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太阳Ⅲ型暴与反向Langmuir波的产生

ISSN号：0001-5245
期刊名称：《天文学报》
时间：0
分类：P182[天文地球—天文学]
作者机构：[1]中国科学院紫金山天文台,南京210008, [2]中国科学院研究生院,北京100871
相关基金：国家自然科学基金（10333030）资助项目

关键词：太阳, 射电辐射, 物理数据与过程, 等离子体, 辐射机制, 方法, 数值, Sun： Radio Radiation, Physical Data and Processes： Plasmas, Methods：Numerical

中文摘要：

一般认为，Langmuir波（LW）转换为电磁波是太阳Ⅲ型射电暴的产生机制．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型暴二次谐波的原因，但反向LW的色散方程和产生机制尚未得到充分研究．对含有温度的双流不稳定性的方程进行了解析求解，发现温度和柬流速度分别对反向和正向LW色散关系具有显著影响，并采用粒子模拟（PIC）方法部分证实了解析推导的结果．通过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，其能量基本上都是由正向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 dispersion relation of the Langmuir Waves （LW） is analytically studied. And also the generating mechanism of the backward propagating LW and the second harmonic LW is studied by particle in cell （PIC） simulations. This paper focus on the study of plasma radiation mechanism. The dispersion relation and mechanism of the backward propagating LW are carefully studied. Generally, the conversion of LW into electromagnetic radiations is an important mechanism of solar type Ⅲ bursts. LW can be easily excited by electron beam instability. The second harmonic waves of type Ⅲ bursts are produced through the coalescence of forward and backward propagating LW, which are studied in this paper analytically and numerically, in the equations of two stream instability with thermal velocity. It is found that the dispersion relation of the forward propagating LW strongly depends on the beam speed, and dispersion relation of the backward propagating LW only varies with the thermal velocity, when the other parameters are fixed. The analytical results are partly confirmed by the particle in cell （PIC） simulations. It is confirmed that the ions play a key role in exiting the backward propagating Langmuir waves. The PIC simulations shows that the dispersion relation strongly depends on the plasma temperature. The slopes of both sides of dispersion curves increase with the temperature. The speed of beam elec- trons only has a weak influence on the dispersion curves in both of k 〉 0 and k 〈 0 sides. We also analyze the mechanism of the generation of the backward propagating LW by using PIC simulations. We use the forward propagating LW instead of the beam electrons, as the free energy to excite the backward propagating LW and the forward propagating LW at the second harmonic. It is found that the electron beam can hardly convert into backward LW directly, but it can partly amplify the second harmonic LW directly.

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