FRBHAU —  Process Tuning and Feedback Systems 2   (14-Oct-11   10:45—12:15)
Chair: M. Lonza, ELETTRA, Basovizza, Italy
Paper Title Page
FRBHAULT01 Feed-forward in the LHC 1302
  • M. Pereira, X. Buffat, K. Fuchsberger, M. Lamont, G.J. Müller, S. Redaelli, R.J. Steinhagen, J. Wenninger
    CERN, Geneva, Switzerland
  The LHC operational cycle is comprised of several phases such as the ramp, the squeeze and stable beams. During the ramp and squeeze in particular, it has been observed that the behaviour of key LHC beam parameters such as tune, orbit and chromaticity are highly reproducible from fill to fill. To reduced the reliance on the crucial feedback systems, it was decided to perform fill-to-fill feed-forward corrections. The LHC feed-forward application was developed to ease the introduction of corrections to the operational settings. It retrieves the feedback system's corrections from the logging database and applies appropriate corrections to the ramp and squeeze settings. The LHC Feed-Forward software has been used during LHC commissioning and tune and orbit corrections during ramp have been successfully applied. As a result, the required real-time corrections for the above parameters have been reduced to a minimum.  
slides icon Slides FRBHAULT01 [0.961 MB]  
FRBHAULT02 ATLAS Online Determination and Feedback of LHC Beam Parameters 1306
  • J.G. Cogan, R. Bartoldus, D.W. Miller, E. Strauss
    SLAC, Menlo Park, California, USA
  The High Level Trigger of the ATLAS experiment relies on the precise knowledge of the position, size and orientation of the luminous region produced by the LHC. Moreover, these parameters change significantly even during a single data taking run. We present the challenges, solutions and results for the online luminous region (beam spot) determination, and its monitoring and feedback system in ATLAS. The massively parallel calculation is performed on the trigger farm, where individual processors execute a dedicated algorithm that reconstructs event vertices from the proton-proton collision tracks seen in the silicon trackers. Monitoring histograms from all the cores are sampled and aggregated across the farm every 60 seconds. We describe the process by which a standalone application fetches and fits these distributions, extracting the parameters in real time. When the difference between the nominal and measured beam spot values satisfies threshold conditions, the parameters are published to close the feedback loop. To achieve sharp time boundaries across the event stream that is triggered at rates of several kHz, a special datagram is injected into the event path via the Central Trigger Processor that signals the pending update to the trigger nodes. Finally, we describe the efficient near-simultaneous database access through a proxy fan-out tree, which allows thousands of nodes to fetch the same set of values in a fraction of a second.  
slides icon Slides FRBHAULT02 [7.573 MB]  
FRBHAULT03 Beam-based Feedback for the Linac Coherent Light Source 1310
  • D. Fairley, K.H. Kim, K. Luchini, P. Natampalli, L. Piccoli, D. Rogind, T. Straumann
    SLAC, Menlo Park, California, USA
  Funding: Work supported by the U. S. Department of Energy Contract DE-AC02-76SF00515
Beam-based feedback control loops are required by the Linac Coherent Light Source (LCLS) program in order to provide fast, single-pulse stabilization of beam parameters. Eight transverse feedback loops, a 6x6 longitudinal feedback loop, and a loop to maintain the electron bunch charge were successfully commissioned for the LCLS, and have been maintaining stability of the LCLS electron beam at beam rates up to 120Hz. In order to run the feedback loops at beam rate, the feedback loops were implemented in EPICS IOCs with a dedicated ethernet multicast network. This paper will discuss the design, configuration and commissioning of the beam-based Fast Feedback System for LCLS. Topics include algorithms for 120Hz feedback, multicast network performance, actuator and sensor performance for single-pulse control and sensor readback, and feedback configuration and runtime control.
slides icon Slides FRBHAULT03 [1.918 MB]  
FRBHAULT04 Commissioning of the FERMI@Elettra Fast Trajectory Feedback 1314
  • G. Gaio, M. Lonza, R. Passuello, L. Pivetta, G. Strangolino
    ELETTRA, Basovizza, Italy
  Funding: The work was supported in part by the Italian Ministry of University and Research under grants FIRB-RBAP045JF2 and FIRB-RBAP06AWK3
FERMI@Elettra is a new 4th-generation light source based on a single pass Free Electron Laser (FEL). In order to ensure the feasibility of the free electron lasing and the quality of the produced photon beam, a high degree of stability is required for the main parameters of the electron beam. For this reason a flexible real-time feedback framework integrated in the control system has been developed. The first implemented bunch-by-bunch feedback loop controls the beam trajectory. The measurements of the beam position and the corrector magnet settings are synchronized to the 50 Hz linac repetition rate by means of the real-time framework. The feedback system implementation, the control algorithms and preliminary close loop results are presented.
slides icon Slides FRBHAULT04 [2.864 MB]