Analysis Of Electromagnetic Characteristics Of An Improved Multisection Gyrotron Oscillator

As a terahertz radiation source with great potential applications,the frequencytunable gyrotron has received widespread attention.Many technical fields using gyrotron will be further boomed with the development of the frequency-tunable gyrotron.By exciting a series of modes only with different axial index,the frequency-tunability of gyrotron can be realised.The gyrotron overcomes the scaling effect,so that it can work with a larger beam-wave interaction cavity.Then,by improving the cavity structure,it becomes possible to improve the frequency-tunability of the gyrotron.The improvement of the resonant cavity involves the input section,the interaction section and the output section in the traditional three-section cavity.Improvement to the input section and output section is to add the up-tapered cylindrical waveguide;the improvement of the interaction section is to change its angle and maintains its length unchanged.Proper improved cavity structure will reduce the starting current for highorder axial modes and increase the starting current for low-order axial modes.Therefore,the frequency tunable bandwidth of the gyrotron becomes wider under certain operating conditions.The main work of this article is as follows:1.With the first-order transmission line equation and the boundary conditions,the resonance frequencies and the diffractive factor of the volume,gallery and symmetric modes are investigated.The expression of the ohmic factor is derived,then the ohmic factor of different modes is obtained,and the total factor is obtained with the diffractive factor of different modes.2.In the different improved cavities,the changes of resonance frequency,the diffractive factor,the ohmic factor,and the total factor of the three kinds of modes mentioned above are analyzed.It is obtained that the structure improvement of the input section,the structure improvement of the interaction section and the structure improvement of the output section have different effects on the parameters above,which provides a basis for the design of the improved gyrotron cavity.3.To calculate the effective length of the gyrotron cavity,two ideas are given: one is based on the scattering matrix and the other is based on the simulation software.In this paper,the effective length of the gyrotron cavity is simply analyzed by using the simulation method.4.Based on the investigation above,an improved gyrotron resonat cavity is designed.Compared with the traditional three-sections cavity,the frequency tunability in an improved gyrotron resonant cavity can be enhanced..