Yongfeng Kang

Nonparaxial Accelerating Electron Beams

We investigate nonparaxial accelerating electron beams theoretically in two and three dimensions. Starting from the Klein–Gordon equation, we obtain the Helmholtz equation for electron beams. We demonstrate that the electron beams can accelerate along semi-circular, parabolic, and semi-elliptic trajectories. The shape of the trajectory is determined by the input beam, which can be constructed by using phase masks that reflect the shape of the relevant special functions: half-Bessel, Weber, or half-Mathieu. The corresponding self-healing and ballistic-like effects of the nonparaxial accelerating beams are also demonstrated. The depth of the focus of the electron beam can be adjusted by the order of the function that is included in the input. Our investigation enriches the accelerating electron beam family, and provides new choices for improving the resolution of transmission electron microscope images.

Research of electron beam welding focusing deflection system

The combined focusing deflection system is the fundamental part of the electron beam welding system. An improved 12-pole magnetic deflector applied to the combined focusing deflection system is designed and calculated, which can generate a strong deflection field. From the simulation results, this improved deflection system meets the requirements of high scanning frequency and large scanning field. At the same time, an actual 12-pole magnetic deflector is also manufactured and its performance is consistent with the simulation results.

A novel numerical calculation method for electron guns

The problem of initial thermal velocity and the space charge effect of electron guns in numerical simulations have been investigated deeply. In general, the current software can meet the engineering requirements. However, the electrons initial thermal velocity and the space charge effect lack sufficient consideration. The above two factors significantly limit the performances of electron guns. Moreover, the parameters of electron guns are approximated based on a limited number of electron trajectories. Thus, the statistical distribution of the beam electron resulting from its initial thermal velocity is not considered adequately in present software. This paper introduces the equivalent meridional projected trajectory equation and the curvilinear axis evolution theory of the current density of toroidal electron sub-beam, and subsequently the current and charge density distributions in electron guns can be derived through iteration calculation. Based upon, the virtual crossover of an electron gun is determined by its current density distribution. As well as, a relevant numerical algorithm is developed and the related program is modified based on the popular commercial software SOURCE. Tungsten cathode guns, LaB6 cathode guns, field mission guns and Pierce guns are simulated respectively by examples. The calculations prove that the modified software is effective and practical.

A new surface treatment for suppressing multipactor in microwave components

Multipactor breakdown is a serious risk in all types of high power microwave components for satellite applications. In order to suppress multipactor, a new surface treatment with low secondary electron emission yield (SEY) is developed. The silver substrate is etched by ion beam to form micro porous, then several nanometers thick amorphous carbon coating is sputtered. The SEY of both new treated surface and silver substrate are measured. The maximum SEY of treated surface is reduced by 37.1 percent compared to untreated silver substrate. Using measured SEY, the numerical simulation of multipactor threshold is calculated in Full-wave Electromagnetic Simulation Tool. The simulation result shows that the multipactor threshold of treated surface is higher than silver coating.