Pulsed Electron Beam Generator Research Articles

Study of nanosecond pulsed hollow-cathode electron beam generation and transportation based on PIC-MCC simulation

This work employs the PIC-MCC (Particle-in-Cell Monte-Carlo collisions) method to study the nanosecond pulsed electron beam time-varied beam current profiles through the hollow-cathode discharge plasma evolution and electron beam transportation process. The electron beam’s energy and current distribution characteristics at the anode hole are investigated, and the simulation’s grid and step sizes are set as 0.04 µm and 5×10-13s, respectively. Experimental parameters are used in the simulation, and experimental results are also used to verify the simulation accuracy. The simulations investigate the transportation characteristics of the electron beam under different conditions and obtain the effects of voltage, current, and ion density on the distribution characteristics of the electron beam. The electron beam current generated by the hollow-cathode discharge is gradually transformed from a random distribution in the central region to a Gaussian distribution. Due to the ion-forced channel formed by the runaway electron pre-ionization, the high-energy electron beam achieves focused transport over a certain distance, and the high-energy electron beam has a smaller Gaussian radius than the source input. Besides, the ion-focusing channel formed by the high-energy electron transportation process can realize the transportation of the high-current electron beam in the conduction stage.

Bacterial eradication by a low-energy pulsed electron beam generator

Low-energy electron beams (LEEB) are a safe and practical sterilization solution for in-line industrial applications, such as sterilizing medical products. However, their low dose rate induces product degradation, and the limited maximal energy prohibits high-throughput applications. To address this, we developed a low-energy ‘pulsed’ electron beam generator (LEPEB) and evaluated its efficacy and mechanism of action. Bacillus pumilus vegetative cells and spores were irradiated with a 250 keV LEPEB system at a 100 Hz pulse repetition frequency and a pulse duration of only 10 ns. This produced highly efficient bacterial inactivation at a rate of >6 log10, the level required for sterilization in industrial applications, with only two pulses for vegetative bacteria (20 ms) and eight pulses for spores (80 ms). LEPEB induced no morphological or structural defects, but decreased cell wall hydrophobicity in vegetative cells, which may inhibit biofilm formation. Single- and double-strand DNA breaks and pyrimidine dimer formation were also observed, likely causing cell death. Together, the unique combination of high dose rate and nanosecond delivery of LEPEB enable effective and high-throughput bacterial eradication for direct integration into production lines in a wide range of industrial applications.

Time response measurement of pulsed electron beam from InGaN photocathode

The photocurrent from a semiconductor photocathode with a negative-electron affinity surface can be arbitrarily controlled by the excitation laser power. Applying this characteristic to a scanning electron microscope allows the probe current to be arbitrarily controlled at any location on the sample. A photocathode with a fast time response is required to control the probe current at high speed. This study used an InGaN photocathode for pulsed electron beam generation and investigated its time response. A pulsed electron beam with 3.8 ns pulse width and 8.1 × 103 A cm−2 current density was observed, and the rise and fall times of the photocurrent were found to be 1.7 and 2.0 ns, respectively. The results show that despite the bottleneck of the time response of the laser power, the InGaN photocathode generates an electron beam that can control the probe current on a pixel-by-pixel for a 270 MHz scan speed.

Impact of Irregular Electrode Apertures in Multigap Pseudospark Discharge Geometries for the Generation of High Density and Energetic Electron Beams

In this article, a multigap pseudospark (PS) discharge-based plasma cathode electron (PD-PCE) source is considered for the generation of high density and energetic pulsed electron beams using electrostatic 2-D kinetic particle-in-cell (PIC) simulation code OOPIC Pro. The characteristics of the generated electron beams are very much dependent on the geometrical and operating parameters of PD-PCE source. The size, uniformities, and irregularities of electrode apertures play a significant role on the generation of high density and energetic electron beams. Investigation has been carried out to analyze the effect of the irregular electrode apertures in PD-PCE source for the generation of electron beams. The combinations of irregularities considered in the diameter of electrode apertures are 2, 4, 6, and 8 mm, mostly used for the development of PD-PCE sources. It has been observed that the aperture size of first electrode decides the delay in breakdown of first gap at constant operating conditions. The delay primarily depends on the penetrating behavior of equipotential lines which leads the successive breakdowns in the remaining gaps of multigap PD-PCE source. The latter electrodes of multigap geometry are responsible for guiding the size of electron beams. Dips in the electron beam currents have been observed during its rise, which are dependent on the sequence of irregular electrode apertures and operating conditions. The gas pressure and electrode apertures control the voltage falls in gaps and rise of electron beam current. The study would support the design and the development of PD-PCE sources suitable for extreme ultraviolet (EUV)/soft X-ray, microwave, and surface modification applications.

Stability of electron beam generation by forevacuum-pressure plasma-cathode electron beam source based on a cathodic arc

We describe our experimental research on the stable generation of large-radius pulsed high-current electron beams using a forevacuum-pressure plasma-cathode electron beam source with cathodic arc plasma generation. We find that increased gas pressure and the use of gas with a higher ionization cross-section considerably decrease the stable emission current due to loss of electric strength of the acceleration gap (breakdown). Increased pulse duration results in a decrease in the emission current, but the influence of the gas species and its pressure remains for all pulse durations. There is an extremum in the dependence of emission current on the acceleration gap length and the optimum gap length depends on the gas pressure and the kind of gas. The experiment results can be explained by the effect of back-streaming ion flow, which charges dielectric inclusions on the emission electrode (anode grid) and thereby amplifies the electric field.

Ecton processes in the generation of pulsed runaway electron beams in a gas discharge

As was shown earlier for pulsed discharges that occur in electric fields rising with extremely high rates (1018 V/(cm s)) during the pulse rise time, the electron current in a vacuum discharge is lower than the current of runaway electrons in an atmospheric air discharge in a 1-cm-long gap. In this paper, this is explained by that the field emission current from cathode microprotrusions in a gas discharge is enhanced due to gas ionization. This hastens the initiation of explosive electron emission, which occurs within 10–11 s at a current density of up to 1010 A/cm2. Thereafter, a first-type cathode spot starts forming. The temperature of the cathode spot decreases due to heat conduction, and the explosive emission current ceases. Thus, the runaway electron current pulse is similar in nature to the ecton phenomenon in a vacuum discharge.

Study on nanosecond pulsed electron beam generation

The paper presents the findings of an investigation on volt-ampere characteristics of the diode with explosive emission cathodes of different constructions (blade metal-dielectric (MD-cathode) and solid graphite cathodes) under the change of the anode-cathode gap in wide ranges. The investigations were carried out using the TEA-500 pulsed electron accelerator. The total current of the electron beam was measured using the Faraday cup (FC). A 0.5-mm foiled glass fiber laminate was used as an emitting edge of the cathode in the experimental study with the explosive emission blade MD-cathode. Based on the obtained results, the conclusion was made that the graphite cathode has the most effective efficiency factor.

Spectroscopic Investigation of a Double Discharge Pulsed Electron Beam Generator

ABSTRACT The wide range of applications of the plasma-based electron beam generator make it necessary to diagnose the device with a noninterfering method. The results of experimental and modeling studies of neutral helium and hydrogen beta spectral lines emitted from the double discharge pulsed electron beam generator are presented in this paper. Neutral helium lines emitted from the plasma in the pressure range 0.1–0.4 torr are studied and compared with results of the collisional radiative model. The duration of the electron beam is shorter than 100 ns, and the peak current intensity is of order amperes. The full width at half maximum of the H β spectral line is used for the determination of the plasma electron density, found as 3.16 × 1021 m−3 at 0.3 torr, and good agreement is obtained by comparing with the full computer simulation method.

Generation of high-intensity pulsed low-energy electron beams in a channel spark system

The generation of a high-intensity pulsed beam of low-energy (5–10 keV) electrons in a gun of the channel spark type is considered. It is experimentally established that intense preionization in the transport channel, in combination with a pulsed accelerating voltage applied to the cathode, ensures the generation of pulsed electron beams with a current buildup time above 1011 A/s, a current density above 10 kA/cm2, and an amplitude about 1.5–2 times the characteristic Alfven current.

Synthesis of carbon nanotubes by a plasma based pulsed electron beam generator

Carbon nanotubes (CNTs) were synthesized by using a plasma based electron beam generator, which has a fast filamentary discharge formed from the superposition of an ordinary low-pressure dc glow and a high-current pulsed discharge. To our knowledge, CNTs are synthesized for the first time by this method. Acetylene was used as the carbon source and the iron catalyst coated silica substrates were prepared by the sol-gel technique. The silica plates were first coated with an appropriate iron (III) nitrate solution. After calcination and reduction with hydrogen nano iron particles were formed on the plates. The products were collected from two different zones of the e-beam generator. The products were characterized by transmission electron microscopy and Raman spectroscopy.

Self-confinement of a fast pulsed electron beam generated in a double discharge

The construction of a double discharge pulsed electron beam generator and the study of the characteristics of the beam are presented in this paper. The electron beam generator consists of a fast filamentary discharge in superposition with an ordinary glow discharge in low-pressure gases. The filling gas is argon or helium at approximately 0.1 Torr pressure. The duration of the electron beam is shorter than 50 ns and the peak current intensity is of the order of amperes. The electron density is evaluated by making use of Stark broadening of the Hβ line and compared with the full computer simulation method. The pinch effect of the filamentary discharge is evaluated and its size compared with the diameter of the beam.

Pulsed electron beam generation in a simple discharge device

We report a phenomenon of pulsed electron beam generation in a low-pressure gas discharge device. The cathode of the device is of simple geometry without a hollow cavity that is employed in the transient hollow cathode discharge (THCD) devices. The discharge and beam characteristics are measured and found to be similar to that of THCDs such as pseudospark and channelspark.

Plasma development in the low-pressure channel spark for pulsed intense electron beam generation

Pulsed intense electron beams with remarkable parameters are generated in transient hollow-cathode discharges (THCD). The channel spark is different from the other THCD configurations with respect to the low gas pressure and the tube geometry, which consists of a dielectric capillary tube and an anode mounted on its external surface. In this paper, the channel-spark discharge is systematically studied by electrical and fast shutter camera measurements. The buildup of electrostatic field and the equipotential lines are calculated by the numerical code Electrostatic Field (ElFi) 3.0. The influence of the gas pressure, breakdown voltage, and external capacitance on the discharge current and the beam current are outlined. Depending on the gas pressure, two different discharge modes are observed, i.e., the high resistive and the regular modes, which can be distinguished by the shape of the electrical signals. The plasma development in these modes is studied by electrical and fast shutter camera measurements, performed spectrally integrated and with interference filters to separate the emission of the ions originating from the working gas and capillary material. Compared to the pseudospark, the plasma development in channel spark presents similar as well as specific features due to the low gas pressure and to the capacitive anode-plasma coupling.

Measured Displacement Energies of Oxygen Ions in Zirconolite and Rutile

ABSTRACTOptical emission spectra in the 300-700 nm range were collected from zirconolite and rutile specimens irradiated with a 3 μs pulsed electron beam using a Febetron 706 variable energy pulsed electronbeam generator. The long-lived emissions (up to microseconds after the electron pulse) consist of broad (halfwidths ~ 100 nm) bands centred around ~400 nm. Over the range 0.2 MeV to 0.6 MeV, the emission intensity per unit dose versus electron beam energy data from the rutile sample showed a single stage dependence on electron beam energy, whereas the zirconolite data suggested a two stage dependence. Rutile has a threshold of 0.23 ½ 0.02 MeV, which gives an Ed value of 39 ½ 4 eV for oxygen. Zirconolite has a threshold of 0.26 ½ 0.02 MeV, which gives an Ed value of 45 ½4 eV for oxygen. These data are discussed in the context of previously measured and calculated Ed values for other oxides.

The role of multielectrode geometry in the generation of pulsed intense electron beams in preionization-controlled open-ended hollow-cathode transient discharges

High-voltage hollow-cathode glow discharges are used more and more to generate intense, pulsed electron beams. Such intense electron beams can be produced with high efficiency in preionization-controlled open-ended hollow-cathode transient discharges (PCOHC). This novel discharge is initiated by a low-current dc preionization discharge. The beam parameters are similar to those of the electron beam generated in pseudospark discharges. In this work, we present some measurements of the parameters for the electron beam generated by using a multielectrode (multigap) system instead of the single-gap device in this PCOHC configuration. This kind of multielectrode device was already used in pseudosparks to improve the intensity and collimation of the extracted beam. By using the multigap instead of the single gap, the total beam current (100-120 A) and the energetic part of the beam current (peak current 60-90 A and electron energies higher than approximately 3 keV) were substantially increased. However, the energy spectrum of the fast component has a large fraction of electrons at lower energies (4-10 keV for 26 kV breakdown voltage) when a multigap device is used instead of the single-gap configuration. A comparison between the single-gap and multigap PCOHC-produced pulsed intense electron beam is made too. The differences between the high-power pulsed electron beams produced in single-gap and multigap PCOHC configurations seem to be due to different developments of beam generation phases.

Pulsed intense electron beams generated in transient hollow cathode discharges: fundamentals and applications

For the commercial application of pulsed power, material processing with intense pulsed particle beams is a very interesting subject. Recently, high-voltage (1-70 kV), low-pressure (1-100 Pa) transient hollow-cathode discharges turned out to be sources for pulsed intense electron beam generation suitable for this application. The remarkable parameters of these electron beams-beam currents of 50-1000 A (10-30% of the maximum discharge current) with a high energy component (mean energy of about 0.25-0.75 of maximum applied voltage) of 20-70% of the maximum beam current, power density up to 10 W/cm/sup 2/, beam diameters of 0.1-3 mm, beam charge efficiency of 3-5%-captured the attention not only of the scientific community in the last decade. The electron beam is emitted during the early phases of the discharge, and only weak dependence of the high energetic peak of the beam current was found on the external capacity, which determine the development of the later high-current phases. However, the beam parameters depend on the breakdown voltage, gas pressure, and discharge geometry (including self-capacity). In this paper, the characteristics of the pulsed intense electron beams generated in two configurations-multigap pseudosparks and preionization-controlled open-ended hollow-cathode transient discharges (PCOHC)-are described. Such electron beams already were used successfully in a variety of pulsed power applications in material processing, deposition of superconducting (YBaCuO) and diamond-like thin films, microlithography, electron sources for accelerators, and intense point-like X-ray sources, and some preliminary experiments revealed new potential applications such as pumping of short-wavelength laser active media. These pulsed electron beams could be used further in any kind of pulsed power applications that require high-power density, small or high electron energy, and small-beam diameters.

96/00932 The e-SCRUB machine: An 800 kV, 500 kW average power pulsed electron beam generator for flue-gas scrubbing

96/00932 The e-SCRUB machine: An 800 kV, 500 kW average power pulsed electron beam generator for flue-gas scrubbing

Pulsed electron beam generation via laser stimulation

A new method for pulsed electron beam generation using an UV-laser stimulated Ti Au-layer is presented. This pulsed photocathode can substitute the conventional electron source and the beam-blanking system in any electron beam measuring system for time resolved measurements (e.g. SEM, cathodoluminescence, EBIC, EBIV, electron beam testing). At present, an average electron beam current of 20 nA containing 1640 electrons per pulse with a pulse duration of 36 ps can be obtained with this photocathode. The electron pulse duration and the pulse shape has been determined experimentally with a streak measurement technique. Compared to a conventional LaB 6 thermionic electron source combined with a fast beam blanking system, we got an electron source with a higher electron current, which can improve simultaneously the measurement acquisition time, the signal-to-noise ratio and the spatial resolution.

Generation of intense pulsed electron beams by superposition of two discharges

A pulsed self-collimated intense electron beam of diameter less than 1 mm, a few centimetres in length and up to 280 A peak current, 20 ns pulse duration and 50 Hz repetition rate is produced along the axis of a cylindrical discharge tube using the synergy of two discharges. It needs neither bore holes nor internal electrodes and can be obtained in various gases and for a large range of tube diameters.

Multiple pulsed ion and electron beams produced by the multiplate chamber

Intense pulsed ion and electron beams with energies below 100 keV are difficult to create using the normal ‘‘vacuum diode.’’ In this paper, the generation of intense multiple pulsed ion and electron beams by the multiplate chamber (MPC) based on the field escalation effect is described. Various kinds of target material ions can be produced by bombardment by the electron beam created in the last gap near the anode. Studies of the propagation of intense pulsed particle beams can be conducted with such a MPC.