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.     

Hypervelocity impact testing using an electromagnetic railgun launcher

An electromagnetic (EM) railgun launcher facility has been developed to routinely conduct hypervelocity impact tests. Two types of completely reusable EM launchers have launched sabot/impactor packages between 2 and 43 grams to velocities between 1.5 and 8.5 km/s. The highly reliable railguns have conducted over 250 projectile launchings and have established a projectile/launcer data base covering interior as well as exterior ballistic considerations. A conventional type instrumented ballistics range is compatible with the EM launcher and can be used to conduct anti-armor and lethality experiments at hypervelocities.     

Stress analysis of the rails of a new high velocity armature design in an electromagnetic launcher

In an electromagnetic launcher, the magnetic field creates a dynamic force that moves the armature forward. In an electromagnetic launcher, the armature reaches a critical velocity during the launch which causes high amplitude stress and strain. In addition, high stress and strain damage the rails and reduces its life span. The purpose of this paper is to investigate the effect of armature velocity as well as the rails physical and geometrical properties on the dynamic response of the rails in an electromagnetic launcher. In this study the second moment of inertia of the rails cross-section, Young modulus, foundation stiffness and density of the rails are constant in location and time. In our formulation of governing non-linear differential equations, Maxwell equations and deflection equation are applied to the rails under dynamic loading. To solve the non-linear governing differential equations a finite difference method is utilized.     

Final design of an air core, compulsator driven, 60 caliber railgunsystem

The manufacturing phase of a laboratory-based small-caliber electromagnetic (EM) launcher and compulsator power supply is discussed. The objective of the 29-month program is to develop a compact, lightweight test bed capable of accelerating 32 g masses to 2 km/s at a rate of 10 Hz. Both the power supply and launcher feature significant component design advances which will allow the system to operate at considerably higher energy and power densities than previously demonstrated. The 750 kg compulsator will generate 2.2 kV and the silicon-controlled rectifier (SCR) switch will commutate 386 kA pulses into the 1.6-m long, 0.60 caliber augmented solid armature railgun. The final design and predicted operating characteristics of the compulsator system are described. Overall system performance parameters are reported, including results from the optimization code used to aid in the design of the compulsator system. A system design overview is presented, with emphasis on new materials and state-of-the-art machine components to be used for the first time in a compulsator     

Elastic waves and solid armature contact pressure in electromagnetic launchers

Electromagnetic launchers suffer a phenomenon referred to as armature transitioning: when the armature and rails suddenly lose contact with each other, damage can occur to the armature and the rails of the launcher. In this paper, we explore transient elastic waves as a possible explanation for the transitioning of solid armatures in electromagnetic launchers. We use a finite-element code to model the transient dynamics of a typical electromagnetic launcher guide rail. We found that dynamic rail deflections caused by the movement of the armature are similar in magnitude to those caused by the magnetic field, and that the contact pressure between the armature and the rails changes dramatically when the speed of the armature reaches the critical velocity of the rails.     

A second generation EMET railgun for secondary arc studies

Since 1985 GT-Devices has been operating a pair of railguns with lengths of 0.9 m and 3.6 m, respectively. A new second-generation railgun is now being constructed to improve straightness, stiffness, sealing, and diagnostic access. The basic design consists of a steel tube with a thin lengthwise slit forming two halves in cross section with bolt preloading. The internal structure consists of split tubular G-10 compression blocks with Glidcop AL-15 rails and polycarbonate insulators formed from 90 degree tube sections. A new 0.9 m launcher of the same design is now under construction, with a 3.6 m version to follow. An upgraded electrothermal injector has been developed using modified armature injection module (AIM) hardware. Injection velocities of 2500 m/s have been attained with 1.1 gram polycarbonate projectiles for stored bank energies of 65 kJ. Injection velocities of 3000 m/s may be possible. The design details of the new railgun, injector, and diagnostics are discussed, and some initial experimental results are presented     

Plasma puffing from a railgun armature

A series of experiments has been conducted in which plasma has been allowed to escape from the armature of two railguns. This has enabled improved estimates of armature length to be obtained, as well as direct evidence of armature temperature.     

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.     

Distributed-current-feed and distributed-energy-store railguns

Distributed-type railguns are combinations of power supplies and railguns designed to maintain a nearly constant current in the armature of a railgun and to overcome the accelerator length limitations of simple breech-fed railguns. This limitation arises from the increasing resistance and inductance of the rails with increasing railgun length. The energy efficiency of a railgun system from the primary energy store to the kinetic energy of the projectile can be improved as compared to the simple railgun in some applications. This is accomplished by a reduction of the stored magnetic field energy in the bore of the railgun at the end of a shot and reduction of the resistive losses in the rails. The improved system performance of the distributed railguns over the simple breech-fed railguns is achieved at the expense of greater system complexity. The only distributed-type railguns that have been built to date are distributed-energy-store (DES) railguns. These systems presently use capacitors as the primary energy store, which allows the use of closing switches to initiate current from each of the stores. In this paper a new type of railgun, the distributed-current-feed (DCF) railgun, is presented. The DCF railgun system is a compromise in system complexity and efficiency between the DES railguns and the simple breech-fed railguns. Also, the DCF railgun utilizes closing switches in such a manner as to allow the use of a variety of primary power supplies, including homopolar generators (HPGs), for such electromagnetic propulsion tasks as space launches.     

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     

Rail and armature current distributions in electromagnetic launchers

The current and magnetic field distributions in the rails and armature of an electromagnetic launcher are obtained in closed form for the steady state. These solutions assume that the armature moves with a steady velocity and account fully for the two-dimensional skin effect caused by the relative motion between the rails and the armature. Both solid and laminated armatures are considered. It is found in the case of the laminated armature that the phenomenon can be described by a single dimensionless parameter,frac{ell}{w}frac{sigma_{o}}{sigma_{r}}sqrt{frac{uell}{pieta_{r}}}.     

方口径电磁轨道发射装置导轨及壁板的动力响应

本文将方口径电磁发射装置的导轨及壁板简化为双层弹性基础梁,分别采用Heaviside函数和Dirac函数表示随电枢移动所产生的均布电磁力和电枢作用在导轨上的集中载荷,建立了导轨及壁板的动态响应方程。应用模态正交性及正则化原理,求得了导轨及壁板的位移和应力的解析解。通过算例,分析了给定运动及结构参数的情况下,导轨及壁板的动力响应,并将解析解与采用ANSYS数值分析结果进行了比较,佐证了解析解的可靠性。本文的研究结果可为方口径电磁轨道发射装置的动态特性分析奠定了基础。     

Mass sensitivity studies for an inductively driven railgun

Those areas which result in substantial system mass reductions for an HPG (homopolar generator) driven EML (electromagnetic launcher) are identified. Sensitivity studies are performed by varying launch mass, peak acceleration, launcher efficiency, inductance gradient (L'), injection velocity, barrel mass per unit length, fuel tankage and pump estimates, and component energy and power densities. Two major contributors to the system mass are the allowed number of shots per barrel versus the number required for the mission, and the barrel length. The effects of component performance parameters, such as friction coefficient, injection velocity, ablation coefficient, rail resistivity, armature voltage, peak acceleration, and inductance gradient on these two areas, are addressed     

Muzzle shunt augmentation of conventional railguns

Augmentation is a well-known technique for reducing the armature current, and hence the armature power dissipation, in a plasma armature railgun. In spite of the advantages, no large augmented railguns have been built, primarily due to the mechanical and electrical complexity introduced by the extra conductors required. It is possible to achieve some of the benefits of augmentation in a conventional railgun by diverting a fraction φ of the input current through a shunt path at the muzzle of the railgun. In particular, the relation between force and armature current is the same as that obtained in an n-turn, series-connected augmented railgun with n=1/(1-φ). The price of this simplification is a reduction in electrical efficiency and some additional complexity in the external electrical system. Additions to the electrical system are required to establish the shunt current and to control its magnitude during projectile acceleration. The relationship between muzzle shunt augmentation and conventional series augmentation is developed, and various techniques for establishing and controlling the shunt current are illustrated with a practical example     

The stability and the conditions for initiation of electric-arc discharges in railguns

Characteristic physical features of plasma formations in high-velocity sliding electric contacts are treated, in particular, those in railguns with both electric-arc and metal armatures. Comparison is made of the effect of a number of MHD instabilities (superheating, Rayleigh-Taylor, and erosion-dynamic) on the working capacity of plasma armature. It is demonstrated that the armature compactness may be disturbed both in the case of fairly intensive abrupt drop of current and in the case of increase in the associated mass of the armature, which is defined by the processes of erosion and ablation of the electrodes, walls, and dielectric projectile. The theory of transition of metal contact is generalized in view of the presence of transition electric resistance and external magnetic field.     

Observation and analysis of current carrying plasmas in a railgun

Observation of current-carrying plasma arcs driving solid projectiles in round-bore and square-bore railguns have been made with magnetic induction coils. Both free-running precursor arcs as well as projectile armature arcs are observed. Qualitative behavior of the plasmas is inferred from data and compared to basic physical models. The non-uniform nature of the force on the armature is investigated. Experimental details as well as difficulties in calibration and in quantitative analysis of magnetic probe signals are discussed. Evidence suggesting evolution in the structure of free-running arcs is presented.     

Results of railgun experiments powered by magnetic flux compression generators

Researchers from the Lawrence Livermore National Laboratory and the Los Alamos National Laboratory initiated a joint railgun research and development program to explore the potential of electromagnetic railguns to accelerate projectiles to hypervelocities. The effort was intended to 1) determine experimentally the limits of railgun operation, 2) verify calculations of railgun performance, and 3) establish a data base at megampere currents. The program has led to the selection of a particular magnetic flux compression generator (MFCG) design for a set of initial experiments and the design of small- and large-square-bore railguns to match the expected MFCG power profile. The bore sizes are 12.7 and 50 mm, respectively. In this paper, we briefly describe the design of the railguns and the diagnostic and data reduction techniques, followed by the results of eight experiments with the two railgun types.     

Diamond Materials for Electromagnetic Railguns

The use of diamond film insulator in electromagnetic railguns is currently being seriously considered since the state of the art in synthetic: diamond exceeds the requirements of electromagnetic railguns. The reasons for not using diamond, however, include the major difficulty in producing diamond insulators in the required shape and size that can survive the harsh railgun environment. This paper reviews railgun operation dynamics and potential materials including diamond for high performance of railguns. It further reviews the present status of scientific, technological and commercial developments; of diamond coatings. Alternate coatings and the properties that make them amenable for railgun applications are also discussed.     

Lethality testing involving railgun simulators

The Lethality and Target Hardening (LTH) Program directed by the Defense Nuclear Agency has the mission of developing lethality data for Strategic Defense Initiative (SDI) designated missiles and other targets. For kinetic energy evaluations, data must be developed at various velocities for a variety of projectile masses in order to determine the kill of the targets. The electromagnetic launcher (EML) is theoretically an attractive approach for developing data at projectile velocities greater than 10 km/s. At present, pressure containment, ablation control and plasma armature drag problems are preventing the achievement of the needed velocities. Although railgun weapon and component research is active, the objectives and priorities of that research differ somewhat from the objectives and design needs in building a lethality simulator. An EML lethality simulator is not, for example, encumbered by size, weight or power efficiencies limits. The factors in developing an EML lethality simulator are discussed with an attempt made to find common ground with weapon and component developers for giving proper attention to essential lethality simulator needs.