J. Miles

Accurate determination of the LEP beam energy by resonant depolarization

To improve the measurements of the Z boson mass and resonance width, the 1993 Large Electron Positron Collider (LEP) run was devoted to a three point beam energy scan, with one point close to the peak of the Z resonance and two points roughly 880 MeV below and above the peak. Operational energy calibration by resonant depolarization was successfully commissioned for all three beam energies. 24 energy calibrations were performed at the end of physics fills. The accuracy of each calibration is better than 1 MeV. About one third of the total integrated luminosity was recorded in calibrated fills below and above the resonance and a regular tracking of the beam energies throughout the scan was possible. The evolution of the beam energies in the course of the year showed a large variation of up to 20 MeV. Results from the energy calibrations will be presented and possible explanations for the changes of the beam energy during the year will be described.

Effects of terrestrial tides on the LEP beam energy

Abstract The circular e + e − collider LEP located near Geneva is used to investigate the properties of the Z boson. The measurements of the Z boson mass and resonance width are of fundamental importance for the standard model of the electroweak interactions. They require a knowledge of the LEP beam energy with a precision of ∼ 20 ppm, which is provided by a measurement of the electron spin precession frequency. To extrapolate beam energy calibrations over a longer period of time, effects causing energy changes have to be taken into account. Among these are the terrestrial tides due to the sun and moon which move the Earth surface up and down. The lateral components of this motion modify the 26.7 km LEP circumference by about 1 mm. This change in length results in variations of the beam energy up to 120 ppm. We present results of measurements on the influence of terrestrial tides on the LEP beam energy that have been performed in 1992 and 1993.

A new closed orbit correction procedure for the CERN SPS and LEP

Abstract Using well-known correction techniques and algorithms, we have built a new procedure to correct the closed orbit of the CERN SPS and LEP. The procedure is driven by the input data, and no assumptions on the machine are made. Identical programs can therefore be used for both LEP and the SPS. Several algorithms can be used to correct the closed orbit, and additional features such as first-turn correction and harmonic analysis are incorporated in the procedure. Apart from necessary enhancements to the algorithms, we have defined a new data interface between the programs involved, to achieve high flexibility and language independence and to increase their efficiency. The correction procedure is described in detail and the performance is discussed using results both from the SPS during the lepton commissioning period and from the experience during the LEP startup.

Status report on the LHC main magnet production

The LHC ring will contain 1232 main dipole and 382 main quadrupole double aperture magnets. All main magnets are superconducting and employ Nb-Ti/Cu Rutherford type cables operated at 1.9 K. The dipole production has reached the equivalent of almost three octants of cold masses and nearly four octants of collared coils. The quadrupole production has reached 75 cold masses and over 150 bare magnets. The ramping up of large scale magnet production has posed several challenges which will be discussed, like: the coil size uniformity, coil pre-stress control, cold mass welding technique and the geometrical shape issues. The magnetic measurement results at warm will be presented together with their usage for the quality control in the production. The common features and differences of the three dipole producers will be discussed. The latest version of the production schedule will be presented.

A new closed orbit correction procedure for the CERN SPS

Using well-known correction techniques and algorithms, a procedure has been devised to correct the closed orbit of the CERN SPS (Super Proton Synchrotron). The option to steer beam lines has been included, allowing the establishment and optimization of the first turn in the machine. As a new feature, this correction procedure can take into account limited corrector strength. Apart from necessary enhancements to the algorithms, a data interface between the programs involved has been defined to achieve high flexibility and language independence and to increase efficiency. The correction procedure is described in detail, and the performance is discussed using results from simulations and its first application during the lepton commissioning period and pp collider run in 1988. Initial tests during the machine development periods for lepton commissioning were successful in correcting the first turn and the closed orbit of the particles.<<ETX>>

Lepton beam polarization at LEP

Results from studies on transverse polarization in LEP over the past two years are presented. A single beam transverse polarization level of 57% at 45 GeV was reached adopting strategies to compensate depolarizing effects originating in the four experimental solenoids and from orbit perturbations. Beam Energy Calibration was performed by Resonant Depolarization during the 1993 LEP Run for Physics at three different energies centered around the Z peak. The uncertainty on the beam energy was reduced to about 1 MeV, thus improving the accuracy on the Z‐resonance mass and width with respect to previous results. Successful results obtained at the end of the 1994 LEP Run on polarization with colliding beams are reported and future plans outlined.

Effects of tidal forces on the beam energy in LEP

The e/sup +/e/sup -/ collider LEP is used to investigate the Z particle and to measure its energy and width. This requires energy calibrations with /spl sim/20 ppm precision achieved by measuring the frequency of a resonance which destroys the transverse beam polarization established by synchrotron radiation. To make this calibration valid over a longer period all effects causing an energy change have to be corrected for. Among those are the terrestrial tides due to the Moon and Sun. They move the Earth surface up and down by as much as /spl sim/0.25 m which represents a relative local change of the Earth radius of 0.04 ppm. This motion has also lateral components resulting in a change of the LEP circumference (C/sub c/=26.7 km) by a similar relative amount. Since the length of the beam orbit is fixed by the constant RF-frequency the change of the machine circumference will force the beam to go off-center through the quadrupoles and receive an extra, deflection leading to an energy change given by /spl Delta/C/sub cC/sub cspl sim/-(/spl alphasub cspl Deltasub c/E/E. With the momentum compaction /spl alphasub c/=1.85 10/sup -4/ for the present LEP optics this gives tide-driven p.t.p. Energy excursion up to about 220 ppm, corresponding to /spl sim/18.5 MeV for the Z energy. A beam energy measurement carried out over a 24 hour period perfectly confirmed the effects expected from a more detailed calculation of the tides. A corresponding correction can be applied to energy calibrations.<<ETX>>

Description of the Main Features of the Series Production of the LHC Main Dipole Magnets

The series production of the LHC main dipole magnets was completed in November 2006. This paper presents the organization implemented at CERN and the milestones fixed to fulfill the technical requirements and to respect the master schedule of the machine installation. The CERN organization for the production follow-up, the quality assurance and the magnet testing, as well as the organization of the three main contractors will be described. A description of the design work and procurement of most of the specific heavy tooling and key components will be given with emphasis on the advantages and drawbacks.

Status Report on the Series Production of the Main Superconducting Dipole Magnets for LHC

The LHC accelerator, at present under construction at CERN, Geneva, will make use of 1232 superconducting dipole magnets. The coils are wound with Rutherford type cable based on copper stabilized NbTi superconductors. The LHC machine will be operated at 1.9 K in superfluid helium. The unprecedented mass production of the superconducting dipole magnets, which involves three main contractors in Europe, is running steadily according to plan. This paper reports the outstanding technical issues encountered throughout the execution of the main manufacturing steps, which are the coil winding, curing and clamping in the collar structure, the 15-m long computer-controlled welding, the high-precision positioning operations for the cold mass finishing and the helium leak testing. The achieved production rates are discussed as well as the CERN plan for the completion of these important contracts

Electrical Integrity Tests During Production of the LHC Dipoles

For the LHC dipoles , mandatory electrical integrity tests are performed to qualify the cold mass (CM) at four production stages: individual pole, collared coil, CM before end cover welding and final CM. A description of the measurement equipment and its recent development are presented. After passing the demands set out in the specification, the results of the tests are transmitted to CERN where they are further analyzed. The paper presents the most important results of these measurements. We also report a review of the electrical nonconformities encountered e.g. inter-turn shorts and quench heater failure, their diagnostic and the cures