To study non-linear relations between field emission current density and temperature at top surface of a cathode microprotrusion, thermal effects on cathode microprotrusion are investigated numerically at various applied electric fields. Enhancement factor of electric field at top surface of microprotrusion is different as ratio of top radius to bottom radius is changed. It leads to obvious difference in temperature distribution in microprotrusion when temperature at microprotrusion peak reaches melting point of cathode material. At a given applied electric field, the smaller the ratio of top radius to bottom radius of microprotrusion, the shorter the time delay of explosive emission. Time delay of explosive emission increases exponentially with decrease of applied electric field.

The atmosphere is a kind of non-uniform media,whose density drops rapidly with the increase of height.In order to simulate transport of gamma ray in high-altitude atmosphere,the media is divided into many uniform layers with different densities.To eliminate error,the number of layers should be as many as possible,which results in a large amount of computation.We propose a method without layering.It samples mass distance to replace step length of particles.The results agree well with those calculated directly by MCNP code.The method increases speed of computation considerably.

A nonorthogonal finite difference time domain algorithm is used to model the excitation and resonance processes of a circular resonator with an excitation aperture,where a Gaussian pulse and a sine modulated Gaussian pulse are used as excitation pulses.Resonant frequencies are analysed by the method of fast Fourier transform.The calculated results agree well with theoretical analyses.Simulation results show that several resonant frequencies nearest to the main ferquency of the excitation pulse are excited.

A physical model is presented for linear coupling of microwave pulses into apertures in cavities. The numerical simulation method of FDTD and absorbing boundary conditions are dis cussed. We calculate coupling processes of microwave pulses into apertures with various size and different positions, and an alyse the dependence of coupling on aperture size and polarization direction of the incident field.