The propagation of vortex electromagnetic waves in plasma

At present, there have been many theoretical and experimental researches on the generation methods and applications of vortex electromagnetic waves, but the research on its propagation process is still very lacking, especially the research on the propagation process in ionospheric plasma. In this paper, a finite-difference time-domain method model in a cylindrical coordinate system is established, and the boundary absorption method in a cylindrical coordinate system is deduced. On this basis, the propagation process of vortex electromagnetic waves in vacuum and plasma is calculated, and the space-time evolution process of plasma density under the action of vortex electromagnetic waves is simulated. The simulation results show that the shape of the vortex will not change when the vortex electromagnetic wave generated by the array antenna model propagates in a vacuum. In the plasma medium, the propagation of vortex waves still follows the linear theory, and when vortex waves encounter the plasma of the cut-off frequency, there will be obvious reflections and a standing wave will be generated. At the same time, the vortex wave in the plasma can still maintain the vortex shape; the linear effect of the vortex wave on the plasma makes the plasma also present a vortex state, which is consistent with the observations in the experiment. The above simulation results can provide theoretical support for the experiments of vortex electromagnetic waves heating the ionosphere and applications in shortwave communications in the future. The propagation model of vortex waves in plasma established in this paper also lays the foundation for further research on the nonlinear interaction between vortex waves and plasma.