Author: Baudrenghien, P.
Paper Title Page
MOPPC015 Proposal for an RF Roadmap Towards Ultimate Intensity in the LHC 154
  • P. Baudrenghien, T. Mastoridis
    CERN, Geneva, Switzerland
  The LHC is currently operated with 1380 bunches at 50 ns spacing and 1.4 E11 p per bunch (0.35A DC). In this paper the RF operation with ultimate bunch intensity (1.7 E11 p per bunch) and 25 ns spacing (2808 bunches per beam) summing up to 0.86A DC is presented. With the higher beam current, the demanded klystron power will be increased and the longitudinal stability margin reduced. In addition one must consider the impact of a klystron trip (voltage and power transients in the three turns latency before the beam is actually dumped). In this work a scheme is proposed that can deal with ultimate bunch intensity, without modification to the RF power system. Only a minor upgrade of the LLRF will be necessary: the field set point will be modulated according to the phase shift produced by the transient beam loading, thus minimizing the requested RF power while keeping the strong feedback for stability and reduction of RF noise.  
THPPC084 LHC One-turn Delay Feedback Commissioning 3482
  • T. Mastoridis, P. Baudrenghien, J.C. Molendijk
    CERN, Geneva, Switzerland
  The 1-turn delay feedback is an FPGA based feedback system part of the LHC cavity controller, which produces gain only around the revolution frequency harmonics. As such, it helps reduce the transient beam loading and effective cavity impedance. Consequently, it increases the stability margin for Longitudinal Coupled Bunch Instabilities driven by the cavity impedance at the fundamental and allows reliable operation at higher beam currents. The 1-turn delay feedback was commissioned on all sixteen cavities in mid-October 2011 and was used in operation for the rest of the run. The commissioning procedure and algorithms for setting-up are presented. The resulting improvements in transient beam loading, beam stability, and required klystron power are analyzed. The commissioning of the 1-turn delay feedback reduced the cavity voltage phase modulation from approximately six degrees peak-to-peak to below one degree at 400 MHz.