Beam Control System Research Articles

Hierarchical Fuzzy Logic Scheme with Constraints on the Fuzzy Rule

Abstract This paper presents the hierarchical fuzzy system where the outputs of the previous layer are not used in the IF-parts, but used only in the THEN-parts of the fuzzy rules in the next layer. A certain class of functions is shown to be approximated to any degree of accuracy by the proposed hierarchical fuzzy system. The ball and beam control system is simulated to demonstrate the feasibility of the proposed scheme.

Integral sliding-mode control of a magnetically suspended balance beam: analysis, simulation, and experiment

This paper presents a sliding-mode controller with integral compensation for a magnetic suspension balance beam system. The control scheme comprises an integral controller which is designed for achieving zero steady-state error under step disturbances, and a sliding-mode controller which is designed for enhancing robustness under plant uncertainties. A procedure is developed for determining the coefficients of the switching plane such that the overall closed-loop system has stable eigenvalues. A proper continuous design signal is introduced to overcome the chattering problem. The performance of the balance beam control system is illustrated by simulation and experimental results showing that the proposed integral sliding-mode controller method is effective under external step disturbances and input channel parameter variations.

The ALFA Laser: Beam Relay and Control System

The ALFA laser subsystem uses a 4 watt continuous wave laser beam to produce an artificial guide star in the mesospheric sodium layer as a reference for wavefront sensing. In this article we describe the system design, focusing on the layout of the beam relay system. It consists of seven mirrors, four of which are motor-controlled in closed loop operation accounting for turbulences inside the dome and flexure of the main telescope.The control system features several computers which are located close to analysis and control units. The distribution of the tasks and their interaction is presented, as well as the graphical user interface used to operate the complete system. This is followed by a discussion of the aircraft detection system ALIENS. This system shuts off the laser beam when an object passes close to the outgoing laser.

New scan and control system (ESCOSYS™) for high power electron beam techniques

The electron beam gun is one of the most important heat sources for high rate evaporation applications. Very high power densities are necessary to achieve high evaporation rates. A new electron beam scan and control system (ESCOSYS™) was developed for comfortable and reliable control of the electron beam. An overview of today's electron beam coating technology, and the first results and applications of ESCOSYS will be presented.

First lasing of the UCSB 30 μm free-electron laser

Third harmonic lasing has been achieved in a Free-Electron Laser specifically designed to operate in that mode. So far, 40 W at 41 μm wavelength and 5.16 MeV beam energy has been measured. One of the most difficult challenges has been suppression of lasing at the fundamental wavelength. This is currently achieved with an intracavity cesium iodide restrahlen filter, but eventually, the original grating design will be needed to provide full tunability. Operation of this FEL demands electron beam stability and control system accuracy at the limits of the present system. Further progress in the development of this FEL may require significant improvement in these areas.

New CAMAC based data acquisition and beam control system for Lund nuclear microprobe

A new CAMAC based data acquisition system has been installed at the Lund Nuclear Microprobe facility. This paper reports on the development and present status of the data acquisition system. The system is a true multiparameter CAMAC based system with fast Fera bus readout and in crate memory buffer. The user interface is based on Sparrow Kmax software for a Power Macintosh platform. The system read out and tag the event data with position on-line, which make fast on-line monitoring of spectra or element maps possible.Simultaneously, all data can be saved event by event for off-line analysis. The beam scanning part is software controlled through a timed D/A converter, this allows fast scanning of the beam. With a CCD-camera and video card the area to be analysed could be defined directly from the image, and the sample position can be moved. Any kind of irregular scan patterns could be defined.

Commissioning of the ALPI post-accelerator

The commissioning phase of the ALPI post-accelerator started at the beginning of 1994 with the installation of the medium beta section ( β = 0.11). Test beams of different injection energies and ion species have been accelerated with ALPI and delivered to the experimental halls. The main components of the post-accelerator, namely the cryogenic plant, the pulsing system, the optical and diagnostic elements for the beam transport, the vacuum, rf and control systems was widely tested under different conditions. The average accelerating field over the 44 installed superconducting lead on copper resonators turns out to be 2.5 MV/m and the phase locking procedure for the 48 resonators (accelerating and buncher cavities) is normally completed in about 10 hours. The overall beam transmission towards the post-accelerator is 70% with the DC beam and up to 50% with the pulsed and accelerated beam with currents on the target of the order of some p nA.

Conductive dots, wires, and supertips for field electron emitters produced by electron-beam induced deposition on samples having increased temperature

The procedure for three-dimensional additive lithography with electron-beam induced deposition is applied in a scanning electron microscope equipped with an image processor beam control system for lithography. Employing organometallic materials, which contain gold or platinum, quantum dots, resistors, and field emitter tips are deposited. Changing the current, the properties of the deposited nanocrystalline compound materials can be selected to be insulating or conducting. High resolution and high aspect ratio structures are grown with this technique. To find the mechanism responsible for conductivity in the deposited material, resistors are characterized at temperatures ranging from −150 °C to +180 °C. Measurements are performed in a high-vacuum chamber equipped with a gas cooling system cooled with liquid nitrogen and a resistive heater. Poole–Frenkel plots show that field electron emission and hopping of electrons is the dominant mechanism of conduction. The metal content of the deposits is increased with rising sample temperatures ranging from room temperature to 100 °C. The deposited material features zero-dimensional electron gas in the nanocrystals of the material. Conductive tips with very small tip radius are routinely deposited as supertips on top of etched tungsten tips at elevated temperatures. The tips are investigated in an ultrahigh vacuum field electron microscope. Working supertips have a confined emission and therefore enhanced brightness is obtained routinely. The increase in brightness is at least ninefold for an emission from one site having a confined emission angle of ±7.2°. The emission current may be as large as 10 μA at extraction voltages below 800 V. No single crystalline tip material is needed to generate these supertips. Beam confinement to one emission site is demonstrated the first time for a deposited supertip.

Fabrication of a refractive microlens integrated onto the monomode fiber

The fabrication of microlenses using a dry resist process is described for the first time. Characteristics of the totally dry process were investigated. A technique for lens positioning and exposure was developed for a scanning electron microscope equipped with an image processor beam control system. The microlenses have a computer generated hyperbolic profile. Microlenses of cylindrical, ring, and elliptical geometry were fabricated on a Si wafer and on the end of a monomode quartz fiber. Focusing of visible and infrared light by a fabricated microlens is demonstrated.

New UCSF proton ocular beam facility at the Crocker Nuclear Laboratory Cyclotron (UC Davis)

A new facility has been constructed at the Crocker Nuclear Laboratory at University of California Davis for the purpose of treating ocular tumors using the 67.5 MeV protons from the 76-in. isochronous cyclotron. Beam line design, commissioning, control system, beam characteristics, dosimetry, patient positioner and system performance are discussed. The unmodulated Bragg peak has a penetration of 29 mm in tissue at the isocenter with a peak to plateau ratio of 3.8:1 and a width of 5 mm (FWHM measured in water). The delivered dose is monitored by two transmission ionization chambers which are calibrated against a thimble ionization chamber with an NIST-traceable 60Co calibration factor. The Bragg peak is spread across the target volume by the use of range modulators. The residual range is varied by means of a variable water column. Daily variation in patient dosimetry is within ±3%. The beam penumbra (defined here as the distance between the 90% and 10% isodose levels) is 1.5 mm for a range-modulated beam at a collimator-to-isocenter distance of 50 mm. The beam flatness in a 25 mm diameter beam is within ±2% and the beam symmetry is ±1%. In the first 18 months, 50 patients have been treated with an average field size of 16.8 × 16.6 mm 2. The residual range varied between 13.0 mm to 29.2 mm with an average value of 22.4 mm, and the range modulation varied between 16 mm to 24 mm with an average value of 20 mm. The tumor thickness (height) ranged between 1.2 to 11.5 mm with mean of 5.2 mm. The age of the patients ranged from 25 to 88 yr.

Shape Estimation and Optimal Control of Flexible Space Structures.

Active shape control of a flexible structure consists of estimating the deformed shape from multipoint spatially distributed measurement of the structural deflections and restoring the desired shape actively by means of electromechanical or piezoelectric control actuators. We present a method of determining the structural deflections accurately and of designing the optimal control forces to restore the desired shape. The estimation algorithm is based on an infinite-dimensional approach, where the necessary finite-element truncation and approximation are introduced after solving the estimation problem. Using the same approximation functions the proposed method yields the optimal control forces that minimize the overall restoration error in the sense of least squares. We apply the proposed shape estimation and control method to an experimental tendon control system for a flexible beam and study the optimum moment-arm location.

Photorefractive beam-steering system that uses energy transfer in a BaTiO_3 crystal for a fiber-array interconnect

A beam-control system to write gratings on a holographic plane is studied. The arrangement is designed to interconnect two 1024 monomode fiber arrays. The beam-control system is composed of two subsystems: a beam steerer, which deflects one incident beam toward 1024 positions, and a collimating system, which adapts the shape of the deflected beam to the holographic plane. The collimating system was studied only after the beam steerer had been fully built and tested. It is based on the photorefractive amplification of a beamlet selected by a shutter array. The deflection efficiency is enhanced by a factor 1500 with the photorefractive crystal, and the signal-to-noise ratio is larger than 5500. The influence of the optical aberrations on the coupling losses of the infrared beams in the monomode fibers are evaluated.

Data acquisition and scan control system for nuclear microprobe and other multiparameter experiments

A multipurpose data acquisition and beam control system was developed for use on a personal computer (PC) in an MS Windows graphical environment. Data acquisition is performed via a FAST MPA/PC adapter card and MPA/LBB large bus-box by a host computer. Beam and sample positioning are controlled from another computer connected to the host. Applications in the nuclear microprobe and experimental nuclear physics are presented.

The influence of space charge on the motion of a bunch of particles in an ion optical system

A general formalism in four-dimensional space-time is developed to obtain the electromagnetic field of a three-dimensional, elliptical bunch of particles in the first approximation. The paraxial or Gaussian equations of an impulse space-charge beam in the beam control system are presented and a method of solving these equations is proposed.

Matrix theory of the motion of a charged particle beam in curvilinear space-time Part I. General theory

A general relativistic theory of charged particle beam motion along a curved optical axis, including the gravitational field, is important for designers of optimal beam control systems. In this paper, which is the first of two, a new matrix approach is presented. This allows the development of a relativistic matrix theory for charged particle beam motion in the most general case of a curved reference trajectory, including the gravitational force. This approach is based on three basic matrices: the reference frame matrix, the curvature matrix and the electromagnetic matrix. The equations of the particle beam motion and of the electromagnetic field, including the space charge, are given. The notations used is independent of the units of the measured fields and energies. In a second paper, also published in this issue, the matrix and recursive methods for solving the nonlinear equations of motion will be presented.

Matrix theory of the motion of a charged-particle beam in curvilinear space-time Part II. Nonlinear theory. Formulae and algorithms

A general relativistic theory of the motion of a charged-particle beam motion along a curved optical axis, including the gravitational field, is of great significance in the design of optimal beam control systems. In a first paper, a new matrix approach was presented. In this second paper the expansion of the most general equations of motion and electromagnetic field equations in the Taylor series in powers of the derivation from the reference particle is presented. The nonlinear equations in phase space are reformulated as linear equations in phase moment space. A compact, conservative, recursive method of integrating the equations of motion is proposed. In some cases it is possible to optimize the control system by choosing a definite symmetry. This symmetry is considered in the paper.

Development of the beam transport and control systems of the Yale ESTU tandem

The ESTU tandem at the Wright Nuclear Structure Laboratory at Yale University has a demonstrated capability of accelerating heavy ion beams with a terminal potential in excess of 21 MV. To exploit this resource properly, high mass resolution is required at the ion source and charge selection in the terminal. A new ion injector, including a compact 90° magnet and high output sputter and charge exchange sources, has been assembled and tested. A new terminal, containing two foil strippers, a recirculating charge stripper and an off-axis electrostatic quadrupole charge separator has been designed, built and tested and awaits installation. Test results will be presented for these devices and the performance of the accelerator will be reviewed.

Digital Active Vibration Control of a Cantilever Beam with Piezoelectric Actuators.

A digital optimal regulator technique is introduced to the problem of vibration control of a cantilever beam. A pair of piezoelectrit cells is adhered to the upper and lower surfaces of the beam and used as the actuator. Influences of the mass and the rigidity of the actuator are taken into account in the analysis, and the equations of motion for the beam-control system are derived by applying the trsnsfer matrix method. Simulated transient response of the beam is compared with the experimental result. It is found that the effect of vibration suppression is obtained by means of the present technique which compensates for the delay arising from the computation time.

Measurement of microscopic displacements in graphite/epoxy composite materials using a SEM-generated surface map

Graphite fiber-reinforced resin composite materials have a wide use in aerospace, automotive and sporting goods applications where high strength to weight ratios are requisite. Many of these materials use highly cross-linked epoxy resins as the matrix material. Unfortunately these resins have a low resistance to crack propagation and as a result research efforts have been directed towards reducing this tendency.The ability to measure microscopic displacements and calculate strain fields in the vicinity of a fracture crack tip under experimental conditions was needed in order to help predict the fracture resistance of various composite materials being tested. A technique was developed that made it possible to derive displacement measurements on a micrometer scale in the region of a crack tip from observations of epoxy-based composites being fractured using a tensile stage equipped scanning electron microscope (SEM). Samples were polished on the surface to be observed and sputter coated with 5 to 10 nanometers of either gold or 60:40 gold-palladium prior to mounting on the TS-2 tensile stage of a JEOL JSM-35CF. This instrument was also equipped with a Krisel beam interceptor, a beam current meter, a Tracor Northern TN-2000 x-ray analyzer and a TN-1310 digital beam control system. Using the digital beam and x-ray mapping capabilities a matrix of small dots was “written” onto the surface of the sample as shown in figure 1.

Hardware experiment of a tendon vibration control system for a flexible beam.

The idea of a tendon vibration control system for the flexible space structure has been proposed, and to verify the feasibility of this concept for a cantilever beam-like flexible space structure, a hardware model was constructed in the laboratory. this paper discusses the hardware experiment of the tendon control system for a clamped-free flexible stainless-steel beam hung in the vertical direction. Since the test structure has very low damping, a low-order modal controller becomes unstable due to the truncated modes in the controller design called residual modes. This phenomenon is called spillover. In order to avoid the spillover instability, two different approaches to the control system design are examined both by numerical simulations and by hardware experiments. First, the DVFB(Direct Velocity Feedback Control) which adds damping to all the vibration modes like a passive damper, is applied. Next, a state feedback controller based on a reduced-order model which is called the HAC(High Authority Control), is applied and results in a spillover instability, Finally, a hierarchical controller called LAC/HAC(Low Authority Control/High Authority Control) considering of the DVFB(LAC) for damping augmentation of the truncated modes, and HAC is applied. As the result, the closed-loop system becomes stable and high performance is achieved.