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Measurement of Large, High-Frequency, Short-Pulse Currents Using a Radial Shunt

Description: Abstract: "The measurement of large, high-frequency, short-pulse currents--ordinarily complicated by inductance, stray magnetic fields, and magnetic forces that tend to disassemble the measuring device--is simplified and made with an average error of 2-1/2% by the use of a specially developed noninductive radial shunt in conjuntion with an oscilloscope. The skin-effect correction is derived theoretically and the accuracy of the method is demonstrated."
Date: May 22, 1956
Creator: McFarlane, H. Bruce
Partner: UNT Libraries Government Documents Department

Turbulent Pinch Experiments

Description: This report follows studies that were made the quasi-stable pinch produced by a relatively long duration low voltage capacitor discharge (5ma, 5kv) in a 600 cm long, 15 cm diameter metal tube.
Date: 1957
Creator: Sawyer, G. A. & Stratton, T. F.
Partner: UNT Libraries Government Documents Department

A Direct Current Emission Regulator

Description: The following report describes a current beam modulation designed to replace the standard regulator and to achieve an ion beam free from amplitude modulation.
Date: August 4, 1945
Creator: White, J. R. & Cameron, A. E.
Partner: UNT Libraries Government Documents Department

Direct-Reading Integrator

Description: Abstract: "An instrument is described which makes use of a standard watthour meter in conjunction with an amplifier to register the time integral of a varying voltage. When a suitable current shunt is used as the input element, the instrument becomes a direct-reading coulombmeter. In any of its applications the instrument is accurate to plus or minus two per cent."
Date: 1945
Creator: Waithman, V. B.; Macleish, K. G. & Frey, H. B.
Partner: UNT Libraries Government Documents Department

AC-DC Difference Calibrations

Description: Abstract: This publication collects and summarizes the specialized information needed to operate the ac-dc difference laboratory and calibration service at NIST (Gaithersburg). It also serves as a convenient reference source for the users of this calibration service and other interested people by documenting the service and its underlying background in considerable detail. It contains the following: an annotated table of contents, a topical index, and a glossary of common ac-dc acronyms; an overview of the service; selected published papers; instructions for the operation of the comparator systems; a schedule for the recalibration and periodic checks of the NIST thermal converters; and a sample report of calibration.
Date: May 1989
Creator: Kinard, J. R.; Hastings, J. R.; Lipe, T. E. & Childers, C. B.
Partner: UNT Libraries Government Documents Department

Initial Peak Surge Current Detection Circuits

Description: Test requirements for several components specifies that surge currents be monitored to determine if the initial peak surge current exceeds a certain predetermined amplitude. This report describes and evaluates two circuits which were developed by Organization 2451 to meet this requirement in production testing.
Date: February 1961
Creator: Conrad, Milo M.
Partner: UNT Libraries Government Documents Department

Ramp-up of CHI Initiated Plasmas on NSTX

Description: Experiments on the National Spherical Torus (NSTX) have now demonstrated flux savings using transient coaxial helicity injection (CHI). In these discharges, the discharges initiated by CHI are ramped up with an inductive transformer and exhibit higher plasma current than discharges without the benefit of CHI initiation.
Date: October 29, 2009
Creator: Mueller, D; Bell, R E; LeBlanc, B; Roquemore, A L; Raman, R; Jarboe, T R et al.
Partner: UNT Libraries Government Documents Department

Local field and quantum effects for current perpendicular to planes in multilayers

Description: The calculation of giant-magnetoresistance and in general, of electron transport for multilayers in the case of current perpendicular to the planes (CPP) requires both the two-point conductivity and the solution to the local field problem. In this paper we present a solution to the local field problem at an interface using two approaches. In the first approach we find the semiclassical solution for the local field when there is a band mismatch between two sides of an interface, and examine the deviation of the total resistance from the result of ``self-averaging``, in the lowest order of the value of the potential step. In the second approach, we solve for the quantum correction to the local field through a numerical iterative scheme. The oscillations due to the quantum correction are surprisingly large, but their correction to the total resistance is remarkably small. Our results imply that the ``self-averaging`` of the resistance, which is usually assumed in analysis of CPP, is only approximate. 8 refs., 2 figs., 2 tabs.
Date: December 31, 1996
Creator: Zhang, X.G. & Butler, W.H.
Partner: UNT Libraries Government Documents Department

Logarithmic Electrometer

Description: This report describes the development and design details of an instrument that measures current in the range 10-6 to 10-13 a. and indicates or records this current on a single logarithmic scale. It is frequently desirable to measure a wide range of low current values without range switching. Since no instrument with such characteristics is commercially available, this study was made to determine whether or not the Beckman Model V Micromicroammeter could be modified to provide a logarithmic response. The feasibility of operating this instrument over six decades of input current has been demonstrated. As many as seven decades can be accommodated if a slight non-linearity in the lowest decade is tolerable. This non-linearity is insignificant in most applications. Fewer decades with increased readability and precision can also be obtained.
Date: April 19, 2001
Creator: Morris, J.M.
Partner: UNT Libraries Government Documents Department

Analysis of Alternating-Current Waves by the Method of Fourier, with Special Reference to Methods of Facilitating the Computations

Description: Report issued by the Bureau of Standards over analysis of alternating currents. These currents are applied with the Fourier method. Descriptions of the method, and the results are presented. This report includes tables, and illustrations.
Date: 1913
Creator: Grover, Frederick W.
Partner: UNT Libraries Government Documents Department

New transient surface-current sensor and recorder

Description: It was demonstrated that a transient surface-current pulse can be sensed and recorded by a graded-Hc film, a magnetic film with the coercive force Hc varying along the length of the film. Information on the magnitude of the current can be obtained by comparing the domain-wall location with the distribution of Hc value along the film. The transient characteristic of the current pulse can be deduced from the V-shaped configuration of the domain wall. (auth)
Date: October 19, 1973
Creator: Hsieh, E. J. & Vindelov, K. E.
Partner: UNT Libraries Government Documents Department


Description: Modern weld controllers typically use current to control the weld process. SRS uses a legacy voltage control method. This task was undertaken to determine if the improvements in the weld control equipment could be implemented to provide improvements to the process control. The constant current mode of operation will reduce weld variability by about a factor of 4. The constant voltage welds were slightly hotter than the constant current welds of the same nominal current. The control mode did not appear to adversely affect the weld quality, but appropriate current ranges need to be established and a qualification methodology for both welding and shunt calibrations needs to be developed and documented.
Date: October 11, 2005
Creator: Korinko, P; STANLEY, S & HOWARD, H
Partner: UNT Libraries Government Documents Department

Geometrical Properties of a "Snow-Flake" Divertor

Description: Using a simple set of poloidal field coils, one can reach the situation where the null of the poloidal magnetic field in the divertor region is of a second order, not of the first order as in the usual X-point divertor. Then, the separatrix in the vicinity of the null-point splits the poloidal plane not into four sectors, but into six sectors, making the whole structure looking like a snow-flake (whence a name, [1]). This arrangement allows one to spread the heat load over much broader area than in the case of a standard divertor. A disadvantage of this configuration is in that it is topologically unstable, and, with the current in the plasma varying with time, it would switch either to the standard X-point mode, or to the mode with two X-points close to each other. To avoid this problem, it is suggested to have a current in the divertor coils by roughly 5% higher than in an 'optimum' regime (the one where a snow-flake separatrix is formed). In this mode, the configuration becomes stable and can be controlled by varying the current in the divertor coils in concert with the plasma current; on the other hand, a strong flaring of the scrape-off layer still remains in force. Geometrical properties of this configurations are analyzed for a simple model. Potential advantages and disadvantages of this scheme are discussed.
Date: February 7, 2007
Creator: Ryutov, D D
Partner: UNT Libraries Government Documents Department


Description: A271 STATIONARY HIGH-PERFORMANCE DISCHARGES IN THE DII-D TOKAMAK. Discharges which can satisfy the high gain goals of burning plasma experiments have been demonstrated in the DIII-D tokamak under stationary conditions at relatively low plasma current (q{sub 95} > 4). A figure of merit for fusion gain ({beta}{sub N}H{sub 89}/q{sub 95}{sup 2}) has been maintained at values corresponding to ! = 10 operation in a burning plasma for > 6 s or 36{tau}{sub E} and 2{tau}{sub R}. The key element is the relaxation of the current profile to a stationary state with q{sub min} > 1. In the absence of sawteeth and fishbones, stable operation has been achieved up to the estimated no-wall {beta} limit. Feedback control of the energy content and particle inventory allow reproducible, stationary operation. The particle inventory is controlled by gas fueling and active pumping; the wall plays only a small role in the particle balance. The reduced current lessens significantly the potential for structural damage in the event of a major disruption. In addition, the pulse length capability is greatly increased, which is essential for a technology testing phase of a burning plasma experiment where fluence (duty cycle) is important.
Date: November 1, 2002
Partner: UNT Libraries Government Documents Department

Voltage-probe-position dependence and magnetic-flux contribution to the measured voltage in ac transport measurements: which measuring circuit determines the real losses?

Description: The voltage V{sub ab} measured between two voltage taps a and b during magnetic flux transport in a type-II superconductor carrying current I is the sum of two contributions, the line integral from a to b of the electric field along an arbitrary path C{sub s} through the superconductor and a term proportional to the time rate of change of magnetic flux through the area bounded by the path C{sub s} and the measuring circuit leads. When the current I(t) is oscillating with time t, the apparent ac loss (the time average of the product IV{sub ab}) depends upon the measuring circuit used. Only when the measuring-circuit leads are brought out far from the surface does the apparent power dissipation approach the real (or true) ac loss associated with the length of sample probed. Calculations showing comparisons between the apparent and real ac losses in a flat strip of rectangular cross section will be presented, showing the behavior as a function of the measuring-circuit dimensions. Corresponding calculations also are presented for a sample of elliptical cross section.
Date: December 31, 1995
Creator: Pe, T.; McDonald, J. & Clem, J.R.
Partner: UNT Libraries Government Documents Department

Hybrid modeling of the formation and structure of thin current sheets in the magnetotail

Description: Hybrid simulations are used to investigate the formation of a thin current sheet inside the plasma sheet of a magnetotail-like configuration. The initial equilibrium is subjected to a driving electric field qualitatively similar to what would be expected from solar wind driving. As a result, we find the formation of a raw current sheet, with a thickness of approximately the ion inertial length. The current density inside the current sheet region is supplied largely by the electrons. Ion acceleration in the cross-tail direction is absent due since the driving electric field fails to penetrate into the equatorial region.
Date: July 1, 1996
Creator: Hesse, M.; Winske, D. & Birn, J.
Partner: UNT Libraries Government Documents Department

Distributed monitoring system for electric-motor-driven compressors

Description: Personnel in the Instrumentation and Controls Division at the Oak Ridge National Laboratory, in association with the United States Enrichment corporation (USEC), the Navy, and various Department of Energy sponsors, have been involved in the development and application of motor-current signature analysis (CSA) for several years. In that time CSA has proven to not only be useful for manually applied periodic monitoring of electrically driven equipment but it has also been demonstrated to be well suited for dedicated monitoring systems in industrial settings. Recent work has resulted in the development and installation of a system that can monitor up to 640 motor and compressor stages for various aerodynamic conditions in the gas compressors and electrical problems in the drive motors. This report describes a demonstration of that technology installed on 80 stages at each of the two USEC uranium enrichment plants.
Date: January 1, 1996
Creator: Castleberry, K.N.
Partner: UNT Libraries Government Documents Department

Anomalous loss of DT alpha particles in the Tokamak Fusion Test Reactor

Description: An escaping alpha collector probe has been developed for TFTR`s DT phase. Energy distributions of escaping alphas have been determined by measuring the range of {alpha}-particles implanted into nickel foils located within the alpha collector. Results at 1.0 MA of plasma current are in good agreement with predictions for first orbit alpha loss. Results at 1.8 MA, however, show a significant anomalous loss of partially thermalized alphas (in addition to the expected first orbit loss), which is not observed with the lost alpha scintillator detectors in DT plasmas, but does resemble the anomalous delayed loss seen in DD plasmas. None of the candidate explanations proposed thus far are fully consistent with the anomalous loss observations. An experiment designed to study the effect of plasma major radius shifts on {alpha}-particle loss has led to a better understanding of {alpha}-particle dynamics in tokamaks. Intuitively, one might suppose that confined marginally passing {alpha}-particles forced to move toward higher magnetic field during an inward major radius shift (i.e., compression) would mirror and become trapped particles, leading to increased alpha loss. Such an effect was looked for during the shift experiment, however, no significant changes in alpha loss to the 90{degree} lost alpha scintillator detector were observed during the shifts. It is calculated that the energy gained by an {alpha}-particle during the inward shift is sufficient to explain this result. However, an unexpected loss of partially thermalized {alpha}-particles near the passing/trapped boundary was observed to occur between inward and outward shifts at an intermediate value of plasma current (1.4 MA). This anomalous loss feature is not yet understood.
Date: September 1, 1997
Creator: Herrmann, H.W.
Partner: UNT Libraries Government Documents Department

Scientific basis and engineering design to accommodate disruption and halo current loads for the DIII-D tokamak

Description: Plasma disruptions and halo current events apply sudden impulsive forces to the interior structures and vacuum vessel walls of tokamaks. These forces arise when induced toroidal currents and attached poloidal halo currents in plasma facing components interact with the poloidal and toroidal magnetic fields respectively. Increasing understanding of plasma disruptions and halo current events has been developed from experiments on DIII-D and other machines. Although the understanding has improved, these events must be planned for in system design because there is no assurance that these events can be eliminated in the operation of tokamaks. Increased understanding has allowed an improved focus of engineering designs.
Date: October 1996
Creator: Anderson, P. M.; Bozek, A. S.; Hollerbach, M. A.; Humphreys, D. A.; Luxon, J. L.; Reis, E. E. et al.
Partner: UNT Libraries Government Documents Department