基于CBM-TOF探测器无触发数据获取系统的压缩算法研究

Design of data compression algorithm based on CBM-TOF Trigger-less data acquisition system

针对CBM-TOF(Compression Baryon Material experiment-Time of flight detector)探测器采用的无触发数据获取系统所产生的数据流,本文提出一套完整的数据压缩算法,该算法通过提取数据流中与粒子信息相关的数据,并将数据配对成脉冲信号做进一步的数据筛选来完成。算法通过三个步骤完成对数据的压缩处理,分别是有效性验证、排序及脉宽筛选。有效性验证将初步筛选数据,保留粒子到来的时刻信息(绝对时间/相对时间),再通过后面两个步骤将符合行为的脉冲提取出来。通过压缩来自COSY的束流测试的数据,算法的正确性和有效性得到了验证,数据的压缩率达到94.5%以上,并且完整地保留了有用的数据信息。本算法减轻了无触发数据获取系统链路上数据流的压力,高效快速地将原始数据中有价值的信息提取出来,基本完成了针对CBM-TOF数据预处理的工作要求,对TOF探测器的数据重组有重要的意义。

Background： In order to further study the high baryon number density area in Quantum Chromodynamics Phase Diagram （QCD）, compression baryon material experiment （CBM） and the construction of SIS 100/300 accelerator had been launched in Antiprotons and Ion Research Center of Germany. As for time of flight （TOF） which was the sub-detector at CBM experiment, a set of data preprocessing algorithm was designed in this paper, which played a significant role in the electronic readout system of the entire TOF detector. Purpose： The research aimed to design a complete set of data compression algorithm specific to data flow generated by trigger-free data acquisition system of CBM-TOF detector so as to extract data related to the particle information from such data flow and then match them into pulse signals for further data screening. Methods： C programming language was adopted to write the main part of such an algorithm and compiled them into executable files. By writing script, the executable files were invoked to read raw data files of TOF detector which were input into the compression algorithm for processing. In the end, results obtained were saved in files and drawn into charts through statistics. The core of this algorithm could be classified into three parts and they were validity checking, time ordering and time over threshold checking respectively. Under the action of scripts, algorithm screening was carried out for a large amount ofraw data one by one in accordance with lengths which had been determined in advance; moreover, useful data relevant with blow particles were also extracted. Results： The compressed raw data were derived from beam testing of COSY in November 2011. For this algorithm, raw data volume was compressed to the maximum extent with a compression ratio of 94.5% and above; in addition, the compression algorithm didn＇t lose the useful data including blow information of particles. Conclusion： Regarding this algorithm, not only data flow pressures on trigger-free data acquisition system link were relieved, but also valuable information was extracted from the raw data both efficiently and rapidly. Therefore, operational requirements for CBM-TOF data preprocessing were basically satisfied, which had a great significance for data reconstitution of TOF detector.