The Spray Shield Tube

Secondary electron (SE) emission (SEE) from material surfaces is a frequent phenomenon in space and vacuum environments. SEE modulation is important since it governs the performance of some devices such as electronic multipliers or induces some detrimental effects such as multipactors. Surface coating has been reported to modulate SEE effectively, whereas SEE behaviors of coating structures are not clearly understood yet, and the appropriate theory to describe SEE characteristics quantitatively for coating structures is less developed so far. Here, we have prepared four alumina coatings possessing various thicknesses to research the SEE characteristics of coating structures and have shown how the coating thickness affects the SEE behaviors. Besides, by considering coating/substrate as an ideal double-layer structure, we have derived several equations to describe the producing, transmitting, and escaping processes of excited inner SEs and finally constructed a unidimensional SEE model for double-layer structures. The model is applicable to reveal the dependence of true SE yield (TSEY) on the top and bottom layers’ physical properties and estimate TSEY proportions contributed by the top and bottom layers at random energy points. By employing the concept, SEE characteristics of Al2O3/Si, MgO/Si, and TiO2/Si double-layer structures have been quantitatively interpreted. Moreover, the abnormal SEY curve with a double-hump shape, which is induced by the peak position distinction of SiO2/Si structures, can also be explained. This work is of great significance to comprehend TSEY modulating regularities of various double-layer structures applied in surface engineering.

The investigation of controllable secondary electron emission from single particles

We studied how to measure the secondary electron emission (SEE) of metal and insulating materials used for satellite thermal insulation or other such purposes. SEE yield measurement is very important for analyzing charge accumulation on the satellite surfaces due to the space environment because electron emission due to irradiated electrons influences the amount of surface charge. Therefore, we tried to measure the SEE yield. To measure SEE, we used an improved SEM system for SEE measurement that has a beam blanking unit and a Faraday cup. From this system, we can obtain the characteristics of the SEE yield from insulation materials irradiated by an electron beam with an energy of 600eV to 5keV. In this report, we introduce the SEE yield measurement results of reference materials (Au, Ag and Quartz glass) and insulating materials. From those results, we discuss the characteristics of SEE that depend on each material. Furthermore, we also propose a future plan of SEE measurement for satellite materials.

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.

Summary form only given. Secondary electron emission (SEE) can potentially lead to beam instabilities, material degradation and r.f. breakdown. The past SEE studies have deduced secondary electron yield by invoking a conservation of charge without the need to experimentally account for all measurables. In the spatial distribution studies of SEE, one may not invoke conservation of charge without some knowledge leading to wall loss effects. An electron gun in the SEE test stand at UNLV directs the primary electron beam through a beam drift tube piercing the center of a particle position detector with controlling grid towards the sample under test. Secondary electrons emitted by the sample either drift freely or are drawn by a grid potential to the particle position detector. The location and number of electrons impinging on the detector records the number of electrons and the locations of electron impact. Low primary beam currents are necessary in order to perform these measurements within the resolution of the detector. Because the detector surface is flat and finite in dimension, some loss to the chamber walls will result. Consequential SEE loss to the walls is not measurable in a noise environment even if the experimental apparatus (the SEE test stand) is isolated from the earth ground. To monitor the primary beam current, a C shaped ferromagnetic core coil fitted to the beam drift tube was designed to divert the primary beam to the beam drift tube for measurement with minimal SEE loss from the tube. Assuming successive shots are similar, the total number of incident charge can be deduced statistically. The coil current is then changed to partially null the Earth's magnetic field when experiments are performed. Beam drift tube, grid, and sample currents are monitored and integrated to yield the number of charges collected by each component over time. Along with time resolved, spatially distributed, SEE count from the detector, wall loss may be deduced by invoking conservation of charge. Spatial distributions of secondary electron yield and secondary' electron emission wall loss counts will be reported. Such distributions offer insights in determining the initial conditions on the emitted secondary electrons.

We studied measurement of secondary electron emission (SEE) of metal and insulating materials used for satellite thermal insulation or other such purposes. The SEE yield measurement is very important for analyzing charge accumulation on satellite surfaces for a space environment because electron emission related to irradiated electrons influences the amount of surface charge. Therefore, we tried to measure the SEE yield. Furthermore, we must consider degradation phenomena of surface materials for spacecraft caused by radioactive rays. According to the degradation of materials, those SEE yields might change compared to a non-degradation sample. Therefore, we tried to measure the SEE yields of surface materials for spacecraft which are treated using the degradation process. For preparing a degradation sample, those samples were irradiated by an electron beam and UV to simulate degradation in a space environment. We take three irradiation conditions for electron beam and UV irradiation that related with GEO and operating period. This report introduce a few results of the SEE yield of the satellite materials applied degradation process simulated space environment and discuss the relationship between the SEE yields and sample degradation when irradiated by an e-beam and UV. Furthermore, we also introduce the new SEE measurement system which can irradiated electron with an energy under 0.6 keV.

Secondary electron emission and surface potential of SiO 2 film surface by negative ion bombardment

Fast and slow decay of ion beam induced electron emission in boron doped hydrogenated CVD diamond films

Anomalous secondary electron emission of metallic surfaces exposed to a Glow Discharge plasma

Planar 1-dimensional samples of 2.815 mm thick polymethylmethacrylate (PMMA) were irradiated in vacuum by 1 MeV electrons at constant intensity under three conditions of electrode attachment. Electrodes were either painted on the surface or spaced in vacuum 6.3 mm from the surface. Currents to the electrodes were monitored during the irradiation. The radiation dose penetrating the insulator was also monitored. As the radiation proceeded, the insulators became charged and modified the depth of penetration of the 1 MeV electrons. A simulation code predicts the correct electrode currents and penetrating dose rate only if one allows the low energy secondary electron emission to be a strong function of the electric field just inside the insulator PMMA surface. Secondary emission is enhanced more than a factor of ten with the surfaces at 10 kV/cm.

Effect of Cs and Li atom adsorption on MgO: Secondary emission and work function

The effect of ion doping on the secondary emission characteristics of Mo, Pd and Pd-Ba alloy has been investigated. It was found that as a result of doping with low-energy barium ions, an intermetallic compound of the Pd-Ba type is formed in the Pd surface layer. The formation of a chemical compound between the substrate and the dopant contributes to a significant (threefold) increase in the secondary electron emission (SEE) coefficient. It was found that the Pd and Pd-Ba samples after doping with a large dose of Ba+ ions have almost the same secondary emission parameters. Doping of Pd-Ba first with barium ions, then with oxygen ions with energy of E0≤1 keV leads to a significant increase in the secondary electron emission (SEE) coefficient.

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.

Secondary electron emission from single-walled carbon nanotubes

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.