Study On One-dimensional Photonic Crystal Resonant Cavity For Klystron

The size of traditional klystron cavity must be reduced with the rise of working frequency, especially when frequency is at terahertz frequencies, cavity machining will become very difficult. Although high-order mode cavity can increase its size, the frequency interval of the adjacent mode and working mode will become narrow. This will produce serious interference to working mode, not only limiting the bandwidth but also intensifying miscellaneous mold oscillation. In view of these disadvantages, we introduced resonant cavity with the photonic crystal structure. Photonic crystal has the photonic band gap, and can imprison electromagnetic wave in the forbidden band while the other frequency electromagnetic waves spread outside the cavity, so photonic crystal can reduce the influence of the adjacent mode. The primary work is described as follows: 1. Study on cylindrical cavity of one-dimensional photonic crystals of x-band klystron.Firstly, one-dimensional photonic crystal structure is designed at 10 GHz band-gap center frequency using HFSS software. Then, the study of one-dimension photonic crystal cylindrical cavity and metal cylindrical cavity was performed under the help of ISFEL3D. The results show that TM910 mode adjacent to TM010 only exists in the outermost layer mediator, and will not interfere with TM010 mode. The frequency interval is 213 MHz. The characteristic impedance (94.9 Ω) of one-dimensional photonic crystal cylindrical cavity is smaller than that (129 Ω) of the metal cylindrical cavity, but the former has better consistency. Besides, little effect is also achieved on TM010 when the one-dimensional photonic crystal cylindrical cavity is connected to drift tubes. This indicates that one-dimensional photonic crystal cylindrical cavity has better ability to resist the disturbance of the drift tubes, which is the precondition for its application in high radio-frequency klystron.2. Study on the terahertz-band coaxial cavity of one-dimensional photonic crystals of klystron.500 GHZ and 650 GHZ band-gap structure of one-dimensional photonic crystal is designed using HFSS software.500 GHZ of one-dimensional photonic crystal structure can limit TM810 mode well. It demonstrates the feasibility that is used in THz wave band klystron of one-dimensional photonic crystals coaxial cavity in theory. But its dielectric layer is only 0.05 mm in thickness, and consequently has no mechanical support, leading to the useless in practical application.650 GHZ coaxial cavity of one-dimensional photonic crystals is composed of two circular dielectric layers arranged alternately, which can be fabricated into thin-film production. The research results show that the one-dimensional photonic-crystal dielectric layer can well lock TM10,1,0 mode. The modes under TM10.1.0 and above to 710 GHz don’t exist in the cavity. This suggests that the one-dimensional photonic crystals coaxial cavity can effectively increase the frequency interval, and reduce the interference between modes. Therefore, one-dimensional photonic-crystal coaxial cavity is better than metal coaxial cavity in terms of eliminating adjacent mode interference. Besides, it has little effect on TM10,1,0 when the one-dimensional photonic crystal coaxial cavity is connected to drift tubes. This means that one-dimensional photonic crystal coaxial cavity has better ability to resist the disturbance of the drift tubes, which is the precondition for its application in klystron. Due to the use of dielectric layer in one-dimensional photonic-crystal coaxial cavity, its characteristic impedances are smaller than metal coaxial cavity with the leaking of electromagnetic field, and its uniformity is also worse. But it will not be a serious impact on the performance of the cavity.