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acceleration

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CT02 Determination of Radial Ion Beam Profile from the Energy Spectrum of Residual Gas Ions Accelerated in the Beam Potential space-charge, ion, electron, emittance 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.  
 
CT03 500 fs Streak Camera for UV-Hard X-Rays in 1 kHz Accumulating Mode with Optical 'Jitter Free' Synchronisation laser, accumulation, photon, optics 54
 
  • K. Scheidt, G.A. Naylor
    ESRF, The European Synchrotron Radiation Facility, Grenoble, France
  The development at the ESRF of a jitter-free, laser triggered Streak Camera has now yielded time resolution results as short as 460 fs while operating in accumulating mode. The so-called jitter-free synchronisation between the laser light and the Streak Camera is performed through a GaAs photo-switch in a simple HV circuit that connects directly to the Streak tube’s deflection plates. The novelty of this technique permits to obtain excellent dynamic range measurements in a shot-to-shot accumulation of ultra fast (laser stimulated) events at up to 1kHz without degrading the time resolution. Important insight was obtained on the quality of this optical synchronisation and its dependence on the laser characteristics, the switch circuit, and the structure of the GaAs switch itself. This permitted to suppress the jitter causes and today the 500 fs limitation is imposed by the streak tube’s intrinsic time resolution. This work was done by measuring (with Au or Pd photo-cathodes) the 3rd harmonic (i.e. 267 nm) of a 100 fs Ti:Saph laser. Also important progress was made with the reliability of the photo-switch and problems of HV break-down and structural degradation have been completely resolved. Since the principal use of this system at the ESRF is in ultra-fast X-ray diffraction experiments the exchangeable photo-cathode structure of this tube covers the entire UV-to-X-rays spectrum. The QE of various photo-cathode materials was measured in the 8-30 keV range.  
 
PT02 Real-time betatron tune measurement in the accelerator ramp at COSY-Jülich betatron, synchrotron, diagnostics, feedback 156
 
  • J. Dietrich, I. Mohos
    IKP, Forschungszentrum Jülich GmbH, Jülich, Germany
  A new real-time method for betatron tune measurements at COSY was developed and tested from the early 1997. A bandlimited broadband noise source was used for beam excitation, the transversal beam position oscillation was bunch-synchronous sampled and digitized with a high resolution ADC. The Fourier transform of the acquired data represents immediately the betatron tune. After the first promising experiments an automatic tunemeter was constructed. The tunemeter is used as routine diagnostic tool since end of 1998.  
 
PT05 First results on closed-loop tune control in the CERN-SPS quadrupole, feedback, simulation, controls 165
 
  • L. Jensen, O.R. Jones, H. Schmickler
    CERN, Geneva, Switzerland
  This paper presents the first measurements performed with the SPS Qloop. The emphasis will be laid on the model used for designing the regulation loop and how well it fits reality.  
 
PT10 Emittance and dispersion measurements at TTF emittance, quadrupole, dipole, linac 180
 
  • M. Castellano, A. Cianchi, V.A. Verzilov
    INFN-LNF, Laboratori Nazionali di Frascati dell'INFN, Frascati, Italy
  It is well known that beam dispersion , along with the Twiss parameters and emittance, contributes to the beam spot size. So that, in general, anomalous dispersion is an undesirable event and must be minimized by careful tuning the machine. If not, when the spot size is used to infer beam emittances, as it is the case of the "quadrupole scan" method, basically employed at TTF, the unknown dispersion can lead to overestimated values for the emittance. This paper presents the first attempt to determine the dispersion function at several points of the TTF Linac and to separate its contribution to the local emittance measurement, performed by means of the OTR imaging technique.