Nonlinear Generation Mechanism of EMIC Falling Tone Emissions
Nonlinear Generation Mechanism of EMIC Falling Tone Emissions
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DOI：
10.1002/2017ja023883
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发表时间：
2017-10-01
影响因子：
2.8
通讯作者：
Omura, Yoshiharu
中科院分区：
文献类型：
--
作者：
Shoji, Masafumi;Omura, Yoshiharu
我们进行了自洽混合模拟，成功地再现了音调频率下降的电磁离子回旋加速器（EMIC）发射。混合仿真是在抛物线型环境磁场下实现的。在模拟中，通过非线性波增长产生强氧带位辐射。冷离子密度是由正向和反向传播的氧带位波诱导的静电结构调制的。随着氧带的增长，氦带波也随着增长，因为最初是线性增长，然后是非线性增长。冷等离子体密度调制影响氦带波的非线性增长，氦带发射出现短波包。短波包有效地捕获高能质子，在速度相空间中产生电磁质子丘。质子山形成非线性共振电流，导致主位波的频率下降。我们发现高能质子的速度分布函数有很强的变形，这是由于质子山被共振速度的增加所引导。
We have conducted a self-consistent hybrid simulation, successfully reproducing electromagnetic ion cyclotron (EMIC) emissions with falling tone frequencies. The hybrid simulation is implemented with a parabolic ambient magnetic field. In the simulation, strong oxygen band EMIC emissions are generated through nonlinear wave growth. The cold ion density is modulated by electrostatic structures which are induced by the forward and backward propagating oxygen band EMIC waves. Along with the growth of the oxygen band, the helium band waves also grow because of the initial linear growth followed by the nonlinear growth. The nonlinear growth of the helium band waves is affected by the cold plasma density modulation, and there appear short wave packets of helium band emissions. The short wave packets entrap energetic protons efficiently, resulting in electromagnetic proton hills in the velocity phase space. The proton hill forms a nonlinear resonant current causing the falling frequency of the EMIC waves. We find strong deformation of the velocity distribution function of the energetic protons due to the proton hill being guided by the increasing resonance velocity.