Variation Of Plasma Density Research Articles

Effect of ion transfer on energy gain of ultra-intense crossing laser beams

An interesting phenomenon called ‘ion transfer’, which may obviously affect the energy gain of cross-beams via changing the momentum and density of plasmas, is demonstrated. The increment of plasma momentum induced by it will be proportional to the transferred energy of the cross-beam according to the momentum conservation law. In addition, the ‘ion transfer’-induced variation of plasma density can be attributed to the balance of the ponderomotive force of the cross-beam and the plasma electron thermal pressure, which is proportional to the total intensity of the cross-beam, while inversely proportional to the plasma electron temperature. These results may make up for the deficiency of the existing linear coupled-mode-equations when investigating the cross-beam energy transfer under the action of ultra-intense laser.

Solar wind transient currents: statistical properties and impact on Earth’s magnetosphere

Solar wind discontinuities carry intense transient currents and significantly contribute to the turbulent spectrum and plasma heating. The most-investigated characteristics of these discontinuities are the magnetic field configuration and the current density, whereas plasma characteristics attract less attention. In this study, we utilize eight years of ARTEMIS spacecraft observations in the solar wind to investigate plasma density, velocity, and temperature variations across discontinuities. We also consider the role of discontinuities in the development of Earth’s magnetospheric perturbations. We show that observed discontinuities can be separated into two groups: (i) discontinuities with weak plasma density variations and a significant correlation between the solar wind and Alfven velocities, (ii) discontinuities with significant variations of plasma density and temperature. For most discontinuities, observed density variations anti-correlate with temperature variations, but larger density/temperature variations correspond to stronger current densities. Time intervals characterized by increased occurrence rate of solar wind discontinuities correspond to enhanced geomagnetic activity in the Earth’s magnetosphere as characterized by geomagnetic indices.

Polytropic Behavior of Solar Wind Protons Observed by Parker Solar Probe

Abstract A polytropic process describes the transition of a fluid from one state to another through a specific relationship between the fluid density and temperature. The value of the polytropic index that governs this relationship determines the heat transfer and the effective degrees of freedom during a specific process. In this study, we analyze solar wind proton plasma measurements, obtained by the Faraday cup instrument on board the Parker Solar Probe. We examine the large-scale variations of the proton plasma density and temperature within the inner heliosphere explored by the spacecraft. We then address the polytropic behavior in the density and temperature fluctuations in short time intervals, which we analyze in order to derive the effective polytropic index of small-scale processes. The large-scale variations of the solar wind proton density and temperature, which are associated with the plasma expansion into the heliosphere, follow a polytropic model with a polytropic index ∼5/3. On the other hand, the short-scale fluctuations, which are potentially associated with turbulence, follow a model with a larger polytropic index. We investigate possible correlations between the polytropic index of short-scale fluctuations and the plasma speed, plasma β, and the magnetic field direction. We discuss candidate mechanisms leading to this behavior including energy transfer and possible mechanisms restricting the effective particle degrees of freedom at smaller scales.

Stimulated Brillouin Scattering of high power beam in unmagnetized plasma: Effect of relativistic and ponderomotive nonlinearities

In present communication, Stimulated Brillouin scattering (SBS) of high power beam in unmagnetized plasma is investigated. Relativistic and ponderomotive non-linearities are considered simultaneously. There is generation of scattered wave due to interaction of pump wave with ion-acoustic wave (IAW). Here, nonlinearity in dielectric function of plasma is set up under combined effects of variation in mass of electrons on account of high intense lasers as well as variation in plasma density of electrons as a result of ponderomotive force. As a result of this, there is variation in density profile of plasma in a direction transverse to pump beam axis. Incident wave, IAW and Scattered wave are greatly affected due to variation in plasma density. WKB and paraxial ray approximations are used to set up nonlinear differential equations linked with pump wave, IAW, scattered wave and expression for SBS back-reflectivity. Since, analytical solution is not possible for these equations. So, 4th order Runge-Kutta method is used to solve these equations numerically for studying the variation of beams widths of various waves and SBS back-reflectivity against normalized distance of propagation for established parameters of laser and plasma. Further, SBS back-reflectivity is found to get enhanced due to self-focusing.

Relationship Between Presunset Wave Structures and Interbubble Spacing: The Seeding Perspective of Equatorial Plasma Bubble

AbstractIn this paper, we study on the precursor seed structures well before the prospective occurrence of equatorial plasma bubble (EPB). We use the scanning mode observations made by the 30‐MHz Gadanki Ionospheric Radar Interferometer for estimating interbubble spacing and high time resolution observations made by a collocated digisonde for inferring horizontal wavelength of wave‐like variations prior to the onset of EPB. Horizontal wavelength of wave‐like variations has been inferred from plasma density variations and height variations of isodensity contours; both show consistent results. Remarkable agreement has been found between the estimated horizontal wavelength and interbubble spacing, which demonstrates the potential of digisonde in providing relevant seed structure for a prospective EPB formation. Further analysis based on observational results and numerical simulation of collisional interchange instability shows that while the eventual formation of EPB has a strong bearing on the height of the F layer and density gradient scale length, the growth perspective of the EPB depends on the seed wavelength. These results are presented and discussed keeping the future prospective of EPB forecasting/nowcasting.

In Situ Observations of Ionospheric Heating Effects: First Results from a Joint SURA and NorSat‐1 Experiment

AbstractThis work presents the first results of measurements of artificial plasma disturbance characteristics using the low‐orbit NorSat‐1 satellite, which are excited when the ionospheric F2 layer is modified by powerful high‐frequency (HF) waves emitted by the SURA heating facility. NorSat‐1 carries the multineedle Langmuir probe instrument, which is capable of sampling the electron density at a nominal rate up to 1 kHz. The uniqueness of this experiment lies in the fact that the satellite passes very close to the center of the HF‐perturbed magnetic flux tube and in situ observations are first carried out in winter when the absorption is still small in the morning as the Sun is low above the horizon. There are HF‐induced plasma temperature and density variations at satellite altitudes of about 580 km. Plasma irregularities are detected by in situ measurements down to 200 m at the southern border of the SURA heating region.

Two‐Dimensional Reconstruction of Ionospheric Plasma Density Variations Using Swarm

AbstractSpace weather phenomena such as scintillations of Global Navigation Satellite Systems (GNSS) signals are of increasing importance for aviation, the maritime, and civil engineering industries. The ionospheric plasma irregularities causing scintillations are associated with strong gradients in ionospheric plasma density. To provide nowcasts and forecasts of space weather effects, it is vital to monitor the ionosphere and detect strong density variations. To reconstruct plasma density variations in the polar cap ionosphere, we use total electron content (TEC) estimates from the Swarm satellites' GPS receivers. By considering events where the Swarm satellites are in close proximity, we obtain plasma density variations by inverting TEC measurements on a two‐dimensional grid. We first demonstrate the method using synthetic test data, before applying it to real data. The method is validated using in situ Langmuir probe measurements and ground‐based TEC observations. We find that the new method can reproduce density variations, although it is sensitive to the geometry of the Swarm satellite constellation and to the calculated plasma temperature. Our proposed method opens new possibilities for ionospheric plasma monitoring that uses GPS receivers aboard low Earth orbit (LEO) satellites.

Radio Sounding Measurements of the Solar Corona Using Giant Pulses of the Crab Pulsar in 2018

Observations of the Crab pulsar at 327 MHz were made at the Toyokawa Observatory of the Institute for Space-Earth Environmental Research, during the solar occultation in mid-June 2018 to investigate the coronal plasma density in the weak sunspot cycle, Cycle 24. The dispersion measurements (DMs) were determined using giant pulses detected from observations of the Crab pulsar. The systematic increase in DM over the background level, observed during the period of the closest approach of the Crab pulsar’s line-of-sight to the Sun, was ascribed to the effect of the coronal plasma. A coronal density model assuming spherical symmetry was determined by fitting it to the DM data, and was compared with those determined in past solar cycles. The best-fit model had large errors, and indicated a systematically higher value than those derived from past observations. The results obtained here are likely to be significantly affected by latitude/longitude variation in coronal plasma density, the time variation of the interstellar medium, mainly the Crab nebula, and increased measurement errors due to the reduced occurrence of giant pulses. Hence, further observations are needed to derive conclusions about a change of coronal density in the current cycle.

Expansion dynamics of atmospheric pressure helium plasma jet in ambient air

In this work, the expansion dynamics of a helium plasma jet in ambient air is examined. By using a fast imaging technique, the expansion of plasma jet from glass nozzle to air is captured which is in the form of plasma bullet propagating into the air. To understand the plasma bullet travel path from glass nozzle to plasma jet tip a drag force model is used. Moreover, the spatial variation of plasma density along the plasma jet length is estimated using drift velocity, plasma jet current and the cross-sectional area of the plasma jet. It is observed that the slight increase in plasma density is due to the combined effect of reduction of drift velocity, plasma jet current, and jet cross-sectional area. The obtained plasma density from glass nozzle to jet tip is in the range of (0.069-5.96) × 1012 cm−3. The above parameters can be of the essence in biological and industrial applications.

On the plasma density variation in the F2 region during geomagnetic storms

The features of ionospheric storm given by the percentage change in frequency (dfoF2) have been investigated for four stations. Using the international quietest days as a reference, dfoF2 was computed as the deviation of the storm day critical frequency from the quiet day diurnal variation. The main interest here was to understand the hemispheric and longitudinal differences in the ionospheric storm responses in these mid latitude locations. Clear hemispheric differences were observed in association of the ionospheric storms with geomagnetic storms. The times of significant ionospheric storms were not usually coincident with peak geomagnetic storms. It is suggested that electrodynamic changes in the high latitudes which could be linked to the geomagnetic storm may be forcing the changes in the sub aurora stations, while localized effect dominate the response in the southern hemisphere stations. These findings have important implications for our present understanding of ionospheric variation in the continent.

Plasma-Dielectric Traveling Wave Antenna

The paper investigates the efficiency of transformation of traveling wave into radiation in longitudinally inhomogeneous plasma cylinder. The plasma is limited by a dielectric shell of finite thickness. The investigation involves the use of the method of spectral field expansion in terms of a set of functions including the surface and spatial waves of plasma cylinder with dielectric shell. A system of integro-differential equations for expansion coefficients has been obtained. These coefficients determine the amplitudes of transmitted, reflected, and scattered waves and also radiation patterns (RP). The system of equations is solved for the case of strong longitudinal variation of plasma density. The relationships of the transformation coefficients of surface wave energy as a function of the plasma density gradient, electrical length of section of plasma inhomogeneity, the electric radius of plasma cylinder, dielectric permittivity, and the thickness of dielectric were calculated. The fraction of surface wave energy that is transformed into radiation at acute angles can amount to 35%. The resultant narrow-beam RPs have only one lobe. The radiation maximum fits into an angle of several degrees with respect to the direction of surface wave propagation. With an increase of plasma density gradient, the lobe width is reduced, while its position shifts to 0°. The impact of dielectric properties on radiation characteristics has been also investigated.

Formation of surface ionization waves in a plasma enhanced packed bed reactor for catalysis applications

Plasma enhanced packed bed reactors (PE-PBRs) intrinsically have complex geometries which makes it difficult to apply conventional scaling laws. For example, controlling the manner of discharge propagation between the micro-discharges (MDs) that occur between dielectrics in PE-PBRs and surface ionization waves (SIWs) that propagate along the dielectrics would aid in selectivity during plasma catalysis. An important parameter in that optimization is the pulse power format. In this work, we investigated the role of applied voltage amplitude and polarity on time resolved dynamics in an atmospheric pressure dielectric barrier discharge (DBD) operating in helium having surface topology resembling PE-PBRs using phase and space resolved optical emission spectroscopy (PROES). To enable systematic studies, the DBD uses an array of dielectric semi-spheres imaged through a top transparent electrode and imaged between the two electrodes from the side. The results were compared with 2-dimensional modeling. We identified three discharge mechanisms: filamentary micro-discharges (F-MDs) in the volume (the space between the surface of the dielectrics and the counter electrode), surface micro-discharges (S-MDs) between the dielectric semi-spheres near their contact points, and SIWs over the curved or flat dielectric surfaces. At the lowest voltages, only F-MDs are generated, once in each half cycle. At intermediate voltages, SIWs also appear which transform into S-MDs at the contact points. When voltage is further increased, several additional pulses are observed, which generate S-MDs at the contact points or a combination F-MDs and S-MDs. The voltage amplitude determines the frequency of these pulses. Modeling results show variations in plasma density and electron temperature for each of the three mechanisms which, in turn, impact production of reactive species.

Parametric Sensitivity of the Formation of Reversed Electron Energy Spectrum Caused by Plasmaspheric Hiss

AbstractScattering by plasmaspheric hiss is responsible for the newly reported reversed energy spectra with abundant high‐energy but fewer low‐energy electrons between hundreds of kiloelectronvolts and ~2 MeV in the inner magnetosphere. To deepen our understanding of the contributions of plasmaspheric hiss to the formation of reversed electron energy spectrum, we conduct a detailed theoretical parametric analysis through numerical simulations to explore the sensitivity of hiss‐induced reversed electron energy spectrum to ambient magnetic field, plasma density, and hiss wave distribution properties. Given L‐shell, variations of ambient plasma density and wave frequency spectrum contribute importantly to the formation of reversed electron energy spectrum, while variations of background magnetic field (which usually shows small changes in the plasmasphere) and wave normal angle distribution play a less effective role. Our study suggests that the reversed electron energy spectrum has important implications for unveiling the sophisticated energy‐dependent nature of wave‐particle interactions and energetic particle dynamics in geospace.

A new method of inferring the size, number density, and charge of mesospheric dust from its in situ collection by the DUSTY probe

Abstract. We present a new method of analyzing measurements of mesospheric dust made with DUSTY rocket-borne Faraday cup probes. It can yield the variation in fundamental dust parameters through a mesospheric cloud with an altitude resolution down to 10 cm or less if plasma probes give the plasma density variations with similar height resolution. A DUSTY probe was the first probe that unambiguously detected charged dust and aerosol particles in the Earth's mesosphere. DUSTY excluded the ambient plasma by various biased grids, which however allowed dust particles with radii above a few nanometers to enter, and it measured the flux of charged dust particles. The flux measurements directly yielded the total ambient dust charge density. We extend the analysis of DUSTY data by using the impact currents on its main grid and the bottom plate as before, together with a dust charging model and a secondary charge production model, to allow the determination of fundamental parameters, such as dust radius, charge number, and total dust density. We demonstrate the utility of the new analysis technique by considering observations made with the DUSTY probes during the MAXIDUSTY rocket campaign in June–July 2016 and comparing the results with those of other instruments (lidar and photometer) also used in the campaign. In the present version we have used monodisperse dust size distributions.

Specifics of the focused electron beam transport in the forevacuum range of pressure

We have investigated electron beam transport at an elevated forevacuum pressure of tens of Pascals of helium. The continuous electron beam (6–14 keV, 300 mA) is generated by a forevacuum-pressure plasma-cathode electron source utilizing a hollow-cathode discharge. A beam-plasma discharge is generated in the beam transport zone, which is characterized by increased plasma density in the region of the most intense beam-plasma interaction. We find that the location and distribution of the beam-plasma discharge depend on the electron beam energy and current density. Under certain conditions, we observe that the beam plasma is stratified, with a periodic variation of plasma density and luminosity along the direction of electron beam propagation.

ULF waves observed during substorms in the solar wind and on the ground

We present results of analysis of ultra-low-frequency (ULF) waves observed by the Advanced Composite Explorer (ACE) satellite at the Earth's L1 Lagrangian point (in the solar wind) and the fluxgate magnetometer at the Poker Flat ground station in Alaska, USA. We considered 75 high-intensity substorm events occurring between October 2015 and April 2017. Our goal is to investigate possible correlation between spectral characteristics of the waves observed in the solar wind and on the ground. Our findings show that: 1) ULF waves with the same frequencies are frequently observed at both locations, in particular, about 30% of the cases yield very good correlation between power spectral density of corresponding signals; 2) the waves with frequencies of 0.60 mHz, 0.70–0.75 mHz are most often seen at both locations; 3) the trend of repeating dominant frequencies is consistent throughout the whole period of observation of about a year and a half. There are also some cases of either mismatch of expectation and occurrence of substorm or a poor correlation between the frequencies of ULF waves detected in space and on the ground. Our findings suggest that the variations of plasma density or the magnetic field in the solar wind indeed serves as a driver for the ULF waves in the Earth's magnetosphere-ionosphere system. This system works like a resonator, and when the frequency of the driver matches one of the eigenfrequencies of the resonator, the large amplitude waves are observed on the ground. When the frequency of the driver mismatch the eigenfrequency, the amplitude of the ground oscillations are much smaller.

Characteristics of the Plasma Disturbance Excited at Altitudes of 450–500 km During the “Sura” Facility Operation

We discuss the results of measuring characteristics of the artificial plasma disturbances excited at altitudes of 450–500 km with the ionospheric F2 layer modified by high-power HF radio waves from the Sura facility. It is found that at these altitudes there are plasma temperature and density variations in the HF-perturbed magnetic flux tube. No ducts with increased plasma density that were previously observed at altitudes of about 660 km were detected. The results of the studies are compared with the data from the DEMETER satellite and the results of radiotomographic measurements. It is noted that the field-aligned currents induced in a perturbed ionosphere during the Sura operation were detected for the first time using SWARM satellites.

Tapering of plasma density ramp profiles for adiabatic lens experiments

One of the key elements of the plasma wakefield blowout regime is the strong, linear focusing provided by the ion density. One advantage of this focusing is its extraordinary strength whose gradient is proportional to the local background plasma density, that is particularly important for adiabatic focusing schemes in future compact linear colliders. Local plasma density variations can be obtained in gas-filled capillaries by varying monotonically the diameter of the capillary. Here we present the ongoing study of the plasma density profile obtained for different tapering angles of the capillary shape and we discuss their use for the adiabatic plasma lens experiment proposed at SPARC_LAB.

Stability of electron wave spectra in weakly magnetized plasmas

Analytical models for nonlinear electron plasma waves in weakly magnetized plasmas are developed for single as well as multi-mode conditions, with continuous wave spectra being a limiting case. The conditions for wave decay as well as modulational instabilities are analysed. Our results demonstrate that slow or nearly stationary plasma density variations can be found for weakly magnetized plasmas even for weakly nonlinear electron plasma waves without involving cavitation of large amplitude plasma waves. A reduction of the growth rates for decay as well as modulational instabilities are found when the spectral width of the wave spectrum is increased. Some of our results are relevant for the interpretation of the nonlinearly enhanced ion acoustic lines often observed in non-equilibrium ionospheres.

The Solar Flux Dependence of Ionospheric 150 km Radar Echoes and Implications

AbstractRadar echoes from the daytime equatorial ionospheric F1 region, popularly known as “150 km echoes,” have challenged ionospheric plasma physicists for several decades. Recent theoretical simulations showed that enhanced photoelectron fluxes can amplify the amplitude of plasma waves, generating spectra similar to those of the radar echoes, implying that larger solar fluxes should produce more frequent and stronger 150 km echoes. Inspired by this proposal, we studied the occurrence and intensity dependence of the echoes on the EUV flux observed by SOHO over several years. The occurrence and intensity of the echoes were found to have an inverse relationship with this EUV flux measurement. The multiyear trend is independent of the variability often observed over successive days with nearly identical EUV fluxes. These results imply that the relationship between the echoes and EUV flux is more complex. We propose that gravity waves modulate the amplitude of 150 km echoes through changes in the variations in plasma density and photoelectron fluxes associated with the gravity wave‐induced neutral density modulations.