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A particle-in-cell simulation is conducted to investigate the plasma acceleration process in a micro-cathode vacuum arc thruster. A coaxial electrode structure thruster with an applied magnetic field configuration is used to investigate the effects of the distribution of the magnetic field on the acceleration process and the mechanism of electrons and ions. The modeling results show that due to the small Larmor radius of electrons, they are magnetized and bound by the magnetic field lines to form a narrow electron channel. Heavy ions with a large Larmor radius take a long time to keep up with the electron movement. The presence of a magnetic field strengthens the charge separation phenomenon. The electric field caused by the charge separation is mainly responsible for the ion acceleration downstream of the computation. The impact of variations in the distribution of the magnetic field on the acceleration of the plasma is also investigated in this study, and it is found that the position of the magnetic coil relative to the thruster exit has an important impact on the acceleration of ions. In order to increase the axial velocity of heavy ions, the design should be considered to reduce the confinement of the magnetic field on the electrons in the downstream divergent part of the applied magnetic field.

Low-permeability to ultralow-permeability reservoirs of the China National Petroleum Corporation are crucial to increase the reserve volumes and the production of crude oil in the present and future times. This study aimed to address the two major technical bottlenecks faced by the low-permeability to ultralow-permeability reservoirs by a comprehensive use of technologies and methods such as rate-controlled mercury injection, nuclear magnetic resonance, conventional logging, physical simulation, numerical simulation, and field practices. The reservoir characteristics of low-permeability to ultralow-permeability reservoirs were first analyzed. The water flooding development adjustment mode in the middle and high water-cut stages for the low-permeability to ultralow-permeability reservoirs, where water is injected along the fracture zone and lateral displacement were established. The formation mechanism and distribution principles of dynamic fractures, residual oil description, and expanding sweep volume were studied. The development mode for Type II ultralow-permeability reservoirs with a combination of horizontal well and volume fracturing was determined; this led to a significant improvement in the initial stages of single-well production. The volume fracturing core theory and optimization design, horizontal well trajectory optimization adjustment, horizontal well injection-production well pattern optimization, and horizontal well staged fracturing suitable for reservoirs with different characteristics were developed. This understanding of the reservoir characteristics and the breakthrough of key technologies for effective development will substantially support the oil-gas valent weight of the Changqing Oilfield to exceed 50 million tons per year, the stable production of the Daqing Oilfield with 40 million tons per year (oil-gas valent weight), and the realization of 20 million tons per year (oil-gas valent weight) in the Xinjiang Oilfield.

This paper makes systematic analysis of geological factors of natural gas accumulation in Denglouku formation of Gulong-Changjiaweizi region, including reservoir characteristics, gas source condition, source-reservoir relationship, structural condition, etc. It turned out that K1d2 in Gulong-Changjiaweizi region is generally typical tight sandstone reservoir with low porosity and permeability due to the poor physical properties. The gas source rock of K1d2 formation has larger gas producing capacity.The relationship between source rock and reservoir shows as interbed interfinger or directly contiguity contact, which is beneficial for large-area gas accumulation. The gas generation area of source rock in this region is always in the center and slow downdip direction of Gulong depression with a smaller dip angle on the adjacent tight sandstone reservoir, where faults are rare. The result of comprehensive analysis shows that K1d2 formation in Nothern Songliao Basin and its neighboring layers could be considered as a favorable target of the tight gas reservoir study in Northern Songliao Basin due to its favorable geological conditions of deep basin tight gas reservoir generation, such as tight reservoir, sufficient gas source, communicating source-reservoir relationship and constant flattened structure.

On December 17, 2020, the Chang’e-5 reentry spacecraft landed safely and brought back the lunar sample without damage. This paper describes the recovery system that has critically contributed to the scientific success of the Chang’e-5 missions and presents the technical requirements and constraints of the recovery system for the Chang’e-5 reentry spacecraft and discusses the design process of the recovery system, including the system composition, working procedure, and some other key aspects. Finally, the ground cover rejection tests and air drop and flight tests were carried out to confirm the design configuration. The results showed that the Chang’e-5 reentry spacecraft recovery system was designed correctly, and its functions and performances met the design requirements. A breakthrough in the recovery technology of the reentry spacecraft was achieved for Chinese first lunar sample-return mission.

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The breakdown of a vacuum arc under high applied voltage conditions usually occurs on very short time and space scales, and a deep understanding of these processes is essential to extend the application of vacuum arc devices. To study the time and spatial evolution of plasma parameters during vacuum breakdown, a two-dimensional axial-symmetric particle-in-cell code with Monte Carlo collisions is used in the numerical simulation of tip-to-plate electrode configuration. In this simulation, in addition to considering the primary and secondary ionization of copper atoms, the excitation and de-excitation processes of copper atoms are also introduced so that the evolution of the light intensity of the vacuum arc in the different stages of breakdown processes can be obtained by tracking the de-excitation process of the atoms, which can be considered a virtual camera. In this way, the cathode radiance, anode light expansion, arc channel establishment, and arc quenching processes can be visually observed, and the trends are consistent with the images taken by Intensified Charge-Coupled Device (ICCD) and streak cameras reported in the literature. The analysis of the sputtering amount of the anode material due to the impact of the cathode plasma to the anode surface shows that the contribution of atoms, singly, and doubly ionized ions to the sputtering of the anode material varies at different stages of the discharge.