Secondary emission from dust grains with a surface layer: comparison between experimental and model results

A set of fluid equations is obtained for a dusty plasma, with dust charge and mass distributions, interacting with ambient neutral dust through inelastic collision processes involving dust grain charging and discharging and secondary electron emission from the dust grains. These are obtained as appropriate moments of the Boltzmann–Vlasov equations for the positively and negatively charged dust components, neutral dust component, electrons, and ions. Also obtained are the charge and mass moments of these equations, which bring out a new term involving the charge dispersion in the equation for the phase space charge density. The inelastic collision process involving dust grain charging and discharging and secondary electron emission provides a coupling between the positive and negatively charged dust components and the neutral dust component. The source/sink terms in the equations of continuity, momentum balance, and heat equations then are the proper terms obtained systematically from the Boltzmann–Vlasov equations, as against some ad hoc formulations that have been used earlier. The set of equations so obtained should prove useful in analyzing the various dusty plasma phenomena: waves, instabilities, and nonlinear processes in space and astrophysical scenarios.

The interaction of ionizing radiation with matter is of critical importance in numerous areas of science and technology like space and vacuum technology and even medicine and biotechnology. Secondary electron emission is a consequence of electron irradiation on materials. We achieve extremely low secondary electron emission yield values smaller than 0.2, even up to incident electron energies ~1 keV, due to an undocumented synergy between neighbouring metal and dielectric domains in composite samples. To investigate this experimental discovery, we propose a simple 3D model where the dielectric and metallic domains are arranged in parallel and interleaved. The proposed surface profile has a triangular shape to model the surface roughness. We obtain a continuous equation to describe the electric field that arises between grounded conductors and charged dielectrics domains. The calculated trajectories of secondary electrons in this 3D geometry are used to predict dynamic secondary emission yield, which strongly depends on the charge accumulated in the dielectric domains. This research paves the way to design new materials of low secondary emission yield, addressing the technological problem not yet resolved to inhibit the electron avalanche in RF equipment that limit their maximum working power.

Since the moon has an extremely rarefied atmosphere, the full spectrum of the electromagnetic radiation of the sun reaches the surface, charging the surface dust and affecting its current charge state. Lunar surface dust thus remains electrostatically charged at all times. Charged lunar dust will adversely affect the operations of most mechanical systems required by manned and unmanned exploration missions. Charged dust will also stubbornly adhere to solar panels and thermal radiators, thus reducing their efficiencies. Researches on the charged lunar dust can help to investigate lunar dusty environment as well as to solve those particle-induced problems by both simulation and experiment in laboratory. In this work, two different charging processes of charged lunar dust in the environment of electron beam and the radiation of ultraviolet source are considered. The computer numerical simulation method is used to analyze these two different charging processes of lunar dust, to explore the charging mechanisms of lunar dusts, and to choose an appropriate way of charging for the lunar environment simulation device in laboratory. On the basis of the classic dust charging equation, the charging equation of a dust in pure electron environment is given for the first time in this work. Meanwhile, the charging process under ultraviolet radiation is discussed and combined with the specific application of charging dusts. A solver of fourth-order Runge-Kutta algorithm is made to solve differential equations under two different irradiation sources. The main simulation results show that:1) in electron environment, the surface dust charge number increases as the particle size and the current intensity of electron guns increase, while the charge number increases as the beam spot radius of electron guns decreases; 2) under ultraviolet radiation, the dust charge number increases with the particle size and irradiance increasing, but charging efficiency is slow. A great dust charge number needs a long time radiation from sun (equivalent to 74 deuterium lamps), which means that more ultraviolet radiation sources are essential to speeding up the experiment in laboratory. Although the calculated efficiency of ultraviolet radiation is lower than electron irradiation, the secondary-electron emission, the scattering and the transmission process of electron irradiation are ignored, which can greatly reduce the efficiency of charging by energetic electron guns in the actual experiment. Therefore, comparing these two charging mechanisms and considering the actual design requirements for the space environment simulation device, charging by lots of ultraviolet radiation is an appropriate scheme for electrification of lunar dusts.

Dust grains immersed into a low-temperature plasma are charged negatively because the electron attachment dominates other charging processes. However, increasing energy of impinging electrons leads to the increase of the yield of secondary emission. When this yield exceeds unity, the grain becomes charged positively. Previous laboratory experiments with electron beams have shown that the surface potential of large grains follows roughly an energy dependence of the secondary emission yield. It means that the grain potential reaches its maximum for hundreds of electronvolts of electron energy and then decreases. Model calculations reveal that the decrease of the grain potential with the electron energy can lead to the reversal of charge sign in a certain range of grain diameters. After this reversal, the grain is charged to the negative potential close to the beam energy. We use of this effect for investigations of electron field emission from nonconducting spheres (glass and melamine formaldehyde resin) with the diameter 4-11 /spl mu/m for glass and 5 and 10 /spl mu/m for resin. Single grains were trapped in a Paul trap and bombarded by the electron beam. The beam energy was changed in a range of 0.3-10 keV. The experimental results confirm the aforementioned expectations and an analysis of these results has shown that: 1) the effective work function for electron field emission from charged nonconducting materials (glass and melamine resin) could be as low as 2 eV, but it can be close to 5 eV as expected for insulating materials. The difference is connected with the charging history. 2) The effect of field dependent secondary emission limits the attainable negative potential.

We provide a detailed description of a model and its computational algorithm for the secondary electron emission process. The model is based on a broad phenomenological fit to data for the secondary emission yield (SEY) and the emitted-energy spectrum. We provide two sets of values for the parameters by fitting our model to two particular data sets, one for copper and the other one for stainless steel. We also present details of the electron-cloud simulation code POSINST that are relevant to the secondary emission process. This note expands on our previously published article.

Studies on the pressed yttrium oxide-tungsten matrix as a possible dispenser cathode material

Secondary electrom emission yield (δ) and the surface work function values (φ) were measured for lead zirconium titanate (PZT) doped with lanthanum, strontium, and niobium. The single pulse method was used in LEED/Auger geometry for measuring the secondary electron emission yield δ while the retarding potential technique was employed for measuring the work function. In view of the application of ceramics as continuous dynodes in electron multipliers, the secondary electron emission and electical conductivity data is analysed for reduced PLZT ceramics. Maximum δ of 2.7 was found to remain unchanged after reduction of PLZT. Dionne's equation was used as a basis for analysis of secondary electron emission measurements to estimate escape depth and emission probability.

The heliosphere is a “bubble” of plasma that forms around the Sun through a pressure balance between the outflowing solar wind and the interstellar medium. The Sun is currently traversing the local interstellar medium at a relative velocity of approximately 26 km s−1. Due to the Sun’s motion, interstellar dust grains present in the interstellar medium are transported through the heliosphere’s boundary, from the upwind direction.Dust grains in a space environment are subject to a variety of charging mechanisms, which result in an overall equilibrium charge on their surface. In the interstellar medium and in the solar wind, the primary charging mechanisms are plasma collection, secondary electron emission, and photoelectric emission. The charge acquired by a dust grain depends on several factors, including the size, composition, and structure of the dust grain itself, as well as on the characteristics of the surrounding environment.The trajectories of charged dust grains are influenced by the magnetic field in the environment they are moving through due to the emerging Lorentz force. When approaching the heliosphere, the interstellar magnetic field starts to get disturbed by the solar wind (heliospheric) magnetic field. The amount of trajectory deflection an inflowing interstellar dust grain experiences depends on its charge-to-mass ratio. Consequently, not all interstellar dust grains enter the solar system.We discuss the dust charging with a particular focus on the influence of the space environment conditions that are expected at different locations throughout the heliosphere, including the boundary regions and including short-term and long-term variations of the environmental conditions due to the solar activity. Using these results, we show the influence of heliospheric properties on the dust grain trajectories at the heliospheric interface in specific. The results will help to understand the physical processes occurring at the boundary of the heliosphere.

This study aims to understand how secondary electron emissions influence the behaviour of dusty plasma sheaths. The analysis is carried out within the framework of a non-extensive Tsallis distribution in the presence of dynamically charged dust particles and an oblique external magnetic field. Two main types of secondary emission are considered: those emitted by the dynamically charged dust grains, which are treated using the Sternglass model, and those emitted from the wall bounding the sheath. These are accelerated within the sheath by its electric potential, and modeled using a half-Maxwellian distribution. The objective of this study is to improve our understanding of the mechanisms that govern complex plasma sheaths. It is observed that the combined effect of these secondary emissions significantly alters the properties of the sheath, particularly the dynamics of the dust, the sheath potential, and the density distribution of charged species. This influence is particularly pronounced at lower values of the non-extensive parameter q of the primary electrons.

Secondary photon emission studies of ion bombarded beryllium

Influence of activation parameters on the thickness of MgO thin film on Ag-3Mg alloy and its secondary electron emission property

The plasma-wall interaction in the presence of strong secondary electron or thermionic emission has been studied theoretically and experimentally both as a basic phenomenon and in relation to numerous plasma applications such as, for example, fusion devices and plasma propulsion. For Hall thrusters, existing fluid models predict that secondary electron emission (SEE) is strong enough to enhance electron energy losses at the walls. According to the kinetic simulations, the electron velocity distribution function in a collisionless thruster plasma is non-Maxwellian, anisotropic, and features beams of secondary electrons emitted from the walls. Under such conditions, the effects of SEE on the plasma can be substantially weaker than predicted by the fluid models. This talk will review previous and recent experimental results, including probe measurements in the Hall thruster with various wall materials, which support the predictions of the kinetic studies. It is also shown that the wall material properties affect the electron cross-field transport in the thruster discharge. We will also discuss how these results can help in implementation of highly efficient and stable plasma regimes of the Hall thrusters.

Abstract. The charging by secondary electron emission (SEE) from particles is known as a significant charging process in astrophysical plasmas. This work aims at evaluating the significance of SEE for charging of meteoric smoke particles (MSPs) in the Earth's polar atmosphere. Here, the atmosphere is subject to a bombardment of energetic electrons from the magnetosphere (and partly the sun). We employ the SEE formalism to MSPs in the upper mesosphere using electron precipitation fluxes for three different precipitation strengths. In addition, we address the possible effect of tertiary electron emission (TEE) from MSPs induced by atmospheric secondary electrons for one precipitation case. The SEE and TEE rates from MSPs of different sizes are compared to plasma attachment and photodetachment and photoionization rates of MSPs. The needed concentration of electrons and ions have been modeled with the Sodankylä Ion and Neutral Chemistry (SIC) model with included electron precipitation spectra as an additional ionization source. We find that secondary electron emission from MSPs is not a relevant charging mechanism for MSPs. The electron attachment to MSPs and photodetachment of negatively charged MSPs are the most important processes also during energetic electron precipitation.

Properties of TiN and TiZrV thin film as a remedy against electron cloud

A new method for the determination of the secondary emission yield of dielectrics is discussed. Results are given for Teflon® , Aclar, Kapton® , and Mylar® . Surfaces of dielectrics irradiated with electrons of energies above 2 keV become negatively charged. For lower energies the number of backscattered primaries plus backward emitted secondaries eventually exceeds that of the incoming primaries. Then the surface can be positively charged. It was recognized that this effect might lead to a simple method for the determination of the total backscatter plus secondary emission yield. This effect is used to determine the total emission yield curve in one run with a single beam energy.