Study on antenna characteristics for wave observation including kinetic effects of space plasma

本研究的目的是通过三维电磁PIC模拟，对磁化空间等离子体中的天线特性进行定量的了解，为未来科学卫星上天线的设计提供帮助。我们首先研究了等离子体鞘对天线阻抗的影响。我们发现，在等温等离子体中，当天线周围形成的离子鞘半径变大时，鞘层对天线阻抗的影响变得很小。接下来，我们研究了从天线表面发射光电子的情况。结果表明，天线阻抗受天线附近光电子密度较高的频率影响。我们最后检查了一个热等离子体案例，发现等离子体频率上的共振变得不那么尖锐了。影响天线特性的另一个重要因素是有效长度，它与电流沿天线的分布有关。然而，在天线的接收模式中，电流分布取决于附加在天线上的负载阻抗，因此有效长度可能会被修改。我们将通过EM-PIC模拟来研究有效长度与负载阻抗以及等离子体环境(包括等离子体鞘、光电子发射和等离子体的有限温度)的依赖关系。

The objectives of the current study is to acquire the quantitative understanding of antenna characteristics in a magnetized space plasma by performing three-dimensional electromagnetic PIC simulations, which will be helpful designing the antenna onboard the future scientific satellite. We first examined the plasma sheath effect to the antenna impedance. We found that the sheath effect on the antenna impedance become weak when the radius of ion sheath formed around the antenna in the isothermal plasma becomes large. Next, we studied a case in which photo-electrons are emitted from the antenna surface. It is found that antenna impedance is affected at the frequency corresponding to the high density of photo-electrons in the vicinity of antenna. We finally examined a hot plasma case and found that the resonance at the plasma frequency becomes less sharp. Another important factor in the antenna characteristics is the effective length which is related to the current distribution along the antenna. In the receiving mode of antenna, however, the current distribution depends on the load impedance attached to the antenna and therefore the effective length may be modified. We will examine the dependency of the effective length on the load impedance as well as the plasma environment including plasma sheath, photo-electron emission, and finite temperature of plasma by performing EM-PIC simulations.