An improved secondary electrons energy spectrum model and its application in multipactor discharge

Secondary electron emission(SEE)of metal and dielectric materials plays a key role in multipactor discharge,which is a bottle neck problem for high-power satelliate components.Measurements of both the secondary electron yield(SEY)and the secondary electron energy spectrum(SES)are performed on metal samples for an accurate description of the real SEE phenomenon.In order to simplify the fitting process and improve the simulation efficiency,an improved model is proposed for the description of secondary electrons(SE)emitted from the material surface,including true,elastic,and inelastic SE.Embedding the novel SES model into the electromagnetic particle-in-cell method,the electronic resonant multipactor in microwave components is simulated successfully and hence the discharge threshold is predicted.Simulation results of the SES variation in the improved model demonstrate that the multipactor threshold is strongly dependent on SES.In addition,the mutipactor simulation results agree quite well with the experiment for the practical microwave component,while the numerical model of SEY and SES fits well with the sample data taken from the microwave component.

Fast-electron-impact study on excitations of 4d electron of xenon

The electron energy loss spectrum of the 4d excitations of xenon was measured at an incident electron energy of1500 eV and a scattering angle of 6°. Besides the optically allowed transitions of 4d5/2^-1np and 4d3/2^-1np, the optically forbidden transitions of 4d5/2^-1ns, 4d5/2^-1nd, 4d3/2^-1ns, and 4d3/2^-1nd were observed. The measured features are assigned with the help of the calculation by the Cowan Code. The line profile parameters of both optically allowed transitions and optically forbidden ones were determined and compared with the previous available data. It is found that the natural widths of both dipole-allowed and dipole-forbidden excitations are approximately identical, which means the spectator transitions dominate the resonant Auger effect for both dipole-allowed and dipole-forbidden transitions.

The Micro-structural Studies of Ni-BaTiO_3 Nanocomposite Films by TEM and EELS

Epitaxial BaTiO3 films with embedded metallic Ni nanocrystal （Ni-BaTiO3） were successfully fabricated on SrTiO3 （001） single-crystalline substrate through the laser molecular beam epitaxial （L-MBE） technique.High resolution transmission electron microscopy （HRTEM） and electron energy loss spectrum （EELS） with Kramers-Kronig analysis methods were employed to characterize the microstructures,elementary distribution and the electron structure of these films.HRTEM results suggested that the structure of BaTiO3 was tetragonal with lattice parameters of a=0.399 nm and c=0.403 nm.Energy dispersive X-Ray spectroscopy （EDX） confirmed metallic Ni nanocrystal embedded successfully in BaTiO3 epitaxial films.The Ni-BaTiO3 composite films were compound of the epitaxial BaTiO3 （110） layers alternating with Ni NCs array （111） layers.Furthermore,the existence of the misfit dislocations induced by the embedding of Ni nanoparticles was also clearly demonstrated by the HRTEM images.The Ni L2,3 edges of EELS revealed that Ni NCs in their metallic state were embedded uniformly in the BaTiO3 matrix.A chemical shift of about 7 eV regarding L3 edges in the Ni EELS was also observed.The optical band gap of BaTiO3 in these films was about 3.84 eV,higher than 3.55 eV for pure BaTiO3 films at room temperature.

Pulsating aurora - a review

In this review, the observational facts about pulsating aurorae are summarized and discussed in the frame of the recent develpment of the theories which intend to explain the mechanism of auroral pulsations. Although new data are available some key observations in the magnetosphere are still missing in order to identify the wave mode to precipitate electrons into the atmosphere and in order to understand the role of magnetospheric plasma in producing pulsating aurora. It apters that the Coroniti-Kennel or micropulsation theory needs to be re-visited although the so-called flow cyclotron maser model seems to explain many of the characteristics of auroral pulsations.

Monte Carlo simulation of prompt γ-ray spectra from depleted uranium under D-T neutron irradiation and electron recoil spectra in a liquid scintillator detector

To overcome the problem of inefficient computing time and unreliable results in MCNP5 calculation, a two-step method is adopted to calculate the energy deposition of prompt γ-rays in detectors for depleted uranium spherical shells under D-T neutron irradiation. In the first step, the γ-ray spectrum for energy below 7 MeV is calculated by MCNP5 code; secondly, the electron recoil spectrum in a BC501 A liquid scintillator detector is simulated based on EGSnrc Monte Carlo Code with the γ-ray spectrum from the first step as input. The comparison of calculated results with experimental ones shows that the simulations agree well with experiment in the energy region 0.4–3 MeV for the prompt γ-ray spectrum and below 4 MeVee for the electron recoil spectrum. The reliability of the two-step method in this work is validated.