Weiqun Yuan

Experimental investigation of surface flashover in vacuum using nanosecond pulses

Based on a Marx generator and a coaxial pulse forming line, an experimental investigation of surface flashover characteristics in vacuum is conducted by using nanosecond pulses of 10 ns rise time and 30 ns full width at half maximum (FWHM). Insulator dielectrics chosen for this investigation are Teflon, PMMA and Nylon. The tested factors include gas pressure, cone angle of conical frustum, diameter and length of cylindrical insulator, material and shape of electrode, and contact style between insulator and electrodes. The effects of these parameters on the surface flashover characteristics are described and analyzed in this paper. In addition, the character of flashover time lag in the nanosecond range, and surface flashover theory in vacuum charged by nanosecond pulses are also discussed.

Design and Testing of a 10-MJ Electromagnetic Launch Facility

For basic research on electromagnetic launch technology, the Beijing Institute of Special Electromechanical Technology has initiated a program focusing on the design and testing of a 10-MJ electromagnetic launcher facility with the cooperation of Nanjing University and the Institute of Electrical Engineering, Chinese Academy of Sciences. The facility will consist of a 10-MJ prime energy, a 6-m-long railgun, and a control system. A 3.2-MJ pulse power unit (PPU) with 32 100-kJ modular PFN units has been completed and tested, and its prime energy can be easily extended to 10 MJ. A 6-m-long railgun has been built, which can be easily cut into a 4-m-long railgun by which many firings have been done with the new PPU. Construction and testing of the whole facility are being continued.

Research on the Sliding Electrical Contact of the Rapid Fire Railgun

The sliding electrical contact between the armature and the rails is affected by the high driving current and the friction heating during the launching process, especially in high fire rate applications. The contact performance is closely related to the impedance between the armature and the rails. A rapid fire railgun was designed for this paper of the sliding electrical contact. The pulsed power system consists of ten 100 kJ pulse forming units with a total stored energy of 1 MJ, and the length of the launcher is 1310 mm with a caliber size of 18 × 18 mm. Two types of armatures are adopted, a C-shaped armature and a double C-shaped armature. Two 5 g armatures can be launched at a frequency of 166 Hz with a muzzle speed of 800 m/s. The effect of contact impedance by the temperature rise can be calculated approximately with heating. Experimental results show that the contact impedance is seriously affected by the electromagnetic force and the contact temperature; the contact impedance of the second armature is 0.8-2.6 mΩ, which is higher than that of the first armature (0.2-0.3 mΩ).

Recent Pseudo-Liquid Armature Experiments with Details of the Test Systems

The pseudo-liquid (PSL) armature with air-spring is a novel railgun armature, which has lower mass and more compliance than conventional C-shaped armature. The united research group leaded by Beijing Institute of Special Electromechanical Technology (BISET) has completed a lot of experiments of the PSL armatures with air-spring since 2004. The results of these experiments show this armature can prevent transition with some conditions. This paper presents an overview of PSL armature program including the pulsed power supply, two rail launchers (SRL1 and SRL3), projectiles and some experimental results. As the best result of SRL1 rail launcher tests, it is obtained that muzzle velocity of 1.1 km/s with a 52 g mass. The best performance of SRL3 launcher tests is muzzle velocity of 1.92 km/s with a 45 g mass operating at a stored energy of 1.39 MJ and a flat-top current of 400 kA with about 1.5 ms pulse duration. The further experimental studies are being continued.

Simulations on Elastoplasticity of the Monolithic Aluminum Armature Under the Contact Force

Keeping good contact of the armature-rail interface (ARI) is essential for electromagnetic launch technology. To investigate the contact mechanism of ARI and improve the contact condition, the elastic-plastic deformation of the monolithic aluminum armature (MAA) under the contact force is analyzed. Contact force, contact area, and the distribution of contact pressure are calculated, and several kinds of armatures with different arm lengths are compared under the same conditions. The calculating loads include the pretightening force under the initial preload and the electromagnetic force from the pulse current. The simulation results show that both the contact force and the contact area under the plastic deformation are bigger than those under the elastic deformation, which is due to the higher spring-back force and displacement. A longer arm length can result in better flexibility and lower contact force. The effect of the electromagnetic force versus the contact force is increased with the arm length.

Design of a 3-m-Long Electromagnetic Launcher

A 3-m-long 30-mm square bore launcher has been constructed for electromagnetic launch application at the Institute of Electrical Engineering, Chinese Academy of Sciences. The main purpose of the launcher is to conduct the basic and applied research in electromagnetic launch. An optimum structure of the insulators was adopted through the stress analysis using the software ANSYS. In order to know about the variation of the gap under a certain stress, an air pressure piston (maximum air pressure of 5 MPa) and a position sensitive detector were adopted. The measuring results have shown that the rail gap decreases gradually from breech to muzzle; this kind of design can abate the erosion of the rails caused by arc discharge effectively. A total of 85 tests has been performed, including 17 tests of single-module discharging and 68 tests of nine-module sequential discharging, and a highest muzzle velocity of 1.9 km/s with a 45-g mass was achieved, operating at a current of 410 kA and 2-ms pulse duration. This launcher is now used for the fundamental research on armature structure, performance of the pulsed power supply, and the diagnostic system. A novel launcher based on the previous experimental results is under development.

Investigation on the Time-Varying Inductance Gradient of Railgun

The inductance gradient of railgun is one of the key factors in the EM railgun launcher. Generally, people take it as a constant value during simulation, but in fact it is variable in firing. Better understanding of the inductance gradient during launching is helpful to the predicting of the armature transition velocity. To obtain the waveform of the time-varying inductance gradient, the experimental current waveform was analyzed with time-frequency analysis tools. Thus the frequency-time waveform (f-t waveform) of the load current was obtained. The 3-D railgun model was setup in Maxwell 3D modular of Ansoft Corporation. Frequency points of the f-t waveform corresponding with B-dot signals were input to the simulation model to calculate the corresponding inductance gradient and the time-varying inductance gradient was gained. It is indicated that the inductance gradient of the railgun is decreased rapidly before the load current reaches its peak value. The propelling force on the armature is calculated with the inductance gradient waveform and the load current waveform. The armatures mass will show pseudo increase at the rise of current and decrease rapidly when the armatures wings are soft enough.

Control system based on optical fiber communications for the high-frequency high-voltage charging power supplies' parallel operation

High-frequency high-voltage charging power supply (HFHVCPS) is widely used in electromagnetic lunch, laser and other high current discharge situations. The high reliability of HFHVCPS is required due to the harsh application environment. The reliability of the control system is the key factor for the reliability of power supply, in order to improve the reliability of the control system, the optical fiber communication system was designed, which includes optical fiber communication system for the upper computer and lower computer and optical feedback system for the load voltage. Optical fiber communication system can be used for remote control of charging power supply and improve the anti-jamming performance of the control signal and the feedback signal, thus the reliability of the control system was enhanced. According to the control program and corresponding communication protocol, a control system can be implemented for the parallel control of two or even more than one charging power supplies. The time difference of different power supplies response to the control commands can be reduced by the optical fiber communication system, so that the accuracy of the system was improved. The protection circuits for over-voltage, over-current, over-time over-temperature and other situations were designed, in order to ensure the power supply can run reliably when the system is charging. Once a fault is occurred, the power supply can stop the work immediately and feedback the fault information by the optical fiber communication system, so that the safety of equipment and the operators are ensured by the optical fiber communication system.

Design of a 3-Meter Long Electromagnetic Launcher

A 3-m long, 30-mm square bore launcher has been constructed for electromagnetic launch application at the Institute of Electrical Engineering, Chinese Academy of Sciences (IEECAS).The main purpose of the launcher is to conduct the basic and applied research in electromagnetic launch. An optimum structure of the insulators was adopted through the stress analysis using the software ANSYS. In order to know about the variation of the gap under a certain stress, an air pressure piston (Maximum air pressure 5 MPa) and a position sensitive detector (PSD) were adopted. The measuring results have shown that the rails gap decreases gradually from breech to muzzle; this kind of design can abate the erosion of the rails caused by arc discharge effectively. A total of 85 tests have been performed, including 17 tests of single module discharging and 68 tests of 9 modules sequential discharging, and the highest muzzle velocity of 1.9 km/s with a 45 g mass was achieved operating at a current of 410 kA, 2 ms pulse duration. This launcher is now used for the fundamental research on armature structure, performance of the pulsed power supply and the diagnostic system. A novel launcher based on the previous experimental results is under development.

Thermal Analysis on Electromagnetic Launcher Under Transient Conditions

Since a tactical electromagnetic railgun system is required to fire several times a minute, the thermal load on the rails leads to a higher temperature, which will even result in launch failures and reduce the life span of the launcher. In this paper, the rail temperature was measured during the launch experiment. Furthermore, based on a 3-D transient model with moving armature, mechanically, thermally coupled electromagnetic field analysis using finite-element method is presented. The Joule heating is one of the main heat sources in the rails. Contact resistance and friction force that cause heat between the armature and the rail are also included in the model. The simulation results show that the peak temperature in the rail occurs at the inner surface. Overall, along the direction of armature motion, the temperature of the rail near the breech end is higher than at the muzzle end, and the maximum temperature on the rail appears near the initial position of the armature. The contact resistance contributes much more than friction to the temperature rise in rails.