高功率微波与带孔洞腔体非线性耦合的理论研究

THEORETICAL INVESTIGATIONS ON NONLINEAR COUPLINGS OF HIGH POWER MICROWAVES INTO THE CAVITY WITH A HOLE

从Ｍａｘｗｅｌｌ方程组和电子流体方程组出发，研究了高功率微波束与腔体非线性耦合的过程。用时域有限差分方法计算了不同大气条件下的非线性耦合过程。与线性耦合的结果进行比较，总结了一些新的非线性耦合规律。

AbstractWhen high power microwave(HPM)pulses penetrate an aperture,the field strengths aroundthe aperture may be greater than the incident field magnitude,this is often called enhancement ef-fect.When this phenomenon occurs,even if the incident field magnitude is lower than thebreakdown threshold of microwave in the air,breakdown process may occur.Therefore,when oneinvestigates HPM coupling process,you should consider air breakdown. In this paper,westudied the nonlinear mupling processes of HPM beams into the cavity with an aperture.Field variances were described by Maxwell′s equations,and the ionization process was governedby the ion ization rate equation. Usually,electrons′movements were governed by momen-tum-conservation and energy-conservation equations. When we studied this process,we foundthat some electrons′velocities were greater than light velocity in space if the kinetic equation wasnonrelativistic.It can be explained as follows.Those electrons were continuously aceelerated byHPM pulses,and became relativistic. Therefore,we revised the electron movement equations,andlet them include relativistic effects.Using the method of FDTD(finite-difference time-domain),we solved the equations mentioned above via computer simulations,and obtainedsome nonlinear coupling conclusions.(1)Enhancement effect From our calculated results,we found that electric fields around the aperture were greaterthan that of the incident pulse. The enhancement magnitude depended on the aperture shape,size,and the incident HPM parameters.(2)Distribution of electron density Because the electric field coupled into the cavity was weak,and less than the air-breakdownthreshold,the electron densities inside the cavity didn′t change.The electron densities outs ide the aperture wall were very high, and hence the frequency ofelectron-plasma oscillation was very near that of the incident HPM pulse.(3)Tail-erosion phenomenon Beeause HP M pulses induced high-density plasma,tails of the incident long HPM pulsescan′t penetrate the plasma region. this was called tail-erosion phenomenon.