Railgun Design Research Articles

A long-range naval railgun

The U.S. Navy is considering developing an electromagnetic railgun for use on future ships for long-range shore bombardment missions. The goals are to provide support for ground forces in a timely fashion, increase the ship-to-shore standoff distance, and improve ship survivability in combat situations. This paper describes the parameters of a notional railgun design that may be capable of supporting the Navy's needs. The Naval Surface Fire Support mission requires a railgun capable of firing high-energy projectiles for ranges of 300-500 km with a firing rate of up to 12 rounds per minute. The notional system described here is intended to meet these requirements while providing the ability to take advantage of the integrated electric drive architecture to be used on the next generation destroyer. Several important technology issues will need to be addressed before the feasibility of such a system can be demonstrated. These issues are identified and discussed.

Installation and commissioning of the 9 MJ range gun system 90 mm high L'laminated railgun

In December 1993, The University of Texas at Austin Center of Electromechanics (UT-CEM) completed construction of an high L' railgun for the 9 MJ Range Gun System Program. The 90 mm bore railgun utilizes dispersion strengthened copper rails and incorporates a laminated stainless steel containment structure and filament wound fiber epoxy composite overwrap. In January 1994, the railgun was installed at the Electric Armaments Research Center (EARC) at Picatinny Arsenal, New Jersey, for testing on the 52 MJ capacitor bank power supply. The test program at EARC was designed to allow full 2.8 MA current testing of the railgun, breech connection, and flexible hexapolar cable bus system during completion of the 9 MJ Range Gun System compulsator. The EARC test program allows evaluation of the launcher and flexible bus components prior to the range test program and provides empirical data for concurrent design of other railguns incorporating laminated containment structures. This paper describes installation of the railgun into the EARC facility and discusses performance of the railgun and flexible hexapolar cable bus system during initial testing. The hexapolar cables have been tested to 34 kV and are rated for a nominal current of 200 kA per cable, and the flexible bus system and breech connection have repeatedly performed successfully at gigawatt power levels. The paper also presents the results of the railgun test program firing two variations of the sabot launched electric gun kinetic energy (SLEKE) projectiles along with an evaluation of the performance of the dispersion strengthened copper rails with transitioning solid armatures.

Cannon-caliber electromagnetic launcher

The University of Texas at Austin, Center for Electromechanics (UT-CEM) designed and fabricated a rapid-fire railgun launcher. Three, five-round salvos of 185-g launch packages are to be accelerated to 1,850 m/s at a rate of 5 Hz. The 2.25-m-long series-augmented launcher has a 30-mm round-bore equivalent rectangular geometry and is water-glycol cooled. Rapid-fire operation is achieved by driving the launcher with multiple 835-kA peak pulses provided by the Cannon-Caliber Electromagnetic Gun (CCEMG) compulsator. A single-shot launcher prototype was tested for the CCEMG system at UT-CEM and at the US Army Research Laboratory (ARL). The launcher has demonstrated an efficiency over 50%. A high CCFEMG system efficiency is in part due to the use of a solid armature and is enhanced by having a structurally stiff railgun. Historically, a railgun's stiffness was proportional to its weight. Laboratory-based railguns that have respectable mechanical properties have required massive structures that are nowhere near meeting the requirements of future vehicle integration and weaponization. The CCEMG railgun design incorporates a directional preloading mechanism, ceramic sidewalls, and a composite overwrap, which together give it a structural stiffness dominated by a high-modulus ceramic. The overall mass of the launcher is 273 kg. These characteristics make the cannon-caliber launcher one of the most fieldable railguns built to date.

‘Field’ guns: electromagnetic launchers

The tank weapons of the future may be able to fire without any help from unstable, dangerous chemical reagents. Instead they may use electromagnetic guns. In an electromagnetic gun, the projectile is pushed by an electromagnetic field pressure. In principle this force can be propagated at the speed of light, so in principle, the electromagnetic gun should be able to produce much higher velocities than powder guns. As well as the higher muzzle velocity, the EM gun has logistical advantages for the tank crew that has to use it. These advantages come at a cost in terms of convenience, however. The gun system has a low energy density, which means that the launcher must be heavier and bulkier than a conventional gun barrel. The author describes the formation of the railgun armatures and the design of railguns. The research being carried out in this area in the UK is discussed. The testing of the guns is also discussed.

Current and heat transport in the solid-armature railgun

A numerical model is developed for solving the equations which predict current and heat transport in a series-augmented, solid-armature railgun. The model is two dimensional and fully time dependent. Specific calculations are then carried out to analyze the armature recently designed and developed in the Cannon Caliber Electromagnetic Launcher Program. The most extensive computations are for a situation in which the projectile is started at rest and accelerated to nearly 2 km/s in a time of 2 ms. Results of the calculations can be used to infer, for example, where melting in the armature is most likely to occur and where the electromagnetic stresses are largest. For comparison, calculations are also presented for a situation in which the projectile is held fixed. These calculations are intended to demonstrate the importance of velocity effects in the design of solid-armature railguns.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The use of coupled EM-hydro finite element techniques for the design of railguns

The primary goal of the electric launcher modelling team is to develop techniques to aid our understanding of the physics of railgun launch. This is essential in order to combat the problems which will degrade the performance of railguns from their theoretical limits, especially with the Kirkcudbright facility in mind. In particular, we need to understand die transient material response caused by the launch process. Plasma transitioning and nonideal contact between armature and rail are just two of the problems that analysis codes must be able to address. This paper shows the results of finite element (FE) simulations, at 90 mm scale, of the armature-barrel interaction. Special emphasis is put on the resolution and validation of high temperature hot spots in the armature and in the prediction of transient barrel response. The FE method is based on a soft linking of the 3D FE transient electrical-thermal code MEGA to the dynamic structural code DYNA3D. This version of the MEGA-DYNA3D link has a multi-slide line capability which allows stressing to be calculated by taking into account the hydrodynamic effects of the rail-armature interaction as well as the electromagnetic forces.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A novel railgun launcher design

Higher efficiency, and smaller power supplies are needed for most electromagnetic railgun applications. This paper describes the feasibility evaluation of a novel railgun barrel configuration that addresses these issues. The Hypervelocity High Efficiency (HYPE) railgun concept uses a distributed power feed railgun design, but eliminates the need for many separate distributed power supplies. Nested, segmented main rails are individually connected to a single pair of augmenting secondary rails. The augmenting secondary rails are powered from a single energy source. A 15 mm square bore, 300 mm long HYPE railgun was built and tested to evaluate concept feasibility. Analytical and experimental results show that the HYPE configuration is feasible, at least for low velocity.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Solid-armature railguns without the velocity-skin effect

The performance limits for railguns which are free of the velocity-skin effect are investigated by deriving the upper limits for a specific kind of power supply. Previous performance estimates made for solid-armature railguns are examined in the light of these results and are found to be relatively very optimistic. A novel railgun design has been invented called the muzzle-fed railgun which could allow control of the velocity-skin effect and thereby greatly improve performance of solid armature railguns.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Railgun current guard plates: active current management and augmentation

A system of auxiliary conductors designed to reduce current density peaks in railgun rails is described, and the effects on rail current density and projectile force are discussed. Performance comparisons with simple railguns and typical augmented railguns are made. It is shown that the wrap-around design of the guard plates can produce four to eight times the force produced by the usual augmented railgun design, without increasing local peak current densities. The range of performance contained in the factors between four and eight is primarily a function of the complexity of design. The more complex designs involve allowing the guard plates to overhang the rail slightly (intruding into the bore space, similar to rifling in a conventional gun barrel), and the use of separate power supplies for the rail and guard-plate conductors. These added complexities represent unacceptable complications for many applications, but may be justifiable for others.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Plasma-armature railgun launcher simulations

The authors review three popular loss models currently used at CEM-UT (Center for Electromechanics at the University of Texas at Austin) in modeling EM (electromagnetic) launchers: friction, ablation, and armature drag. In experiments at currents below 500 kA using existing railgun design, the friction model alone was acceptable in predicting performance. In an experiment incorporating a railgun structure modified for higher stiffness and a measured peak railgun current of 700 kA, the effects of each of the loss models were compared to the measured results, and the greatest success at predicting the final projectile velocity and exit time occurred using the velocity-dependent friction model. It is believed that reducing frictional losses and plasma leakage will be instrumental in achieving velocities greater than 6 km/s.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Structural design of cylindrical railguns

A systematic structural design approach to the development of cylindrical electromagnetic launchers has been formulated, using classical analytical methods in preliminary feasibility studies and finite-element methods to simulate static and dynamic structural response. Three-dimensional stress analysis results indicate that conventional assumptions associated with two-dimensional analysis for design are generally valid. Frequency-domain analysis of the subject structure and associated design loads can be used to estimate the significance of inertial effects under dynamic loading. Results of the study show that significant improvements in system performance are possible despite the limitations of nonconducting structural materials currently available for railgun fabrication.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Design and testing of large-bore, ultra-stiff railguns

As part of an EM (electromagnetic) gun technology demonstration program, a systematic design approach targeted at identifying critical gun design constraints affecting hypervelocity projectile performance has been pursued. Results of the study led to a laboratory-based EM gun design that provides bore straightness and tolerances characteristic of light-gas guns, dynamic bore deformations comparable to those of conventional guns, the ability to change and test rail/sidewall insulator materials quickly, and superior in-bore performance diagnostics. A high-stiffness, easily maintained, precision-bore 9-MJ EM launcher has been designed and fabrication is virtually complete. A half-scale prototype of this hydraulically prestressed EM gun design has been fabricated and successfully tested. The authors discuss the railgun design approach and performance parameters, the analytical and empirical railgun structured simulation techniques used to validate the full scale gun design, and the fabrication status and initial performance test results.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Design and development of extremely high velocity electromagnetic launch accelerators-GEDI program

Research is described that has centered around 1, 2, or 8 m long, 12.7 mm square-bore railguns powered by one or more of the following power supplies: a 1 MJ capacitor-bank-driven, pulse-forming network; a 6 MJ homopolar-generator (HPG)-charged coaxial inductor; or one or more of six 10 MJ Balcones-HPG-charged coaxial inductors. Several variations of the 1 and 2 m-long railguns were designed, fabricated, and tested. Railgun design parameters, development, and some test results are described. Parameters of primary importance in designs include sidewall insulator and rail materials; gun length and outer structure materials; stiffness and strength; ease of assembly and disassembly; and availability of methods for supporting, straightening, and honing the guns. Both static and dynamic aspects of railgun structural behavior are discussed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Electrode erosion in high current, high energy transient arcs

Electrode erosion in high current, high energy spark gaps was examined both theoretically and experimentally. A brief description is given of the production of high velocity, high temperature electrode vapor jets which are shown experimentally to be the major source of electrode erosion under these conditions. Consideration of a simple one dimensional thermal model with the vapor jet considered as a transient heat flux onto the electrode surface led to a figure of merit for the electrode materials which was in close agreement with experiments. The rapid decrease in erosion with increasing gap separation was also measured and explained by the vapor jet mechanism. Erosion rates are given for a large number of electrode materials including many copper composites, such as copper niobium and copper tungsten. Possible implications of these results on rail gun design are also given.

Electromagnetic railgun extended-life bore material tests results

During the last five years the LTV Aerospace and Defense Company (LTVAD) has built and operated a Distributed Energy Source (DES) railgun laboratory. As part of the efforts to improve the efficiency of this gun design, research in the area of rail materials erosion phenomena has been one of the major concerns. Studies have been centered around the basic synergies associated with material's erosion and railgun design; such as, the conductors, the insulators, the bore, the projectile and the gas environment. A data base, consisting of well over 200 shots, has been generated on the erosion rates of copper rails and various insulating sidewall materials at current densities ranging from 200 - 475 kAmps/cm. During these tests the insulating support structures suffered from considerably more erosion than the copper rails and will represent the largest deterent to repetitive operation of a railgun system. Consequently, research in the increased erosion resistance of insulating materials is an area of focus at LTVAD. This work was sponsored by the Army Ballistic Missile Defense Advanced Technology Center.

Testing of coaxial railguns in high vacuum

The goal of many railgun investigations is to arrive at a railgun design that is capable of launching projectiles to extremely high velocities (10 to 100 km/s). Often a second goal is for the railgun design to allow for repetitive launches without a total rebuild of the railgun. These two goals are the objectives the Center for Electromechanics at The University of Texas at Austin (CEM-UT) has pursued over the past several years. As part of the investigation, a serious study of coaxial railguns was conducted. Coaxial railguns were studied because the coaxial geometry offers two attractive features. One feature is the simplified construction, and the other is an inherent lower L' value. Studies were conducted on 0.5-and 5.0-m long coaxial railguns. Results were mixed in that high velocities were obtained (37 km/s), and several shots were done on one gun without cleanup or rebuild, but plasma mass amounts were small and not tightly patterned. Experiments are still underway, on a limited basis, to attempt to focus and bunch the plasma during launch and as it exists the muzzle.

An advanced EM railgun design

The design of a large square bore railgun is described. The qualitative features of thermal management, materials of construction and instrumentation are presented.

Design and testing of high-pressure railguns and projectiles

The results of high-pressure tests of four railgun designs and four projectile types are presented. All tests were conducted at the Los Alamos explosive magnetic-flux compression facility in Ancho Canyon. The data suggest that the high-strength projectiles have lower resistance to acceleration than the low-strength projectiles, which expand against the bore during acceleration. The railguns were powered by explosive magnetic-flux compression generators. 1,2 Calculations to predict railgun and power supply performance were performed by Kerrisk.3

Совместимость формул для силы Ампера и силы Лоренца с концепцией виртуальной работы

Whenever the reaction forces between parts of an electric circuit have to be calculated, as in the design of railguns, a choice has to be made between three available formulae which have evolved during the past 160 years. The first was Ampere’s force law for the mechanical interaction between two current elements. Neumann then derived the virtual-work formula from what may be called the Ampere-Neumann electrodynamics. The last to be introduced was the Lorentz force law. This paper investigates whether both the Amperian and the Lorentzian forces are compatible with the virtual-work concept. The conclusion is that only Ampere’s formula agrees in all cases with the virtual-work idea, but in special circumstances the Lorentz law will give the same result. After demonstrating how Ampere’s law can be derived from the virtual-work formula, it is shown that for two closed circuits the relativistic component of the Lorentz force vanishes under the double integral around the two circuits. The remaining nonvanishing term is also present in the Ampere electrodynamics. This is not the case when considering the reaction forces between two parts of an isolated circuit. The Lorentz force is then, in general, not compatible with the virtual-work concept unless the circuit possesses a high degree of symmetry.

Electromagnetic projectile acceleration utilizing distributed energy sources

Circuit equations are derived for an electromagnetic projectile accelerator (railgun) powered by a large number of capacitive discharge circuits distributed along its length. The circuit equations are put into dimensionless form and the parameters governing the solutions derived. After specializing the equations to constant spacing between circuits, the case of lossless rails and negligible drag is analyzed to show that the electrical to kinetic energy transfer efficiency is equal to σ/2, where σ=2mS/ℒq20 and m is the projectile mass, S the distance between discharge circuit, ℒthe rail inductance per unit length, and q0 the charge on the first stage capacitor. For σ=2 complete transfer of electrical to kinetic energy is predicted while for σ&amp;gt;2 the projective-discharge circuit system is unstable. Numerical solutions are presented for both lossless rails and for finite rail resistance. When rail resistance is included, &amp;gt;70% transfer is calculated for accelerators of arbitrary length. The problem of projectile startup is considered and a simple modification of the first two stages is described which provides proper startup. Finally, the results of the numerical solutions are applied to a practical railgun design. A research railgun designed for repeated operation at 50 km/sec is described. It would have an overall length of 77 m, an electrical efficiency of 81%, a stored energy per stage of 105 kJ, and a charge transfer of &amp;lt;50 C per stage. A railgun of this design appears to be practicable with current pulsed power technology.