等离子体填充金属光子晶体Cherenkov辐射源模拟研究

Simulation of cherenkov radiation source in a plasma-filled metallic photonic crystal

等离子体填充能够明显提高真空电子器件的效率和功率,研究等离子体填充器件具有重要的科学价值.本文基于对等离子体填充金属光子晶体慢波结构色散特性的分析,利用粒子模拟方法展示了等离子体填充慢波结构中的注波互作用过程.重点研究了慢波结构中场分布特性、等离子体密度和外部工作条件对频率及输出功率的影响.研究发现,填充一定密度等离子体后,慢波结构内纵向和横向电场强度明显增大,注波互作用增强,输出频率受等离子体影响不大.金属光子晶体结构具有的频率选择特性使器件工作于TM01模态.阴极电压增加使输出功率增大,频率略有增加.引导磁场增加使输出功率先增大后减小,而频率基本不受影响.等离子体填充后器件的输出功率上升,当增加压强至100 m Torr(1 m Torr=0.133 Pa)时,输出功率提高约20%,但只有适当密度下才有较好的角向场分布.通过理论与模拟相结合,发现填充一定密度的等离子体能够提高器件输出功率和效率,为发展新型高功率毫米波振荡辐射源奠定了理论和仿真基础.

Plasma filling can significantly improve the efficiency and power of a vacuum device. In this paper, we first analyze the dispersion properties of a plasma-filled metal-photonic-crystal slow-wave structure（SWS）, and then investigate the interaction procedure between a relativistic electron beam and the Cherenkov radiation in the plasma-filled metallicphotonic-crystal by the particle in cell method. We pay our attention to the influences of plasma density, cathode voltage, and guiding magnetic field on output frequency and power. The results show that the electric field strength in the SWS increases obviously at a fixed plasma density of 50 m Torr（1 m Torr = 0.133 Pa）. The device works at a stable single TM01 mode due to the good mode properties of the metal photonic crystal even if plasma is filled in it.The maximum value of Ezfield along the z axis of the device increases from 46.34 MV/m without plasma to 79 MV/m with plasma. The value along the x axis increases from 136 MV/m without plasma to 185 MV/m with plasma. The working frequency（35.5 GHz） of the device, obtained from simulation, is consistent with the theoretical estimation（35.4GHz）. The power increases with the cathode voltage between 500 k V and 600 k V while the frequency increases only a little. When the magnetic field B increases, the output power first increases and then decreases. But the frequency is not affected due to the dispersion property. The output power of the device increases 20% when the air pressure increases from 0 to 100 m Torr. However, there is a pretty distribution of the field Ezalong the angular direction only in an appropriate plasma density around 50 m Torr. According to the theory and simulation, the output power and efficiency can be improved in an appropriate range of plasma density. These results provide a basis for developing the plasma-filled vacuum devices.