Author: Hillert, W.
Paper Title Page
TUPRO039 Optimizing Polarization with an Improved Integer Resonance Correction Scheme at ELSA 1108
 
  • J.F. Schmidt, O. Boldt, F. Frommberger, W. Hillert, J.-P. Thiry
    ELSA, Bonn, Germany
 
  Funding: DFG
The Electron Stretcher Facility ELSA of Bonn University provides a polarized electron beam of up to 3.2 GeV. In the stretcher ring various depolarizing resonances are crossed during the fast energy ramp of 6 GeV/s. The high polarization degree of up to 70% can only be conserved by taking several appropriate countermeasures. Concerning integer resonances, additional harmonic horizontal fields are applied by orbit correction magnets around the ring to compensate the resonance driving fields. The correction field has to be adjusted by empirical optimization of polarization. Recent developments enhance this optimization process, especially at high energies: A new magnet system allows for higher correction amplitudes and shorter rising times. Furthermore, a modified correction scheme was implemented. It takes into account the additional fields of the quadrupole magnets, arising from the orbit response of the correction magnets.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-TUPRO039  
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TUPRO040 High Bandwidth Closed Orbit Control for a Fast Ramping Electron Accelerator 1111
 
  • J.-P. Thiry, A. Dieckmann, F. Frommberger, W. Hillert, J.F. Schmidt
    ELSA, Bonn, Germany
 
  ELSA is a fast ramping stretcher ring capable of acceleration and storage of polarized electrons with energies up to 3.2 GeV. To preserve the initial degree of polarization, the acceleration is performed by a fast energy ramp with a maximum ramping speed of 6 GeV/s. During acceleration especially the vertical orbit needs to be continuously corrected so that the vertical rms deviation does not exceed 50 μm at any time. In order to compensate the so called integer resonances, which occur at certain energies, the orbit correction system further needs to provide additional, empirically determined, harmonic field distributions. A successful application of these combined correction measures requires a considerably high bandwidth of up to some 100 Hz. In our contribution we will have a closer look at the performance and the acquired bandwidth of the correction system.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-TUPRO040  
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TUPRI016 First Studies on Ion Effects in the Accelerator ELSA 1585
 
  • D. Sauerland, W. Hillert, M.T. Switka
    ELSA, Bonn, Germany
  • A. Markoviḱ, U. van Rienen
    Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany
  • A. Meseck
    HZB, Berlin, Germany
 
  Funding: BMBF (Federal Ministry of Education and Research)
In the ELSA stretcher ring electrons are accelerated by a fast energy ramp of 6 GeV/s to a beam energy of 3.2 GeV. The high energetic electrons ionize the residual gas molecules in the beam pipe by collisions or synchrotron radiation. The generated ions in turn accumulate inside the beam potential, causing several undesired effects such as tune shifts and beam instabilities. These effects are studied experimentally at ELSA using its full diagnostic capabilities. Both tune shifts due to beam neutralization and transversal beam-ion instabilities can be determined from the beam spectrum. Additionally the beam's transfer function can be measured using a broadband transversal kicker. In the stretcher ring at a beam energy of 1.2 GeV, a periodic beam blow-up was detected in the horizontal plane. Additional measurements of the transversal beam spectrum and ns-time resolution observations with a streak camera identified this blow-up as a coherent dipole oscillation of the beam. This horizontal instability is presumably caused by trapped ions, as there is a strong correlation with the high voltage-bias of the clearing electrodes.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-TUPRI016  
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TUPRI046 Dynamics of Ion Distributions in Beam Guiding Magnets 1668
 
  • A. Markoviḱ, G. Pöplau, U. van Rienen
    Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany
  • W. Hillert, D. Sauerland
    ELSA, Bonn, Germany
  • A. Meseck
    HZB, Berlin, Germany
 
  Funding: Supported by the German Federal Ministry of Education and Research (BMBF) under contract number 05K13HRC.
Ions generated by synchrotron radiation and collisions of the beam with the rest gas in the vacuum chamber could be a limiting factor for the operation of electron storage rings and Energy Recovery Linacs (ERL). In order to develop beam instability mitigation strategies, a deeper understanding of the ion-cloud behaviour is needed. Numerical simulations of the interaction between electron beams and parasitic ions verified with dedicated measurements can help to acquire that knowledge. This paper presents results of detailed simulations of the interaction in quadrupole magnets and drift sections of the Electron Stretcher Accelerator ELSA in Bonn. The focus is on the evaluation of the dynamics of different ion species and their characteristic distribution in quadrupole magnets.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-TUPRI046  
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TUPRI097 Radiation Protection Concepts for the Beamline for Detector Tests at ELSA 1799
 
  • N. Heurich, F. Frommberger, P. Hänisch, W. Hillert
    ELSA, Bonn, Germany
 
  At the electron accelerator ELSA, a new external beamline is under construction, whose task is to provide a primary electron beam for detector tests. In the future the accelerator facility will not only be offering an electron beam to the currently implemented photoproduction experiments for hadron physics, but to the new "‘research and technology center detector physics"',whose task is to develop detectors for particle and astroparticle physics. To dump and simultaneously measure the current of the electron beam behind the detector components a Faraday cup consisting of depleted uranium is used. The residual radiation leaving the cup is absorbed in a concrete casing. The radiation protection concept for the entire area of the new beamline was designed with the help of the Monte Carlo simulation program Fluka. In addition the concrete casing, radiation protection walls were taken into account to allow a safe working environment in the room created by the shielding walls. The presentation gives an overview of the different radiation protection concepts for the new beamline for detector tests at ELSA. Furthermore, progresses at the beamline will be reported.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-TUPRI097  
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WEPME062 A New Digital LLRF System for a Fast Ramping Storage Ring 2418
 
  • M. Schedler, F. Frommberger, W. Hillert, D. Proft, D. Sauerland
    ELSA, Bonn, Germany
  • D. Teytelman
    Dimtel, San Jose, USA
 
  At the Electron Stretcher Facility ELSA of Bonn University, an upgrade of the maximum stored beam current from 20 mA to 200 mA is planned. The storage ring operates applying a fast energy ramp of 6 GeV/s from 1.2 GeV to 3.5 GeV and a slow extraction afterwards over a few seconds to the hadron physics experiments. The intended upgrade is mainly limited by the coupled-bunch instabilities and the ability of bunch-by-bunch feedback systems to suppress such instabilities. In order to achieve optimum bunch-by-bunch feedback performance, the beam phase with respect to the master oscillator and the synchrotron frequency have to stay constant. This paper reports on a new high performance low level RF (LLRF) system. The system stabilizes the cavity field and is capable of executing fast voltage and phase ramps. The LLRF uses FPGA-based digital signal processing and includes cavity tuner control as well as fast interlocks and extensive diagnostics.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-WEPME062  
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THPRO101 Setup of a History Storage Engine based on Hypertable at ELSA 3128
 
  • D. Proft, F. Frommberger, W. Hillert
    ELSA, Bonn, Germany
 
  The electron stretcher facility ELSA serves external hadron physics experiments with a beam of unpolarized and polarized electrons of up to 3.2 GeV energy. Its in house developed control system is able to provide real time beam diagnostics as well as steering tasks in one homogeneous environment. The existing archive engine, a simple application logging parameter changes to a file storage, was unable to cope with the rising amount of parameter updates per second. Therefore a new storage system based on the non-relational database system hypertable has been introduced. It is capable of storing huge amounts of data to distributed storage systems, thus being able to handle the recording of every parameter change at any given time. The data can be read back with low latency to a newly developed graphical data browser using a C++ interface. This contribution will give details on the setup and performance of the history storage engine on top of hypertable.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-THPRO101  
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THPME098 Set up of a Synchrotron Light Monitor at the 2.5 GeV Booster Synchrotron at ELSA 3468
 
  • T. Schiffer
    Uni Bonn, Bonn, Germany
  • P. Hänisch, W. Hillert, M.T. Switka
    ELSA, Bonn, Germany
 
  For the upgrade of the accelerator facility ELSA towards higher stored beam currents, a non-destructive beam analysis is being implemented at the 2.5 GeV booster synchrotron. It is a fast ramping combined function synchrotron with an extraction repetition rate of 50 Hz. Typically, beam currents of 10 mA are accelerated from 20 MeV to the extraction energy of 1.2 GeV within 8.6 ms, hence the magnetic field is increased by up to 85 T/s. A synchrotron light monitor as the primary diagnostic tool will be utilized for measuring the transversal position and intensity distribution of the beam. Its dynamics on the fast energy ramp is of distinct interest. The proposed set-up of the synchrotron light monitor and the current development are presented.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-THPME098  
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THPME099 Synchrotron Radiation Diagnostics Performance at ELSA 3471
 
  • M.T. Switka, F. Frommberger, P. Hänisch, W. Hillert, D. Proft, M. Schedler, S. Zander
    ELSA, Bonn, Germany
 
  Funding: Work funded by the DFG within SFB/TRR16.
The pulse stretcher ring ELSA delivers polarized and non-polarized electrons with an adjustable beam energy of 0.5 - 3.5 GeV to external experimental stations. To meet the growing demands of the user community regarding beam intensity and quality, the upgrade of vital accelerator components is an ongoing process. This includes the improvement of the beam diagnostics in order to resolve and monitor intensity and quality limiting effects. ELSA has recently been equipped with a diagnostic synchrotron radiation beamline housing a streak camera as main beam imaging device. It extends the diagnostics capabilities into the picosecond temporal resolution regime and captures fast longitudinal and transverse beam dynamics. The obtained measurements provide crucial feedback for further machine optimization. The overall performance of the streak camera system and machine relevant measurements are presented.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-THPME099  
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