Author: Lens, D.E.M.
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TUPRI073 Impact of Simplified Stationary Cavity Beam Loading on the Longitudinal Feedback System for SIS100 1736
 
  • K. Groß, H. Klingbeil, D.E.M. Lens
    TEMF, TU Darmstadt, Darmstadt, Germany
  • H. Klingbeil
    GSI, Darmstadt, Germany
  • D.E.M. Lens
    TU Darmstadt, RTR, Darmstadt, Germany
  
  Funding: Work supported by the German Federal Ministry of Education and Research (BMBF) under the project 05P12RDRBF.
The main synchrotron SIS100 of the Facility for Antiproton and Ion Research (FAIR) will be equipped with a bunch-by-bunch feedback system to damp longitudinal beam oscillations. In the basic layout, one three-tap finite impulse response (FIR) filter will be used for each single bunch and oscillation mode. The detected oscillations are used to generate a correction voltage in dedicated broadband radio frequency (RF) cavities. The digital filter is completely described by two parameters, the feedback gain and the passband center frequency, which have to be defined depending on the longitudinal beam dynamics. In earlier works*, the performance of the closed loop control with such an FIR-filter was analyzed and compared to simulations and measurements with respect to the damping of coherent dipole and quadrupole modes, the first modes of oscillation. This contribution analyzes the influence of cavity beam loading on the closed loop performance and the choice of the feedback gain and passband center frequency to verify future high current operation at FAIR.
* H. Klingbeil et al., IEEE Trans. Nuc. Sci., Vol. 54, No. 6, 2007 and D. Lens et al., Phys. Rev. STAB 16, 032801, 2013. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-TUPRI073  
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THPRO102 Generation of RF Frequency and Phase References on the FAIR Site 3131
 
  • B. Zipfel, H. Klingbeil, U. Laier, K.-P. Ningel, S. Schäfer, C. Thielmann
    GSI, Darmstadt, Germany
  • U. Hartel, H. Klingbeil
    TEMF, TU Darmstadt, Darmstadt, Germany
  • D.E.M. Lens
    TU Darmstadt, RTR, Darmstadt, Germany
  
  Based on the Bunch Phase Timing System (BuTiS)* local analog radio frequency reference signals (RF references) like the particle revolution frequency and their multiple harmonics will be generated. These references are used to control the phase of the accelerator cavities to altering harmonics of the bunch revolution frequency. Delay or phase shifts from the FAIR-Center to references at the BuTiS endpoints are already compensated by the BuTiS receivers. Phase shifts from the RF reference generators to LLRF electronics can be compensated by controlling the output phases of the DDS modules of the RF references. However phase shift delays of multiple harmonics at the same interconnecting electrical path are not identical at the same time. Configurable electronics** manage phase calibration of the RF references to their endpoints. Calibration may depend on frequency and harmonic of the RF reference, aging as well as on thermal effects. The electrical length and impedance of interconnecting cables for phase control loops can be compensated. This is an important feature, in particular if control loops are switched between different harmonic frequencies.
*B. Zipfel, P. Moritz: Proc. IPAC 2011, San Sebastian
**S. Schäfer, et al.: Proc. IPAC 2013, Shanghai 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-THPRO102  
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