Suppression of secondary emission in a magnetic field using triangular and rectangular surfaces (original) (raw)
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Sharp reduction of the secondary electron emission yield from grooved surfaces
Journal of Applied Physics
The effect of an artificially enhanced rough surface on the secondary electron yield (SEY) was investigated both theoretically and experimentally. Analytical studies on triangular and rectangular grooved surfaces show the connection between the characteristic parameters of a given geometry to the SEY reduction. The effect of a strong magnetic field is also discussed. SEY of grooved samples have been measured and the results agree with particle simulations using a Monte Carlo approach.
Monte Carlo Simulation of Secondary Electron Emission from Rough Surface
Japanese Journal of Applied Physics, 1994
Surface adsorption of N 2 molecules is a critical factor to limit the reduction of secondary electron (SE) yield (SEY) in many fields of applied physics. On the basis of the Polanyi potential theory, we describe a multi-layer N 2 physical adsorption model to arrange the distribution of N 2 molecules adsorbed on a Cu (1 1 0) surface. Considering six scattering types, we used a Monte Carlo method to develop a three-dimensional numerical model that simulated the scattering processes between electrons and adsorbed molecules. Thus, the SEY of a surface covered by an adsorbed layer could be obtained by statistical analysis of the final SE states. We found that the maximum of total SEY decreased exponentially with increasing N 2 pressure between 0 and 0.1 Torr and decreased linearly with increased adsorbed layer thickness between 0 and 10 nm. The reduction in SEY was due mainly to the elastic scattering of large scattering angle and ionization of energy consumption in the scattering processes of electrons and adsorbed molecules. Accordingly, our model and results provide a powerful tool to fully understand the microcosmic mechanism of the SE emission of a metal surface with adsorbed layer.
Influence of the Electric Field on Secondary Electron Emission Yield
AIP Conference Proceedings, 2008
We present results of the investigation of secondary electron emission from spherical amorphous carbon grains of 3 to 6 micrometers in diameter affected by a high surface field. In our experiment, we have applied a technique based on levitation of a single charged grain in the quadrupole trap. This grain was charged by an electron beam with an energy tunable up to 10 keV. During this process, the grain charge is continuously monitored. If the grain is charged by an appropriate energetic electron beam, its charge (and the corresponding surface potential and surface electric field) is set to a value when the yield of secondary emission is equal to unity (crossover point). The investigations reveal that the energy corresponding to the crossover point changes proportionally to the grain potential. This effect was attributed to an increase of the yield of secondary emission due to a large electric field at the grain surface. Moreover, the measurement of the net current on the grain induced by electrons with the energy between first and second crossover points indicates similar increase of the yield.
The Secondary Electron Yield of Technical Materials and its Variation with Surface Treatments
2000
Secondary electron emission of surfaces exposed to oscillating electromagnetic field is at the origin of the multipacting effect that could severely perturb the operation of particle accelerators. This contribution tries to illustrate by measurement results, the origin of the secondary electron emission as well as the main reasons for the discrepancies between technical materials and pure metals. The variation of
A rapid technique for the determination of secondary electron emission yield from complex surfaces
Journal of Applied Physics, 2019
Plasma-wall interaction in the presence of secondary electron emission (SEE) can lead to a degradation and reduction in the performance of plasma devices. Materials with complex surface architectures such as velvet, fuzz, and feathered surfaces have a lower SEE yield than the same materials with a flat surface and can, therefore, be useful for plasma applications. This reduction in the SEE is due to the trapping of secondary electrons in the microcavities formed by complex surfaces. In this paper, we present a rapid method for a simultaneous comparison of the SEE yield and surface properties of materials with different surface architectures. The method uses Scanning Electron Microscopy to simultaneously evaluate the surface morphologies and SEE yield properties for a microarchitectured surface. This technique was applied to carbon velvets, and results show agreement with recent theoretical models and with the direct determination of the SEE yield from measurements of the currents of...
On the dynamics of secondary-electron and anion emission from an surface
Surface Science, 1997
Kinetic energy distributions and absolute yields of negative oxygen ions and secondary electrons resulting from positive ions impacting an aluminum surface have been determined as a function of the oxygen coverage of the surface. The experiments have been carried out with positive sodium ions at collision energies below 500 eV. Both the negative ion and secondary electron yields are observed to be strongly dependent on the oxygen coverage of the aluminum surface. The kinetic energy distributions of the dominant negative ion, O-, peak at approximately 1.0 eV and have a significant high-energy tail. The secondary electron kinetic energy distributions peak between 0.8 1.0 eV, have widths of 1.0 1.5 eV and exhibit no features indicative of discrete spectra. For both the ions and the electrons, the most probable kinetic energy is essentially independent of the impact energy and there is no correlated electron anion emission. A mechanism is proposed to augment the collision cascade in order to model the sputtering of O and the emission of electrons. Finally, the secondary processes are investigated with a partial coverage of sodium which serves to reduce the surface work function.
Engineered surfaces to control secondary electron emission for multipactor suppression
2016 IEEE National Aerospace and Electronics Conference (NAECON) and Ohio Innovation Summit (OIS), 2016
A significant problem for space-based systems is multipactor-an avalanche of electrons caused by repeated secondary electron emission (SEE). The consequences of multipactor range from altering the operation of radio frequency (RF) devices to permanent device damage. Existing efforts to suppress multipactor rely heavily on limiting power levels below a multipactor threshold. 1 This research applies surface micromachining techniques to create porous surfaces to control the secondary electron yield (SEY) of a material for multipactor suppression. Surface characteristics of interest include pore aspect ratio and density. A discussion is provided on the advantage of using electroplating (vice etching) to create porous surfaces for studying the relationships between SEY and pore aspect ratio & density (i.e. porosity). Preventing multipactor through SEY reduction will allow power level restrictions to be eased, leading to more powerful and capable space-based systems.
2013
High secondary electron yield of metallic surfaces used in accelerator and also in space applications is of general concern. In addition to several well-known coating preparation techniques and microscopic or macroscopic mechanical roughness (grooves) which may significantly increase microwave losses the concept of magnetic surface roughness has been proposed recently to lower the effective secondary electron yield (SEY). In this concept a smooth and very good conducting surface with low microwave losses is maintained, but underneath this surface a large number of tiny permanent magnets are located to build a rough magnetic equipotential structure. In this paper we present and discuss measurement of the SEY and the improvement in terms of SEY for different parameter ranges.
Low-Secondary Electron Yield of Ferrromagnetic Materials and Magnetized Surfaces
2010
We are presenting first results of direct measurements of the secondary electron emission yield (SEY) for several magnetic materials like ferrites at energies of primary electrons from 5 to 1000 eV. In order to minimize the impact of surface charging, the primary electron beam had a short pulse modulation of 400ns with a very low repetition rate. This paper discusses a method of developing a secondary-electron-suppressing highly textured ferrite surface with low SEY by depositing a layer of very fine ferrite particles onto a substrate. The experimental results indicate that the SEY of the particulate ferrite surfaces is much lower than that of flat ferrites. In comparison we have confirmed that ordinary carbon coating with rather large grain size returns SEY value close to unity. However, a surface with very finely powdered carbon has a much smaller secondary emission yield of about 0.5, but the adhesion of these carbon powders to the surface is often not reliable enough for many ap...
Emittance, surface structure, and electron emission
Physical Review Special Topics - Accelerators and Beams, 2014
The emittance of high brightness electron sources, particularly field emitters and photocathodes but also thermionic sources, is increased by surface roughness on the emitter. Such structure causes local field enhancement and complicates both the prediction of emittance and the underlying emission models on which such predictions depend. In the present work, a method to find the emission trajectories near regions of high field enhancement is given and applied to emittance predictions for field, photo, and thermal emission for an analytically tractable hemispherical model. The dependence of the emittance on current density, spatial variation, and acceleration close to the emission site is identified and the impact of space charge discussed. The methodology is extensible to field emission from close-spaced wire-like structures in particular and extensions to that configuration are discussed. The models have application to electron sources for high frequency vacuum electronics, high power microwave devices, and Free-Electron Lasers.