Studying a multibeam microwave drift-tube K-band oscillator with an electrodynamic system of two slot-coupled resonators

The possibility is shown of creating a new low-voltage multibeam oscillator of monotron type operating in the K band of wavelengths. The operating principle of this device is based on autogeneration of electromagnetic oscillations during the interaction of a multibeam electron stream with a high-frequency electric field of π type in a two-gap slot resonator having high-frequency voltages across gaps with different amplitudes. The results of theoretical and experimental studies of a 19-beam prototype of the device are presented. For the first time, a microwave-emission power of more than 600 W was obtained experimentally with an electronic efficiency of 45% and a total efficiency of 30% at an accelerating voltage of 2.6 kV and a frequency of 18.14 GHz.     

低压运用电子枪的计算及其在SEM中的应用

本文叙述了用于SEM的低压运用电子枪的设计计算方法及结果。计算中对采用点源的阴极区,利用球座标系统进行处理,从而提高了计算精度。计算表明在一定的几何尺寸范围内,通过调整调制极电压,均可得到较小的交叉斑尺寸。将计算结果直接应用到国产SEM中,采用LaB_6点状阴极做发射源,在加速电压为1kV时,分辨率优于150nm;为2kV时,优于80nm;为5kV时,优于20nm。实验证明计算方法是可靠的,具有实际的指导意义。     

Measurement of high dc voltages by means of an electron-diffraction camera

Conclusions The above technique and the cited examples for computing the voltage from electron-diffraction patterns of NaCl show that it is already possible to measure by means of an electron-diffraction camera éG-100 A high dc voltages up to 100 kV with an error of 0.1–0.2% For certain specimens whose electron gun can withstand voltages up to 120–150 kV the maximum measurement range is extended accordingly. Therefore, the above method of measuring high dc voltages can be used for checking high-tension instruments, including electrostatic kilovoltmeters. Moreover, the same method can be used for measuring the ratios of high-tension dividers directly with the operating voltages across them, which could not be done so far. In measuring the ratio of dc dividers by comparing them with reference resistors at low voltages it is impossible to evaluate the errors due to the heating of resistors by the operating current, to corona discharges, to leakages and space charges along the surface of the divider.The utilization for these purposes of an absolute method which consists of measuring high voltages by the diffraction of electrons raises the reliability of test results and undoubtedly will be of interest for practical application.     

An Automatic System for AC/DC Calibration

An automatic ac/dc difference calibration system using direct measurement of thermoelement EMFs is described. The system operates over a frequency range from 20 Hz to 100 kHz, covering the voltage range from 0.5 V to 1 kV. For all voltages, the total uncertainty (including the uncertainty of the specific reference thermal converters used) is 50 ppm at frequencies from 20 Hz to 20 kHz, inclusive, and 100 ppm at higher frequencies up to 100 kHz. In addition to ac/dc difference testing, the system can be used to measure some important characteristics of thermoelements, as well as to calibrate ac voltage calibrators and precision voltmeters. Results of intercomparisons between the new system and the manual NBS calibration system, using single-range, coaxial-type, thermal voltage converters as transfer standards, are reported. The results indicate that the ac/dc differences measured are accurate to well within the combined total uncertainty limits of the two systems.     

Variable frequency heavy-ion linac,RILAC: I. Design,construction and operation of its accelerating structure

A variable frequency linear accelerator at RIKEN (IPCR), which is named RILAC, is designed to accelerate ions of almost every element in the periodic table. In this report, the design, construction and performance of the resonator cavities of this linac are described. A new accelerating structure was developed for the variable frequency scheme. The principal aim of the development was to obtain a configuration within the cavity to keep a uniform voltage distribution along the accelerating axis over the wide range of resonant frequencies required. The final form adopted is a coaxial quarter-wave type resonator with a race-track-like cross section for its coaxial inner and outer conductors. It has a movable shorting device as a frequency tuner and its open end is enlarged and loaded with drift tubes, connected to the inner and outer conductors alternatingly. The structure can maintain the required uniformity of the accelerating voltage within 10% in spite of resonant frequency tuning between 17 and 45 MHz. A relatively modest accelerating gradient was chosen so that cw operation could be realized. The RILAC is composed of six such cavities which are independently excited and it succeeded in the acceleration of a beam through all the cavities in 1981.     

Ultralow-voltage generator of chaotic microwave oscillations with secondary-emission cathode

A new scheme of an effective ultralow-voltage generator of broadband chaotic microwave oscillations is considered. The device operates on counterpropagating turbulent electron beams, one of which is created by a secondary-emission cathode. Results of an experimental investigation of the device prototype operating in various regimes are summarized. Promising features of the proposed ultralow-voltage oscillator are the relatively low accelerating voltages (below 500 V), increased efficiency (up to 14–15%) compared to analogs, broad band of generated oscillation frequencies, high level of integral output power (up to 35 W), the possibility of fast and easy control over the generation regimes (from almost monochromatic to broadband), and small dimensions of the device.     

Simple position sensorless starting method for brushless DC motor

Position sensorless methods for brushless DC motors based on back-EMF zero crossing suffer from a starting problem since there is no back-EMF at standstill. A simple method by which the motor is started from standstill up to a speed wherein sensorless methods will be able to detect the correct commutation instants is proposed. The proposed method relies on a difference of line voltages measured at the terminals of the motor. It is shown that this difference of line voltages provides an amplified version of an appropriate back-EMF at its zero crossings. It is further demonstrated that this information can be used to trigger devices so as to develop an accelerating torque from zero speed. This method is simple to implement and it can reliably start the motor even with load. The effectiveness of the proposed method is demonstrated through simulation and hardware results.     

Small-size ultralow-voltage generator of chaotic microwave oscillations

The scheme of a small-size ultralow-voltage generator of broadband chaotic microwave oscillations is considered. Results of numerical modeling and experimental investigation of the device prototype operating in various regimes are summarized. Good prospects of the proposed ultralow-voltage generator (vircator) are related to the relatively low accelerating voltages (below 1000 V), rather high electron beam currents (up to 800 mA), good efficiency (up to 5%), and small dimensions of the device.     

Application of PIN photodiodes on the detection of X-rays generated in an electron accelerator

PIN photodiodes are used in a novel application for the determination, within the energy range from 90 to 485 keV, of the intensity of X-rays generated by an experimental electron accelerator. An easily assembled X-ray monitor has been built with a low-cost PIN photodiode and operational amplifiers. The output voltage signal obtained from this device can be related to the electron beam current and the accelerating voltage of the accelerator in order to estimate the dose rate delivered by bremsstrahlung.     

Error and Transient Analysis of Stepwise-Approximated Sine Waves Generated by Programmable Josephson Voltage Standards

We are developing a quantum-based 60 Hz power standard that exploits the precision sinusoidal reference voltages synthesized by a programmable Josephson voltage standard (PJVS). PJVS systems use series arrays of Josephson junctions as a multibit digital-to-analog converter to produce accurate quantum-based dc voltages. Using stepwise-approximation synthesis, the system can also generate arbitrary ac waveforms [i.e., an ac programmable Josephson voltage standard (ACPJVS)] and, in this application, produces sine waves with calculable root mean square (rms) voltage and spectral content. The primary drawback to this ACPJVS synthesis technique is the uncertainty that results from switching between the discrete voltages due to finite rise times and transient signals. In this paper, we present measurements and simulations that elucidate some of the error sources that are intrinsic to the ACPJVS when used for rms measurements. In particular, we consider sine waves synthesized at frequencies up to the audio range, where the effect of these errors is more easily measured because the fixed transition time becomes a greater fraction of the time in each quantized voltage state. Our goal for the power standard is to reduce all error sources and uncertainty contributions from the PJVS-synthesized waveforms at 60 Hz to a few parts in 10⁷ so that the overall uncertainty in an ac power standard will be a few parts in 10⁶.     

Advanced control for PWM converter and variable-speed induction generator

The paper describes a simple control structure for a vector-controlled stand-alone induction generator (IG) used to operate under variable speeds. Deadbeat current control is developed for a voltage source PWM converter and the three-phase variable speed squirrel-cage IG to regulate DC-link and generator voltages with newly designed phase-locked-loop circuit. The required reactive power for the variable-speed IG is supplied by means of the PWM converter and a capacitor bank to build up the voltage of the IG without the need for a battery and to reduce the rating of the PWM converter with the need for only three sensors. This proposed scheme can be used efficiently for variable speed wind or hydro energy conversion systems. The measurements of the IG system at various speeds and loads are given and show that this proposed system is capable of good AC and DC voltages regulation     

Tunnelling through diamond-like carbon nanofilms deposited by electron-beam-induced deposition

The tunnelling properties in metal/diamond-like carbon (DLC)/semiconductor junctions and structural characteristics of thin DLC films produced using different electron beam conditions were studied. We show that under the same electron dose conditions, thicker DLC films were obtained using lower accelerating voltages (2 kV) than when using higher accelerating voltage (20 kV). However, under the settings used the thicker films showed worse insulating performance than the thinner films. We attribute this effect to the variation of tunnelling barrier height in DLC deposited using different accelerating voltages. DLC films with a tunnelling barrier height of up to 3.12 eV were obtained using a 20 kV electron-beam, while only 0.73 eV was achieved for 2 kV DLC films. The X-ray photoemission spectra of the C 1s core level in these films reveal components at 284.4 ± 0.1 eV and 285 ± 0.1 eV, which were identified as the sp² and sp³ hybrid forms of carbon. The sp³/sp² concentration ratio increased with increasing electron beam accelerating voltage. We show how this effect is responsible for the barrier height variation.     

Switching of 100-kV pulses in a planar “open” discharge with generation of counterpropagating electron beams

Some results of studying a planar “open” discharge with generation of counterpropagating electron beams at high voltages and appreciable working gas pressures up to atmospheric one are presented. The possibility of its functioning in helium at a voltage above 100 kV is demonstrated, and an increase in the working voltage does not prevent fast breakdown with characteristic switching times of ~1 ns. A specific feature of this type of discharge is the existence of a gas-pressure region, where the discharge-development delay time nonmonotonically depends on the voltage due to the competition between emission processes leading to breakdown.     

Growth of tungsten nanodendrites on SiO2 substrate using electron-beam-induced deposition

Tungsten nanodendrite structures were fabricated on an insulator SiO2 substrate using an electron-beam-induced deposition process in a high voltage transmission electron microscope. The effect of electron beam accelerating voltage on the nanodendrite structures was investigated. The morphologies and their growth rates did not have obvious difference for the deposition at accelerating voltages from 400 to 1000 kV. A mechanism for the growth and morphology of the nanodendrite structure was proposed involving charge-up produced on the surface of the substrate, movement of charges to and accumulation at the convex surface of the substrate and the tips of the deposits. High-energy electron irradiation enhanced diffusion of W atoms in the nanodendrites, promoted crystallization of W grains, so that more crystallized W nanodendrite structures were achieved by the electron-beam-induced deposition process using higher energy electron beams.     

An electron source with a multiarc plasma emitter for obtaining submillisecond pulsed megawatt beams

An electron source with a plasma emitter based on an arc-discharge system with six cathodes and a common cylindrical hollow anode is described. Upon synchronous initiation of vacuum-arc discharges, the space of the hollow anode is filled by dense low-temperature plasma, the emission boundary of which is stabilized by a fine-structure metal grid with a 150-cm² area. The arc-current amplitude for each cathode amounts to 100–300 A. Under the action of a constant accelerating voltage applied between the plasma emitter and grounded accelerating electrode combined with the drift tube, electrons are extracted from plasma and accelerated. At a working pressure of 0.04 Pa, an electron beam with a maximum current amplitude of 1 kA has been obtained at an initial accelerating voltage of 80 kV and pulse duration (FWHM) of 100 μs, which has been transported in a longitudinal magnetic field of 0.035 T over a distance of 80 cm.     

Strong Spatial Dependence of Electron Velocity, Density, and Intervalley Scattering in an Asymmetric Nanodevice in the Nonlinear Transport Regime

Using a 2-D ensemble Monte Carlo method, we have studied the electron transport in a self-switching device, which is a semiconductor rectifier consisting of an asymmetric nanochannel. Apart from obtaining a good agreement between the theoretical and experimental current–voltage characteristics, the focus is to study the detailed electron transport inside the nanochannel. Our simulations reveal a drastic spatial dependence of the electron velocity, density, and intervalley scatterings along the channel direction because of the strongly nonlinear transport combined with the asymmetric device geometry. We show that pronounced negative differential electron velocity actually occurs in certain regions inside the channel and changes under different bias conditions. Electron intervalley transfer is also found to depend strongly on the sign of the bias voltage as well as the spatial location in the channel. Moreover, we find that it can take a distance of up to 1 $mu$m for the hot electrons to relax their energy after passing through the nanochannel at high biases. The implications on device operating speed and integration are discussed.      

A fully tunable single-walled carbon nanotube diode

We demonstrate a fully tunable diode structure utilizing a fully suspended single-walled carbon nanotube. The diode's turn-on voltage under forward bias can be continuously tuned up to 4.3 V by controlling gate voltages, which is ～6 times the nanotube band gap energy. Furthermore, the same device design can be configured into a backward diode by tuning the band-to-band tunneling current with gate voltages. A nanotube backward diode is demonstrated for the first time with nonlinearity exceeding the ideal diode. These results suggest that a tunable nanotube diode can be a unique building block for developing next generation programmable nanoelectronic logic and integrated circuits.     

A study of the electromagnetic properties of a resonator for multichannel acceleration of light ions

We present an experimental study of a modified Interdigital-H-resonator which can be used for multichannel acceleration of light ions. The distribution of the electromagnetic fields is investigated with a perturbation method. Furthermore, measurements of the resonance frequency, resonator parallel resistance and quality factor are discussed. The measurements have been done on three types of accelerating structures, which have a different capacitance per unit length. The results are compared with an elementary model, in which the resonator is described in terms of discrete circuit elements. It is found that the resonance frequency can be calculated with good accuracy. For the other parameters scaling laws are derived.     

Design and characterization of a photometer-colorimeter standard

A photometer and tristimulus colorimeter has been developed at the National Institute of Standards and Technology (NIST) to realize a color scale. A novel construction was developed to implement the spectral-responsivity-based scale with small uncertainty. The new device can be used as a reference illuminance and luminance meter as well. Temperature-controlled filter combinations, with 5-8 layers in one package, are used to match the responsivity of a silicon tunnel-trap detector to the CIE color-matching functions with small spectral mismatch values (f1'). Design considerations to extend the tunnel-trap detector with replaceable single and double apertures and changeable filter combinations are described. The design and fabrication of the filter packages and the dependence of the f1' values on the thickness of the filter layers are discussed. The colorimeter was characterized for angular, spatial, and spectral responsivity. An improved preamplifier can convert current to voltage in an 11-decade dynamic range with 0.01% uncertainty.     

Progress Towards an Acoustic Measurement of the Molar Gas Constant at INRIM

Progress in developing an experiment for the determination of the molar gas constant R and the Boltzmann constant k at INRIM is reported. The experiment involves simultaneous measurements of the acoustic and microwave resonance frequencies of a stainless steel spherical resonator for which its hemispheres were deliberately misaligned. For the present work, these frequencies were measured in helium near 273.16 K, in the pressure range from 100 to 800 kPa. From microwave data, the radius of the resonator was determined as a function of pressure with an estimated uncertainty of 6.0 ppm. Using acoustic data and the microwave determination of the resonator radius, the speed of sound in helium was deduced, and these values were compared with those predicted by recent accurate ab initio calculations. Over most of the pressure range, the present values agreed with the ab initio values within the uncertainty of the measurements (standard uncertainty of approximately 7.0 ppm). Many suggestions for reducing the uncertainty are provided.