Shulin Liu

PMT overshoot study for the JUNO prototype detector

The quality of PMT signals is crucial for large-size and high-precision neutrino experiments, but most of these experiments are affected by the overshoot of PMT signals from the positive HV-single cable scheme. Overshoot affects the trigger, dead time and charge measurement from a detector. For the JUNO prototype detector, we have performed a detailed study and calculation on PMT signal overshoot to control the ratio of overshoot to signal amplitude to ~1%, with no effect on other PMT parameters.

Evaluation of new large area PMT with high quantum efficiency

The neutrino detector of the Jiangmen Underground Neutrino Observatory (JUNO) is designed to use 20 kilotons of liquid scintillator and approximately 16 000 20 inch photomultipliers (PMTs). One of the options is to use the 20 inch R12860 PMT with high quantum efficiency which has recently been developed by Hamamatsu Photonics. The performance of the newly developed PMT preproduction samples is evaluated. The results show that its quantum efficiency is 30% at 400 nm. Its Peak/Valley (P/V) ratio for the single photoelectron is 4.75 and the dark count rate is 27 kHz at the threshold of 3 mV while the gain is at 1 × 107. The transit time spread of a single photoelectron is 2.86 ns. Generally the performances of this new 20 inch PMT are improved over the old one of R3600.

Development of the large area MCP-PMT

To adapt the specific demands of photomultiplier tubes (PMTs) in the Jiangmen Underground Neutrino Observatory, we design and manufacture a new type of micro-channel plate PMT (MCP-PMT) with the following performance indicators: the PMTs’ glass shell adopts the formula of GG-17 which have no K2O, and very low background (the contents of 232Th, 238U and 40K in the raw materials are less than 40 ppb, 20 ppb and10 ppb, respectively). Its main body is sphere with 500 mm external diameter, 4 mm wall thickness and the tails that using a gradual transition of kinds of low radiation background glasses, then sealing with the Kovar. The photocathode material with lowest dark noise is bi-alkali photocathode which spectral region matches the liquid scintillator emission spectral (400~440 nm). The front and back hemisphere is transmission and reflective photocathode separately. Two sets of double-stack micro-channel plates replacing the dynode chain are used to detect the photoelectrons from both sites. The focusing system makes the photoelectrons hit into the inside of MCPs to the uttermost. The anode and lead make sure charge signal is no distortion. No matter made by transfer equipment or not, the peak value of quantum efficiency of the PMT should reach 30%, and the peak-to-valley ratio of single photoelectron spectrum has surpassed 2.5:1. In a word, the MCP-PMT’s reliability and other characteristics meet the need of Jiangmen Underground Neutrino Observatory.

High voltage pulse gated power supply with adjustable pulse width

Image intensifier is the key components of low-light level night vision device. In order to extend its dynamic range of the night vision sight, a high voltage pulse gated power supply (HVPGPS) for image intensifier cathode is researched in this paper. The HVPGPS with pulse width adjustable is optimally designed for the image intensifier cathode power supply. Its pulse amplitude is 250 V, with 1 kHz frequency. Two different circuits are combined to get the adjustable pulse width from narrow to wide. The pulse width parameters are: the narrow pulse circuit is from 20 ns to 300 ns, and its wide pulse circuit is 300 ns – millisecond (ms). This HVPGPS can achieve the advantages of small size circuit, low power consumption, and which meets the requirements of image intensifier cathode power supply.

Status of the 20 inch MCP-PMT prototype development for JUNO experiment

A new concept of large area photomultiplier based on MCPs was conceived for JUNO by the scientists in IHEP, Beijing. In the past 5 years by collaborative work of the MCP-PMT collaboration in China, 8 inch and 20 inch prototypes were produced. Test results show that this type of MCP-PMT can have similar photon counting performance as the traditional dynode type PMTs. With the better collection efficiency, low after pulse rate, low Low-Potassium Glass, the JUNO ordered 75% about 15,000 20 inch MCP-PMT from NNVT at the end of 2015. This manuscript just give the overview this type of MCP-PMT, the R&D process and the main characteristics.

The Status of the Batch Test of 20 inch MCP-PMT

The JUNO needs the 20 in. large area photo detector with 20,000 PMTs, which have large sensitive area, high quantum efficiency, high gain for good single photoelectron detection. In 2009, the IHEP researchers have designed a new type of 20 in. PMT for JUNO. Using the small MCP units replace the bulky Dynode chain in the large area PMTs for better performance improvement. After many years R&D process, a lot of prototypes were produced within 5 in., 8 in., 20 in. for the performance test by the MCP-PMT evaluation system built at IHEP. The final version 20 in. MCP-PMT was produced at the end of 2015, The PMT mass production and batch test system were ran in 2017 achieving quick test of all performance for every PMT instead of sampling. This manuscript will introduce this batch test equipment and it’s preliminary result.

Secondary Electron Yield of Nano-Thick Aluminum Oxide and its Application on MCP Detector

Nano-thick aluminum oxide thin film was deposited by atomic layer deposition (ALD) technique. The secondary electron properties of such thin film have been studied by pulsed-yield measurement. Conventional lead glass microchannel plate (MCP) was coated with such thin film. The gain, the single electron resolution and the peak-to-valley ratio of the new MCP detector were improved.

Spherical Measuring Device of Secondary Electron Emission Coefficient Based on Pulsed Electron Beam

In order to improve the performance of the microchannel plate, a material having a high secondary electron emission coefficient (SEEC) is required, and the SEEC of this material needs to be accurately measured. For this purpose, a SEEC measuring device with spherical collector structure was designed. The device consists of vacuum system, electron gun, main chamber, sample stage, test system and test software. The measurement of the SEEC from a wide incident energy range (100 eV–10 keV) and a large incident angle (0°–85°) is realized by using the pulsed electron beam as the incident electron. The energy distribution of the secondary electrons is measured by a multi-layer grid structure. The SEEC of the metallic material was tested by using this device, which proves that the device is stable and good.

Influence of band gap grading of intrinsic layer and annealing post on the optical and electrical performance of amorphous silicon germanium thin film solar cells

Hydrogenated amorphous silicon germanium (a-SiGe:H) single junction pin sequence solar cells with different bandgap structure of intrinsic layer were prepared by radio frequency plasma enhanced chemical vapor deposition (RF-PECVD). Three kinds type of intrinsic layer using in this study were non-grading structure, V type grading and reverse V type grading. The effects of different intrinsic layer structure on solar cell performance were systematically studied. The results showed that the optimized structure of intrinsic layer was the reverse V type grading structure. And the performance of a-SiGe:H solar cell with reverse V type grading after annealing also were studied. The results revealed that the performance was improved after first annealing, but was deteriorate for further annealing. And, we have studied the dark I-V curves in order to contribute to a better understanding of the basis of solar cells.