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IT05 The Comparison of signal Processing Systems for Beam Position Monitors insertion, collider, single-bunch, storage-ring 12
 
  • G. Vismara
    CERN, Geneva, Switzerland
  At first sight the problem of determining the beam position from the ratio of the induced charges of the opposite electrodes of a beam monitor seems trivial, but up to now no unique solution has been found that fits the various demands of all particle accelerators. The purpose of this paper is to help instrumentalist in choosing the best processing system for their particular application. The paper will present the different families in which the processing systems can be grouped. A general description of the operating principles with relative advantages and disadvantages for the most employed processing systems is also presented.  
 
IT07 Bunch Length Measurements laser, radiation, linac, gun 19
 
  • M. Geitz
    DESY, Deutsches Elektronen Synchrotron, Hamburg, Germany
  An rf photo-injector in combination with a magnetic bunch compressor is suited to produce high-charged sub-picosecond electron bunches required for electron-drive linacs for VUV and X-ray FELs. This report summarizes time- and frequency domain bunch length measurement techniques with sub-picosecond resolution.  
 
IT09 Diagnostics in Heavy Ion Machines ion, heavy-ion, diagnostics, linac 28
 
  • P. Strehl
    GSI, Gesellschaft für Schwerionenforschung, Darmstadt, Germany
  An overview of the measurements of most important beam parameters in heavy ion machines is given. The special characteristics of heavy ions concerning the great variety of parameters with respect to the type of accelerator (linac, circular machine), the species of accelerated ions as well as their energy, beam intensity, beam emittance and time structure are considered. The consequences for the design of beam diagnostic systems are discussed. Typical examples of measuring systems are given. Experimental results taken during the long operating time of the GSI facilities, covering a wide range of parameters, are reported.  
 
IT12 Use of Superimposed Alternating Currents in Quadrupoles to Measure Beam Position with Respect to their Magnetic Centre quadrupole, storage-ring, lattice, radiation 38
 
  • N. Marks
    CLRC, Daresbury Laboratory, Warrington, UK
  The positional stability of the electron beam in a modern state-of-the-art synchrotron radiation source is critical, as the many experimental users require consistency in the position and dimensions of the incoming photon beams which are incident on their experimental samples. At the Daresbury Synchrotron Radiation Source (SRS), inaccuracies in the measurements of the positions of both beam position monitors and the lattice quadrupoles can be overcome by measuring the position of the electron beam with respect to the magnetic centres of the quadrupoles. This was achieved by superimposing an alternating ('ripple') current on the direct current excitation of a single lattice quadrupole and examining the resulting beam oscillations at remote positions in the storage ring. If the electron beam is then subjected to a local distortion at the position of this quadrupole, the amplitude of the beam oscillation induced by the superimposed current is minimised (nominally zero) when the beam is at the quadrupole's magnetic centre. This paper presents details of the electrical circuit developed to inject an alternating current into the coils of individual quadrupoles and gives details of the results achieved to date.  
 
CT02 Determination of Radial Ion Beam Profile from the Energy Spectrum of Residual Gas Ions Accelerated in the Beam Potential space-charge, ion, emittance, acceleration 50
 
  • R. Dölling
    IAP, Institut für angewandte Physik der Johann Wolfgang Goethe Universität
  Residual gas ions (RGI) created from collisions of positive beam ions (BI) with residual gas atoms are accelerated out of the ion beam by its space charge potential. It is demonstrated that with one-dimensional radial symmetry the radial distributions of BI density and space charge potential can be determined from the energy distribution of RGI radially leaving the beam tube. RGI energy spectra were taken with an electrostatic analyser of Hughes-Rojansky type on a 10 keV 1.5 mA He+ beam. For comparison the radial BI density distribution was determined with a radial wire probe, an electron beam probe and a beam transport calculation based on an emittance measurement located downstream.  
 
CT07 The ELETTRA Streak Camera: System Set-Up and First Results synchrotron, single-bunch, storage-ring, cathode 72
 
  • M. Ferianis
    ELETTRA, Sincrotrone Trieste, Trieste, Italy
  At ELETTRA, a Streak Camera system has been installed and tested. The bunch length is a significant machine parameter to measure, as it allows a direct derivation of fundamental machine characteristics, like its broadband impedance. At ELETTRA the Light from a Storage Ring Dipole is delivered through an optical system to an Optical Laboratory where it can be observed and analysed. The Streak Camera is equipped with different timebases, allowing both single sweep and dual sweep operation modes, including the Synchroscan mode. The Synchroscan frequency equal to 250 MHz, which is half of the ELETTRA RF frequency, allows the acquisition of consecutive bunches, 2ns apart. To fully exploit the performances of the Streak Camera, an optical path has been arranged which includes a fast opto-electronic shutter. By doing so, the optical power deposited on the photo-cathode is reduced in the different ELETTRA fillings.  
 
CT10 Real Time Display of the Vertical Beam Sizes in LEP Using the BEXE X-Ray Detector and Fast VME Based Computers positron, luminosity, synchrotron, radiation 87
 
  • R. Jones, A. Manarin, G. Pignard, E. Rossa, H. Schmickler, M. Sillanoli, C. Surback
    CERN, Geneva, Switzerland
  Fast X-ray detectors based on CdTe photoconductors have been installed in LEP since the beginning of its operation in 1989. The angular divergence of the high energy photons from the synchrotron radiation (x-rays) and the narrow spacing of the 64 photoconductors of the detector allow a good measurement of vertical beam profiles down to an rms beam size of 300 mm. This paper presents some specific parameters and experimental results of an upgrade program in which the local processing power of the front-end electronics has been increased by a factor 50. Such a powerful tool has allowed a real time display of the time evolution of the vertical beam sizes. An online correlation plot between the electron and positron beam sizes (turn by turn) is also displayed. These online video images are available in the LEP control room and are used in daily operation for luminosity optimisation.  
 
PS10 Ionisation losses and wire scanner heating: evaluation, possible solutions, application to the LHC. proton, lepton, ion, vacuum 120
 
  • C. Fischer
    CERN, Geneva, Switzerland
  Harmful heating mechanisms, resulting in wire breakage, limit the utilisation of wire scanner monitors to below a given beam intensity. This threshold depends on the accelerator design parameters. In lepton colliders, the short beam bunches generate strong wake-fields inside the vacuum pipe which are sensed by the wire and are the predominant current limit. These effects can be minimised by a smooth design of the monitor cross section and by choosing a wire made of an insulating material. A second source of energy deposition inside the wire, also present in hadron machines, and even when the wire material is insulating, results from collision and ionisation of the wire material atoms by the incident beam particles. Calculations are presented to evaluate the efficiency of this process and a possible solution is suggested which may reduce this limitation. An example is given for the case of the LHC.  
 
PS11 Ionisation profile monitor tests in the SPS ion, proton, space-charge, insertion 123
 
  • C. Fischer, J. Koopman
    CERN, Geneva, Switzerland
  A beam profile monitor, from DESY, based on the ionisation of the rest gas, was installed in the SPS in 1997. Horizontal beam profiles obtained from the extracted positive ions are presented. It is known that in this case some broadening affects the signal, which limits the monitor resolution. This broadening results from the transverse momentum that the ions gain within the space charge field of the circulating beam. In order to improve the resolution for LHC applications, the monitor was modified during the 1998/99 winter stop. A magnetic focusing was incorporated. The aim is to analyse the signal provided by collecting the electrons, rather than the ions, of the ionised rest gas. The details of this new set-up and the expectations for the resolution limit will be compared to the measurement results.  
 
PS14 Comparative test results of various beam loss monitors in preparation for LHC proton, ion, beam-losses, simulation 132
 
  • J. Bosser, G. Ferioli
    CERN, Geneva, Switzerland
  Beam loss detectors will play an important role in the protection of the superconducting LHC magnets. Different types of detectors have been tested in the SPS ring and secondary beam lines with a view to their possible use for this application. This paper describes the measurements made with: microcalorimeters at cryogenic temperatures, PIN diodes, ionisation chambers, scintillators, and ACEMs. Measurements made using proton beams showing their relative sensitivities, linearities in counting or analog mode and minimum detection level will be presented.  
 
PS19 Photon counting detectors for fill structure measurements at visible wavelengths photon, storage-ring, single-bunch, diagnostics 144
 
  • H.L. Owen
    CLRC, Daresbury Laboratory, Warrington, UK
  When making accurate measurements of the relative populations of electron bunches in a storage ring, notably in light sources operating with only a single bunch filled, the method of time-correlated single photon counting gives the greatest dynamic range. The timing resolution and background noise level of the photon detector employed is critically important in determining the overall performance of the system; hitherto the best performance has been obtained detecting X-ray photons using avalanche photodiodes. On the SRS at Daresbury a visible light diagnostic station offers greater ease of access to instrumentation and operational advantages. A review is given of the detector types which have been employed, and the performances which can be obtained using visible light.  
 
PS20 A current digitizer for ionisation chambers/SEMS with high resolution and fast resoponse ion, power-supply, pick-up, monitoring 147
 
  • H. Reeg
    GSI, Gesellschaft für Schwerionenforschung, Darmstadt, Germany
  A current-to-frequency converter (CFC), recently developed, exhibits a response time up to the ms region. The frequency limit is raised beyond 1 MHz, extending the linear range by a factor of 100. The conversion factor reaches 10-13 C/pulse. The converter is employed, combined with ionization chambers (IC) and secondary electron emission monitors (SEM), to measure the intensity of the extracted beam in the transfer lines adjoining GSI's heavy ion synchrotron (SIS). Fast intensity fluctuations during the particle spill can be observed. Reduced hum and noise pickup, better handling and mounting flexibility as well as reduced costs are achieved building up the spill monitoring system with distributed components.  
 
PT01 Closed-orbit correction using the new beam position monitor electronic of Elsa Bonn closed-orbit, quadrupole, resonance, alignment 153
 
  • J. Dietrich, I. Mohos, J. Keil
    IKP, Forschungszentrum Jülich GmbH, Jülich, Germany
  RF and digital electronics, developed at the Forschungszentrum Jülich/IKP were integrated to form the new beam position monitor (BPM) system at the Electron Stretcher Accelerator (ELSA) of the University of Bonn. With this system the preservation of the polarization level during acceleration was currently improved by a good correction of the closed-orbit. All BPM offsets relative to the magnetic quadrupole centers were determined by the method of beam-based alignment. The optics functions measured by the BPM system are in good agreement with theoretical predictions.  
 
PT12 Aspects of bunch shape measurements for low, intense ions beams ion, target, scattering, rfq 186
 
  • P. Forck, F. Heymach, U. Meyer, P. Moritz, P. Strehl
    GSI, Gesellschaft für Schwerionenforschung, Darmstadt, Germany
  For the characterisation of the ion beam delivered by the new High Current LINAC at GSI, the time structure of bunches and the knowledge concerning their intensity distribution in longitudinal phase space is of great importance. At least 100ps time resolution and the capability of measuring long tails in the distribution were design parameters. Taking advantage of Rutherford-scattering to reduce the count rate, a direct time of flight measurement technique using diamond detectors can be applied. First results are reported. Plans for determine the energy of individual ions by detecting secondary electrons emitted from a thin C foil using 1m drift are discussed.  
 
PT15 High current precision long pulse electron beam position monitor kicker, instrumentation, diagnostics, target 193
 
  • S.D. Nelson, Y.J. Chen, T. Fessenden, C. Holmes
    LLNL, Lawrence Livermore National Laboratory, Livermore, CA, USA
  Precision high current long pulse electron beam position monitoring has typically experienced problems with high Q sensors, sensors damped to the point of lack of precision, or sensors that interact substantially with any beam halo thus obscuring the desired signal. As part of the effort to develop a multi-axis electron beam transport system using transverse electromagnetic stripline kicker technology, it is necessary to precisely determine the position and extent of long high energy beams for accurate beam position control (6 - 40 MeV, 1 - 4 kA, 2 μs beam pulse, sub millimeter beam position accuracy.) The kicker positioning system utilizes shot-to-shot adjustments for reduction of relatively slow (< 20 MHz) motion of the beam centroid. The electron beams passing through the diagnostic systems have the potential for large halo effects that tend to corrupt position measurements.