High Current Power Supply Research Articles

Advanced generation of rotatable magnetron technology for high performance reactive sputtering

Magnetron performance is ultimately the determining factor in the productivity of glass sputter coating technology. Maximum power density, target utilization and efficiency, coating uniformity, material deposition rates, vacuum reliability, arc and debris control, quick turn-around and ease of maintenance all contribute to the overall efficiency of any magnetron sputter source. The state of the art in magnetron sputter deposition is now based upon reactive sputtering of rotatable cylindrical magnetrons using AC power supplies. A new generation of rotatable sputter magnetrons is based upon design from first principles for optimized use with high current mid-frequency AC sputtering power supplies. Improved target designs result in more robust vacuum sealing and greater than 90% material utilization. Improved magnet fixtures and process control results in stable, high deposition rates for reactive sputtering with 3% uniformity range. Results from lifetime testing and production systems are presented. Critical performance features including current handling capability, seal lifetime, and process uniformity are discussed.

Thyristor crowbar system for the high current power supplies of ASDEX upgrade

The ohmic heating system and the poloidal field coils of ASDEX upgrade are supplied by 15 thyristor converter units with an installed apparent power of 600 MVA. To protect the thyristor converters against dc overvoltage arising from abnormal operations and resulting damages caused by the large energy stored in the AUG magnet coils an overvoltage protection system was required. The paper describes the motivation for—and the design and testing of the thyristor crowbar system representing the thyristor converter overvoltage protection system. It will present the layout, analyse the results of measurements obtained during commissioning, compare them to the calculated (design) values and report on the first experience of operation on the AUG coils improving the safety of the equipment.

HTS Flux Pump for Cryogen-Free HTS Magnets

A reliable method for persistent-current mode operation of HTS magnets is still not available. As an alternative solution to external high-current power supplies we have developed a cryogen-free operating transformer-rectifier type HTS flux pump. Using this device only small ac currents have to be supplied into the cryogenic system. Both thermally triggered HTS thin film switches as well as cryogenic MOSFET switches have been used to operate a conduction-cooled 0.5 T HTS magnet coil. This paper presents results of experimental test and modeling of the flux pump operation.

Effect of Resonant Transition on Efficiency of Forward Converter With Active Clamp and Self-Driven SRs

Forward converter with active clamp is a suitable topology for a low output voltage and high output current dc-dc power supply module. The topology can be used in a resonant transition manner to obtain a low voltage over the main switch at turn-on instant. A low voltage can be obtained by adjusting the magnitude of the magnetizing current of the transformer and the delay between the two primary side switches. An increased magnetizing current, however, increases conduction losses in the primary side of the converter and may consume the advantage gained in the switching losses. The converter can also be easily used for self-driven synchronous rectification. However, pursue for low switching losses for the primary side switch may deteriorate performance of the self-driven synchronous rectifiers, particularly at high loads. This paper presents a study of the applicability and advantage of the use of the resonant transition in Forward with active clamp and self-driven synchronous rectifiers. The emphasis is on the comparison of the achieved efficiency with different voltage levels over the primary switch prior to turning on. Measurement results show that, at low loads, a reduced voltage level improves the efficiency but, on the other hand, at high loads the advantage is not so significant, or it may be totally lost, mainly due to the increased losses of the self-driven synchronous rectifiers. The paper includes discussion on the effect of the magnetizing inductance on the efficiency of the converter and the optimal voltage level at which the primary switch should be turned on. Measurement results from a 3.4-V 30-A prototype converter are included.

Isolation of Copper from a 5-Cent Coin. An Example of Electrorefining

The United States 5–cent coin commonly known as a "nickel" is made of an alloy containing 75% copper and 25% nickel. In this experiment, an electrolytic cell is set up using a 5-cent coin as the anode, a graphite post as the cathode, and a bath of 6 M hydrochloric acid as the electrolyte. Aqueous copper and nickel ions are produced at the anode, and pure copper metal is isolated at the cathode. The experiment is a visually appealing illustration of the process of electrorefining using selective reduction. The experiment requires a 6-V battery (or high-current power supply), appropriate patch cords, 6 M HCl, and a 250-mL beaker. Using a current of approximately 1 A, an easily measured quantity of pure copper can be collected in less than 30 minutes. If the current during the experiment is measured, a percent yield of copper (based on the number of electrons transferred) can be calculated.

電池による大電流超伝導磁石電源

Since superconductors do not require voltages, a high-current power supply could run with low power if the voltage is sufficiently reduced. Even a battery-powered power supply could give as much as 2, 000A for a superconductor. To demonstrate this hypothesis, a battery-powered 2, 000A power supply was constructed. It uses an IGBT chopper and Schottky diode together with a specially arranged transformer to produce a high current with low voltage. Testing of 2, 000A operation was performed for about 1.5hr using 10 car batteries. Charging time for this operation was 8hr. Ramping control was smooth and caused no trouble. Although the IGBT frequency ripple of 16.6kHz was easily removed using a passive filter, spike noise remained in the output voltage. This ripple did not cause any trouble in operating a pancake-type inductive superconducting load.

Characteristics of a plasma electrolytic nitrocarburising treatment for stainless steels

In this work, we investigate the feasibility of a plasma electrolytic nitrocarburising (PEN/C) treatment applied to AISI 316 stainless steel using a modified aqueous solution of urea as the treatment electrolyte. The substrate samples were connected cathodically to a high-current DC power supply and biased with a negative voltage in the range 220–260 V. The treatment time was typically in the range of 30–60 s. Investigations of the characteristics of the treated component show that the friction coefficient against a WC–Co ball counterface can be slightly reduced, and that the wear rate decreases by several decades. The microstructure of the treated layers depends strongly on the electrical parameters (e.g. the applied voltage, which controls the treatment temperature) and can be adjusted from a single expanded austenite phase (γ N) to multi-phase combinations, including mixtures of Fe(Fe,Cr) 2O 4, γ N and (Cr,Fe)N x . The corrosion properties of the treated layers are closely correlated to the microstructure and composition and can be significantly improved, particularly if a thin, but dense, magnetite-based iron–chromium oxide layer is produced at the surface. For improvement of the tribological properties of substrates treated at low temperature, a diamond-like-carbon coating was deposited on the PEN/C pre-treated substrate using a plasma-immersion ion-assisted deposition (PIAD) process. Such duplex treatments show great potential for surface modification of stainless steels for applications in aggressive corrosive-wear environments.

Demonstrating forces between parallel wires

A simple, highly effective demonstration of mutual repulsion (attraction) between parallel conductors is described for the classroom. The physical effects are clearly elucidated using readily available materials in conjunction with a high-current (20 A) dc power supply.

The design of a compact cryogen-free superconducting wavelength shifter for synchrotron radiation

A compact three-pole superconducting magnet with a warm bore for electron orbit has been designed to serve as a wavelength shifter for Taiwan synchrotron radiation light sources. The wavelength shifter will have a warm beam duct, which is 600 mm in length, 100 mm in width and 20 mm in high. Three pairs of racetrack superconducting coils were designed to create a central field and to adjust the integral field close to zero. A maximum magnetic field of 6.5 Tesla at the central pole will be generated. To avoid induced currents, all six coils are connected electrically in series and powered by a high current power supply. Two low current trim power supplies are used to adjust currents on the two side pairs of coils in order to eliminate the first and the second magnetic field integrals. The shape of pole pieces and superconducting coils are specially designed to minimize the higher harmonic terms of the magnetic field, especially the sextupole field component. Both the superconducting coils and the iron yokes are cooled by a single 1.5 W Gifford-McMahon cryo-cooler. The normal operation of the 6.5 T wavelength shifter will be cryogen free.

Development path of low aspect ratio tokamak power plants

Recent advances in tokamak physics indicate that a spherical tokamak may offer a magnetic fusion development path that can be started with a small size pilot plant and progress smoothly to larger power plants. Full calculations of stability to kink and ballooning modes show the possibility of greater than 50% β-toroidal with the normalized β [ β N= β T/(I/aβ)] as high as 10 and fully aligned 100% bootstrap current. Such β-values coupled with 2–3 T toroidal fields imply a pilot plant about the size of the present DIII-D tokamak could produce ∼800 MW thermal, 160 MW net electric, and would have a ratio of gross electric power over recirculating power ( Q PLANT) of 1.9. The high β values in the ST mean that E×B shear stabilization of turbulence should be ten times more effective in the ST than in present tokamaks, implying that the required high quality of confinement needed to support such high beta values will be obtained. The anticipated β values are so high that the allowable neutron flux at the blanket sets the device size, not the physics constraints. The ST has a favorable size scaling so that at 2–3 times the pilot plant size the Q PLANT rises to 4–5, an economic range and 4 GW thermal power plants result. Current drive power requirements for 10% of the plasma current are consistent with the plant efficiencies quoted. The unshielded copper centerpost should have an adequate lifetime against nuclear transmutation-induced resistance change and the low voltage, high current power supplies needed for the 12-turn TF coil appear reasonable. The favorable size scaling of the ST and the high β mean that in large sizes, if the copper TF coil is replaced with a superconducting TF coil and a shield, the advanced fuel D-He 3 could be burned in a device with Q PLANT∼4. If the anticipated physics of the ST regime can be proven in near-term experiments and engineering challenges (such as the high power density to be exhausted and centerpost neutronics issues) can be met, then the ST offers the possibility of a magnetic fusion development path with a minimal cost initial step and exciting further possibilities.

A method for harmonic reduction on the source side of a parallel-connected thyristor converter having an interphase reactor

A parallel-connected twelve-pulse thyristor converter consisting of two six-pulse groups with an interphase reactor has been used for low-voltage high-current dc power supplies because of its high efficiency compared with a series one. It seems to be the most suitable converter for superconducting magnetic energy storage systems (SMES), which are expected to be used in actual power systems in the near future as a power system stabilizer. Harmonic reduction on the source side is required for such large-capacity thyristor converters. A number of methods have been proposed. These methods, however, require additional devices. Thus, a simple parallel-connected converter without any additional devices remains to be constructed to reduce harmonic currents on the source side.This paper attempts to construct a simple 12-pulse thyristor converter by proposing a novel design concept of the interphase reactor. This method proposed here requires no additional devices and only reducing the inductance of the interphase reactor. The source current of the 12-pulse thyristor converter with the reduced inductance interphase reactor approaches sinusoidal waveforms, which are approximately equivalent to those of the 36-pulse thyristor converter. Simulation results show that decreasing the inductance of the interphase reactor contributes to reducing harmonic currents on the source side. In addition to the simulation results, experimental results verify the validity and practicability of the proposed novel design concept of the interphase reactor.

A high current, battery-operated power supply with power control through an on–off fast switch

A simple high current power supply is described. It can be assembled from readily available and relatively cheap components which can be itemized as follows: (1) commercial batteries; (2) fast high current switch; (3) feedback sensor; (4) PC with peripherals for controlling the switch. The apparatus was assembled for heating at very high heating rate with a low resistant load such as a graphite or vitreous carbon tube used as an atomizer in electrothermal atomization-atomic absorption spectroscopy measurements. The high heating rate must, however, be combined with a fairly good control of the temperature of the tube at various levels. This was obtained with a PC and relative peripherals which, directly or through a feedback circuit, control the switch. The system can be easily modified and adapted for other kinds of measurements as long as the high noise of the switching does not interfere with signal recovery. With the atomic spectrometer used (Perkin–Elmer Model 1100B), however, no worsening of the signal noise was observed. The level of current that can be used is mainly determined by the switch since, within a certain range, the voltage and the internal resistance of the power supply can be changed by the type of batteries and the way they are connected.

A Method for Harmonic Reduction on the Source Side of a Parallel-Connected Thyristor Converter Having an Interphase Reactor.

A parallel-connected twelve-pulse thyristor converter consisting of two six-pulse groups with an interphase reactor has been used for low-voltage high-current dc power supplies because of its high efficiency compared with a series one. It seems to be the most suitable converter for superconducting magnetic energy storage systems (SMES), which are expected to be used in actual power systems in the near future as a power system stabilizer. Harmonic reduction on the source side is required for such large-capacity thyristor converters. A number of methods have been proposed. These methods, however, require additional devices. Thus, a simple parallel-connected converter without any additional devices remains to be constructed to reduce harmonic currents on the source side.This paper attempts to construct a simple 12-pulse thyristor converter by proposing a novel design concept of the interphase reactor. This method proposed here requires no additional devices and only reducing the inductance of the interphase reactor. The source current of the 12-pulse thyristor converter with the reduced inductance interphase reactor approaches sinusoidal waveforms, which are approximately equivalent to those of the 36-pulse thyristor converter. Simulation results show that decreasing the inductance of the interphase reactor contributes to reducing harmonic currents on the source side. In addition to the simulation results, experimental results verify the validity and practicability of the proposed novel design concept of the interphase reactor.

High current power supply for electrothermal atomic absorption spectrometry

A new power supply for electrothermal atomization — atomic absorption spectrometry (ETA-AAS) with associated equipment for temperature control is presented. The system is composed of two high current commercial batteries and a MOSFET switch which controls the temperature of the atomizer by switching the current in an on-off way through a feedback loop connected to a personal computer and suitably programmed peripherals. The delivered power can be changed from 0 to 100% in 1% steps which gives the possibility of roughly controlling both the temperature at low power when the temperature sensor is not working and the heating rate. With this system, curves for which the simultaneous presence of all atoms injected in the atomizer is claimed, have been extended to Pb, Ag, Tl and Zn. With a more conventional power supply previously used, such a claim could be made only for Cd and Hg.

A Flicker and Harmonic Compensator Using a Series Active Filter.

A specially designed twelve-pulse thyristor rectifier of 5-8MVA is required as a low-voltage high-current dc power supply for super-conductive material tests. It is, however, too susceptible to low frequency variation of the utility voltage, or to the so-called “flicker” to generate a strong magnetic field with high stability.This paper presents a flicker and harmonic compensator based on the combined system of a small-rated series active filter and a conventional shunt passive filter. The main purpose of the compensator is to remove susceptibility to the flicker from the thyristor rectifier. The series active filter, which is connected in series with the utility, can compensate for flicker components present at the utility grid, the frequency range of which is from 1Hz to 20Hz. In addition, it helps almost all harmonic currents produced by the thyristor rectifier to flow into the shunt passive filter installed in parallel with the harmonic-producing load, i.e. the thyristor rectifier.

Modeling and control of magnet power supply system with switch-mode ripple regulator

This paper presents the dynamic performance analysis and closed-loop design of a new power supply system for a high-current magnet load. This new system introduces a series switch-mode ripple regulator (SMRR) into a phase-controlled rectifier to improve system dynamic response and to reduce the harmonic content in the magnet current. In this paper, the new system control configuration is explained. The small signal dynamic model is established. The function of the SMRR as a speed-up feed-forward path during dynamic transients is assessed. The criteria of the closed-loop regulator design are identified. The theoretical analyses are accompanied by computer simulation and experimental results. The systematical design procedure is outlined by an example which offers better performance than ever reported on high-current magnet power supplies in terms of fast dynamic response (closed-loop bandwidth several kHz) and low harmonic content (less than 10 ppm) in the magnet current.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Improvement of a high current DC power supply system for testing the large scaled superconducting cables and magnets

A DC 75 kA power supply system was constructed to test the SC (superconducting) R&D (research and development) cables and magnets for the Large Helical Device (LHD). It consists of three 25 kA unit banks. A unit bank has two double-star-rectifier connections with the inter-phase reactors. A digital feedback control method is applied to the automatic current regulation (ACR) in each unit bank. For shortening the dead time of the feedback process, a new algorithm of a digital phase controller for the ACR is investigated. A Bode diagram of the feedback process is directly measured. It is confirmed that the dead time of the feedback process is reduced to one sixth, and that the feedback gain of PID (proportional, integral and differential) compensation is improved by a factor of two from the original method. >

Plasma thruster development program at the IRS

Since the early eighties the development of plasma thrusters has been an important research topic at the IRS, where a broad spectrum of stationary plasma thrusters has been investigated experimentally as well as theoretically. High power MPD thrusters (50 kW-1 MW) and a wide range of thermal arcjets (0.5–150 kW) are developed under contracts with ESA, NASA, USAF, USNAVY and with German funding. The IRS has excellent installations for continuous tests of high power accelerators. The high current power supply is a current regulated d.c. thyristor rectifier of 6 MW. The maximum current is 48 kA with a ripple less than 1%. The vacuum system is a roots pump system consisting of four stages with a total suction power of about 250,000 m 3/h at 1 Pa. Eight vacuum tanks of different sizes are connected to this system; six of them are used for plasma thruster development and two serve as plasma wind tunnels. For low power arcjet development and basic cathode erosion experiments four additional independent test stands are available.

A high-current, high-voltage power supply with special output current waveform for APS injector synchrotron dipole magnets

The authors describe a high-voltage, high-current power supply for the injector synchrotron dipole magnets at the Advanced Photon Source (APS). To reset the dipole magnets in each cycle, two different current waveforms are suggested. The first current waveform consists of three sections: DC-reset, linear ramp, and recovery sections where injection is done on the fly. The second current waveform consists of six different sections: DC-reset, transition to injection level, injection flat level, parabolic, linear ramp, and recovery sections. The effect of such waveforms on the beam is discussed, and the power supply limitations to follow such waveforms are given. The power supply limitations are due to the power components and control loops. The reference for the current loop is generated by a digital-to-analog converter which is discussed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A rapid-temperature-cycling apparatus for oxidation testing

An oxidation test with rapid temperature cycling was developed to evaluate small coated parts. The samples in the form of wire or foils are resistively heated with a high-current AC power supply, allowing fast heating and cooling of the samples. Fast temperature cycling of the samples permits to complete more than 100 cycles in one day. A variety of steels coated with silicon diffusion coatings were tested and the results compared with oxidation via traditional thermal cycling. The test accurately predicts enhanced performance for siliconized 1010 steel, an increase by a factor of three for the life of siliconized 302 stainless steel, and an inadequate siliconized coating for 410 stainless steel. Details of the rapid temperature cycling apparatus as well as testing of the coated steels are described in the paper.