• J. Harasimowicz, C.P. Welsch
  Cockcroft Institute, Warrington, Cheshire
• J. Harasimowicz
  The University of Liverpool, Liverpool

Capacitive pick-ups for closed-orbit measurements are presently under development for an Ultra-low energy Storage Ring (USR) at the future Facility for Low-energy Antiproton and Ion Research (FLAIR). Low-intensity, low-energy antiprotons impose challenging demands on the sensitivity of the monitoring system. The non-destructive beam position monitors (BPMs) should be able to measure 10⁷ particles and give sufficient information on the beam trajectory. This contribution presents the status of the BPM project development. Main goals of the investigation include optimization of the mechanical design and preparation of a narrowband signal processing system.

• D. B. Belohrad, L.K. Jensen, O.R. Jones, M. Ludwig, J.-J. Savioz
  CERN, Geneva

The fast beam current transformers (FBCTs) for the Large Hadron Collider (LHC) were designed to provide bunch to bunch and turn by turn intensity measurements. The required bunch to bunch measurements together with a large machine circumference call for stringent control of the transmission bandwidth, droop and DC offsets in the front-end electronics. In addition, two measurement dynamic ranges are needed to achieve the required measurement precision, increasing the complexity of the calibration. This paper reports on the analysis of the measurement and calibration methods, discusses theoretical precision limits and system limitations and provides a comparison of the theoretical results with the real data measured during the LHC start-up.

• V. Ptitsyn, A. Marusic, R.J. Michnoff, M.G. Minty, G. Robert-Demolaize, T. Satogata
  BNL, Upton, Long Island, New York

Slow variations of the RHIC closed orbit have been strongly influenced by diurnal variations. These variations affect the reproducibility of RHIC operation and might have contributed to proton beam polarization degradation during past polarized proton runs. We have developed and commissioned a slow orbit feedback system in RHIC Run-10 to diminish these variations and improve energy ramp commissioning and tuning efficiency. This orbit feedback uses multiple dipole correctors and orbit data from an existing beam position monitor system. The precision of the orbit feedback system has resulted directly from application of an improved algorithm for measurement of the average orbit, from improved survey offsets and various measures taken to ensure deterministic delivery of the BPM data. Closed orbit corrections are calculated with an online model-based SVD algorithm, and applied by a control loop operating at up to 1 Hz rate. We report on the feedback design and implementation, and commissioning and operational experience in RHIC Run-10.