磁化等离子体鞘套内太赫兹波传播特性的研究

Recently China paid great attention to the development of its technologies of ballistic missile, manned space engineering and the hypersonic cruise flight. To find the mitigation scheme for the blackout problem became a significant and urgent concern for the strategy of Chinese national defense and technology. The terahertz (THz) communication is considered as an effective mitigation scheme for the blackout problem. However, due to the significant energy loss of THz waves in both neutral atmosphere and plasma sheaths, the THz waves are not always able to penetrate the plasma sheath effectively. In the present project a new idea to mitigate the blackout is presented: the transmission rates of THz waves at atmospheric window frequencies (<1THz) in plasma sheaths could be enhanced by the implementation of onboard instrument which could generate strong electromagnetic field, since the onboard electromagnetic field reduces the electron density and increase the transmission rate for the THz waves. In such a case the blackout could be mitigated. In the present project, a new magnetized hypersonic fluid model will be developed in order to investigate the time evolution of the magnetized plasma sheath. Based on the new model the propagation properties of THz waves in magnetized plasma sheaths will be studied. Furthermore, the generation and the evolution of turbulence in magnetized plasma sheaths will be investigated based on the new model. Also, the impact of the turbulent flow on the propagation properties of THz waves in magnetized plasma sheaths will be studied. The present research project will establish the theoretical basis for the new idea for blackout mitigation.

近年来我国弹道导弹、载人航天和长航时高超音速飞行器技术迅猛发展，解决等离子体鞘套造成的黑障问题成为国防和科技发展的迫切需求。太赫兹通讯被认为是解决黑障问题的有效途径之一。然而太赫兹波在大气层和等离子体鞘套内传播时存在能量衰减，难以有效穿透等离子体鞘套层。本项目中提出了应对黑障问题的新思路：基于大气窗口频率(<1THz)的太赫兹通讯辅以机载强电磁场，降低等离子体鞘套的局部电子密度，提高太赫兹波在鞘套内的透射率，从而削弱黑障对通讯的影响。本项目拟在前期研究基础上建立新的磁化等离子体鞘套随时间演化的流体动力学模型以及太赫兹波在磁化等离子体鞘套内的传播模型，研究太赫兹波在磁化等离子体鞘套内的传播特性。除此以外，本项目拟深入研究磁化等离子体鞘套内湍流生成和演化的过程及机制，以及湍流对太赫兹波传播特性的影响。本项目的研究将为新的黑障应对方法奠定理论基础。

本项目的研究主要针对再入航天器和高超音速飞行器通信黑障问题开展，提出了太赫兹通信加强电磁场调控再入航天器等离子体鞘套消减通信黑障的新思路，并围绕该思路，从磁化/非磁化太赫兹波传播特性、太赫兹通信信号体制设计、太赫兹天线设计与安装位置等角度开展研究，并基于本项目的研究，为未来高超音速飞行器器载太赫兹通信系统设计提出了建议。本研究的主要内容包括：太赫兹电磁波在非磁化/磁化等离子体鞘套中的传播特性、飞行器外形和飞航条件对太赫兹波传播的影响、太赫兹调制信号在等离子体鞘套中的传输特性及其对通信系统的影响、应用于高超音速飞行器和再入航天器的器载太赫兹天线设计理论。本研究首次发现了等离子体鞘套中“间断面”结构造成的反射衰减，并对其物理机制进行了分析。此外，研究发现，从抑制太赫兹波衰减和提高通信系统稳定性角度出发，器载太赫兹天线应安装在飞行器侧壁靠近尾部区域。太赫兹信号调制方式应采用调频或调相模式，其中调相模式优于调频模式。此外，研究发现了磁化等离子体鞘套中太赫兹波的非线性传播现象。本研究亦对器载太赫兹天线理论开展了研究，发现了天线性能劣化现象，并对其物理机制进行了分析。根据本研究，建议器载太赫兹通信系统采用0.14THz载波，辅以外加强电磁场，信号采用调频或调相模式，天线指向和增益可调，以最大限度消减通信黑障带来的影响。

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