Beam Focusing System Research Articles

An automatic beam focusing system for MeV protons

An automatic focusing system for MeV protons has been developed. The focusing system utilises rapid real time proton induced secondary electron imaging of a calibration grid coupled with a modified Gaussian fit in order to take into account the enhanced secondary electron signal from the calibration grid edge. The focusing system has been successfully applied to MeV protons focused using a coupled triplet configuration of magnetic quadrupole lenses (Oxford triplet). Automatic beam focusing of a coarse beamspot of approximately (5×3.5) micrometres in the X and Y directions to a sub-micrometre beamspot of approximately (0.7×0.6) micrometers was achieved at a beam current of about 50pA.

Existence of positive periodic solution for the electron beam focusing system

AbstractIn this paper, we study the mathematical model of electron beam focusing system where a>0,b⩾0 are constants, find conditions for the existence of positive π‐periodic solution of the above equation by using analytical method and comparison theory, and prove the existence of positive π‐periodic solution by the continuously dependent theory of initial value problem. Copyright © 2004 John Wiley & Sons, Ltd.

Gap Bifurcations and Stability Properties in Periodically Focused Beams

We investigate orbital bifurcations of a class of equations describing beam focusing systems. Gaps may exist as we vary the relevant control parameters within which no solution displaying the same periodicity of the external drive exists. We call this nonlinear mechanism gap bifurcations and discuss possible implications to the transport of intense particle beams. The stability of beam transport against both axisymmetric and non axisymmetric perturbations is analyzed.

Differential algebraic method for arbitrary order curvilinear-axis combined geometric–chromatic aberration analysis

The principle of differential algebra is applied to analyse and calculate arbitrary order curvilinear-axis combined geometric–chromatic aberrations of electron optical systems. Expressions of differential algebraic form of high order combined aberrations are obtained and arbitrary order combined aberrations can be calculated numerically. As an example, a typical wide electron beam focusing system with curved optical axes named magnetic immersion lens has been studied. All the second-order and third-order combined geometric–chromatic aberrations of the lens have been calculated, and the patterns of the corresponding geometric aberrations and combined aberrations have been given as well.

Design of a single-channel millimeter-wave interferometer system for Korea Superconducting Tokamak Advanced Research

A simple single-channel horizontal millimeter-wave interferometer has been designed for plasma electron density measurements on the Korea Superconducting Tokamak Advanced Research (KSTAR). To measure line integrated plasma densities of 2×1019 m−2 in the initial phase of the KSTAR, Gunn oscillator frequency of 280 GHz has been chosen to optimize errors due to both vibration on the beam path and refraction in the plasma. To reduce the free propagation length of the probing beam and to obtain small beam width on the vacuum windows, a retractable cassette system for deep positioning of the diagnostic system has been designed, where microwave parts are located as close as possible to the tokamak with a shielding box. A beam focusing system with concave reflecting mirrors has been designed on the cassette and on the inner wall of the tokamak to reduce beam losses and to minimize beam width in the plasma. The estimated total transmission loss is about 25 dB, and beam widths are reduced significantly in the range of 20–50 mm.

Compact focusing system for ion and electron beams

A compact ion and electron beam focusing column design has been developed in Plasma and Ion Source Technology Group at Lawrence Berkeley National Laboratory. The electrostatic ion beam-focusing column was simulated using 2D IGUN [R. Becker and W. B. Herrmansfeldt, Rev. Sci. Instrum. 63, 2756 (1992)] ion extraction and beam transport code. A new method has been developed to include finite ion temperature to the IGUN simulation (Reijonen et al., Proceedings of the LINAC Conference, 2000). The focused ion beam system includes an ion temperature collimator, which eliminates the large angle beam trajectories resulting in a small beam spot size. The small holes in the column electrodes are laser drilled, and are aligned by an optical comparator. Simulations show that focused beam spot size as small as 147 nm is achievable for a 40 keV argon beam. The compact electron beam focusing system consists of three elements: the plasma cathode, an electron temperature collimator (similar to the ion beam temperature collimator), and the focusing electrode elements. The total length of the system is less than 10 mm. The column design is performed using EGUN (W. B. Herrmansfeldt, Slac Report No. 331, 1988), electron beam computation code, and IGUN. Space charge effects as well as the electron temperature are incorporated in the computation. The simulations show that focused beam spot size of 60 nm can be achieved. Both columns use similar type rf-induction plasma generator. P+, BF2+, and O2+ ion species production by such source is also demonstrated.

Adaptive optics based on analog parallel stochastic optimization: analysis and experimental demonstration

Wave-front distortion compensation using direct system performance metric optimization is studied both theoretically and experimentally. It is shown how different requirements for wave-front control can be incorporated, and how information from different wave-front sensor types can be fused, within a generalized gradient descent optimization paradigm. In our experiments a very-large-scale integration (VLSI) system implementing a simultaneous perturbation stochastic approximation optimization algorithm was applied for real-time adaptive control of multielement wave-front correctors. The custom-chip controller is used in two adaptive laser beam focusing systems, one with a 127-element liquid-crystal phase modulator and the other with beam steering and 37-control channel micromachined deformable mirrors. The submillisecond response time of the micromachined deformable mirror and the parallel nature of the analog VLSI control architecture provide for high-speed adaptive compensation of dynamical phase aberrations of a laser beam under conditions of strong intensity scintillations. Experimental results demonstrate improvement of laser beam quality at the receiver plane in the spectral band up to 60 Hz.

Measurement of the beam size at the compact superconducting storage ring by the SR interferometer

The beam size in the compact superconducting storage ring AURORA was measured using the SR interferometer developed by one of the present authors. The spatial coherence of the radiation beam in the visible range was derived from the visibility of the interferogram recorded by a CCD camera and its dependence on the spatial frequency has shown that the beam profile is described by a Gaussian. Analysis of the data has yielded the beam size to be 10.5 μm in the vertical direction, which is unexpectedly small for the storage ring having only a weak beam focusing system.

Existence and uniqueness of elliptic periodic solutions of the Brillouin electron beam focusing system

We find conditions for the existence of an elliptic periodic solution of a singular equation that governs the motion of a magnetically focused axially symmetric electron beam with Brillouin flow by using a monotone iterative scheme starting from a couple of upper and lower solutions on the reversed order. Also, a uniqueness result is proved by using Brouwer degree and index of solutions. Copyright © 2000 John Wiley & Sons, Ltd.

Particle optics for a plasma-based beam focusing and transport system

The ion optical properties of plasma-based final focusing and transport for a heavy ion ICF reactor are discussed. The advantages of plasma-based final focusing are mainly the structure of the field, the beam charge- and current neutralization and the reduction of beam rigidity due to stripping of electrons in the plasma. Two possible focusing modes are considered: the first one, more traditional, is the so-called coherent mode; it is based on the symmetric strong focusing which can be obtained with a cylindrical, or eventually shape optimized, “short” lens. The optical properties are in this case favorable compared to quadrupole lenses. The lens is, in particular, highly insensitive to chromatic aberrations. The disadvantage of this focusing scheme, in an ICF scenario, is the relatively short focal length, which requires a design with the lens integrated in the reactor chamber. A very interesting alternative is the use of a transport plasma channel, which can provide the required standoff distance from the pellet. In this case one can exploit the incoherent focusing of an adiabatic lens. The adiabatic lens has an extremely large acceptance both of beam emittance and momentum spread. Two examples of final focusing and transport systems adapted to different accelerator and target designs are presented in detail.

History and development of the uhv Helmer gauge as an analytic instrument

The development of the Helmer gauge in 1966 traces from work at the National Research Council of Canada, to the University of Illinois, and thence to the Vacuum Research Laboratory at Varian Associates. Key to the design was our study of the Bayard–Alpert structure as an ion beam source, defining the unexpectedly narrow energy dispersion of the ion beam. This allows use of a cylindrical focusing deflector, with the aperture and ion collector at conjugate focal points. The sensitivity of the Bayard–Alpert gauge is retained. New stainless-steel and VacIon pump technology was used to obtain pressures in the E-13 torr range, low enough to measure an X-ray limit near 1E-14 torr, thus showing that stainless-steel is as good as glass for creating UHV. Following introduction of a commercial Helmer gauge, the physical study of its properties continued in Europe, principally at PTB and CERN, where the design was optimized. Modulation of the beam-focusing system provides an exquisite, diagnostic fingerprint through which residual collector currents may be analyzed. © 1998 Published by Elsevier Science Ltd. All rights reserved

Periodic Solutions of Liénard Equations with Singular Forces of Repulsive Type

In this paper we will use the coincidence degree to give an existence result of periodic solutions for the scalar Liénard equations with singular forces of repulsive type. The main result of this paper clearly describes what balance conditions between the singular force at the singularity and at the infinity should be imposed if the equation has a periodic solution. As an application, we will improve the results of Ding, Ye, and Wang for the Brillouin electron beam focusing system.

Theory and Design of Charged Particle Beams

Review of Charged Particle Dynamics. Beam Optics and Focusing Systems Without Space Charge. Linear Beam Optics with Space Charge. Self-Consistent Theory of Beams. Emittance Variation. Beam Physics Research from 1993 to 2007. Appendices. List of Frequently Used Symbols. Bibliography. Index.

Holographic contrast transfer theory

With the advent of reliable cold field emission transmission electron microscopes there is substantial interest in using the amplitude and phase information recorded in electron holograms to optically or numerically correct for the coherent aberrations of transmission electron microscopes. However electron holography cannot compensate for incoherent aberrations. The derivation of the contrast transfer function for off axis electron holography in this paper shows there is no fundamental improvement in resolution for electron holography over conventional transmission electron microscopy.Evaluating the contrast transfer function involves mathematically following an electron beam through a field emission electron microscope set up for off axis electron holography. Due to the high coherence of the field emission electron beam coherent aberrations caused by the pre-specimen beam focusing system must be accounted for. Starting with a spacial frequency distribution, C(v), for the electron beam leaving the gun, the electron beam is limited by the condenser aperture and coherently aberrated by the condenser lens and objective pre-field as it passes to the specimen region:

The grid shadow technique as a tool for beam focusing in nuclear microprobes

A technique is presented which greatly facilitates the focusing of nuclear microprobe ion beams down to sizes of about one micrometer. It is based on the visual observation of the pattern created by the ion beam when impinging on a scintillating screen after first having passed through a 2000 mesh copper grid (grid period 12.7 μm) placed in the image plane. No additional electronic components or detectors are required. Apart from aiding the user in the focusing of the beam, the generated patterns give information concerning the quality of the ion beam focusing system and is therefore recommended as a permanent part of any nuclear microprobe setup.

Development of an automatic ion beam focusing system for a nuclear microprobe

If a nuclear microprobe with a beam size in the submicron region is to be attained, an objective measure of beam profile is a prerequisite. We have developed an automatic beam-focusing system for the Lund achromatic lens system. Using a knife-edge method, projections of the beam profile are determined. The resolutions of the measured profiles are then used as feedback in an automatic focusing procedure which uses computer-controlled power supplies for the electrostatic and magnetic focusing lenses. The beam spot size is minimized using a modified SIMPLEX iterative method. The system can use signals from any detectors, which permits it to be used informing the highest resolution microbeams.

A universal high-current implanter for surface modification of materials

A new high-current implanter dedicated for surface modification of materials has been developed and is now in operation at the Danish Tribology Centre in Aarhus, Denmark. The implanter contains a high-current multipole reflex-discharge ion source (CHORDIS) and produces mass analysed beam currents on the samples in the 5–10 mA range at energies up to 200 keV. A versatile ion beam focusing system combined with two-dimensional magnetic beam scanning offers high flexibility in the shaping of the implantation area (maximum 1600 cm 2) and control of local current densities. The large target chamber contains a remote-controlled water-cooled sample manipulator with one linear and two rotational movements. Continuous monitoring of the sample temperature and interlocks prevents overheating of surfaces during implantation. The paper describes the general design of the implanter as well as ion beam performance and operational experience from implantations of “industrial” samples.

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B, Sb and Si Liquid Metal Alloy Ion Sources for Submicron Fabrication

B, Sb and Si liquid metal alloy ion sources have been fabricated and basic characteristics such as current-voltage relations, angular current intensity, energy distribution and mass spectra have been measured. Characteristics of ion beam focusing systems are also discussed. It was observed that the energy distribution width (FWHM) of various ion species obtained for Sb alloy sources decrease with increasing the charge to mass ratio of the ion beam. It was also observed that the mass spectra varied slightly with a total ion source current. These ion sources could be operated for more than 10 h without any change in mass spectra.

Design Study of a 200 KeV Scanning Proton Microprobe Using a Field Ionization Source

A preliminary design study has been conducted for constructing a 200 KeV scanning proton microprobe which utilizes the phenomenon of field ionization in hydrogen gas to create a proton source of extremely small dimensions and high brightness. Calculations for the focusing action of a non-uniformly graded accelerating column, in conjunction with a superconducting magnetic solenoid indicate a final beam-spot size better than 50 A. The ultimate aim is to construct a high energy proton or heavy-ion microprobe which will rival or even excel the field emission scanning electron microscopes presently in use. Justification for using high energy protons (or heavy-ions) as probe particles instead of electrons has been presented in this paper, along with details of the beam transport and focusing system.