For certain nucleus radii, it is found that the velocity of particles can be reversed at a particular height, leading to a local gathering of particles near the boundary layer, which then forms small-scale ice particle density structures. The spatial scale of the density structures can be affected by vertical wind speed, water vapor density, and altitude, and it remains stable as long as these environmental parameters do not change. The influence of the stable small-scale structures on electron and ion density is further calculated by a charging model, which considers the production, loss, and transport of electrons and ions, along with dynamic particle charging processes. Results show that the electron density is anti-correlated to the charged ice particle density and ion density for particles with radii of 11 nm or less due to plasma attachment by particles and plasma diffusion. This finding is in accordance with most rocket observations. The small-scale electron density structures created by small-scale ice particle density irregularities can produce the polar mesosphere summer echo (PMSE) phenomenon.

Long‐Lasting Latitudinal Four‐Peak Structure in the Nighttime Ionosphere Observed by the Swarm Constellation

AbstractIn this study, we provide for the first time observation of the latitudinal four‐peak structure of F region electron density in the nightside ionosphere. The special configuration of Swarm satellites, Swarm B having the chance to resample the regions of Swarm A/C with successively increasing time differences, provides an unprecedented opportunity to check the evolution of these nightside electron density peaks. Overall, the latitudinal four‐peak structures have very low occurrence rates, only 4% of the Swarm orbits. The two mid‐latitude peaks prefer to appear close to ±40° magnetic latitude, while the two low‐latitude peaks appear within ±20° magnetic latitude. Such latitudinal four‐peak structures can persist throughout the night until sunrise hours. No clear seasonal dependence is found for the two mid‐latitude peaks, while the two low‐latitude peaks are almost symmetric about the magnetic equator during equinoxes but are located at slightly higher latitudes in the summer hemisphere around solstices. The two low‐latitude peaks at late‐night hours are believed not to be remnants of the dusk‐side equatorial ionization anomaly (EIA) crests, as (a) example shows that Swarm A/C observe the development of shoulders at the flanks of the two EIA crests after sunset hours, and the shoulders become peaks 3 h later when Swarm B resamples the same region; (b) statistic results reveal that the two low‐latitude peaks during post‐midnight hours do not propagate towards the magnetic equator, as expected for EIA crests, but move slowly poleward. We suggest that the enhanced meridional wind at postmidnight hours is one possible driver for causing such latitudinal four‐peak structure of F region electron density. In addition, the simultaneous magnetic measurements from Swarm satellites are also analyzed, but they show no obvious diamagnetic effect that could help to maintain pressure balance within these electron density peaks.

Search for Helices of Atomic Electron Density As a Structural Basis of Optical Activity in α-TeO2 Crystal

An X-ray diffraction study of the atomic structure of paratellurite (α-TeO2) crystal in the temperature range of 86–500 K has been performed. Regions of atomic electron density, shaped as helices with axes oriented parallel and perpendicular to the optical axis, are selected; these regions are found to be the structural basis of the optical activity of crystal. All helices turned out to be right-handed. The values of optical rotation in the directions parallel and perpendicular to the optical axis have been calculated using structural data. These values have identical signs, as was suggested proceeding from the identical twist of electron density helices.

The FRB 121102 Host Is Atypical among Nearby Fast Radio Bursts

Abstract We search for host galaxy candidates of nearby fast radio bursts (FRBs), FRB 180729.J1316+55, FRB 171020, FRB 171213, FRB 180810.J1159+83, and FRB 180814.J0422+73 (the second repeating FRB). We compare the absolute magnitudes and the expected host dispersion measure DMhost of these candidates with that of the first repeating FRB, FRB 121102, as well as those of long gamma-ray bursts (LGRBs) and superluminous supernovae (SLSNe), the proposed progenitor systems of FRB 121102. We find that while the FRB 121102 host is consistent with those of LGRBs and SLSNe, the nearby FRB host candidates, at least for FRB 180729.J1316+55, FRB 171020, and FRB 180814.J0422+73, either have a smaller DMhost or are fainter than FRB 121102 host, as well as the hosts of LGRBs and SLSNe. In order to avoid the uncertainty in estimating DMhost due to the line-of-sight effect, we propose a galaxy-group-based method to estimate the electron density in the intergalactic regions, and hence, DMIGM. The result strengthens our conclusion. We conclude that the host galaxy of FRB 121102 is atypical, and LGRBs and SLSNe are likely not the progenitor systems of at least most nearby FRB sources. The recently reported two FRB hosts differ from the host of FRB 121102 and also the host candidates suggested in this paper. This is consistent with the conclusion of our paper and suggests that the FRB hosts are very diverse.

Lunar Tide in the F Region Ionosphere

AbstractIn this paper the magnetic latitude (±50°) and longitude, local solar time (LST), and month‐to‐month variability of the M2 lunar semidiurnal tide in the ionosphere is revealed through analysis of topside F region electron density measurements by the Planar Langmuir Probe instrument on the CHAMP satellite during the two 5‐year periods 2001–2005 and 2005–2009. The local time precession rate of CHAMP is such that 5 years is required to obtain full LST coverage for every month of the year at each latitude of interest. Thus, each 5‐year period is compressed into one equivalent year. M2 amplitudes, expressed in terms of percent residuals from a background value, range between about 3% and 20% and vary considerably with LST and magnetic longitude. Longitude variations in principle arise from zonal asymmetries in lunar tidal forcing due to Earth and ocean tides, as well as magnitude of Earth's magnetic field. The O1 diurnal tide is also discussed in the context of CHAMP and other measurements of the F region ionosphere.

Finding High-Quality Metal Ion-Centric Regions Across the Worldwide Protein Data Bank.

As the number of macromolecular structures in the worldwide Protein Data Bank (wwPDB) continues to grow rapidly, more attention is being paid to the quality of its data, especially for use in aggregated structural and dynamics analyses. In this study, we systematically analyzed 3.5 Å regions around all metal ions across all PDB entries with supporting electron density maps available from the PDB in Europe. All resulting metal ion-centric regions were evaluated with respect to four quality-control criteria involving electron density resolution, atom occupancy, symmetry atom exclusion, and regional electron density discrepancy. The resulting list of metal binding sites passing all four criteria possess high regional structural quality and should be beneficial to a wide variety of downstream analyses. This study demonstrates an approach for the pan-PDB evaluation of metal binding site structural quality with respect to underlying X-ray crystallographic experimental data represented in the available electron density maps of proteins. For non-crystallographers in particular, we hope to change the focus and discussion of structural quality from a global evaluation to a regional evaluation, since all structural entries in the wwPDB appear to have both regions of high and low structural quality.

Driving Planetary Period Oscillations From the Hall Conducting Layer of Saturn's Upper Atmosphere

AbstractWe develop a simple physical model of the planetary period oscillations (PPOs) observed in Saturn's magnetosphere. The model couples together flows and currents in five two‐dimensional systems: an upper and lower atmospheric layer in each hemisphere, and the equatorial magnetosphere. We neglect the curved geometry of the planet and the magnetosphere but use a simple scaling argument to account for the very different sizes of the two systems. We show that it is possible to drive a PPO current system with many of the observed properties by invoking a twin vortex system in the Hall conducting layer of either hemisphere. The twin vortex system is able to generate divergent currents because our model includes a representation of the latitudinal variation of conductance. The large inertia and low Pedersen conductance of this layer of the atmosphere means that the twin vortex system and the PPO currents have a very stable rotation velocity and a very long dissipation timescale, explaining the long term persistence and stability of the PPO current systems. For a range of realistic parameters, part of the PPO current system closes through the equatorial magnetosphere, and part through the opposite hemisphere, as observed. We make predictions about the phase relationships between these closure currents that allow our model to be tested. Although the wind speeds required to produce the observed currents are implausibly large, interaction with enhanced electron density in the auroral regions reduces the necessary wind speeds to plausible values.

Spectral fluctuation analysis of ionospheric inhomogeneities over Brazilian territory Part II: E-F valley region plasma instabilities

The turbulent-like process associated with ionospheric instabilities, has been identified as the main nonlinear process that drives the irregularities observed in the different ionospheric regions. In this complementary study, as proposed in the first article of this two-paper series (Fornari et al., 2016), we performed the detrended fluctuation analysis of the equatorial E-F valley region electron density fluctuations measured from an in situ experiment performed over the Brazilian territory. The spectral consistency with the K41 turbulent universality class is analyzed for E-F valley region from the DFA spectra for four electron density time series. A complementary detrended fluctuation analysis for four time series of the F-layer electric field is also presented. Consistent with the results obtained for the F region, the analysis for the E-F valley region also shows a very high spectral variation (≫50%). Thus, the spectral analysis performed in both parts of the series suggest that a process such as the homogeneous turbulence K41 (β=-5/3±2%) is inappropriate to describe both the fluctuations of electron density and the electric field associated with the main ionospheric instabilities.

Sigma-holes from iso-molecular electrostatic potential surfaces.

Visualization of the halobenzene σ-hole region of molecules (PhX, X = Cl, Br, I) was conducted to investigate the nature of the σ-hole present between covalently bonded elements of groups IVB-VIIB (known as halogen bonding for group VIIB) and corresponding negative sites, such as Lewis base lone electron pairs, π-electrons, or anions. The σ-hole consists of a region of poor electron density and often relatively positive electrostatic potential surrounding the outermost portion of the halogen atom along the A-X bond axis. In this work, molecular electrostatic potential (MEP) isosurfaces for PhX obtained from ab initio calculations are examined to determine the σ-hole in 3D, showing the surfaces of corresponding positive and negative regions. Surfaces were mapped for isopotentials of PhX molecules as low as 0.003V and scaled up by factors of 10 up to 3V. The σ-hole is revealed as a positive region exposed underneath a predominantly negative MEP isosurface. As isopotential values move away from zero, this hole grows in radius; conversely, its presence completely fades as potential approaches zero with increasing distance from the molecule. This technique can also be used to compare behaviors of neutral molecules and their ionic counterparts like the case of neutral PF6 (not observed experimentally) and the hexafluorophosphate anion, PF6-, a typical counter-ion in commercial Li-ion batteries. The pnictogen halide PF5 features similar MEP trends as the neutral PF6, which features reactive sites, shown as negative potential caps, at specific points in the molecule, similar to those of PF5. The portrayal of MEP behavior in iso-surfaces at specific and practical values of chemical interest is crucial when defining lump parameter sets for Coulombic force fields for molecular dynamics simulations to be used in systems that go from biological macromolecules to crystal engineering to devices to final products. Active chemical sites can be described by the MEP function, V(r), more proficiently than just wavefunctions or electron densities that intrinsically contain the same information, and this is fully enhanced when color-coding electron densities on isopotential surfaces are shown. Graphical abstract The hidden features of orbital holes depicted by iso-potentials.

A Combined Experimental (FT-IR) and Computational Studies of 9-Chloroanthracene

The experimental FT-IR spectral analysis of 9-chloroanthracene has worked out by using density functional theory (DFT). The optimized molecular structure and minimum energy of 9-chloroanthracene has analyzed using DFT/B3LYP functional employing 6-311++G(d,p) basis set. The vibrational frequencies along with IR intensities were computed, scaling was used for a better fit between the experimental and computed frequencies, they agreed with rms error 8.48 cm-1 for 9-chloroanthracene. The NLO behaviour of the molecule is investigated from first-order hyperpolarizability. The HOMO and LUMO energies are evaluated to demonstrate the chemical stability, reactivity of molecule. The MESP over the molecules were plotted to evaluate electron density regions and thermodynamic parameters are calculated. Hyper conjugative interactions and charge delocalization of the molecule study from NBO analysis and Fukui functions are evaluated for 9-chloroanthracene. The molecular docking studies were performed against anticancer protein targets Tyrosinase and HER2.

Analysis of vibrational autoionization of CaF Rydberg states.

We report calculations of vibrational autoionization rates of CaF Rydberg states, based on the results of a global multi-channel quantum defect theory (MQDT) fit. Our goal is to use intuitive physical models to interpret and extend the results from the MQDT calculations and, in particular, to characterize the physical mechanisms for the interaction between the Rydberg electron and the ion-core. The calculations indicate that, among the six strongly l-mixed core-penetrating (CP) Rydberg series of CaF, the n.36 p^Π Rydberg series has the fastest Δv = 1 vibrational autoionization rate, which is at least four times larger than that for the other CP Rydberg series, in agreement with experimental results. We first demonstrate that the rotational level dependence of the vibrational autoionization rate of the n.36 p^Π series is satisfactorily explained by l-uncoupling interactions, which differ for the positive and negative Kronig symmetry levels. Next, we interpret the relative vibrational autoionization rates of all six CP Rydberg series in the context of a valence-precursor (VP) model. The VP model is a consequence of Mulliken's rule, which states that the innermost lobe of the Rydberg wavefunction remains invariant in both the nodal position and shape for members of the same Rydberg series. The electronic properties of the six VP states, which are the terminus states (lowest-n) of each of the six CP Rydberg series, are further characterized in terms of a ligand-field model, providing insight into the intimate relationship between the Rydberg electron density in the ion-core region and the vibrational autoionization rate.

Physical Processes Driving the Response of the F2 Region Ionosphere to the 21 August 2017 Solar Eclipse at Millstone Hill

AbstractThe high‐resolution thermosphere‐ionosphere‐electrodynamics general circulation model has been used to investigate the response of F2 region electron density (Ne) at Millstone Hill (42.61°N, 71.48°W, maximum obscuration: 63%) to the Great American Solar Eclipse on 21 August 2017. Diagnostic analysis of model results shows that eclipse‐induced disturbance winds cause F2 region Ne changes directly by transporting plasma along field lines, indirectly by producing enhanced O/N2 ratio that contribute to the recovery of the ionosphere at and below the F2 peak after the maximum obscuration. Ambipolar diffusion reacts to plasma pressure gradient changes and modifies Ne profiles. Wind transport and ambipolar diffusion take effect from the early phase of the eclipse and show strong temporal and altitude variations. The recovery of F2 region electron density above the F2 peak is dominated by the wind transport and ambipolar diffusion; both move the plasma to higher altitudes from below the F2 peak when more ions are produced in the lower F2 region after the eclipse. As the moon shadow enters, maximizes, and leaves a particular observation site, the disturbance winds at the site change direction and their effects on the F2 region electron densities also vary, from pushing plasma downward during the eclipse to transporting it upward into the topside ionosphere after the eclipse. Chemical processes involving dimming solar radiation and changing composition, wind transport, and ambipolar diffusion together cause the time delay and asymmetric characteristic (fast decrease of Ne and slow recovery of the eclipse effects) of the topside ionospheric response seen in Millstone Hill incoherent scatter radar observations.