Plasma Armature Research Articles

Prospects of use of electromagnetic railgun as plasma thruster for spacecrafts

Estimation of a possibility to use an electromagnetic plasma railgun as a safe and reliable plasma thruster based on calculations of the thrust force and specific impulse of a plasma jet flowing from an accelerator channel is presented. Theoretical and experimental investigations of acceleration of a plasma armature in railguns filled with inert gases (argon, xenon) carried out at Ioffe Institute are described.

Three-dimensional MHD modeling of railgun plasma armature with the CE/SE method

Three-dimensional (3-D) numerical simulations have been carried out taking into account the magnetohydrodynam- ics (MHD) effect of the railgun plasma armature. The 3-D space-time conservation element and solution element (CE/SE) method is derived for solving the coupled Navier-Stokes equations and Maxwell equations. The results show that a steeper gradient of the magnetic field and pressure that appears along the direction of the rail can be observed. The temperature dis- tribution is affected by the boundary conditions for the radiative heat flux, with the maximum temperature appearing in the center near the base of the projectile. Circulation patterns of velocity that are evident in both the rail-to-rail plane and the insulator-to-insulator plane result from the convection and unbalanced force between the Lorentz force and pressure gradient. The periodical variation of the temperature and acceleration is obvious until a new steady state is achieved. This model can efficiently evaluate the dynamics of the plasma motion, and provide a basis on understanding the much more complex physical phenomena.

Evaluation of a Novel Plasma Launcher Behavior Using Magneto Hydro Dynamic Modeling-Coupled Time Varying Electron Energy Distribution Function

An Electro Magnetic (EM) launcher can be used as an experimental tool to accelerate small-mass specimens up to 300 m/s to study impact phenomena. A plasma armature is employed to avoid the friction produced by a sliding metal armature and, in particular, to prevent high-Z impurities from entering the tokamak. High currents are used to achieve high accelerations, resulting in high plasma temperatures. For this purpose, 2-D and axisymmetric plasma models are widely used as these are less complicated and fairly available. The presented model solves the entire set of magneto hydro dynamic, including transport equations of mass, momentum, and energy along, with the vector potential form of Maxwell's equation-coupled time-varying electron energy distribution function for the novel EM launcher in axial symmetry domain. Radiation of the energy balance is calculated using the P-1 radiation method by dividing the electromagnetic spectrum into several gray bands. Simulations are performed using Comsol Multiphysics 4.2 software.

Merging of high speed argon plasma jets

Formation of an imploding plasma liner for the plasma liner experiment (PLX) requires individual plasma jets to merge into a quasi-spherical shell of plasma converging on the origin. Understanding dynamics of the merging process requires knowledge of the plasma phenomena involved. We present results from the study of the merging of three plasma jets in three dimensional geometry. The experiments were performed using HyperV Technologies Corp. 1 cm Minirailguns with a preionized argon plasma armature. The vacuum chamber partially reproduces the port geometry of the PLX chamber. Diagnostics include fast imaging, spectroscopy, interferometry, fast pressure probes, B-dot probes, and high speed spatially resolved photodiodes, permitting measurements of plasma density, temperature, velocity, stagnation pressure, magnetic field, and density gradients. These experimental results are compared with simulation results from the LSP 3D hybrid PIC code.

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.

Optimization of Launched Parameters of the Railgun with Internal Penalty Function Method

The launched speed of projectile is one of the most important parameters in the design of railgun, in order to explore the influence of the launched speed of projectile by the length of rail and the driving current. Therefore, it is meaningful that gets the optimum speed of projectile. In this paper, main resistances (plasma viscous drag, inertial drag and air drag) was full considered in the motion process of plasma armature, and the optimization model includes the speed of the armature,driving current and the length of rail were build,then it was optimization calculated with internal penalty function method. The optimization result shows that the launched speed of projectile is maximum when the driving current and the length of rail are fixed value. The purpose lies in adjusting the width and the length of the rail and the distance between two rails so as to adjust the launched speed of projectile. The result of research laid a theoretical foundation for designing and manufacture of the railguns.

Optimization Calculation and Analysis of Moving Load of the Railgun by Newton Method

To explore influences from drive current on the projectile launched speed, and the spacing and width of rails on the maximum value of current in the electromagnetic gun. The motion equation of plasma armature is analyzed by the Newton method. In this paper, considering armature motion subjected to plasma viscous drag and inertial drag, the optimization model between armature speed and drive current was built. The results showed that the projectile launched speed would get the maximum value when the drive current was the specific value. Moreover, the influences from spacing and width of rails on the maximum value of current and the projectile launched speed were proved. Therefore, the optimization model that was built by the Newton method research the electromagnetic railgun is of great significance.

A 40-Stage Synchronous Distributed Energy Railgun

The development process pertaining to the design, fabrication, and testing of a 40-stage free-running arc synchronous distributed energy railgun is presented. Research efforts are still ongoing to suppress the restrike phenomenon that is responsible for causing a velocity ceiling around 6 km/s to exist on plasma armature breech-fed railguns. Numerous solutions have been theorized as viable methods of restrike prevention but lack experimental verification. In collaboration on an AFOSR Multidisciplinary University Research Initiative project, the team at Texas Tech University is responsible for characterizing a functional scale model of a synchronous distributed energy railgun to investigate the effectiveness of a distributed energy scheme to suppress the plasma 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. Synchronous operation refers to the speed of an electromagnetic wave in the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> transmission line formed by the rails and capacitors being matched to the velocity of the armature. The railgun drives a hypervelocity (8 km/s) plasma armature, with no payload, to emulate the conditions of a high-altitude microsatellite launch while relieving the financial burden of a large stored energy facility. Experimental data collected from a seven-stage prototype distributed energy system are discussed which will mimic the design and operation of the first seven stages associated with the final 40-stage system, which is currently under construction. The data collected from this prototype as well as the final 40-stage system will be analyzed for secondary arc formation in an attempt to verify the distributed energy scheme's success in suppressing restrike formation.

Plasma Armatures for Railguns

Renewed interest has arisen in plasma armatures as evidenced by two papers presented at the 2008 EML Symposium. It is hoped that the work at the University of Texas described in these papers succeeds. There may, however, be some uncertainties related to the nature of plasma armatures in that work. The thoughts we offer here may help. It is not yet obvious how the 6-km/s velocity limit encountered in the Canberra railgun can be overcome. In the years following this discovery, a considerable number of experiments were conducted on the subject with no clear outcome. One strategy for overcoming the velocity limit may be to vent the bore behind the armature. In order to do this, it is necessary to find out how long the armature must be to be effective. Too long would make the venting process unwieldy. Too short and the armature losses will rise to unacceptable levels. Further, the method we suggest for implementing the venting strategy may be extended to prevent damage to the railgun rails caused by the arcing current transfer from rails to armature. We examine the possibilities and implications involved in implementing these strategies.

Experimental Results on a 7-m-Long Plasma-Driven Electromagnetic Launcher

The Institute for Advanced Technology (IAT) at The University of Texas at Austin has been conducting research aimed at achieving muzzle velocities in excess of 7 km/s using a plasma-driven electromagnetic launcher. Plasma-driven railguns are susceptible to bore effects that limit muzzle speeds to about 6 km/s. The velocity ceiling is believed to be the result of the viscous drag of material ablated from the bore of the launcher. Ablation of bore materials, especially the insulators, is caused by the intense heat radiated by plasma armatures, especially at low speeds. The experiments reported in this paper are focused on overcoming the velocity ceiling of 6 km/s. A proof-of-principle experiment has been designed to launch 5-10 g polycarbonate projectiles to muzzle velocities in excess of 7 km/s with modest acceleration loads of 500 kG. Our approach to controlling bore ablation involves the following elements: (1) using magnetic augmentation to reduce power dissipation in the plasma; (2) using high-purity alumina insulators to raise the ablation resistance of the bore; (3) using pre-acceleration to prevent ablation of the bore materials at low velocity; and (4) using a synchronously driven distributed power supply to electrically isolate stages. This paper describes the consequences of excessive bore ablation, the rationale for the IAT experiment, and the results obtained during testing in 2009.

Analytical Study of the Injection of a Moving Projectile Into a Railgun

Calculations are performed for an initially moving projectile into a railgun. The injection velocity is provided by a 26-mm-diameter conventional propellant gun. A plasma armature is assumed for the railgun. A capacitor-based pulsed-power supply, located at Barricade C, Aberdeen Proving Ground, MD, is assumed to provide the electrical energy for boosting the velocity to 2.5 km/s. Various scenarios are examined with respect to electrical pulse shape, the effect on stored electrical energy, and its distribution in the railgun. Three types of comparisons are used to illustrate the effect of injection velocity on stored electrical energy: (1) efficiency; (2) peak loads; and (3) energy storage. Examples for each category are discussed, illustrating complementary areas for propellant gun and railgun operation. Results are promising; however, the initial velocity must be considered in detailed simulations in order for any advantages to be realized.

IAT Armature Development

This paper provides a brief overview of railgun armature development undertaken at the Institute for Advanced Technology (IAT) and elsewhere over the last decade. The fundamental physics issues that govern the armature requirements are described. These include the operating requirements, minimum parasitic mass, material action limits, contact interface pressures, electromagnetic skin effects and current nonuniformities, magnetic sawing, launch package interactions, material surface treatments, melt lubrication, gouging, and transition to arcing contact. Different bore geometries-square, rectangular, round, augmented, -turn-are also described and require matching armature and launch package designs. Novel designs are discussed, including forward tabs, magnetic obturators, splined armatures, fiber contacts, pseudoliquid armatures, plasma, and hybrid armatures.

Characterization of EM Emission During the Operation of Solid and Plasma Armature Rail Launchers

We present the results of an experimental analysis aimed at investigating the electromagnetic (EM) emission during rail launcher operation. In order to obtain such data, an experimental setup was assembled in a shielded semi-anechoic chamber, consisting of a pulsed power source-unit, a power coaxial cable and a rail launcher prototype. Several experiments were performed for different operating conditions and results were repeatable. Finally, we provide a qualitative modeling of some sources of electromagnetic transients and we discuss basic aspects driving the EM emission phenomena in railgun systems.

Cross-field plasma injection into mirror geometry

The Maryland Centrifugal Experiment (MCX) and HyperV Technologies Corp. are collaborating on a series of experiments to test the use of a plasma gun to inject mass and momentum into a magnetic-confinement device. HyperV has designed, built and installed a prototype coaxial gun to drive rotation in MCX. The gun has been designed to avoid the blow-by instability via a combination of electrode shaping and a tailored plasma armature. Preliminary measurements at HyperV indicate the gun generates plasma jets with a mass of 160 µg, velocities up to 90 km s−1 and plasma density in the high 1014 cm−3. This paper emphasizes characteristics of the plasma gun and penetration of the plasma jet through the MCX magnetic field. Plans for future injection experiments are briefly discussed.

A contoured gap coaxial plasma gun with injected plasma armature

A new coaxial plasma gun is described. The long term objective is to accelerate 100-200 microg of plasma with density above 10(17) cm(-3) to greater than 200 km/s with a Mach number above 10. Such high velocity dense plasma jets have a number of potential fusion applications, including plasma refueling, magnetized target fusion, injection of angular momentum into centrifugally confined mirrors, high energy density plasmas, and others. The approach uses symmetric injection of high density plasma into a coaxial electromagnetic accelerator having an annular gap geometry tailored to prevent formation of the blow-by instability. The injected plasma is generated by numerous (currently 32) radially oriented capillary discharges arranged uniformly around the circumference of the angled annular injection region of the accelerator. Magnetohydrodynamic modeling identified electrode profiles that can achieve the desired plasma jet parameters. The experimental hardware is described along with initial experimental results in which approximately 200 microg has been accelerated to 100 km/s in a half-scale prototype gun. Initial observations of 64 merging injector jets in a planar cylindrical testing array are presented. Density and velocity are presently limited by available peak current and injection sources. Steps to increase both the drive current and the injected plasma mass are described for next generation experiments.

Dense Plasma Injection Experiment at MCX

We present preliminary results of the High Density Plasma Injection Experiment at the Maryland Centrifugal Experiment (MCX). HyperV Technologies Corp. has designed, built, and installed a prototype coaxial gun to drive rotation in MCX. This gun has been designed to avoid the blow-by instability via a combination of electrode shaping and a tailored plasma armature. An array of diagnostics indicates the gun is capable of plasma jets with a mass of 160 μg at 70 km/s with an average plasma density above 1015 cm−3. Preliminary measurements are underway at MCX to understand the penetration of the plasma jet through the MCX magnetic field and the momentum transfer from the jet to the MCX plasma. Data will be presented for a wide range of MCX field parameters, and the prospects for future injection experiments will be evaluated.

2-D viscous magnetohydrodynamics simulation of plasma armatures with the CE/SE method

A possible two-dimensional viscous magnetohydrodynamics (MHD) model is applied to investigating the plasma armature in a railgun. The space-time conservation element and solution element (CE/SE) method for solving the coupled Navier-Stokes equations and Maxwell equations was devised. The distributions of physical parameters of the plasma may thus be evaluated. The results show that extremely high pressure can always be observed ahead of the projectile, and the Lorentz force is the main propulsion. The distribution of temperature is in a good agreement with the results predicted by the law of radiation at the boundaries. Due to convection, the circulation patterns of velocity are evident in both the cases considering inviscid and viscous effect. Furthermore, the velocity and acceleration oscillate over time until a new steady state is achieved. This model efficiently captures the salient features of the physical phenomena, and contributes to further studies of MHD problems in plasma armature.

Advancements in the Development of a Plasma-Driven Electromagnetic Launcher

The institute for advanced technology (IAT) is developing a plasma-driven railgun to launch low-mass projectiles of 5-10 g to a velocity in excess of 7 km/s. Accomplishing this goal requires overcoming the problem of bore ablation, which has been linked to an observed velocity ceiling of about 6 km/s in plasma-armature launchers. Bore ablation is a direct consequence of the intense heat radiated by plasma armatures. Controlling bore ablation requires a coordinated approach that includes magnetic augmentation to reduce power dissipation in the plasma, high-purity alumina insulators to raise the ablation resistance of the bore, and pre-acceleration to prevent ablation of the bore materials at low velocity. This paper describes the consequences of excessive bore ablation, the rationale for the IAT experiment, and results obtained from the hardware that has been designed and tested to date.

Progress on Hypervelocity Railgun Research for Launch to Space

The Universities of Texas, Minnesota, and New Orleans, and Texas Tech University are undertaking research supported by the Air Force Office of Scientific Research on critical issues for a launch to space from a railgun carried on an airborne platform. The University of Texas at Austin is studying techniques to achieve hypervelocity with a goal of 7 km/s: So far, 5.2 km/s has been achieved in a 7-m augmented railgun using a preinjected plasma armature. Texas Tech University is studying distributed power feed concepts that will improve the efficiency of launch for a long railgun: So far, 11 km/s has been achieved with a plasma arc in a five-stage system. The Universities of Minnesota and New Orleans are investigating the aerothermal behavior of a 10-kg projectile for flight from a high-altitude launch into orbit: So far, the results show that an acceptable amount (~ 15 mm) of nosetip ablation will occur. This paper provides an overview of progress in these areas; more details on specific topics are provided in companion papers.

Secondary Arc Formation Within a Distributed Energy Railgun

Experimental results comparing a breech-fed scheme and two distributed energy schemes for a free-running arc are presented. Analysis and observations of the issues associated with distributed energy switching of a plasma arc in the railgun are explored. The use of a free-running arc allows experiments to emulate the ablation and restrike phenomenon of a plasma armature railgun at high speeds (> 5 km/s) without the requirement of a large amount of stored energy. Numerous experimental tests were conducted to investigate the dynamics of plasma arcs within a distributed energy source railgun. Variations of switch timing, bore pressure, bore material, current amplitude, and current pulse length within each stage have been tested. These data reveal important design parameters for distributed energy railguns. The arc length, stage length, and stage trigger timing play a crucial role in distributed energy railgun performance. Failure to take these parameters into consideration will result in velocity reduction through plasma arc restrike and/or splitting.