An efficient cathode for generating an supershort avalanche electron beam in air at atmospheric pressure

The cathodes of accelerators intended for generating an ultrashort electron beam in air at atmospheric pressure were studied. A cathode allowing an increase in the amplitude of the beam current behind the foil by several times has been developed. The beam current amplitude obtained at a half-height pulse duration of ∼100 ps is ∼80 A.     

Note: Measurement of extreme-short current pulse duration of runaway electron beam in atmospheric pressure air

This note reports the time-amplitude characteristic of the supershort avalanche electron beam with up to 20 ps time resolution. For the first time it is shown that the electron beam downstream of small-diameter diaphragms in atmospheric pressure air has a complex structure which depends on the interelectrode gap width and cathode design. With a spherical cathode and collimator the minimum duration at half maximum of the supershort avalanche electron beam current pulse was shown to be ～25 ps. The minimum duration at half maximum of one peak in the pulses with two peaks can reach ～25 ps too.     

A coaxial chopping gap filled with air at atmospheric pressure with a pulse decay time ≤100 ps

The results of experimental studies of a coaxial chopping gap filled with air at atmospheric pressure are presented. At a pulse rise time of 100–300 ps and a voltage pulse amplitude of 30–145 kV, the obtained duration of the voltage-pulse decay time is ≤ 100 ps. The high stability of the gap operation is attained in the presence of the edge with a small radius of curvature on one of the electrodes. The fast voltage decay across the gap is determined by the preionization of the gap by runaway electrons.     

Detection of x-ray emission in a nanosecond discharge in air at atmospheric pressure

Measurement of x-ray emission is an important parameter to investigate runaway behavior of fast electrons produced in nanosecond-pulse gas discharge. An online detection system of x rays is described in this paper, and the system consists of an x-ray detector with NaI (Tl) scintillator and photomultiplier tube, and an integrated multichannel analyzer. The system is responsible for detecting x-ray emission signal, processing the detected signals, and scaling the energy distribution. The calibration results show that every channel of the detection system represents a given x-ray energy and various x rays can be divided into different energy ranges between 10 and 130 keV. For a repetitive nanosecond-pulse breakdown between highly nonuniform gaps in open air, an energy distribution is obtained using the online detection system. It shows that the x-ray emission is a continuous spectrum and the x rays of above 60 keV dominate in the detected energy distribution.     

Recording transmitted beam current for X-ray microanalysis in a scanning transmission electron microscope

A method of measuring transmitted beam current stability during and between X-ray microanalyses in a STEM is described. This facility also allows analytical artefacts due to charging, drift, contamination and mass loss to be detected during an analysis.     

The effect of electron range on electron beam induced current collection and a simple method to extract an electron range for any generation function

The effect of electron range on electron beam induced current (EBIC) is demonstrated and the problem of the choice of the optimal electron ranges to use with simple uniform and point generation function models is resolved by proposing a method to extract an electron range-energy relationship (ERER). The results show that the use of these extracted electron ranges remove the previous disagreement between the EBIC curves computed with simple forms of generation model and those based on a more realistic generation model. The impact of these extracted electron ranges on the extraction of diffusion length, surface recombination velocity and EBIC contrast of defects is discussed. It is also demonstrated that, for the case of uniform generation, the computed EBIC current is independent of the assumed shape of the generation volume.     

Technique for the measurement of the amplitude and phase velocity of a slow space charge wave on a relativistic electron beam

A technique is described for the measurement of the axial electric field of a slow space charge wave. The measurement employs a double probe arranged to give an output proportional to the rate of change of magnetic flux linking the probe loop. This output may be related to the electric field of the wave. Two such probes used in an interferometer arrangement allow for the measurement of the phase velocity of the wave.     

An experimental model of beam broadening in the variable pressure scanning electron microscope

In the variable pressure scanning electron microscope (VP-SEM) the incident electrons pass through a gaseous environment and the beam is scattered by these interactions. We show here that the experimental intensity profile of the scattered beam can be described as Gaussian in form to a high level of accuracy. This provides a rapid means of accounting for the effects of beam scatter in imaging and microanalysis because the standard deviation of the Gaussian is a simple function of parameters such as working distance, beam energy, gas type and pressure.     

In situ electron beam induced current measurements of the local thickness in semiconductor devices

A quantitative electron beam induced current method is shown, applicable in situ for electron beam current measurement on a semiconductor sample without the need for a Faraday cup. As a validation technique, the measurement of top overlayer thickness in the semiconductor structure was chosen for two reasons. First, the measured thickness is easily verified using the same electron microscope in the secondary electron mode by measuring the layer thickness at the layer edges. Second, the measurement of a layer thickness and its local variations constitute an important issue in semiconductor processing and characterization. The proposed method is used in the planar view of the sample, and also for locations far from the layer edges. Quasi‐three‐dimensional maps of the thickness spatial distribution are presented.     

Microstructure and tribological properties of Al-Pb alloy modified by high current pulsed electron beam

In the present work, Al-Pb alloy was irradiated by high current pulsed electron beam. X-ray diffractometer, electronic probe microanalysis, scanning electron microscopy and Knoop hardness indentation were used to characterize the microstructure and mechanical property of Al-Pb alloy. The results show that the microstructure and mechanical property can be greatly improved. The tribological properties of high current pulsed electron beam irradiated Al-Pb alloy were investigated under dry sliding conditions using a pin-on-disc type wear testing machine. The overlapped zone beneath the melted zone exhibits good resistance to wear. Optical observation and scanning electron microscopy analysis reveal that the low wear rate and lowest level in coefficient of friction at high load level for irradiated Al-Pb alloy are due to a lubricious tribolayer covering almost the entire worn surface. The wear mode varies from oxidative wear at low load to film spalling at high load and, finally, adhesive wear.     

The use of helium gas to reduce beam scattering in high vapour pressure scanning electron microscopy applications

Both image quality and the accuracy of x-ray analysis invariable pressure scanning electron microscopes (VPSEMs) are often limited by the spread of the primary electronbeam due to scattering by the introduced gas. The degree of electron scattering depends partly on the atomic number Z of the gas, and the use of a low Z gas such as helium should reduce beam scattering and enhance image quality. Using anuncoated test sample of copper iron sulphide inclusions in calcium fluorite, we show that the reduction in beam scatter produced by helium is more than sufficient to compensate for its reduced efficiency of charge neutralisation. The relative insensitivity to pressure of x-ray measurements in a helium atmosphere compared with air, and the consequent ability to work over a wider range of working distances, pressures, and voltages, make helium potentially the gas of choice for many routine VPSEM applications.     

Behaviour of an intrinsic fission-couple in a long duration neutron pulse

This paper presents a theoretical analysis of the development of fission-couple output in a long duration neutron pulse, and in a steady neutron flux. It also explains why the behaviour of the fission-couple is very different in the long duration pulse compared to that in a short neutron burst.     

电子束应用于快速成型(RP)之初探

探讨将电子束的加工方法引进到快速成型技术中,用以替代SLS技术中的激光作为加工热源,以此去掉快速成型系统中激光扫描部分的机械传动部分,简化系统装置及控制系统的软件设计。     

Electron cyclotron resonance plasma production by using pulse mode microwaves and dependences of ion beam current and plasma parameters on the pulse condition

We measure the ion beam current and the plasma parameters by using the pulse mode microwave operation in the first stage of a tandem type ECRIS. The time averaged extracted ion beam current in the pulse mode operation is larger than that of the cw mode operation with the same averaged microwave power. The electron density n(e) in the pulse mode is higher and the electron temperature T(e) is lower than those of the cw mode operation. These plasma parameters are considered to cause in the increase of the ion beam current and are suitable to produce molecular or cluster ions.     

Airborne particles detection and sizing at single particle level by a novel electrical current pulse sensor

A novel method for detecting and sizing airborne particles at single particle level is presented in this paper. When a particle hits a metal electrode which is grounded, electrostatic charges will be transferred between the particle and the electrode. As a result, an electrical current pulse will be generated in the measurement system. The number of the signal pulse represents the number of particles in the sample. To determine the effect of the particle size on the magnitude of the signal, the correlation between the magnitude of the signal and the size of particle was experimentally investigated. The results show that the magnitude of the measured signal is linearly proportional to the square of particle’s diameter. Such a correlation can be used to evaluate particle size from the measured signal. The airborne particle detection method presented in this paper can be used for counting and sizing airborne particles at single particle level.     

The dependence of extracted current on discharge gas pressure in neutral beam ion sources on HL-2A tokamak

The discharge gas pressure is a key factor to influence the extracted current of ion source. In this paper, the dependence of extracted current on discharge gas pressure was investigated in detail at different arc discharge currents. The discharge gas pressure with a very broad range (0.1 Pa-2.7 Pa) was scanned for the first time. It is turned out that, with the increasing of discharge gas pressure, the extracted current increases and the arc voltage decreases at different arc currents; however, when the discharge gas pressure exceeds a certain value, the extracted current decreases. For the same discharge gas pressure, the higher the arc current, the higher the arc voltage and the extracted current are. The arc efficiency was also calculated, and its dependence on gas pressure was almost the same with the dependence of extracted current on gas pressure, but at the same discharge gas pressure, the lower the arc current, the higher the arc efficiency is and the lower the extracted current is.     

The effect of the electron beam on various mounting and coating media in scanning electron microscopy

Eight commonly used specimen adhesives were examined under the ‘Stereo-scan’ scanning electron microscope to determine the effects of the electron beam on their surface topography. The adhesives were initially examined uncoated, and then coated variously with carbon, and seven different metals and alloys. The effect of the beam on the coated and uncoated adhesives was recorded. The results are presented in tabular form. The purpose of the experiments was to determine the extent of the damage, if any, produced by the beam, on the adhesive, and to try to discover the most damage-resistant combinations. While combinations are damage-free, some of the more easily damaged adhesives are regarded as being suitable for certain specialized purposes, where their special properties over-ride their susceptibility to beam damage.     

Simulation and test of a point focused electron beam emitter

We present the design analysis of a point focused electron beam emitter using numerical techniques. Simulation and modeling were performed followed by the calculation of emission parameters using programming codes EGUN and CST-PS. Beam emittance, average current density and perveance were calculated and are in agreement with the experimental values obtained at 10 kV acceleration potential. The emission parameters were evaluated up to 110 kV. This confirms possibilities of potential application of emitter for a linear accelerator.     

The reduction of the beam gas interactions in the variable pressure scanning electron microscope with the use of helium gas

This paper presents experimental observations on electron scattering by gases (helium and air) in the specimen chamber of a variable pressure scanning electron microscope. It shows an important reduction of the beam scattering with the use of helium gas, and the consequences for the x-ray microanalysis are discussed.     

Ion source with longitudinal ionization of a molecular beam by an electron beam in a magnetic field

A high-efficiency ion source for a mass-spectrometer’s detector of molecular beams and their scattering products is described. The ion source is designed according to a scheme of impact ionization of a beam particle by a longitudinal electron beam in a magnetic field with a strength of up to 130 mT. The design of the source developed is very flexible and has no limitations for use in any experiments with molecular beams. An ionization efficiency of particles of an atomic helium beam of 10^?3 ions/atom has been achieved. The useful signal-to-background ratio in the detector’s chamber is 3 × 10⁴ during detection of ions with mass-to-charge ratio m/q = 4 amu.