摘要
本文根据ISSE-3飞船对太阳耀斑产生的高能电子流及相关的Langmuir波和Ⅲ型爆的观测结果,讨论了几种激发Langmuir波的线性理论,并得到:1)由于截止频率的限制,经典的双流不稳定性不能放大Langmuir波,而仅使Langmuir波沿磁力线即电子流的方向传播,其群速度等于电子流的平均速度。2)由共振性波粒相互作用可激发Langmuir波,但在Langmuir波的色散方程中必须考虑电子流的影响,从而产生了Langmuir波的两个分支,其中慢Langmuir波的增长率和实测的Langmuir波的增长时标的倒数具有相同的量级。3)由磁化等离子体的Cerenkov共振条件可放大Z模(即慢反常模的纵波分量),其性质与La-ngmuir波有本质的差别。4)从Langmuir振荡的能量守恒条件,可预期实测的Langmuir波的强度基本维持在热辐射的水平(大约只占非热电子平均能量的10^(-6)),确实难以解释相应的Ⅲ型爆发。
The discrepancy between the classical theory of plasma emission and solar type-Ⅲ bursts. is as follows. The intensity of the observed Langmuir waves is low, and the conversion efficiency from the Langmuir waves into the transverse electromagnetic waves is low too. In this paper, the possible mechanisms for the excitation of Langmuir waves are studied and compared with a typical observation of the energetic electron streams and relevant Langmuir waves by the ISSE-3 rocket. The main results are: 1) There is a cut-off frequency for the classical two-stream insta- bility. So the Langmuir waves cannot be excited and they propagate only along magnetic field lines. The order of magnitude of their phase velocity is the same as the average velocity of the energetic electron streams. 2) The resonant wave-particle interaction can excite Langmuir waves. The growth rate or the time scale is consistent with the observation by the ISSE-3 rocket. The Cerenkov resonance can also excite Z-modes (slow extraordinary modes), but the properties of Z-modes are quite different from Langmuir waves. 3) The intensity of Langmuir waves is al- most at the level of the ambient thermal radiation (about one millionth of the average energy of the non-thermal electrons). This is not sufficient to explain the relevant solar type-Ⅲ bursts. A possible mechanism to avoid the discrepancy of the classical theory of plasma emission is the direct excitation of electromagnetic waves by plasma instabilities. The recent researches on this subject are reviewed.
出处
《天文学报》
CSCD
北大核心
1992年第1期101-108,共8页
Acta Astronomica Sinica
