强磁化等离子体中X模的电磁波透射
Electromagnetic wave transparency of X mode in strongly magnetized plasma
摘要：
从真空落在等离子体介质上的电磁脉冲可以在等离子体中反射或传播，这取决于它是过密还是欠密。然而，在磁化等离子体中，通常存在几个用于EM波的通带和阻带，这取决于磁场相对于传播方向的取向。在等离子体中传播的EM波可以在等离子体中激发静电扰动[1，2]。在这项工作中，粒子在细胞模拟已经进行了说明完全透明的电磁波传播内的强磁化等离子体。外部磁场被选择为垂直于电磁波的波传播方向和电场，这是X模式配置。尽管存在带电的电子和离子物种，等离子体介质表现得像真空。借助于粒子漂移可以理解这种观察。结果表明，虽然两种粒子在电磁场的影响下运动，但它们的运动不会导致任何电荷或电流源改变介质中传播的电磁波的色散关系。此外，它也表明，在这种制度的电磁波的阻带收缩到零宽度的谐振点和截止点彼此接近。因此，在这种强磁化的情况下，对EM辐射的透明性似乎是一种规范。这可能在天体物理学场景中具有重要意义。例如，围绕在恒星和磁星周围的等离子体经常被强磁场穿透。
英文摘要：
An Electromagnetic (EM) pulse falling on a plasma medium from vacuum can either reflect or propagate inside the plasma depending on whether it is overdense or underdense. In a magnetised plasma, however, there are usually several pass and stop bands for the EM wave depending on the orientation of the magnetic field with respect to the propagation direction. The EM wave while propagating in a plasma can excite electrostatic disturbances in the plasma [1, 2]. In this work Particle - In - Cell simulations have been carried out to illustrate the complete transparency of the EM wave propagation inside a strongly magnetised plasma. The external magnetic field is chosen to be perpendicular to both the wave propagation direction and the electric field of the EM wave, which is the X mode configuration. Despite the presence of charged electron and ion species the plasma medium behaves like a vacuum. The observation is understood with the help of particle drifts. It is shown that though the two particle species move under the influence of EM fields their motion does not lead to any charge or current source to alter the dispersion relation of the EM wave propagating in the medium. Furthermore, it is also shown that the stop band for EM wave in this regime shrinks to a zero width as both the resonance and cut-off points approach each other. Thus transparency to the EM radiation in such a strongly magnetised case appears to be a norm. This may have important implications in astrophysical scenarios. For instance, the plasma surrounding objects like pulsars and magnetars is often threaded with strong magnetic fields.
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