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In this paper, magnetic Gd atom is firstly introduced into the type-I clathrate Eu8Ga16Ge30. A sample with nominal composition Eu6.5Gd1.5Ga16Ge30 was synthesized by combining arc melting (ARC) and melt spinning (MS) techniques. The lattice parameter decreases due to the smaller ionic radius of Gd3+ than that of Eu2+. The sample experiences a paramagnetic to ferromagnetic magnetic transition at about 31.5 K. It is about 3 K lower than that of Eu8Ga16Ge30. Under the applied magnetic field of 3 T, the maximum magnetic entropy change - Δ S M max around TC is 4.8 J/kg·K. This value is much lower than that of the undoped Eu8Ga16Ge30 (6.0 J/kg·K). The reduction of saturation magnetization is mainly responsible for the reduction of magnetic entropy change. The large critical exponent β confirms the inevitability of the decrease of magnetic entropy change. On the other hand, Gd-doping strengthens the small second magnetic transition at low temperature. Coexistence of two magnetic transitions widens the - Δ S M (T) curves and results in large values of refrigerant capacity (RC) and relative cooling power (RCP). [ABSTRACT FROM AUTHOR]

A pulsed power supply of a 1.5-MJ capacitor bank has been developed for high-current high-velocity sliding electrical contact studies in railgun launches. The system consists of 8 small modules, each with a capacitance of 15 mF, and one large module with a capacitance of 54mF. All of nine modules use triggered spark gaps as the main switches. Various shapes of high-current pulse can be formed by controlling the charging voltage and firing time of each module. The small module has been designed for the maximum operating voltage of 5 kV, the peak current of 140 kA, the pulse rise time of 0.9 ms, in which semiconducting diode stack is used as crowbar switch. Since the large module has no crowbar switch and relatively small pulse forming inductance, it can supply high-amplitude oscillating current waveform. The effects of the large module are threefold. First, the large module provides a basic current on which the currents of small modules superimpose to form a nearly constant driving current of armature. Second, the oscillating nature of the current can drastically reduce the muzzle arc current; hence suppression of the muzzle arc can be obtained. Third, the crowbar switch can be removed and therefore the cost of the system can be reduced. The experiments were performed to verify the operation performances of the two kinds of modules, where the modules were discharged simultaneously and/or sequentially. The feasibility of large module on the muzzle arc control is also examined. The results of the experiments show that a total current of 400 kA with a 1.5 ms flat-top time can be obtained and all the modules show good performance during the railgun firing. Index Terms--Capacitor bank, electrical sliding contact, pulsed power supply, railgun.

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 Electromechauical 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. Index Terms--PSL armature, pulsed power supply, rail launcher, transition.

The unique properties of the plasma utilized in ETC guns, such as the low viscosity, high momentum and high temperature, can lead to a more uniform ignition over the entire cartridge volume, even in large-caliber guns. Since 2002, the united research group leaded by Beijing Institute of Special Electromechanical Technology (BISET) has completed a lot of experiments with a novel surface discharge plasma igniter, which generates plasma from a cylindrical surface and distributes it through radial port. The results of these experiments have shown this igniter can present perfect ignition. This paper presents an overview of this ETC program including the igniter, pulsed power supply, 120 mm ETC launchers, and some experimental results. The further experimental studies are being continued. Index Terms--Electro-thermal chemical, gun, plasma ignition.

Armor vehicles have traditionally been protected by the armor based on steel. This gives rise to extremely heavy structures which produce logistic problems due to the need to transport the vehicle to a battle field [1]. Many kinds of technique have been developed to meet this change. A new concept--Active Electromagnetic Protection System (AEMPS) has the advantage of short trigger delay time, good controllability, repetition uniformity and convenient logistic service. So it must be the development trend of the active protection system. At present, there is not much research on the effect of AEMPS. In order to better understand the effect of AEMPS, establishing a numerical model to simulate the interception process is required. In this paper, taking pole armor piercing projectile as example for it has heavy threat on armor, numerical simulation was performed with the finite element software LS-DYNA3D. The simulation shows good result. After being intercepted, pole armor piercing projectile's warhead turns blunt and inflected, its velocity slows down and the ability to penetrate the same armor decreases about 20-25 percent. Good practical effect of AEMPS is based on intercepting target successfully. Since pole armor piercing projectile has high velocity, it requires that AEMPS has high accuracy of interception. In order to evaluate the launching direction accuracy, a new launching apparatus was made and the accuracy test was carried out in the laboratory. The experimental result showed that the direction accuracy of launched interceptor is less than 0.5 degree. So it can intercept target successfully in the range of five meters. Index Terms--Accuracy, AEMPS, effect, numerical simulation.

This paper describes preliminary experiments conducted at zero speed using the pseudo-liquid armature with air-spring. Measurements made during these experiments include current, muzzle voltage, and gas pressure in the air spring. Armature action was obtained by simulating the current pulse. From this specific action was obtained by using the actual armature conducting area. The results obtained for the seven experiments conducted are presented. We discuss the results and make recommendations for future work in this area. Index Terms--Aluminum pseudo-liquid armature, arcing resistance, muzzle voltage, rail surfaces, transition into arcing contact, zero speed.

Currently, the bore shape in an electromagnetic launcher is usually a rectangle, round, or an inverted arc. A comparison of the current density distribution, induction gradient, moment of inertia, contact pressure, contact state, structure manufacture, and launching precision between the rectangle and inverted arc bore shapes was carried out. We got some results about the effect of bore shape on the electromagnetic launcher. The results show that the inverted arc shape performed better than the rectangle in these areas: current density distribution, induction gradient, moment of inertia, contact state, and the accuracy of armature running. [ABSTRACT FROM PUBLISHER]

The energy density of the inductive energy storage systems is one order of magnitude higher than that of the capacitive ones. The slow transfer of energy through capacitive hybrid (STRETCH) meat grinder with inverse current commutation with semiconductor (ICCOS) devices put forward by Tsinghua University is a typical inductive pulsed-power supply for electromagnetic launch system, which has remarkable current amplification ability as a single module. However, one module cannot provide enough amplitude and width for the load current of the railgun launching. Therefore, the collaborative work of multiple inductive source modules is necessary for practical usage. In this paper, the designed inductive power supply system of about 1 MJ is composed of 40 STRETCH meat grinders with ICCOS modules. All the main switches are opened simultaneously to reduce the magnetic field coupling among the modules and make the current rising edge steep. The modules are divided into several groups. The triggering delays of the thyristors between every two adjacent groups are carefully designed. After the first triggers for all the modules, the energy stored in the capacitors can be further utilized with the second triggers. The numerical simulation results show that the appropriate collaborative triggering delay can increase the adjustability of the output current width and the second triggers can further increase the current width and the system efficiency. Therefore, the load current with flat shape, appropriate amplitude, and longer duration can be provided with modular design and collaborate triggering discharge of the multiple modules. This can provide a theoretical foundation for the future study and implementation. [ABSTRACT FROM PUBLISHER]

The STRETCH meat grinder is one typical inductive pulsed-power supply topology for electromagnetic launch system. It has remarkable current amplification ability as a single unit, but one module cannot provide enough amplitude and width for the load current of the railgun launching. This paper discusses the effects of different triggering delays on the load current with two STRETCH meat grinder modules. To reduce the magnetic field coupling between the two modules, the two main switches are opened simultaneously. To make the load current waveform with no notch, the thyristor of the first module is triggered when its pulse-forming capacitor is fully reversely charged. For the thyristor of the second module, we consider several time points of triggering delay. Because of the practical constraint for the maximum rail current that ensures no rail erosion, the rectangular waveform is the most appropriate load current waveform. Therefore, the comparing criterion can be defined as the ratio of the load current waveform area and its maximum rectangle area at different current levels. Higher ratio means that the current is more like a rectangular wave and is better accordingly. Based on the above criterion and extensive simulation research, we found that the best delay time is the moment when the capacitor is reversely charging the inductor completely. This paper and the result are of great theoretical significance for the further study on the collaborative triggering of multiple STRETCH meat grinder modules. [ABSTRACT FROM PUBLISHER]

The stored-to-kinetic energy conversion efficiency of railgun system is investigated by simulation and experiment methods. There are many factors, which might affect the conversion efficiency of the railgun system. These factors include the parameter values of pulsed power supply (PPS), the velocity of armature, the inductance gradient of rail, and so on. To analyze the stored-to-kinetic energy conversion efficiency, a novel electric circuit simulation model for the railgun system is built. The simulation results show that the less resistance, the more inductance of PPS, the more inductance gradient of launcher, and the higher muzzle velocity of armature can improve the energy conversion efficiency of the railgun system. Some experimental results with the 6-MJ railgun system at Beijing Institute of Special Electromechanical Technology are also presented in this paper, which can illustrate the correctness of the analysis and the simulation results. [ABSTRACT FROM PUBLISHER]

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. [ABSTRACT FROM AUTHOR]