• M. Sapinski, B. Dehning
  CERN, Geneva
• A. Priebe
  Poznań University of Technology, Poznań

The LHC beam loss measurement system is mainly used to trigger the beam abort in case a magnet coil quench level is approached. The predicted heat deposition in the superconducting coils of the magnets have been determined by particle shower simulation codes, while the liquid helium cooling capacity of the system has been both simulated and measured. The results have been combined to determine the abort thresholds. Measurements of the energy depositions of lost protons from the initial beams in the LHC are used to determine the accuracy of the beam abort threshold settings. The simulation predictions are reviewed and compared with the measurement results.

• C. Kurfuerst, B. Dehning, E.B. Holzer, A. Nordt, M. Sapinski
  CERN, Geneva

Particle losses in the LHC arcs are mainly expected in the interconnection region between a dipole and quadrupole magnet. The maximal beam size, the maximal orbit excursion and aperture changes cause the enhancement of losses at this location. Extensive Geant4 simulations have been performed to characterise this particular region to establish beam abort settings for the beam loss monitors in these areas. Data from first LHC beam loss measurements have been used to check and determine the most likely proton impact locations. This input has been used to optimise the simulations used for the definition of thresholds settings. The accuracy of these settings is investigated by comparing the simulations with actual loss measurements.

• M. Jonker, E.B. Holzer, S. Mallows, D. Manglunki, G. Morpurgo, Th. Otto, M. Sapinski, F. Tecker, J.A. Uythoven
  CERN, Geneva

The proposed Compact Linear Collider (CLIC) is based on a two-beam acceleration scheme. The energy of high intensity, low energy drive beams is extracted and transferred to low intensity, high energy main beams. Direct ionization loss by the beam particles is the principal damage mechanism. The total charge gives a single drive beam-train a damage potential that is two orders of magnitude above the level causing structural damage in copper. For the main beam, it is the extreme charge density due to the microscopic beam size that gives it a damage potential of four orders of magnitude above the safe level. The machine protection system has to cope with a wide variety of failures, from real time failures (RF breakdowns, kickers misfiring), to slow equipment failures, to beam instabilities (caused by e.g. temperature drifts, slow ground motions). This paper discusses the baseline for the CLIC machine protection system which is based on passive, active and permit based protection. As the permit based protection depends on the measured performance of the previous pulse, the bootstrap procedure with safe beams and stepwise increase in beam intensities, is also discussed.

• M. Sapinski, B. Dehning, E.B. Holzer, M. Jonker, S. Mallows, Th. Otto
  CERN, Geneva
• C.P. Welsch
  Cockcroft Institute, Warrington, Cheshire

The Compact Linear Collider (CLIC) is a proposed multi-TeV linear electron-positron collider being designed by a world-wide collaboration. It is based on a novel two-beam acceleration scheme in which two beams (drive and main beam) are placed in parallel to each other and energy is transferred from the drive beam to the main one. Beam losses on either of them can have catastrophic consequences for the machine because of high intensity (drive beam) or high energy and small emittance (main beam). In the framework of machine protection, a Beam Loss Monitoring system has to be put in place. This paper discusses the requirements for the beam loss system in terms of detector sensitivity, resolution, dynamic range and ability to distinguish losses originating from various sources. A particular attention is given to the two-beam module where the protection from beam losses is particularly challenging and important.

• B. Goddard, V. Baggiolini, W. Bartmann, C. Bracco, L.N. Drosdal, E.B. Holzer, V. Kain, D. Khasbulatov, N. Magnin, M. Meddahi, A. Nordt, M. Sapinski
  CERN, Geneva
• M. Vogt
  DESY, Hamburg

The quality of the injection into the LHC is monitored by a dedicated software system which acquires and analyses the pulse waveforms from the injection kickers, and measures key beam parameters and compares them with the nominal ones. The beam losses at injection are monitored on many critical devices in the injection regions, together with the longitudinal filling pattern and maximum trajectory offset on the first 100 turns. The paper describes the injection quality check system and the results from LHC beam commissioning, in particular the beam losses measured during injection at the various aperture limits. The results are extrapolated to full intensity and the consequences are discussed.

• W. Bartmann, R.W. Assmann, C. Bracco, B. Dehning, B. Goddard, E.B. Holzer, V. Kain, M. Meddahi, A. Nordt, S. Redaelli, A. Rossi, M. Sapinski, D. Wollmann
  CERN, Geneva

The movable LHC injection protection devices in the SPS to LHC transfer lines and downstream of the injection kicker in the LHC were commissioned with low-intensity beam. The different beam-based alignment measurements used to determine the beam centre and size are described, together with the results of measurements of the transverse beam distribution at large amplitude. The system was set up with beam to its nominal settings and the protection level against various failures was determined by measuring the transmission and transverse distribution into the LHC as a function of oscillation amplitude. Beam losses levels for regular operation were also extrapolated. The results are compared with the expected device settings and protection level, and the implications for LHC operation discussed.