[en] Published in summary form only

[en] Statistical estimates of the perturbation of the linear lattice functions (Twiss parameters, dispersion and betatron coupling) are made for LEP; they complement imperfection studies by simulation and provide a better understanding of the relative importances of the imperfection sources. They allow in addition to draw some scaling laws which demonstrate why imperfections do not simply scale with machine size. Estimates of the resulting luminosity losses help in defining the correction needs and their resolution

[en] This paper reports on a thorough analysis of the requirements for application software presently done for LEP. To complement and unify this approach, a synthetic or generic model of the LEP control has been developed. The accelerator is viewed as an automaton with a limited number of macroscopic states. Each state is represented by a data structure. The transition between states is actuated by tasks (application programs); they are grouped into families with similar functionalities with respect to the machine states. It is shown how this organization attempts to map the requirements of reliability, flexibility and extendability into the LEP control system

[en] This paper analyzes the first-order depolarizing mechanisms responsible for the transverse polarization degree by means of simulation programs. It is shown that the Sokolov-Ternov effect causes the beam to polarize at a lever of 4 to 30% with a time constant of 90 mn on well corrected standard optics. Further specific orbit manipulations (harmonic spin matching) yield up to 60% polarization using the nominal LEP wigglers and more than 70% if stronger and more asymmetric wigglers are used. First-order depolarizing mechanisms are thus shown not to prevent transverse polarization in LEP. The depolarization caused by the spin rotators and by the energy spread strongly enhanced by the wigglers is under study

[en] The LEP data include information relevant to the construction, installation, operation and maintenance of the accelerator. This paper describes their proposed organisation into a unified semi-integrated system. To provide the required efficiency and flexibility, the data will be grouped into various structures, optimised with respect to their functionality. Interactive databases are the primary source of information; these will also allow relational access to the archive of the control system. Live data structures, initialized from the interactive data, allow simultaneous manipulation of three independent representations of the accelerator (reference, current and target machines). A user-friendly access to the control system entities is provided by a Data Dictionary

[en] Previously stabilization of large beams against the transverse resistive wall instability was achieved in the ISR by active damping and by imposing a constant chromaticity over the energy aperture. The introduction of the beam transfer function set-up has opened up the possibility of measuring the actual beam stability diagram. Based upon it, the stability margin is estimated. The influence of the complex wall impedance and of the betatron distribution is compensated by modulation of the chromaticity. A 55 A stack has been accumulated under such conditions. (Auth.)

[en] The LEP integrated luminosity has increased by a factor of two between 1990 and 1991. Part of this improvement is expected as well from a tighter control of the optical imperfections, especially the position of the insertion quadrupoles. The availability of LEP for physics was 45%, with a down-time of the main ring of 12%. The analysis of the beam dynamics limitations show that LEP has still a significant potential for performance improvement. A method of artificial depolarization was developed, allowing an accurate measurement of the beam energy. In 1992, the LEP magnetic optics will be drastically modified to prepare the exploitation of a pretzel scheme, with a potential of doubling the luminosity, and the energy increase to 90 GeV. (author) 6 refs.; 3 figs.; 4 tabs

[en] A method has been developed to measure operationally the linear and non-linear effects of the interaction region triplets, that gives access to the multipole content through the action kick, by applying closed orbit bumps and analyzing tune and orbit shifts. This technique has been extensively tested and used during the RHIC operations in 2001. Measurements were taken at 3 different interaction regions and for different focusing at the interaction point. Non-linear effects up to the dodecapole have been measured as well as the effects of linear, sextupolar and octupolar corrections. An analysis package for the data processing has been developed that through a precise fit of the experimental tune shift data (measured by a phase lock loop technique to better than 10^-5 resolution) determines the multipole content of an IR triplet

[en] The vertical response of a beam subject to a horizontal transverse excitation defines a coupling beam transfer function. From the equations of the coupled motion, an analytical expression is found, which directly relates the complex coupling coefficient to the transfer function. The accuracy and sensitivity of the method have allowed a fine dynamic compensation of betatron coupling on 'physics' stacks, as well as studies on coupling sources. (Auth.)

[en] The first evidence of a measurable signal of transverse polarization was observed at the end of 1990. In 1991, polarized beams were repeatedly obtained with average and peak polarization levels of 10 and 19% and used to calibrate the beam energy by resonant depolarization. Simulation studies show that the polarization level can be increased above the 50% by harmonic spin matching. This is sufficient to open the possibility of doing physics with longitudinally polarized beams. A spin rotator has been designed for LEP. The feasibility study of operating LEP in this mode concludes at the possibility of providing polarized beams at a good performance level, if the high photon background can be reduced to a tolerable level. (author). 10 refs, 3 figs, 5 tabs