中文摘要：

一般认为,Langmuir波（LW）转换为电磁波是太阳Ⅲ型射电爆的产生机制。由电子束流不稳定性可以很容易地激发LW,正向LW和反向LW的相互作用被认为是产生Ⅲ型爆二次谐波的原因,但反向LW的色散方程和产生机制尚未得到充分研究。通过粒子（Particle In Cell,PIC）模拟研究了反向LW的产生机制,发现反向LW不能由电子束流直接激发,其能量基本上是由正向LW散射得到的。然而,电子束流对正向LW的二次谐波有直接放大作用。

英文摘要：

The conversion of Langmuir waves into electromagnetic radiations is an important mechanism of Type Ⅲ solar bursts. Langmuir Waves （LW） can be easily excited by electron-beam instabilities, and they can become backward propagating throuth the wave-wave interaction. Generally, the backward-propagating LW are very important for the second-harmonic waves of Type III solar bursts. In this paper we pay particular attention to the mechanism of the backward-propagating LW as revealed through numerical simulations based on the Partical-in-Cell （PIC） method. We found that ions play a key role to excite the backward-propagating LW, with draw much of their energy from the scattering of the forward-propagating LW. Moreover, an electron beam can hardly generate backward-propagating LW directly, but may directly amplify second-harmonic forward-propagating LW.