Study Of The Beam Pipe And Its Thermal Controlling System In Beijing Electron Positron Collider

In order to keep up the priority to the high energy physics research in the world, our country has upgraded the Beijing Electron Positron Collider to BEPCII. The Beijing Spectrometer, which is a large-scale detector of BEPC, has been upgraded to BESIII accordingly. The beam pipe, only which connects the BESIII and the accelerator, is located in the centre of the BESIII. The electrons and positrons collide at the centre of the beam pipe. When the BEPCII operates, there are uniform high order module heat load and zonal synchrotron radiation heat load on the inner face of the beam pipe. The luminosity of the upgraded BEPCII is about 100 times than before, which results in the heat loads on the inner face of the beam pipe to increase greatly. The working conditions of the Drift Chamber, which is a sub-detector nearest to the beam pipe in the BESIII, require the temperature of the beam pipe to be controlled strictly.Aim at the detecting requirement of the BESIII, the beam pipe and its thermal controlling system were studied deeply in this paper. This study mainly included the following innovations. (1) A reasonable cooling structure of the beam pipe was designed according to the requirement of the BEPCII experiments. An effective measure for controlling the temperature on the transition sects without cooling was put forward. The first suit of beam pipe system with the function of temperature controlling was developed successfully inland. (2) In order to assure the reliably of beam pipe for long time working, the cooling system for the beam pipe was developed to control the uncertain and stochastic heat loads in the beam pipe by the scheme of fixing flow rates and compensating powers. This system has the properties of a high precise and a high reliability compared with the overseas cooling system for beam pipe, which can satisfy the requirement of the BEPCII experiment. (3) A complex finite element model of beam pipe was built, which includes the heat transfer between two kinds of fluid and several metals and the turbulent flow and laminar flow in the different regions. The thermal contact conductances between different metals were considered. The cooling process of the beam pipe was simulated correctly by this model. The influences caused by some main factors on the temperature field of the beam pipe were studied, which supply the theoretic support and direction for the reliable use of the beam pipe.The beam pipe was divided into a center beryllium pipe and two extension copper pipes according to the requirements of the high energy physics study in this paper. Considering the ten years designed lives of the beam pipe, The spark machining oil no. 1 with little erodibility to beryllium was selected to cool the centre beryllium pipe and the de-ionized water was adopted to cool the extension copper pipes. The mathematical models for fluid flow and heat transfer were built based the working conditions of the beam pipe in this paper. The finite element method was used to calculate the cooling parameters for the centre beryllium pipe and the extension copper pipes, respectively. The safe pressure of the inlet for the cooling oil and the limited value for the temperature of the inner beryllium pipe were confirmed. Based the detecting requirement of the BESIII and the safety of the beam pipe, the optimum width of the cooling channel and the optimum flow rate of the cooling oil were selected. The safe pressure of the inlet of the cooling water for the extension copper pipes was checked. The optimum flow rate of the cooling water was affirmed, which can satisfy the temperature controlling requirement for the outer face of the extension copper pipes.The cooling system for the beam pipe was developed according to the requirement of the outer face temperature controlling of the beam pipe. The programmable logic controller (PLC) and the monitoring and controlling system on the remote computer were used to collect and control the parameters of the cooling system, such as temperatures, pressures and flow rates. The OPC protocol was used to communicate the remote computer with the PLC, which solved the problem of complex multi-station in communication. The use of the OPC also made the communication between the remote computer and the centre control system easy. After the cooling system being finished, the function of this system was tested. The testing results showed that the temperature controlling precision was in the range of±0.3℃and this cooling system can run safely and reliably, which can satisfy the requirements of BEPCII experiment.In order to assure the reliability of the cooling structure, an experiment for temperature controlling was taken on the beam pipe model with a size of 1:1. The outer face temperature difference on the cooled sects of the beam pipe was less than 2.0℃at the conditions of the maximum heat loads and the optimum flow rates of cooling liquid. Thus the cooling structure was in reason. The thermal controlling finite element model for the beam pipe was built according to the real material and size of the beam pipe model. The theoretical values of temperature, which were calculated with laminar flow in the narrow cooling channel of the centre beryllium pipe and turbulent flow in the other zones, have a higher precision compared with the experimental values. The maximum error of the temperature on the outer face between the theoretical values and the experimental values was 0.6℃.Based the finite element model of the whole beam pipe, the influences on the temperature field of the beam pipe were studied, which were caused by the heat loads, the flow rates, the thermal conductivity and the positions of the inlet and outlet of the cooling liquid. This study supplied the direction for the reliable and safe use of the beam pipe. The length of the sliver alloy in the transition sects were increased according to the study, which can decrease the temperature of the transition sects. .According to the properties of the heat transfer in the region between the beam pipe and the inner barrel of the Drift Chamber, the natural convection heat transfer model in three-dimension cavity was built to study the temperature distribution of the inner barrel of Drift Chamber caused by the higher temperatures on the transition sects of the beam pipe without cooling. An measure for the temperature protecting with heat insulation covers over the transition sects was put forward, which made the temperature of the inner barrel in the range of 20.0±1.0℃when the beam pipe working normally.The beam pipe and its cooling system, which were designed and developed according to the study in this paper, have already passed the acceptance test and have been installed in position to run in. The running state is all right so far, which play an important role in the debugging and the experiment of BEPCII.