High-voltage Capacitor Bank Research Articles

Explosively Driven Expansion and Fragmentation Behavior for Cylinders, Spheres and Rings of 304 Stainless Steel

Explosive loading techniques are applied to expand tubular cylinders, spherical shells and rings of 304 stainless steel to fragmentation, and the effects of wall thicknesses, explosive driver diameters and the constant proportionality of the in-plane biaxial stretching rates are investigated on the deformation and fracture behavior of three basic structures experimentally and numerically. In the cylinder tests, the driver is a column of high explosive PETN, inserted coaxially into the bore of a cylinder and initiated by exploding a fine wire bundle at the column axis using a discharge current from a high-voltage capacitor bank. In case of the ring tests, ring specimens are placed onto a single cylinder filled with the PETN as a expansion driver, and for sphere tests, specimens filled with the PETN are also initiated by exploding a fine copper wire line with small length located at the central point. Two types of experiments are conducted for every specimen and test condition. The first type uses high speed cameras to observe the deformation and crack generation of expanding specimens showing the final maximum in-plane stretching rate of above , and the second uses soft capturing system recovering typically most fragments successfully. The fragments are measured and investigated using a fragmentation model. The effects of test parameters on the deformation and fracture behavior for three types of structures are discussed in need of modified fragmentation model for shell structural elements.

スペースデブリを対象とした爆発破砕モデルの開発

This paper will examine the applicability of the National Aeronautics and Space Administration (NASA) standard breakup model 2000 revision to explosion breakup in space. The cylinder specimens of stainless steel with smooth were explosively expanded to fragmentation. The driver was a column of the high explosive PETN inserted into the central bore and initiated by exploding a bundle of fine copper wires using a discharge current from a high-voltage capacitor bank. Expansion rate and the collection fragments will be analyzed based on the method used in the NASA standard breakup model 2000 revision to be compared with the explosion model adopted in the NASA standard breakup model. And this paper evaluated NASA standard breakup model 2000 revision model about size distribution, average cross-section area, area mass ratio distribution, delta velocity distribution.

Deformation and fragmentation behaviour of exploded metal cylinders and the effects of wall materials, configuration, explosive energy and initiated locations

Tubular metal specimens are explosively expanded to fragmentation, and the effects of wall materials, thicknesses, notches in walls, explosive driver diameters and the initiated locations are investigated on the deformation and fracture behavior of the cylinders experimentally and numerically. In the standard tests, the driver is a column of low density powder of high explosive PETN, inserted coaxially into the bore of a smooth-walled cylinder and initiated by exploding a bundle of fine copper wires at the column axis using a discharge current from a high-voltage capacitor bank. Notched cylinders with single axial slit, various grooves in the walls, and smooth cylinders with varied wall thicknesses were tested. Low-carbon steels and an aluminum alloy A5052 were provided in addition to the standard smooth-walled 304 stainless steel cylinder, and they were fully or partially charged with varying explosive column diameters. The initiated locations in the explosive column are changed for comparison, placing the bundle of fine copper wires eccentrically from the central axis or replacing the fine wire bundle into a bold wire line except the middle portion at the central axis for central point initiation. Additionally an explosive-filled cylindrical vessel with welded endplate at the one end is initiated at the other end explosive surface exploding wire-rows and expanded by axially propagating explosive detonation to fracture for comparison with the uniform expansion. Deformation and crack initiation of expanding cylinders are observed with high speed camera, and most of the fragments have been recovered successfully. Recovered fragments have been measured and investigated using a fragmentation model. The effects of test parameters on the deformation and fracture behavior of metallic cylinders are discussed with use of numerical simulations, indicating applicability of the fragmentation model and suggesting future necessary studies.

Analysis of Explosion Combustion Phenomenon with Ammonium Nitrate

In this study, an explosion combustion phenomenon of ammonium nitrate (ρ=1.7kg/cm3) was used instead of the explosive PETN and the ultra-high-speed destruction phenomenon of aluminum cylinder was analyzed. The mix powder obtained by mixing aluminum powder (ρ=2.7kg/cm3) and ammonium nitrate was used instead of the explosive PETN, and an explosive combustion phenomenon was generated using copper wire explosion by high-voltage capacitor bank (40kV, 12.5 /F). Ammonium nitrate and aluminum powder are kneaded in a combination ratio of 5 : 1 in mass. An aluminum cylinder was destroyed by the phenomenon. The experiments were conducted using various diameters of ammonium nitrate particle and the photographs of the phenomenon were taken by the high-speed camera (IMACON468) and the high-speed video camera (HPV-1). The fragments of aluminum cylinder were collected and their dimensions were measured. The explosion phenomenon and fragments were compared with the result by explosive PETN. This paper presents these experiments and analysis result. And, hydro codes have been applied to simulate the deformation behavior of the aluminum cylinder.

Crack tip behavior under pulsed electromagnetic loading

This paper describes a series of experiments and their numerical simulations in which cracks were created in conductors by using high-transient magnetic fields. The tests were conducted on small samples of 7075 aluminum alloy in a test fixture that placed the samples in series with a high-voltage capacitor bank and constrained the samples from moving. Notches were machined in the samples at various depths for the purpose of creating an initiation site for the cracks. After each pulse, the samples were unmounted and examined under an optical microscope. The peak current was varied to examine its effect on crack tip behavior. It was found that the crack tip extended linearly, was blunted by cavitation (blowholes formed due to intense heating), or bifurcated-depending on the level of the peak current. Multiple pulses were also applied to one sample to study the effects of repeated pulsing on crack extension. Finite-element computations were performed using the three-dimensional finite-element analysis program EMAP3D in conjunction with the stress code DYNA3D. The computational results confirm most of the features observed in the experiments.

Pulsed magnets for strong and ultrastrong fields

Recent developments in the design of pulsed laboratory magnets are reviewed. There are two general categories with many variations: nondestructive magnets for fields below 100 T with pulse durations from 0.1 ms to 1 second, and destructive magnets with pulse durations from 0.1 to 10 /spl mu/s. Nondestructive magnets are mostly wire-wound coils with internal and external reinforcement. The peak field depends on the strength of the materials (strong wires, fibre composites) and on the geometry (bore size, distribution of reinforcement and current density) which can be optimized. Megagauss magnets rely on inertial confinement; this is the reason for the short pulse duration. The field is either generated by magnetic flux compression, driven by high explosives or by electromagnetic forces, or in a small single turn coil that explodes violently in the process. The single turn coil is usually driven by a very fast high voltage capacitor bank. Special measuring techniques must be developed for use with the different types of pulsed magnets.

An electrical discharge steam bubble acoustic source

Electrical energy stored in a high-voltage capacitor bank is rapidly discharged into seawater, producing a steam bubble. The expansion and subsequent collapse of the bubble compresses the surrounding fluid and radiates acoustic energy. The source process is divided into three stages: heating, expansion, and collapse. The fluid is rapidly heated by the large electrical currents passing between the electrodes. The heated fluid expands as compressed steam with a rapid increase in volume. Inertia causes the steam pressure to eventually fall below hydrostatic and the steam bubble collapses. Experimental data are presented for 1.9-cm-diam electrodes separated by 1.0 mm in 20.0-ohm cm seawater. Field strengths as high as 90 kV/cm and discharge times of between 5 and 10 μs were achieved without electrical breakdown. A thermoacoustic efficiency of 1.5% was measured.

Thermo-acoustic efficiency of a pulse-heating, electrical discharge source.

Electrical energy stored in a high-voltage capacitor bank is rapidly switched across a pair of electrodes immersed in a conductive fluid, such as seawater. As electrical current passes between the transducer electrodes, the fluid is rapidly heated and expands, producing acoustic waves. The current density defines the spatial distribution of the heating as well as the electrical resistance of the transducer. Computed and measured resistance agrees within experimental accuracy (a few percent). Using the wave equation, with an appropriate source heating term, the acoustic efficiency (acoustic energy/heat energy) of the pulse-heating mechanism is shown to increase linearly in proportion to the heat-energy density and to decrease inversely in proportion to the square of the heating time. The validity of this scaling relationship is confirmed experimentally for energy densities below 200 J/cc. Extrapolation of this relationship predicts 10% efficiency at 1000 J/cc, although this has not yet been confirmed experimentally.

Seismic isolation in New Zealand

Bridges, buildings, and industrial equipment can be given increased protection from earthquake damage by limiting the earthquake attack through seismic isolation. A broad summary of the seismic responses of base-isolated structures is of considerable assistance for their preliminary design. Seismic isolation as already used in New Zealand consists of a flexible base or support combined with some form of energy-dissipating device, usually involving the hysteretic working of steel or lead. This paper presents examples of the New Zealand experience, where seismic isolation has been used for 42 bridges, 3 buildings, a tall chimney, and high-voltage capacitor banks. Additional seismic response factors, which may be important for nuclear power plants, are also discussed briefly.

High speed forming of metal sheets by electromagnetic force. 2nd report. Analysis of the electromagnetic impulsive force generated by a spiral flat coil.

An analytical method to predict the electromagnetic force in an electromagnetic forming system is presented. A spiral flat coil is approximated by coaxial circular rings carrying the discharge current from a high voltage capacitor bank. The penetration of the magnetic field of the coil into a conductive circular disk is analyzed based on the boundary-value problem for the diffusion equation. The thickness of the disk is assumed to be large compared with the skin depth. Magnetic field, eddy currents and electromagnetic force density in the disk are calculated numerically. Coil current and the magnetic field distribution in the gap between the coil and the disk agree well with the experiment, showing the validity of the analysis.

A capacitor bank charger using a high-frequency link resonant circuit

A high-voltage compact capacitor bank charger is required in sonar applications. A resonant high-frequency link is employed which provides fast response to an external command, high efficiency for the convertor and isolation between the input and the output of the convertor. The convertor circuit is analysed and the design procedure is given. Experimental results obtained from a 1200 J charger are discussed.

An electromagnetic, plane stress-wave generator

This paper describes a unique device that has been developed for the transient loading of models along straight and curved boundaries and that operates by discharge of a high-energy, high-voltage capacitor bank. In its present configuration, this device can generate uniform pressures from 1500 psi (10 MPa) to pressures that approach 100,000 psi (690 MPa) and that rise from zero to maximum pressure in 2 μs and decay to approximately zero in another 2 μs. The transient stress-wave patterns in photoelastic models loaded with this device have been recorded by a dynamic polariscope. The dynamic polariscope presently in use is identical to a static polariscope except that the light source is of a short enough duration (½ μs) to photographically stop the movement of the photoelastic-fringe patterns caused by the stress wave. With the stress-wave generator and the dynamic polariscope, transient photoelastic patterns have been recorded in a number of models. These patterns indicate that the scatter from duplicate shots performed with this technique is on the order of 3 percent. This represents considerable improvement over the 15-percent scatter normally experienced with sheet-explosive loading techniques. This improvement and the rapid turnaround between shots (approximately 5 min) are distinct advantages this system has over other methods of dynamic loading.

A Pulsed Beam Shutter for Radio-Frequency Separated Beams at the ZGS

A pulsed beam shutter magnet is required to deflect a beam of separated high energy particles into a beam stop after a desired number of particles have reached the 12-ft bubble chamber at the ZGS. The magnet has a core, wound from 2 mil grain-oriented steel, an aperture 15 cm × 15 cm, and a ∫Bdl=1kGm. The pulse has a risetime of ≤3 #x003BC;s and a flattop of 40 μs. The above is achieved by discharging a high voltage capacitor bank into the magnet inductance, followed by a power-crowbar. The design of the magnet and the switching circuits is described and formulas for calculating the pulse shapes are given. Graphs of calculated flattops to 500 μs are shown.

Transient Surface Temperature Response of Liquid Crystal Films

Abstract Various commercially available microencapsulated cholesteric liquid crystal films and coatings were tested to determine their response to rapid heating. The rapid response data are required for the diagnostic devices to be used to measure the spatial energy distribution in lasers and electron beams. These films, which reversibly change color at discrete temperatures, were placed on tapered stainless steel strips that were pulse heated to a predetermined level in 30 μsec by discharging through the steel strip the stored charge from a high-voltage low-inductance capacitor bank. The taper introduced a temperature gradient along the length of the strip with the higher temperature at the narrow end. A high-speed movie camera and time fiducial system recorded the color change movement along the length of the bar as a function of time. The response time is the time required for the material to achieve its event temperature when the ratio of event temperature less initial temperature to substrate temperature rise is 0.9. These data are reported in tabular form for each material tested. In general, the response is inversely proportional to the film thickness squared since this is one of the limiting factors for heat diffusion. Various techniques to reduce film and coating thickness and enhance response were demonstrated and are discussed in the paper.

A Technique for Measuring Equilibrium Thermodynamic States of Liquid Metals at High Temperatures and Pressures

This paper presents a method for overcoming temperature and pressure limitations inherent in conventional techniques for measuring equilibrium thermodynamic data. The method can be applied to conducting materials that can be resistively heated and that do not dissociate in the liquid phase; and it is thus particularly suitable for investigating pure liquid-metal thermodynamic data. The technique has been applied extensively to lead at temperatures exceeding 5000 K and at pressures up to 2 kilobars. A cylindrical material specimen 1 mm in diameter and 25 mm long is interposed between two current leads and mounted axially concentric with a high-pressure cell. After the cell is pressurized with helium, a current pulse from the overdamped discharge of a high-voltage capacitor bank heats the wire at such a rate that its expansion is nearly isobaric. The energy deposited in a central segment of the sample is computed by integrating the product of the current flowing in the segment with the resistive voltage developed across it. With these data, sample resistance can also be calculated during a major portion of the time that current flows. Because mounting constraints limit sample expansion to the radial dimension, the equilibrium volume is calculated from the expanded diameter, which is measured by means of pulsed x-radiography.

A 100 kV, Fast, High Energy, Nonuniform Field Distortion Switch

A fast closing, high voltage, high energy, nonuniform field distortion switch has been developed. This switch, filled with free-flowing one atmospheric sulfur-hexafluoride gas, operates in the cascade mode, and is able to handle 36 kJ at 85 kV. These switches have been tested and put into operation with the Columbia high voltage capacitor bank. The over-all jitter between the six switches used is less than 10 nsec at 85 kV.

A Vacuum Tube Compensated Flat Top High-Current Pulse Supply for Symmetrical Torus Machine

The conversion of the Model C Stellarator to a symmetrical torus machine produced a longer plasma confinement time. This, In turn, required a longer ohmic heating current pulse than could be supplied by the existing vacuum tube system controlling the total energy flow. A new energy supply, consisting of a high-voltage capacitor bank and crowbar coupled with a low-voltage pulse-forming network of electrolytic capacitors, has been added In parallel with the existing vacuum tube system such that the two are complementary. The composite supply is capable of producing longer pulses with a greater amplitude and, at the same time, permits modulation of the flat top.

Interaction of Capacitor-Bank-Produced Megagauss Magnetic Field with Small Single-Turn Coil

Experiments on the production of high magnetic fields in single-turn coils by means of high-voltage capacitor banks are described. Fields as high as 3.5 megagauss have been produced. Numerical analysis of the interaction of this field with the metal wall shows that magnetic diffusion and wall compression are the principal interaction phenomena. In addition, experimental and theoretical evidence are presented for the emission of a vapor cloud by the wall into the magnetic-field volume. Finally, a simple approximate method for calculating the early time history of the magnetic field and coil motion is shown to give reasonable agreement with experiment.

High Voltage Capacitor Bank Charging through a Series Vacuum Tube

The use of a vacuum tube as the isolating element in the charging of a high voltage capacitor bank was investigated analytically and experimentally. The series tube effectively open circuited a 60 kV power supply from a 20 μF capacitor bank upon command during bank discharge and when there was a ``crowbar'' or fault in the rf system. The tube cutoff capability allowed its operation as a switching regulator, providing precision voltage regulation for the capacitor bank. Programming the series tube grid circuitry for constant charging current allowed reduction of the peak current requirements of the charging power supply and smoothing of the load on the utility lines. Analysis of the modes of operation, description of the circuitry employed, and operational results are presented.

The Brookhaven-Columbia Plasma Lens

A uniform current density plasma is generated by discharging a high voltage capacitor bank into two electrodes in a low pressure gas. The magnetic field within the plasma produces achromatic focussing of pions and kaons travelling along the electrode axis.