engArtoos, KDezillie, BMompo, RSiemko, ATommasini, DStudy of Mechanical Disturbances in Superconducting Magnets using Piezoelectric Sensors and Quench AntennaAccelerators and Storage RingsLHC-Project-Report-498CERN-LHC-Project-Report-498Mechanical disturbances in superconducting magnets were studied by recording and characterising the signals induced in piezo-electric ceramic sensors (piezos) and accelerometers by spontaneous acoustic emission (AE) during magnet excitation. The localisation of AE sources as recorded by the piezos corresponds to the localisation obtained by another, indirect technique, the so-called Quench Antenna. Dominant acoustic wave velocities along the magnet were measured by using selected piezos as active actuators. A mechanical disturbance energy calibration is shown and a way to estimate the minimum energy needed for quenching is proposed. A statistical approach is given in order to estimate the most probable amplitude of AE.2001-08-27http://cds.cern.ch/record/517568http://cds.cern.ch/record/517568oai:cds.cern.ch:517568 2001-09-13T22:00:00Zhttp://cds.cern.ch/record/517567http://cds.cern.ch/record/517567oai:cds.cern.ch:CERN-LHC-Project-Report-497 engDahlerup-Petersen, KErokhin, AKazmine, BMedvedko, A SSytchev, V VVasilev, L BEnergy Extraction in the CERN Large Hadron Collider: a Project OverviewAccelerators and Storage RingsLHC-Project-Report-496CERN-LHC-Project-Report-496In case of a resistive transition (quench), fast and reliable extraction of the magnetic energy, stored in the superconducting coils of the electromagnets of a particle collider, represents an important part of its magnet protection system. In general, the quench detectors, the quench heaters and the cold by-pass diodes across each magnet, together with the energy extraction facilities provide the required protection of the quenching superconductors against damage due to local energy dissipation. In CERN's LHC machine the energy stored in each of its eight superconducting dipole chains exceeds 1300 MJ. Following an opening of the extraction switches this energy will be absorbed in large extraction resistors located in the underground collider tunnel or adjacent galleries, during the exponential current decay. Also the sixteen, 13 kA quadrupole chains (QF, QD) and more than one hundred and fifty, 600 A circuits of the corrector magnets will be equipped with extraction systems. The extraction switch-gear is based on specially designed, mechanical high-speed DC breakers, in certain cases combined with capacitive snubber circuits for arc suppression. This paper is an overview of the complete project with emphasis on the arguments and motivation for the choice of equipment and methods. It presents the basic properties of the principal components, the operational aspects and the present state of advancement. Finally, it highlights the implications of the extraction process on other systems of the LHC collider.2001-08-27http://cds.cern.ch/record/517566http://cds.cern.ch/record/517566oai:cds.cern.ch:517566 engAleksa, MartinBazan, MRussenschuck, StephanAn Improved Method using RBF Neural Networks to Speed up Optimization AlgorithmsAccelerators and Storage RingsLHC-Project-Report-495CERN-LHC-Project-Report-495The paper presents a method using Radial Basis Function (RBF) neural networks to speed up deterministic search algorithms used for the optimization of superconducting magnets for the LHC accelerator project at CERN. The optimization of the iron yoke of the main LHC dipoles requires a number of numerical field computations per trial solution as the field quality depends on the excitation and local iron saturation in the yoke. This results in computation times of about 30 minutes for each objective function evaluation (on DEC-Alpha 600/333). In this paper we present a method for constructing an RBF neural network for a local approximation of the objective function. The computational time required for such a construction is negligible compared to the deterministic function evaluation, and thus yields a speed-up of the overall search process. The effectiveness of this method is demonstrated by means of two- and three-parametric optimization examples. The achieved speed-up of the search routine is up to 30 %.2001-08-27http://cds.cern.ch/record/517565http://cds.cern.ch/record/517565oai:cds.cern.ch:517565 engAleksa, MartinRussenschuck, StephanVöllinger, ChristineMagnetic Field Calculations Including the Impact of Persistent Currents in Superconducting FilamentsAccelerators and Storage RingsLHC-Project-Report-494CERN-LHC-Project-Report-494The magnetic field in the coils of superconducting magnets induces so-called persistent currents in the filaments. Persistent currents are bipolar screening currents that do not decay due to the lack of resistivity. The NbTi-filaments are type II superconductors and can be described by the critical state model. This paper presents an analytical hysteresis model of the filament magnetization due to persistent currents which takes into account the changing magnetic induction inside the filament. This model is combined with numerical field computation methods, taking local saturation effects in the ferromagnetic yoke into consideration.2001-08-27http://cds.cern.ch/record/517562http://cds.cern.ch/record/517562oai:cds.cern.ch:517562 doi:10.1016/S0042-207X(02)00226-9engBaglin, VCollins, I RGröbner, OswaldGrünhagel, CJenninger, BMolecular desorption by synchrotron radiation and sticking coefficient temperatures for H$_{2}$, CH$_{4}$, CO and CO$_{2}$Accelerators and Storage RingsLHC-Project-Report-518CERN-LHC-Project-Report-518A cryogenic vacuum system has been used to study both the surface pumping of gases and the molecular photodesorption yield from OFE copper in the temperature range from 5 K to 300 K. The sticking coefficient on a `bare surface´ was found to increase with decreasing temperature of the substrate and below 20 K, to be in the range of a few percent for all gas species studied. The molecular photodesorption yield for the `bare surface´ was found to decrease with decreasing temperature and below 20 K, after an accumulated photon dose of 3.1 1022 photons m-1, to be in the range of 10-4 molecules photon-1 for H2 and 10-5 molecules photon-1 for the other gas species. These measured values are used to predict the evolution of the gas densities in the LHC. Implications to the LHC are discussed.2001-11-01http://cds.cern.ch/record/52510110.1016/S0042-207X(02)00226-9http://cds.cern.ch/record/525101oai:cds.cern.ch:525101 engHauviller, ClaudeHygromechanical behaviour of CFRP under cyclic humidity loadingsAccelerators and Storage RingsCERN-LHC-2001-002-CRIStable lightweight structures are key issues in the design and construction of the LHC high precision particle detectors. This paper presents the results of long term measurements performed on plates manufactured in Carbon Fibre Reinforced Plastics (CFRP), material selected for these structures, subjected to cyclic humidity loadings. Test procedures are detailed; results on moisture absorption are described together with the related displacement measurements. These results indicate that cycling composites in the operating conditions of the LHC trackers does not provoke any major internal damage.2001-06-22http://cds.cern.ch/record/513001http://cds.cern.ch/record/513001oai:cds.cern.ch:513001 engBoutboul, TCharifoulline, ZDenarié, C HOberli, L RRichter, DCritical Current Test Facilities for LHC Superconducting NbTi Cable StrandsAccelerators and Storage RingsLHC-Project-Report-520CERN-LHC-Project-Report-520The Rutherford-type superconducting Cu/NbTi cables of the LHC accelerator are currently mass-produced by a few industrial firms. As a part of the acceptance tests, the critical current of superconducting multifilamentary wires is systematically measured on virgin strands to qualify the wires and on extracted strands to qualify the cables. For this purpose, four test stations are in operation at CERN to measure the critical current of strands at both 4.2 K and 1.9 K in magnetic fields in the 6-11 T range. The measurement setup and procedures of these facilities are reported in this article. The quality of the critical current test is guaranteed by supervising the SPC (Statistical Process Control) charts of a reference sample. The measurement repeatability and reproducibility of the stations are found to be excellent. Moreover, the measured critical current of a strand is found to be almost independent of the test station in which the measurement is performed.2001-11-27http://cds.cern.ch/record/528591http://cds.cern.ch/record/528591oai:cds.cern.ch:528591