The Research On The Readout Electronics For The Prototype Array Of LHAASO WCDA

Cosmic Rays from the outer space are high energy particles, which are the only material we can receive from the outer space. The researches about comic rays have became one of the important subjects of astrophysics, and many kinds of methods and experiments are used to study relative questions of the cosmic rays, including the composition and origin of the cosmic rays and the corresponding physics process.Large High Altitude Air Shower Observatory (LHAASO), a large all sky survey system for gamma astronomy with an air shower particle detector array of 1 Km2 is proposed to be built in Yangbajing, Tibet, China. The essential scientific goal of LHAASO project is to discover the origins of cosmic rays and the cosmological evolution, as well as the research on high energy astro evolution and dark matter. Water Cerenkov Detector Array (WCDA) is one of the important components of LHAASO. Aiming at sub-TeV gamma astronomy, WCDA is designed to be 90000 m2 in dimension and has 3600 PhotoMultiplier Tube (PMT) to detect air showers deduced by cosmic rays. At the pre-research period of LHAASO, a prototype array of WCDA which consists of nine PMTs is being built in the Yangbajing National Cosmic Ray Observatory, and the performances of the detector are tested through platform of engineer constructions and physical experiments. The main work of this paper is the research of readout electronics for the prototype array of WCDA. Time and charge measurement of PMTs is required in the readout electronics for the prototype array, the mainly specifications are : time resolution < 1 ns, precision <0.5ns; the dynamic range of charge measurement ranges from S.PE to 4000 PE, and the precision is less than 10% at S.PE and less than 5% at 4000PE.The cosmic rays, and the research on them, as well as the LHAASO and WCDA in detail are introduced in Chapter one.In chapter two, several experiments that using water Cerenkov detector as all or part of their detector are introduced and readout schemes of PMTs are discussed in detail. These readout schemes are classified and summarized, as the reference of the design of readout electronics of the prototype array.In chapter three, the prototype, including the construction of the array, the PMT and the detailed specification of readout electronics, are introduced in detail. Then the scheme of the readout electronics are introduced in brief, the readout electronics is composed of two parts: nine preamplifiers in the front end and a digitalizing module in the back end. These preamplifiers and the digitalizing module are connected via 100 meter coaxial cable.In chapter four, the design of the dual-gain low noise preamplifier are introduced. Preamplifier locates at the forefront of the electronics, the performance of readout electronics depends on the preamplifier mainly. The preamplifier is designed to have dual-gain due to the large dynamic range of PMT signal, and the low noise design is essential because the pulse height of the S.PE is very small. After the design and compare of several amplifiers, the final version of preamplifier achieves low noise amplification and good linearity in large dynamic range.In chapter five, the design of main functions in the digitalizing module is introduced. The digitalizing module, receives 18 ways of signal coming from 9 preamplifiers, and obtains the time and charge information of these signals (only signals from high gain of preamplifier are taken time measurement). Besides, the trigger decision and data readout are also fulfilled by the digitalizing module.In chapter six, the test of the digitalizing module and whole readout electronics is introduced. The resolution of TDC is 0.893ns, and time interval precision and the single shot timestamp precision of the readout electronics are 0.475ns and 0.335ns respectively. The precision of charge measurement at S.PE is less than 7% and less than 5% for other signals. The test results show that the performance of readout electronics meet the design specifications.The conclusion and outlook are introduced in chapter seven.