AC Operation Research Articles

Effective erosion rates for selected contact materials in low-voltage contactors

Effective and absolute erosion rates are reported for contact materials from vacuum interrupters used for low voltage contactors. The effective erosion rates were determined from the linear erosion of both contacts with 60 Hz half cycle currents (from 630 to 685 A peak) and maximum gaps of /spl sim/2.2 mm. The contacts were opened at a present time in a half cycle, and the drawn arc continued to the next and final current zero. The polarity of the current automatically changed for each operation to ensure uniform erosion history for both contacts during many thousands of operations. Afterwards, the contacts were removed and placed in a demountable arcing chamber for determination of the absolute dc erosion rate of the cathode material. The absolute cathodic erosion rates were determined with applied dc current pulses on the order of 100 A and maximum gaps of 8.5 mm. With ac operation at a gap of 2.2 mm, a significant fraction of the ions and neutral vapor leaving one contact deposits on the other contact, so the effective erosion rate is markedly smaller than the absolute erosion rate. The materials investigated were Ag-WC, Cu-Cr, and Cu-Cr-Bi.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A feasibility study on a world-wide-scale superconducting power transmission system

The author has conceptually designed two types of superconducting DC power cable (SCDCPC) using high temperature superconductors. One is cooled by liquid hydrogen, and the other is cooled by liquid nitrogen. The former has a capacity of 50 GW, and the latter has a capacity of 20 GW, So as to reduce losses as low as possible, the DC system has been selected. The rated voltage for both systems is /spl plusmn/250 kV. Because of the merit of DC operation, these cables generate neither conductor loss nor dielectric loss induced by AC operation, and so have extremely high efficiency. In the case of 10,000 km transmission, Including the refrigeration power, the total loss is lower than 1%. A concept of a world-wide superconducting power transmission system using SCDCPCs is presented. >

Degradations in PZT thin film capacitors

Abstract Degradations in ferroelectric capacitors are categorized as DC and AC types. In memory applications, AC type degradations appears to be more serious than those of DC type. Breakdown, for example, occurs earlier under AC operation than DC. AC type degradations were reviewed and induction period was also discussed extensively. An induction mechanism was proposed based on domain rearrangement under AC conditions. Curve fitting was demonstrated according to induction equation. It is suggested that the fatigue equation should be modified when induction period is considered.

Performance summary of a 4,000 a high temperature superconducting cable conductor prototype

Multifilamentary superconducting Bi-2223 tapes made with a powder-in-tube process have been used to assemble multistrand, multilayer cable conductor prototypes. The electrical performance of these conductors has been evaluated at 77 K in self-field with DC and AC transport currents. Results show that these conductor prototypes, carrying up to 4,200 A DC, approach the 2,000 A AC operation threshold required for the commercial application of HTS power transmission cables. Combined with recent improvements in tape mechanical performance, stability, and long-length manufacturability, these results show the potential for use of HTS tapes in power transmission cables.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Nonlinear gain coefficients in semiconductor quantum-well lasers: effects of carrier diffusion, capture, and escape

Effective nonlinear gain coefficients due to the effects of carrier diffusion, capture, and escape are derived from the carrier transport equations. The quantum capture and escape processes between the confined states and the unconfined states are calculated from first principles by evaluating the carrier-polar longitudinal optical phonon interactions. The dc and ac capture times and escape times are derived from evaluating the net capture current of carriers. The differences in capture and escape times between dc and ac operating conditions are numerically investigated. We find that both dc and ac escape times are strongly dependent on the quantum well structure. This differs from the dc and ac capture times that are not sensitive to the quantum well structure. We also find that the dc escape time predicted by the classical thermionic emission theory will no longer be valid for narrow or shallow quantum wells. We show that both dc and ac capture and escape time ratios will increase as the carrier temperature and the carrier density in the quantum well increase. Therefore, we suggest that the possible cause of the resonant frequency degradation and dramatic increase in the damping rate results from the increase of the ac capture to escape time ratio by the effects of carrier heating. Two theoretical models (2N and 3N models) were used to study the effects of carrier diffusion-capture-escape on the modulation response of quantum-well lasers and a distributed model of carrier transport in quantum-well lasers is proposed. Their implications in designing high-speed quantum-well lasers are discussed. >

Preliminary Experimental Results of ac Operation in the CT-6B Tokamak

The preliminary experimental results of ac plasma discharges in the CT-6B tokamak have been achieved by an active plasma current feedback system and the keys to a smooth transition through current zero and some phenomena related to the current reversal phase are also presented.

酸化物超伝導電流リード 高温超電導電流リードの技術要素と開発の現状

Technological aspects and recent advances in the current leads incorporating high temperature superconductor (HTS) are described. HTS of sintered Bi-2223, melt cast Bi-2212, unidirectional Y-123 and Ag- or Ag alloy-sheethed Bi-2223 are being investigated and tested in models of current lead systems. Reduction of refrigerator power by a factor of 3 to 5 is demonstrated by model tests. Easy operation and a cryogen-free superconducting magnet has become available using HTS current leads. Researches concerning safety and reliability are being made, ac operation models are tested, and design studies for specific application in large systems are underway. We can expect that all of the Cu current leads will be replaced by HTS current leads.

High- Tc edge-geometry SNS weak links on silicon-on-sapphire substrates

High-quality superconductor/normal-metal/superconductor (SNS) edge-geometry weak links have been produced on silicon-on-sapphire (SOS) substrates using a new SrTiO 3/“seed-layer”/cubic-zirconia (YSZ) buffer system. The seed layer is a thin YBa 2Cu 3O 7- x (YBCO) or PrBa 2Cu 3O 7- x (PBCO) film, which provides a template for growth of the SrTiO 3. This multilayer buffer system eliminates problems with series grain-boundary weak links seen in edge junctions on single YSZ buffer layers on SOS, while the use of moderate-dielectric-constant SOS substrates should benefit high-frequency applications and enable integration with silicon circuitry. SNS weak links fabricated on SOS with PBCO and Co doped YBCO normal-metal layers exhibit current-voltage characteristics qualitatively consistent with the resistively shunted junction model, with modulating AC Josephson steps and operation to temperatures above 77 K. These are the first reported epitaxial edge-geometry SNS devices on SOS substrates.

Research and development of AC superconductors in super-GM

R&D of the superconductors (NbTi and Nb3Sn) for AC use has been conducted with theobject of their application to power apparatuses. As for three types of NbTi strands, values of hysteresis loss (Wh) divided by λ Jc were successfully reduced, and the lowest value consists of Wh of 11 J/m 3 (50 Hz, ± 0.5 T) and λ Jc of 2160 A/mm 2 (at 0.5T). Thus, AC 1 to 2 kA class NbTi conductors were developed. As for six types of Nb 3Sn strands, the values were also reduced, and the lowest value consists of λ Jc of 2650 A/mm 2 (at 0.5 T) and Wh of 2300 J/m 3 (at ± 0.5T). The test coils wound with the Nb 3Sn stranded wires allowed AC operation (50 Hz) more than 90% of lc on the load line. The data of these coils are greater than those of NbTi conductors.

Continuous-wave laser pump light sources: new concepts

The relatively short lifetime of rare-gas discharge pump light sources for high-power cw solid-state lasers is caused mainly by vaporized cathode emitter material reacting with the thermally highly loaded quartz wall. The introduction of new bipolar electrodes without special emitter materials mounted on hot-ended molybdenum-cup seals, together with 60-kHz ac operation, makes possible the application of a tungsten halide cleaning cycle within the lamp bulb. This new type of high-power rare-gas pump light source exhibits 20% better radiation efficiency, 20% lower Nd:YAG laser threshold, and considerably extended lifetime.

AC versus DC hot-carrier degradation in n-channel MOSFETs

The origins of the enhanced AC hot-carrier stress damage are examined. The enhancement in hot-carrier stress damage under AC stress conditions observed with respect to damage under DC stress conditions can fully be explained by the presence of three damage mechanisms occurring during both DC and AC operation: interface states created at low and mid-gate voltages, oxide electron traps created under conditions of hole injection into the oxide, and oxide electron traps created under conditions of hot-electron injection. It is shown that the quasi-static contributions of these mechanisms fully account for hot-carrier degradation under AC stress. The AC stress model is applied to devices from several different technologies and to several different AC stress waveforms. Excellent agreement is obtained in each case. The results demonstrate the validity of the model for frequencies up to 1 MHz. The absence of any transient effect indicates that the model could be applicable at much higher frequencies. >

Hot carrier evaluation of MOSFETs in ULSI circuits using the photon emission method

Photon emission from MOSFETs by hot carrier effect under AC operation is studied. A method to estimate the lifetime of MOSFETs in LSI chips, which uses the photon emission, is proposed. This method is based on experimental data showing that the lifetime of hot-carrier degradation is described by a universal curve with respect to the photon count at a wavelength of 200 nm. Quantitative estimations of lifetimes of MOSFETs in a real LSI are reported. This method is applied to the lifetime estimation of a CMOS microprocessor. >

Pulsed RFEC probe response

A finite element/finite difference algorithm is described for modeling the pulsed excitation of a remote field eddy current (RFEC) probe used in steel pipeline inspection. Previous work has largely been concerned with the steady-state AC operation of the probe and physical explanations, based on finite element studies, of the probe's sensitivity to outer wall defects. In the present work, the authors discuss the probe response to a sinusoidal pulse and show that such an excitation mode can also be used for outer wall defect detection.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

高温超電導体を用いた浮上走行モデルの試作

A linear motor car using the diamagnetism of a high Tc superconductor has been manufactured. In this model the track is constructed by Sm-Co permanent plate magnets magnetized perpendicularly to the plane. The car is comprised of Tl based superconductor with a critical temperature of 120K. When it is cooled by liquid nitrogen down to 77K, it becomes superconductive and levitates above the magnet track by the repulsive forces due to the diamagnetism. The levitating car moves smoothly along the track by applying traveling magnetic field by the propulsion coils which are layed at uniform intervals on the magnet track. According to 3-phase AC operation, the propulsion coils generate a traveling magnetic field and the car runs with the slip to the synchronous speed. As a results, we think that the driving mechanism is similar to induction motor. Because there are eddy current paths due to the grain boundary normalized in the superconductor.

An Alternating Current Tokamak Reactor with Ohmic Ignition and Bootstrap Current

In this paper an alternating current (ac) tokamak reactor with ohmic ignition and long pulses due to bootstrap current is proposed as a simple and quasi-continuous fusion power plant. An ohmic plasma current of 23 MA with a high toroidal field of {approximately} 10 T in the alternating Current Tokamak Reactor-Upgrade (ACTR-U) (10-m major radius and 2-m minor radius) provides the ohmic ignition. After entering the ignition regime, the plasma current is reduced by one-half to enhance the bootstrap current with a high-beta poloidal field ({beta}{sub p} {approximately} 2) to prolong the pulse length. When the ohmic transformer reaches the maximum flux, the plasma current is ramped down and reversed; ac operation follows. The authors thus demonstrate that an ohmic transformer alone is in principle sufficient for a quasi-continuous deuterium-tritium fusion reactor.

Optical bistable and limiting behaviors in ferroelectric liquid crystal and optical processing

Abstract Optical bistability and limiting have been studied in surface stabilized ferroelectric liquid crystal (SSFLC) with electrical feedback. Optical bistability and limiting are observed for the cases of positive and negative feedback gains, respectively. The hysteresis in the voltage-transmission curve which is characteristic of the SSFLC is found to contribute to the expansion of the optical bistable region in the positive feedback and to the appearance of the bistability in the negative feedback. Dynamic characteristics of switching between optical bistable states by an incident light pulse have also been studied. A new multi-logic element with both OR and AND functions which can be selected by controlling the duration of the reset light pulse can be realized. Besides of dc voltage operation, the ac operation of the feedback without dc bias voltage is also realized in the liquid crystal which shows antiferroelectric behavior and a symmetrical voltage-transmission curve.

Hybrid Optical Bistability Using Antiferroelectric Behavior in Ferroelectric Liquid Crystal

Hybrid optical bistability with an electrical feedback in surface stabilized ferroelectric liquid crystal which shows antiferroelectric behavior has been studied. The ac operation of the feedback without dc bias voltage is also realized in the liquid crystal which shows a symmetrical transmission-voltage curve. Dynamic characteristics of the switching between optical bistable states by an incident light pulse have also been studied.

Fluorescent lamps: Dynamic analysis with two-temperature representation of electron energy distribution

A dynamic simulation method which has been developed for a low-pressure mercury rare-gas positive column is applied to an analysis of an AC operation of fluorescent lamps. Calculations are carried out for fluorescent lamps with inner diameters of 15.5 mm, 18 mm and 24 mm driven by an AC power source through a single choke at the frequencies of 60 Hz and 50 kHz. Calculated waveforms of lamp voltage and current agree well with experimental ones for both operating frequencies. This technique gives us dynamic characteristics of plasma parameters, and opens a way to computer aided design of the fluorescent lamps.

AC hot‐carrier degradation due to gate‐pulse‐induced noise

AbstractAC hot‐carrier degradation due to gate‐induced noise has been clarified, and a method to suppress noise and to predict ac lifetime is proposed. There have been many arguments on the ac degradation mechanism. This is because the degradation acceleration factor due to the measurement noise was not separated and caused confusion. In particular, the noise generated on the source‐drain electrodes during the gate pulse rise has been found to be an important factor in ac degradation acceleration.The noise is an inductive noise generated by the rapid change in channel current during gate on and off amplified by an inductance due to the source and drain interconnects. If the noise is suppressed, at least for the rise time of more than 10 ns, the carrier trapping and detrapping accompanied by the ac operation can be ignored, and the lifetime can be predicted by the dc hot‐carrier degradation lifetime and the duty cycle.In the future, attention must be given to the ac degradation acceleration due to the increase in the inductive noise by the interconnect scaling. Thus, an interconnect design rule based on the suppression of the source‐drain induced noise is proposed.

Power system design for fiber to the home systems

The overall topology of the AT&T fiber to the home (FTTH) system is reviewed with particular emphasis on power. The focus is on the issues that arise in powering the customer end of the fiber, i.e., the distant terminal. It is shown that flexible power arrangements are required for distant terminals in the fiber system in the local plant. Architectures must be able to accommodate local exchange carrier preferences for AC or DC pedestal operation. The system must readily accommodate new as well as existing applications in growth areas and also rehabilitation applications.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>