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.     

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.     

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     

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     

Thunderbolt [railguns]

The Thunderbolt program facility will provide 60 MJ of energy at 21 kV from capacitor banks for powering breech-fed or distributed energy railgun electromagnetic launchers. After discharge from the capacitor banks, the energy pulse is shaped with room-temperature solenoidal inductors, with switching being provided by D and E-sized ignitrons. Fast recharging of the capacitor banks could permit repetitive operation. A screened room provides protection for the control and data acquisition equipment, while a single-point ground scheme protects against ground loops. A substantial foundation provides support for the catch tank, while high-vacuum equipment will permit operation at high velocities with the round-bore railgun. Preinjection of the test projectiles to velocities of about 1 km/s is provided by a helium gas gun to minimize damage to the breech section of the railgun. In addition to providing details on Thunderbolt, operating experience and results obtained with a subscale launcher are described     

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.     

High quality railgun HYPAC for hypervelocity impact experiments

The characteristic of a very high quality railgun HYPAC (10 kV, 6,000 μ F, 300 kJ) at the Institute of Space and Astronautical Science (ISAS) which is capable of accelerating a 1–2 gram projectile of 10–20 mm diameter made of polycarbonate to a hypervelocity of 7.8 km/sec and its utilization in hypervelocity impact experiments are reviewed. Also shown are further efforts to increase the velocity, to improve the quality of the projectile such as the acceleration of metal powder and to explore a new application of this facility.     

MAGRAC--A railgun simulation program

We have developed and validated a computer simulation code at the Lawrence Livermore National Laboratory (LLNL) to predict the performance of a railgun electromagnetic accelerator. The code, called MAGRAC (MAGnetic Railgun ACcelerator), models the performance of a railgun driven by a magnetic flux compression current generator (MFCG). The MAGRAC code employs a time-step solution of the nonlinear time-varying element railgun circuit to determine rail currents. From the rail currents, the projectile acceleration, velocity, and position are found. We have validated the MAGRAC code through a series of eight railgun tests conducted jointly with the Los Alamos National Laboratory. This paper describes the formulation of the MAGRAC railgun model and compares the predicted current waveforms with those obtained from full-scale experiments.     

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     

Development of railgun accelerator combined with two-stage light gas gun

The status of railgun development at T.I.T. is summarized. A Zm railgun combined with two-stage light gas gun has been developed for high pressure research. Further multi-acceleration experiments using two railguns connected in series are in preparation. The purpose of this experiment is to establish the techniques for multi-stage railgun. Computer simulations show that the segmented multi-stage railgun has enough potential for use in the field of Impact Fusion.     

电磁轨道炮发射过程的轨道变形研究

电磁轨道炮发射电枢过程中,移动载荷对轨道的作用会引发轨道挠度变形。本文依据试验电流波形数据确定电枢速度和滑动距离,根据弹性梁的动力学响应方程,考虑电枢的作用力及磨损,求解了轨道的挠度幅值。对比了电枢作用力和轨道斥力对轨道变形幅值的影响,获得了轨道的挠度变化随轨道位置和发射时间的变化曲线,为进一步分析轨道炮寿命和绝缘支撑体结构设计提供参考依据。     

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     

dynamics of armature acceleration in a railgun channel

We have analyzed the results of experiments on the acceleration of an aluminum armature with a mass of about 3 g in a railgun with steel rails. The experiment was aimed at studying processes in a high-velocity contact at a velocity close to the transition value related to the contact velocity skin effect. In the absence of high-current arcs, a velocity of 1.2 km/s has been reached with the aid of armature pressing to the rails. A retarding force that acts upon the armature that moves in the railgun channel has been determined.     

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     

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     

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     

Preliminary study of a reverberation chamber method for multiple-source testing using intermodulation

The illumination of a system under test by multiple sources can lead to intermodulation (IM) effects that give rise to threat signals at the IM frequencies. The result of this is that the electromagnetic (EM) compatibility and signal integrity of that system may be compromised by two or more signals that are, individually, out of the frequency band of concern. As the EM environment continues to be increasingly polluted and electromagnetic compatibility (EMC) tests rely, predominantly, on a single-source illumination, this is an issue that is ripe for further investigation. The statistical nature of the reverberation chamber and its behaviour in isolating the test environment from the ambient (outside) environment indicates that this is a facility worth considering for multiple source (IM) testing. This study discusses the need for such an expansion in test methods, driven by an increasing interest in functional safety. It presents the results of a preliminary, simulation based, study of the reverberation chamber used with multiple sources. The purpose of this study is to demonstrate that the reverberation chamber can provide a facility where worst-case multiple-source EM interference effects can be tested. It concludes that the proposed approach has the potential to be viable and suggests experimental studies to confirm the behaviour and also to confirm that this approach can be used as an indirect method of reducing the lowest working frequency of the reverberation chamber.     

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.     

The national ignition facility high-energy ultraviolet laser system

The National Ignition Facility (NIF), currently under construction at the Lawrence Livermore National Laboratory, is a stadium-sized facility containing a 192-beam, 1.8 MJ, 500 TW, ultraviolet laser system together with a 10-m diameter target chamber with room for nearly 100 experimental diagnostics. When completed, NIF will be the world's largest and most energetic laser experimental system, providing an international center to study inertial confinement fusion and the physics of matter at extreme energy densities and pressures. NIF's 192 energetic laser beams will compress fusion targets to conditions required for thermonuclear burn, liberating more energy than required to initiate the fusion reactions. Other NIF experiments will allow the study of physical processes at temperatures approaching 10⁸ K and 10¹¹ Bar, conditions that exist naturally only in the interior of stars, planets and in nuclear weapons. NIF is now entering the first phases of its laser commissioning program. The first four beams of the NIF laser system have generated 106 kJ of infrared light and over 10 kJ at the third harmonic (351 nm). NIF's target experimental systems are also being installed in preparation for experiments to begin in late 2003. This paper provides a detailed look the NIF laser systems, the significant laser and optical systems breakthroughs that were developed, the results of recent laser commissioning shots, and plans for commissioning diagnostics for experiments on NIF.