Distributed Energy Store Research Articles

Numerical Calculation Model and Efficiency Analysis of Distributed-Energy-Store Railgun

In order to study the factors affecting the launch efficiency of the distributed-energy-store (DES) railgun, a numerical calculation model of the DES railgun is established in this article. Taking the six-stage equidistant DES railgun with 4-MJ initial energy storage as an example, the simulation results show that the launch efficiency of DES railgun is 21.14%, and the resistance loss and the residual magnetic energy of rail account for a small proportion of 6.47% and 3.77%, respectively. The resistance loss of power supply and other energy losses (the losses caused by the equivalent resistance produced by the armature and its related physical effects) accounted for the highest proportions, respectively, 23.91% and 37.52%. Therefore, these two parts of losses should be reduced to further improve the system launch efficiency. The influence of system parameters on launch efficiency was analyzed, and the parameters include capacitance, charging voltage, inductance, equivalent internal resistance, rail length, interval of current feed point, armature mass, inductance gradient, and rail height. Among them, inductance gradient has the most significant impression on launch efficiency, followed by equivalent internal resistance, rail length, and interval of current feed point. The conclusions can guide the selection of the feeding mode of the electromagnetic launch system and provide reference to the further optimization of the DES railgun launch system.

Theoretical and Experimental Analysis of Breech Fed and 40-Distributed Energy Stage Plasma Arc Railguns

The design and experimental results of a 40-stage distributed energy store (DES) plasma arc railgun are presented. The railgun drives a free running hypervelocity plasma arc, one that is not pushing a payload, to velocities in excess of 10 km/s. These high velocities are of interest as they are required to successfully launch payloads into low earth orbit (LEO). The ability to launch payloads into LEO using a hypervelocity electromagnetic launcher has many financial benefits over the more conventional chemical combustion launchers. In collaboration with an Air Force Office of Scientific Research funded Multidisciplinary University Research Initiative project, the Center for Pulsed Power and Power Electronics at Texas Tech University in Lubbock, Texas has been responsible for developing and investigating a functional scale model of a multistage DES railgun to determine its effectiveness to suppress restrike phenomenon and increase plasma armature railgun performance. The distributed energy scheme is theorized to suppress restrike arc formation because the back emf voltage is localized to active stage regions where high gas density and low temperature inhibits breakdown. B-dot sensors positioned along the length of the launcher provide data to measure the plasma arc velocity and detect restrike, arc splitting, or additional secondary arc formation phenomena.

Design of a Distributed-Energy-Store Railgun

A distributed-energy-store (DES) railgun was designed, which excels at higher efficiency in comparison with a breech-fed one. Such a structure was first proposed by Marshall and had been testified to lessen the energy remaining in the rails and reduce the rails' resistive loses. The pulsed-power supply consists of eight modules of capacitor banks, which can provide a maximum energy of 200 kJ. A 4-m-long 15-mm square bore railgun with several energy feed-in points distributed along the length of the gun was built to test the DES railgun concept. A simulation model was built up to analyze its performance. A comparison between the simulation results of different systems was made. Ten-gram projectiles could be accelerated to 1323 m/s through the simulation, and the overall efficiency of the system could be increased from 6.8% to 9.0% in comparison with a breech-fed one. An important issue for the DES railgun is the discharging sequence of the PFN modules. An ideal discharging sequence was obtained from the simulation result to get a higher efficiency. A real-time control system was designed to trigger the PFN modules properly.

A review of US patents in electromagnetic launch technology

There have been several pioneering railgun technologies documented in patents issued over the last 20 years. In this survey, US patents issued during the period 1980 to 1999 are analyzed. The patents are separated into three categories: novel concepts and designs, materials and fabrication improvements, and better performance and sub-system interfaces. Uses of electromagnetic (EM) launcher technology in military and civilian applications underpin some of the ground-breaking designs such as the omni-directional railgun and the miniature railgun engine igniter. Novel technologies for more efficient EM launchers are also disclosed. It is these efficiency-enhancing launcher technologies and their evolution that are emphasized in this work. Topical areas of interest include muzzle arc suppression, energy recovery circuits, field augmentation, advanced rail and barrel design, ablation resistant insulators, lightweight high L' launchers, and the distributed energy store electromagnetic railgun. Later, a set of under-explored technologies for superconducting levitated armatures, laser-controlled semiconductor armatures, and hybrid armatures are disclosed.

Design and testing of an ultra distributed energy store system (UDESS)

A Distributed Energy Store (DES) powered railgun has been built to evaluate DES projectile acceleration performance and launcher efficiency. We describe the design, fabrication, and initial test results of the launcher, lightweight launch package, and the trigger control system. The launcher has a 19 mm square bore and consisted of three stages; a light gas injector, a 1 m long breech fed EM launcher, and 6.25 m of DES launcher. The launcher is designed to be sealed for vacuum operation and incorporates the current feeds for the 32 stage power supplies. The trigger control system uses signals from B-dot probes to determine when to fire the individual stage power supplies. The system has been tested using both plasma and metallic armatures. For this paper, the results and discussion are limited to plasma armature tests.

The distributed energy store railgun, its efficiency, and its energy store implications

The distributed energy store railgun system is examined for a particular application, with emphasis being placed on the fundamental requirements that must be taken into account. A breech-fed railgun system is examined for the same requirements to enable a reasonable comparison between the two systems to be made. Resistive and inductance losses of energy are compared when it is assumed that the same constant current flows within the 4 calibers of the railgun immediately behind the rear of the armature. Also examined is the breech-fed case when inductive energy in the bore is recovered at different rates. The requirements for the ideal flux pump needed for powering the distributed energy store railgun are presented and estimates made of its mass and volume. The numbers obtained are speculative because such a flux pump has not yet been built.

Distributed energy store powered railguns for hypervelocity launch

It is noted that several deficiencies hamper full-scale railgun development for hypervelocity applications. Two key deficiencies are lack of hypervelocity performance (i.e., >6 km/s) and lack of compact power supplies. Highly distributed power supplies address these deficiencies. A railgun powered by highly distributed energy stores reduces the rail-to-rail voltage behind the main armature, reducing the tendency to secondary armature current formation. Secondary current elimination is necessary to overcome the velocity limit. Feasibility assessments of two distributed energy store schemes have been completed. A nested rail, distributed energy store (NESDES) system and an ultra distributed energy store system (UDESS) have been used to remove the rail-to-rail voltage. Analytical and experimental data are presented on both schemes. The results indicate that the aforementioned deficiencies are addressed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

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

Distributed energy store (DES) railgun development

Over the past four years LTV Aerospace and Defense Company [LTVAD) has operated on a regular basis two high-energy electromagnetic (EM) railguns with over 200 shots, 100 firings since the last EM launcher technology symposium, making this to our knowledge the most productive launcher laboratory in the nation. The development work has focused on launcher efficiency, projectile compatibility, and barrel material life improvements. The 20 mm DES launcher has also become known as a workhorse for hypervelocity kinetic energy lethality experiments, operating in the velocity range of 2 to 6 km/sec. This paper describes the recent LTVAD EM Propulsion Laboratory developments and improvements with the DES launcher, power supply, controls, instrumentation, and ballistic range. Results on DES launcher efficiency optimization with factors greater than 2 over breech fed railguns are presented. Methods of tailoring the launch acceleration force and test results 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.

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.

Efficiency equations of the railgun

Efficiency of railguns will ultimately determine the scale of their use since it determines the size of the power source. Equations are derived for the losses and efficiencies of breech supplied, segmented and distributed energy store guns and evaluated for a 5 gram mass accelerated to 10 km/s under various conditions. Constant current is assumed.

The use of nested chevron rails in a distributed energy store railgun

Electromagnetic launchers which require the use of large amounts of energy will almost certainly require that energy stores be distributed along their length. For a railgun launcher, the nested chevron rail construction will enable a launcher to be produced in which most of the switching requirements for the launcher/energy store system are met automatically.

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.