Design of three-Section Traveling Wave Tube

A Terahertz three-section Traveling Wave Tube with folded waveguide Shielded by Photonic Crystals was designed and optimized by CST simulation. The results show that when the working voltage is 13kV, the working current is 56mA, the input signal power is 5mW, the output power is 5.84W and the gain is higher than 30dB at the center operating frequency of 225GHz. Compared with the traditional folded waveguide slow wave structure with the same structural parameter size, the results show that the output power of the slow wave structure with photonic crystals is higher, the gain is bigger and the stability is better

The traveling wave tube is a more mature vacuum terahertz source, but with the increase of the working frequency, the terahertz wave tube faces the problems, such as the narrow band, the low output power and the mode competition. Slow wave circuit is the core part of traveling wave tube, so explore the new interaction mechanism will help solve the above problems. The photonic bandgap (PBG) structure is a new pattern artificial material. The stability of TWT can be enhanced if the operating mode of TWT is within PBG for PhCs have the capability of wave filtering. This paper presents the design and analysis of a three-section traveling Wave Tube with FW circuit shielded by PhC arrays. The gain of the traveling wave tube is improved by using the cascade method. The wedge attenuator and the use of photonic crystals to load the slow wave structure can improve the working stability of the traveling wave tube.

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Photonic crystals are known to provide a very efficient and flexible technology to design electromagnetic waveguides by simply introducing linear defects within the periodic lattice. PhCs are placed outside the SWS and are optimized to have the operating frequency band inside the PBG and the potential oscillation frequencies inside the passband of the PhCs. Dispersion curves and Interaction impedance of the PhC FW slow-wave circuit and the conventional FW slow-wave circuit are given in Fig 1. Fig 1(a) shows that when the phase shift per pitch is the same, the eigen-frequency of the PhC FW slow-wave circuit is higher than that of the conventional FW slow-wave circuit. The interaction impedance of the PhC FW slow-wave circuit is little higher than that of the conventional FW slow-wave circuit and The interaction impedance of the PhC FW slow-wave circuit is 3.7Ȑ at 0.225THz.

In the simulation process, the parameters are set as follows: the injection emitter of the circular electron is selected in the slow-wave circuit model. The electron emitter model of the PIC solver is DC, the number of particles is set to 54, the particle transport energy is set to13 keV, the electron injection current is 56 mA, the electron injection radius is 75 μm (corresponding to a current density of 316 A / cm2), and the electron fill ratio is 69%. PIC solver set port 1 for the excitation 225GHz signal, longitudinal magnetic field of 0.4T uniform magnetic field, can be bound electron. Figure 3 shows the electron energy changes with axial distance. The electrons are modulated over a long distance of the high frequency field. The number of electrons decelerated at the end of the interaction region is significantly more than that of the accelerated and the electronics transfer their energy to the electromagnetic signal.