Coaxial Conductor Research Articles

Slotted and Loose Braid Cables Brief Conclusions of a Comparative Study

An analytical comparison is made of the electromagnetic characteristics of the coaxial mode of longitudinally slotted coaxial cables and loose braid coaxial cables in free space. Four aspects are considered: radial decay of the fields, percentage of power that travels outside the coaxial structure, characteristic impedance, and conductor loss.

Stimulated Raman scattering by an intense relativistic electron beam in a long rippled magnetic field

For the first time, the parametric coupling of the negative-energy cyclotron and space-charge modes to a fast coaxial waveguide structure is observed. The coaxial waveguide smooth center conductor is internally loaded to maintain a 5% ripple of 1.4-, 1.6-, or 2.0-cm periods on the background axial magnetic field throughout the interaction region of 70 cm. The parametric coupling may be considered a stimulated scattering process with the rippled magnetic field of zero frequency in the lab frame appearing as an electromagnetic pump wave in the beam frame, with 30-MW/${\mathrm{cm}}^{2}$ power density imparting to the electrons a quiver velocity ${V}_{\mathrm{os}}\ensuremath{\simeq}0.1c$. As predicted by theory, the frequency of the microwave radiation generated by the negative-energy cyclotron mode decreases with increasing magnetic field while remaining constant for the negative-energy space-charge mode. Power levels from 1 to 5 MW have been measured at mm and cm wavelengths. Radiation at frequencies of $\frac{2{\ensuremath{\gamma}}^{2}V}{L}$, where $V$ and $L$ are the beam velocity and ripple period, respectively, has been observed at high magnetic fields with an exponential-growth rate consistent with parametric coupling theory. This mechanism could be employed as a tunable generator of millimeter and submillimeter wavelength radiation.

Lightning protection — A proven system

A unique integrated lightning protection system is described, which uses an electrode assembly enhanced by electron sources. The electrode is coupled to a high voltage coaxial grounding conductor to offer hitherto unattainable performance.

Misalignment of Coaxial Conductors

Compressed gas insulated coaxial transmission lines are being developed which withstand 1200-kV rms phase-to-phase voltage and carry 3000 A continuous current. As a method of instrumenting the voltage on a single-phase of coaxial line, an isolated capacitive section approximately one meter in length is inserted between the conductors. The resulting displacement current due to line voltage is detected with low voltage electronics. In the present work, misalignment of the coaxial conductors is investigated theoretically and experimentally to determine the effect of small relative displacements on the amount of capacitance of the isolated section. Capacitance change due only to conductor misalignment is found not to restrict severely the metering accuracy of the isolated section, provided reasonable tolerances for the position of the isolated section are maintained. Forces due to imbalance of surface charge when the conductors are slightly misaligned are calculated and shown to be small, suggesting that a "voltage coefficient" of capacitance also should not severely restrict the metering accuracy of the isolated section.

Limiting currents in the compression of magnetic flux between flat and coaxial conductors

Experiments are described on magnetic flux compression by flat and coaxial conductors. As the initial current I0 is increased the final current I1 obtained as a result of flux compression at first increases proportionally to I0 and then reaches a maximum and remains constant for further increases in I0. Analysis of the experiments shows that in coaxial structures when a small explosive charge accelerates the conductors the limiting current is determined by the maximum work which a conductor can perform in compressing the magnetic field. In experiments with flat busbars and large explosive charges the limiting currents appear to be determined by the flux losses in short-circuited voids formed in the linking of irregular surfaces of the busbars. This assumption is shown to be in qualitative agreement with experiment.

A Coaxial Interconnection System for High Speed Digital Processors

The cost of interconnecting integrated circuits in large arrays has always been a considerable factor in establishing the operating cost effectiveness of high speed digital processors. Now, with the introduction and increasing use of ICs operating at subnanosecond speeds, interconnection systems have become even more of an economic factor because of the electrical limitations they can impose on the maximum speeds at which information can be processed. The electrical effects exerting the greatest influence are propagation velocities, internal crosstalk, sensitivity to RFI and the need for impedance matching between devices. While there are additional mechanical problems in miniaturization, heat dissipation and production costs, the electrical problems have provicled a sufficient incentive to undertake the development of a more compatible interconnecting system. The resulting new system is a discretionary wired, fully shielded and coaxial interconnection system. It has been primarily designed for use with logic elements having pulse rise times in the subnanosecond range, and in its present form is capable of handling pulse rise times of less than 100 picoseconds. A typical system employs conductors with a characteristic impedance of 50 ohms and is capable of .050 center connections. The primary interconnections are made with .010 O.D. 50 ohm TFE insulated coaxial conductors that are formed in-situ by the manufacturing process. The system is fully compatible with printed circuit techniques and additional non-critical circuitry may be added to the system by these means. The system can also be made compatible with multilayer technology, and Hybrid systems may be produced. Although the system has many unique features, it is constructed with state-of-the-art materials and processes. It is capable of manufacture, in-process and final inspection by numerically controlled automatic machines. In the basic systern all interconnections are made by a mass process on an exposed surface of the assembly. Since these connections are exposed, changes, while they must be made manual y, can be accommodated. The reliability of the system has not been estab ished but its simplicity, coupled with the fact that it generated no more connections than those of the original circuit diagrams, leads us to believe that it will be very good. It has been established that this new interconnection system can provide predefined and easily controlled characteristics of impedance, minimum attenuation and delay with the precision necessary for constructing high speed processors. In SO doing it can either eliminate or substantially reduce other problems of an electrical nature and offers a maximum of design flexibility with a minimum of engineering and its accompanying costs.

A High Accuracy Self-Calibrating Bridge with Coupled Inductive Ratio Arms Used for Standard Inductors Comparison

A bridge with inductively coupled ratio arms based on a seven decade inductive voltage divider is described. It is used for mutual comparisons between the standard inductors which form the IEN reference bank of inductance. Provided some auxiliary balances are made, this bridge is able to measure its own residual inductances, both the inductances of the standard-to-bridge connections (about 2 ?H), made constant by the rigidity of the system geometry within a few nanohenries, and those of the variable resistance elements, also known within a few nanohenries. The self-calibrations are sufficiently accurate because the bridge has a high sensitivity even in comparisons of 1-?H inductors and in the use of ratios up to 1:100. Three variable resistance components are used to balance the bridge: a commercial box of 1-? steps, with calibrated inductance increments; a two-material helicoidal-motion wire resistor (0 to 1 ?), suitably designed with inductance variations less than ±1 nH; and a constant-geometry three-decade Kelvin-Varley divider, also designed for this specific purpose, with its total and partial inductance measured, and its total inductance kept constant within 1 nH. Where possible, connections between bridge components are realized by rigid tetra-axial conductors (4 coaxial tubular conductors). To avoid inductive coupling between the standards and the third tubular conductor, it is made of coated wires aligned along the generatrices of a cylinder. Provided the phase errors of the inductive voltage divider are known only within 1 ?rad, the bridge has an estimated ratio accuracy of ±[2.

50 Hz loss measurements on superconducting niobium coaxial conductors

A method is described for the measurement of ac losses in a cylindrical conductor forming part of a coaxial superconducting pair. Results given for 25 μm niobium are substantially lower than previous values obtained for this material when tested in the form of narrow strips, and show that, if used as the conductor in a superconducting power cable, the material could carry a peripheral current density of 360 A cm −1 with tolerable losses (< 10 μW cm −2) at temperatures of up to 7 K.

Self Fields and Particle Oscillation Frequencies in a Rotating Electron Sheet Beam Loaded with Positive Ions

An approximate analytical treatment is presented for the electric and magnetic self fields of a long rotating sheet beam between coaxial conductors. By suitable choice of the conductor radii and/or by apply ing a voltage between the conductors it is possible to shift the potential minimum to the major radius of the beam; the condition for this is derived. Expressions for the equilibrium fields and gradients and for the particle oscillation frequencies in various geometries are presented.

Chebȳshev quarter-wave stepped balun transformer

The design of a balun transformer from coaxial to open-wire line is presented, in which conventional quarter-wave-matching theory is used to produce a compact device with optimal Cheby̅shev performance over its passband. Included in the design are the evaluation and corrections for the junction capacitances caused by stepping the outer coaxial conductor.

Ferrite-Loaded Helical Line with Coaxial Inner Conductor (Correspondence)

A transcendental characteristic equation of a thin-wire cylindrical helix with coaxial inner conductor uniformly filled with circumferentially magnetized gyromagnetic medium is derived in terms of modified Bessel functions and confluent hypergeometric functions. Two special cases of the structure are considered.

The Pulsitron a Compact, High-Current Electron Beam Accelerator

A coaxial high current electron beam accelerator design is discussed. A novel feature of this design is that approximately one-half of the required energy is initially stored capacitively in a volume inside the beam. The cylindrical beam is accelerated with a Marx-like circuit. After acceleration, the beam is focused between coaxial biconic conductors to a small cross section. The design incorporates features which have been discussed by others. A specific accelerator module design storing 70 kilojoules and capable of producing beam currents greater than a million amperes at 1 million volts is described. The principal advantage of this design is that its compact size will make possible multi-module machines which will have an output far exceeding anything thought practical today.

Special Diagnostic Devices

In contrast to plasma diagnostic probes having linear motion only, recent years have seen an increase in the number of special diagnostic devices having multiple degrees of freedom. In addition, the single custom-built probe tip has gradually yielded to the concept of mounting several pre-set probe tips on plug-in type probe holders. Several of the special diagnostic devices, designed to solve particular positioning and measurement problems, are described and illustrated. In particular, the problems associated with achieving the various mechanical movements within a vacuum, and the methods employed in controlling the coaxial conductors from the probe tip to the vacuum feedthrough are discussed.

A high-speed, opening-closing plankton sampler (Catcher II) and its electrical accessories

The Catcher II described is a high-speed plankton sampler, of moderate size, fitted with an opening-closing gate valve operable either electrically by means of an underwater solenoid, or by two messengers and a two-pin release mechanism. Associated electronic telemetry equipment includes underwater sensors for depth, flow and temperature, data from which are transmitted by frequency multiplex via an armoured towing cable containing a single, coaxial conductor. Signals, displayed on deck, include a trace of the sampler's depth on echo-sounder records. The gear is easy and rapid to operate.

Paper 2: Glandless Pump–Motor Units for Feed Heating Plant in Central Power Stations

This paper outlines the need for glandless pump–motor units in modern feed heating plant. It describes the design, construction, and testing of a prototype glandless centrifugal pump with integral squirrel cage motor. The composite unit is for deaerator lift duty in the feed heating system of a 500-MW generating set. The principal hydraulic features, mechanical construction, motor cooling and bearing lubrication system, and stator and rotor construction are outlined. An account is given of the glands used to bring the electrical connections through the pressure casing wall and of the special terminal arrangement. Works and site testing are described and the results discussed. Preparations for transport and precautions required during storage and installation at site to minimize corrosion are considered. Machines developed from the prototype are described, with particular reference to the use of coaxial stator conductors, combined pressure casing/stator frame construction, improved water lubrication system, resiliently mounted thrust bearing, suction stage axial inducer, and axial entry diffuser.

An Experimental 224 Mb/s Digital Repeatered Line

An experimental digital repeatered line has been developed which transmits information at a rate of 224 Mb/s as part of an experimental highspeed digital transmission system. The PCM terminals and time division multiplex portions were described by J. S. Mayo and others in the November 1965 issue of the Bell System Technical Journal. The repeatered line is described in this paper. The performance of this line is shown to be suitable for coast-to-coast operation. The line utilizes 0.270-inch copper coaxial transmission lines and regenerative repeaters at one-mile intervals. Ten repeaters have been operated in tandem to form ten miles of repeatered line. Each repeater uses 25 transistors, most of them a new germanium design with a cutoff frequency, f <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i</inf> , of 4 GHz. Esaki diodes provide the decision thresholds for the regeneration. Power to the repeaters is supplied by dc over the center coaxial conductor. The pulse transmission code is paired selected ternary (PST).

A Synchronization Pulse for the Princeton-Pennsylvania Accelerator

The basic synchronizing pulse in the P.P.A., tying the injection pulse and the R. F. to the magnetic field, is derived from the total current flowing through one of the Accelerator magnets. This pulse is generated in a biased toroidal coil wound on a supermalloy core, by the magnetic field H(t) created by the magnet current in a coaxial conductor. This method has provided us with a synchronization signal pulse with excellent long term stability and very little time-jitter. Part of the time-jitter may be attributed to the variations of dH/dt at the time of the reversal of the magnetization of the core due to variations of Imin in the magnets. A method has been developed to effectively cancel out the dH/dt effect in the supermalloy core.

Induced Electric Fields in Coaxial Geometry

Although electromagnetic theory has been known for a century, and Biot's (also called Ampere's) formula in its simple form, dH = (1/4π)(Idl sinθ/r2), is often used, the corresponding relationship, dE = −(1/4π) (φdl sinθ/r2), for the electric field induced in space by a filament of time-varying magnetic flux, seems not to have been recognized or used to any great extent. The discussion here presented, using the example afforded by coaxial conductors, illustrates some aspects of how this latter relationship may be used to solve for induced electric fields, including those for coaxial systems of both finite and infinite length with hollow or solid center conductors. The magnetically induced electric field fringes outward near the shorted end of a coaxial system, and a method is shown for finding the radial positions of a given line of electric force when coaxial conductors of different dimensions are connected together.

Theory of Simulated-Skin-Effect Filters a Thin Film Approach to EMI

The theory of a new, ceramic lowpass filter, highly effective at very high frequencies, is discussed. Its excellent performance is based on simulation of the skin effect whereby the VHF, UHF and microwave currents are forced along a thin, electrically permeable resistive film deposited inside a high-? dielectric tube while a large dc current may flow through the coaxial conductor. Theory and experiment are in excellent agreement. In several respects these filters are better than cascaded filters (ferrites and dielectrics combined) which were, thus far, considered the best available. The simulated-skin-effect filter shows great promise of becoming a significant means in combatting conducted electromagnetic interference.

Leakage of Electromagnetic Interference along Stationary Conductors Passing through Conducting Walls

A mechanism by which electromagnetic energy at quasistatic frequencies may leak out of seemingly shielded compartments via conductors such as external shields of cables, pipes, shafts, bolts, etc., protruding from the interior of the compartment is investigated both theoretically and experimentally. The mechanism involved may be illustrated by considering a conductor, such as a shaft passing through a hole in a conducting wall, and contacting the wall at a finite number of contact regions. These regions represent a short circuit to the TEM mode, however higher modes may pass along the guide whose walls may be represented by the actual regions of contact and the inner and outer coaxial conductors. Attenuated transmission may thus occur at frequencies below the cutoff frequency of the higher modes. As verification of the above hypothesis an impedance relationship, representing the shunt impedance that the contact regions offer at below cutoff frequencies (in particular f = 15 kc), was developed and checked experimentally for continuous pressure and soldered contacts. The experimental data show relatively close comparison with the theoretical model.