Beam Current Values Research Articles

A Novel Method for Rigorously Analyzing Beam Loading Effect Based on the Macro-Particle Model

The beam loading effect is a considerable issue for a high average current beam. We apply a novel method without utilizing the specious beam current value to rigorously analyze the beam loading effect in S-band linacs. By tracking every macro-particle's state and using the energy conservation law, power dissipated from the beam is calculated in each cell. In the new particle-based algorithm, the concept of equivalent beam current is proposed. Its value is not constant and it has a small variation through the accelerating structure. Also, we introduce the iteration algorithm as comparison and we find that the two algorithms coincide with each other very well.

Investigation of contactless electron transmission through dielectric channels

The effect of the contactless transmission (guiding) of 10 keV electrons through cylindrical dielectric channels and planar channels formed by glass plates is studied. The capture and propagation of an electron beam along the channel axis, usual in these cases, are observed in the experiments with two plates. The deviation of the reflection angle from the specular angle and its dependence on the plate length and beamcurrent value under beam reflection from a single plate are investigated.

Improving the survivability of Nb-encapsulated Ga targets for the production of 68Ge

At the Los Alamos Neutron Science Center (LANSCE) Isotope Production Facility (IPF), radioisotopes are produced for medical, scientific, and industrial applications by irradiating various targets with a 100MeV, 230μA proton beam. The medical isotope germanium-68 is produced by irradiating Nb capsules containing molten Ga target material. During irradiation, the Nb is subjected to intense radiation damage, corrosive attack by Ga, and mechanical and thermally-induced stresses for an extended period. Maintaining the structural integrity of the Nb target capsules during irradiation is crucial to contain the molten Ga target and the radioisotope product. In the present work, we focus on potential material related factors and assess the effect of the Nb stock material on target durability. We do so by comparing post-irradiation target mortality information to data collected during pre-irradiation ultrasound testing and X-ray imaging. We also explore possible failure mechanisms by using MCNP6 simulations and ANSYS codes to predict the induced atom displacement levels, hydrogen gas built-up, temperature distribution, and mechanical stresses. Our analysis, performed entirely in the context of an aggressive production program that allows for only limited diagnostic interference, suggests that using Nb stock with reasonably large and uniform grains is the most important factor in reducing early target failure at integrated beam current values <18mAh and random failure at the face of the rear window at <60mAh. We discuss possible failure mechanisms of failed targets that were fabricated using the same stock material and grain structure and then irradiated to integrated beam current values of up to 60mAh and more. Based on these observations, we have enacted new specifications for Nb stock material quality, target design, and limits on integrated beam current. These changes have resulted in improved Nb capsule survivability.

Cathodoluminescence and Electroluminescence of Semiconductor Structures in SEM

Cathodoluminescence (CL) in SEM and electroluminescence (EL) techniques are widely used for investigation of optical properties of electronic structures. It is assumed that the CL signal represents the local properties of the region irradiated by the electron beam. However, this assumption is true if there is no electric field in the excitation region. In the opposite case the electron-hole pairs generated by the electron beam are separated by the electric field and the local voltage source is generated. The voltage is distributed all over the structure through resistance paths and it causes a current flow, which presence affects the registered CL signal. A range of this effect depends on the resistance distribution within the structure and on the value of electron beam current. The range may be much longer than the diffusion length of minority carriers. When EL signal is measured in SEM, it represents the mean properties of the whole structure. The comparison of the CL results with the EL ones detected in SEM gives valuable information about the examined structures, as will be shown in the present investigations. The AlGaAs/GaAs heterostructures with 8 nm InGaAs quantum well have been examined. For that aim also special test structures for CL and EL measurements have been formed on standard epitaxial structures.

Self-excitation and establishment of generation in a two-section relativistic diffraction generator

Starting conditions for generation and features of oscillation establishment in a relativistic diffraction generator for different beam current values are numerically studied using the matrix multimode method. The efficiency boost and generation frequency stabilization are found to arise at overlap of two electron mechanisms—excitation of the fundamental oscillation of the system in the region of the 2π-type frequencies with a resonance near the cutoff frequency of the bulk mode nearest to the 2π type in a smooth waveguide.

Pulsed ion beam parameters to ensure maximum coefficients of metal surface erosion

Erosion of metal surface under pulsed ion beams is investigated using a two-phase evaporation model. The coefficients of erosion due to evaporation are calculated for aluminum, iron and copper under irradiation by submicrosecond ion beams of carbon with the initial particle energy within the range 10–1000 keV. The ion energy and ion beam current density values of the most efficient erosive impact are determined.

ナノプロセス用電子ビーム多価イオン源の開発 ＩＩ

An Electron beam ion source was developed for the application to nanoprocesses using highly charged ions. The ion source has been modified from the original design to approach the designed value of electron beam current, and presently the ion source can be operated with electron beam current up to 150 mA. Ion beam intensity of Arq+ with relatively lower charge states (q<13) exceeds 1 nA, however higher charge states are suppressed due to the presence of residual gases.

Optimisation of cold cathode ion source model

This paper represents the results of the optimisation of cold cathode ion source model with 5 cm extraction aperture diameter. In this model, the glow discharge is utilised for generation of electrons in the cathode of the ion source. The various models with different lengths of cathode and anode are tested. The shortest model with 4.5 cm in length of cathode and anode each shows satisfactory operation and can be used in cases when the high values of extracted ion current are not required. The best model from the point of view of ion beam current value and efficiency of the discharge is the model with cathode length of 7 cm and anode length of 7 cm. In this case, the obtained maximum ion beam current is 110 mA when the discharge current is 1000 mA. In case when moderate values of extracted ion beam current are necessary, it is possible to operate the ion source even without the anode magnetic system.

Effect of the zero spatial harmonic in a slow electromagnetic wave on operation of relativistic backward-wave oscillators

A linear theory of resonant backward-wave oscillators (BWOs) that takes into account the zero spatial harmonic is developed. It is shown that, depending on the phase shift, this harmonic can either increase or decrease the starting current of the device. The nonlinear theory shows the same effect of the phase shift on the maximum efficiency of the BWO. The numerical analysis of nonstationary processes has also demonstrated the effect of the phase shift on the range of beam current values in which the BWO operates in a steady-state single-frequency regime. The effect of boundary conditions at the cathode end of the slow-wave structure on the phase shift between harmonics is also analyzed.

The effect of initial microstructure on heat-affected zone microfissuring in Incoloy 903

Studies were undertaken on electron beam welded thermomechanically processed Incology 903 with varying proportions of duplex grain size distributions, to determine quantitatively the effect of variation in the volume fraction of fine grains to warm worked grains on heat-affected zone (HAZ) microfissuring. Extensive microfissuring was observed in samples consisting primarily of large warm worked grains, which, however, could be minimized by increasing the proportion of the fine recrystallized grains outlining the large warm worked grains. Microfissuring was also observed to be reduced by decreasing the welding speed for any given value of electron beam current. A solidification structure composed of γ/carbide eutectic reaction was observed on the boundaries that developed microfissures. The fine grain boundaries that were devoid of microfissures exhibited liquid film migration and formation of niobium-enriched γ phase and were devoid of γ/carbide eutectic constituents. It is suggested that one of the major causes of minimal microfissuring on fine grains in Incoloy 903 is due to the occurrence of liquid film migration towards curvature on some of the grain boundaries. The existence of substantial mean grain boundary curvature on the fine grains is thus the major factor responsible for the reduced microfissuring in Incoloy 903.

Optical observations of the beam-plasma discharge phenomenon

Spectroscopic observations of optical emissions from the beam-plasma discharge (BPD) phenomenon were made with NASA's vacuum chamber facility, at the Johnson Space Center, configured to simulate the physical conditions of magnetospheric electron beam injection into the ionospheric/upper-atmospheric environment. Nonlinear N 2 and N + 2 optical emission growth rates (with respect to incremental electron beam current values) were observed from the chamber gas during transition to the BPD state. For electron-beam currents ( I) near the BPD transition value ( I c ), the band emissions from the chamber gas produced by relatively low energy (⩽ 50 eV) electrons interacting with N 2 were anomalously more intense than those requiring higher energy (> 100 eV) electrons to excite them. For I ⪢ I c , the optical emissions increased linearly with I (as was the case for I < I c ) and their ratios decreased significantly from the peak values attained when I ≈ I c ). These observations suggest that during BPD some of the energy of the primary electron beam is efficiently transferred, via wave-particle interactions, to local electrons produced through ionization of the chamber gas; the resulting suprathermal electrons provide an additional source of excitation for the relatively low energy states ( A, B and C) of N 2. Such nonlinear excitation of upper atmospheric gas may occur in certain auroral events wherein the current due to the precipitating electrons approaches a value close to I c . It may explain the unusual red enhancement in the spectral distribution of optical radiation from type-B red-lower-border auroras, and the formation of the auroral thin layer.

Performance investigation of a focused ion beam for sputter deposition

Recently, focused ion beam sources have been widely used in various film deposition. This paper introduces the performance investigation of a focused ion beam source for sputter deposition. A 3.5-cm-diam ion source was used in the experiments. The results of the tests show that (1) at given ion beam energy there is an optimum value of ion beam current which gives the maximum value of ion beam current density; (2) at higher beam energy the peak of ion beam current density is higher and is obtained at larger beam current; (3) the ion beam current density increases with increasing magnetic flux density but there is an optimum value of magnetic flux density, and (4) the ion beam current density increases with increasing discharge voltage and gas flow rate, decreases with increasing accelerator voltage. Finally, these results are analyzed and discussed.

A modified electrostatic ion source

The oscillating electron ion source has been modified to obtain an improved form by extracting more low-energy ions from it. It has been found that biasing of the oscillating ions by applying a negative potential to the cathodes would increase the output beam current to about three times its value for the same ion source plasma parameters, whereas applying the same negative potential on the screens and Faraday cups, while the cathodes connected to earth will increase the beam current five times its value. The discharge starts at lower values of discharge voltage, or higher values of beam current are obtained at the same value of discharge voltage as the applied negative potential is increased. It is concluded that the electrode configuration constitutes a convergent lens when the negative potential on the screens and Faraday cups is only one-ninth as large as that of the positive anode electrode.

Production of needle-type liquid-metal ion sources and their application in a scanning ion muscope

A tungsten wire is electrochemically etched in NaOH to produce tip radii of 4–10 μm for use in liquid-metal ion sources (LMIS). To ensure complete wetting of the needle with the liquid metal (Sn, Ga), the needle has to be annealed at 800–1000°C by electron bombardment in a vacuum. It is then immediately dipped into the liquid metal in the same vacuum chamber. An anode prepared in this way is part of a triode system, followed by an octupole stigmator, an electrostatic einzel lens and the scanning unit. Upon application of a high voltage the liquid metal will form a Taylor cone at the needle tip. In the resulting high electrical field ions are extracted through field evaporation. Typical beam current and spot size values during scanning ion muscope (SIM) operation are 2.5 μA and 10 μm respectively. An Everhart-Thornley detector and a quadrupole mass spectrometer are available to allow analysis of secondary particles emitted from the target.

Ion extraction systems: optics and design

Abstract The ion beam formation process and extraction systems are treated in this paper from a rather practical standpoint, with emphasis on, but not strict limitation to, the case of high-current beams extracted from plasma ion sources. Some basic principles of ion extraction optics are discussed and beam quality parameter definitions outlined. Based on the characteristics of an actual extraction system, a general scaling model is then derived for a wide range of beam current and energy values. It allows a determination of the main parameters of systems to be built under specific constraints, or a judgment of the performance of an existing system in terms of one figure of merit. Finally, some examples of special-purpose systems are presented, including multi-aperture, slit, and compound systems. The detailed mechanical contours of these systems are shown to scale in all cases.

High-current ion sources for ion implantation

Ion beam techniques have now reached the limit imposed by the currently used ion sources, due to the trend towards higher target throughput rates as well as the need for higher irradiation doses for special applications. The next generation of implanters will routinely make use of 10–100 mA beams at energies between about 30 and 250 keV, and 1–10 mA above 1 MeV. Apart from beam current and brightness values, the criteria to judge ion sources for industrial applications are: stability, lifetime, and general reliability; range of available ion species, and fraction of multiply charged ions to upgrade existing accelerators towards higher energies. In this paper, positive-ion source development concepts are outlined in view of these criteria, and performance data are given for existing sources that deliver the mentioned beam currents and can be combined with various accelerators to cover the energy range in question.

High resolution, low-voltage probes from a field emission source close to the target plane

In conventional electron beam systems the minimum value of beam diameter and the maximum value of beam current is set by lens aberrations, beam brightness, and by space charge interaction over many centimeters. The limits are more serious as the beam voltage (V0) is reduced. The scanning tunneling microscope (STM) represents a drastic change in electron beam configuration in that the path length is of the same order as the beam radius. We have modeled a modified STM configuration as a field emitting spherical electrode close to the target plane for values of accelerating potential (V0) in the range 50–1000 V. For a given value of V0 and maximum field E0 there are corresponding optimum values of sphere radius R and sphere-to-plane separation S. It appears that it should be possible to confine a beam of 100 V electrons to a radius of 0.02 μm with a current limited only by practical effects at the target or plane.

Thermal sensitive paper as a diagnostic for intense relativistic electron beam dynamics

Thermal sensitive paper has been used as a diagnostic for an intense relativistic electron beam propagating in a rippled magnetic field. The E(r)xB(z) rotation of the beam has been measured from the exposed pattern on the thermal paper and used to calculate the electrostatic field of the beam E(r), and the corresponding values of electron density and beam current. Exposed strips of thermal paper show longitudinal modulation of the radial electron velocity with a period corresponding to that of a rippled magnetic field; modulation of the radial electron velocity at the cyclotron frequency has also been observed.

Some Reliability Characteristics of CRT Cathode Assemblies

Six types of CRT cathode assembly are described, including the traditional cap-cylindrical shank-ceramic wafer assemblies which have been in use for many years and two of the more modern heat-shield assemblies. The range of operating temperature is no larger than 60 K for either of the heat-shield assemblies and may be as large as 295 K for the older types. Spontaneous variations in temperature of up to 97 K, downward drifts in temperature of as much as 40 K after peak temperature has been reached, and increases of up to 154 K as a result of reprocessing have been observed. These effects are generally much smaller with the heat-shield assemblies. The 60 K range of the heat-shield assemblies implies a variability of more than 4 to 1 in life and performance. The ranges of the older assemblies imply a variability of from 64 to 1 to more than 1000 to 1. The spontaneous variations in temperature are responsible for appreciable changes in the grid bias required to obtain a fixed value of beam current, or, conversely, large changes in the beam current obtained at a fixed grid bias.

Amplification of the Traveling Wave Tube

A method is presented for solving the equation which determines the modes of a helix with an electron beam [Chu and Jackson, Proc. Inst. Radio Engrs. 36, 853 (1948)]. The essential idea is to consider the modes as a perturbation of the modes produced by the cold helix. From the solution of the equation, the dependence of the amplification factor of the tube upon the geometrical parameters and the operating conditions is explicitly determined. The solution shows also that the tube will not amplify for too large values of the dc electron beam current.