Transverse Dimensions Of Beam Research Articles

The Numerical Investigation of Thin-Walled Beams with Modified C-Sections

Abstract Demand for thin-walled structures has been increasing for many years. Cold- formed, thin-walled channel beams are the subject of presented research. The local elastic buckling and limit load of these beams subjected to pure bending are investigated. This study includes numerical investigation called the Finite Strip Method (FSM). The presented results give a deep insight into behaviour of such beams and may be used to validate analytical models. The number of works devoted to the theory of thin-walled structures has been steadily growing in recent years. It means that is an increasing interest in practical methods of manufacturing cold-formed thin-walled beams with complicated cross-sections, including also beams with web stiffeners. The ratio of transverse dimensions of beam to its wall-thickness is high, therefore, thin-walled beams are prone to local buckling that may interact with other buckling modes. The stability constraints should be always considered when using cold-formed thin-walled beams.

Controlling the transverse dimensions of the electron beam in the solenoidal field of a magnetron gun

The results of the study on the formation of transverse dimensions of an electron beam by a magnetron gun with a secondary emission cathode in the voltage range of 25..90 kV are presented. Investigations of the formation of electron beams in electron sources with cold metal cathodes operating in the secondary emission regime are carried out. The electron source is a magnetron gun. The principle of operation of such gun s is based on the reverse bombardment of the cathode by electrons returned by the magnetic field, the formation of an electron cloud near the cathode a nd the formation of a beam in crossed electric and magnetic fields. Their main difference from thermionic guns is the large current density from a unit of the cathode’s cross-sectional area ~ 50 A/cm² and a long service life. Therefore, the search and investigation of electron sources with a long service life is an urgent task. On the basis of a magnetron gun with a secondary-emission cathode, an electron accelerator is created in which an axial electron beam is used to irradiate metal targets and the inner cylindrical surface with a radial electron beam. The article presents the experimental data and the results of modeling calculations on the formation and control of the electron beam distribution by a magnetron gun with a secondary-emission cathode in motion in a solenoidal magnetic field. The dependence of the formation of the radial dimensions of the electron beam on the amplitude and gradient of the solenoidal magnetic field in the gun, which grows or falls in the channel of the beam transport, is studied. The results of numerical simulation of the motion of a tubular electron beam in a magnetic field of a solenoid are presented. Based on the motion model of the electron beam, the characteristics of the resultant electron beam are considered. It is shown that the diameter of the beam can be adjusted by varying the control magnetic field. The results of numerical modeling on the motion of a tubular electron flux in a magnetic field of a solenoid are given. The possibility of controlling the transverse dimensions of the beam is studied.

Nonintercepting electron beam size monitor using optical diffraction radiation interference

In recent years, the use of diffraction radiation (DR), emitted when a charged particle beam passes through a rectangular slit, has been proposed and successfully tested as a nonintercepting diagnostic of high brightness beams. However, some problems related to the control of the particle trajectory through the slit still remain. If an additional slit is placed in front of the first one, at a distance shorter than the radiation formation length, interference between the forward diffraction radiation from the upstream slit and the backward diffraction radiation from the downstream slit can be observed. In this paper we report the first experimental observation of this effect, which we call here optical diffraction radiation interference (ODRI). If the two slits have different dimensions and are not aligned on the same axis, the properties of the ODRI pattern can be effectively used for nonintercepting beam diagnostics, especially for the unambiguously determination of the beam size. Indeed, the advantage of ODRI compared with a single aperture DR screen is due to the reduction of synchrotron radiation background, the increase of sensitivity for transverse beam dimensions, and the possibility to separate effects caused by the beam size and by beam offset within the slit.

Quasimonochromatic resonant diffraction radiation as a possible tool for non-invasive beam diagnostics

A simple model for calculating the resonant diffraction radiation (RDR) characteristics from a particle moving through an ideally conducting tilted grating made of spaced strips has been developed. The influence of initial beam divergence and transverse beam dimensions on the RDR line form is noted. By measuring either a spectrum with a constant grating tilt angle or an orientation dependence (theta-scan) with a constant wavelength there is in principle the possibility to determine both the beam divergence and the transverse beam dimensions.

Results of a gas-ionization beam size monitor at the final focus test beam

A new type of gas-ionization monitor, built at Orsay, has been used to optimize and measure the transverse beam dimensions of the Final Focus Test Beam at SLAC. This monitor detects the ions created by the beam to probe its space charge field and to derive both transverse dimensions. The ultimate values measured with the monitor are 1.5 μ m × 60 nm. Moreover, the high sensitivity of the monitor has been used to detect and cancel out detrimental “banana” shapes of the beam.

Accurate analytic off-axis electron trajectories in realistic two-dimensional transverse wigglers with arbitrary magnetic field variation.

For several reasons, it is essential to have analytic descriptions of single-electron trajectories for wigglers and undulators. (a) They give a better insight into the complicated dependence of the electron motion on quantities like the injection conditions or the wiggler parameter K; (b) one can hope to calculate the radiation pattern from a particular wiggler or undulator only if at least the single-electron velocity is given in closed form; (c) analytic single-particle trajectories are an essential starting point for investigating advanced problems like stability analyses and free-electron laser performance. Therefore, single-electron motion was studied in wigglers with two-dimensional magnetic fields that are transverse and periodic but otherwise arbitrary on axis, and satisfy Maxwell's equations off axis. In this class of fields, the energy and one component of the canonical momentum are conserved and can be used to reduce the trajectory problem to the integration of a single complicated second-order ordinary differential equation, which, for all realistic electron-beam emittances and for all realistic values of ${\ensuremath{\delta}}_{w}$=K/\ensuremath{\gamma}, is weakly nonlinear and lends itself to a two-level two-scale analysis, through which an accurate analytic description of the complete electron trajectory can be established. This analytic trajectory exhibits all the features that one expects to find in off-axis motion, such as small-amplitude rapid wiggler oscillations superimposed on large-amplitude slowly varying betatron oscillations. The accuracy of this analytic trajectory was tested for a sinusoidal on-axis field variation by comparison with a numerical trajectory, and it was found that even for far-off-axis electrons, the agreement was excellent, typically on the order of one part in a thousand. This high accuracy in the off-axis regime is an important feature, since in many devices real transverse beam dimensions, initial beam velocity spreads, lateral beam injection, and a small undulator period ${\ensuremath{\lambda}}_{0}$ lead to electrons traveling considerably off axis.

A high resolution wire scanner for micron-size profile measurements at the SLC

Fine conductive fibers have been used to measure transverse beam dimensions of a few microns at the Stanford Linear Collider (SLC). The beam profile is obtained by scanning a fiber across the beam in steps as small as 1 μm, and recording the secondary emission signal at each step, using a charge sensitive amplifier. We first outline the mechanical construction and the analogue electronics of the wire scanner. We then describe its performance in test beams and in actual operation. The article closes with a brief discussion of performance limitations of such a beam profile monitor.

Fast Beamprofile Measurement

The paper deals with a set-up utilizing synchrotron light which allows a fast measurement of beam width and beam height. The most important component of this device is a combination of an image-converter tube with an electron multiplying dynode system. The scan velocity is between .1 and .3 mm/μs and could be made even faster. This makes possible the measurements of acceptance, beam emittance, dynamical change of beam position and change of transverse beam dimensions during an accelarating cycle in an electron synchrotron. The device has also been used to measure fast cross section changes in the PETRA storage ring.

Method of measuring beam aperture in an accelerator chamber without disturbing it

A method is described for obtaining information about the transverse dimensions of a beam without disturbing it. Experimental results obtained from measurements of the transverse dimensions of an electron beam are in good agreement with calculation.