A 2D numerical simulation program is developed for nonlinear evolution of magneto-Rayleigh-Taylor instability(MRTI). Based on an ideal magnetohydrodynamic model, a 5th WENO scheme is employed to calculate MHD equations and a projection scheme is used to clean spurious magnetic field divergence. The method is validated with MRTI compared with theory of linear stability. It is shown that the vertical magnetic field suppresses evidently MRTI in both linear and nonlinear stages. The parallel magnetic field has weak effect on MRTI in linear stage. However, it reduces remarkably Kelvin-Helmholtz instability and overall instability in nonlinear regime. High order harmonic occurs in the nonlinear evolution of single mode, and many modes except fundamental modes and harmonic occur in the evolution of double modes. In MRT evolution of multi-mode seeds inverse cascade occur, which means that perturbations evolve from short wavelength to long wavelength in the nonlinear stage.

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.

With Fokker-Plank equation of pitch-angle diffusion,a numerical method for atmospheric diffusion loss of radiation belt trapped electrons is shown.Flux and energy spectrum are calculated as atmospheric scattering of fission β spectrum electrons injected in radiation belt by high altitude nuclear detonation.Diffusion due to atmospheric scattering is remarkable as L < 1.3.Low energy electrons are removed more rapidly than those with high energy.Electron flux decays rapidly at an initial phase and then decays gradually as an exponential function of time.

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.

Charge transfer in He⁺-H^- collisions is investigated using two-center atomic orbital close-coupling(TC-AOCC) method.All bound states of He⁺ (nl) with n≤7,as well as 1s bound states and ns(n=2~6) quasi-continuum states of H^- are included in the AOCC basis.Energies of bound states calculated are in good agreement with NIST data and theoretical results.The total and state-selective cross sections are calculated within a range of energy from 4 to 400 keV.For low-energy collisions,dominant capturing channels are those with quantum numbers n=3-5.With increasing incident energies,transfer of charge to n=2 becomes the dominant reaction.Moreover,for low-energy collisions,cross sections for electrons capture to higher-l states are bigger than that to lower l states.For high-energy collisions,dominant channel is to l=1 states.Charge exchange spectrum due to electron captured to excited states is calculated.Importance of cascade effects is found.

We develop a general-purpose two-dimensional semiconductor simulator (GSS),by which the drift-diffusion model and hydrodynamic model are calculated.It calculates steady-state and transient responses of the devices with different materials structures and is applied to an NPN transistor and MESFET.IV curves,electron density distribution and temperature variation are obtained.

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.