Current Electron Beam Research Articles

Charge Catastrophe and Dielectric Breakdown During Exposure of Organic Thin Films to Low-Energy Electron Radiation

The effects of exposure to ionizing radiation are central in many areas of science and technology, including medicine and biology. Absorption of UV and soft-x-ray photons releases photoelectrons, followed by a cascade of lower energy secondary electrons with energies down to 0eV. While these low energy electrons give rise to most chemical and physical changes, their interactions with soft materials are not well studied or understood. Here, we use a low energy electron microscope to expose thin organic resist films to electrons in the range 0-50eV, and to analyze the energy distribution of electrons returned to the vacuum. We observe surface charging that depends strongly and nonlinearly on electron energy and electron beam current, abruptly switching sign during exposure. Charging can even be sufficiently severe to induce dielectric breakdown across the film. We provide a simple but comprehensive theoretical description of these phenomena, identifying the presence of a cusp catastrophe to explain the sudden switching phenomena seen in the experiments. Surprisingly, the films undergo changes at all incident electron energies, starting at ∼0 eV.

High-Power Microwave Oscillator of Twistron Type with Efficiency of 55% for Electron Energy of 180 keV

Highly effective mode of generation of a relativistic microwave oscillator of twistron type is calculated by numerical simulation using an axisymmetric version of completely electromagnetic PiC-code KARAT. With accelerating voltage of 180 kV, electron beam current of 1.2 kA, and 1.9 T guiding magnetic field strength, the simulated stationary generation power is 120 MW at an operating frequency of 10.7 GHz. The efficiency of electron beam power conversion to electromagnetic radiation is 55%, and the electronic efficiency of the oscillator calculated from the change of the initial electron energy is 64%.

A tapered multi-gap multi-aperture pseudospark-sourced electron gun based X-band slow wave oscillator

The experimental study of a tapered, multi-gap, multi-aperture pseudospark-sourced electron gun based X-band plasma assisted slow wave oscillator is presented. The designed electron gun is based on the pseudospark discharge concept and has been used to generate a high current density and high energy electron beam simultaneously. The distribution of apertures has been arranged such that the field penetration potency inside the backspace of the hollow-cathode is different while passing through the tapered gap region. This leads to non-concurrent ignition of the discharge through all the channels which is, in general, quite challenging in the case of multi-aperture plasma cathode electron gun geometries. Multiple and successive hollow cathode phases are reported from this electron gun geometry, which have been confirmed using simulations. This geometry also has led to the achievement of ∼71% fill factor inside the slow wave oscillator for an electron beam of energy of 20 keV and a beam current density in the range of 115–190 A/cm2 at a working argon gas pressure of 18 Pa. The oscillator has generated broadband microwave output in the frequency range of 10–11.7 GHz with a peak power of ∼10 kW for ∼50 ns.

High current nonlinear transmission line based electron beam driver

A gigawatt-class nonlinear transmission line based electron beam driver is experimentally demonstrated. Four experimental series, each with a different Marx bank charge voltage (15, 20, 25, and 30 kV), were completed. Within each experimental series, shots at peak frequencies ranging from 950 MHz to 1.45 GHz were performed. Peak amplitude modulations of the NLTL output voltage signal were found to range between 18% and 35% for the lowest frequency shots and between 5% and 20% for the highest frequency shots (higher modulation at higher Marx charge voltage). Peak amplitude modulations of the electron beam current were found to range between 10% and 20% for the lowest frequency shots and between 2% and 7% for the highest frequency shots (higher modulation at higher Marx charge voltage).

Fast Rise Time High Current Electron Beam: Emission, Acceleration, and Drift Motion

Fast processes associated with emission, acceleration, and drift motion of a high current, moderately magnetized electron beam (particles energy ~300 keV; current ~3 kA) were studied experimentally when tubular explosive-emission cathode was supplied by subnanosecond rise time voltage pulse. Kinematic effect causes the sharpening of the observed beam front which was proven by particle-in-cell numerical modeling. The angular structure of tubular beam was studied through the current waveform records from collector probe after beam propagation through a radial-slit collimator. Current waveforms had time resolution no worse than 10 ps and provided the analysis of the beam temporal structure after its acceleration as well as in the process of further electrons drift motion in a finite guiding magnetic field.

Characteristics of the Shanghai high-temperature superconducting electron-beam ion trap and studies of the space-charge effect under ultralow-energy operating conditions

A high-temperature superconducting electron-beam ion trap (EBIT) has been set up at the Shanghai EBIT Laboratory for spectroscopic studies of low-charge-state ions. In the study reported here, beam trajectory simulations are implemented in order to provide guidance for the operation of this EBIT under ultralow-energy conditions, which has been successfully achieved with a full-transmission electron-beam current of 1–8.7 mA at a nominal electron energy of 30–120 eV. The space-charge effect is studied through both simulations and experiments. A modified iterative formula is proposed to estimate the space-charge potential of the electrons and shows very good agreement with the simulation results. In addition, space-charge compensation by trapped ions is found in extreme ultraviolet spectroscopic measurements of carbon ions and is studied through simulation of ion behavior in the EBIT. Based on the simulation results, the ion-cloud radius, ion density, and electron–ion overlap are obtained.

Cs‐Corrected STEM Imaging of both Pure and Silver‐Supported Metal‐Organic Framework MIL‐100(Fe)

AbstractMetal‐organic frameworks (MOFs) are a family of porous solids combining organic and inorganic moieties with tunable porosity. Their structural parameters have converted MOFs into suitable compounds for gas storage or drug delivery. However, despite the excellent crystallinity they tend to exhibit their analysis through transmission electron microscopy is extraordinarily complicated owing to the high instability under the electron beam irradiation. In here, high‐resolution Cs‐corrected STEM imaging was used for the observation of the building units of MIL‐100(Fe), and special attention was paid to the electron beam current. In addition, MIL‐100(Fe) was reacted with AgNO3 through a solid‐state reaction technique, which resulted into the formation of metal nanoparticles on the surface. The incorporation of Ag into the porous network has been also investigated.

Simulation of Irradiation-Based Processing System for Natural Rubber Vulcanization

Natural rubber is an important export product of Thailand, which presently contributes about 40% of global production and export. In order to make the natural rubber latex to be durable material, the proper vulcanization process is needed. In typical vulcanization process, chemical substances are added to improve the rubber properties. This may cause some problems e.g. toxicity, blooming effects and unpresented smell due to the additive substances. Vulcanization using an accelerated electron beam does not need to add possibly toxic chemical compounds, especially sulfur. Thus, it was proved to be an alternative method for high quality natural rubber vulcanization. This paper presents about simulation of electron beam irradiation for natural rubber vulcanization with variable electron beam energy and current of 0.5-4 MeV and 10-100 mA, respectively. These ranges of the electron beam energy and current will give adjustable absorb dose, which is the most important parameter for electron beam processing. The absorb energy and its distribution in the natural rubber latex are simulated by using a Monte Carlo method program, GEometry ANd Tracking 4 (GEANT4), with the aim to find the optimal conditions of electron beam properties for sufficient natural rubber vulcanization. Study results of the energy distribution for electron beam penetration in the natural rubber latex are presented and discussed in this paper.

A plasma electron source for generating beam plasma at low gas pressures

A plasma electron source design for generating beam plasma at low gas pressures is reported. The designed plasma electron source can run stably in the pressure range between 0.1 Pa and 4 Pa. The electron source emission current increases as the working pressure increases. The DC electron beam can reach 11 A at an extraction voltage of 400 V and a gas pressure of 4.0 Pa, which is experimentally verified in this article. This low energy and high current electron beam interacts with gas molecules to generate a beam plasma, which increased the plasma electron source output current. As the working pressure and emission current increased, the beam plasma emission spectrum intensity increased.

Generation of runaway electron beams in high-pressure nitrogen

In this paper the results of experimental studies of the amplitude-temporal characteristics of a runaway electron beam, as well as breakdown voltage in nitrogen are presented. The voltage pulses with the amplitude in incident wave ≈120 kV and the rise time of ≈0.3 ns was used. The supershort avalanche electron beam (SAEB) was detected by a collector behind the flat anode. The amplitude-time characteristics of the voltage and SAEB current were studied with subnanosecond time resolution. The maximum pressure at which a SAEB is detectable by collector was ∼1 MPa. This pressure increases with decreasing the voltage rise time. The waveforms of the discharge and runaway electron beam currents was synchronized with the voltage pulses. The mechanism of the runaway electron generation in atmospheric-pressure gases is analyzed on the basis of the obtained experimental data.

Flexible foils formed by a prolonged electron beam irradiation in scanning electron microscope

The ubiquitous presence of hydrocarbon contamination on solid surfaces alters their inherent physical properties and complicates the surface analyses. An irradiation of sample surface with electron beam can lead to the chemical transformation of the hydrocarbon layer to carbon films, which are flexible and capable of acting as a barrier for chemical etching of an underlying material. The growth of these foils is limited by supply of hydrocarbons to the writing beam position rather than the electron dose or electron beam current. The prepared films can find their applications in fabrication of surface nanostructures without a need of an electron sensitive resist material.

Relativistic twistron based on backward-wave oscillator with modulating reflector and an efficiency of 56%

Using numerical simulation, the operating mode of a relativistic Cherenkov microwave generator of the twistronic type has been demonstrated. The generator includes an electrodynamic system based on a backward-wave oscillator and modulating reflector with nonmonotonous, highly nonuniform energy exchange along the length of the system. The efficiency of power conversion from the electron beam to electromagnetic radiation is 56%, and the electronic efficiency is 66%. For an accelerating voltage of 340 kV and an electron beam current of 3.3 kA, the simulated generation power is 630 MW at a frequency of 9.7 GHz and a guiding magnetic field of 2.2 T.

Ultrafast electron microscopy integrated with a direct electron detection camera.

In the past decade, we have witnessed the rapid growth of the field of ultrafast electron microscopy (UEM), which provides intuitive means to watch atomic and molecular motions of matter. Yet, because of the limited current of the pulsed electron beam resulting from space-charge effects, observations have been mainly made to periodic motions of the crystalline structure of hundreds of nanometers or higher by stroboscopic imaging at high repetition rates. Here, we develop an advanced UEM with robust capabilities for circumventing the present limitations by integrating a direct electron detection camera for the first time which allows for imaging at low repetition rates. This approach is expected to promote UEM to a more powerful platform to visualize molecular and collective motions and dissect fundamental physical, chemical, and materials phenomena in space and time.

0.2-THz Dual Mode Sheet Beam Traveling Wave Tube

Equipping the adjustable horizontal focusing electrodes (FEs), a dual mode electron gun providing different current beams, has been proposed and evaluated. Employing this tunable FE electron gun, a continuous wave (CW)/pulsed dual mode, 0.2-THz sheet beam traveling wave tube (SB-TWT) has been designed. The tube employs a high density and high current sheet beam for pulsed mode operation, and a reduced size and lower current sheet beam for the CW mode. This scheme provides CW mode increased efficiency and higher beam transmission factor than other, more conventional, dualmode techniques such as by changing the RF drive power. Using a 1.2-T uniform focusing magnetic field, both beams are predicted to have excellent transmission factor (more than 99%) to the collector through the 65-mm beam tunnel. Driven by the pulsed, high current electron beam, the 0.2-THz SB-TWT exhibits more than 100-W power over a 20-GHz bandwidth. Driven by the low current electron beam, the tube provides 20-dB gain and 10-W CW output power over the required bandwidth of 0.19 THz-0.21 THz.

Effect of emission on subnanosecond breakdown in a gas diode at low pressure

The paper presents experimental and numerical research results on the operation of gas diode at low pressure. A high dispersion in the runaway electron beam current (from 20 to 100 A) with respect to the average one (∼50 A) is observed for a tubular cathode with a working edge radius of 30 μm, nitrogen pressure of 30 Torr, and an interelectrode gap of 6 mm. Numerical simulation data show that the low beam current (∼20 A) is due to the early electron emission from the cathode (at the stage of low-voltage prepulse), in which the runaway electron beam is formed from the boundary of plasma layer developing early in the breakdown. The high beam current (∼100 A) is due to the delayed electron emission from the cathode, which increases the diode voltage and the runaway electron beam current. In the latter case, the runaway electron beam is formed directly at the cathode.

Formation of Ti-Ta-based surface alloy on TiNi SMA substrate from thin films by pulsed electron-beam melting

TiNi shape memory alloys (SMAs) are unique metallic biomaterials due to combination of superelastisity and high corrosion resistance. Important factors limiting biomedical applications of TiNi SMAs are a danger of toxic Ni release into the adjacent tissues, as well as insufficient level of X-ray visibility. In this paper, the method for fabrication of protective Ni-free surface alloy of thickness ∼1 μm of near Ti70Ta30 composition on TiNi SMA substrate has been successfully realized. The method is based on multiple alternation of magnetron co-deposition of Ti70Ta30 thin (50 nm) films and their liquid-phase mixing with the TiNi substrate by microsecond low-energy, high current electron beam (≤15 keV, ∼2 J/cm2) using setup RITM-SP (Microsplav, Russia). It was found by AES, XRD, SEM/EDS and HRTEM/EDS examinations, that Ti-Ta surface alloy has an increased X-ray visibility and gradient multiphase amorphous-nanocrystalline structure containing nanopores.

Multiscale models of metal behaviour and structural change under the action of high-current electron irradiation

We present our models of the tensile fracture of metals in the solid and molten states, the melting and the plastic deformation of the solid metals. Also we discuss implementation of these models for simulation of the high current electron beam impact on metals. The models are constructed in the following way: the atomistic simulations are used at the first stage for investigation of dynamics and kinetics of structural defects in material (voids, dislocations, melting cites); equations describing evolution of such defects are constructed, verified, and their parameters are identified by means of comparison with the atomistic simulation result; finally, the defects evolution equations are incorporated into the continuum model of the substance behaviour on the macroscopic scale. The obtained continuum models with accounting of defects subsystems are tested in comparison with the experimental results known from literature. The proposed models not only allow one to describe the metal behaviour under the conditions of intensive electron irradiation, but they also allow one to determine the structural changes in the irradiated material.

Effect of emission on subnanosecond breakdown in a gas diode at low pressure

The paper presents experimental and numerical research results on the operation of a gas diode at low pressure. A large scattering in runaway electron beam current (from 20 to 100 A) with regard to the average (∼50 А) is observed for a tubular cathode with a working edge radius of 30 μm, nitrogen pressure of 40 mbar, and interelectrode gap of 6 mm. Numerical simulation data show that the low beam current (∼20 A) is due to early electron emission from the cathode (at the stage of low-voltage prepulse) in which the runaway electron beam is formed from the boundary of a plasma layer developed early in the breakdown. The high beam current (∼100 A) is due to delayed electron emission from the cathode, which increases the diode voltage and the runaway electron beam current. In the latter case, the runaway electron beam is formed directly at the cathode.

Stability of runaway electron beam currents in nitrogen at 100 Torr. Experiments and numerical simulation

This paper reports on a series of identical experiments and on a respective particle-in-cell and Monte Carlo simulation to investigate the stability of runaway electron beam currents produced in nitrogen at a highly inhomogeneous electric field. The experiments demonstrate a strong effect of cathode emissivity on the beam current. The numerical simulation shows that the cathode emissivity influences not only the current of the beam but also the mechanisms of its formation.

Demonstration of narrowband X-ray beam by inverse Compton scattering with stored spontaneous emission

We achieved the generation of narrowband X-ray beams by inverse Compton scattering using stored spontaneous emission and electron bunches in the infrared free-electron laser system of the storage ring NIJI-IV. Using stored spontaneous emission with a resonant wavelength of 1530 nm and an electron beam with an energy of 310 MeV, an X-ray beam with the energy spread of approximately 10% and the Compton edge of 1.2 MeV was observed using a LaBr3(Ce) scintillation detector in the 3-bunch operation. X-ray beams were generated by inverse Compton scattering using stored spontaneous emission in the full-bunch (16-bunch) operation, and an increase in the bunch number is shown to be effective for increasing the Compton X-ray yield. The total yield of the Compton X-ray beam reached 3.1 × 104 photons/s at the electron-beam current of 43.5 mA in the full-bunch operation. These experimental results are likely to be useful for the development of narrowband X-ray beams with energies above 1 MeV, for use in energy recovery linacs and third-generation storage rings.