Showing papers on "Beam (structure) published in 1993"

Particle accelerator physics

Abstract: Tools We Need.- Of Fields and Forces.- Particle Dynamics in Electromagnetic Fields.- Electromagnetic Fields.- Beam Dynamics.- Single Particle Dynamics.- Particle Beams and Phase Space.- Longitudinal Beam Dynamics.- Periodic Focusing Systems.- Beam Parameters.- Particle Beam Parameters.- Vlasov and Fokker-Planck Equations.- Equilibrium Particle Distribution.- Beam Emittance and Lattice Design.- Perturbations.- Perturbations in Beam Dynamics.- Hamiltonian Resonance Theory.- Hamiltonian Nonlinear Beam Dynamics.- Acceleration.- Charged Particle Acceleration.- Beam-Cavity Interaction.- Coupled Motion.- Dynamics of Coupled Motion.- Intense Beams.- Statistical and Collective Effects.- Wake Fields and Instabilities.- Synchrotron Radiation.- Fundamental Processes.- Overview of Synchrotron Radiation.- Theory of Synchrotron Radiation.- Insertion Device Radiation.- Free Electron Lasers.

Magnetic scanning system for heavy ion therapy

Abstract: Beams of heavy ions have favourable physical and biological properties for the use in radiotherapy. These advantages are most pronoucced if the beam is delivered in a tumor-conform way by active beam scanning. A magnetic scanning technique is used to spread the beam laterally. The range of the particles in tissue is controlled by the variation of the beam energy in the accelerator. Computer simulations were used to compare a discrete scan mode (pixel scan) with a continous scan mode (raster scan). It was found that both methods lead to nearly identical results. The design and technical realization of the magnetic scanning system at GSI combines features of both scan techniques. First results using the lateral beam scanning method as well as the combination of the active energy variation with the magnetic beam scanning are presented.

Observation of self-trapping of an optical beam due to the photorefractive effect.

Abstract: Recently, a new type of spatial soliton has been predicted to be observable in a photorefractive crystal.1,2 For example, consider an input laser beam that is diverging because of diffraction as it passes through a photorefractive material. Interference between the beam’s spatial-frequency components can be considered to write photorefractive gratings on the crystal. These gratings, or spatial variations in the index of refraction, have one component that is in phase and another that is 90° out of phase with their parent intensity pattern.

Deformable grating apparatus for modulating a light beam and including means for obviating stiction between grating elements and underlying substrate

Abstract: A modulator for modulating incident rays of light, the modulator comprising a plurality of equally spaced apart beam elements, each of which includes a light reflective planar surface. The elements are arranged parallel to each other with their light reflective surfaces parallel to each other. The modulator includes means for supporting the beam elements in relation to one another and means for moving the beam elements relative to one another so that the beams move between a first configuration wherein the modulator acts to reflect the incident rays of light as a plane mirror, and a second configuration wherein the modulator diffracts the incident rays of light as they are reflected therefrom. At least one of the facing surfaces of the beam elements and underlying substrate is configured to reduce any tendency to stick as they are pulled together. In operation, the light reflective surfaces of the beam elements remain parallel to each other in both the first and the second configurations and the perpendicular spacing between the reflective surfaces of adjacent beam elements is equal to m/4 times the wavelength of the incident rays of light, wherein m=an even whole number or zero when the beam elements are in the first configuration and m=an odd number when the beam elements are in the second configuration.

Relativistic and ponderomotive self‐focusing of a laser beam in a radially inhomogeneous plasma. I. Paraxial approximation

Abstract: The propagation of a high‐irradiance laser beam in a plasma whose optical index depends nonlinearly on the light intensity is investigated through both theoretical and numerical analyses. The nonlinear effects examined herein are the relativistic decrease of the plasma frequency and the ponderomotive expelling of the electrons. This paper is devoted to focusing and defocusing effects of a beam assumed to remain cylindrical and for a plasma supposed homogeneous along the propagation direction but radially inhomogeneous with a parabolic density profile. A two‐parameter perturbation expansion is used; these two parameters, assumed small with respect to unity, are the ratio of the laser wavelength to the radial electric‐field gradient length and the ratio of the plasma frequency to the laser frequency. The laser field is described in the context of a time envelope and spatial paraxial approximations. An analytical expression is provided for the critical beam power beyond which self‐focusing appears; it depend...

Optimization of beam orientations in radiation therapy: Some theoretical considerations

Abstract: The problem of optimizing beam orientations for irradiations with multiple fixed beams is investigated. It is shown that this is a complex, in mathematical terms 'non-convex', optimization problem whose solution requires sophisticated techniques. In this work, the optimization is performed with the method of simulated annealing. In order to keep the calculation time within reasonable limits, the problem is expressed in the spatial frequency domain using Parseval's theorem. All calculations are then performed in the frequency domain. The algorithm is described in detail. Various treatment techniques, including intensity modulation, are considered. The results for various exemplary cases are presented. They are based on a simplified dose calculation model. A general conclusion is that the optimum beam configuration for multiple-beam irradiations (with more than three beams) tends to be an even distribution over an angular range of 0 to 2 pi .

Laser pattern generation apparatus

Abstract: An improved laser pattern generation apparatus. The improved pattern generation apparatus of the present invention uses a laser beam to expose a radiant sensitive film on the workpiece to print circuit patterns on a substrate. The laser beam is aligned using a beam steering means. The laser beam is split into 32 beams to create a brush. The brush scans the workpiece through use of a rotating polygonal mirror. Each beam of the brush may have one of seventeen intensity values. The beams are modulated by an Acousto-Optical Modulator. Signals provided to the Acousto-Optical Modulator define the pattern to be generated. These signals are created by a rasterizer. Increased print speed is accomplished through the use of a wider brush and a print strategy that eliminates physical stage passes.

Beam tests of the ZEUS barrel calorimeter

Abstract: A fully compensating uranium—scintillator calorimeter was constructed for the ZEUS detector at HERA. Several of the barrel calorimeter modules were subjected to beam tests at Fermilab before shipping them to DESY for installation. The calibrations of the modules used beams of electrons and hadrons, measuring the uniformity of the response, and checking the resolution. The runs also provided opportunity to test a large fraction of the actual ZEUS calorimeter readout system in an integrated beam environment more than one year before HERA turn on. The experiment utilized two computer controlled mechanical structures, one of which was capable of holding up to four modules in order to study shower containment, and a magnetic spectrometer with a high resolution beam tracking system. During two running periods, beams of 6 to 110 GeV containing e, μ, π, and p were used. The results show energy resolutions of 35%/ E for hadrons and 19%/ E for electrons, uniformities at the 1% level, energy nonlinearity less than 1%, and equal response for electrons and hadrons.

Efficient radially polarized laser beam generation with a double interferometer.

Abstract: Conversion of a linearly polarized CO2 laser beam into a radially polarized beam is demonstrated with a novel double-interferometer system. The first Mach–Zehnder interferometer converts the linearly polarized input beam into two beams with sin2 θ and cos2 θ intensity profiles, where θ is the azimuthal angle. This is accomplished by using two spiral-phase-delay plates with opposite handedness in the two legs of the interferometer to impart a one-wave phase delay azimuthally across the face of the beams. After these beams are interfered with, the resulting beams are sent directly into the second Mach–Zehnder interferometer, where the polarization direction of one beam is rotated by 90°. The beams are then recombined at the output of the second interferometer with a polarization-sensitive beam splitter to generate a radially polarized beam. The output beam is ≈ 92% radially polarized and contains ≈ 85% of the input power. This system will be used in upcoming laser particle acceleration experiments.

Comparison of techniques for measuring both compressive and tensile stress in thin films

Abstract: New stress-measurement devices for measuring both tensile and compressive strain in single structures have been realized. The investigation is concentrated on the development of two techniques: (i) buckling and (ii) rotation. The buckling technique is based on the buckling of a beam when exceeding a critical strain level. Therefore, an array with different beam lengths is required. The rotation technique, on the other hand, converts the extension or contraction of the material into a rotation, which can be easily measured. These structures have been modelled, simulated, and tested experimentally, using thin polysilicon films. Both techniques have been shown to be promising methods for simple and accurate on-chip thin-film strain measurements.

Magnetic head suspension assembly fabricated with integral load beam and flexure

Abstract: A magnetic head suspension assembly is fabricated with an integral piece which includes a load beam section, a flexure section, a rear mount section and a leaf spring section between the load beam and rear mount. A tongue extends from the load beam to the flexure and has a down-facing load dimple which contacts the non-air bearing surface of an attached air bearing slider. The flexure includes narrow thin legs adjacent to a cutout that delineates the load beam tongue. The head suspension is characterized by a high first bending mode frequency and low pitch and roll stiffness.

Analysis of laser beam quality degradation caused by quartic phase aberrations.

Abstract: Simple formulas are derived for the degradation in the beam-quality factor, M(2), of an arbitrary laser beam caused by quartic phase distortions such as those that might occur in a spherically aberrated optical component, a thermally aberrated laser output window, or a divergent beam emerging from a high-index dielectric medium as in a wide-stripe, unstable-resonator diode laser. A new formula for the defocus correction that is needed to collimate optimally a beam with quartic phase aberration is also derived. Analytical results and numerical examples are given for both radially aberrated and one-dimensionaltransversely aberrated cases, and a simple experimental measurement of the beam-quality degradation produced by a thin plano-convex lens is shown to be in good agreement with the theory.

Dynamic Stiffness and Substructures

Abstract: 1 Harmonic Analysis.- 1.1 Steady State.- 1.2 Multiple Degrees of Freedom.- 1.3 Modal Analysis and Acceleration.- 2 Finite Elements and Continuum Elements.- 2.1 Formulation.- 2.2 Bar Elements.- 2.3 Beam Elements.- 2.4 Continuous Mass Model.- 2.5 Rectangular Plate.- 2.6 Interaction Between Beams and Plates.- 2.7 Leung's Theorem.- 2.8 Simpson's Hypothesis.- 2.9 Sturm's Theorem.- 2.10 Wittrick-Williams Algorithm.- 2.11 Derivatives of the Dynamic Stiffness.- 3 Dynamic Substructures.- 3.1 Exact Dynamic Condensation.- 3.2 Dynamic Substructures.- 3.3 Dynamic Flexibility.- 3.4 Dynamic Transformation.- 3.5 Damped Substructures.- 3.6 Multilevel Substructures.- 3.7 Non-conservative Substructures.- 3.8 Substructure Response.- 3.9 Periodic Structures.- 3.10 Derivatives of Substructure.- 4 Dynamic Stiffness.- 4.1 Follower Force.- 4.2 Parametrically Excited Members.- 4.3 Effects of In-Plane Moment.- 4.4 Reponse Analysis.- 4.5 Non-conservative Modal Analysis.- 4.6 Exponentially Varying Harmonic Excitations.- 5 General Formulation.- 5.1 Initial Stress Formulation.- 5.2 Finite Element Method.- 5.3 Dynamic Stiffness Method.- 5.4 Thin-Walled Beam.- 5.5 Shear Deformable Thin-Walled Beam.- 5.6 Analytical Dynamic Stiffness.- 5.7 Curved Thin-Walled Beam.- 5.8 Helix.- 5.9 Curvature Effect.- 5.10 Extensions.- 5.11 Symmetry of the Dynamic Stiffness Matrix.

Particle accelerator physics : basic principles and linear beam dynamics

Abstract: This text serves as an introduction to the field of high-energy particle accelerator physics and particle-beam dynamics. It covers the dynamics of relativistic particle beams, the basics of particle guidance and focusing, lattice design, the characteristics of beam transport systems and circular accelerators. Particle-beam optics is treated in the linear approximation, using sextupoles to correct for chromatic aberrations. Perturbations to linear beam dynamics are analyzed in detail and correction measures are discussed. Basic lattice design features and building blocks leading to the design of more complicated beam transport systems and circular accelerators are studied. Characteristics of synchrotron radiation and quantum effects due to the statistical emission of photons on particle trajectories are derived and applied to determine particle-beam parameters. The discussions specifically concentrate on relativistic particle beams and the physics of beam optics in beam transport systems and circular accelerators such as synchrotrons and storage rings.

Intimate source and detector and apparatus employing same

Abstract: There is provided a system of detecting mark-sense indicia wherein the images of a light source (26) and the region of sensitivity (122) of a light sensor are substantially coaxial, coplanar, and coextensive throughout the working depth of field (21). This system is insensitive to the laminate and the diffusion effects. A light source (26) is aimed at a beam splitter (15) that diverts a portion of the light beam (36) through optics (14) that focus the light on a reflective target (12) containing a bar code symbol (17) to be scanned. The reflected beam (38) is returned through the optics (14) and the beam splitter (15), and a portion of the reflected beam is conducted to a light sensor (24). In this manner, the light path from the source (26) to the optical sensor (24) is split twice by the beam splitter (15). The optics (14) are configured so that the light beams that define the field of illumination and the region of sensitivity and which pass between the optics (14) and the target (12) are congruent, having identical optical axes and angles of divergence (16, 18). The region of sensitivy is congruent with the field of illumination in any plane throughout the depth of field of the optics. Field stops (20, 22) may be optionally provided for the light source (26) and the light sensor (24) in order to better define the dimensions of the field of view and field of illumination.

Stability and confinement of nonrelativistic sheet electron beams with periodic cusped magnetic focusing

Abstract: Sheet electron beams focused by periodically cusped magnetic (PCM) fields are stable against low‐frequency velocity‐shear instabilities (such as diocotron mode). This is in contrast to more familiar unstable behavior in uniform solenoidal magnetic fields. Two rectangular‐cross‐section magnetic configurations capable of focusing in both transverse dimensions are investigated: (i) a closed‐side two‐plane PCM configuration that is topologically equivalent to conventional round‐cross‐section PPM focusing; and (ii) an open‐side configuration that uses ponderomotive PCM focusing in the vertical plane and simple vzBy Lorentz force focusing in the horizontal plane. Both configurations are capable of stable sheet beam confinement. The open‐side configuration appears more practical both for focusing and for realizing matched (cold) beam conditions in which the beam envelope is free from oscillations. For realistic beams with finite emittance, the existence of a matched cold beam solution implies less emittance grow...

Influence of steel fibers on the shear resistance of lightweight concrete i-beams

Abstract: The paper assesses the effectiveness of steel fibers used alone as shear reinforcement in lightweight concrete beams. The tests were carried out on full-size I-beams with thin webs and varying tension steel and shear span. The fibers reduced the beam deformations substantially at all load levels, controlled dowel and shear cracking, reduced spalling in the cover, and helped to preserve the ductility and overall integrity of the structural member. The ultimate shear strength was increased by amounts of 60 to 200 %., but flexural failure was achieved only in beams with 1.55 % tension steel and in beams with 2.76 % tension steel tested at large shear spans. A truss model is proposed to predict the the ultimate shear strength, and it is shown that the model predicts satisfactorily the shear resistance of both lightweight and normal weight concrete beams.

Beam supply device

Abstract: A beam supply device for supplying a particle or radiation beam to therapy or experiment equipment includes a beam generation device 1, a pre-branching beam transportation device 2, a rotatable deflection electromagnet 3, a rotatable beam transportation device 4, and a plurality of beam utilization rooms 5 disposed around the rotational axis of the rotatable deflection electromagnet 3 at a predetermined distance therefrom. The rotatable deflection electromagnet 3 and the rotatable beam transportation device 4 are rotated together to a predetermined rotational angle, such that the beam is guided to the room in which the beam is to be utilized.

Model Precast Concrete Beam-to-Column Connections Subject to Cyclic Loading

Abstract: H. S. Lew, Ph.D. Chief Building and Fire Research Laboratory National Institute of Standards and Technology Gaithersburg, Maryland Experimental results of eight ~-scale model precast concrete beam-to-column connections are presented. The test specimens consisted of interior connections designed in accordance with the 1985 Uniform Building Code provisions for Seismic Zones 2 and 4. These tests constitute the second and third phases of a multi-year test program being conducted at the National Institute of Standards and Technology. The objective of the test program is to develop guidelines for an economical precast beam-tocolumn connection for regions of high seismicity. Variables considered in the research program include location of the post-tensioning steel, the use of post-tensioning bars vs. prestressing strands and fully bonded vs. partially bonded strands. Specimens were subjected to reversed cyclic loading according to a prescribed displacement history. Comparisons were made between the behavior of precast concrete specimens and the monolithic specimens tested previously in Phase I. These comparisons were based on connection strength, ductility and energy dissipation characteristics. Comparison of results with the monolithic test specimens indicates that the post-tensioned precast concrete specimens had comparable connection strengths, higher ultimate displacement ductilities and total energy dissipation to failure, but lower energy dissipation per cycle.

Measuring device e.g. water or moisture sensor

Abstract: The measurement arrangement has a light emitting diode (10) whose emitted radiation is fed into a plate or wall (11) which is transmissive for a defined wavelength, esp. a reflection path (11a). The light is coupled directly into the wall or plate from the diode. The surface (10a) of the diode facing the wall or plate is matched to the surface shape of the wall or plate. The light emitting diode is a commercially available type with a bright chip whose surface is cut to match that of the wall or plate. The light is coupled into the wall or plate as a beam and at an angle of incidence which essentially differs from a normal to the plate or wall by more than the refraction angle of total reflection.

X-ray flux enhancement in thin-film waveguides using resonant beam couplers.

Abstract: We present experimental evidence for achieving significant x-ray flux enhancement by coupling a highly collimated and monochromatic synchrotron x-ray beam into a Si/polyimide/SiO 2 thin-film waveguide. The observed 20-fold flux increase agrees with theoretical predictions and was limited only by absorption of the 1 A x rays in the waveguide structure

Analysis of a mixed mode fracture specimen: the asymmetric double cantilever beam

Abstract: An asymmetric double cantilever beam (ADCB) is a simple but effective specimen for the measurement of polymer/polymer and polymer/non-polymer bimaterial interface fracture toughness. In order to characterize fully the bimaterial interface strength, and to control the crack trajectory, the critical energy release rate, G c, and the phase angle, ψ, of the applied stress field as functions of loading and geometry of the specimen should be obtained. For most practical cases, ψ has to be evaluated numerically. In this work, a boundary element analysis is carried out to obtain G and ψ for the ADCB specimen at different material and geometry combinations. An expression for the energy release rate, G, based on Kanninen's beam on elastic foundation model is compared with the numerical results. Limitations on the use of the ADCB specimen are also discussed.

A Closed Form Solution for the Energy Release Rate of the Double Cantilever Beam Specimen with an Adhesive Layer

Abstract: A simple, yet accurate, strength of materials approach is used to derive a closed form solution for the compliance and energy release rate of the double cantilever beam specimen with an adhesive layer and cohesive cracks. Such capability currently is not available in the literature. The results are valid for either isotropic or orthotropic mate nals in plane stress or plane strain. The specimen is modelled as a beam partially free and partially supported by an elastic foundation. The solution is an extension of previous work by Kanninen [1] for the special case of a homogeneous material (e.g., no adhesive layer). The closed form results are subsequently verified using the finite element method. Ex cellent agreement is found for a variety of crack lengths and material properties. It is shown that, for composite adherends, shear deformation must be taken into account in ad dition to elastic foundation effects. The present results are useful in analyzing test results to determine the fracture toughness of ad...

Strong self-focusing in nematic liquid crystals.

Abstract: We present an experimental study of strong self-focusing in nematic liquid crystals. In a planar geometry, a linear dependence of the focal power on the input intensity for 100-\ensuremath{\mu}m-thick samples turns into an exponential one when thicker samples are used. A transverse visualization of the beam structure is performed in a cylindrical geometry. We observe an undulation and a filamentary structure of the laser beam for large intensities. Also, multiple focal points appear along the beam axis in this configuration. Undulation and filamentation of the beam are also observed in a spherical geometry.

Thin film forming apparatus using laser

Abstract: A thin film forming apparatus using laser includes a chamber (1), a target (5) placed therein, a laser light source (10) for emitting laser beam to target (5), and a substrate holder (3). When target (5) is irradiated with laser beam (16), a plume (15) is generated, and materials included in plume (15) are deposited on the surface of a substrate (2) held by substrate holder (3). The laser beam emitted from laser light source (10) has its cross section shaped to a desired shape when passed through a shielding plate (4804), for example, so that the surface of the target (5) is irradiated with the beam having uniform light intensity distribution. Therefore, a plume (15) having uniform density distribution of active particles is generated, and therefore a thin film of high quality can be formed over a wide area with uniform film quality, without damaging the substrate.

Seismic Design and Performance of Composite Coupled Walls

Abstract: The cyclic response of steel coupling beams embedded into reinforced concrete boundary elements was studied. Three half‐scale subassemblies representing a portion of a prototype structure were designed, constructed, and tested. The main test variables were the amount of vertical tension/compression stresses in the boundary element, and presence of auxiliary bars attached to the beam flanges for a smoother transfer of bearing stresses. The steel coupling beams exhibited very stable hysteresis characteristics, and could develop the theoretical plastic moment when the boundary and, hence, the connection region were subjected to normal compressive stresses. Tensile stresses in the boundary element reduced the stiffness, and smaller moments could be developed. A significant amount of dissipated energy could be accounted by that energy dissipated in “plastic hinges” formed in the exposed portion of the coupling beam. The stiffness was found to be different depending on whether the boundary element was under com...