Study of Coronal Type III Solar Radio Bursts

调查人员将充分评估他们新开发的关于在日冕中产生“III型”无线电发射的机制的概念。主要的工作是产生一个详细的射线追踪分析的伯恩斯坦到快波模式转换过程，以及具体演示的俯仰角散射过程中的高能电子，内在的磁流体湍流的水平和俯仰角散射的程度之间的关系。分析还将考虑与第三类排放有关的其他重要观测方面，如低频截止问题和该机制与第五类排放的相关性。该研究方案的科学目标是研究无线电发射过程，特别是日冕中的第三类爆发，其不稳定机制是在存在内禀磁流体波的情况下由沿着环境磁场传播的高能电子束激发的。该机制涉及热电子回旋谐振模的激发，在文献中称为伯恩斯坦模。这些波的激发是以牺牲电子的自由能为代价的，电子的动量分布函数具有正的垂直斜率。这种特征是由于低频磁流体湍流对流动电子的俯仰角散射造成的，因为它们沿着开放磁场线穿过。激发的伯恩斯坦波然后模式转换成自由空间的X和O模式，并观察到的基本和谐波III型爆发。这个模型与III型爆发的标准发射机制非常不同，III型爆发依赖于光束产生的朗缪尔波，朗缪尔波被非线性地转换为电磁波。标准发射机制有许多困难，特别是在电晕附近应用时。新的机制似乎对解决其中许多问题大有希望。

The investigators will fully assess their newly developed concept regarding the mechanism that generates "type III" radio emission in the solar corona. The main effort is to produce a detailed ray tracing analysis of the Bernstein-to-fast wave mode-conversion process, as well as a concrete demonstration of the pitch-angle scattering process of energetic electrons, the relation between the level of intrinsic hydromagnetic turbulence and the degree of pitch-angle scattering. The analysis will also consider other crucial observational aspects related to type III emissions such as the low-frequency cutoff problem and the relevance of the mechanism to type V emissions. The scientific objective of the research program is to investigate the radio emission process, particularly the type III bursts in the solar corona, in terms of an instability mechanism excited by a beam of energetic electrons propagating along the ambient magnetic field in the presence of intrinsic hydromagnetic waves. This mechanism involves the excitation of thermal electron cyclotron harmonic modes, known as the Bernstein modes in the literature. The excitation of these waves occurs at the expense of free energy in the electrons whose momentum distribution function possesses positive perpendicular slope. Such a feature results from the pitch-angle scattering of streaming electrons by low-frequency hydromagnetic turbulence, as they traverse along the open magnetic field line. The excited Bernstein waves are then mode-converted into free-space X and O modes, and observed as the fundamental and harmonic type III bursts. This model is very different from the standard emission mechanism for type III bursts, which rely on beam-generated Langmuir waves, which are nonlinearly converted to electromagnetic waves. There are many difficulties with the standard emission mechanism, especially when applied near the corona. The new mechanism appears to be promising with respect to many of these problems.