太阳Ⅲ型射电暴等离子体辐射的粒子模拟研究

Particle-in-cell simulations of the plasma emission in typeⅢsolar radio bursts

太阳Ⅲ型射电暴由相对论性电子束流沿着开放磁场从日冕向行星际传播所产生.本文利用2.5D相对论性电磁粒子模拟程序,研究了电子束流在非均匀等离子体中的传播,分析了在不同电子束流入射角的情况下,由束流-等离子体不稳定性所产生的等离子体辐射.模拟结果表明,电子束流入射角、等离子体密度梯度以及束流-等离子体相互作用过程中的密度扰动显著影响了静电波和电磁波的时空演化.我们得到了与观测一致的朗缪尔波波包结构,发现了密度扰动在静电波向电磁波的转换过程中起关键作用,并首次模拟出高达五次谐频的电磁辐射,其动态频谱表现出频漂特征和精细结构.这些模拟结果有助于理解太阳射电辐射的产生机制.

TypeⅢsolar radio bursts are produced by relativistic electrons propagating along open magnetic fields from the corona into interplanetary space.We performed 2.5-dimensional particle-in-cell simulations to investigate the plasma emission excited by electron beams with different pitch angles in non-uniform magnetized plasma.The electron pitch angle,plasma density gradient,and density perturbations play important roles in exciting the electrostatic and electromagnetic emissions.In simulations,the Langmuir wave packets are consistent with real observations,and the plasma density perturbations play a key role in the mode conversion,from electrostatic waves to electromagnetic waves.For the first time,we reproduced electromagnetic waves up to the fifth harmonic,which are characterized by drifting frequencies and fine structures.Our simulation results dedicate to shed light on the mechanisms of solar radio emissions.