Goddard, Brennan 2010 2010 This note presents the final assessment of the static heat loads in the LHC arc cryostats, using different experimental methods during the first commissioning period in 2007. This assessment further develops and completes previous estimates made during the commissioning of sector 7_8 [1]. The estimate of the helium inventory, a prerequisite for the heat load calculation, is also presented. Heat loads to the cold mass are evaluated from the internal energy balance during natural as well as powered warm-ups of the helium baths in different subsector. The helium inventory is calculated from the internal energy balance during powered warm-ups and matched with previous assessments. Furthermore, heat loads to the thermal shield are estimated from the non-isothermal cooling of the supercritical helium in line E. The comparison of measured heat loads with previous estimates and with budgeted values is then presented, while their correlation with some important parameters like insulation vacuum pressure and some heat interception temperatures is proposed and discussed. Scheuerlein, C Pong, I Senatore, C Di Michiel, M Thilly, L Gerardin, A Reluner, B Oberli, L Willering, G Bottura, L 2009 2009 The degradation mechanisms of state-of-the-art Nb-Ti/Cu superconductors are described, based on in-situ synchrotron X-ray diffraction measurements during heat treatment. A quantitative description of the Nb-Ti/Cu degradation in terms of critical current density, Cu stabiliser resistivity and mechanical composite strength is presented. In an applied magnetic field a significant critical current degradation is already observed after a 5-minute 400 °C heat treatment, due to variations of a-Ti precipitate size and distribution within the Nb-Ti alloy filaments. A strong degradation of the strand mechanical properties is observed after several minutes heating above 550 °C, which is also the temperature at which the formation of Cu Ti intermetallic phases is detected. Several minutes heating at 250 °C are sufficient to increase the RRR of the strongly cold work strands inside a Rutherford type cable from about 80 to about 240. Heating for several minutes at 400 °C does not cause a significant conductor degradation in self-field and, thus, leaves enough temperature margin for the electrical interconnection of Nb-Ti/Cu conductors with common low temperature solders. Scheuerlein, C Di Michiel, M Thilly, L Buta, F Peng, X Gregory, E Parrell, J A Pong, I Bordini, B Cantoni, M 2009 2009 The evolution of Nb containing phases during the diffusion heat treatment of three different high critical current Nb$_{3}$Sn strand types is compared, based on synchrotron X-ray diffraction results that have been obtained at the ID15 beam line of the European Synchrotron Radiation Facility (ESRF). In all strands studied, Nb$_{3}$Sn formation is preceded by the formation of a Cu-Nb-Sn ternary phase, NbSn2 and Nb6Sn5. As compared to the PIT and Tube Type strand, the amount of these phases formed in the RRP strand is relatively small. In the RRP strand subelements with a fine filament structure Nb$_{3}$Sn grows more quickly, thereby preventing to a large extent the formation of the other higher tin phases. Rossi, L Supercond. Sci. Technol. 10.1088/0953-2048/23/3/034001 034001 23 superconductivity LHC 2010 2010 The Large Hadron Collider - LHC, the particle accelerator at CERN, Geneva, is the largest and probably the most complex scientific instrument ever built. Superconductivity plays a key role because the accelerator is based on the reliable operation of almost 10,000 superconducting magnets cooled by 130 tonnes of helium at 1.9 and 4.2 K and containing a total stored magnetic energy of about 15,000 MJ (including detector magnets). The characteristics of the 1200 tonnes of high quality Nb-Ti cables have met the severe requests in terms of critical currents, magnetization and inter-strand resistance; the magnets are built with an unprecedented uniformity, about 0.01% of variation in field quality among the 1232 main dipoles which are 15 m in length and 30 tonnes in weight. The results of this 20 year long enterprise will be discussed together with problems faced during construction and commissioning and their remedies. Particular reference is made to the severe incident which occurred nine days after the spectacular start-up of the machine on 10th September 2008. The status of repair and the plan for the physics program in 2010 are also presented. Carlier, E Antoine, A Chanavat, C Goddard, B Kain, V Magnin, N Uythoven, J Voumard, N 2010 2010 The beam dumping system of the Large Hadron Collider (LHC) provides a loss-free fast extraction of the circulating beams. It consists per ring of 15 extraction kickers, followed by 15 septum magnets, 10 dilution kickers and an external absorber. A dump request can occur at any moment during the operation of the collider, from injection energy up to collision energy. All kickers must fire synchronously with the beam abort gap to properly extract the whole beam in one single turn into the extraction channel. Incorrect operation of the extraction kickers can lead to beam losses and severe damage to the machine. The control system of the LHC beam dump kickers is based on a modular architecture composed of 4 different sub-systems, each with a specific function, in order to detect internal failures, to ensure a correct extraction trajectory over the whole LHC operational range, to synchronise and distribute dumps requests, and to analyse the transient signals recorded during the beam dumping process. The control architecture is presented and the different steps performed for its validation, from the individual sub-systems tests to the final commissioning with beam, are described Schipper, J Bleus, B Boucly, C Carlier, E Fowler, T Gaudillet, H Noulibos, R Sermeus, L 2010 2010 To reduce the beam losses when preparing high intensity proton beam for the CERN Neutrino to Gran Sasso (CNGS) facility, a new Multi-Turn extraction (MTE) scheme has been implemented in the PS, to replace the present Continuous Transfer (CT) to the SPS. Industrial off-the-shelf components have been used for the low-level part of the MTE kicker control system. National Instruments PXI systems are used to control the high voltage pulse generators and a SIEMENS programmable logic controller (PLC) handles the centralised oil cooling and gas insulation sub-systems Andreassen, O O Baggiolini, V Castaneda, A Gorbonosov, R Khasbulatov, D Reymond, H Rijllart, A Romera Ramirez, I Trofimov, N Zerlauth, M 2010 2010 The LHC with its unprecedented complexity and criticality of beam operation will need thorough analysis of data taken from systems such as power converters, interlocks and beam instrumentation during events like magnet quenches and beam loss. The causes of beam aborts or in the worst case equipment damage have to be revealed to improve operational procedures and protection systems. The correct functioning of the protection systems with their required redundancy has to be verified after each such event. Post mortem analysis software for the control room has been prepared with automated analysis packages in view of the large number of systems and data volume. This paper recalls the requirements for the LHC Beam Post Mortem System (PM) and the necessity for highly reliable data collection. It describes in detail the redundant architecture for data collection as well as the chosen implementation of a multi-level analysis framework, allowing for automated analysis and qualification of a beam dump event based on expert provided analysis modules. It concludes with an example of the data taken during first beam tests in September 2008 with a first version of the system. Pezzetti, M Tavares, D O Coppier, H 2010 2010 CERN, during last decade, has extensively applied the CERN/UNICOS framework to large scale cryoplant control system. An increase of interested to advanced control techniques and innovative simulation environment applied to cryogenic processes has also occur. Since new control algorithm development into UNICOS framework requires significant time, a control testing platform which can be externally connected can improve and simplify the procedure of testing advanced controllers implementation. In this context, the present paper describes the development of a control testing tool at CERN, which allows rapid control strategies implementation through the Matlab/Simulink® environment, coupled with the large scale cryogenics UNICOS control system or with the CERN PROCOS simulation environment. The time delays which are inherently introduced by network links and communication protocols are analyzed and experimentally identified. Security and reliability issues are also discussed. Pezzetti, M Bradu, B Gayet, P Vasseur, J 2010 2010 The off-line commissioning step, through reliable simulation of physical models, aims to correct and validate control systems before their implementation into real equipments. It prepares and minimizes plant commissioning phase and at the same time validates the efficiency of the new process control logic. This paper describes how different CERN/UNICOS cryogenic control systems have been pre-commissioned off-line, using the CERN cryogenic simulation environment PROCOS. Some examples are reported. Additionally the presented simulation environment will be used for operator training. The second part of the paper will presents the simulation platform and the first feedback from the operation crew. Gomes, P Blanco, E Casas, J Fluder, C Fortescue, E Le Roux, P Penacoba, G Pezzetti, M Soubiran, M Tovar, A Zwalinski, L 2010 2010 The Large Hadron Collider (LHC) was commissioned at CERN and started operation with beams in 2008. Several months of operation in nominal cryogenic conditions have triggered an optimisation of the process functional analysis. This lead to a few revisions of the control logic, which were realised on-the-fly. During the 2008-09 shut-down, and in order to enhance the safety, availability and operability of the LHC cryogenics, a major rebuild of the logic and several hardware modifications were implemented. The databases, containing instruments and controls in-formation, are being rationalized; the automatic tool, that extracts data for the control software, is being simplified. This paper describes the main improvements and sug-gests perspectives of further developments. Fernandez Penacoba, G Casas Cubillos, J de la Gama Serrano, J Gousiou, E 10.5170/CERN-2009-006.161 2009 2009 There are more than 6000 electronic cards for the instrumentation of the LHC cryogenics, housed in crates and distributed around the 27 km tunnel. Cards and crates will be exposed to a complex radiation field during the 10 years of LHC operation. Rad-tol COTS and rad-hard ASIC have been selected and individually qualified during the design phase of the cards. The test setup and the acquired data presented in this paper target the qualitative assessment of the compliance with the LHC radiation environment of an assembled system. It is carried out at the CNGS test facility which provides exposure to LHC-like radiation field. Dupont, T Courty, J C Perinic, G AIP Conf. Proc. 10.1063/1.3422381 3-10 1218 2010 2010 After having served for the surface tests of the Compact Muon Solenoid (CMS) magnet, the cold box and ancillaries of the CMS helium refrigerator have been dismantled, moved and re-installed in the USC55 cavern in 2007. The full re-commissioning in the cavern has been followed by several tests of the refrigerator to confirm its nominal performance before it was used for the magnet and detector tests in 2008. During these tests the safety modes of the refrigeration system have been tested and improved. After a nine-year project both, the magnet and the refrigeration system are now ready for the CMS operation. Darve, C Balle, C Casas-Cubillos, J Claudet, S Feher, S Ferlin, G Kerby, J Metral, L Perin, A Peterson, T Prin, H Rabehl, R Vauthier, N Wagner, U van Weelderen, R AIP Conf. Proc. 10.1063/1.3422296 1283-1290 1218 2010 2010 The insertion regions located around the four interaction points of the Large Hadron Collider (LHC) are mainly composed of the low-b triplets, the separation dipoles and their respective electrical feed-boxes (DFBX). The low-b triplets are Nb-Ti superconductor quadrupole magnets, which operate at 215 T/m in superfluid helium at a temperature of 1.9 K. The commissioning and the first operation of these components have been performed. The thermo-mechanical behavior of the low-b triplets and DFBX were studied. Cooling and control systems were tuned to optimize the cryogenic operation of the insertion regions. Hardware commissioning also permitted to test the system response. This paper summarizes the performance results and the lessons learned. Ferlin, G Claudet, S Tavian, L Wagner, U AIP Conf. Proc. 10.1063/1.3422295 1275-1282 1218 2010 2010 The superconducting magnets of the Large Hadron Collider (LHC) distributed over eight sectors of 3.3-km long are cooled at 1.9 K in pressurized superfluid helium. During the commissioning campaign of the sectors in 2008, cold standby periods at nominal operating temperature have allowed to measure the overall static heat inleaks reaching the magnet cold masses at 1.9 K by enthalpy balance in steady-state operation. In addition, during electrical powering of the different magnet circuits, helium II calorimetry based on precision thermometry has been implemented to assess with an accuracy of 100 mW/m the additional heat loads due to resistive heating and to detect possible abnormal heat dissipation during powering. This paper describes the method applied to perform these measurements, compares the results with the expected specified values and discusses the impact of the measured values on cryo-plant tuning and operational margins. Pereira, H Haug, F Silva, P Wu, J Koettig, T AIP Conf. Proc. 10.1063/1.3422264 1039-1046 1218 2010 2010 The loop heat pipe (LHP) is among the most effective heat transfer elements. Its principle is based on a continuous evaporation/condensation process and its passive nature does not require any mechanical devices such as pumps to circulate the cooling agent. Instead a porous wick structure in the evaporator provides the capillary pumping forces to drive the fluid [1]. Cryogenic LHP are investigated as potential candidates for the cooling of future small-scale particle detectors and upgrades of existing ones. A large spectrum of cryogenic temperatures can be covered by choosing appropriate working fluids. For high luminosity upgrades of existing experiments installed at the Large Hadron Collider (LHC) (TOTEM) and planned ones (FP420) [2-3] being in the design phase, radiation-hard solutions are studied with noble gases as working fluids to limit the radiolysis effect on molecules detrimental to the functioning of the LHP. The installation compactness requirement of experiments such as the CAST frame-store CCD detector cooling system impels also the design of a compact shaped LHP [4]. This paper reports on the design and experimental results of a general purpose LHP for temperatures as low as 110 K, for which the performances were measured using a Gifford-McMahon (GM) cooler as the cold source, combination envisaged for the cooling of future particle detectors. van Weelderen, R Goiffon, T Perin, A Darve, C Doohan, R S Gilankar, S G AIP Conf. Proc. 10.1063/1.3422299 1301-1308 1218 2010 2010 The Large Hadron Collider (LHC) now under commissioning at CERN is a 26.7 km collider based on several thousand high-field superconducting magnets, the majority of which operating in superfluid helium below 2 K and some isolated magnets operating in normal helium at 4.5 K. Four superconducting links (DSLs) of about 76 m in length and one of about 517 m in length, were designed, constructed and installed over a three year period. Their purpose is to transport current over long distances whenever underground LHC space constraints prevents to put power converters, current feed boxes and magnets in each others’ proximity. The four 76 m long DSLs transport current between current feed boxes and several of the isolated magnets, whereas the 517 m long DSL transports current between two current feed boxes. The links are comprised of cryogenic, vacuum-insulated, transfer lines housing one or more superconducting cables. The operating temperatures are about 5 K for the DSL part that houses the cable and about 60 K for the heat shield. Their commissioning and performance results at first operational experience in the beginning of 2008 are discussed. Haug, F Pereira, H Silva, P Pezzeti, M Pavlov, O Pirotte, O Metselaar, J Efthymiopoulos, I Fabich, A Lettry, J Kirk, H G McDonald, K T Titus, P Bennett, J R J AIP Conf. Proc. 10.1063/1.3422261 1023-1030 1218 2010 2010 MERIT is a proof-of-principle experiment of a target station suitable as source for future muon colliders or neutrino factories. When installed at the CERN (European Organization for Nuclear Research) PS (Proton Synchrotron)complex fast-extracted high-intensity proton beams intercepted a free mercury jet inside a normal-conducting, pulsed 15-T capture solenoid magnet cooled with liquid nitrogen. Up to 25 MJ of Joule heat was dissipated in the magnet during a pulse. The fully automated, remotely controlled cryogenic system of novel design permitted the transfer of nitrogen by the sole means of differential pressures inside the vessels. This fast cycling system permitted several hundred tests in less than three weeks during the 2007 data taking campaign. Claudet, S Lebrun, Ph Tavian, L Wagner, U AIP Conf. Proc. 10.1063/1.3422294 1267-1274 1218 2010 2010 The Large Hadron Collider (LHC) at CERN features the world’s largest helium cryogenic system, spreading over the 26.7 km circumference of the superconducting accelerator. With a total equivalent capacity of 145 kW at 4.5 K including 18 kW at 1.8 K, the LHC refrigerators produce an unprecedented exergetic load, which must be distributed efficiently to the magnets in the tunnel over the 3.3 km length of each of the eight independent sectors of the machine. We recall the main features of the LHC cryogenic helium distribution system at different temperature levels and present its exergy analysis, thus enabling to qualify second-principle efficiency and identify main remaining sources of irreversibility.. Perin, A. Casas-Cubillos, J. Claudet, S. Darve, C. Ferlin, G. Millet, F. Parente, C. Rabehl, R. Soubiran, M. van Weelderen, R. Wagner, U. AIP Conf. Proc. 10.1063/1.3422300 1309-1316 1218 2010 2010-04-23 The LHC is made of eight circular arcs interspaced with eight Long Straight Sections (LSS). Most powering interfaces to the LHC are located in these sections where the particle beams are focused and shaped for collision, cleaning and acceleration. The LSSs are constituted of several unique cryogenic devices and systems like electrical feed-boxes, standalone superconducting magnets, superconducting links, RF cavities and final focusing superconducting magnets. This paper presents the cryogenic commissioning and the main results obtained during the first operation of the LHC Long Straight Sections. Bordry, F Nisbet, D Thiesen, H Thomsen, J 2010 2010 The LHC particle accelerator uses a string of superconducting quadrupole magnets called the Inner Triplet to focus the beams before collision. This paper describes the powering of the magnets using nested circuits, and their control by decoupling of the currents using state feedback loops, and presents commissioning results. Peron, R Guennegues, V Pouliquen, JL Gollentz, B Bordry, F Burnet, JP 2010 2010 The Proton-Synchrotron (PS) accelerator at CERN will be supplied by a new power system. The pulsed operation of the PS accelerator requires a specific design of the main components of the power system. This paper presents some key elements of the design of DC/DC power converters in terms of aging of power semiconductors, the strategy of harmonics voltage suppression and the design of the output filters. Finally, the performance of this new power system is presented. Cravero, J M De Almeida Martins, C Garcia Retegui, R Wassinger, N Benedetti, M 2010 2010 A new high current, low rise time and high precision pulse generator is presented. The topology is based on the use of different stages, each one specific for a particular operation range in terms of power and switching frequency. The design and operating principle of the proposed topology are described. Finally, the results obtained from an implemented reduced scale prototype are compared with the simulation ones in order to validate the design Martins, C A Bordry, F Simonet, G 2010 2010 A solid state pulsed power generator rated at 100 kV, 2 MWpeak, 0.8 ms/2 Hz suited for klystrons cathode power supply (klystron modulator) is proposed as an alternative to traditional topologies, requiring thyratrons and PFN’s, for long pulse width applications (ms range). Some technological issues and design criteria of the proposed circuit main sub-systems (solid state switch, pulse transformer, undershoot network, droop compensation bouncer) will be presented. The principle of the klystron arc detection electronics and protection strategy is described. An optimization will be developed allowing the achievement of the required pulse flat-top precision (1%) with minimum volume and costs. Finally, experimental results obtained on a resistive dummy load and on a 1.3 MW klystron will be presented and discussed. Meddahi, M Bart Pedersen, S Boccardi, A Butterworth, A Fisher, A S Gianfelice-Wendt, E Goddard, B Hemelsoet, G H Höfle, W Jacquet, D Jaussi, M Kain, V Lefevre, T Shaposhnikova, E Uythoven, J Valuch, D 2010 2010 Unbunched beam is a potentially serious issue in the LHC as it may quench the superconducting magnets during a beam abort. Unbunched particles, either not captured by the RF system at injection or leaking out of the RF bucket, will be removed by using the existing damper kickers to excite resonantly the particles in the abort gap. Following beam simulations, a strategy for cleaning the abort gap at different energies was proposed. The plans for the commissioning of the beam abort gap cleaning are described and first results from the beam commissioning are presented. Goddard, B Bartmann, W Bracco, C Kain, V Meddahi, M Mertens, V Uythoven, J LHC Beam dump systems Aperture 2010 2010 The commissioning of the beam transfer systems for LHC included detailed aperture measurements in the injection regions and for the beam dump systems. The measurements, mainly single pass, were made using systematic scans of different oscillation phases and amplitudes, and the results compared with the expectations from the physical aperture model of the LHC. In this paper the measurements and results are presented and compared with the specified apertures in these critical areas. Goddard, B Aiba, M Bracco, C Carli, C Meddahi, M Weterings, W J M stripping foil PSB 160 MeV 2010 2010 Beam physics considerations for the stripping foil of the 160 MeV PSB H- injection systems are described, including the arguments for the foil type, thickness, geometry and positioning. The foil performance considerations are described, including expected stripping efficiency, emittance growth, energy straggling, temperature and lifetime. The different beam loss mechanisms are quantified in the context of the aperture limits, operational considerations and collimation requirements. Goddard, B Kain, V Meddahi, M emittance growth 450 GeV 2010 2010 The beam profile screens in the long SPS-to-LHC transfer lines were used to measure with high precision the emittance growth arising from scattering. The effective thickness of the scatterer could be varied by adding thick Al2O3 fluorescent screens, with the emittance measurement made using very thin Ti OTR screens. The technique allows the intrinsic variation in the emittance from the injector chain to be factored out of the measurement, and was applied to Pb82+ and protons, both with 450 GeV rigidity. The results are presented and the possible applications to the accurate benchmarking of nuclear interaction codes discussed. Puccio, B Castañeda Serra, A Kwiatkowski, M Romera Ramirez, I Todd, B beam interlock 2010 2010 A complex Machine Protection System has been designed to protect the LHC machine from an accidental release of the beam energy, with about 20 subsystems providing status information to the Beam Interlock System that is the backbone of machine protection. Only if the subsystems are in the correct state for beam operation, the Beam Interlock System receives a status flag and beam can be injected into LHC (Large Hadron Collider). The Beam Interlock System also relays commands from the connected subsystems in case of failure for triggering the LHC Beam Dumping System. To maintain the required level of safety of the Beam Interlock System, the performance of the key components is verified before every fill of the machine and validated after every emergency beam dump before beam operation is allowed to continue. This includes all critical paths, starting from the inputs from connected systems triggering a beam dump request, followed by the correct interruption and propagation sequence of the two redundant beam permit loops until the final extraction of the beam via the LHC beam dumping system. In this paper we report about the experience with the Beam Interlock System that has been deployed for some years in the Super Proton Synchrotron (SPS), in its transfer lines and recently in LHC. Formenti, F Charifoulline, Z Coelingh, G J Dahlerup-Petersen, K Denz, R Honma, A Ravaioli, E Schmidt, R Siemko, A Steckert, J Feher, S Flora, R H Pfeffer, H Quench protection system LHC 2010 2010 Two events, occurring in 2008 during commissioning of the LHC circuits, lead to fundamental changes to the scope of circuit protection. The discovery of aperturesymmetric quenches and the accidental rupture at 9 kA of an interconnecting busbar resulted in an emergency program for development and implementation of new protection facilities. The new scheme comprises a distributed busbar supervision system with early warning capabilities based on high-precision splice resistance measurements and system interlocks for rapid deexcitation of the circuit in case of sudden splice resistance increase. The developed symmetric quench detectors are digital systems with radiation-resistant FPGA logic controllers, having magnet heater firing capabilities. This program successfully allowed a safe re-powering of the collider. The concept of the new electronics boards and the powering modules will be described. More than 14600 extra cables and 6000 new detector and control cards were added to the existing Quench Protection System (QPS). A first evaluation of the system performance as well as a number of interesting discoveries made during the commissioning will be presented. Castañeda Serra, A Kwiatkowski, M Todd, B Programmable logic devices 2010 2010 Mission critical systems at the European Organisation for Nuclear Research (CERN) make extensive use of Programmable Logic Devices (PLDs) such as Field Programmable Gate Arrays (FPGAs) to implement their safety critical functions. The dependability of these safety critical functions is difficult to determine using traditional techniques. A robust approach is needed if PLD technology is to be accepted in mission critical systems. This paper discusses techniques which are being developed and employed by CERN to give confidence in the use of PLDs in mission critical systems, the Safe Machine Parameter system development is used as an example Kramer, T Bartmann, W Bracco, C Goddard, B Meddahi, M protection asynchronous dumps LHC 2010 2010 The LHC beam dump system has to safely dispose all beams in a wide energy range of 450 GeV to 7 TeV. A 3 ms abort gap in the beam structure for the switch-on of the extraction kicker field ideally allows a loss-free extraction under normal operating conditions. However, a low number of asynchronous beam aborts is to be expected from reliability calculations and from the first year's operational experience with the beam dump kickers. For such cases, MAD-X simulations including all optics and alignment errors have been performed to determine loss patterns around the LHC as a function of the position of the main protection elements in interaction region six. Special attention was paid to the beam load on the tungsten collimators which protect the triplets in the LHC experimental insertions, and the tracking results compared with semi-analytical numerical estimates. The simulations are also compared to the results of beam commissioning of these protection devices. Borburgh, J Balhan, B Barnes, M J Fowler, T Hinterschuster, F Hourican, M Kramer, T Palm, M Prost, A Sermeus, L Stadlbauer, T 2010 2010 The MedAustron facility, to be built in Wiener Neustadt (Austria), will provide protons and ions for both cancer therapy and research. Different types of bumpers, septa and kickers will be used in the low energy beam transfer line, the synchrotron and the high energy extraction lines.They are presently being designed in collaboration with CERN. Both 2D and 3D finite element simulations have been carried out to verify and optimize the field strength and homogeneity for each type of magnet and, where applicable, the transient field response. The detailed designs for the injection and dump bumpers, the magnetic septa and the fast chopper dipoles are presented. A novel design for the electrostatic septa is outlined. Bartmann, W Assmann, R Bracco, C Dehning, B Goddard, B Holzer, E B Kain, V Meddahi, M Nordt, A Redaelli, S Rossi, A Sapinski, M Wollmann, D 2010 2010 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. Beam loss 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. Senaj, V Ducimetière, L Vossenberg, E 2010 2010 The vertical beam dump system of the CERN Super Proton Synchrotron (SPS) uses two matched magnets with an impedance of 2 W and a combined kick strength of 1.152 Tm at 60 kV supply voltage. For historical reasons the two magnets are powered from three 3 W pulse forming networks (PFN) through three thyratronignitron switches. Recently flashovers were observed at the entry of one of the magnets, which lead, because of the electrical coupling between the kickers, to a simultaneous breakdown of the pulse in both magnets. To improve the reliability an upgrade of the system was started. In a first step the radii of surfaces at the entry of the weak magnet were increased, and the PFN voltage was reduced by 4%; the kick strength could be preserved by reducing the magnet termination resistance by 10 %. The PFNs were protected against negative voltage reflections and their last cell was optimised. In a second step the two magnets will be electrically separated and powered individually by new 2 W PFNs with semiconductor switches.. Uythoven, J Carlier, E Ducimetière, L Goddard, B Kain, V Magnin, N LHC beam dump kicker system 2010 2010 The LHC beam dump system was commissioned with beam in 2009. This paper describes the operational experience with the kicker systems and the tests and measurements to qualify them for operation. The kicker performance was characterized with beam by measurements of the deflection angles, using bunches extracted at different times along the kicker sweep. The kicker performance was also continuously monitored for each dump with measurement and analysis of all kick pulses, allowing diagnostic of errors and of long-term drifts. The results are described and compared to the expectations. Schoerling, D Baumbach, T Bernhard, Burkart, F Ehlers, S Gerstl, S Grau, A Peiffer, P Rossmanith, R Wollmann, D shimming undulator 2010 2010 The monochromaticity and intensity of synchrotron light emitted by undulators strongly depend on the undulator field quality. For the particular case of superconductive undulators it was shown recently that their field quality can be significantly improved by an array of coupled high temperature superconductor loops attached to the surface of the superconductive undulator. Local field errors induce currents in the coupled closed superconducting loops and, as a result, the hereby generated magnetic field minimizes the field errors. In previous papers the concept was described theoretically and a proof-of-principle experiment was reported. This paper reports on a prepatation experiment for the first quantitative measurement of the phase error reduction in a 13-period short model undulator equipped with a full-scale induction shimming system. Meddahi, M Fartoukh, S Fuchsberger, K Goddard, B Herr, W Kain, V Kaltchev, D Mertens, V Wenninger, J 2010 2010 In 2008, the SPS-to-LHC transfer line operation allowed for the first time to perform beam measurements in the last part of the lines and into the LHC. Beam parameters were measured and compared with expectation. Discrepancies were observed in the dispersion matching into the LHC, and also in the vertical phase advance along the line. In 2009, extensive theoretical and simulation work was performed in order to understand the possible sources of these discrepancies. This allowed establishing an updated model of the beam line, taking into account the importance of the full magnetic model, the limited dipole corrector strengths and the precise alignment of beam elements. During 2009, beam time was allocated in order to perform further measurements, checking and refining the optical model of the transfer line and LHC injection region and validating the different assumptions. Results of the 2009 optics measurements and comparison with the beam specification and model are presented.. Hessler, C Goddard, B Meddahi, M HiRadMat high radiation 2010 2010 The High Radiation to Materials facility - hereafter HiRadMat - is designed to allow testing of accelerator components, in particular those of the LHC and its injectors, with the impact of high-intensity pulsed beams. The facility is currently under construction, as an approved CERN project. The installation of the dedicated primary beam line and experimental area is planned during the 2010-2011 technical stop. It will be ready for users after commissioning and some test running in October 2011. A detailed proton beam line design has been performed in order to fulfil the beam parameter specification, in particular the demanding optics flexibility at the test stand location. The studies presented include trajectory correction and aperture studies as well as specifications of magnetic systems, power converters, beam instrumentation and vacuum systems Sermeus, L Barnes, M J Fowler, T PS multi-turn extraction 2010 2010 A five-turn continuous extraction has up to now been used to transfer the proton beam from the CERN PS to the SPS. This extraction uses an electrostatic septum to cut the filament beam into five slices, causing losses of about 15 %. These losses would be an even greater drawback when the beam intensity is increased for the CERN Neutrinos to Gran Sasso (CNGS) facility. To overcome this Multi-Turn Extraction (MTE) has been implemented, in which the beam is separated, prior to extraction, into a central beam core and four islands. Each beamlet is extracted using a set of kickers and a magnetic septum. For the kickers two new pulse generators have been built, each containing a lumped element Pulse Forming Network (PFN) of 12.5 W, 80 kV and 10.5 ms. For cost reasons existing 15 W transmission line kicker magnets are reused. The PFN characteristic impedance deliberately mismatches that of the magnets to allow a higher maximum kick. The PFN design has been optimised such that undesirable side-effects of the impedance mismatch on kick rise-time and flat-top remain within acceptable limits. The kicker systems put in place for the current first phase of MTE are presented. Barnes, M J Ducimetière, L Goddard, B Hessler, C Mertens, V Uythoven, J LHC injection kickers 2010 2010 Proton and ion beams are injected into LHC at 450 GeV by two kicker magnet systems, producing magnetic field pulses of up to 7.8 ms flat top duration with rise and fall times of not more than 900 ns and 3 ms, respectively. Both systems are composed of four travelling wave kicker magnets, powered by pulse forming networks. One of the stringent design requirements of these systems is a field flat top and postpulse ripple of less than ±0.5 %. A carefully matched high bandwidth system is required to obtain the required pulse response. Screen conductors are placed in the aperture of the kicker magnet to provide a path for the image current of the, high intensity, LHC beam and screen the ferrite against wake fields. However, these conductors affect the field pulse response. Recent injection tests provided the opportunity to directly measure the shape of the kick field pulse, with high accuracy, using a pilot beam. This paper details the measurements and compares the results with predictions and laboratory measurements. Buzio, M Beaumont, A Galbraith, P Golluccio, G Giloteaux, D Gilardoni, S Petrone, C Walckiers, L control injector chain 2010 2010 The control of five of the accelerators in the CERN injector chain (PS, PS Booster, SPS, LEIR and AD) is based upon real-time measurements in a reference magnet. These so-called “B-train” systems include a field marker to signal the achievement of a given field value, complemented by one or more pick-up coils to integrate flux changes. Recently, some concerns were raised about long-term reliability and performance improvements, in terms of both resolution and operational flexibility, for these systems. This paper reports the status of three related R&D activities, namely: the development of a novel dynamic NMR field marker for the PS; a campaign aimed at the detailed measurement of the magnetic state of a PS main magnet; and the design of a standardized electronic signal acquisition and conditioning system. Williams, L R Caspers, F Dalin, J M Haemmerle, V Tiseanu, I Tock, J P Sauerwein, C inspection LHC 2010 2010 For the inspection of certain critical elements of the LHC machine a mobile computed tomography system has been developed and built. This instrument has to satisfy stringent space, volume and weight requirements in order to be transportable and usable to any interconnection location in the LHC tunnel. Particular regions of interest in the interconnection zones between adjacent magnets are the plug in modules (PIM), the soldered splices in the superconducting bus-bars and the interior of the quench diode container. This system permits detailed inspection of these regions without needing to break the insulation vacuum. Limited access for the x-ray tube and the detector required the development of a special type of partial tomography, together with suitable reconstruction techniques for 3 D volume generation from radiographic projections. The layout of the complete machine, the limited angle tomography, as well as a number of radiographic and tomographic inspection results is presented. Bertinelli, F Catalan Lasheras, N Fessia, P Garion, C Mathot, S Perin, A Scheuerlein, C Sgobba, S ten Kat, H Tock, J P Verweij, A Willering, G consolidation LHC 7 TeV 2010 2010 Following the analysis of the September 2008 LHC incident, the assembly process and the quality assurance of the main 13 kA interconnection splices were improved, with new measurement and diagnostics methods introduced. During the 2008-2009 shutdown ~5% of these 10 000 splices were newly assembled with these improvements implemented, but essentially maintaining the original design. It is known today that a limiting factor towards 7 TeV operation is the normal conducting resistance of ~15% of the original main 13 kA interconnection splices, associated to the electrical continuity of the copper stabiliser. A “Splices Task Force” has been set up at CERN to evaluate the need for, develop and test design improvements and prepare the implementation of a consolidation campaign. Important issues of splice design, process choice, resources and time requirements are considered. Walckiers, L Arpaia, P Bottura, L Buzio, M Dunkel, O Fiscarelli, L Montenero, G Garcia Perez, J Todesco, E LHC dynamic errors FiDeL 2010 2010 One of the main requirements for the magnet operation of the Large Hadron Collider at CERN is the correction of the dynamic multipole errors produced. In particular, integrated sextupole errors in the main dipoles must be kept well below 0.1 units to ensure acceptable chromaticity. The feed-forward control of the LHC magnets is based on the Field Description for the LHC (FiDeL), a semi-empirical mathematical model capable of forecasting the magnet’s behaviours in order to suitably power the corrector scheme. Measurement campaign were recently undertaken to validate the model making use of a novel Fast rotating-coil Magnetic Measurement Equipment (FAME), able to detect superconductor decay and snapback transient with unprecedented accuracy and temporal resolution. We discuss in this paper the test setup and some measurement results confirming the FiDeL model. Perin, A Van Weelderen, R Claudet, S LHC superconducting links 2010 2010 In the LHC, a large number of superconducting magnets are powered remotely by 5 superconducting links at distances of 70 up to 520 m. This innovation allowed choosing more convenient locations for installing the electrical feedboxes and their related equipment. The consolidations performed after the first commissioning campaign and the operational experience with the superconducting links over a period of several months are presented. Based on the successful application of superconducting links in the LHC, such devices can be envisaged for powering future accelerator magnets. Several possible cryogenic configurations for future superconducting links are presented with their respective figures of merit from the cryogenic and practical implementation point of view. Todesco, E Aquilina, N Auchmann, B Bottura, L Buzio, M Chritin, R Deferne, G Deniau, L Fiscarelli, L Hagen, P Garcia Perez, J Giovannozzi, M Lamont, M Montenero, G Muller, G Pereira, M Redaelli, S Remondino, V Sammut, N Schmidt, F Steinhagen, R Strzelczyk, M Tomas, R Venturini Delsolaro, W Wenninger, J Wolf, R 2010 2010 The relation between field and current in each family of the Large Hadron Collider magnets is modelled with a set of empirical equations (FiDeL) whose free parameters are fit on magnetic measurements. They take into account residual magnetization, persistent currents, hysteresis, saturation, decay and snapback during initial part of the ramp. Here we give a first summary of the reconstruction of the magnetic field properties based on the beam observables (orbit, tune, coupling, chromaticity) and a comparison with the expectations. The most critical issues for the machine performance in terms of knowledge of the relation magnetic field vs current are pointed out. Ducimetière, L Uythoven, J Barnes, M J CLIC pre-damping rings 2010 2010 The Compact Linear Collider (CLIC) study is exploring the scheme for an electron-positron collider with high luminosity (1034-1035 cm-2s-1) and a nominal centre-of mass energy of 3 TeV: CLIC would complement LHC physics in the multi-TeV range. The CLIC design relies on the presence of Pre-Damping Rings (PDR) and Damping Rings (DR) to achieve the very low emittance, through synchrotron radiation, needed for the luminosity requirements of CLIC. In order to limit the beam emittance blow-up due to oscillations the combined flat top ripple and droop of the field pulse, for the DR extraction kickers, must be less than 0.02 %. In addition, the allowed beam coupling impedance is also very low: a few Ohms longitudinally and a few MW/m transversally. This paper discusses initial ideas for achieving the demanding requirements for the PDR and DR kickers. Ams, A Bernhard, A Karppinen, M Maccaferri, R Peiffer, P Rossmanith, R Schoerling, D 2010 2010 Each of the proposed CLIC electron and positron damping rings will be equipped with 76 wigglers. The length of each wiggler is 2 m, the period length lambda 40 to 50 mm, and the beam-stay-clear gap 13 mm. The minimum required mid-plane field B0 is 2.5 T, that can only be obtained with superconducting technologies. In order to demonstrate the feasibility of such a wiggler, a short model with a period length of 40mm was built and successfully tested at CERN. The measured mid-plane field was 2 T at 4.2K and 2.5 T at 1.9 K in the center of a 16mm gap. The currents were 730 and 910 A, respectively. To fulfill the field specification for the CLIC damping rings at 4.2 K it is planned to replace the Nb-Ti wire with a Nb$_{3}$Sn wire. Fowler, T Ravida, G Rodriguez, I Toral, F Barnes, M J CTF3 2010 2010 The goal of the present CLIC Test Facility (CTF3) is to demonstrate the technical feasibility of specific key issues of the CLIC scheme. The extracted drive beam from the combiner ring (CR), a pulse of 35 A magnitude and 140 ns duration, is sent to the new CLic EXperimental area (CLEX). A Tail Clipper (TC) kicker is required, in the CR to CLEX transfer line, to allow the duration of the beam pulse to be adjusted: the unwanted bunches are kicked into a collimator. The TC must have a fast field rise-time, of not more than 5 ns, in order to minimize uncontrolled beam loss. Striplines are used for the TC: to establish the required fields, the applied pulse wave front must fully propagate along the striplines. To reduce the wave front propagation time, the overall length of the stripline assembly is sub-divided into 4 sections. The TC has been designed with the aid of detailed numerical modelling: the stripline cross-section and coaxial-to-stripline transitions were carefully optimized using a 3D code. The results of simulations and the measured behaviour of the striplines are presented; in addition measured current pulses are shown. Lorin, C Todesco, E 2010 2010 In 2008, hardware commissioning of the LHC showed larger than expected loss of training retention for the magnets manufactured in Firm3. In this report we review the training data during surface test at SM18 along the production to point out difference between Firms. In particular, we study (i) the evolution during the production, (ii) the quench location, and (iii) the behaviour after thermal cycle. Some specificity of the behaviour of Firm3 magnets are singled out, namely a slower training at lower field, and some differences in the location of the second and third virgin quenches. Moreover, the Firm3 magnets also showed a larger loss of training retention after thermal cycle. The correlations between training in virgin conditions and after a thermal cycle are used to work out an estimate of the training in each sector. This partially explains the behaviour observed in sector 5-6 in 2008. Finally, we study the correlation between retraining during hardware commissioning and two features of the production: the storage time of the cold masses with or without cryostat. In both cases there is no evidence of any correlation. Auchmann, B Flemisch, B Kurz, S IEEE Trans. Magn. 10.1109/TMAG.2010.2045224 3508-3511 46 2010 2010 We describe a general formalism that allows to reduce the spatial dimension of a field problem from 3-D to (2+1)-D. Subsequently we identify conditions under which the third dimension can be eliminated.We see that the resulting 2-D field problems only decouple if an orthogonality criterion is fulfilled.The approach is based solely on differential-form calculus and can therefore be easily transferred into a discrete setting. As a numerical example we compute the field of twisted wires. Schwerg, N Auchmann, B Russenschuck, S IEEE Trans. Appl. Supercond. 10.1109/TASC.2011.2157344 3509-3513 21 5 2011 2011 The hardware commissioning of the Large Hadron Collider (LHC) required the testing and qualification of the cryogenic and vacuum system, as well as the electrical systems for the powering of more than 10000 superconducting magnets. Non-conformities had to be resolved within a tight schedule. In this paper we focus on the role that electromagnetic field computation has played during hardware commissioning in terms of analysis of magnet quench, electromagnetic force calculations in busbars and splices, as well as field-quality prediction for the optimization of powering cycles. Cantoni, M Scheuerlein, C Pfirter, P Y de Borman, F Rossen, J Arnau, G Oberli, L Lee, P 2010 2010 The Sn concentration gradients across the A15 phase have been studied by Energy Dispersive X-ray Spectroscopy (EDS) measurements. High spatial resolution EDS measurements in the Transmission Electron Microscope reveal a comparatively strong Sn concentration gradient from the periphery towards the centre of individual (Nb Ta)3Sn grains. Ballarino, A Taylor, Th IEEE Trans. Appl. Supercond. 10.1109/TASC.2010.2042044 2031-2034 20 2010 2010 In certain cases it is necessary to extract the energy from a superconducting magnet when it quenches, in order to limit the heat generated by the event and thus prevent irreversible damage. This is usually achieved by opening a contact breaker across a resistor in the circuit feeding the magnet. For the heavy currents used to excite large magnets such switches incorporate sophisticated devices to limit arcing during the operation; besides being quite large and expensive, such switches have a limited lifetime. It is therefore interesting to consider the use of superconducting switches to perform this function, the advantage being that such switches would (i) not require maintenance and (ii) would be housed within the cryogenic environment of the magnet, and thus avoid permanent diversion of the current in and out of that environment to the mechanical switch (which operates at room temperature). However, practical switches for such an application are made up of superconductor in a metal matrix, and it is convenient to work with a relatively low resistance to approximate to the open circuit. This leads to scaling laws for superconducting switches for this application which relate the operating current and stored energy of the magnet system, the type of superconductor, and the necessary size of the device. Borgnolutti, F Todesco, E Mailfert, A 10.1109/TASC.2010.2043239 1790-1793 20 2010 2010 In this paper we present a novel method to optimize quadrupole coil cross-sections based on the cos2q-type. We first approximate real coil blocks made of cables with concentric sectors powered with a constant current density to make use of analytical expressions of the magnetic field based on the Fourier series development. This allows a rapid evaluation of the field harmonics which permits an almost exhaustive scan on sectors position and dimensions for coil layouts made of up to five sectors. The coil layouts having a larger short-sample gradient can be further explored, approximating them with blocks of Rutherford cables. This second step requires a second fine tuning of the cross-section around the previously found optimum. The method has been used to design a proposed coil cross-section for the new inner triplet quadrupole for the LHC Bordini, B Bajko, M Caspi, S Dietderich, D Felice, H Ferracin, P Rossi, L Sabbi, G L Takala, E IEEE Trans. Appl. Supercond. 10.1109/TASC.2010.2040600 274-278 20 2010 2010 In the framework of the US LHC Accelerator Program (LARP), three US laboratories BNL, FNAL and LBNL are developing Nb$_{3}$Sn quadrupole magnets for the Large Hadron Collider (LHC) luminosity upgrade. At present CERN is supporting this activity by testing some of the LARP 1 m long 90 mm aperture magnets. Recently two magnets using a shell based key and bladder technology (TQS) have been tested at CERN. These magnets (TQS02c, TQS03a) share the same mechanical structure and use a 27 strand Rutherford cable based one on the 0.7 mm RRP® strand produced by Oxford Superconducting Technology (OST). The main difference between the two magnets is the strand sub-element layout (54/61 in TQS02c versus 108/127 in TQS03a) and the strand critical current. The TQS03a wire has a significantly lower critical current, a larger amount of copper stabilizer, and a larger number of superconducting sub-elements with respect to the TQS02c strand. The tests show that TQS02c was stable between 4.3 K and 2.7 K while it was limited by the self-field instability at lower temperatures. TQS03a was not limited by magneto-thermal instabilities and reached 93% of the short sample limit both at 4.3 K and 1.9 K. In this paper the results are summarized and compared with the stability measurements performed at CERN on individual strands. Bordini, B Regis, F Crettiez, O Fessia, P Guinchard, M Perez, J C Sexton, I IEEE Trans. Appl. Supercond. 10.1109/TASC.2009.2039707 1511-1514 20 2010 2010 At present Nb$_{3}$Sn Rutherford Cables seem to be the most suitable conductors for next generation superconducting accelerator magnets. These magnets will have a peak field in the coils larger than 10 T and the large Lorentz forces will impose coil pre-stresses significantly larger than 100 MPa. Since Nb$_{3}$Sn is strongly sensitive to strain it is mandatory to characterize the cable under a transverse pressure comparable to the one experienced in future magnets. As a part of its High Field Magnet program, CERN is developing a sample holder for the FRESCA Facility that allows testing 10 mm wide superconducting Rutherford cables under a transverse pressure up to 200 MPa.The sample holder will be able to house cables up to 20 mm wide. In this paper the conceptual design is presented together with the experimental results of the mechanical test performed on a 40 cm long model. The results show that the structure can apply a transverse pressure larger than 200 MPa on 10 mm wide cables with sufficiently high pressure homogeneity. Lorin, C Siemko, A Todesco, E Verweij, A IEEE Trans. Appl. Supercond. 10.1109/TASC.2010.2043076 135-139 20 2010 2010 The LHC hardware commissioning has shown a considerable difference of performance between the three dipole manufacturers (Firm1, Firm2 and Firm3). More than 90% of the quenches occurred in the dipoles made by Firm3, less than 10% in Firm2, and no one in Firm1. In this paper we propose a Monte-Carlo method based on the quench performance data of individual magnets that accounts for this behavior. The model relies on the data of the virgin training and on correlations with quench after a thermal cycle as measured on a sample of magnets. This model is used to derive estimates of the training behavior in the machine. A comparison with data gathered during the hardware commissioning shows that the model works well for low fields, and that, starting from fields corresponding to an energy of about 6.3 TeV, a slower training in the magnets of one manufacturer is observed. 2010 2010 Both superconducting and resistive magnets need a proper pre-cycling to have a reproducible behaviour, namely to provide the same field at the same level of current. Depending on the type of magnet, the type of pre-cycle stems from different physical phenomena, and reproducibility can be obtained through different pre-cycle strategies. For the Large Hadron Collider (LHC), the final goal is to have reproducibility within the tight beam dynamics requirements (of the order of 10-4) with a minimum pre-cycle time. Too long pre-cycle reduces the time available for the beam collisions, i.e. the integrated luminosity. In this report we give the pre-cycle strategy adopted for the LHC in 2009 an 2010. Koratzinos, M Bertinelli, F Charifoulline, Z Dahlerup-Petersen, K Denz, R Flora, R H Pfeffer, H Scheuerlein, C Schmidt, R Siemko, A Strait, J Verweij, A 2010 2010 At each interconnection between LHC main magnets a low-resistance solder joint must be made between superconducting cables in order to provide a continuous current path through the superconductor and also to the surrounding copper stabilizer in case the cable quenches [1]. About 10,000 such joints exist in the LHC. An extensive campaign has been undertaken to characterize and map the resistances of these joints. All of the superconducting cable splices were measured at 1.9 K and no splices were found with a resistance larger than 3 nW. Non-invasive measurements of the stabilizer joints were made at 300 K in 5 of the 8 sectors, and at 80 K in 3 sectors. More precise local measurements were made on suspect interconnects that were opened up, and poor joints were repaired. However, it is likely that additional imperfect stabilizer joints still exist in the LHC. A statistical analysis is used to place bounds on the remaining worst-case resistances. This sets limits on the maximum operating energy of the LHC, prior to a more extensive intervention [2]. Thiesen, H Cerqueira Bastos, M Hudson, G King, Q Montabonnet, V Nisbet, D Page, S 2010 2010 Since restarting at the end of 2009, the LHC has reached a new energy record in March 2010 with the two 3.5 TeV beams. To achieve the performance required for the good functioning of the accelerator, the currents in the main circuits (Main Bends and Main Quadrupoles) must be controlled with a higher precision than ever previously requested for a particle accelerator at CERN: a few parts per million (ppm) of nominal current. This paper describes the different challenges that were overcome to achieve the required precision for the current control of the main circuits. Precision tests performed during the hardware commissioning of the LHC illustrate this paper. Arpaia, P Buzio, M Fiscarelli, L Montenero, G Garcia Perez, J Walckiers, L 2010 2010 One of the main requirements for the operations of the Large Hadron Collider (LHC) at the European Organization for Nuclear Research (CERN) is a suitable correction of multipole errors in magnetic field. The feed-forward control of the LHC is based on the Field Description for the LHC (FiDel), capable of forecasting the magnet’s behavior in order to generate adequate current ramps for main and corrector magnets. Magnetic measurements campaigns aimed at validating the model underlying FiDel highlighted the need for improving the harmonic compensation of the third-harmonic (b3) component of the main LHC dipoles. In this paper, the results of a new measurement campaign for b3 harmonic compensation, carried out through the new Fast Acquisition Measurement Equipment (FAME), are reported. In particular, the mechanism and the measurement procedure of the compensation, as well as the new perspectives opened by preliminary experimental results, are illustrated. Koratzinos, M Bertinelli, F Flora, R H Pfeffer, H Scheuerlein, C Siemko, A Strait, J 2010 2010 Following the QPS review in February 2009, a potential source of problems with the main circuit bus bar splices was identified: discontinuity in the copper stabilizer, coupled with lack of contact of the superconducting cable to the copper, in the vicinity of a splice. A campaign was launched to measure all such cases in the LHC. Non-invasive measurements were performed at room temperature or at about 80K in all sectors. A number of splices, following an indication obtained from these measurements, were opened and repaired. The resistance of these splices was also measured before and after the repair. We here present the results of this measuring campaign, together with the analysis that estimates the highest splice resistance left in the machine, which is a limiting factor to the maximum safe energy at which the LHC can operate