Electrostatic Focusing System Research Articles

A synchroscan streak tube with high deflection sensitivity

A synchroscan streak tube with high spatiotemporal resolution and high deflection sensitivity is proposed, which contains several innovation designs. Some measures are taken to improve the imaging performances of the streak tube. Firstly, in order to obtain a high deflection sensitivity, the difference in voltage between the photocathode and anode and the length of the equipotential region of the streak tube are reduced as much as possible. Secondly, by introducing a hyperfine grid behind the cathode, reasonably designing the voltages applied to the six-electrode electrostatic focusing system, and moving the electron beam crossing point to the entrance of the deflection plates, the temporal dispersion and the temporal distortion of the streak tube are reduced, and the spatiotemporal resolution of the streak tube is improved. Besides, the streak tube is technically analyzed by tracking the temporal and spatial distribution of electrons under an operating voltage of 7000 V with the aid of computer simulation technology (CST) software. The results show that the deflection sensitivity is 125 mm/kV, the physical temporal resolution is better than 1.83 ps @MTF = 10%, and the static spatial resolution on the photocathode is better than 38 lp/mm @MTF = 10% over the effective photocathode area with a size of 10 mm × 4 mm. By applying a synchronous scanning voltage with a repetition frequency of 250 MHz to the deflection electrode, the results show that the dynamic spatial resolution of the streak tube is better than 16 lp/mm, the limit of the dynamic temporal resolution is 1.39 ps, and two rectangular electron pulses with a size of 10 mm × 20 μm and an interval of 2.3 ps emitted from the photocathode can be well resolved by the streak tube. In addition, the experimental measurements are conducted with a streak tube developed in our laboratory. The results demonstrate that the photocathode of the streak tube can work in the entire visible light region, and the response in the short wavelength region is significantly better than that in the long wavelength region. The static spatial resolution of this streak tube is 40 lp/mm in the center of the photocathode. The temporal resolution of this streak tube is 5.55 ps measured under a synchronous scanning voltage with a repetition frequency of 75 MHz.

A powerful pulsed “point-like” neutron source based on the high-current ECR ion source

The paper presents recent results of a "pointlike" neutron source development based on a D-D fusion in a D-loaded target caused by its bombardment with a sharply focused deuterium ion beam. These developments are undergoing at the Institute of Applied Physics of Russian Academy of Sciences in order to study a possibility to create an effective and compact device for fast-neutron radiography. The last experiments with a beam produced by a gasdynamic high-current ECR ion source and its focusing with a magnetic lens demonstrated that 60 mA of deuterium ions may be constricted to a transversal size of ∼1 mm at the focal plane. With a purpose to improve this result in terms of the beam current and its size, a combined electrostatic and magnetic focusing system is proposed and analyzed. It is shown that the combined system may enhance the total beam current and reduce its footprint down to 0.13 mm. All numerical analysis was performed using the IBSimu code.

The vacuum arc ion source for indium and tin ions implantation into phase change memory thin films.

One of the most prospective electrical and optical nonvolatile memory types is the phase change memory based on chalcogenide materials, particularly Ge2Sb2Te5. Introduction of dopants is an effective method for the purposeful change of Ge2Sb2Te5 thin film properties. In this work, we used the ion implantation method for the introduction of In and Sn into Ge2Sb2Te5 thin films by a Multipurpose Test Bench (MTB) at the National Research Center "Kurchatov Institute"-Institute for Theoretical and Experimental Physics. For Sn and In ion implantation into Ge2Sb2Te5, the following MTB elements were used: a vacuum arc ion source, an electrostatic focusing system, and a system for current and beam profile measurements. The MTB parameters for Sn and In ion implantation and its effect on the material properties are presented. Implanted Ge2Sb2Te5 thin films were irradiated by femtosecond laser pulses. It was shown that the ion implantation resulted in a decrease in the threshold laser fluence necessary for crystallization compared to the undoped Ge2Sb2Te5.

Geometric distortion correction for streak camera imaging

As streak tube imaging is a concentric spherical electrostatic focusing system, geometric distortion is caused by the relative change in radial magnification. This reduces the spatial resolution of imaging. The physical principle of changing the radial magnification of an electronic optical imaging system is analyzed to correct the geometric distortion of the imaging system and to improve spatial resolution. Distortion is corrected using the calibration model of a spherical optical system. The contrast of a reticle intensity image is compared before and after correction, and the ultimate resolution is calculated. Contrast is increased by ∼4 % , and the ultimate resolution is increased by ∼2 lp / mm after correction.

Experimental Study of Electron Gun With Hollow-Anode Vacuum-Arc-Plasma Cathode

This paper presents experimental results of a novel electron gun with a vacuum-arc-plasma cathode used in microwave tube devices. The plasma cathode is based on a vacuum-arc discharge with a novel hollow anode and a Pierce-type electrostatic focusing system. The experimental result shows that this type of electron gun can be used to generate an electron beam of several amperes with a long pulsewidth. Based on the test results, a longer pulsewidth can theoretically be obtained by adjusting the parameters of the vacuum-arc discharge and ignoring heat dissipation and electrode erosion.

Factors enhancing production, extraction and focusing of positive ion beams

In this work, historical review about different kinds of ion sources and their applications are reviewed and discussed. Principle of plasma generation and ion extraction are discussed and investigated. In all types of ion sources, ions are produced by various types of gas discharge including electron collisions with gas particles. The general parameters are a source of electrons, a small region of relatively high gas pressure, an electric field to accelerate the electrons in order to produce an intense gas discharge (plasma) with a relatively high electron and ions density and some mechanism for extracting a collimated parallel high current ion beam. Types of gas discharges and different ionization processes are described. Optimum extraction conditions are reached whenever the plasma meniscus has an optimum curvature for a given current density. Also, different patterns of emittance diagrams for a typical illustration pictures with the aid of SIMION computer program are given. Indeed, theory of ion focusing is given and some examples on electrostatic focusing systems as two and three cylinder lens systems are given. These studies clearly demonstrate the importance of being able to produce, focus and adjust the extraction region in order to ensure high quality, minimum divergence (highly transportable) ion beams. The ion source is evaluated by; the large ion current extracted from it, the large percentage of ions in the beam, the higher degree of ionization inside the atom, the small gas consumptions, and the degree of divergence of the extracted ions must be small.

Studying a kind of portable ultra-bright microfocus x-ray source

This paper studies the properties of a kind of portable ultra-bright microfocus x-ray source with the Monte-Carlo method in detail. The new x-ray source consists of an electron-emission system, an electrostatic focusing system and a metal target. A crystal Lanthanum Hexaboride cathode, a Wehnelt grid and an extracted electrode compose the triode electrode electron-gun system. Two equal radius cylinder electrodes form the focusing system. The key factors determining the focus properties of the electron beam such as the ratio Dw/H, grid bias Vg, and the properties of the extracted electrode are numerically studied. The calculated results reveal that when Dw/H, Vg, the length of the extracted electrode, and the distance between the grid and the extracted electrode equals 5, –0.6 kV, 10 mm, and 8 mm respectively, the electron beam focal spot can be concentrated down to 9 μm in radius and a reasonable focal length about 72.5 mm can be achieved, at the same time, the cathode emission currents can be as high as 30 mA.

Performance of a multi-anode photomultiplier employing a weak electrostatic focusing system (Hamamatsu R8900 series)

We have developed and tested a new type of multi-anode photomultiplier: Hamamatsu R8900-03 series. The main feature of the R8900-03 series is a highly sensitive surface: ∼ 83 % of the physical area. In this paper we report on the results of measurements we performed to check several parameters of this new type of photomultiplier. R8900-03 photomultipliers are devices suitable for experiments where large collection area and uniform detection efficiency are essential characteristics.

Laboratory and in-beam tests of a novel real-time beam monitor for hadrontherapy

Real time monitoring of hadrontherapy beam intensity and profile is a critical issue for the optimization of dose delivery to carcinogenic tissue, patient safety and operation of the accelerator complex. For this purpose an innovative beam monitor, secondary electron emission for low interception monitoring (SLIM) is being developed in the framework of the EC-funded silicon ultra-fast cameras for electrons and gamma sources in medical application (SUCIMA) project. The detector system is based on the secondary emission of electrons by a nonperturbative, sub-micron thick Al foil placed directly in the extracted beam path. The secondary electrons, accelerated by an electrostatic focusing system, are detected by a monolithic silicon position-sensitive sensor, which provides the beam intensity and its position with a precision of 1 mm at a 10 kHz frame rate. The results of the laboratory tests of the first system prototype with thermoionic electrons emitted from a hot Tungsten wire are presented together with the measurements performed on a low intensity hadron beam at the Cyclotron of the Joint Research Centre in Ispra.

Secondary emission monitor for low-interception monitoring (SLIM): an innovative nondestructive beam monitor for the extraction lines of a hadrontherapy center

Real-time monitoring of hadrontherapy beam intensities and profiles is a critical issue for the optimization of the dose delivery to the patient tumour tissue, the patient safety, and the operation of the accelerator complex. For this purpose, an innovative beam monitor, based on the secondary emission of electrons by a nonperturbative, submicrometer-thick Al target placed directly in the extracted beam path, is being proposed. The secondary electrons, accelerated by an electrostatic focusing system, are detected by a monolithic silicon position sensitive sensor, which provides the beam intensity and position with a precision of 1 mm at a 10-kHz frame rate. The conceptual design and the engineering study optimized for hadrontherapy are presented together with the results of the laboratory tests with thermoionic electrons and the first measurements in a hadron beam.

Electron stimulated desorption of negative ions: A time-of-flight experiment

We present a setup for stimulated desorption experiments of negative ions using low energy incident electrons and time-of-flight identification of the desorbed ions. It consists of a pulsed electron gun, an electrostatic focusing system, and a channel plate detector setup. Electron beams down to sub-eV energies can be used due to electrostatic shielding and the compensation of the earth’s magnetic field by a set of Helmholtz coils. The main advantage is the large acceptance for ions of all masses, energies, and desorption angles at the same time, which keeps measuring time reasonably short and allows us to gain information before degeneration of the irradiated sample occurs, even if weak desorption channels are investigated. We demonstrate the power of our setup with first results from a boron doped, (100)-oriented diamond sample, which is partly oxidized and partly hydrogenated with some water contaminations on it. Different binding states of oxygen are disclosed clearly by different desorption thresholds. The C–O binding on oxidized diamond forms a carbonyl group. The 1b2 orbital of water can be seen in a O desorption threshold. The yield of negative hydrogen desorption shows a linear increase for incident electron energies higher than 13 eV. It results from a dipolar dissociation as has been published previously.

Numerical synthesis of an optimal microprobe focusing system

An electrostatic microprobe focusing system including a separated Russian quadruplet and two slits (or diaphragms) is numerically synthesized, taking into consideration all geometrical aberrations of the third order. The matrizant method is applied to minimize the beam spot size for a fixed beam current. For quadrupoles consisting of four copper rods, the electric field inside of the quadruplet is computed using an accurate version of the boundary charge method. The minimum spot size, the appropriate radii of the diaphragms, the distance between them, the effective length and the polarisation for different diameters of the rods are found.

Synthesis of electrostatic focusing and deflection systems

In this article, we present synthesis of an ion beam column as a single entity, based on combined focusing and deflection (CFD). We present seven cases as examples of designing CFD systems by synthesis. Four of those are examples resulting from the a priori given multielectrode approach using a multipurpose multipole system with nine or five units. In these cases, the units have short cylindrical rings or disks cut into segments with geometrically octupole symmetry. In one example we are using the cubic spline method. The other two cases are examples obtained by using both methods in the case of a separate group of axially symmetric electrostatic lenses and electrostatic postlens deflectors. By using a sequential optimization technique combined with the gradient method and the Hooke–Jeeve’s method for a multipurpose multipole system with nine units, our calculations show that one can produce a beam spot radius less than 7 nm and current density of 614 A/cm2, scanned over a 2-mm-square field for a field ionization source. We also present comparison of our CFD system with other published data. The results display substantial improvements, especially for a field ionization source with smaller energy spread ΔU=1 eV and higher acceptance half-angle γ0=2.3 mrad. A sensitivity analysis is given, and the optimum working distances of a given CFD system are presented for the minimum beam spot radius.

A 6.9‐in. high‐resolution projection CRT for an HDTV display

Abstract— The focusing characteristics of a 6.9‐in. projection CRT with a combined electromagnetic and electrostatic focusing system were improved for an HDTV‐display application. To improve the focusing characteristics, a new densely packed phosphor screen with reduced spot growth due to light scattering within the phosphor screen was developed, together with an optimally designed unipotential focusing (UPF) electron gun. Furthermore, a new green phosphor was used to improve the luminance. As a result, beam spot diameters of 0.15 and 0.35 mm were achieved at cathode currents of 0.5 and 5 mA, respectively, with a luminance of 1.3 × 105 cd/m2 at a cathode current of 5.0 mA. An experimental 46‐in. TV set using this projection CRT achieved 900‐TV‐lines horizontal resolution and 1500‐cd/m2 peak luminance. In summary, this projection CRT improves the state of the art of HDTV displays.

Electrostatic focusing and electrostatic deflection systems with reduced aperture aberrations

Electrostatic focusing and electrostatic deflection (SS) electron beam systems have been investigated to increase the resolution of SS camera tubes. SS camera tubes have pattern electrodes formed on their inner walls. The pattern electrodes comprise deflection electrodes and a cylindrical electrode. The deflection electrodes form a band around the inner wall at one end of the tube. Four leads project longitudinally from this band, dividing the cylindrical electrode into four parts. An octopole lens is created around the leads of the deflection electrodes. To increase tube resolution, the electron optical characteristics were evaluated, taking into account the effects of the octopole lens. It was revealed that, due to the octopole lens, the aberration spot is not isotropic and its diameter is about three times that produced by a cylindrical lens. New pattern electrodes with zig‐zag shaped leads were devised. It was found that the aberration spot became almost round and its diameter was reduced to the value obtained with a cylindrical lens.

Theoretical analysis for the relativistic electron beam in a centrifugal electrostatic focusing system

A fundamental analysis of negative-mass instability in the interaction between a relativistic electron beam and TE mode in a centrifugal electrostatic focusing system is given. A kinetic theory is presented and corresponding discussion on practical application is carried out.

Bunching mechanism and kinetic analysis of the relativistic electron beam in centrifugal electrostatic focusing system

This paper proposes an azimuthal bunching-mechanism of a relativistic electron beam with circular orbits in the centrifugal electrostatic focusing system (CEFS). A kinetic theory is given which is in principal agreement with the proposed bunching-mechanism. A new proposal is presented that the electron beam is obliquely injected into CEFS.

Circular-Beam Ray Tracing on a Microcomputer

A computer code is described that traces charged particles through a system of electrostatic and magnetic solenoid lenses. This code requires symmetry about the beam axis, but it incorporates a useful approximation for handling beam emittance and variable space-charge neutralization. It features a friendly and versatile user interface and runs efficiently on an Apple II microcomputer. There are a number of both ray-tracing and matrix beam-transport codes available for simulating particle-beam focusing and transport systems. The popular, linear code TRACE, for example, is a versatile simulation code that can trace outer beam profiles through a variety of both accelerating and transport structures. TRACE provides a first-order approximation for external fields, space charge, and beam emittance. Because the code is so common and runs relatively quickly, it is a valuable tool for checking performance of various designs. However, I wanted a small and simple code that could run on a readily available microcomputer and that would be more interactive than many existing codes. To keep the new code short and simple, it had to be somewhat limited in versatility. The major restriction is that the beam profile must be circularly symmetric, which eliminates quadrupole transport but allows simulation of a useful variety of electrostatic and solenoidal focusing systems.

Computerized optimization of electron-beam lithography systems

An optimization program has been developed for designing combined focusing and dual-channel deflection systems with low aberrations for electron beam lithography. The program can handle any combination of magnetic and electrostatic lenses and deflectors, and uses the damped least squares method for minimizing a weighted sum of squares of aberrations, subject to specified physical constraints. The program has been used to optimize the design of several types of lithography system. The results show that, in many cases, the program can yield designs with extremely low aberrations. For example, a system with one magnetic lens and two deflectors has been found which, at the corners of a 5 mm scan field with 5 mrad aperture, has only 0.19 μm overall aberration before dynamic corrections; by adding an electrostatic retarding field, this can be reduced to 0.12 μm. By adjusting the strengths and positions of the deflectors, several of the aberrations can be individually eliminated, including field curvature. It is also shown that electrostatic subfield deflectors can be added without significantly increasing the aberrations, and a pure electrostatic focusing and deflection system for ion beam lithography has been designed which is limited almost entirely by axial chromatic aberration.

1903. Optimal magnification of the electrostatic focusing system for different methods of electron beam deflection: A E Gershberg and Z I Kuz'minova, Zh Tekh Fiz, 37 (6), June 1967, 1035–1044 ( in Russian)

1903. Optimal magnification of the electrostatic focusing system for different methods of electron beam deflection: A E Gershberg and Z I Kuz'minova, Zh Tekh Fiz, 37 (6), June 1967, 1035–1044 ( in Russian)