• S. Redaelli, O. Aberle, R.W. Assmann, C. Bracco, B. Dehning, M. Jonker, R. Losito, A. Masi, M. Sapinski, Th. Weiler, C. Zamantzas
  CERN, Geneva

A full scale prototype of the Large Hadron Collider (LHC) collimator was installed in 2004 in the CERN Super Proton synchrotron (SPS). During three years of operation the prototype has been used extensively for beam tests, for control tests and also to benchmark LHC simulation tools. This operational experience has been extremely valuable in view of the final LHC implementation as well as for estimating the LHC operational scenarios, most notably to establish procedures for the beam-based alignment of the collimators with respect to the circulating beam. This was made possible by installing in the SPS a first prototype of the LHC beam loss monitoring system. The operational experience gained at the SPS, lessons learnt for the LHC operation and various accelerator physics effects that could limit the efficiency of the collimator alignment procedures are presented.

• T.T. Boehlen, R.W. Assmann, C. Bracco, B. Dehning, S. Redaelli, Th. Weiler, C. Zamantzas
  CERN, Geneva

The LHC collimators are protected against beam caused damages by measuring the secondary particle showers with beam loss monitors. Downstream of every collimator an ionisation chamber and a secondary emission monitor are installed to determine the energy deposition in the collimator. The relation between the energy deposition in the beam loss monitor and the collimator jaw is based on secondary shower simulations. To verify the FLUKA simulations the prototype LHC collimator installed in the SPS was equipped with beam loss monitors. The results of the measurements of the direct impact of the 26 GeV proton beam injected in the SPS onto the collimator are compared with the predictions of the FLUKA simulations. In addition simulation results from parameter scans and for mean and peak energy deposition with its dependencies are shown.

• B. Dehning, D. Bocian, T.T. Boehlen, E. Effinger, J. Emery, F. Follin, V. Grishin, E.B. Holzer, H. Ikeda, S. Jackson, D.K. Kramer, G. Kruk, P. Le Roux, J. Mariethoz, M. Misiowiec, L. Ponce, C. Roderick, M. Sapinski, M. Stockner, C. Zamantzas
  CERN, Geneva
• A. Priebe
  Poznań University of Technology, Poznań

The LHC beam loss monitoring system (BLM) consists of about 4000 monitors observing losses at all quadrupole magnets and many other likely loss locations. At the first LHC operation in August and September 2008 all monitors were active and used to observe the losses during the initial beam steerings, at collimators, at the LHC dump and during aperture scans. The different loss patterns will be discussed and compared with the expectations originating from simulations. The observed signals of the BLM system will be analysed in terms of response time, sensitivity cross talk between channels and noise performance.