Research Of Data Transmission And Trigger System For The External Target Experiment In HIRFL-CSR

With the devolopment of large-scale heavy ion accelerators and the particles detection technology, the heavy ion physics becomes an inportant field in nuclear physics. The heavy ion accelerators are the prerequisites to the heavy ion physics, and various heavy ion accelerator facilities have been built or under construction. In order to make an accomplishment in the research of heavy ion physics, the Heavy Ion Research Facility at Lanzhou (HIRFL) is built in China.The external target experiment detector system of the HIRFL Cooling Storage Ring(CSR) consists of one start time detector, one y detector, one big dipole, six Multi-Wire Drift Chambers(MWDCs), three time of flight(TOF) walls and one neutron wall, etc. These detectors are located at different places in the experiment hall, with different measurement goals and output signals. Several types of Front End Electronics (FEE) measurement modules are designed, and the overall electronics system is based on a distributed structure.In the external target experiment, there are not only valid secondary paticles but also many invalid paticles that can be detected. Moreover, noises exist in the detectors and the readout electronics. To reject these invalid data and background noises, a trigger system must be designed. According to the time and logic relationship among the valid secondary paticles, the trigger system generates a global trigger signal and transimits it back to the FEE measurement modules for valid data readout. Meanwhile, reliable data transmission is indispensable for collecting all the valid data and transferring them to the DAQ.In this dissertation, we made an investigation of the trigger electronics and the data transmission in large-scale physics experiments in China and abroad, and then we researched data transmission and trigger electronics according to the requirement of the external target experiment in HIRFL-CSR.Data transmission is implemented with multiple function nodes, and event building is executed with three steps. All the FEE measurement modules are designed based on the PXI6U standard; they buffer and packet the measurement data, as well as finishing the primary event building. And then, they transfer these data to the PXI system controller with a DMA transmission method named master mode burst write transaction. The system controller is also responsible for the secondary event building. All the data are further collected by the DAQ through ethernet for the final event building. To get complete valid event data, good stability, data correctness and integrity must be guaranteed in data transmission.The trigger system is organized in several hierarchies. The FEE measurement modules identify the "hit" of the detector and send the "hit" information to the corresponding sub-trigger module in each PXI crate, which is responsible for generating the sub-trigger information. A global trigger module collects all the sub-trigger information and generates the global trigger signal, which is transmitted back to the sub-trigger modules, and further to FEE measurement modules through the PXI star buses. Fiber-based communication is employed between the global trigger module and sub-trigger module over a long distance. All the trigger logic is implemented in FPGA devices, which is remarkable for abundant programmable inner connections and logic resources in it, so reconfigurable trigger electronics can be realized. And thus the trigger algorithms can be upgraded online for future experiment requirements without hardware modifications.Based on the above structure, the data transmission and trigger electronics are implemented. To evaluate the performance of the system, we conducted tests in the laboratory. Eye pattern and bit error rate tests were used to evaluate transmission performance based on fiber. After verifying the trigger functions, we finished the tests on data transmission. The test results indicate that the data transmission is stable and reliable, and the trigger system functions well, which meets the experiment requirements.In the final chapter, we conclude the research on data transmission and trigger system for the external target experiment in HIRFL-CSR, and give an outlook for the next work.