• J. Strait
  Fermilab, Batavia
• R. Bailey, M. Bednarek, B. Bellesia, N. Catalan-Lasheras, K. Dahlerup-Petersen, R. Denz, C. Fernandez-Robles, R.H. Flora, E. Gornicki, M. Koratzinos, M. Pojer, L. Ponce, R.I. Saban, R. Schmidt, A.P. Siemko, M. Solfaroli Camillocci, H. Thiesen, A. Vergara-Fernández
  CERN, Geneva
• Z. Charifoulline
  RAS/INR, Moscow
• P. Jurkiewicz, P.J. Kapusta
  HNINP, Kraków

The incident of 19 September 2008 at the LHC was apparently caused by a faulty inter-magnet splice of about 200 nOhm resistance. Cryogenic and electrical techniques have been developed to detect other abnormal splices, either between or inside the magnets. The quench protection system is used in a special mode to measure the voltage across each magnet with an accuracy better than 0.1 mV, allowing internal splices with R > 10 nOhm to be detected. Since this system does not cover the bus between magnets, the cryogenic system is used in a special configuration* to measure the rate of temperature rise due to ohmic heating. Accuracy of a few mK/h, corresponding to a few Watts, has been achieved. This allows detection of excess resistance of more than a few tens of nOhms in a cryogenic sub-sector (2 optical cells). Follow-up measurements, using an ad-hoc system of high-accuracy voltmeters, are made in regions identified by the cryogenic system. These techniques have detected two abnormal internal magnet splices of 100 nOhms and 50 nOhms respectively. In 2009, this ad-hoc system will be replaced with a permanent one which will monitor all splices at the nOhm level.

*L. Tavian, Helium II Calorimetry for the Detection of Abnormal Resistive Zones in LHC Sectors, this conference.

• B. Bellesia, M.P. Casas Lino, R. Denz, C. Fernandez-Robles, M. Pojer, R.I. Saban, R. Schmidt, M. Solfaroli Camillocci, H. Thiesen, A. Vergara-Fernández
  CERN, Geneva

The Large Hadron Collider has 1572 superconducting circuits which are distributed along the eight 3.5 km LHC sectors. Time and resources during the commissioning of the LHC technical systems were mostly consumed by tests of each circuit of the collider: the powering tests. The tests consisted in carrying out several powering cycles at different current levels for each superconducting circuit. The Hardware Commissioning Coordination was in charge of planning, following up and piloting the execution of the test program. The first powering test campaign was carried out in summer 2007 for sector 7-8 with an expected duration of 12 weeks. The experience gained during these tests was used by the commissioning team for minimising the duration of the following powering campaigns to comply with the stringent LHC Project deadlines. Improvements concerned several areas: strategy, procedures, control tools, automatisation, resource allocation led to an average daily test rate increase from 25 to 200 tests per day. This paper describes these improvements and details their impact on the operation during the last months of LHC Hardware Commissioning.

• A. Vergara-Fernández, B. Bellesia, C. Fernandez-Robles, M. Koratzinos, A. Marqueta Barbero, M. Pojer, R.I. Saban, R. Schmidt, M. Solfaroli Camillocci, J. Szkutnik, J. Wenninger, M. Zerlauth
  CERN, Geneva

The core task of the commissioning of the LHC technical systems was the individual test of the 1572 superconducting circuits of the collider, the powering tests. The two objectives of these tests were the validation of the different sub-systems making each superconducting circuit as well as the validation of the superconducting elements of the circuits in their final configuration in the tunnel. A wide set of software applications were developed by the team in charge of coordinating the powering activities (Hardware Commissioning Coordination) in order to manage the amount of information required for the preparation, execution and traceability of the tests. In all the cases special care was taken in order to keep the tools consistent with the LHC quality assurance policy, avoid redundancies between applications, ensure integrity and coherence of the test results and optimise their usability within an accelerator operation environment. This paper describes the main characteristics of these tools; it details their positive impact on the completion on time of the LHC Hardware Commissioning Project and presents usage being envisaged during the coming years of operation of the LHC.

• S. Wagner, R. Nibali
  ETH, Zurich
• R. Schmidt, J. Wenninger
  CERN, Geneva

The design and operation of the LHC Machine Protection System (MPS) implicates the trade-off between machine safety and beam availability, defined by MPS reliability in terms of missed emergency beam dumps and false dumps. A generic methodology, including almost 5000 MPS components modeled as individual objects and Monte Carlo simulation, has proved feasible and useful to address that trade-off*. The resulting MPS reliability numbers allow for the comparison of different system configurations with regard to safety and availability. In search of a solution to reduce the simulation time needed for addressing the rare events involved, an analytical description of the model has been developed. Its numerical solution provides an advanced verification of the simulation results and the basis for a rare event approach. The paper introduces the analytical description and the verification of the reliability numbers resulting from the simulations. It specifies to which extent the simulations can be replaced by the analytical model description and where the latter reaches its limits. Furthermore, the meaning of the analytical description as a basis for simulation time reduction is discussed.

*S.Wagner, Balancing Safety and Availability for an Electronic Protection System, ESREL08; S.Wagner, Reliability Analysis of the LHC Machine Protection System: Terminology and Methodology, EPAC08

• N.A. Tahir
  GSI, Darmstadt
• V.E. Fortov, I. Lomonosov, A. Shutov
  IPCP, Chernogolovka, Moscow region
• D.H.H. Hoffmann
  TU Darmstadt, Darmstadt
• R. Piriz
  Universidad de Castilla-La Mancha, Ciudad Real
• R. Schmidt
  CERN, Geneva

When the LHC will work at full capacity, two counter rotating beams of 7 TeV/c protons will be generated. Each beam will consist of 2808 bunches while each bunch will comprise of 1.15x10¹¹ protons. Bunch length will be 0.5 ns whereas two neighboring bunches will be separated by 25 ns . Intensity in the transverse direction will be Gaussian with σ = 0.2 mm. Each beam will carry 362 MJ energy, sufficient to melt 500 kg of Cu. Safety is an extremely important issue in case of such powerful beams. We report two–dimensional numerical simulations of hydrodynamic and thermodynamic response of a solid copper cylinder that is facially irradiated by one of the LHC beams in axial direction. The energy loss of protons in copper is calculated employing the FLUKA code and this data is used as input to a hydrodynamic code, BIG2. Our simulations show that the beam will penetrate up to 35 m into the solid copper target. Since the target is strongly heated by the beam, a sample of High Energy Density (HED) matter is generated. An additional application of the LHC, therefore will be, to study HED matte. This is an improvement of our previous work [Tahir et al., PRL 94 (2005) 135004].