Electron Beam Source Research Articles

Generation of focused high-current electron beam with millisecond pulse duration by a forevacuum plasma-cathode electron source based on cathodic arc

We describe our work on the generation of low-energy (up to 10 keV) pulsed high-current electron beams with pulse duration up to 7 ms, compressed (focused) by a magnetic field in the forevacuum pressure range (3–30 Pa). We show that the focusing system, consisting of two coaxially arranged coils, provides effective compression of the beam. In the forevacuum pressure range, the gas pressure and type of gas affect the focusing of the beam at fixed emission current, accelerating voltage and magnetic field. Increased pressure leads first to increased beam current density, but beyond a certain optimal value further pressure increase leads to a decrease in the current density of the electron beam. The use of gas with greater ionization cross-section results in stronger compression of the beam at lower gas pressure, but also leads to decreased maximal operating gas pressure of the plasma-cathode electron beam source. Variation of magnetic fields provides control of the beam current density and the position of the beam crossover (focus). A low-energy electron beam with current density up to 15 A·cm−2 and pulse duration up to 7 ms is obtained in the forevacuum pressure range. The use of the focused beam for evaporation of high-temperature ceramics is demonstrated.

Design of a compact integrated high-average power superconducting radio-frequency (SRF) electron beam source

There exists a need for reliable, high-power electron sources for applications including those in discovery science, security, medical and industrial engineering. Today, there are many examples of high-average-power electron sources, but they are not, for instance, simultaneously compact, highly efficient, and available at a reasonable cost. Exploiting recent advances in superconducting, radio-frequency (SRF) cavities and RF power sources as well as innovative solutions for the SRF gun and cathode system, we have developed a design concept for a truly compact, SRF, high-average power electron linac source integrating a thermionic cathode system. Potentially capable of 50 kW average power and continuous-wave operation, this accelerator design will produce electron beams with energies up to 10 MeV. In this paper, we present in detail the electromagnetic design results of our 9-cell accelerating structure with its integrated, thermionic cathode structure.

Design Approach for a Miniaturized Pseudospark-Based High-Current-Density Sheet Electron Beam Source

In this article, the design approach for a miniaturized high-current-density sheet electron beam (SEB) source has been reported. A study through simulation using COMSOL Multiphysics has been carried out to analyze the role of geometrical parameters of the hollow cathode in miniaturized SEB generation. These geometrical parameters play a very important role in defining the discharge inside the hollow cathode geometry and subsequent beam generation through a rectangular aperture. The hollow cathode diameter “D”, the length of the hollow cathode “L”, and the aspect ratio of the sheet beam defined by the aperture size in front of the hollow cathode region have been optimized for the generation of a SEB. The ratio of the length to the width of the rectangular aperture defines the aspect ratio of the SEB. It has been found that the beam aspect ratio plays an important role in the penetration of the accelerating field inside the hollow cathode geometry, which affects the transient behavior of the discharge. The hollow cathode dimensions have been optimized for the applied gap voltage varying between 15 and 25 kV, while the beam aspect ratio has been analyzed for the range between 5:1 and 12:1 keeping the fill factor constant.

Electron-beam ion source/trap charge breeders at rare-isotope beam facilities

At accelerator facilities, charge breeders convert ion beams of low charge states (mostly singly charged) into multiply charged ion beams to extend the energy range of beams accelerated and delivered to experiments. A field of application that has grown over the past decades is charge breeding of rare-isotope beams (RIBs). RIBs are of interest in nuclear physics and astrophysics to study nuclear structure and the origin of the chemical elements. Several postaccelerators at RIB facilities in operation and under construction employ electron-beam ion source and trap (EBIS/T) breeders. Compared with other breeding techniques, EBIS/Ts have many advantages: high efficiency, fast and variable breeding times, small beam emittances, and high beam purity. This publication reviews the use of EBIS/T breeders at RIB facilities with a particular emphasis on their use for postacceleration along with advances in related fields.

Forevacuum plasma electron source of a ribbon electron beam with a multi-aperture extraction system

The article presents the results of using a multi-aperture extraction system in the source of a ribbon electron beam. The optimal size of the holes in the anode and extractor, as well as the distance between the anode and the extractor at which the beam losses are minimal, are investigated.

Dosimetry Study of a VARIAN 600 C/D Linear Accelerator Head Model using MCNP5 Monte Carlo Code

In radiotherapy treatment planning, tools that improve the accuracy and quality of the radiation treatment for cancer are important for the decreased death of healthy tissue and the probability to produce cancer cells. The purpose is to establish the simulation principles in MCNP reproducing the x-ray generation from the electron beam to the resultant photon beam used for radiotherapy in a LINAC VARIAN 600 C/D, being the main goal to approximate the x-ray spectrum, the profile dose and the relative dose to experimental ones. This analysis shows the difficulties to simulate the linear accelerator and how they are represented in the profile dose and relative dose and the probable margin of error obtained compared to the real case. These difficulties are due to the lack of information from the suppliers to the academic public. Therefore, some parts of the model should be inferred, such as the electron beam source and its angle. The results show the experimentally measured data comparison to the Monte Carlo results, where the measurements of PDD are inside the margin of error for buildup region and the flat region for the beam profile dose according to reference criteria. The developed model would help to optimize the simulation of patient dosimetry in radiotherapy treatment planning.

Boron 10B—11B Isotope Substitution as a Probe of the Mechanism Responsible for the Record Thermionic Emission in LaB6 with the Jahn—Teller Instability1

We have tested the conduction band electrons of lanthanum hexaboride that is among the most effective electron-beam sources with one of the highest brightness of thermionic emission. We performed infrared spectroscopic, DC (direct current) resistivity and Hall-effect studies of LaB6 single crystals with various 10B and 11B isotope contents. We find that only a small amount of conduction electrons behave as Drude-type charge carriers while about 70% of the electrons are involved in collective oscillations of electron density coupled to vibrations of both the Jahn-Teller unstable rigid boron cage and rattling modes of La-ions loosely bound to the lattice. We suggest that exactly these non-equilibrium conduction electrons determine the extraordinary low work function of thermoemission in LaB6.

A Plasma Focus device as ultra-high dose rate pulsed radiation source. Part II: X-ray pulses characterization

A PF device has been setup, studied and evaluated as a fast pulsed self-collimated electron beam source for X-ray generation for radiotherapy applications. The worth of this source stands on the extremely short generation time (50 ns as reference delivery time) and on its intensity, being able to produce X-ray pulses able to transfer a dose in the order of 1 Gy each. The electron-X-ray conversion process for several metal targets is here analyzed using Monte Carlo simulations based on measured electron spectra discussed in Part I; some results have been benchmarked with experimental data. The perspectives of the development of a medical source based on this technology are finally evaluated.

Forevacuum plasma source of continuous electron beam

AbstractWe describe here the design, main parameters, and characteristics of a forevacuum-pressure plasma-cathode electron source based on a hollow-cathode discharge. The source generates a continuous focused electron beam with energy up to 30 keV and current up to 300 mA at a pressure of 10–50 Pa. The focused electron beam reaches a maximum power density of 106 W/cm2. The source utility has been demonstrated by its application for processing and cutting of ceramic.

Modeling of diamond field emitter arrays for a compact source of high brightness electron beams

Many applications, such as compact accelerators and electron microscopy, demand high brightness electron beams with small source size and ultralow emittance. Diamond emitters manufactured with semiconductor processes can be employed in such compact beam sources. The micrometer-scale pyramid structure of the emitter allows enhancement of the external field compared to that at the substrate, leading to electron emission with small beam size. We investigate the dependence of the field enhancement on the shape of the emitter and the resulting emission characteristics. The beam formation and dynamics are simulated with the LSP [D. Welch, D. Rose, R. Clark, T. Genoni, and T. Hughes, Comput. Phys. Commun. 164, 183 (2004)] particle-in-cell code to obtain the macroscopic observables. To account for the semiconductor charge transport in the bulk material and the tunneling through the surface, a first-principle semiclassical Monte Carlo emission model is developed and applied to the diamond pyramid. Using this Monte Carlo emission model and the result from the geometric field enhancement calculation, we construct a simple model to qualitatively explain the measured emission characteristics. A comparison between our model and experiments indicates that the beam current is mostly emitted at the apex of the emitter.

Effect of oxygen flow rate on the low temperature deposition of titanium monoxide thin films via electron beam evaporation

In this study, titanium monoxide thin films were evaporated by an electron beam source under different oxygen atmospheres at deposition temperatures not exceeding 80 °C. Deposition of thin films at low temperatures is a prerequisite for heat sensitive substrates. XRD results showed that crystallinity of titanium monoxide is achieved without the requirement of high temperature annealing. When oxygen is introduced into the coating chamber, a titanium peak is formed at exactly the Ti+2 position together with a small amount of Ti+3 and Ti+4 peaks. According to XPS analysis, the structure is transformed into mostly the Ti+4 state when the oxygen flow rate is over 25 sccm. The bandgap of thin films increases from 3.0 to 3.8 eV with an increase in oxygen flow rate from 1 to 50 sccm. Both optical transmission and Hall effect measurements showed the change in carrier type from p to n when the flow rate reaches 25 sccm. Electrical resistivity increases with additional oxygen in the structure, and minimum resistivity is obtained as 1.7 × 10−4 Ω cm when no oxygen is admitted into the chamber. Highly conductive thin films were also observed via ultraviolet photoelectron spectroscopy measurements which yield a high density state showing a metallic character with degenerated oxide semiconductor nature.

Partially Ionized Beam Growth of Tungsten Oxide Nanowires by Oblique Angle Deposition

Tungsten oxide flux from an electron-beam evaporation source was partially ionized through electron bombardment. The positive ions travel through an electric field established by a pair of electrodes with applied voltage Va and are accelerated toward the substrates positioned at an oblique incident angle of 85° with respect to substrate normal. Uniform and well-aligned nanowires were formed with a tilt angle of 50° measured from the substrate normal as observed in scanning electron microscope images. The lengths and heights of nanowires shrink with the introduction of energetic ions in the deposition vapor, which are accelerated toward the substrate by a voltage higher than 2 kV. X-ray diffraction (XRD) patterns of the nanowire samples revealed that the crystal growth was promoted by the partially ionized tungsten oxides. The main XRD peak can be related to the [022] crystallographic planes of the β-phase tungsten oxide (β-WO3) in the orthorhombic structure. The intensity of the [022] diffraction peak inc...

On Solar Recurrent Coronal Jets: Coronal Geysers as Sources of Electron Beams and Interplanetary Type-III Radio Bursts

Abstract Coronal jets are transitory small-scale eruptions that are omnipresent in solar observations. Active regions jets produce significant perturbations on the ambient solar atmosphere and are believed to be generated by microflare reconnection. Multiple sets of recurrent jets are identified in extreme-ultraviolet filter imaging. In this work we analyze the long timescale recurrence of coronal jets originating from a unique footpoint structure observed in the lower corona. We report the detection of penumbral magnetic structures in the lower corona. These structures, which we call “coronal geysers,” persist through multiple reconnection events that trigger recurrent jets in a quasi-periodical trend. Recurrent jet eruptions have been associated with Type-III radio bursts that are manifestations of traveling non-thermal electron beams. We examine the assumed link, as the coronal sources of interplanetary Type-III bursts are still open for debate. We scrutinized the hypothesized association by temporally correlating a statistically significant sample of six Geyser structures that released at least 50 recurrent jets, with correspondent Type-III radio bursts detected in the interplanetary medium. Data analysis of these phenomena provides new information on small-scale reconnection, non-thermal electron beam acceleration, and energy release. We find that the penumbral Geyser-like flaring structures produce recurring jets. They can be long-lived, quasi-stable, and act as coronal sources for Type-III bursts, and, implicitly, upward accelerated electron beams.

CLO19-032: Skin Cancer of the Nose: Outcome in 405 Cases Treated With Accelerated High Dose Rate Radiation Therapy

Overview: Between 2013 and 2016, we treated 1,500 cases of nonmelanoma skin cancer using high-dose radiation therapy. In this series, 405 cases involved the nose. Patient selection was limited to age >35 years, tumor size <40 mm in diameter and <5 mm thick. Demographics included 86.7% basal, 12.8% squamous, 1 lymphoma, 1 melanoma. Size by treatment field: 66.9% 10mm, 28.1% 20mm, 4.7% 35mm, and <1% 50mm. Age: 76.8 years median (37.3–99.7 years) Methods: Radiation therapy was administered following guidelines suggested by ASTRO and AAPM using either a 6MeV LINAC electron beam or 50kV x-ray source. The majority of patients received 4,000 cGy in 500 cGy fractions given twice weekly. Prescribed treatment depth was zero (0) mm for non-bulky disease. Bolus was used for all electron treatments. Wax-coated nasal shields were used for lateralized or large midline lesions. Devitalized tumor was debrided and/or treatment depth modified during treatment as needed. Treatment interruptions were rare, usually due to infection, and limited to less than 2 weeks. Results: 99% of patients maintained a complete response at 2 years (0.2–3.7 years) median follow-up, with 1 edge-of-field progression and 1 in-field recurrence. Side effects seen included transient nasal mucositis (10%) limited to lateralized or large midline lesions, superficial infection (<1%) limited to patients with a history of moderate to severe acne and/or patients applying cosmetic concealers during treatment. No chronic nasal dryness, cartilage necrosis, ophthalmic injury, nasolacrimal disruption, or dental complications occurred. Patient satisfaction/cosmesis: patient-scored functional and cosmetic outcomes ranged from very good to excellent in 100% of patients. Conclusion: Accelerated high dose rate radiation therapy using either LINAC electron beam or electronic brachytherapy is an effective and well-tolerated treatment option for carefully selected patients with basal and squamous cell skin cancer of the nose. Response rates for electron beam or low-energy x-rays with this dose schedule were similar. When compared to surgery, radiation therapy results in high patient satisfaction and excellent cosmesis without the need for lengthy postoperative care or reconstruction. When compared to conventional radiation therapy, the high response rates, smaller field sizes, shorter treatment times, and reduced radiation dose to adjacent critical tissues makes electronic brachytherapy a useful addition to standard techniques.

Alumina coating deposition by electron-beam evaporation of ceramic using a forevacuum plasma-cathode electron source

We have explored the formation of alumina coatings by electron beam evaporation of bulk alumina ceramic using a forevacuum-pressure plasma-cathode electron beam source at a pressure of 60 mTorr of air. The alumina e-beam target material is evaporated at a rate up to 4.2 g/h, and the coating deposition rate is up to 18 μm/h. The evaporated ceramic is partially ionized by the energetic electron beam, and we have measured the plasma composition as a function of beam power. The deposited alumina coatings were characterized by scanning electron microscopy and energy-dispersive x-ray spectroscopy and found to be uniform and pore-free with a composition that is over 99% aluminum and oxygen, with less than 1% impurities including carbon, silicon and calcium.

Advanced Characterization Tools for Probing Anionic Redox in Layered Cathode Materials

Rechargeable Li-ion batteries with higher energy density are in urgent demand to address the global challenge of energy storage. In comparison with anode materials, the relatively low capacity of cathode oxides, which exhibit classical cationic redox activity, has become one of the major bottlenecks to reach higher energy density. Recently, anionic activity, such as oxygen redox reaction, has been discovered in the electrochemical processes, providing extra reversible capacity for certain transition-metal oxides. Consequently, a more complete understanding and precise controlling on anionic electrochemical activity in these high-capacity oxides have become a flourishing, yet challenging subject. Compared to TM cations, oxygen anion electrochemical activity is more challenging to experimentally prove and quantify for the following reasons: First, oxygen participates in the electrochemical activity at highly charged states when the partially delithiated oxides are typically very sensitive to high energy electron beam or X-ray source exposure. Second, peroxo-like species and O-holes resulted from oxygen oxidation are extremely reactive and unstable in air and carbonate based liquid electrolytes. Third, M(nd)−O(np) metal−ligand hybridization and rehybridization make it intricate to quantify and differentiate cation and anion contributions to electronic structure changes as well as their contributions to the extra capacity. Based on the above considerations, a multimodal characterization approach must be established for oxygen anion electrochemical activity. Here, we select Li1.2Mn0.54Co0.13Ni0.13O2 as the model compound and systematically study its structure response to the oxygen redox activity by combing neutron pair distribution function, X-ray absorption spectrum, resonant inelastic X-ray scattering and DFT calculation. An obviously increased short O-O pairs accompanying oxygen redox reactions is for the first time detected, and which should be ascribed to the shrink of the interlayer O-O distance. Also, theoretical analysis indicates that the selective decrease of O-O distance is originated from the different oxygen chemical coordination environment. Further, a coupling relationship between the oxygen redox and transitions metals migration is experimentally demonstrated, which reveals the structural origin of the stable lattice oxygen redox reactions. Based on these understandings in our work, an optimization guidance for anionic acitvity is unambiguously presented: designing a robust layered structure with high-covalency TMs while constructing a flexible local structure with high-ionicity TMs to achieve the reversible high energy density. Figure 1

Фрагментация молекулы глютамина электронным ударом

Using the mass-spectrometric analysis technique, formation of the ionic products of the single and dissociative ionization of the glutamine molecule (C5H10N2O3) at its interaction with the low (70 eV) and high (11.5 MeV) energy electrons has been studied. The experimental mass-spectra of the above molecule measured at different irradiation doses (5, 10 and 20 kGy) and the near-threshold areas of the ionic fragment yield functions have been analyzed, the absolute ion fragment appearance energies have been found. The three-electrode electron gun and the electron accelerator (microtron) were used as the electron beam sources. The analysis of the behaviour of the measured glutamine molecule mass-spectra irradiated at the above doses demonstrates, as compared to the irradiated molecule mass-spectrum, that the high-energy irradiation of the initial molecule results in the irreversible changes of its structure.

Лазерное и электронно-лучевое упрочнение металлов с наноуглеродным покрытием

The results of experiments on modifying metal surface by applying nanocarbon coating followed by laser or electron beam treatment are generalized. Soot produced as a result of electric arc sputtering of graphite electrodes followed by extraction of fullerenes, graphene oxide thermally reduced at different temperatures, and С60 fullerene were used as nanocarbon coating. An impulse laser with a wavelength of 1.064 μm, impulse energy at a level of 10 J, and impulse duration around a few milliseconds was used as a source of high-energy irradiation. An accelerator providing electron energy of 60 keV and a stationary beam current up to 250 mA was used as an electron beam source. The accomplished experiments point to a considerable (up to 8 times) increase in the microhardness of the treated steel surface which is accompanied by a decrease of the friction coefficient by several tens percent. It has also been found that the microhardness of the treated surface is a non-monotonic function on the laser or electron beam irradiation energy.

Computational analysis of the electron beam source with hollow anode

The computational analysis of the plasma source with the hollow anode is performed using the two-dimensional Particle-in-Cell Monte Carlo collisions model. This source operates in two molecular gases (CO2 and N2) in the abnormal glow mode, i.e., it is supported by the secondary electron emission from the cathode. It is obtained that this plasma source can be used for the generation of high-energy electrons (energy > 100 eV) only if the cathode potential exceeds 500 V. Otherwise, the high-energy electrons generated in the high-voltage cathode sheath dissipate almost all their energy in the plasma column and get thermalized.

Получение мощных электронных пучков в источнике с плазменным анодом и питанием от генератора Маркса с согласованными нагрузками

Получение мощных электронных пучков в источнике с плазменным анодом и питанием от генератора Маркса с согласованными нагрузками