Mr Xiaokun Zhao (USTC)
The Large High Altitude Air Shower Observatory (LHAASO) project is scheduled to be built at Sichuan province in China. As a large scale complex of various detectors, its primary scientific goals are exploring the origin of the galactic cosmic ray, searching for very high energy gamma ray sources, and the precise measurement of the components at the knee region. To accomplish these tasks, the proposed project consists of three detector arrays: $1\ km^2$ extensive air shower array (KM$2$A, including ED and MD), $75000\ m^2$ Water Cherenkov Detector Array (WCDA) and Wide Field of view Cherenkov Telescope Array (WFCTA). Among them, WCDA and MD will employ the large area photomultiplier tube (PMT) as the readout of its cell detector. WCDA is proposed to target gamma astronomy at energies between $100$ GeV and $30$ TeV. The WCDA covers an area $75000\ m^2$, configured as $3120$ small ponds ($5\ m × 5\ m × 4\ m$ depth). A $8-9$ inch hemispherical PMT is located at the bottom-center of each cell, facing upward, to collect the Cherenkov light produced by shower particles in water. The PMTs require not only good single photoelectron (SPE) resolution and small transit time spread (TTS), but also a large charge dynamic range from $1$ to $4000$ photoelectrons (PE) at the inciting light pulse width of $6.4$ ns. Bases for the candidate PMTs Hamamatsu R$5912$, Beijing Hamamatsu CR$365$ and HZC Photonics XP$1805$ are designed, respectively. The voltage divider is a purely resistive chain and the base comprises two different outputs obtained by using the anode and the dynode. The results show that at the working gain of $3×10^6$, the characteristics of all the three PMTs satisfy the demands of WCDA. Additionally, a high dynamic range photomultiplier tube base for Hamamatsu R$5912$ and HZC XP$1805$ are designed for the underground Muon Detector (MD), which is another major detector in LHAASO and used to detect the muon components in the extensive air shower. The cell detector of MD requires the dynamic range up to $15000$ muons which means output current of $1.8$ A from the PMT. For R$5912$ as an example, the divider is designed to extract the signals from the $7$th dynode (DY$7$) and the anode. The charge ratio between the anode and DY$7$ is around $160$ and the equivalent anode peak current non-linearity of DY$7$ within $5$% is up to $1.87$ A, which satisfies the dynamic range requirement in the MD.
Mr Xiaokun Zhao (USTC)