Coaxial Power Research Articles

Developments in coaxial power standards at NPL

A 2.4 mm twin line coaxial calorimeter is the first microwave power standard in this line size to be developed at the National Physical Laboratory (NPL). The design is based on a twin line coaxial calorimeter where RF power dissipated in one load is measured in terms of a DC power dissipated in a similar load with its effective efficiency derived from a thermal and electrical analysis of the twin lines. The calorimeter will provide traceable power measurements from DC to 50 GHz between power levels of 0.1 and 10 mW with an uncertainty ranging from 0.5% at 10 MHz to 2.3% at 50 GHz at the 1 standard deviation level.

3.5 mm coaxial power standard

A 3.5 mm twin line coaxial calorimeter is the first microwave power calorimeter in this line size to be constructed at the National Physical Laboratory. The instrument consists of two terminated coaxial lines with a length of high thermal resistance line between an APC-3.5 mm input connector and a tractorial load. The principle of operation is to measure RF power dissipated in one of the loads in terms of DC power dissipated in the other load. A temperature change due to the dissipation of power is detected by platinum resistance thermometers (PRTs) fixed on the coaxial line in the region of the load. Two PRT sensors connected in series on both sides of each coaxial line are incorporated in an AC bridge and detection circuit. Initially the output from the detection circuit is zero but once power is applied to the RF line the bridge goes out of balance. This signal is then used to control a feedback voltage to the DC line until the bridge output is returned to zero. The final DC feedback voltage that balances the bridge is then used to determine the RF power to the calorimeter. The instrument operates over the frequency range DC to 26.5 GHz at power levels 0.1–10 mW. The calculated effective efficiency for the calorimeter ranges from 102.4% at 0.1 GHz to 99.3% at 26.5 GHz. The VSWR of the RF line ranges from 1.006 at 1 GHz to 1.06 at 26.5 GHz with a maximum of 1.12 at 25.1 GHz.

A compact, high-power, low-loss,L-band coaxial 18-way power divider/combiner

A compact, high-power, low-loss,L-band coaxial 18-way power divider/combiner

Determination of mismatch factor with RF power calibration using air-line impedance standards

A method to calibrate a coaxial rf power meter by comparison with a standard power meter is described, the ratio of the mismatch factors being determined using two calculable coaxial air-line impedance standards. An initial investigation of the uncertainty of calibration has been made, and initial experimental results of measurements performed with the 7 mm coaxial system and for type N connectors at frequencies from 2 GHz to 18 GHz are presented.

International comparison GT-RF 75 A 11: RF power at 12 GHz, 14 GHz and 17 GHz in 50 Ω coaxial line

This paper deals with the results of an international comparison measurement of the effective efficiency E of commercial 50 /spl Omega//7 mm coaxial thermistor RF power standards fitted with PC-7 precision connectors. The measurement frequencies were 12 GHz, 14 GHz and 17 GHz. The national laboratories of metrology of eight countries (Australia, Canada, France, Hungary, Italy, the Netherlands, USA and Germany) participated in this comparison which was organized by the Radio Frequency Working Group of the Comite Consultatif d'Electricite (CCE). The Physikalisch-Technische Bundesanstalt (PTB, Germany) acted as the pilot laboratory. The standards showed only a small linear negative drift in E, as found by linear regression analysis. For most of the mean values of E reported by the laboratories, the deviations from the regression values were small (not larger than 0.004); only in two cases were the deviations 0.006 and 0.0085.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Design and Development of Coaxial Microcalorimetric Power Standard in the 10 MHz—18 GHz Frequency Range

Coaxial microcalorimetric power standard has been designed and developed to determine effective efficiency of the coaxial bolometer mounts in the frequency range of 10 MHz to 18 GHz with highest ac...

Intense light ion beam divergence in single- and two-stage diodes

Two types of beam-extraction intense light ion diodes are investigated. One is a single-stage applied-B ion diode installed on a simple coaxial pulsed power machine. Beam flux and beam divergence angle are measured simultaneously with spatial resolution using an arrayed ion pinhole camera (APC). Measured data show some relation between the distribution of beam divergence and beam flux. This result implies the importance of this type of diagnostics for studying the light ion diode. Experiments with another type of diode, a two-stage ion diode, are performed on an induction adder accelerator. In this diode, the output beam of the first stage is injected into the second-stage diode. The operation of the second diode is controlled by the injected beam. Shadow-box measurements on the two-stage diode indicate an improvement of beam divergence (half width full maximum) from 52+or-18 mrad to 27+or-6 mrad due to acceleration at the second diode. This improvement of beam divergence is in agreement with a calculated value using voltages of the first and the second stage diode. >

Rapid and uniform electromagnetic heating of aqueous cryoprotectant solutions from cryogenic temperatures

Devitrification (ice formation during warming) is one of the primary obstacles to successful organ vitrification (solidification without ice formation). The only feasible approach to overcoming either devitrification or its damaging effects in a large organ appears at present to be the use of some form of electromagnetic heating (EH) to achieve the required high heating rates. One complication of EH in this application is the need for warming within a steel pressure vessel. We have previously reported that resonant radiofrequency (RF) helical coils provide very uniform heating at ambient temperatures and low heating rates and can be modified for coaxial power transmission, which is necessary if only one cable is to penetrate through the wall of the pressure vessel. We now report our initial studies using a modified helical coil, high RF input power, and cryogenic aqueous cryoprotectant solutions [60% ( w v ) solution of 4.37 M dimethylsulfoxide and 4.37 M acetamide in water and 50% ( w w ) 1,2-propanediol]. We also describe the electronic equipment required for this type of research. Temperatures were monitored during high-power conditions with Luxtron fiberoptic probes. Thermometry was complicated by the use of catheters needed for probe insertion and guidance. The highest heating rates we observed using catheters occurred at temperatures ranging from about −70 to −40 °C, the temperature zone where devitrification usually appears in unstable solutions during slow warming. We find that in this range we can achieve measured heating rates of approximately 300 °C/min in 30- to 130-ml samples using 200 to 700 W of RF power without overheating the sample at any point. However, energy conservation calculations imply that our measured peak heating rates may be considerably higher than the true heating rates occurring in the bulk of our solutions. We were able to estimate the overall true heating rates, obtaining an average value of about 20 °C/min/100 W 100 ml, which implies a heating efficiency close to 100%. It appears that it should be possible to warm vitrified rabbit kidneys rapidly enough under high-pressure conditions to protect them from devitrification.

Theory of magnetically insulated electron flows in coaxial pulsed power transmission lines

The Cartesian magnetically insulated transmission line (MITL) theory of Mendel et al. [Appl. Phys. 50, 3830 (1979); Phys. Fluids 26, 3628 (1983)] is extended to cylindrical coordinates. A set of equations that describe arbitrary electron flows in cylindrical coordinates is presented. These equations are used to derive a general theory for laminar magnetically insulated electron flows. The laminar theory allows one to specify the potentials, fields, and densities across a coaxial line undergoing explosive electron emission at the cathode. The theory is different from others available in cylindrical coordinates in that the canonical momentum and total energy for each electron may be nonzero across the electron sheath. A nonzero canonical momentum and total energy for the electrons in the sheath allows the model to produce one-dimensional flows that resemble flows from lines with impedance mismatches and perturbing structures. The laminar theory is used to derive two new self-consistent cylindrical flow solutions: (1) for a constant density profile and (2) for a quadratic density profile of the form ρ=ρc[(r2m−r2)/(r2m−r2c)]. This profile is of interest in that it is similar to profiles observed in a long MITL simulation [Appl. Phys. 50, 4996 (1979)]. The theoretical flows are compared to numerical results obtained with two-dimensional (2-D) electromagnetic particle-in-cell (PIC) codes.

Lightweight power bus for a baseload nuclear reactor in space

Space environmental interactions with the power distribution/power processing subsystem can become a serious problem for power systems rated at tens to hundreds of kilowatts. Utilization of ceramic superconductors at 1000 A/cm/sup 2/, which has already been demonstrated at 77 K, in a conductor configuration may eliminate both bus mass and distribution voltage problems in a high-power satellite. The analytical results presented demonstrate that a superconducting coaxial power transmission bus offers significant benefits in reduced distribution voltage and mass. >

Performance of Radial Focus Applied-B Ion Diode on a Coaxial Pulse Power Machine

A high-power magnetically insulated ion diode with radial geometry was successfully operated on a Reiden IV-H (2 MV, 200 kA) coaxial pulse power machine with across-current feed converter. The generated proton beams were focused ballistically onto the axis. Data of the beam trajectory measurements showed a large aberration of beam focusing in the diode gap region. This may be due to the electron virtual cathode distortion. The reduction of beam focusability was improved simply by correcting the shape of the anode surface. The focused beam intensity of 3×10 10 W/ cm 2 , which was measured by an ion pinhole camera, was compared with predicted values from the trajectory measurements and the beam brightness. Focus reduction factors in the diode were improved from 0.15 to 0.41.

Principles of time domain reflectometometry applied to measurement of rock mass deformation

Time Domain Reflectometry (TDR) is an electrical pulse testing technique originally developed to locate faults in coaxial power transmission cables. Recently, this technique has been adapted for monitoring deformation of cables grouted into rock masses. Rock mass movements deform the grouted cable, which locally changes cable capacitance and thereby the reflected wave form of the voltage pulse. By monitoring changes in these reflection signatures, it is possible to monitor both local extension and local shearing. This paper concentrates on the electromagentic wave theory necessary to quantitatively relate changes in cable geometry to changes in reflected voltage signatures. A finite element model is employed to numerically simulate capacitance changes for deformed geometries produced in the laboratory, and the effect of signal attentuation and resolution of two deformities is assessed on the basis of laboratory test results. Finally, these models are employed to extract heretofore unrealized information from previously from previously collected field data.

The microcalorimeter as a national microwave power standard

The simple construction and good accuracy of the microcalorimeter has resulted in its adoption by many countries as their national standard of microwave power in hollow waveguide. Its use is increasing as a national standard for coaxial microwave power measurement.

Fundamental and Higher Order Mode Couplers on Superconducting RF Cavities for Electron Storage Rings

The design of a coaxial high power loop coupler for use on a 500 MHz superconducting (sc) accelerating cavity of spherical shape is described. Nonsuperconducting construction materials (copper and copper plated stainless steel) are used. Cooling is obtained by cold helium gas in counter flow. The coupler is located at the cavity equator and a choke provides an uncritical RF joint at a minimum current flow position. For the coupling required (Qext = 105-106) the loop does not protrude into the cavity. Test experiments up to 70 kW incident RF power with a matched copper cavity and up to 17.5 kW with a superconducting cavity (corresponding to an acceleration field Eacc = 3.6 MV/m) are described. Design and measurements with two types of compact higher order mode (hom) couplers, coupling to the magnetic and electric field respectively are described. Both couplers are manufactured from Nb and are low Q resonant devices with their centrefrequency matched to the relevant part of the cavities' higher order mode spectrum. All couplers have been operated with a sc cavity up to the design field level.

Slow Formation and Sustainment of Spheromaks by a Coaxial Magnetized Plasma Source

Two steps have been taken towards determining if the flux absorption and relaxation properties of a spheromak will allow dc-powered electrodes to form and sustain a steady-state spheromak. Without changing the physical properties of the spheromak, the formation time was increased from an Alfv\'en time to a tearing time, reducing the coaxial source power from \ensuremath{\sim} 10 GW to \ensuremath{\sim} 500 MW. With use of \ensuremath{\sim} 50 MW, spheromaks were formed and then sustained at constant density and field for 1 ms, much longer than a magnetic-energy decay time.

Coaxial incident power converters

Coaxial incident power converters

Measurement of losses in multiconductor cable transmitting in the dipole-mode

A series of attenuation measurements on various kinds of multiconductor cable sample have been made in the frequency range 300 MHz to 3 GHz to investigate dipole-mode propagation. Two different approaches have been used. In the first, short lengths of cable, about 1m long, were resonated between two end-plates to determine the Q-factor, from which the attenuation was calculated after elimination of losses in the endplates, and in the coupling slots. In the other approach sample lengths of about 50m of cable were investigated by transmission measurements. Here high-efficiency launching devices were required instead of the weak-coupling probes used in the resonator measurements. For the transmission work a new type of launching device was examined, comprising an 8-way coaxial power divider whose output supplied the separate wires of the dipole-mode cable with currents of appropriate amplitude and phase. In the series of loss measurements, all the attenuation figures observed were in quite good agreement with theory. In the course of the work, it was shown by calculation that dipole-mode cable exhibited minimum values of attenuation which could be considerably smaller in magnitude than those of ‘corresponding TEM’ coaxial cable, for which the outer remains unchanged while the inner comprised a copper rod of the same diameter as the outside diameter of the mjultiwire structure exployed in dipole-mode transmission.

Transient thermal blooming of single and multiple short laser pulses

Energy transfer through absorbing media with pulses short compared to the acoustic transit time has been investigated experimentally and theoretically for collimated beams in a homogeneous wind field. Two experimental approaches were used: a low intensity cw CO(2) laser probe beam technique giving a continuous record of the lensing of the medium following the transmission of a coaxial high power TEA laser pulse and a direct determination of high power pulse train blooming using a thermofax covered drum. The experimental results support the predictions of a geometric optics perturbation solution as well as those of existing propagation codes. An interesting case, namely, enhancement resulting in a 20-30% increase of the original nonbloomed peak intensity is observed when the pulse separation time is approximately 1-2 times the wind flow time across the beam.

Maximally null partial response for an MLSE digital data system involving high loss coaxial cable

Digital data systems are considered in which reception is based on the principle of maximum-likelihood sequence estimation (MLSE) and in which the channel has the coaxial cable power transfer characteristic <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">e^{-\alpha \mid \omega \mid ^{1/2} }</tex> . When only the average transmitter output power and the response memory ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\nu</tex> ) are constrained, it is shown that, as <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\alpha</tex> increases, the optimal overall system impulse response tends to a partial response for which the corresponding frequency characteristic is proportional to the unique normalized trigonometric polynomial having <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\nu</tex> th order zeros at the Nyquist bandlimits. These same partial responses result if <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\alpha</tex> is fixed and the band rate is increased. This observation helps explain a recent numerical study by Fredricsson that has stirred wide-spread interest. The minimum distance associated with such an optimal response is tabulated for various values of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\nu</tex> and various numbers of levels.

四端子回路網理論の多線条系化と同軸ケーブルき電方式の回路解析

四端子回路網理論の多線条系化と同軸ケーブルき電方式の回路解析