Research On Thermal Performance Of Compact Low-energy High-power LINAC Tube And Collinear Absorbing Load

Low-energy and high-power LINAC is now widely used in industry, agriculture, medical service, military and national security. In order to accommodate the diversification and off-site production of radiation processing products, as well as the complexity and diversity of national anti-terrorism tasks, the irradiation devices are required to be high-power, small-size and high-mobility.Microwave absorbing load of remanent power is an integral part of the accelerator. The traditional dry load which is attached to the end of accelerator tube by using output coupler is the major bottleneck of the miniaturization. The main task of the subject is to research and realize a collinear load which can replace dry load and make accelerator structure compact. The collinear load can bring convenience to fix the focus coils and cooling system and enhance the quality of beam.There are two key points in the realization of high-power collinear load. The first is to find high-attenuation microwave absorbing materials and an appropriate coating technology. The second is to propose a reasonable, energy-saving, low-cost solution to design the structure and parameters of collinear load cooling system.This paper focuses on the second point. At first, thermal performance of accelerating tube and the collinear absorbing load are researched. Based on the results, best cooling method and cooling structure and the most appropriate distribution of absorbing coating are studied, and then the parameters of the cooling system are optimally designed. The research work refers to mechanical engineering, heat transfer theory, electromagnetism and accelerator theoritical and applied technology. Heat-solid-electromagnetic field coupled numerical simulation method is adopted.3D reconstruction method, which is common in CAGD, is employed to-study the frequency changes of the deformed cavities for the first time. In the process of reconstruction, the interpolation skinning surface technology is used to rebuild the deformed geometric model of the accelerating cavities by the finite element model obtained in numerical simulation. The deformed geometric model can be exported to CST Microwave Studio to do the electromagnetic field analysis, so as to realize the structure-electromagnetic field coupled analysis of accelerating cavities in isomerism platform. This method can evaluate the accuracy influence on resonant frequency by thermal deformation, and also provides reliable criterion on the design of collinear load's cooling system. Based on the 3D reconstruction method, the relations between the temperature distribution, the thermal deformation distribution, the frequency changes and the copper loss, the parameters (structure, admittance area, water flux, the temperature of the water) of cooling system is researched in this paper in-depth.Then, a kind of optimization design method of the cooling parameters based on the minimum frequency changes of the cavities is proposed. In this method, the dispersion and overall change of the cavities'frequency can be controlled by changing water flux and inlet temperature of cooling water. It is indicated that compared to the traditional design method based on temperature control, this method reduces the cooling water flux and water pressure difference greatly, and obviously brings down the invested and run cost of cooling system.Cooling strategies of collinear absorbing load coated with Kanthal alloy (resistance-type absorbing material) or sintered FeSiAl alloy (magnetic hysteresis absorbing material) are studied. Then thermal performance of the six-cavity collinear load is researched under the conditions of various remanent power and different water flux. It is shown that the collinear load with Kanthal alloy coatings can only absorb remanent power of lOkW when that water flux is smaller than 3kg/s and the inlet temperature is higher than 20℃. While on the same cooling condition, the collinear load with FeSiAl coatings can absorb the remanent power of 20kW.The overall thermal performance of the accelerating tube with collinear absorbing load is finally analyzed. It is shown that separation of cooling structures for accelerating tube and collinear load can enhance the cooling effect greatly, and also saves energy highly. The two-way cooling structure only brings little effects to joint cavities of accelerating tube and collinear load.The research work is sponsored by the National Natural Science Foundation of China (No.10775128).