Structure Design And Performance Test Of The Module Of Cryosorption Pump

Cryovacuum system,as one of the subsystems of Negative Neutral Beam Injector(NNBI),is responsible for providing the distributed environment of the vacuum gradient required during beam generation and transmission.A good vacuum environment plays a key role in improving the neutralization efficiency and reducing the reionization loss of the beam.With the development of fusion devices,the high neutralization efficiency of negative neutral beam injection(NNBI)will be an inevitable trend in the future.The cryovacuum system of NNBI has the characteristics of greater gas load,longer continuous gas pumping time,presence of helium and neutron radiation in the pumped gas.Compared with the condensation pump,cryosorption pump has better performance,such as the ultimate pressure is higher;the pumping capacity is larger;it can still adsorb hydrogen at a temperature of about 15K and has a stronger anti-interference ability against cooling supply fluctuations and radiation.Therefore,cryosorption pump becomes the first choice for the cryovacuum system of NNBI.The NNBI beamline vacuum chamber is rectangular in shape.According to the experiences of cryopump on various fusion devices,a modular design idea is proposed to be adopted for the cryosorption pump from the perspective of easy installation and maintenance.The pump body is cuboid in shape,which is assembled by 8 groups of modules with the same structure.Because the beam is generated from one end of an ion source in a vacuum chamber and transmitted to the drift pipe at the other end,the pump body is arranged on both sides of the vacuum chamber wall surface,which is conducive to pumping the gas along the way.The main research contents include cryogenic array,cooling system and support system,etc in the structural design of cryosorption pump.The design of the cryogenic array is the primary issue,which is the core component that undertakes the task of extracting gas.Its design needs to take into account the factors such as pumping speed,heat loads and costs.Combined with these factors,the structural design of cryopanels and radiation baffles in the pump and the combination mode between them are proposed.The idea of series design of cooling pipeline is put forward to improve the cooling effect.The methods of controlling the valve opening and monitoring the outlet pressure difference of liquid helium pipeline are adopted to regulate and control the temperature of liquid nitrogen and liquid helium pipelines,respectively.The support system of pump body and the key components are proposed to solve the fixed problem of pump body to the wall and components to pump body.Finally,the thermal loads of liquid nitrogen pipeline and liquid helium pipeline is calculated theoretically.which provides a reference for the cooling of cryosorption pump.The combination of cryogenic arrays is called the cooling structure.The cooling structure affects transmission probability and radiant heat transfer,both are important parameters that affect the pumping performance and operation economic performance of cryosorption pumps.The transmission probability is almost proportional to the pumping speed,however the refrigeration system of the cryopump can bear the appropriate heat loads.So,the structure design aims to reduce the radiation heat transfer as much as possible on the basis of increasing the pumping speed.Molflow software based on Monte-Carlo principle and Steady-Thermal module of ANSYS are used to analyze the effects of cooling structure number,cryopanels arrangement and structural parameters(L1,L2,L3 andα)on transmission probability and radiation heat transfer.It is determined that the area aspect ratio(h1/L1)between cooling structures is the main factor affecting the transmission probability and radiation heat transfer.Through research,it is determined that the area aspect ratio(h1/L1)between cooling structures is the main factor affecting the transmission probability and radiation heat transfer,and proposed the design principle of reducing h1/L1 and a as much as possible while keeping the radiation doesn’t directly radiate to the third-level cryopanel.Cryopanels and radiation baffles are the main components of the cryosorption pump.The cryopanel at the liquid helium temperature absorbs hydrogen,its isotopes and helium.The radiation baffle is used to block the heat radiation from room temperature and cools the gas molecules reaching the cryopanel,so as to reduce the heat loads of cryopanel.Cryopanels and the radiation baffles shall ensure that the structure don’t leak during the temperature cycle of cooling and heating regeneration.The processing technology of various components has been explored.It is proposed that the laser welding process is adopted for the cryopanel.Vacuum pressure impregnation process is used for the radiation baffle.In order to verify the above requirements of components,the components that experienced temperature cycling are used as the experimental group and those that didn’t experience temperature cycling are used as the control group.Finally,the metallurgical microscope is used to observe the weld surface and the impregnated surface.The results show that the temperature cycle doesn’t cause obvious cracks,which proves that the above process meet the requirements of structural stability.In order to verify the rationality of the cryosorption pump’s structural design,the pumping performance test system of cryosorption pump test prototype is designed and built to study the physical factors that affect the pumping performance according to international standards.The results show that cryosorption pump has excellent pumping performance,which verifies the rationality of the structural design of the cryosorption pump and can meet the requirements of NNBI for vacuum environment.