Research On Vacuum System Design For Beamlines

The beamline is a vacuum-optical composite system by which the synchrotron radition light is transmitted to the experimental station. The vacuum system is the basement of it. It is only the vacuum environment where the synchrotron light can be transmitted to the corresponding experimental station by optical elements. Therefore, the main goal of beamlines vacuum system is to obtain and maintain an reasonable vacuum environment, keep it running steadily.There are various of vacuum and optical components in the beamline vacuum systems, thus a pumping system would be needed for removing the air from the system. Consequently, to set up a required beamline vacuum system, engineers have to calculate the data of trial system pressure, the pumping speed of the pump, pipe geometric parameters such as size and extraction again and again, based on the known conditions. In the meantime, in order to satisfy the requirement of scientific experiment, the designing must be high accurate and adept in the complicated condition of the beamline. Therefore, several key points in the design of beamline vacuum system has important scientific research value.At present, when the domestic vacuum practitioners calculate the related parameters of all kinds of vacuum system, some of the used formulas are semi-empirical while some others are old、backward and even deviating from the actual situation. Unreasonable ratio of the vacuum equipments would also cause many problems in the subsequent work, such as the mismatching of the pipe size, insufficient speed of main pump and so on. This paper discusses about the viscous flow pipe under the average stress values. Through the analysis we can see that when the pumping speed of vacuum pump is small or pipe is relatively short, the speed value approximates to constant and the error is very small; but in the beam line of vacuum system, the pipeline is in slender shape, namely, the greater the pumping speed of pump error is, the greater the average pressure error values. In addition, under the molecular flow regime, due to the special structure, some beam line formulas used for calculating the transmission probability as well as some calculation methods are not applicable to the steady type vacuum system. Therefore, this article studied the viscous and molecular flow conductance and transmission probability.In this paper, we use Nawyn-Meyer method to calaculate a lot about the transmission probabilities of length-diameter ratio from 0.01 to 300. We also analysis the errors produced by n and the errors produced by length-diameter ratio in same n values. Straight round pipe geometric factor expression was deduced for the first time, and elaborated the reflection coefficient r is not equal to 1 under the condition of the influencing factors of transfer probability calculation. Through calculating the European atomic energy research institute Molflow+software in this paper, the calculation results between the length-diameter ratio of 0.01～5 error after the decimal point 6, the length-diameter ratio between 6～300, error in 5 decimal places.In this paper, "beaming effect" has been proved with combination of equivalent diameter and combination of unequal diameter pipeline transmission probabilities, by changing the ssticking factor of enter and exit surface, we used under different adhesive chance only by the entry, exit and affected by into, exit at the same time the transmission probability values (length to diameter ratio5. In the mean time, the effect of the slenderness ratio on the transmission probability value under the same adhesive probability was also researched. Range on the basis, the diameter combination probability calculation formula of pipeline transmission has been developed. This paper discusses differences among the current popular Monte Carlo method、the analytic method and numerical method, points out the error factor that restricts the Monte Carlo method. At the last, this paper illustrates the use-method of the Molflow+software based on the Monte Carlo algorithm and attention points for the accurate transmission probability.In addition, this paper, by using the CFX software, simulates the slender pipe under vacuum, based on the value of each observation point in the pipeline pressure points, and thus calculates the average pressure pipeline at some point and then calculates the slender pipe flow conductivity value. After that, with VacMaster Demo, large amounts of data have been carried out to verify the accuracy of the formula.The results show that provided by using CFX software to simulate the vacuum pipeline suction, calculation error margin of the pipe pressure is 13%～17% on average.Through the research of the above three questions, the designer can get more accurate flow conductance and transmission probability in viscous flow state and the molecular flow regime.And slender beam line of vacuum system pipeline and various combinations with diameter ranging pipe flow calculation to provide theoretical basis and guidance method. It is notable that the related research in this paper is not only applicable for beamline vacuum system, but also would guide the general computational work.