Passive Conductors Research Articles

Submicron electrical current density imaging of embedded microstructures

We have developed a scanning magnetic microscopy technique for noninvasively imaging submicron magnetic fields from embedded microscopic electrical circuits. We are able to extract from the field data a complete profile of current densities using a mathematical algorithm. As an example, we provide current density images of micron-scale passivated conductors undergoing electromigration.

Combined thermionic-thermoelectric refrigerator

A combined thermionic-thermoelectric refrigerator is proposed. The passive metal conductor in a vacuum thermionic refrigerator is replaced by an active p-type thermoelectric element, so that the Peltier cooling power can be exploited. Complete analytic formulas of performances are derived for the two types of thermionic refrigerators at both maximum cooling power density and optimum coefficient of performance. In employing the ideal material properties as Nolas and Goldsmid have done [J. Appl. Phys. 85, 4066 (1999)], we have proved quantitatively the combined thermionic-thermoelectric refrigerator to be more effective and efficient than a thermionic or thermoelectric device.

Requirements for power line magnetic field mitigation using a passive loop conductor

Magnetic field mitigation for overhead power lines using a passive loop conductor was studied. The aim of this study is to clarify the requirements for effective mitigation not in a specific region such as at the edge of the ROW (right of way) but everywhere around the conductors. For this purpose, the concept of current dipole moment was introduced and applied to the problem. First to determine the validity of the derived formula which estimates the induced current to the passive loop, a miniature transmission line model experiment was performed. Then, the mitigation effectiveness of the actual dimensions of several kinds of overhead transmission line arrangements were estimated by the calculation. The application of a current dipole moment, was sufficient for explaining the differences in the mitigation effectiveness depending on the conductor arrangement and for clarifying the requirements for effective mitigation.

A comparison of projected thermoelectric and thermionic refrigerators

Expressions for the coefficient of performance and the cooling power of a thermionic refrigerator are derived taking into account the losses associated with thermal radiation and the need for a so-called passive conductor in the electrical circuit. Specific calculations are made for a thermionic device with a work function of 0.3 eV and it is shown that the performance is generally superior to that of a thermoelectric refrigerator made from materials with a dimensionless figure of merit ZT equal to 4.

A model for the dynamic magnetic field identification at the first wall of the RFX machine in presence of passive conductors

A method for the computation of the induction field in presence of open and closed passive conductors has been developed. It solves uniquely the inverse problem to determine the eddy currents needed in the passive conductors to produce a given flux. The method has been applied to the case of the RFX experimental machine to the induction field inside the vacuum vessel.

Improved control signal distribution for very wide VLSI data buses

A new technique for distributing electronic signals by way of a conducting path across large spatial distances with minimal temporal dispersion is presented. It provides for the delivery of a common signal to any number of different receivers located along the signal path, with near zero skew and little degradation of the signal's rise/fall transition times. The method involves the placement of an active routing structure in parallel with, and appropriately strapped to, a conventional passive conductor. The concept is demonstrated in the paper, within the context of VLSI design, by a solution to the problem of distributing an on-chip control signal to the many lines of a physically very wide data bus.

Separate effects tests for gothic condensation and evaporative heat transfer models

The gothic computer program, under development at NAI for EPRI, is a general purpose thermal hydraulics computer program for design, licensing, safety and operating analysis of nuclear containments and other confinement buildings. The code solves a nine-equation model for three-dimensional multiphase flow with separate mass, momentum and energy equations for vapor, liquid and drop phases. The vapor phase can be a gas mixture of steam and non-condensing gases. The phase balance equations are coupled by mechanistic and empirical models for interface mass, energy and momentum transfer that cover the entire flow regime from bubbly flow to film-drop flow. A variety of heat transfer correlations are available to model the fluid coupling to active and passive solid conductors. This paper focuses on the application of gothic to two separate effects tests: condensation heat transfer on a vertical flat plate with varying bulk velocity, steam concentration and temperature, and evaporative heat transfer from a hot pool to a dry (superheated) atmosphere. Comparisons with experimental data are included for both tests. Results show the validity of two condensation heat transfer correlations as incorporated into GOTHIC and the interfacial heat and mass transfer models for the range of the experimental test conditions. Comparisons are also made for lumped vs. multidimensional modeling for buoyancy-controlled flow with evaporative heat transfer.

E-beam probe station with integrated tool for electron beam induced etching

A novel technique for electron-beam induced etching has been integrated into an e-beam probe station. Measurement windows are etched into insulation layers on IC's enabling direct e-beam probing on buried or passivated conductors of integrated circuits. Sample preparation by focused-ion-beam or chemical removal of passivation layers are no longer necessary. Measurement windows of 2μm × 2μm are etched into 1 μm passivation in less than one minute. The etch rate thus is approximately 5 μm 3/min. Etching of insulator material such as SiO 2, Si 3N 4 and polyimide has been demonstrated. Voltage signals can thus be accurately probed, e.g. through an etched window of 3μm × 3 μm diameter and 2.5 μm depth on a buried line of 2μm width. The novel etch tool is a part of the regular e-beam probing procedure. E-beam probing thus remains a versatile technique, especially for the analysis of high density and high frequency circuits.

Axisymmetric Magnetic Control Design in Tokamaks Using Perturbed Equilibrium Plasma Response Modeling

A model of linearized tokamak plasma response to variations in external toroidal currents is developed for purposes of axisymmetric control analysis. The plasma model is based on free-boundary equilibria with perturbations in the poloidal field coils. Plasma response to currents in arbitrary passive conductors such as the vacuum vessel is approximated by mapping their effect to equivalent poloidal field coil currents. Ideal magnetohydrodynamic flux conservation is satisfied approximately by allowing total plasma current and current-density profile to vary. The resulting flux-conserving plasma response model including vacuum vessel effects is used along with multivariable control system techniques to design high-performance axisymmetric control systems for the Alcator C-Mod tokamak to stabilize the vertical instability and to provide stable shape control.

Calculations of Axisymmetric Stability of Tokamak Plasmas with Active and Passive Feedback

A new linear MHD stability code, NOVA-W, has been developed in order to study feedback stabilization of the axisymmetric mode in deformable tokamak plasmas. The NOVA-W code is a modification of the non-variational MHD stability code NOVA that includes the effects of resistive passive conductors and active feedback circuits. The vacuum calculation has been reformulated in terms of the perturbed poloidal flux to allow the inclusion of perturbed toroidal currents outside the plasma. The boundary condition at the plasma-vacuum interface relates the instability displacement to the perturbed poloidal flux. This allows a solution of the linear MHD stability equations with the feedback effects included. The passive stability predictions of the code have been tested both against a simplified analytic model and against a different numerical calculation for a realistic tokamak configuration. The comparisons demonstrate the accuracy of the NOVA-W results. Active feedback calculations are performed for the CIT tokamak design demonstrating the effect of varying the position of the flux loops that provide the measurements of vertical displacement. The results compare well with those computed earlier using a less efficient nonlinear code.

A Simple Model for Stress Voiding in Passivated Thin Film Conductors

A model is proposed for stress voiding in passivated thin film conductors. The rate limiting step is argued to be the formation of vacancies at dislocation jogs which then diffuse to void sites.

Effects of plasma deformability on the feedback stabilization of axisymmetric modes in tokamak plasmas

The effects of plasma deformability on the feedback stabilization of axisymmetric modes of tokamak plasmas are studied. It is seen that plasmas with strongly shaped cross-sections have unstable motion different from a rigid shift. Furthermore, the placement of passive conductors is shown to modify the nonrigid components of the eigenfunction in a way that reduces the stabilizing eddy currents in these conductors. Passive feedback results obtained using several equilibria of varying shape and aspect ratio are presented. The eigenfunction is also modified under the effects of active feedback. This deformation is seen to depend strongly on the position of the flux loops that are used to determine the plasma vertical position for the active feedback system. The variations of these nonrigid components of the eigenfunction always serve to reduce the stabilizing effect of the active feedback system by reducing the measurable poloidal flux at the flux loop locations. Active feedback results are presented for the PBX-M tokamak configuration

Stabilization of axisymmetric instability in a tokamak with a diverter

We consider the stabilization of vertical instability of a toroidal plasma pinch using passive ring conductors. The analysis is conducted by two techniques: by numerical solution of the system of linearized MHD equations and by applying the energy principle. We investigate the dependence of plasma stability on the location and the number of conductors and examine the effect produced by closing the conductors into sections. For an INTOR plasma pinch we show that a small number N ∼ 4 of properly placed conductors of reasonable size may suppress vertical instability.

Feedback stabilization of the axisymmetric instability of a deformable tokamak plasma

The paper presents an analysis of the magnetohydrodynamic stability of the axisymmetric system consisting of a free boundary tokamak plasma with non-circular cross-section, finite resistivity passive conductors, and an active feedback system with magnetic flux pickup loops, a proportional amplifier with gain G and current carrying poloidal field coils. A numerical simulation of the system when G is set to zero identifies flux loop locations which correctly sense the plasma motion. However, when certain of these locations are incorporated into an active feedback scheme, the plasma fails to be stabilized, no matter what value of the gain is chosen. Analysis on the basis of an extended energy principle indicates that this failure is due to the deformability of the plasma cross-section.

30] Proton conduction through proteins: An overview of theoretical principles and applications

Publisher Summary This chapter provides an overview of theoretical principles and applications of proton conduction through proteins. The proton currents in biological systems involve only a small percentage of the atoms composing the system and the bonds in the proton conductors are constantly being broken by the reorientation of the conducting groups. These two aspects of the biological proton transport make its detection exceedingly difficult. Two studied proton transport systems are the membrane protein bacteriorhodopsin, which functions as a light-driven proton pump in Halobacterium halobium, and the proteolipid of ATPase, which functions as a passive proton conductor. The constituents of a biological proton conductor are most likely the molecules of bound water or the polar amino acid side groups of the protein. The molecular dynamics calculations on the ion channel in gramicidin indicate that a linear water channel may be the conducting pathway in ion channels as well. The observables that are suitable to elucidate the structure and function of biological proton conductors are summarized in the chapter.

The ASDEX Upgrade toroidal field magnet and poloidal divertor field coil system adapted to reactor requirements

ASDEX Upgrade is a tokamak experiment with external poloidal field coils that is now under construction at IPP Garching. It can produce elongated single-null (SN), double-null (DN), and limiter (L) configurations. The SN is the reference configuration with asymmetric load distributions in the poloidal field (PF) system and the toroidal field (TF) magnet. Plasma control and stabilization require a rigid passive conductor close to the plasma. The design principles of the coils and support structure are described.

Tilt stability of rotating current rings with resistive conductors

The combined effects of rotation and resistive passive conductors on the stability of a rigid current ring in an external magnetic field are studied. Numerical and approximate analytical solutions to the equations of motion are presented, which show that the ring is always tilt unstable on the resistive decay time scale of the conductors, although rotation and eddy currents may stabilize it over short times. Possible applications of our model include spheromaks which rotate or are encircled by energetic particle rings.

Passive Control of the Vertical Instability in Intor

In the international tokamak reactor (INTOR), the problem of the passive control of the vertical instability is to be solved by means of suitably shaped saddle coils to be embedded in the blanket structure. The efficiency of such a system depends on the characteristics of the passive conductors and on the plasma equilibrium as well as on the type of plasma displacement assumed. To cover the physical uncertainties caused by the model assumptions for the plasma with respect to the motion on a slow time scale (of the order of several tens of milliseconds) corresponding to efficient passive stabilization, four different plasma displacement models are considered and compared with each other. A stability analysis is performed using the energy principle, expressed in circuital form. The results of the INTOR analysis are presented and discussed showing in particular that under very general conditions the optimum stabilization efficiency is obtained for passive conductors situated at about 60 deg above and below the horizontal midplane at the outboard side. The effect of the geometric parameters of the saddle coils (e.g., area and shape of the cross section, toroidal segmentation, etc.) on the stabilization efficiency is investigated; a parametric study of these dependences ismore » presented. General conclusions applicable to INTOR are drawn.« less

The asdex upgrade toroidal field magnet and poloidal divertor field coil system adapted to reactor requirements

ASDEX Upgrade is a tokamak experiment with external poloidal field coils that is now under construction at IPP Garching. It can produce elongated single-null (SN), double-null (DN), and limiter (L) configurations. The SN is the reference configuration with asymmetric load distributions in the poloidal field (PF) system and the toroidal field (TF) magnet. Plasma control and stabilization require a rigid passive conductor close to the plasma. The design principles of the coils and support structure are described.

Numerical Simulation of the Plasma Current Quench Following a Disruptive Energy Loss

The plasma/electromagnetic interaction with poloidal field coils and nearby passive conductor loops during the current quench following a disruptive loss of plasma energy is simulated. By solving a differential/algebraic system consisting of a set of circuit equations (including the plasma circuit) coupled to a plasma energy balance equation and an equilibrium condition, the electromagnetic consequences of an abrupt thermal quench are observed. Limiters on the small and large major radius sides of the plasma are assumed to define the plasma cross section. The presence of good conductors near the plasma and a small initial distance (i.e., 5 to 10% of the plasma minor radius) between the plasma edge and an inboard limiter are shown to lead to long current decay times. For a plasma with an initial major radius R0 = 4.3 m, aspect ratio A = 3.6, and current Ip = 4.0 MA, introducing nearby passive conductors lengthens the current decay from milliseconds to hundreds of milliseconds.