Electromagnetic gun/projectile interface considerations

Projectile/electromagnetic-gun interface design considerations for electromagnetic gun weapon system (EMGWS) area D1 projectiles, area B-guns, and area C-guns are presented. Projectile/EM gun interfaces are primary considerations in the projectile structural design and the design of the sabot obturator/bore rider, pusher plate, and armature. Acceleration profile, armature type and mass, preinjector characteristics, bore pressure, magnetic fields, and plasma temperature are all key issues in the ultimate projectile performance. Armature design is a critical technical issue for both the projectile and EM gun design because of the high masses involved. Solid armatures are heavier than plasma armatures, but operate at higher electrical efficiencies. Plasma armatures are both being considered for the B-guns and C-guns. Performance tradeoffs are presented for penetration versus peak acceleration and armature mass. Contributors to projectile dispersion such as in-bore balloting, projectile spin, and EM launcher muzzle arc effects are assessed     

The DES raligun facility at CEM-UT

The Center for Electromechanics at The University of Texas at Austin (CEM-UT) has constructed a facility for the operation of electromagnetic (EM) launcher experiments. The facility was specifically designed to investigate distributed-energy-store (DES) railguns. Experiments conducted in the facility have demonstrated the DES railgun concept using a 1-m long, four-stage DES railgun. Investigations have begun on a 4-m, ten-stage DES railgun to demonstrate operation of such a system at higher projectile velocities. The capabilities and design of the major components of the facility are described. Also presented is a review of the experimental development of the railgun system. The DES railgun facility is a versatile laboratory test bed facility for EM acceleration experiments.     

Basic principles of coaxial launch technology

Coaxial launchers have received very much less attention than railguns because of their greater complexity, but they offer several significant advantages. They require no physical contact with the projectile, scale readily to very large diameter, can distribute thrust over the length of the projectile, have more adaptable energy supply and impedance requirements (being a multi-turn device), offer higher efficiency, positive control over the launch cycle, and permit component redundancy to achieve any desired degree of reliability. Thrust for a given current can be a hundred times higher than in a railgun, but the current must be synchronized with projectile motion. The voltage required to do so increases with velocity, and high voltage commutation capability represents the technological limit to launch velocity. Present research activity is concerned with commutation in the low and high velocity domains, position sensing techniques, dynamic stress containment in drive coils, and design of the first practical EM launcher: a Nimitz class aircraft catapult.     

High velocity linear induction launchers

Electromagnetic launchers (EMLs) have received great attention in the last decades because of their potential application to a variety of energy, transportation, space, and defense systems. Particularly, they can serve as kinetic weapons, such as ground-based and naval artillery, space-based anti-missile guns, Earth-to-Orbit launcher, and mass transportation. The main advantage is that EMLs can accelerate projectiles to hyper velocities, i.e. velocities greater than those achievable with conventional cannons. The Linear Induction Launcher (LIL) is an air-cored electromagnetic coil launcher operating on the principle of the induction motor. Polyphase excitation of the coils constituting the barrel is designed to create an electromagnetic wave packet, which travels with increasing velocity from the breech to the muzzle. The projectile is a hollow conducting cylinder (sleeve) carrying the payload within it. Relative motion (slip) of the wave packet with respect to the projectile induces azimuthal currents in the sleeve that interacts with the exciting magnetic field to produce both propulsive and centering forces. This paper deals with the design of a high velocity linear induction launcher with muzzle velocity up to 6000 m/s. It addresses the design specifications of the launcher and utilizing a projectile weighing 1 kg. In the paper, the design specifications with simulation results for the phase voltages, the currents, the velocity, and the temperature rise of the sleeve are presented.     

United Kingdom EM gun programme

The authors review the progress in the RARDE (Royal Armament Research and Development Establishment) electromagnetic gun (REMGUN) program. They cover research on both railgun and LIA (linear induction accelerator) technology, including work on modeling, projectile/barrel interactions armatures, switching, and instrumentation. They also describe the major research facilities. Progress is reported in the identification and development of single-shot switches, integrated switch/barrel concepts, armatures and pulse power supplies as well as the integration of railgun components. LIA research has concentrated on launcher design and projectile/barrel interactions, highlighting the problems of pulse power systems for this form of electromagnetic launcher     

机载焰弹发射装置弹药储运防护设计

目的为了近一步加强和提高人工影响天气行业机载焰弹发射装置弹药的安全储运和防护问题。方法依据焰弹的贮运要求和对现有机载催化作业设备的材料、技术指标、性能要求、结构原理和加工工艺等方面进行分析和研究。结果该装置由发射器、电路控制器和Ag I焰剂构成。经试验和初步应用证明,该发射装置具有手自一体2种发射模式,携弹量为400枚,可连续作业达4 h以上,与目前所使用的相关机载焰弹发射装置相比,在作业方式、作业效率和弹药安全防护等方面都有了极大的改善和提升。结论新型机载焰弹发射装置的成功研发有效地弥补了机载焰弹设备在弹药携行方面的不足和缺陷,并为其他类似的产品设计提供参考。     

Explosive gun launcher for impact studies

We have modified the design of an explosive gun launcher described at the Third Symposium on Hypervelocity Impact for use with pre-cast explosive charges and to provide performance information for steel projectiles. Other modifications include additional confinement of the detonation products, a longer barrel and longer conical transition from breech to barrel, provision for dynamic sealing of the access hole for the detonator wires, and additional buffering to prevent spall fracture of the projectile in the barrel. The modified gun launched a 12.1 gram steel projectile to a measured velocity of 3.2 km/s. Computational simulations have been performed to determine the effects of changes in the projectile density, confinement material density, and explosive type. The use of recyclable confinement material is discussed.     

Continuous measurements of in-bore projectile velocity

The application of velocity interferometry to the continuous measurement of in-bore projectile velocity in a small-bore three-stage railgun is described. These measurements are useful for determining projectile acceleration and for evaluating gun performance. The launcher used in these studies consists of a two-stage light gas gun used to inject projectiles into a railgun for additional acceleration. Results obtained for projectile velocities to 7.4 km/s with the two-stage injector are reported, and potential improvements for railgun applications are discussed     

Railgun performance with a two-stage light-gas gun injector

Results obtained with the HELEOS (hypervelocity experimental launcher for equation of state) railgun, which uses a two-stage light-gas gun (2SLGG) as an injector, are presented. The high-velocity 2SLGG injector preaccelerates projectiles up to ~7 km/s. The high injection velocity reduces the exposure duration of the railgun barrel to the passing high temperature plasma armature, thereby reducing the ablation and subsequent armature growth. The 2SLGG also provides a column of cool, high-pressure hydrogen gas to insulate the rails behind the projectile, thereby eliminating restrike. A means to form an armature behind the injected projectile has been developed. In preliminary tests, the third-stage railgun has successfully increased the projectile velocity by 1.35 km/s. Extensive diagnostics have been used to determine the behavior of the armature and track the launcher's performance. Insome cases, velocity increases in the railgun section have been achieved, which are in close agreement with theoretical predictions, whereas in other experiments deviations from theoretical have been observed. The reasons for and implications of these results are addressed. Recent tests are reported     

The reconnection gun

An electromagnetic launcher called the reconnection gun is introduced. Its potential performance is shown to be superior to that of a modern railgun for projectiles with mass greater than a few hundred grams. It has a "characteristic velocity" which is an order of magnitude lower for much lower energy loss to ohmic heating. Also, it has several advantages for producing higher acceleration including; no barrel, no drop in acceleration with increase in projectile mass, higher peak pressure on the projectile and smaller differences between average and peak pressure. Experimental results and plans for high-performance, multi-stage designs are briefly discussed.     

Electromagnetic induction launchers

The electromagnetic launcher consists of a system of stator coils producing a traveling field which accelerates an armature carrying currents induced by the traveling field (induction accelerator [1,2]) or persistent currents supplied from otner sources (synchronous accelerator [2,10]). The fact that their armature has no electrical contact with the stator, essentially riding on the crest of a traveling magnetic wave, makes induction accelerators very attractive for a large number of applications. This paper is devoted exclusively to the accelerator of the induction type. Efficiency considerations require that the traveling wave should accelerate at approximately the same rate as the projectile. This can be achieved either using variable (increasing) winding pitch or a continuously increasing power supply frequency or a combination of both. A new dimension was added to the induction coaxial accelerator technology with the definition at the Center for Electromechanics at The University of Texas at Austin (CEM-UT) of a new electrical machine, the Rising Frequency Generator (RFG) representing a more attractive integrated power source for induction accelerators which had previously been forced to conform to constant frequency power supplies. This paper outlines the principles of design and shows two applications of induction coaxial launchers; a half-scale aircraft launcher in which the system also acts as an electromagnetic brake, stopping the shuttle and driving it in the opposite direction, and a high performance, 18-m long launcher capable of accelerating a 1-kg aluminum projectile to a velocity of 10 km/s at an average acceleration of 250,000 G.     

Influence of the critical velocity on deformation of launcher components

This paper is related to the dynamics of hypervelocity electromagnetic launchers. A projectile accelerating along launcher rails may cross a range of critical velocities and induce structural resonance. As a result, the rails and other components exhibit increased displacements and stress that may affect launcher performance and lead to premature launcher failure. This work is a continuation of our previous studies of the critical velocity and resulting transient resonance that was performed for a notional hypervelocity launcher [Nechitailo NV, Lewis KB. Critical velocity for rails in hypervelocity launchers. In: Proceedings of the 2005 hypervelocity impact symposium. International Journal of Impact Engineering Dec. 2006; 33: 485–495; Lewis KB, Nechitailo NV. Transient resonance in hypervelocity launchers at critical velocities [Selected papers from the 13th Electromagnetic Launch Technology (EML) Symposium, Potsdam, Germany, May 22–25, 2006]. IEEE Transactions on Magnetics Jan. 2007; 43 (No. 1, Part II): 157–162 [1,2]]. Analytical models including Bernoulli–Euler model of a beam resting on an elastic foundation and the Timoshenko and Flügge tube models as well as finite element tools helped to better understand the transient resonant regimes in launcher components and offered insight on how to alter the launching device materials and geometry to reduce the critical-velocity effects. Analysis showed that the various components of a launcher can have different critical velocities and there is a possibility of enhanced group resonance in the assemblies. The resonance in the launcher assembly can be reduced by controlling the bending stiffness of the individual components. Finite element models were used to illustrate the influence of variations in materials of launcher components on the resulting critical velocities, intensity of the group resonance, and resulting maximum displacements and stress.     

High-efficiency, medium-caliber helical coil electromagnetic launcher

Research progress in the development of a 40 mm/spl times/750 mm helical-coil electromagnetic launcher (HCEL) is presented and discussed. Significant technical problems that have been solved in this research include efficient stator commutation methods and the ability to simultaneously implement high-inductance gradient armatures. The HCEL is able to launch a 525-gram projectile to a velocity of 140 m/s. Power for the HCEL is derived from a 62.5 kJ sequentially fired pulse forming network (PFN) of 900 V (maximum) electrolytic capacitors. The experimentally measured HCEL efficiency of 18.2% is substantially greater than a conventional or augmented railgun of similar scale (i.e., equivalent mass, bore-size, and velocity). The HCEL's high launch efficiencies result from its 150 /spl mu/H/m inductance gradient, which is approximately 300 times greater than the inductance gradient of a conventional railgun. HCEL computer model predictions are given and compared to experimentally measured HCEL and PFN parameters including peak current, inductance gradient, acceleration time, parasitic mass ratios, and electrical-to-kinetic conversion efficiency. Scaling relationships for the HCEL are also presented and used to predict launcher operation at higher velocity and with a larger diameter bore size.     

Transient magnetic field and temperature modeling in large magnetapplications

A coupled magnetic/thermal model for studying heat and magnetic field diffusion in conducting materials subject to time-varying external fields has been developed, using the General Dynamics Thermal Analyzer code. Applications include energy storage devices, pulsed power transformers, and electromagnetic launchers, and the time scales of interest range from a magnetic field pulse of a microsecond to hundreds of seconds. The results of this model, showing the time and spatial variation of the magnetic field and temperature, are discussed for the projectile of an electromagnetic launcher     

Hypervelocity macroparticle accelerator experiments at CEM-UT

Several railgun experiments designed to accelerate projectile masses of 2 to 5 g to velocities greater than 6 km/s were performed. Two parallel rail-type accelerators with 12.7 mm square bores were used for the experiments. One gun is 2 m long, has molybdenum rails and alumina ceramic insulators. The other is 1 m long, has molybdenum rails and granite insulators. The greatest velocity achieved to date during the experiments was 5.1 km/s. During the test program, the following ideas to enhance launcher performance were tested: stiff-gun structures to reduce plasma leakage and rail movement, refactory bore materials to reduce ablation and frictional losses, and prefilling the gun bore with gases which will eliminate precursor arcs. After three experiments utilizing the 2 m long launcher, with peak currents ranging from 660 to 780 kA, a gun barrel comprised of 96% pure alumina ceramic insulators and 99.9% pure molybdenum rails has survived with minimal damage and no degradation of seals     

Predicting bore deformations and launcher stresses in railguns

The structural responses of launchers are important because they affect the projectile performance and the operating limits of the railgun system. Structural analysis makes it possible to make better decisions in launcher design. Example analyses of the Los Alamos HIMASS and Lethality Test System launchers are presented in this paper. Also, a discussion of the benefits and limitations of these analyses is included.     

A hypervelocity projectile launcher for well perforation

Current oil well perforation techniques use low- to medium-velocity gun launchers for completing wells in soft rock. Shaped-charge jets are normally used in harder, more competent rock. A launcher for a hypervelocity projectile to be used in well perforation applications has been designed. This launcher will provide an alternative technique to be used when the conventional devices do not yield the maximum well perforation. It is an adaptation of the axial cavity in a high explosive (HE) annulus design, with the axial cavity being filled with a low density foam material. Two configurations were tested; both had an HE annulus filled with organic foam, one had a projectile. Comparison of the two shots was made. A time sequence of Image Intensifier Camera photographs and sequential, orthogonal flash x-ray radiographs provided information on the propagation of the foam fragments, the first shock wave disturbance, the projectile motion and deformation, and the direct shock wave transmission from the main HE charge. Perforation tests of both device configurations (with and without the pellet) into steel-jacketed sandstone cylinders were made. Static radiographs of the cavities in the sandstone showed similar cavities, however, the perforation of the steel cap was larger in response to the pellet. DYNA2D calculations were made to assist in the interpretation of the experimental records. The preliminary results show promise that a useful perforating tool can be developed. Plans for an extended experimental program are outlined.     

Review of modern hypervelocity impact facilities

The paper describes three hypervelocity impact facilities, their instrumentation, the laucher systems, the launch techniques for a large variety of projectile geometries, and the launcher performance. A very brief review is given of the research in the areas of military applications, meteorite impact simulation, basic impact research, and efforts to improve the performance of the light-gas guns and measurement techniques. An outline at future research programs is given.     

The use of hypervelocity launchers to explore previously inaccessible states of matter

The dynamic response of materials at very high pressure and temperature is important in a wide variety of scientific and programmatic applications. Thermodynamic regions of interest include the high-pressure response of condensed phases and the highly expanded states of materials. Since these regimes are normally studied with flat-plate impact techniques, it is necessary that projectile velocities achievable with highvelocity launchers be sufficient to access the desired thermodynamic regions. In this paper, we discuss the equation-of-state regions that would be accessible with a plate impact capability of 15 km/s and summarize the status of a hypervelocity launcher under development which will provide the required velocity capability.