Jinshou Tian

The influence of temperature on low cycle fatigue behavior of nickel base superalloy GH4049

Low cycle fatigue tests on nickel base superalloy GH4049 were conducted at various temperatures from 500 to 850°C in laboratory air. The strain-life and cyclic stress-strain data were analyzed and the change in fatigue life behavior and fatigue parameters with increasing temperature was discussed. At low and intermediate total strain amplitudes, the fatigue life was found to decrease with increasing temperatures. The fracture surface of the fatigue specimens was studied using scanning electron microscopy. It was found that fatigue crack initiation is transgranular, however, fatigue crack growth exhibits a strong dependence on temperature. The cyclic deformation process, creep and oxidation are thought to be the main causes of fatigue life reduction and intergranular cracking.

High temperature fatigue behavior of wrought nickel-base superailoy GH4049

Push-pull total strain-controlled fatigue tests without and with a hold period were carried at elevated temperatures for wrought nickel base superailoy GH4049. The influence of the testing temperature and strain hold period on fatigue behavior was determined. The alloy would exhibit either cyclic strain hardening, softening or stability during cyclic straining. Fatigue life depends strongly on the testing temperature and the introduction of the strain hold period. Observations on fatigue specimens using transmission electron microscopy (TEM) showed that the dislocations were distributed mostly in the γ matrix. It was observed by scanning electron microscopy (SEM) that cracks initiated always in a transgranular mode, but their propagation mode was closely related to the testing temperature. In addition, the fatigue life was predicted by linear damage summation (LDS), strain range partitioning (SRP) and the strain energy partitioning (SEP) method. The results of life prediction indicated that the SRP and SEP methods were in a good agreement as to the measured and predicted life at lower temperatures, while the LDS method showed better predictability at higher temperature as compared to the SRP and SEP methods.

Status of the large area MCP-PMT in China

For the next generation neutrino experiment, number of experienced researchers and engineers in research institutes and companies related to PMT fabrication in China jointly worked on the large area MCP-PMT collaboration group. In the past 5 years by collaborative work, the 8-inch and 20-inch prototypes were produced. And also get the high detection efficiency 20-inch MCP-PMT for JUNO in 2015, and get the 75% order of the JUNO-PMT. This manuscript will introduce the progress of the R&D of this new design of the MCP-PMT, also the performance tested result in the PMT Lab in IHEP.

Numerical analysis of the surface-conduction electron-emitter with a new configuration

A new kind of surface-conduction electron-emitter (SCE) with a triangular dielectric layer under the conductive film is proposed. The influences of the vertex angle (𝜃) of the triangular dielectric layer and the anode voltage (Ua) on the electron emission efficiency and the focusing capability have been investigated with the finite integration technique (FIT). The numerical simulation results show that SCE with a small vertex angle guarantees higher electron emission efficiency even with a low anode voltage. But the focusing capability of the electron emitter will get worse when the 𝜃 or Ua becomes too small. Take both the electron emission efficiency and focusing capability into consideration, the structure with a vertex angle (𝜃) between 60∘–100∘ and the anode voltage of 1500V is suggested.

Analysis of the influence of nanofissure morphology on the performance of surface-conduction electron emitters

A simulation model was built to numerically investigate the electron emission property of a new surface-conduction electron emitter (SCE) with a raised emitter structure. The model calculated the electric field distribution, the electron emission characteristics, and the electron trajectories, which were useful for analyzing and understanding the microscopic mechanism of the electron emissions of the new SCE structure. It was found that the new structure increased the probability of electrons being collected by the anode which led to an increase of the anode current despite of the decrease of field emission current. This study benefits the advanced design of emitter structures in nanoscale technology for new types of electron sources.

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.

A compact large-format streak tube for imaging lidar

The streak tubes with a large effective photocathode area, large effective phosphor screen area, and high photocathode radiant sensitivity are essential for improving the field of view, depth of field, and detectable range of the multiple-slit streak tube imaging lidar. In this paper, a high spatial resolution, large photocathode area, and compact meshless streak tube with a spherically curved cathode and screen is designed and tested. Its spatial resolution reaches 20 lp/mm over the entire Φ28 mm photocathode working area, and the simulated physical temporal resolution is better than 30 ps. The temporal distortion in our large-format streak tube, which is shown to be a non-negligible factor, has a minimum value as the radius of curvature of the photocathode varies. Furthermore, the photocathode radiant sensitivity and radiant power gain reach 41 mA/W and 18.4 at the wavelength of 550 nm, respectively. Most importantly, the external dimensions of our streak tube are no more than Φ60 mm × 110 mm.

Optimizing codes for compressed ultrafast photography by the genetic algorithm

The compressed ultrafast photography (CUP) technique, providing the fastest receive-only camera so far, has shown to be a well-established tool to capture the ultrafast dynamical scene. This technique is based on random codes to encode and decode the ultrafast dynamical scene by a compressed sensing algorithm. The choice of random codes significantly affects the image reconstruction quality. Therefore, it is important to optimize the encoding codes. Here, we develop a new scheme to obtain the optimized codes by combining a genetic algorithm (GA) into the CUP technique. First, we measure the dynamical scene by the CUP system with random codes and obtain the dynamical scene image at each moment. Second, we use these reconstructed dynamical scene images as the optimization target and optimize the encoding codes based on the GA. Finally, we utilize the optimized codes to recapture the dynamical scene and improve the image reconstruction quality. We validate our optimization scheme by the numerical simulation of a moving double-semielliptical spot and the experimental demonstration of a time- and space-evolving pulsed laser spot.

Small-size streak tube for imaging lidar

Streak tube imaging lidar, as a novel flash lidar, due to its advantages of higher resolution for low contrast conditions, compact and rugged physical configurations, small image distortions owing to its scannerless design, and higher image update rates, has immense potential to provide 3D single-laser-pulse scannerless imaging, 3D multispectral imaging, 3D multispectral fluorescence imaging, and 3D polarimetry. In order to further reduce the size and enlarge the field of view (FOV) of the lidar system, we designed a super small-size, large photocathode area and meshless streak tube with spherical cathode and screen. With the aid of Computer Simulation Technology Software package (CST), a model of the streak tube was built, and its predominant performances were illustrated via tracking electron trajectories. Spatial resolution of the streak tube reaches 20lp/mm over the entire ∅28mm photocathode working area, and its temporal resolution is better than 30ps. Most importantly, the external dimensions of the streak tube are only ∅50mmx100mm. And several prototypes are already manufactured on the basis of the computer design.

Electro-optical design of a long slit streak tube

A small size and long slit streak tube with high spatial resolution was designed and optimized. Curved photocathode and screen were adopted to increase the photocathode working area and spatial resolution. High physical temporal resolution obtained by using a slit accelerating electrode. Deflection sensitivity of the streak tube was improved by adopting two-folded deflection plates. The simulations indicate that the photocathode effective working area can reach 30mm × 5mm. The static spatial resolution is higher than 40lp/mm and 12lp/mm along scanning and slit directions respectively while the physical temporal resolution is higher than 60ps. The magnification is 0.75 and 0.77 in scanning and slit directions. And also, the deflection sensitivity is as high as 37mm/kV. The external dimension of the streak tube are only ∅74mm×231mm. Thus, it can be applied to laser imaging radar system for large field of view and high range precision detection.