Thermal Analysis Of Microwave Tube

For the development of wider bandwidth, high efficiency, high power, reliability and long lifetime of microwave tube, it is important to improve the performance of the tube by thermal design. The thermal analysis of microwave tube includes the thermal strain and heat dissipation. The thermal strain under high temperature affects the reliability of tube, and poor heat dissipation will decrease the output power and lifetime and limit the development of high power and small size tube.The thermal analysis of traveling-wave tubes (TWT's) and magnetron such as thermal strain and heat dissipation are studied, and the effects of thermal deform on the characters are involved. The proposed methods of theory analysis and simulation are helpful to the thermal design of microwave tube as well as other powerful microwave tube and electronic components. The main studies are as follows:1. Thermal deform and thermal management of magnetronWith the high output power, highest efficiency, smaller size and lower cost, magnetrons are already used not only in the military affairs but also the civil affairs. The heat transfer with great efficiency is important to keep the high power tube work correctly. The thermal performances of the forced convection heat sink for magnetron have calculated for different geometry, different number and material of fins, as well as different air velocity. The effects of some parameters on thermal performance are compared. An optimum asymmetry heat sink for magnetron is presented and evidenced by experiment data. This kind of heat sink enhances heat dissipation economically and decreases the cost largely for the batch production of magnetron, and could be applied to the forced convection heat sink of any other devices. The factors affect the frequency of magnetron are presented, and the thermal shift of frequency resulted from thermal deform is calculated and show agreement with experiment.2. The helix slow-wave tube remains the mainstay of the widely used TWT's because of its exceptionally wide bandwidth and high gain, and takes main pole among the microwave amplifier. But the poor heat transfer of the slow wave structure (SWS) limits its output power. Overheating would affect the reliability and stabilization, and the thermal calculation became necessary. The characters of electronic gun, SWS and collector varies with the temperature are presented.(1) The thermal expansion is bigger on the edge of cathode than that at the centre in axial direction, and the diameter of cathode becomes bigger. These result to the increase of the convergence angle and the decrease of the shot distance, waist radius and perveance of the electron beam, and then increase the rate of area compress.The thermal and structure analysis would kill much time of tube designer because the complex structure of gun, so a simple model is supposed. The results of thermal and structural analysis for complex and simple model were compared. The results of thermal analysis are helpful to the optimizing design of electronic gun.(2)In the thermal analysis of SWS, the temperature study by theory, experiment and simulation are introduced. The factors determined the heat transfer such as the thermal contact resistances between the helix rod and shell are discussed. The equations of estimate temperature rise from shell to helix are developed, and compared with experimentally measured results, the agreement is good. Include the thermal contact resistances and variable thermal conductivity of materials, accurate predictions can be made for given power dissipation on the helix by simulation model established by this paper. These results and the computational techniques can serve as a general guide for TWT's design.The calculations of cold-test circuit performance such as dispersion and on-axis interaction impedance through theory equations and software have been introduced and compared. The computer code MAFIA is used in this analysis to determine the variety of dispersion and on-axis interaction impedance for thermal expansion. The dispersion and on-axis interaction impedance were calculated for several variations on the temperature. The phase velocity decreased uniformly across the bandwidth, and the impedance is varied slightly across the bandwidth. For the different temperature on the whole slow wave structure, so the phase velocity will vary along the SWS. Because the increase of the helical tape width and thickness are very small and could be ignored, so the variation of phase velocity is resulted mainly from the expansion of support rod which made the distortion of helix in radial dimension.(3) The thermal dissipation of TWT collector is explored by simulation. The ways of applying boundary condition that effect the distribution of collector temperature are compared. An overview of the thermal behavior for collectors with different structure and different cooling methods such as free convection, forced convection, single and double channel water cooling, are given. The results of calculation agree with the experimental data..3. According to results of the thermal analysis of microwave tube, the software "Thermal Performance of Helix TWT's" and "Heat Transfer of Magnetron CAD" based on ANSYS are developed for estimate the temperature of helix and magnetron respectively. The software make the tube designer have convenience and rapid tools of thermal analysis, and get good guide for tube thermal design.