Electron Beam Source Research Articles

First-principles dynamic simulations of field emission from carbon nanotubes on gold substrate

In order to investigate the usability of carbon nanotubes as electron-beam sources, we carry out dynamic simulations of the field emission of open-tip armchair single-wall carbon nanotubes in a fully first-principles manner. By including a metallic substrate in the structure, the charge transfer from the substrate to the carbon nanotubes under external electric fields is self-consistently taken into account and the description of the potential becomes more realistic. It is found that $s$-like $\ensuremath{\pi}$ states near the Fermi level make a major contribution to the emission current. The emission patterns of the $s$-like $\ensuremath{\pi}$ states take the shape of a small spot at the center and a ring around it.

전계방출 주사전자 현미경의 전자광학계 유한요소해석

A scanning electron microscope (SEM) is well known as a measurement and analysis equipment in nano technology, being widely used as a crucial one in measuring objects or analyzing chemical components. It is equipped with an electron optical system that consists of an electron beam source, electromagnetic lenses, and a detector. The present work concerns numerical analysis for the electron optical system so as to facilitate design of each component. Through the numerical analysis, we investigate trajectories of electron beams emitted from a nano-scale field emission tip, and compare the result with that of experimental observations. Effects of various components such as electromagnetic lenses and an aperture are also discussed.

Floating bare tether as upper atmosphere probe

Use of a conductive bare tape electrically floating in low Earth orbit as an effective electron beam source to produce artificial auroral effects, free of problems that mar standard beams, is considered. Ambient ions impacting the tape with keV energies over most of its length liberate secondary electrons that race down the magnetic field, excite neutrals in the E layer, and result in auroral emissions. The tether would operate with both a power supply and a plasma contactor off at nighttime; power and contactor would be on at daytime for reboost. Tomographic analysis of auroral emissions from the footprint of the beam, as observed from the spacecraft, can provide density profiles of dominant neutral species in the E layer. A characteristic tether system, at altitude ∼300 km and moderate orbital inclination, would involve an aluminum tape with a length of ∼20 km, a width of ∼15 mm, and a thickness of ∼0.2 mm for a full‐system mass around 1200 kg, with two thirds going into the power subsystem.

Plasma localization in an extended hollow cathode of the plasma source of a ribbon electron beam

The plasma density distributions in the slit aperture of the extended rectangular hollow cathode of the source of a ribbon electron beam are investigated experimentally. It is found that a local maximum whose parameters are determined by the discharge current appears in the density distribution when the slot width is less than a certain threshold value. This maximum results in an inhomogeneous current density distribution in the beam. It is shown that the appearance of the local maximum in the plasma density is related to the overlapping of the ion sheaths in the slit aperture of the hollow cathode.

Time-Resolved Spot Size Measurements From Various Radiographic Diodes on the RITS-3 Accelerator

Sandia National Laboratories is leading an intensive research effort into fielding and diagnosing electron-beam flash radiographic X-ray sources. Several X-ray sources are presently being studied, including the self-magnetic pinched diode, the immersed Bz diode, and the plasma-filled flat cathode (paraxial) diode. These studies are being carried out on RITS-3, an inductive voltage adder accelerator capable of delivering 140 kA at 5 MV with a radiation pulse of 70-ns full width at half maximum. The interactions of the electron beam with plasmas created at the anode and/or cathode, for the self-pinched and Bz diode or in the plasma cell for the paraxial diode, can greatly effect the temporal behavior of the radiation spot size. Measuring the dynamic behavior of the beam size and coupling this with theoretical models of the beam plasma interactions can lead to improvements that can be made in these sources. A time-resolved spot size diagnostic (TRSD) has been developed and fielded on RITS-3. This diagnostic consists of a linear array of scintillating fibers, shadowed by a tungsten rolled edge. The scintillating array is optically coupled to a streak camera, and the output is recorded on a charge-coupled device. This paper presents a description of this second-generation TRSD as well as data on the time history behavior of the spot sizes for these three diodes

Bent-crystal Laue spectrograph for measuring x-ray spectra (15<E<100keV)

A bent-crystal Laue {or Cauchois [J. Phys. Radium 3, 320 (1932)] geometry} spectrograph is a good compromise between sensitivity and spectral resolution for measuring x-ray spectra (15<E<100keV) from large area x-ray sources because source-size spectral broadening is mitigated. We have designed, built, and tested such a spectrograph for measuring the spectra from electron-beam x-ray sources with diameters as large as 30cm. The same spectrograph geometry has also been used to diagnose (with higher spectral resolution) smaller sources, such as x-ray tubes for mammography and laser-driven inertial fusion targets. We review our spectrograph design and describe the performance of different components. We have compared the reflectivity and spectral resolution of LiF, and Ge diffracting crystals. We have also measured the differences in sensitivity and spectral resolution using different x-ray to light converters (plastic scintillator, CsI, and Gd2O2S) fiber optically coupled to an intensified charge-coupled device camera. We have also coupled scintillating fibers to photomultiplier tubes to obtain temporal records for discrete energy channels.

Microfabrication processes on cylindrical substrates – Part II: Lithography and connections

Cylindrical microfabrication offers the opportunity to fabricate electrical or mechanical devices around the surfaces of cylinders. Standard processes developed for planar substrates such as silicon wafers must be adapted to curved surfaces. This paper focuses on lithography of and connections to cylinders. Results from lithographic testing includes dose exposure curves using laser and electron beam sources as well as the minimal effects of surface curvature on linewidth. Bonding included ultrasonic wedge bonding, silver epoxy, and solder paste. Electrical and mechanical characteristics of these bonding methods are presented.

Dose control circuit for digital electrostatic electron-beam array lithography

This paper demonstrates a technique for controlling the electron emission of an array of field emitting vertically aligned carbon nanofibers (VACNFs). An array of carbon nanofibers (CNF) is to be used as the source of electron beams for lithography purposes. This tool is intended to replace the mask in the conventional photolithography process by controlling their charge emission using the "Dose Control Circuitry" (DCC). The large variation in the charge emitted between CNFs grown in identical conditions forced the controller design to be based on fixed dose rather than on fixed time. Compact digital control logic has been designed for controlling the operation of DCC. This system has been implemented in a 0.5 ?m CMOS process.

Electron beam formation in an anomalous glow discharge

Scaling parameters that account for the efficient formation of electron beams in sources based on an anomalous glow discharge are considered, and the processes leading to the violation of scaling laws are analyzed. Estimates show that the working pressure range in such sources can be increased significantly. The results obtained can be used to optimize discharge regimes with required electron beam parameters. It is demonstrated that sources with plane-parallel continuous electrodes can operate at pressures as high as 100 Torr (which is one to two orders of magnitude higher than that in similar existing electron beam sources), provided that parasitic spark breakdowns at the insulator near the discharge cathode are suppressed. The sources designed can be used for direct excitation of laser working media or their preionization by soft X-rays.

Combined target-ion source unit for production of rare nuclides

A combined target-ion source unit (ionizing target) has been developed for the on-line production of radioactive single-charged ions. The target is able to withstand temperatures of up to 2500 °C and also acts as an ion source of surface, electron-beam, and laser ionizations. Using tantalum foil as a target material, the on-line combined target-ion source unit efficiency, which is the product of the ionization and release efficiencies, has been obtained for neutron-deficient isotopes of Eu, Gd, and Yb. These nuclides were ionized by the surface ionization inside a hot tungsten target container, holding tantalum foils as a target material. The results of the combined target-ion source unit use for on-line laser resonant ionization spectroscopy investigation of neutron-deficient Gd isotopes have been also presented. For neutron-rich isotopes produced from a high-density UC target, which were ionized by the surface ionization inside the target container, the ionization efficiency values have been obtained close to 100% for Rb and Cs and 10% for In. For Ag and Sn neutron-richisotopes, the values of the electron-beam ionization efficiency in the volume of the targetcontainer, correspondingly equal to 4% and 2%, have been obtained.

The REX-ISOLDE charge breeder as an operational machine

The charge breeding system of radioactive beam experiment at ISOLDE (REX-ISOLDE), consisting of a large Penning trap in combination with an electron-beam ion source (EBIS), is now a mature concept after having delivered radioactive beams for postacceleration to a number of experiments for three years. The system, preparing ions prior to injection into a compact linear accelerator, has shown to be versatile in terms of the ion species and energies that can be delivered. During the experimental periods 2004 and 2005 a significant part of the ISOLDE beam time was dedicated to REX-ISOLDE experiments. Ion masses in the range between A=7 and 153 have been handled with record efficiencies. High-intensity as well as very-short-lived isotope beams were proven to be feasible. Continuous injection into the EBIS has also been successfully tested. Two means of suppressing unwanted beam contaminations were tested and are now in use. In addition, the experience gained from the trap-EBIS concept from a machine operational point of view will be discussed and the limitations described.

A miniature electron-beam ion source for in-trap creation of highly charged ions

Measurements of the anomalous magnetic moment of the electron bound in hydrogen-like ions with spinless nuclei have proven to be highly sensitive tests of corresponding calculations based on bound-state quantum electrodynamics. Currently, an experiment on hydrogen-like calcium Ca19+40 is being prepared, which is expected to yield a precision in the 10−9 level for the electronic g factor. This experiment makes use of an in-trap electron-beam ion source with which the charge breeding of the ions is performed by electron-impact ionization.

Charge breeding of isotope on-line-created radioactive ions using an electron cyclotron resonance ion trap

In the coming years huge ion-beam projects are foreseen. They deal with specific isotope on-line (ISOL) beams such as ISOL-created radioactive ions. The beam intensities are exceptionally high (>1012ions∕s), the radioactive lifetimes are short (⩽1s), and the ion energy is very high (⩾150GeV∕u). In general in order to minimize the size of the accelerator one needs highly charged ISOL ions and therefore charge breeders are a must. In contrast with the CERN system, utilizing a Penning trap and an electron-beam ion source charge breeder (where the maximum ion beam cannot exceed 106ions∕s) the Grenoble group launched in 1995 an electron cyclotron resonance (ECR) system capable of storing 1012ions∕s and delivering highly charged ISOL ions. In this article we show that this storage is possible for low-ion-energy ISOL ions following classical slowing down theory. In this case the injected ISOL ions are slowed down by ion-ion collisions which yield ion storage inside the ECR plasma, but also charge breeding by the energetic ECR electrons bombarding the slowed down ions.

Study of a liquid metal ion source for external ion injection into electron-beam ion source

A liquid metal ion source (LMIS) has several attractive features as an external injector of primary ions (mostly metallic ions) into electron-beam ion source (EBIS). It does not use a buffer gas and therefore it provides only a very small gas load to the system; its control and operation are simple, power consumption does not exceed 10W, and beam pulses are very stable. A gold-silicon LMIS was supplied by FEI Company (http://www.feibeamtech.com/pages/liquid.html) and tested in a pulsed regime with an ion pulse width of 2ms and frequency up to 5Hz. Total extracted ion current reached 50μA and the normalized emittance of the total ion beam was 0.05πmmmrad. The results of this test, as well as results of experiments in which this ion source is used for injection of Au ions into EBIS, are presented.

Experimental study of electron- and ion-beam properties on the BNL electron-beam ion source and comparison with theoretical models

The maximum achievable perveance of the electron beam in the ion trap region and in the electron collector of the BNL Test electron-beam ion source (EBIS) has been measured for different electron-beam currents. These perveances determine the maximum degree of electron-beam retardation in these areas, which limits for the first case the maximum capacity of the ion trap, and for the second case the minimum dissipated power on the electron collector, for a given electron current. The results are compared with the results of optical simulations of the electron beam. In another set of experiments, data on Test EBIS ionization efficiency for different experimental conditions were obtained. These results are presented and compared with calculations based on stepwise ionization assuming 100% ion confinement in the trap. Finally, a series of experimentally measured longitudinal-energy spectra of the extracted ion beam are presented, and will be compared with the calculated energy spread.

Optical beam profile diagnostic for low energy, long pulse, moderate current electron beams

Currently ongoing at Los Alamos National Laboratory is a program to develop high-power, planar 100–300GHz traveling-wave tubes. An enabling technology for this effort is a sheet electron beam source and much of our effort has been geared toward understanding sheet beam generation and transport. Toward this end we have developed a robust, high resolution optical diagnostic for measuring the transverse density profiles of our electron beams. The diagnostic consists of a thin metal foil followed by an YAG:Ce or YAP:Ce scintillator crystal, both mounted on a vacuum actuator that allows us to position the foil/scintillator combination at arbitrary positions along the beam’s longitudinal axis. The electron beam strikes the metal foil and is stopped, generating Bremsstrahlung x rays that are imaged by the scintillator crystal. This image is then captured by an optical system using a high-speed, intensified gated camera. Using this diagnostic, we have measured beam profiles with resolutions as low as 0.05mm from ...

Characteristics of treatment of diesel flue gas by irradiation of pulsed, intense relativistic electron beam

Diesel flue gas in a chamber spatially isolated from electron-beam source has been successfully treated by pulsed, intense relativistic electron beam (PIREB). A flue gas treatment chamber, 1.6-m isolated from the PIREB source, is filled up with the diesel flue gas at the pressure of 200 kPa, and is irradiated by the PIREB [2 MV, 0.1 kA, 65 ns (full-width at half-maximum)]. We have obtained that 85%-97% of nitrogen oxide (NO/sub x/) is removed by firing 10 shots of the PIREB irradiation. The net energy efficiency of NO/sub x/ removal has been found to be 210 g/kWh. It is found that the rapid reduction of NO/sub x/ at the first shot of the PIREB irradiation is caused by the effect of water vapor in the diesel flue gas. The treatment of sulfur dioxide (SO/sub 2/) by the PIREB irradiation depends strongly on the initial concentration of SO/sub 2/ in the diesel flue gas.

Source of low-energy coherent electron beams

The coherence of the electron beam emitted at a low applied field from a single micrometer size mineral particle deposited on a carbon membrane is demonstrated by holography experiments. The experimental design combining this electron source with a conventional electrostatic lens system opens a way to holographic microscopy with low-energy electrons.

Tether-induced airglow: Collisionless effects

Martinez-Sanchez and Sanmartin [1997] showed that a bare conducting tether can be used as a source of an energetic electron beam. Interacting with the E region atmosphere, the beam should produce airglow thus making possible to deduce the neutral density on a continuous basis. Fujii et al. [2005] suggested that this idea be tested in a specially-designed sounding rocket experiment. We show that collisionless beam-plasma interactions (BPI) complement direct impact, leading to appreciable green-line (557.7 nm) emissions in the F region. In the E region, BPI develops near the entry in the valley, resulting in a narrow layer of strongly-elevated and airglow. Besides, neutralizing electric currents carried by ionospheric electrons in the valley can become unstable or even insufficient to compensate the beam current. Developing plasma waves inhibit neutralizing currents. In the extreme case, the beam might be locked in the valley (the 'virtual cathode'). In addition to optical observations, these effects can also be observed by radiophysical means.

Laser Photo-Cathode RF-Gun

High quality beam generation project based on High-Tech Research Center Project, which has been approved by Ministry of Education, Culture, Sports, Science and Technology in 1999, has been conducted by advance research institute for science and engineering, Waseda University. In the project, laser photo-cathode RF-gun has been selected for the high quality electron beam source. RF cavities with low dark current, which were made by diamond turning technique, have been successfully manufactured. The low emittance electron beam was realized by choosing the modified laser injection technique. The obtained normalized emittance was about 3 mm mrad at 100 pC of electron charge. The soft X-ray beam generation with the energy of 370 eV, which is in the energy region of so-called “water window” , by inverse Compton scattering has been performed by the collision between IR laser and the low emittance electron beams.