Explosive foil injection (EFI) pre-accelerator for electromagneticlaunchers

The use of an explosive foil injection system (EFI) for imparting an initial velocity on a projectile prior to its entering the breech of a railgun is demonstrated. This will substantially reduce the dwell time of the main arc at the breech end of the rails, which will greatly reduce the rail and dielectric ablation of the bore when compared to standing start systems. The preinjection system uses a small capacitor bank (6 kJ at 15 kV) to explode a fine nickel chrome wire and a disk of aluminum foil. The explosive energy produced is harnessed in a 99.5% pure aluminum driving plate assembly, which is free to move in the direction of the projectile only. The projectile (9.9 mm cube of Lexan) is in contact with the driving plate via a driving slug and is thus propelled along a flight tube into the breech of the main railgun. Preinjection velocities of up to 300 m/s have been obtained with a stored energy of only 2.7 kJ     

Direct measurement of rail resistance

An experimental technique for directly measuring rail resistance during a railgun firing is described. A simple railgun flux loop is the only additional instrumentation (beyond standard instrumentation) required to determine rail resistance. Several tests were conducted to verify this rail resistance measurement technique. Typical test data for current, dI/dt, flux loop voltage, breech voltage and muzzle voltage are shown. It is concluded that the technique will permit the evaluation of advanced rail and railgun concepts such as cryogenic rail operation and transposed conductor rail performance     

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.     

Mechanical design aspects of the HYVAX railgun

The hypervelocity experiment (HYVAX) railgun (Fig. 1) is designed to produce projectile velocities greater than 15 km/s in a 13-m-long, round bore gun. The HYVAX gun incorporates a modular design enabling it to operate in either a distributed energy-storage mode or a single-stage mode. The gun is composed of seven O.3-m-long power input modules and nine 1.2-m-long accelerating modules. The gun is designed for a 100-shot life. To accommodate this, the bore may be enlarged from an initial diameter of 10.8 mm to a final diameter of 12.7 mm. This will allow the bore to be refinished several times during the life of the gun. To minimize mechanical and arc damage to the gun between bore refinishing operations, the gun will incorporate a low pressure helium projectile injector. Projectiles will be injected under vacuum at 350 m/s. The gun will be operated at a peak current and voltage of 600 kA and 6 kV respectively. The gun will undergo three phases of testing. The first phase will be the characterization of the gun's performance using a 3.0-m-long section of the gun comprising two power modules and two accelerating modules. This testing will be accomplished using two of the seven capacitor bank modules shown in Fig. 1. The second test phase will use a distributed power configuration and seven capacitor bank modules, as shown in Fig. 1, to demonstrate a velocity of 15 km/s with a 1-g projectile. The predicted performance of the gun for this test phase is illustrated in Fig. 2. In the third phase of testing we will use a magnetic flux compression generator (MFCG) to power the gun with a goal of demonstrating a velocity of 25 km/s.     

The CEM-UT rapid-fire compulsator railgun system-recent performanceand development milestones

Twenty-seven compulsator-powered railgun experiments have been performed, including a 1.0 MJ discharge at 3510 r/min. In this test, a 724 kA current pulse accelerated an 80 g, aluminum armature to 2.05 km/s, thus exceeding the projectile velocity goal at 73%-rated machine speed. Furthermore, operation with a single gun barrel has been achieved using a parallel path, solid-state closing switch to deliver 132 kA to the railgun injector. The latest data are presented from the rapid-fire compulsator railgun facility. Included is a discussion of the energy transfer, power output, and system efficiency during a 1.0 MJ discharge. Also shown are the injector current, voltage, and di/dt curves for this test which were used in the design of the solid-state closing switch. Results of railgun experiments using the solid-state switch are analyzed     

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     

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.     

The TAERF scientific railgun theoretical performance

The successful demonstration of direct-current railguns during the last decade has shown that these simple devices have the capability of accelerating gram-sized projectiles to very high velocities, provided that the current and energy is fed into the accelerator in an appropriately controlled manner. Two current-control devices have been used successfully, the large inductor and the explosive flux compressor. In the experiments done to date, only a single power supply device has been used, connected to the breech end of the rails. The performance of these railguns was limited by such factors as the electrical resistance of the rails, however, and improved performance is expected to be obtained by using many energy stores distributed along the length of the gun The Center for Electromechanics at the University of Texas at Austin is funded to build a distributed energy store railgun. The theoretical performance of this gun is examined for several cases in which different numbers of energy stores are used.     

Distributed energy store railgun: the limiting case

When the limiting case of a distributed energy store railgun is analyzed, (i.e. the case where the space between adjacent energy stores become indefinitely small) three important results are obtained. First, the shape of current pulse delivered by each store is sinusoidal with an exponential tail. Secondly, the rail-to-rail voltage behind the rearmost active store approaches zero. Thirdly, it is not possible to choose parameters in such a way that capacitor crowbars can be eliminated     

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.     

Railguns powered by explosive driven flux compression generators

Explosive driven flux compression generators (FCG's) are single-shot devices that convert part of the energy of high explosives into electromagnetic energy. Some classes of these generators have served quite well as railgun power sources. In this paper and the following paper we describe strip and helical type FCG's, both of which are in use in the Los Alamos railgun program. Advantages and disadvantages these generators have for railgun power supplies will be discussed, together with experimental results obtained and some of the diagnostics we have found particularly useful.     

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     

Electromechanical railgun model

The electromechanical aspects of railgun motion are modeled analytically. A Lagrangian formulation is used to obtain the force and circuit equations, which are then solved for energy conservation and resistive flux decay. The resulting integral equation is solved for the barrel length as a measure of the launcher size and cost. The solution for a lossy railgun with multiple conductors (augmented case) is explained, and energy recovery is discussed.<>     

High velocity contact properties

It is noted that electrical contacts have not been experimentally investigated at velocities above a few hundred meters per second. The authors describe a ballistic technique which can be used to measure friction coefficient and contact resistance at velocities up to several kilometers per second (i.e. at railgun armature operating conditions). The theoretical basis of the technique is described, and the experimental hardware 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.     

Maintenance strategy based on a multicriterion classification of equipments

In an industrial plant, the level of maintenance provided to individual equipment is directly related to the availability that is expected from it. Thus, it is hoped that the most critical equipments will not fail or, at least, that any failure will be rapidly detected and corrected in the minimum time possible. Since resources are limited, it is necessary to determine how they should be distributed, so that no important equipment remains neglected while more resources are concentrated on the most critical items. Therefore, it is necessary to classify equipment in an objective way according to its importance. The method of multicriterion classification of critical equipments (MCCE)², which is described in the present work, allows systematic and detailed quantification of the criticality of all equipment, that is to say, it provides an evaluation of the importance that its correct operation has for the plant. To provide this information, the consequences for a company of any failure in the equipment concerned are analysed. Finally, a real case example of an urban wastewater treatment plant is described, in which the MCCE method is applied.     

Analysis and implementation of a soft switching interleaved forward converter with current doubler rectifier

A soft switching interleaved forward converter with current doubler rectifier is presented. Active clamp circuit is used in the primary winding of transformers to recycle the energy stored in the leakage inductor and the magnetising inductor so that the voltage stresses of switches are reduced. The leakage inductance of transformers, the magnetising inductance and the clamp capacitance are resonant to achieve zero-voltage switching (ZVS) of clamp switches. The resonance between the leakage inductance of transformers and output capacitance of switch will achieve ZVS operation for the main switches in the proposed converter. The interleaved operation can reduce the current ripple on the output capacitor. Two current doubler rectifiers with ripple current cancellation are connected in parallel at the output side to reduce the current stress of the secondary winding of the transformer. All these features make the proposed converter suitable for the DC-DC converter with high output current. The operation principle and system analysis of the proposed converter are provided in detail. Finally, experimental results, taken from a laboratory prototype rated at 125 W, are presented to verify the feasibility of the proposed converter.     

Design and Performance of the First Dual-Coil Magnet at the Wuhan National High Magnetic Field Center

The first 80 T dual-coil magnet was manufactured and tested at the Wuhan National High Magnetic Field Center (WHMFC). The inner coil consists of 8 layers of 2.8 mm × 4.3 mm CuNb microcomposite wire developed in China; the bore diameter is 14 mm and the outer diameter 135 mm. The outer coil was wound directly on the inner coil with 12 layers of 3 mm × 6 mm soft copper. Each conductor layer of both coils was reinforced by Zylon/epoxy composite. The inner and outer coil were driven by a 1.6 MJ/5.12 mF capacitor bank and by eight 1 MJ/3.2 mF modules, respectively. At the voltage of 14.3 kV for the inner coil and 22 kV for the outer coil, the inner and outer coils produced peak fields of 48.5 T and 34.5 T respectively, which gave a total field of 83 T. This was the first combined operation of the new capacitor banks installed at the WHMFC. We present details of the design, manufacture and test of the dual-coil magnet and discuss crucial material properties. Based on this experience, a second dual-coil magnet will be designed; the enhanced design will be discussed. With the total energy of 12.6 MJ, peak field up to 90 T is expected.     

Pulse forming network for railgun launcher

The pulse forming network program complex for parameter calculation of capacitive energy store is developed for obtaining a preset shape current in a railgun launcher. A different scheme analysis of capacitive pulse forming networks is given for obtaining current pulses with a flat peak in the railgun launcher. It is shown that a scheme of a pulse forming network where the start switches are all triggered together is the most simple scheme for the formation of quasi-rectangular current pulses