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Magnetics, IEEE Transactions on

Issue 1  Part 1 • Date Jan. 1997

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Displaying Results 1 - 25 of 119
  • [Transactions on Magnetics - Table of contents: includes content from 8th Electromagnetic Launch Technology (EML) Symposium]

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  • Conference Author Index [8th Electromagnetic Launch Technology (EML) Symposium]

    Page(s): 657 - 658
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  • Design and testing of the power electronics for the cannon caliber electromagnetic gun system

    Page(s): 484 - 489
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    The University of Texas Center for Electromechanics (UT-CEM) is in the final fabrication and testing phase of a power electronics system required to operate a skid mounted compulsator-driven railgun. Design goals for the self-excited air core compulsator include a 95 MW rectifier/inverter bridge for field coil self-excitation. Initial field coil seed energy is supplied by a 50 kJ capacitive discharge from the field initiation module. The field coil is passively protected from voltage transients by an array of metal oxide varistors. Other system power modules include the gun closing switch and explosive opening switch. This paper presents a brief system overview and detailed design of the rectifier/inverter bridge module with performance data from shots up to 6 View full abstract»

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  • A diagnostic technique for understanding startup of metal armatures

    Page(s): 115 - 118
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    Metal armature performance throughout a launch is affected by the initial loading conditions. An improper fit at startup reduces the desired contact loads and leads to increased power dissipation at the armature-rail interface which affects both armature performance (at startup and throughout the launch) and the rail life. Ensuring proper fit and understanding the initial contact loading condition is hard to do in high performance railguns because they are built without any room for instrumentation. In a recent program, we designed and built a specialty railgun with one side made of clear material to allow for visual examination and used high speed photography (25,000 frames per second) with an instrumented rail and armature to understand the effects of initial contact loading on the armature performance. In this paper, we describe the technique used, present typical test data, and summarize the findings View full abstract»

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  • Solid state switches for electric gun applications

    Page(s): 490 - 494
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    The Army Research Laboratory has conducted experimental evaluations on commercially available solid state switches for application to electric gun systems. These switches were developed largely for the electric power industry and were designed for high average current, long term operation. Operating these devices at the short pulse lengths required by electric guns enables the peak currents to exceed the nominal ratings by more than an order of magnitude. These devices are all thyristor types chosen for high surge current capability and low forward drop losses. The investigation includes thyristors of domestic and foreign manufacture and also novel control structures and packaging. The silicon wafers vary in diameter from 50 mm to 100 mm and have a minimum off-state blocking voltage rating of 2 kV. The evaluations were performed using pulsers with low impedances (10 to 250 milliohms), with pulse widths varying from 0.5 ms (FWHM) to 2.0 ms (FWHM). The inverse capabilities of symmetric devices under short circuit conditions were studied and the ability to withstand full voltage reversals after high forward surge currents was demonstrated. Series, parallel and phased operation of multiple switches was also demonstrated View full abstract»

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  • An all-electric vehicle technology demonstrator with a 35-mm electrothermal gun system

    Page(s): 647 - 650
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    Within the German R&D programmes on the application of electrical energy for all main subsystems within a battle field tank, electric drive and electric firing have already been independently demonstrated successfully. The performance of an electric drive system has been demonstrated successfully based on a MARDER 1 chassis as well as on a 8×8 wheel chassis. The performance of electric gun systems has been investigated extensively using laboratory setups. For a next step the integration of the different technologies into a mobile demonstrator with the incorporation of all electric systems is proposed. The paper gives the results of a first conceptual study. Based on a MARDER 1 chassis the different subsystems have been specified and first layouts due to the technology status were generated in detail. These subsystems are: electric drive, 2-MJ capacitive pulsed power, 35-mm repetitive firing electrothermal gun. An integration concept of the different subsystems into the chassis is described View full abstract»

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  • Finite element modelling of flux concentrators for coilguns

    Page(s): 175 - 177
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    The use of flux concentrators in coilguns is an attractive proposition since they combine the strength and durability of a single turn coil with the versatility of a multiturn winding. The primary winding can be of large radius when compared to the bore size of the gun, enabling stresses to be reduced. Unfortunately, efficiency is rather poor, and so Finite Element models are used to investigate the various loss mechanisms and their relative significance. By comparing with full 3D models, 2D approximations are shown to be reasonable. This provides fast solutions for the purpose of design optimisation View full abstract»

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  • Hypervelocity electric discharge accelerator

    Page(s): 305 - 309
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    The achievement of accelerating macro-particles to high velocities has fundamental significance of research connected with solid state physics. A set of experimental data, obtained using 16 mm hypervelocity accelerator of macroparticles is presented. Compact polymer cylinders of 2-4 g were used as projectiles. As the result of the experiments the dependencies was obtained which characterize the accelerator's efficiency. Data is given on the electric discharge system's work in the range of the following parameters: pulse pressure-up to 700 MPa, pulse current-up to 1.5 MA, the velocity of the accelerated macro-particles-up to 7 km/s. On the basis of the presented data conclusions are drawn concerning the further approaches to the increase of efficiency of this method of acceleration and macro-particles velocity View full abstract»

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  • The AMT maglev test sled-EML weapons technology transition to transportation

    Page(s): 379 - 383
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    Technology spinoffs from prior electromagnetic launcher work enhance a magnetic levitation transportation system test bed being developed by American Maglev Technology of Florida. This project uses a series wound linear DC motor and brushes to simplify the magnetic levitation propulsion system. It takes advantage of previous related work in electromagnetic launcher technology to achieve success with this innovative design. Technology and knowledge gained from developments for homopolar generators and proposed rail gun are control are key to successful performance. This contribution supports a cost effective design that is competitive with alternative concepts. Brushes transfer power from the guideway (rail) to the vehicle (armature) in a novel design that activates the guideway only under the vehicle, reducing power losses and guideway construction costs. The vehicle carries no power for propulsion and levitation, and acts only as a conduit for the power through the high speed brushes. Brush selection and performance is based on previous EML homopolar generator research. A counterpulse circuit, first introduced in an early EML conference, is used to suppress arcing on the trailing brush and to transfer inductive energy to the next propulsion coil. Isolated static lift and preliminary propulsion tests have been completed, and integrated propulsion and lift tests are scheduled in early 1996 View full abstract»

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  • Preoptimization of large calibre plasmaburners with a full scale experimental simulator

    Page(s): 340 - 344
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    In order to investigate the electrical behaviour of a high power gas discharge within a volume equal to those of the plasmaburner of a large calibre electrothermal gun experimental investigations with a firing simulator were performed. After giving the initial design parameters which are defined by those of the large calibre ET-gun, the paper presents the mechanical set-up of the large calibre firing simulator. 25 firing experiments with different initial parameters were performed. The results of three characteristic experiments are presented. By the discussion of these results the influence of the initial parameters on the electrical behaviour of the gas discharge within the plasmaburner is shown. A similiar behaviour can be expected when firing the large calibre ET-Gun with the pre-optimized initial parameters obtained from the experiments with the simulator View full abstract»

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  • Analysis of solid propellant combustion behavior under electrothermal plasma injection for ETC launchers

    Page(s): 278 - 283
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    Enhanced burn rates of solid propellants through plasma erosion has been studied showing evidence of increased burn rate with injection of electrothermal plasmas into the propellant. These experiments are designed to evaluate the effectiveness of maximizing energy versus momentum transport, and the influence of geometry on the burn rates of the JA-2 solid granular propellant. A series of experiments has shown evidence of enhanced burn rate at pressures between 55 and 90 MPa (8,000 and 12,000 psi, respectively) over 400 ps pulse length. A 20 to 40% enhancement in the burn rates has been observed when plasma is injected parallel to the surface of the propellant. When plasma is injected normal to the surface, the burn rate increases by about a factor of three. A set of experiments has been designed to measure the burn rates when the electrothermal plasma is injected at various angles, from 0° to 90°, to the surface of the propellant. Experiments were conducted at a constant input energy of 5 kJ±2% to the electrothermal plasma source and constant base pressure of 15 Torr, which provides a 12,300 psi plasma pressure at the source exit close to the surface of the propellant. Results indicate increased burn rates with increased angle of injection. Optical emission spectroscopy measurements revealed a decrease in plasma temperature, at the plasma-propellant interface, with increased angle of injection View full abstract»

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  • The railgun experiments on head-on collision of different mass bodies in 10-15 km/s range

    Page(s): 528 - 531
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    Existing techniques allow the launch of solid imparters up to only about 10 km/s. A way of doubling the effective velocity for collision experiments is to use two accelerators to produce a head-on collision. However, light-gas guns and conventional EM launchers with pre-accelerators are not suitable for this mode of operation due to the difficulty of synchronizing the projectile motion when travelling through long bores (from a few meters to tens of meters). The compacted plasma armature railgun (RG) developed at the Ioffe Institute has a much shorter bore because it operates at a constant-along-the-barrel acceleration close to the maximum value allowed by the projectile strength or electrothermal explosion of rails. Acceleration of a typical 1 cm body reaches ~1-5 MGees, so that 7 km/s is achieved in 56 cm bore. The short acceleration length makes it possible to synchronize the motion in two counter-firing RGs. We have done experiments with two sets-ups, one using two RGs having identical square bores of 2 mm across and the other using an 8 mm square bore RG opposed to a 2 mm bore. Exploiting a rotating-mirror camera and a laser we have photographed collision processes at relative velocities of 4.9+5.1=10 km/s and 5.9+4.5=10.4 km/s, respectively. The potentials of this approach are far from being exhausted View full abstract»

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  • Silicon carbide thyristors for electric guns

    Page(s): 432 - 437
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    The feasibility of using silicon power thyristors for electric gun pulsers has been established. The advantages of solid state switches are highly significant for electric gun systems. Nevertheless, the size and weight of a solid state pulser built using silicon devices is non-optimal due to limited device performance. The improved material properties of silicon carbide offer the potential of reducing the size and weight of the pulser by increasing device power density and di/dt capabilities. Studies have estimated the improvement to be a significant 60% reduction in both volume and weight, mainly due to improvement in di/dt capability. This improvement is highly desirable to build a solid state pulser capable of meeting the size and weight constraints of a tactical system. In this paper, we present a quantitative theoretical assessment of high-power silicon carbide (SiC) thyristor capabilities for EML applications based on the experimental evaluation of high power density prototype SiC thyristors and the design and performance modeling of a 4 kV SiC thyristor. This information provides the technical background to assess device performance improvement and claims for reduced pulser size and weight. This study confirms that a current density of 6 kA/cm2 is feasible, and that a di/dt improvement of 2.5 times is a reasonable expectation, and further indicates the potential to operate SiC thyristors at current densities above 10 kA/cm 2 and at much higher di/dts View full abstract»

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  • A study of operating modes for compulsator based EM launcher systems

    Page(s): 495 - 500
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    The compensated pulsed alternator (compulsator) is a versatile power supply capable of interfacing with the electromagnetic launcher in various ways. The method that has been explored at length with several systems is the single phase option. Several variants of this option, some using advanced pulse shaping techniques, have been discussed in prior publications. Besides this basic single pulse method of operating there are several other methods each with its pros and cons. The multiphase option is discussed in this paper. Within the broad class of multi-phase systems there are further sub-classes, namely alternating current drive and unidirectional current drives. Thus the branching of these operating modes gives rise to a variety of operating modes. Each one of these operating modes is described and simulation results are presented View full abstract»

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  • Viscoelastic behavior of composite rotors at elevated temperatures

    Page(s): 413 - 418
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    The composite rotor of a pulsed-power machine is built with radial precompression to enhance mechanical performance; however, the preload might decrease due to the viscoelastic behavior of materials at elevated temperatures. In this investigation, an analytical solution is developed to study the viscoelastic problem of thick-walled cylinders. The analysis accounts for ply-by-ply variations of rotor structural properties, ply orientations, and temperature gradients through the thickness of rotors. Fiber-reinforced composite materials generally illustrate extreme anisotropy in viscoelastic behavior. The viscoelasticity exists mainly in matrix dominant properties, such as transverse and shear, while the fiber dominant properties behave more like elastic mediums. Accordingly, the viscoelastic characteristics of composite cylinders is quite different from those of isotropic cylinders. Currently, finite element packages such as ABAQUS, ANSYS, and DYNA3D are not very suitable for the viscoelastic analysis of composite cylinder because of the lack of anisotropic viscoelastic elements. The prestress in the hoop-wound fiber, which generates radial compression In the rotor, might decrease due to Poisson's effect alone from the creep behavior in the transverse properties of composite. The result also shows the effects of layup construction and fiber orientations on the anisotropic behavior of composite rotors View full abstract»

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  • A modular 300-kJ capacitive pulsed power supply system for the Swedish ETC programme

    Page(s): 449 - 452
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    Under contract of the Swedish FMV Defence Material Administration a research and development programme on electrothermal-chemical launchers was started in 1995. Two containerized 300-kJ capacitive pulsed power supply (PPS) systems providing a large flexibility by their modular setup were designed and fabricated at the German TZN R&D Center. After describing the general technical requirements realized within each PPS system the paper gives some results obtained from the performance simulations conducted to define the operating parameters for the different discharge conditions of the system. Based on the results of the performance simulations the design solutions for the power conditioning circuits, the control system and the auxiliary systems are presented. Each PPS system consists of four 75-kJ capacitors with two different capacitances at full energy level. Each capacitor can be charged individually to an adjustable voltage and can be discharged via four adjustable pulse forming inductance values either sequentially or simultaneously. Both PPS systems can be connected together in order to obtain one 600-kJ discharge system View full abstract»

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  • Measurement of the muzzle dynamic pressure of the plasma dynamic accelerator

    Page(s): 384 - 389
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    The plasma dynamic accelerator comprises a coaxial railgun-like first stage that accelerates a plasma to very high velocities. The second stage, the compressor coil, compresses this plasma into a fast and dense plasma flow. A series of experiments was conducted to measure the dynamic pressure in front of the muzzle. Kistler Type 6157 BA pressure probes served as pressure gauges. The evaluation of these measurements was assisted by measurement of the current in the coil ground loop, the inductance of the system and by high speed photography three different coil shapes were used to evaluate the influence of the coil shape on the compression. A non-conducting coil with a shape identical to one of these coils was tested to determine the contribution of aerodynamic forces to the plasma compression. Additional tests were performed with a non-conducting conical tube to see whether a coil has aerodynamic benefits compared to closed contour. Finally, the coil was completely omitted. Only the coil holder, attached to the ground loop, remained in the system. This configuration forced a mainly axial discharge from the tip of the coaxial accelerator's center electrode to the holder and allowed the investigation of the contribution of the z-pinch to compression. This paper describes the configurations used in these experiments and presents the results of the measurements. These results are compared to each other and conclusions are drawn on how to improve the coil View full abstract»

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  • Computer modeling and prediction of solid armature contact wear and transitioning in electromagnetic guns

    Page(s): 74 - 79
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    A 30 mm round bore solid armature development and test program has been completed at the Electric Armaments Research Center at Picatinny Arsenal, New Jersey. The program has furthered the understanding of solid armature contact wear and how it relates to the subsequent loss of the solid armature to rail contact. The Army Railgun Modular Simulator (ARMS) computer code has been improved to provide a 1D model of the parasitic effects of the contact ohmic and the melt layer viscous shear heating on contact wear at the rail to armature Interface. The theoretical premise for the simulator asserts that contact wear is a result of the loss of contact material from a sliding melt layer which forms between the armature and the rail. The melt layer interface Is sustained by the heat inputs to the armature from both ohmic and viscous shear heating. The net contact force at any time is a resultant of both the mechanical force arising from the contact interference and stiffness product and the induced magnetic force. As the contact wear progresses, the resulting loss of interference between the armature and rail reduces the net contact force in proportion to the armature stiffness to the point where the mechanical contact force component ceases to assist the induced magnetic force. Transition of the contact from a low voltage/efficient sliding interface is shown to occur when the mechanical contact force is equal and opposite to the magnetic force, resulting in near zero contact force. This paper describes the 30 mm armature test plan, the computer model theoretical premise, the thermodynamic and electromechanical modelling techniques utilized and compares the simulation results to the 30 mm armature test cases View full abstract»

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  • Summary of the hypervelocity weapon system field experiment

    Page(s): 636 - 641
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    The Hypervelocity Launcher Product Office of the US Army Space and Strategic Defense Command has completed the first field experiment for the Hypervelocity Weapon System (NVWS). The HVWS is being developed as a cost-effective, bottom-tier element of the overall Theater Missile Defense (TMD) architecture. The HVWS is C-130 transportable and will complement the total spectrum of TMD assets. The objective of the overall field experiment is to assess the suitability of the HVWS technology to meet the requirements for TMD and Air Defense (AD) missions. To achieve this objective, program effort is focused on resolution of four key HVWS issues: interceptor launch survivability, fire control tracking accuracy, interceptor guidance to intercept, and intercept lethality. Intermediate field experiments will assess the launch survivability, guidance and control issues of the D2 interceptor, and the tracking accuracy of the fire control system. The final field experiment is planned to culminate in the intercept of a SCUD-type target as well as other TMD and AD targets. This paper presents a summary of the results of the first field experiment, which was conducted at the US Army Hellfire Range on Eglin AFB, FL. The specific objectives of an approach used for the field experiments are discussed. Descriptions of the HVWS subsystem technologies employed during the FY93 experiments are presented along with discussions of the experimental results in the key HVWS issue areas View full abstract»

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  • Electromagnetic processes and launch efficiency of railgun systems

    Page(s): 532 - 537
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    Detailed analysis of electromagnetic processes in railgun armatures shows that an electromagnetic drag mechanism caused by the generation of eddy currents is an ubiquitous effect in any railgun system. The results of an energy balance analysis allowed us to construct the equivalent electric circuits of railgun armatures. The acceleration in any railgun is equivalent, from an energetic point of view, to charging of a leaking capacitor. Simple numerical evaluations of the value of the electromagnetic drag force show that its role in the acceleration process is unavoidable for typical railgun launcher experimental conditions, although a quantitative evaluation of the drag force is difficult to make. Even discounting any known performance loss mechanism of a non-electromagnetic nature, our study gives a consistent qualitative explanation for all irreconcilable phenomena known from experiments; the saturation of attainable velocities, the degradation of plasma armatures, and the problem of high velocity sliding contact for metal armatures. Possible ways of optimizing railgun acceleration and achieving a higher velocity are discussed View full abstract»

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  • Liquation cracking and its effects in aluminum alloy armatures

    Page(s): 419 - 425
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    Experiments were performed using four different aluminum alloy armatures to study liquation cracking and its effects on armature performance. The four materials tested were Al 1100, Al 6082, Al 7075, and Al 7475. Of these, only the Al 1100 (commercially pure aluminum) armatures were free of gross cracking after exit from the launcher. The Al 6082, Al 7075, and Al 7475 armatures experienced fracture and structural deterioration as observed in high speed photographs of the in-flight bodies and the condition of the recovered armatures. Metallography of the recovered armatures revealed that liquation of the grain boundary phases in Al 7075 and Al 7475 had contributed to the structural failures in these armatures. The results suggest that a composite armature should be designed using different aluminum alloys to separately perform the sliding contact and structural functions View full abstract»

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  • Spatial effects in a railgun plasma armature

    Page(s): 92 - 97
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    The results of mathematical simulation of thermal, mechanical and electromagnetic interaction of railgun plasma armature and channel walls are presented. A generalized 2D-approach taking into account turbulent friction, radiative and turbulent heat transfer and spatial inhomogeneity of the magnetic field was used. The heat regime of electrodes was considered in the 2D-approach. The momentum and energy transfer from the flow core to the electrodes and the process of involving the erosion mass into acceleration were investigated in detail. It has been shown that magnetic field inhomogeneity causing the appearance of spatial induction currents influences essentially the momentum, energy and mass balance in the near-electrode region and the armature characteristics as a whole. It leads to an additional drag force and the release of Joule heat near the rail surface and to the increase in erosion. Under some conditions this can cause instability of plasma armature and its sharp extension. Calculations have shown that the electrode melting, destruction of the liquid film, involving of drops into acceleration and their vaporization in the flow seem to be the most probable mechanism of plasma mass increase for typical regimes of railgun operation View full abstract»

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  • Design and evaluation of carbon fibre-reinforced launch packages with segmented, copper and molybdenum fibre armatures

    Page(s): 119 - 124
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    Fibre armatures have been studied both dynamically and statically to gain insight into their electrothermal and mechanical behaviour. In the first part of this paper, the results of launch experiments with single and multi-segment copper and molybdenum fibre armatures integrated in carbon-fibre reinforced launch packages are discussed. The launch experiments with Cu fibre armatures showed an improved reproducibility and a higher transition velocity. The poor results of the launch experiments with the Mo fibre armatures thus far, are explained with results of armature compliance and resistance measurements. In the second part, results are presented which are obtained from static experiments in an armature test bed. Using miniature B-dot probes and Rogowski coils, the magnetic field diffusion into monobloc and fibre armatures with identical geometry has been studied. The results show a significant difference in diffusion behaviour between the two types of armatures. It appears that the magnetic field diffuses faster into the fibre armature. The experimental data are compared with the results of calculations of the magnetic field distribution in both armatures based on 2D- and 3D-finite element computer simulations. The results of the 2D-simulations appear to confirm the measured results for monobloc and fibre armatures only qualitatively. The experimental results obtained with monobloc armatures agree with the results of the 3D-simulations in a quantitative sense View full abstract»

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  • On the nature of the armature-rail interface: liquid metal effects

    Page(s): 140 - 145
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    This is an experimental study of the nature of the armature-rail interface during hypervelocity launch in a railgun. It is part of a multidisciplinary modeling and experimental effort to improve the understanding of contact physics. Conditions that occurred at the interface are inferred from studies of the surfaces of recovered copper rails. Melt lubrication is observed at the armature-rail interface. Liquid aluminum metal from the contact faces of the solid aluminum armature forms at the armature-rail interface as a result of frictional and joule heating. The liquid aluminum is quenched by the relatively cool copper rail, and a quenched metal deposit is formed. Characterization of the deposit has shown a rapidly quenched microstructure. The mean grain size measured by transmission electron microscopy is 200 nm-the finest grain size reported for a melt quenched aluminum alloy film. The deposit thickness is less than 25 μm and is rough with an oxidized surface. The thicker films crack, curl, and detach easily from the rail surface. The experiments were performed in a 25-mm square-bore railgun, with a ratio of interface current to armature contact width of 20-35 kA/mm. The liquid production rate by armature melting at the interface is found to be about 1 mg/C, We conclude that in solid armature railguns with sufficiently thick, liquid aluminum melt lubrication, the rail does not erode. Instead a deposit forms on the rail surface. Depending upon the film thickness and the quench stresses, the film detaches easily View full abstract»

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  • Arcing phenomena in transitioned solid armatures

    Page(s): 80 - 85
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    In this study of arcing phenomena in transitioned solid armatures it is proposed that following forward acceleration of the arc plasma, re-strikes occur towards the rear of the contact surface resulting in commutation of current to the re-strike arcs. Thus a repetitive sequence of current conduction is predicted at a frequency dependent on the arc transit time along the armature surface. An analytical solution of the proposed theoretical model for the arcing phase evaluates the transient rail/armature gap voltages due to arc voltage, rail and armature resistances and magnetic flux changes. Comparison of the predicted rail/armature gap voltages at the front of the armature with measured muzzle voltage waveforms for a typical 90 mm armature shows sufficiently close agreement to support the validity of the theoretical model. The additional resistive losses as a result of transition are estimated to be >30% of the exit kinetic energy of 10 MJ. The deposition of most of this as thermal energy in the rail/armature gaps is expected to have a significant impact on structural design requirements View full abstract»

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Aims & Scope

IEEE Transactions on Magnetics publishes research in science and technology related to the basic physics and engineering of magnetism, magnetic materials, applied magnetics, magnetic devices, and magnetic data storage.

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Editor-in-Chief
Pavel Kabos
National Institute of Standards and Technology