The Research On High-Speed Data Transmission In Direct Dark Matter Searches

Since astronomers discovered the existence of dark matter, the exploration for the essence of dark matter have become very important and meaningful. Particle physicists put forward a most possible candidate for dark matter particle model-WIMP, and many direct detection experiments with the purpose of searching WIMPs have been carried out in particle physics field. On the one hand, with the constantly improved accuracy of the detection cross section, the neutrino background is much more closer than before. And in order to get more closer, the scale of the detectors for dark matter must continue to expand. As a result, the increase of trigger rate and electronic channel number leads to a much higher rate on real-time data transmission. On the other hand, the detection accuracy has greatly improved as the digital waveform technology develops, that makes further improvement in data rate of acquisition system. Therefore, there is a requirement for reasonable solution to explain how to transmit high-rate mass data in real time in the large direct detection experiment for searching dark matter.In the past, dark matter detection experiments usually accomplished data acquisition via VME bus and Gigabit Ethernet because of the small scale of detection and the low trigger rate. However, once the system bandwidth need to be extremely high for real-time data transmission, the system hardware and cables must be multipled in the original transmission method. The system structure will be too complex and at a disadvantage in future upgrading. In recent years, some of the large particle experiment outside the dark matter detection have already met with this pressure of sharply increased data rate. For example, CBM experiment and ATLAS experiment, they ended up with a series of optical connections with data rate of 10Gbps per link for data acquisition. At the same time, PXI Express bus and 10 Gigabit Ethernet become more and more mature and popular with a good performance on both data rate and reliability in the field of industrial and communications. Moreover,40Gbps and 100Gbps links are under research in network transmission, that indicates a trend of higher data rate in data transmission network. As a result, this thesis proposed a lOGbps data acquisition system based on PXI Express bus and 10 Gigabit Ethernet based on the requirement of direct detection experiment for dark matter in China. It also implemented some key technologies in the lOGbps link and carried out the research work. The structure of this thesis is arranged as following:In chapter one, the background of dark matter detection has been introduced such as the background and the research significance of dark matter and dark energy, the evidence listed to prove dark matter is existed and the candidates for dark matter particles expecially WIMPs. The methods and technologies of dark matter detection experiments as well as the development of waveform identification and waveform digitization technology were also introduced in this chapter. Because of the growing numbers of electronic channels and the higher performance of ADCs, the data acquisition system must be with capability of high-speed real-time transmission.The second chapter showed the research on readout electronics in the dark matter detection experiments and other particle experiments with the need for high-rate transmission. According to the research results, the electronics readout system for the future direct detection of dark matter was presented.The third chapter studied the structure and characteristics of data acquisition system for dark matter detection experiments. A readout electronics architecture was proposed for large-scale two-phase argon dark matter detectors. There was an emphasis on how to determine the parameters of ADCs according to the pulse shape in front-end. Theoretical analysis was made on each part of readout system, including the front system, clock system and data acquisition system.The fourth chapter put forward the back-end data transmission scheme which is suitable for data acquisition system with high data rate. The architecture of 10Gbps transmission link based on PXIE bus and 10 Gigabit Ethernet was introduced. First, the overall plan of back-end data transmission link was illustrated. Then, the key technology in the transmission link was pointed out. Next, the implementation of the lOGbps transmission link including hardware details was presented as well as the introduction of the testing software under Linux system. Finally, this transmission link scheme was summarized.Chapter five expounded the data integration module in detail which is the key point in the transmission link. It was designed to accept the data from the front-end FADC modules and send data to the back-end in lOGbps rate. The controller on the module is an FPGA of Xilinx. The control logic and interfaces realization inside the FPGA were also introduced specifically.Chapter six studied the method of lOGbps transmission link, the specific realization method and test results. First of all, the test methods of data transmission and high speed serial link were made clear. Then according to the actual resources the test plan was worked out without network tester. Finally, the test results verified the performance of this system.Chapter seven summarized this thesis and prospected for the future work.