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模拟获得磁化空间等离子体中天线特性的定量理解，这将有助于未来科学卫星上天线的设计。我们首先研究了等离子体鞘层对天线阻抗的影响。我们发现，在等温等离子体中，天线周围形成的鞘层半径越大，鞘层效应对天线阻抗的影响越小。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，在天线附近光电子密度较高的频率处，天线阻抗会受到影响。最后，我们研究了一个热等离子体的情况下，发现在等离子体频率的共振变得不那么尖锐。天线特性中的另一个重要因素是有效长度，其与沿着天线的电流分布有关。然而，在天线的接收模式中，电流分布取决于附接到天线的负载阻抗，因此可以修改有效长度。我们将研究的依赖性的有效长度上的负载阻抗，以及等离子体环境，包括等离子体鞘层，光电子发射，和有限的温度等离子体通过执行EM-PIC模拟。

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.