High Current Power Supply Research Articles

Superconducting current transducer (for cable testing facility)

The construction and performance of an electric current meter that operates in liquid He and mechanically splits apart to permit replacement of the current carrying conductor are described. It permits the measurement of currents induced in a loop of superconducting cable and expeditious exchange of such loops. It is a key component for a short sample cable testing facility that requires no high-current power supplies or high-current leads. Its superconducting pickup circuit involves a nonmagnetic core toroidal split-coil that surrounds the conductor and a solenoid whose field is sensed by a Hall probe. This toroidal split-coil is potted inside another compensating toroidal split-coil. Currents of up to 10 kA can be measured with a precision of 150 mA.

On the current balance of phase-controlled thyristor converter having interphase reactors.

A parallel connected thyristor converter with an interphase reactor has been used widely as a low voltage high current DC power supply because of high efficiency, compared with a series one. It seems to be the most suitable for superconducting magnetic energy storage systems in particular. If the parallel converter consisting of two thyristor converters is operated under different firing angles in the two due to imperfect adjustment in the control circuit or something like that, unbalance may occur in the output DC current of each converter.The purpose of this paper is to discuss the current unbalance of a parallel thyristor converter in detail. The main points are summarized as follows:(1) It is clarified theoretically that the unbalance of DC output current may occur even when the difference of firing angles is less than 1°.(2) It is verified experimentally that the proposed simple current feedback makes it possible to balance the DC output current of the parallel thyristor converter.(3) An interphase reactor without gap is able to take the place of a conventional interphase reactor with gap which is used widely. Compared with the conventional one, the volume of the interphase reactor without gap is much small.

Unity power factor high current slew rate magnet power supply

The author presents an alternative design scheme which utilizes a conventional AC-to-DC n-pulse bridge and a DC-side commutation network. With the addition of a commutator, converter device latching current problems are overcome; a current slew rate can be preprogrammed within certain limitations; magnet current can be commutated safely in the event of a line voltage collapse; and the main converter can be designed to operate at rated load with a unity power factor. The major focus of the present work is to develop a simple analytical model of the converter commutator and magnet system suitable for design purposes. The model has been verified experimentally. Practical limitations of this circuit are described.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Stress Analysis for Design of Electromagnetic Launchers

The recent development of very high current pulsed power supplies provides an opportunity for order of magnitude improvements in electromagnetic launcher performance. Consideration of design objectives and constraints suggests that a ceramic-steel construction offers significant advantages over conventional composite-steel railguns. Structural analysis of such a system focuses upon material specific stress concentrations produced by dynamic and asymmetric electromagnetic loads.

Compact homopolar generator developed at CEM-UT

For electromagnetic launchers (EMLs) to become practical devices, they must evolve from laboratory test beds to field-portable systems. Such systems require the development of compact, lightweight, high-energy, high-current power supplies. Investigation of the candidate systems -- flux compressors, capacitors, inductors, batteries, and rotating machines -- showed the homopolar generator (HPG) to be a device with immediate potential for development. HPGs were selected because of their demonstrated ability to produce the high-energy, high-current electrical pulse required of an EML power supply from a relatively compact light-weight machine. By taking state-of-the-art HPG technology and integrating it with a machine designed specifically for high energy density, a field-portable HPG-powered EML system can be realized.

A new high current laboratory and pulsed homopolar generator power supply at the University of Texas

The University of Texas at Austin is constructing a spacious facility for research in pulse power technology at the Balcones Research Center, located in north Austin. The arrangement and capacity of the facility are intended to support high-current experiments. The laboratory power supply being designed consists of six homopolar generators, each capable of delivering ten megajoules of energy. The output bus is configured such that various series, parallel, and series-parallel circuits of homopolar generators are possible. Both resistive and inductive loads can be driven from the power supplies. Research programs will be supported with a wide range of physical facilities, including materials handling, machine shop, data acquisition and analysis, engineering and operating personnel, chemical analysis and metallurgical laboratories, and an information center. These facilities will be available to the U. S. technical community through several types of arrangements with The University through the Center for Electromechanics. Each of the six homopolar generators is designed to deliver 1 MA at 100 V, with a maximum repetition rate of a discharge every five minutes. In addition to EM launch research and applications, other intended uses of the power supply include welding of large cross-sections of metal (up to 650 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> or 100 in. <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> of steel), generation of high magnetic fields in low-impedance magnets, and testing of high-current opening switches. Status of major elements of the project is reported.

SURF's up at NBS: A Progress Report

The NBS Synchrotron UV Radiation Facility (SURF-II) is a 250 MeV single-magnet, weak-focusing electron storage ring, with 10 MeV microtron injector. Circulating beams of up to 35 mA at energies up to 250 MeV have been achieved. Beam lifetime, limited by Touschek effect, is extended to several hours by resonant vertical rf excitation. At low energies bunch shape oscillations occur, involving coherent synchrotron oscillations, negative-mass-type blowup and loss of beam. Effective avoidance and suppression techniques are discussed. A new set of high current gradient correction coils and power supplies, plus additional pancakes for the main field coils are being obtained. These are expected to extend SURF operation to 280 MeV and provide useful light output to 0.4 keV photon energies.

Study of Pulse Stretching in High Current Power Supplies Using Multipulse Techniques

Considerable interest exists at Fermilab to increase the pulse width of the Neutrino Focusing Horn to permit an increase in beam spill length from twenty (20) microseconds to one (1) millisecond. Two techniques to do this have been examined: 1) A high current transformer, and 2) Increased bank capacitance using the multi-power supply technique. The transformer is the most straightforward conceptually; it is, however, a complicated device requiring sizable changes to the existing horn power supply. This alternative will be briefly reviewed. The second scheme involves pulsing a 20 KV 200 KA power supply to establish the required load current and then maintaining this current by the sequential pulsing of a number of low voltage high current power supplies. This alternative will be discussed in detail with the results of tests performed on the Fermilab Focusing Horn System.

Simple inexpensive high-current power supply

Simple inexpensive high-current power supply

Short Sample Test of Superconducting Wire

Two different techniques were used for short sample tests of superconducting wires. One method was done with a DC transformer and the other with a high current DC power supply. Three different types of sample holders were used for the latter. Their relative merits and demerits are compared. Many wire designs representing half a dozen companies have been tested, and their results are presented. For the short sample test, quench current and current at various resistivities was determined. Resistivity ratios of ρ300/ρ12 were found for copper, and the effect of cola work on these ratios was investigated.

Design and Performance Aspects of a Precision High-Current Power Supply

Design and Performance Aspects of a Precision High-Current Power Supply

The NAL Booster Synchrotron Magnet Power Supply Servo

The booster magnet power system operates 48 magnet modules for equilibrium orbit field control. The power system consists of four high current power supplies having a common thyristor firing control chassis. The power supplies were manufactured by Brentford Electric Ltd. The mangent energizing current waveform is I(t) = Idc - Iaccos2?ft where f is the 15 Hz series resonant frequency of the high Q circuit. The dc and ac components are generated with one power source, not two as in eariler designs for rapid-cycling synchrotrons (e.g., NINA, DESY, CEA, PPA, and Cornell) Magnet power system parameters are summerized as follows: Operation Energy BMag IMag ESource Injection 200 MeV 488 G 74 A 64 V Extraction 8GeV 6.7KG 1023 A 890 V

A 2-to-10 Watt Monolithic Integrated Power Amplifier

This paper presents some unique device characteristics and typical applications of a power amplifier. The device incorporates such features as high current capability, temperature shut down and short circuit protection. It also offers a choice of operation over a wide range of output loads and supply voltages. Simple external circuitry and minimal circuit components make this IC an outstanding candidate for low to medium power audio systems, high power audio driver, servo motor driver, low voltage high current adjustable power supply and numerous thick film applications.

Experimental Superconducting Transformer for Current Set Up

For certain applications one would like to use relatively few turns of a high current conductor to make superconducting magnets. High current conductors introduce the problem of large heat leaks, and also the problem of a high current power supply. These problems would be simplified if one could make a suitable current step-up transformer. A design equation for such a transformer is presented. An experimental test was performed on a transformer made of superconducting solenoids which we had on hand. It had a primary current of 79.2 A, and supplied 670 A to a small load solenoid. The transformer was operated in two modes. In the first, the primary current was held constant for 24 h. The magnetic field in the load solenoid was monitored and the rate of decay in field could be measured. In the second mode, the primary current was regulated to maintain constant field in the load solenoid. The time constant of the secondary circuit was 1.4×106 sec. Such a system could be operated for a number of weeks without recycling.

Magnetic components for an efficient low-voltage high-current regulated power supply employing pulsewidth modulated inverter techniques

Magnetic components for an efficient low-voltage high-current regulated power supply employing pulsewidth modulated inverter techniques

A High-Current Low-Pass Filter for Magnet Power Supplies

The majority of high-current dc power supplies for beam bending magnets have well known LCR low-pass ripple filters. To avoid prohibitive heat losses, the filter damping resistor is in series with the capacitor and not in the dc path. Such filters, when critically damped, attenuate high frequencies by 6 dB/octave. This paper analyzes an improved underdamped LCR filter which attenuates high frequencies by 12 dB/octave. Depending on the application, the improved filter can be designed to have an oscillatory or a non-oscillatory response to a step change of the input voltage. Design curves are given which show the frequency response and the time response to a unit step of a normalized improved filter for various degrees of damping.

Application of the Two-Power-Supply Method to the Ferrite Bias of an RF Resonator of a Rapid-Cycling Synchrotron

Ferrite bias equipment for the RF resonators of high-repetition-rate synchrotrons is expensive because of the high voltage necessary to overcome the back EMF of the unsaturated ferrite at the beginning of the sweep and the high current necessary to saturate the ferrite at the end of the sweep. The high-frequency resonators of the Omnitron, which sweep in 8 ms require 70 V initially, but only 20 V after the second millisecond, when the current reaches 5 kA. The voltage remains low for the remainder of the sweep, while the current increases to 20 kA. To meet these requirements as inexpensively as possible, a pulse-type power supply is used during the first 2 ms, and a high-current power supply through the remainder of the sweep. Smooth current transfer is an inherent property of the circuit. Inductance, which is surprisingly costly, is kept to a minimum by a sandwich bus bar technique. A silicon-controlled rectifier (SCR) switch reverses the current every other sweep so that the full hystereses loop of the ferrite is used. A regulator circuit forces the bias current to follow a reference pulse.

Gamma-Ray Circular Polarization Analyzer Using a Rapidly Alternating Magnetic Field

Gamma rays from substances with half-lives approaching 0.1 sec may be analyzed using a magnet whose saturated field reverses in 0.4 msec. Laminated magnetic material and transistor circuitry are used to achieve the fast field reversal. The magnet consists of 4-mil Supermendur tape wound on a toroidal core. The high permeability and low loss of this material permits it to be driven by a single turn at reasonable currents. The circuit uses a low voltage, high current power supply, and charging inductors to provide the necessary voltage pluses. These pulses are developed across switches consisting of ten 2N1358 power transistors operated in parallel. The system has operated 2000 h without a failure.

Corbino Disk

When a disk with concentric inner and outer electrical contacts is placed in a magnetic field parallel to its axis, and current is made to flow through the disk, the lines of current flow have a spiral shape. This spiral current flow produces its own magnetic field, which interferes constructively or destructively with the applied field, depending upon whether the carriers spiral inward or outward, respectively. For ordinary conductors and ordinary currents the effect of the self-field of the current is very small. But the effect should be large in materials of very high mobility such as has been recently reported for bismuth at 4.2°K. In this paper the theory of the effect is given for the case in which the mean free path of the carriers is small compared to the inner radius of the disk. The analysis shows that the disk behaves as a rectifier. The easy direction of flow corresponds to outward spiraling of the carriers, which at large currents results in the explusion of the magnetic field from the disk. In the hard direction of flow the magnetic field at the center of the disk may be several orders of magnitude larger than the applied field. It is suggested that the corbino disk may be a useful rectifier in applications requiring extremely low impedance. It may also be a useful voltage regulator in a very low-voltage high-current power supply. A device consisting of the disk and a coil to provide the magnetic field is discussed in some detail. The static characteristics when the coil is connected through a suitable resistance in parallel with the disk exhibits a negative resistance. This negative resistance is useful in ac operation if a condenser is also connected in series with the coil. The equations and boundary conditions which determine the electrical properties of the disk in the time-dependent case are formulated. In the small-signal approximation the complex impedance is obtained for the limiting cases of low and high frequency. At low frequency the reactance is that of a negative inductance (-iωL). At high frequencies there is a skin effect on the tangential component of current, which causes most of the signal current to be radial and causes the impedance to reduce to the resistance of the disk.

Precision high-current computer power supplies

THE increasing size and complexity of analogue and digital computers has resulted in an ascending demand for expanding quantities of well-regulated and filtered d-c power. Regulated power demands have gone from milliamperes to hundreds of amperes.