Number Density Of Free Electrons Research Articles

Landau damping effects on dust ion-acoustic solitary waves in a nonthermal pair-ion plasma

The Landau damping effects on the nonlinear propagation of dust ion-acoustic solitary waves (DIASWs) are studied in an electron-free unmagnetized collisionless dusty pair-ion plasma. The two species of nonthermal ions (positive and negative) are described by the kinetic Vlasov equations, whereas the massive charged dust grains form only the background plasma. Using the multi-scale reductive perturbation technique generalized for the applications to the Vlasov equation, we derive a modified Korteweg–de Vries (KdV) equation that governs the evolution of DIASWs with the effects of linear resonance, in particular, linear Landau damping. The properties of the phase velocity and the Landau damping rate of DIASWs are studied with the effects of positive and negative-ion nonthermality parameters ( α p , α n ), the ratios of the positive to negative ion masses (m) and temperatures (T) as well as the dust to negative-ion number density ratio (δ). It is found that, depend on the degree of positive to negative ion mass ratios (m), both of damped and growing oscillations occur in a collisionless dusty pair-ion plasma due to the resonance phenomena between the wave and the nonthermal particles of the system. The properties of the decay rates of the amplitude of the KdV soliton with a small effect of Landau damping are also studied with the above system of parameters. The results may be useful for understanding the localization of solitary pulses and associated resonance damping and/or growing oscillations of the wave in laboratory and space plasmas, in which the number density of free electrons is much smaller than that of ions and highly charged heavy, micron seized dust grains.

Influence of High-frequency localized surface plasmon polariton effect of Al nanoparticles on luminescence efficiency of deep-blue BCzVBi OLED

It is difficult to enhance the blue or purple luminescence efficiency of organic light-emitting device ( OLED) for practice display applications. In this work, aluminum nano particles (Al-NPs) are inserted into the light-tight TmPyPb electron transporting layer (ETL) of ITO/PEDOT:PSS/TAPC/BCzVBi:BCPO/TmPyPb/Liq/Al OLEDs, in which BCzVBi can emit deep-blue fluorescent light, with the attempts to overcome the above deficiency through the local surface plasmon polariton(LSPP) effect excited in Al-NP at higher resonance frequencies by the luminescence radiations from BCzVBi. The distances of Al-NPs from BCzVBi:BCPO fluorescent layer are chosen as <i>x</i> = 4, 8, 12 nm. The morphologies observed by atom force microscope and scan electron microscope show that the Al film with a thickness of 1 nm, deposited at room temperature by vacuum heat evaporate, is composed of separated Al grains (therefore, called Al-NPs) with sizes on a 10 nm scale. By inserting these Al-NPs into the TmPyPb ETL, both the current density and luminance at the same voltage decrease in comparison with the counterparts of reference devices (i.e. ones without Al-NPs) due to the worsened carrier mobility. However, the current density and luminance both rebound significantly at <i>x</i> = 8 nm. This may be due to the fact that the fluorescence quenching strongly occurs at <i>x</i> < 8 nm, and on the other hand, the local surface plasmon polariton is weakened too much at <i>x</i> > 8 nm due to attenuated radiation from BCzVBi. At <i>x</i> = 8 nm, the voltage (9 V) at which the luminance reaches a maximum value is the same as that for the reference device, but the maximum luminance itself decreases from 4200 Cd/m<sup>2</sup> to 3500 Cd/m<sup>2</sup>. However, the current density also decreases from 335.19 mA/cm<sup>2</sup> to 145.71 mA/cm<sup>2</sup>. This conversely results in a promising great increase of current efficiency from 0.88 Cd·A<sup>–1</sup> to 2.36 Cd·A<sup>–1</sup>. Subsequently, the external quantum efficiency (EQE) is enhanced by 170%, while the efficiency roll-off ratio decreases from 78% to 30.5%, with a decrement of 61% . At a high current density of 270 mA/cm<sup>2</sup>, EQE enhances 66.5%. The coupling between fluorescence excitation state and local surface plasmon polariton is determined by the overlapping between fluorescence emitting peak and plasmon resonance peak. As aluminum has a number density of free electrons, 18.1×10<sup>22</sup> cm<sup>–3</sup>, much larger than those for the other normally used metals (such as gold and silver), its spectrum of local surface plasmon polariton is enough to cover the fluorescence wavelength range of BCzVBi. These research results show that the luminescence efficiency of deep-blue OLEDs can be turned better by LSPP excited in Al-NPs at higher resonance frequencies.

Transient electron temperature and density changes in water breakdown induced by femtosecond laser pulses

When a femtosecond laser pulse travels through water, optical breakdown occurs when the laser intensity exceeds a certain threshold. This photoionization (PI) process and the resulting laser-induced plasma can strongly influence the laser ablation of substances, including transparent biological tissue, etc. However, numerical models of the initial evolution of the laser plasma and its early electron temperature remain inadequate. Here, a transient ionization rate equation involving the solvation process is proposed for calculating the free-electron number density (FED) generated during the interaction of the femtosecond laser with the water surface, along with the temporal evolution of the electron temperature in the focusing region during the entire femtosecond laser pulse utilizing an improved temperature model. The predictions of the proposed model are in better agreement with the experimentally determined breakdown thresholds. The results indicate that the existence of solvated electrons has a considerable influence on the determination of the optical breakdown threshold in water, which may also be one of the reasons why traditional numerical models consistently fail to forecast the actual breakdown threshold.

Patchy Kinetic Sunyaev–Zel’dovich Effect with Controlled Reionization History and Morphology

Using the novel semi-numerical code for reionization AMBER, we model the patchy kinetic Sunyaev–Zel’dovich (kSZ) effect by directly specifying the reionization history with the redshift midpoint z mid, duration Δz, and asymmetry A z. We further control the ionizing sources and radiation through the minimum halo mass M h and the radiation mean free path λ mfp. AMBER reproduces the free-electron number density and the patchy kSZ power spectrum of radiation–hydrodynamic simulations at the target resolution (1 Mpc h −1) with matched reionization parameters. With a suite of (2 Gpc/h)3 simulations using AMBER, we first constrain the redshift midpoint 6.0 < z mid < 8.9 using the Planck 2018 Thomson optical depth result (95% CL). Then, assuming z mid = 8, we find that the amplitude of scales linearly with the duration of reionization Δ z and is consistent with the 1σ upper limit from South Pole Telescope (SPT) results up to Δ z < 5.1 (Δ z encloses 5%–95% ionization). Moreover, a shorter λ mfp can lead to a ∼10% lower and a flatter slope in the scaling relation, thereby affecting the constraints on Δ z at ℓ = 3000. Allowing z mid and λ mfp to vary simultaneously, we get spectra consistent with the SPT result (95% CL) up to Δ z = 12.8 (but A z > 8 is needed to ensure the end of reionization before z = 5.5). We show that constraints on the asymmetry require ∼0.1 μ k 2 measurement accuracy at multipoles other than ℓ = 3000. Finally, we find that the amplitude and shape of the kSZ spectrum are only weakly sensitive to M h under a fixed reionization history and radiation mean free path.

On positively charged dust in the coma of comet 67P

ABSTRACT Moment analysis of ion spectrograms measured by the Ion Composition Analyser (ICA) in the coma of comet 67P typically produces an ion number density estimate markedly lower than the number density of free electrons as measured by the Mutual Impedance Probe and the dual Langmuir Probe. While there are good reasons to distrust the ion density moment estimate in these circumstances, the issue cannot yet be considered fully understood and it is of interest to see whether any natural non-instrumental cause is possible. An obvious such cause would be whether a significant fraction of the positive charge density resides in positively charged dust grains that are not measured by the ICA. Here, we show that this scenario is highly unlikely, even near perihelion where photoemission is the strongest. In our semi-analytical grain charging model, we balance the current contributions to grains of photoelectron emission and electron attachment so as to find the expected charge state for a grain of a given radius. The charge state is affected by the ambient electron number density, the electron temperature, and the heliocentric distance. While at times the bulk of the dust population around comet 67P could be charged positive, dust charging, including photoelectron emission, should have a negligible influence on the overall ionization balance in the cometary coma simply because the dust particles are not ubiquitous enough.

The interaction of laser radiation with strongly coupled plasmas

New results of measurements of s- and p-polarized reflectivity of nonideal plasma at the frequency of the external electromagnetic field ν las = 2.83 × 1014 s−1, free-electron number density n e = 3.3 × 1021 cm−3 (Coulomb nonideal plasma parameter Γ = 1.2) and n e = 5.2 × 1021 cm−3 (Γ = 1.4) are presented. These data are the result of the next stage of study of optics of a warm dense matter. We present a microscopic approach to describe the entire set of experimental data on the optics of strongly correlated plasma.

Dark Photon Oscillations in Our Inhomogeneous Universe.

A dark photon kinetically mixing with the ordinary photon represents one of the simplest viable extensions to the standard model, and would induce oscillations with observable imprints on cosmology. Oscillations are resonantly enhanced if the dark photon mass equals the ordinary photon plasma mass, which tracks the free electron number density. Previous studies have assumed a homogeneous Universe; in this Letter, we introduce for the first time an analytic formalism for treating resonant oscillations in the presence of inhomogeneities of the photon plasma mass. We apply our formalism to determine constraints from cosmic microwave background photons oscillating into dark photons, and from heating of the primordial plasma due to dark photon dark matter converting into low-energy photons. Including the effect of inhomogeneities demonstrates that prior homogeneous constraints are not conservative, and simultaneously extends current experimental limits into a vast new parameter space.

Laser Breakdown in Water Induced by λ = 532 nm Nanosecond Pulses: Analytical Calculation of the Number Density of Free Electrons

In this paper a model for laser induced breakdown in water is presented, that includes the net gain and losses of the free electron density. In this regard we adopted a simple theoretical formulati...

An analytic model for [O iii] fine structure emission from high redshift galaxies

ABSTRACT Recent ALMA measurements have revealed bright [O iii] 88 micron line emission from galaxies during the Epoch of Reionization (EoR) at redshifts as large as z ∼ 9. We introduce an analytic model to help interpret these and other upcoming [O iii] 88 micron measurements. Our approach sums over the emission from discrete Str$\ddot{\mathrm{o}}$mgren spheres and considers the total volume of ionized hydrogen in a galaxy of a given star-formation rate. We estimate the relative volume of doubly ionized oxygen and ionized hydrogen and its dependence on the spectrum of ionizing photons. We then calculate the level populations of O iii ions in different fine-structure states for H ii regions of specified parameters. In this simple model, a galaxy’s [O iii] 88 μm luminosity is determined by the typical number density of free electrons in H ii regions (ne), the average metallicity of these regions (Z), the rate of hydrogen ionizing photons emitted (QH i), and the shape of the ionizing spectrum. We cross-check our model by comparing it with detailed cloudy calculations, and find that it works to better than 15${{\ \rm per\ cent}}$ accuracy across a broad range of parameter space. Applying our model to existing ALMA data at z ∼ 6–9, we derive lower bounds on the gas metallicity and upper bounds on the gas density in the H ii regions of these galaxies. These limits vary considerably from galaxy to galaxy, with the tightest bounds indicating Z ≳ 0.5Z⊙ and nH ≲ 50 cm−3 at 2 − σ confidence.

Influence of dust particles on ionization equilibrium in partially ionized plasmas.

A chemical model is proposed for a dusty plasma consisting of electrons, ions, neutrals, and positively charged dust particles all being at thermodynamic equilibrium. An expression is derived for the Helmholtz free energy, which comprises the ideal part, taking into account the charge of dust particles, and the excess part, evaluated in the framework of the self-consistent chemical model [Phys. Rev. E 83, 016405 (2011)PLEEE81539-375510.1103/PhysRevE.83.016405]. The ionization potential depression for a dust-free partially ionized hydrogen is analytically evaluated for weakly and strongly ionized states to consistently account for the presence of charged and neutral components. An ad hoc interpolation of the ionization potential depression, valid across the whole ionization region, is put forward and subsequent solution of the generalized Saha equation is found to be in a perfect agreement with exact calculations. Minimization of the Helmholtz free energy of dusty plasmas provides the number densities of free electrons, free ions, neutrals, and the dust electric charge as well. Based on consideration of weakly and strongly ionized states, a straightforward comparison is made of the ionization equilibrium in a partially ionized plasma with and without dust particles to demonstrate that at thermal equilibrium positively charged dusts are responsible for an increase in the number density of free electrons and a decrease in the number density of free ions. It is analytically proved that nonideality effects result in a growth of the number densities of free electrons and ions by obtaining the so-called electron and proton ionization potential depressions. Electric charge of dust particles is systematically studied as a full plasma component rather than considering a detailed balance of the electron and ion fluxes on the surface of a solitary dust grain.

Counting the Electrons Hopping in Ultrafast Time Scales in an Ag–CdTe Hybrid Nanostructure

In a metal–semiconductor hybrid nanostructure, exchange of carriers between the two constituents is a crucial process determining its utility for various applications. Although the transfer of carriers from the metal to semiconductor (or vice versa) shows up in several ways, it is not easy to get a quantitative estimate of the process. In this paper, we show that it is possible to obtain a fair estimate of the number of carriers hopping from or to a metal nanoparticle by performing transient absorption measurement near the localized surface plasmon resonance peak. For demonstrating this concept, a specific Ag–CdTe hybrid nanostructure was prepared such that plasmon resonance of the Ag nanoparticles could be excited well below the band gap of the CdTe quantum dots. Using a simple Drude model and the changes in the number density of free electrons, we show that the transient optical response of the hybrid is governed by both free-electron temperature and the number of carriers transported in and out of the metal nanoplates. It is also shown that using the linear absorption spectra as reference, it is possible to estimate the number of carriers hopping between the two constituents of the hybrid. The estimate of the number of electrons hopping at ultrafast time scales can provide a way to optimize the design of a metal–semiconductor hybrid system for specific applications.

Numerical investigation on interaction mechanisms between flow field and electromagnetic field for nonequilibrium inductively coupled plasma

In this paper, the inductively coupled plasma (ICP) wind tunnel, which is widely used in the development of thermal protection system for reentry vehicle in the aerospace field, is studied. The distribution properties and the interaction mechanism of the flow field and electromagnetic field are investigated by numerically solving the multi-physics fields coupling among the flow field, electromagnetic field, thermodynamic field and turbulent field. In the numerical simulation, the thermochemical non-equilibrium plasma magneto-hydrodynamic model is used to accurately simulate the high-frequency discharge, Joule heating, energy conversion, and internal energy exchange of air ICP. Finally, the distribution of electron temperature, particle number density, Lorentz force, Joule heating rate, velocity, pressure and electric field strength of air plasma are obtained through the multi-physics field coupling calculation. The results show that the plasma flow is in a thermodynamic non-equilibrium state near the torch wall in the induction coil region and that the Lorentz force plays an important role in controlling the momentum transfer. A strong eddy flow occurs between the inlet and the second turn of the inductive coil. The eddy flow has a close relationship with the negative pressure gradient and the electromagnetic heating phenomenon in the induction coil region. The radial Lorentz force is always negative. This indicates that the free electrons are generated near the wall due to the fact that the skin effect are always subjected to a force making them move to the central axis of the ICP torch. The maximum value of the radial Lorentz force is 3.95 times higher than that of the axial Lorentz. This indicates that the momentum transfer is predominantly radial. The Joule heating effect of the air particles is also affected by the radial Lorentz force. The maximum value of &lt;i&gt;E&lt;/i&gt;&lt;sub&gt;I&lt;/sub&gt; is 2.9 times larger than the real part of electric field, &lt;i&gt;E&lt;/i&gt;&lt;sub&gt;R&lt;/sub&gt;. The positive &lt;i&gt;E&lt;/i&gt;&lt;sub&gt;I&lt;/sub&gt; is generated by the free electrons inside the plasma. The number density of free electrons reaches a maximum value at a distance of 5.5 mm far from the inner wall surface of the torch below the second induction coil. 91% of N&lt;sub&gt;2&lt;/sub&gt; are dissociated into atomic N near the central axis. The maximum electron and translational temperature simulated in this paper are 9921 K and 8507 K, respectively.

Optical diagnostics for density measurement in high-quality laser-plasma electron accelerators

Implementation of laser-plasma-based acceleration stages in user-oriented facilities requires the definition and deployment of appropriate diagnostic methodologies to monitor and control the acceleration process. An overview is given here of optical diagnostics for density measurement in laser-plasma acceleration stages, with emphasis on well-established and easily implemented approaches. Diagnostics for both neutral gas and free-electron number density are considered, highlighting real-time measurement capabilities. Optical interferometry, in its various configurations, from standard two-arm to more advanced common-path designs, is discussed, along with spectroscopic techniques such as Stark broadening and Raman scattering. A critical analysis of the diagnostics presented is given concerning their implementation in laser-plasma acceleration stages for the production of high-quality GeV electron bunches.

In-situ plasma cleaning to decrease the field emission effect of half-wave superconducting radio-frequency cavities

The in-situ plasma cleaning technique using the chemical reactive oxygen plasma to remove the hydrocarbon contaminants, the outmost layer of the inner surface of the HWR cavity, has been explored at Institute of Modern Physics, CAS. For the purpose of cleaning the HWR cavity in the cryomodule by plasma, an offline apparatus for the plasma discharge study was set up, which duplicates the assembly of the cavity inside the cryomodule. Plasma ignition procedures were investigated. And the plasma parameters such as free electron number density, electron temperature and dissociated oxygen atom intensity were diagnosed by optical emission spectra to optimize the operation conditions for plasma in-situ cleaning of the HWR cavity. To evaluate the efficiency of the plasma in-situ cleaning of the HWR cavity, the related experiments were carried out on the vertical test stand. The results show that the hydrocarbon contaminants on the inner surface of the cavity were removed, and the maximal available accelerating gradient of the cavity was improved by 29% due to the mitigation of field emission inside the cavity after plasma cleaning. Details of these experimental results and observations are discussed in this article.

Landau damping of Gardner solitons in a dusty bi-ion plasma

The effects of linear Landau damping on the nonlinear propagation of dust-acoustic solitary waves (DASWs) are studied in a collisionless unmagnetized dusty plasma with two species of positive ions. The extremely massive, micron-seized, cold, and negatively charged dust particles are described by fluid equations, whereas the two species of positive ions, namely, the cold (heavy) and hot (light) ions are described by the kinetic Vlasov equations. Following Ott and Sudan [Phys. Fluids 12, 2388 (1969)], and by considering lower and higher-order perturbations, the evolution of DASWs with Landau damping is shown to be governed by Korteweg-de Vries (KdV), modified KdV (mKdV), or Gardner (KdV-mKdV)-like equations. The properties of the phase velocity and the Landau damping rate of DASWs are studied for different values of the ratios of the temperatures (σ) and the number densities (μ) of hot and cold ions as well as the cold to hot ion mass ratio m. The distinctive features of the decay rates of the amplitudes of the KdV, mKdV, and Gardner solitons with a small effect of Landau damping are also studied in different parameter regimes. It is found that the Gardner soliton points to lower wave amplitudes than the KdV and mKdV solitons. The results may be useful for understanding the localization of solitary pulses and associated wave damping (collisionless) in laboratory and space plasmas (e.g., the F-ring of Saturn), in which the number density of free electrons is much smaller than that of ions and the heavy, micron seized dust grains are highly charged.

Electron excitation effect on scattering near-field and far-field ablation material processing by femtosecond laser irradiation

Femtosecond laser nano-processing by enhanced light scattered from nanospheres has received much attention. Enhanced scattered near field enables us to ablate nanoholes at nanometer scales below the diffraction limit. In addition, the interference between the scattered far field and the irradiated laser enables us to fabricate spatially controlled periodic surface structures. In this paper, we simulated the time evolution of scattered near field and far field during the free electron excitation in silicon (Si) by femtosecond laser irradiation. The optical property of Si changes from dielectric to metal-like Si due to the increase of the free electron number density excited by femtosecond laser pulse. It is elucidated that the scattered field of Si shifts from Mie scattering to plasmonic scattering during laser irradiation. We achieved the optimal free electron density and laser intensity for precisely controlled periodic surface structures fabrication. We explained the temporal behavior of the scattering near field and far field from the standpoint of dielectric function of the materials.

Comment on comment by Markus Rapp and Franz‐Josef Lübken on “Ice iron/sodium film as cause for high noctilucent cloud radar reflectivity”

Rapp and Lübken (RL09) state that there is excellent, precise agreement between observations and polar mesosphere summer echo (PMSE) models based on radar reflection by gas‐phase electrons and conclude that because of this excellent, precise agreement other models should not be considered. In particular, they provide figures demonstrating quantitative agreement between observations and a heating/overshoot model. Careful consideration of the models presented by RL09 shows that there are inconsistencies in the assumptions regarding Lambda (i.e., the ratio of the number density of electrons attached to aerosol particles to the number density of free electrons) and there are quantitative errors in the calculation of the radar reflection. In addition, RL09's claim that the correlation between PMSE maximum and bite‐outs is either spurious or misrepresentative is refuted using radar measurements. Finally, it is shown that there is a shortcoming (not discussed by RL09) in the Bellan 2008 model, and a modification addressing this shortcoming is briefly described.

Modeling the meteoric dust effect on the equatorial electrojet

Dust particles of meteoric origin in the lower E-region can affect the conductivity parameters by varying the effective collision frequency and by causing electron bite outs through the capture of ambient electrons. In magnetized plasma, neutral dust particles can alter the effective collision frequency parameters and thus affect the Pedersen and Hall conductivities in the electrojet region. The Cowling conductivity profile is determined by the height profiles of the Hall and Pedersen conductivities. The collision parameters altered by the neutral dust particles can be considerably different from those estimated from atmospheric models, in the lower E-region heights where dust particles of meteoric origin are known to exist in large numbers. A significant fraction of these dust particles may capture free electrons from the ambient medium and get charged negatively. This can result in reduction in the number density of free electrons especially below the electrojet peak where the dust particles can be present in large numbers, at least on days of large meteor showers. This, in turn, can once again alter the vertical profile of the east–west Hall current driven by the vertical Hall polarization field and under favorable conditions, can even account for the reversal of the electrojet currents below the current peak. Assuming a realistic model for the distribution of neutral dust particles, the conductivity parameters are estimated here. Conditions under which the dust particles can cause partial reversals in the electrojet currents are critically examined here.

Simulation of DC-hopping conduction in spinel ferrites using free electron gas model

In this work, DC-hopping conductivity in spinel ferrites is simulated using free electron gas model. This simulation is performed by two substitutions: first, the mean free time in theory of independent electron approximation with the tunneling time of electrons between two adjacent octahedral sites in spinel structure and, second, the number density of free electrons with the number density of tunneled electrons in the hopping process. The barrier's width is obtained from the geometry of spinel lattice and its height from the electrostatic potential of two adjacent oxygen cation. The results of this simulation were compared with experimental values of DC-hopping conductivity for different compositions of zinc, nickel and manganese ferrites. A reasonable agreement was observed in a wide range of temperatures.

On the height variation of the E-region cowling conductivity – effect of charged dust particles

Abstract. Height profiles of the Cowling conductivity in the electrojet region, estimated using the atmospheric parameters given by the existing models like CIRA or MSIS and measured electron density profiles, consistently show the heights of the electrojet current intensity peak to be more than 3 km below those estimated from in-situ measurements using magnetometers on board sounding rockets. Kulkarni and Muralikrishna (2005) attempted to explain this to be due to the effect of neutral dust particles. They reported that neutral dust particles, when they exist in sufficient numbers, can modify the collision parameters, especially in the lower E-region, where dust particles of meteoric origin are known to exist in large numbers, and thereby can modify the Cowling conductivity profile in the electrojet region. This work is extended here to include the effect of charged dust particles. Dust particles can become charged negatively by the attachment of ambient free electrons, and can thus reduce the number density of free electrons especially below the electrojet peak. This can alter the vertical profile of the east-west Hall current driven by the vertical Hall polarization field, thereby causing a net reduction in the electrojet current. Such a decrease in the electrojet current may be observed on the ground magnetograms. This mechanism, as proposed here, can operate only during periods of strong meteor shower activity, when the dust particle density at the assumed deposit height of 103 km can reach extreme values (for example, 5×104 cm−3 of 1-µm diameter dust particles). Such a dense dust layer may even cause a reversal in the normally upward vertical Hall polarization field, within the dust layer, causing a reversal of the electrojet currents below the current peak.