Railgun Experiments Research Articles

Muzzle-fed railgun experiments with 3-D electromagnetic simulations

The UTSI 2.4 m transaugmented railgun was reconfigured so that current was fed from the breech to the muzzle along the outer rails and then returned to the armature along the inner rails. Experiments were performed using plasma armatures at peak currents of 70 and 100 kA. At a peak current of 100 kA the measured increase in projectile velocity was approximately 500 m/s; less than half of that obtained from a conventional configuration in the same railgun, and considerably less than predicted for the muzzle-fed configuration. B-dot probes showed that the armature was very compact, but separated from the projectile soon after fusing. Three-dimensional (3-D) finite element electromagnetic simulations on the UTSI railgun structure showed that the electromagnetic force on the armature was much less than predicted by the simple force model. The reduction in force was due primarily to axial forces exerted in the rails.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Velocity limiting magnetohydrodynamic effects in railgun plasma armatures

The results of a four-year theoretical and experimental research program in railgun armature physics at the University of Tennessee Space Institute are reviewed with an emphasis on understanding how the magnetohydrodynamic (MHD) flowfield and electromagnetic interactions limit the velocity in plasma and hybrid armature railguns. The understanding of the 3D plasma armature flowfield has been developed through a combination of highly instrumented railgun experiments, secondary arc performance models, and 2D MHD calculations. These 2D calculations are only qualitative in nature, but they provide insight into the complex armature flow and indicate that the formation of secondary armatures, ablation drag, and primary armature preparation are interrelated. Experimental evidence suggests that 3D MHD flow effects are very important in controlling these phenomena. >

Experimental comparison of conventional and trans-augmented railguns

A 2.4-m-long, 1-cm-diameter round bore railgun was constructed to perform careful experiments which compared the performance of conventional and transaugmented plasma armature railguns. Conventional railgun experiments were performed over a range of currents to characterize the base performance of the railgun and to provide data for the development of ablation drag and thermal propulsive models. Experiments were then performed for a range of (separately powered) augmentation currents but with railgun currents equal to those used in the conventional experiments. The enhanced performance provided by augmentation was found to be significantly less than predicted by theory, even though the railgun operated without the formation of secondary armatures or restrikes.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Design of a 500 MJ, 5 MA power supply

The Battery Upgraded Supply (BUS) program, a pulsed power supply designed to provide 500 MJ at 5 MA for railgun experiments, is discussed. Approximately 50000 12 V lead acid batteries are required to reach this level. BUS will be required to perform up to two discharges per week. Therefore, BUS is designed to be a low-maintenance, reliable, and fault-tolerant power supply. Additionally, since BUS will be the largest power supply of its kind ever built, personnel safety is a prime concern. The design of BUS and the details of its subsystems are described. >

Solid armature coaxial railgun experiment results

A solid armature coaxial railgun was built to demonstrate theoretical performance and reduction of the electromagnetic pulse forward of the armature. The experimental results demonstrated that the coaxial railgun barrel geometry provides an electromagnetic accelerating force on the armature, and that the magnetic field forward of the armature is less by an order of magnitude than that of an equivalent parallel conductor geometry. There appears to be no electromagnetic pulse forward of the armature other than that leaked past the armature contact points which form breaks in the closed barrel armature surfaces. This feature eliminates or reduces the need for shielding to protect payload electronics.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Railgun experiments at the University of Texas Center for Electromechanics

The Center for Electromechanics at the University of Texas at Austin (CEM-UT) presently has five experimental electromagnetic (e.m.) launchers or railguns in operation. An additional ten fully operational railguns are presently decommissioned and five new launchers are being fabricated. Several different parallel rail configurations and geometries are being studied as well as augmented rails and coaxial launchers. Recent tests utilizing the magnetic flux generated in a coil have produced promising results for work with coilgun launchers. Electromagnetic launchers at CEM-UT have been used in a wide variety of experiments. Particles of 50–500 μm in diameter have been accelerated up to 11 km/s to determine the effects of micrometeorite impacts on materials used in space applications and 2.5-kg packages have been launched to 2.6 km/s (8.1 MJ muzzle energy) in ballistic tests. Paper studies on launching 100-kg payloads at 10 km/s have also been conducted to determine the feasibility of launching satellites with e.m. launchers.

The CEM-UT rapid-fire compulsator railgun system-recent performance and 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.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

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.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Railgun experiments with Lexan insulators

A series of railgun experiments has been performed using Lexan insulators in both round and square bores, and with closed-breech and open-breech/injected configurations. Measured armature lengths have been roughly constant at 5-10 cm in a 1-cm bore for all Lexan insulator shots, indicating that the ablated Lexan is not swept up. Projectiles have been observed to reach peak velocity of 5.65 km/s with clean armature structures: i.e. no separated secondary arc or restrike. However, in most cases a secondary arc does occur with Lexan and limits the achievable velocity. Occasionally, stationary secondary arcs have also been observed for a particularly leaky gun assembly. The effect of insulator ablation on performance is discussed, indicating that Lexan may be useful at up to 8-10 km/s for well-sealed railguns. >

High power switches at the Center for Electromechanics at the University of Texas at Austin

Three high coulomb explosively actuated opening switches which have demonstrated reliability and fast switching in railgun experiments are presented. Two of these switches first provide a low conductivity path to transfer energy from homopolar generators to inductive energy stores and then open to commutate current to the railgun. One is a monolithic aluminum element with machined stress concentrations, and the other uses reloadable cartridges mechanically clamped. The third switch is designed to interrupt current in a compulsator powered railgun experiment. In the event of a short circuit fault, the switch automatically opens in order to prevent overheating of the compulsator armature windings. The design and excellent performance of these switches are reviewed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Testing of a high performance, precision-bore railgun

This paper discusses the results of high-pressure (up to 350 MPa) railgun experiments. The gun is designed both to be capable of high-pressure operation without structural damage and to be readily disassembled for inspection, maintenance and component testing. Considerable effort has been invested to develop techniques to produce and measure smooth, extremely precise (>5µm of variation) bores. We have not deliberately varied bore precision to determine the effect of precision on performance, but our experience suggests that if two otherwise identical railguns, one with a polished, high-precision bore, were fired under identical conditions, the precisely finished gun would achieve a higher muzzle velocity. Very high accelerations have been achieved (>10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> m/s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ). A 2-g projectile has been accelerated to 5 km/s in a 13 mm square-bore gun only 1 m long. Projectiles with an L/D as small as 0.65 have been successfully accelerated. Projectiles with smaller L/Ds have not yet been tested to determine the minimum L/D which can be successfully accelerated. A number of different insulator materials ranging from common float glass to fused quartz have been tested. The best results have been obtained with fused quartz, which shows promise of being reusable. In the course of testing, the importance of gasketing the rail-to-insulator seams to prevent loss of plasma has become apparent. We have made progress in gasket design, but more work is needed. Rail gouging has been a continuing problem. Gouging may be dependent on bore precision, projectile fit, rail mechanical properties, projectile L/D, structural stiffness, operating pressure, velocity, and shape of the current pulse.

Railgun experiment at tokyo institute of technology

An electromagnetic railgun for the purpose of shock wave experiment has been developed at Tokyo Institute of Technology. In order to eliminate the destruction of projectile and plasma blow-by during acceleration, we have developed a new structure of railgun bore, techniques for precise bore manufacturing, and a diagnostic system. This paper details such efforts and some experimental results.

Development of railgun accelerator at NCLI

Railgun experiments have been made at National Chemical Laboratory for Industry (NCLI). Two types of railguns having 30 mm square bore and round bore of 14 mm in diameter were made. A pulse transformer was employed in a capacitor bank energy source system in order to increase a efficiency of acceleration. The performance of the system was examined. A projectile position detector using a continuous X-ray beam was developed and employed together with a X-ray shadowgraph apparatus to determine the precise positions of acceralated projectiles. This diagnostic system including ordinary electromagnetic and optical probes for plasma have enabled us to obtain the relative position of the projectile and the plasma armature experimentally.

Development of a high-energy distributed energy source electromagnetic railgun with improved energy conversion efficiency

Vought Corporation in cooperation with the Center for Electromechanics at the University of Texas (CEM-UT) has developed under sponsorship by the Defense Advanced Research Projects Agency (DARPA) and the Army Armament, Munitions, and Chemical Command (AMCCOM) a high-energy distributed energy source (DES) electromagnetic (EM) railgun accelerator. This paper discusses the development and current status of the DES railgun which has the design capability to launch projectile masses up to 60 grams to the 3-4 km/sec velocity regime with energy conversion efficiencies above 35 percent. These goals are being accomplished through utilization of scaled-energy CEM-UT railgun experiments for sequenced timing/staging and a full energy (575 kJ) design at Vought for high efficiency capability. The operational Vought single-pulse railgun forms the baseline for the full energy testing.

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.