Author: Rossi, C.
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MOPOR012 Study of the Beam-Cavity Interaction in the PS 10 MHz RF System 618
  • G. Favia, H. Damerau, M. Morvillo, C. Rossi
    CERN, Geneva, Switzerland
  • M. Migliorati
    University of Rome "La Sapienza", Rome, Italy
  The eleven main accelerating cavities of the Proton Synchrotron (PS) at CERN consist of two ferrite-loaded coaxial λ/4 resonators each. Both resonators oscillate in phase, as their gaps are electrically connected by short bars. They are in addition magnetically coupled via the bias loop used for cavity tuning. The cavities are equipped with a wide-band feedback system, limiting the beam loading, and a further reduction of the beam induced voltage is achieved by relays which short-circuit each half-resonator gap when the cavity is not in use. Asymmetries of the beam induced voltage observed in the two half-cavities indicate that the coupling between the two resonators is not as tight as expected. The total cavity impedance coupling to the beam may be affected differently by the contributions of both resonators. A dedicated measurement campaign with high-intensity proton beam and numerical simulation have been performed to investigate the beam-cavity interaction. This paper reports the result of the study and the work aiming at the development of a model of the system, including the wide-band feedback, which reproduces this interaction.  
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-MOPOR012  
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MOPOR013 The PS 10 MHz High Level RF System Upgrade 622
  • G. Favia, H. Damerau, V.D. Desquiens, S. Energico, M. Morvillo, D. Perrelet, C. Rossi
    CERN, Geneva, Switzerland
  In view of the upgrade of the injectors for the High Luminosity LHC, significantly higher bunch intensity is required for LHC-type beams. In this context an upgrade of the main accelerating RF system of the Proton Synchrotron (PS) is necessary, aiming at reducing the cavity impedance which is the source of longitudinal coupled-bunch oscillations. These instabilities pose as a major limitation for the increase of the beam intensity as planned after LS2. The 10 MHz RF system consists in 11 ferrite loaded cavities, driven by tube-based power amplifiers for reasons of radiation hardness. The cavity-amplifier system is equipped with a wide-band feedback that reduces the beam induced voltage. A further reduction of the beam loading is foreseen by upgrading the feedback system, which can be reasonably achieved by increasing the loop gain of the existing amplification chain. This paper describes the progress of the design of the upgraded feedback system and shows the results of the tests on the new amplifier prototype, installed in the PS during the 2015-16 technical stop. It also reports the first results of its performance with beam, observed in the beginning of the 2016 run.  
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-MOPOR013  
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