A. Faugier

LEP operation in 1992 with a 90/spl deg/ optics

The optics for physics operation in LEP was changed from 60/spl deg/ to 90/spl deg/ at the start of 1992 with a view to improved Z/sup 0/ production, preparation for future operation at higher energies and the use of the same optics in machine developments. The developments included running LEP with twice the number of bunches and using resonant depolarisation for energy calibration, Perturbation to steady operation was felt at the start of the year but was soon overcome as the benefits of smaller emittances were realised. The peak luminosity increased to 1.15 10/sup 31/ and the luminosity lifetime improved. New operational software halved the time taken between dumping one coast and the start of data taking on the next. The 8+8 bunch operation was introduced as routine operation for the last month. Overall, there was an increase in integrated luminosity from 17.6 inverse picobarns per experiment in 1991 to 28.6 in 1992. Along with improvements in detector efficiency, almost 3 million hadronic Z/sup 0/s were recorded by the four experiments, an increase from 1.27 million in 1991.<<ETX>>

High luminosity performance of the SPS proton-antiproton collider

In September 1988, the CERN SPS (Super Proton Synchrotron) collider was brought into operation for the first physics production run with the improved antiproton production and accumulation complex (AAC). The increased antiproton flux immediately resulted in a considerable improvement in the machine performance with initial luminosities exceeding 2.4*10/sup 30//cm/sup 2/ s, and weakly integrated luminosities an order of magnitude greater than achieved in the past. A total integrated luminosity of 3.4 inverse pbarns was produced, a factor of 5 greater than the best achieved in previous years. Performance statistics and operational experience in this new regime are discussed.<<ETX>>

The SPS as accelerator of Pb/sup 82+/ ions

In 1994 the CERN SPS was used for the first time to accelerate fully stripped ions of the Pb/sup 208/ isotope from the equivalent proton momentum of 13 GeV/c to 400 GeV/c. In the CERN PS, which was used as injector, the lead was accelerated as Pb/sup 53+/ ions and then fully stripped in the transfer line from PS to SPS. The radio frequency swing which is needed in order to keep the synchronism during acceleration is too big to have the SPS cavities deliver enough voltage for all frequencies. For that reason a new technique of fixed frequency acceleration was used. With this technique up to 70% of the injected beam could be captured and accelerated up to the extraction energy, the equivalent of 2.2/spl times/10/sup 10/ charges. The beam was extracted over a 5 sec. Long spill and was then delivered to different experiments at the same time.

First two years operational experience with LEP

The authors summarize the experience over the first two years of LEP (Large Electron-Positron colliding beam accelerator) operation giving typical and peak performance figures. During 1989 a beam of positrons was injected into LEP from the SPS (Super Proton Synchrotron) and the first full turn was completed. Experiments detected their first Z/sup 0/ particles. The machine was operated in a mixed mode of machine studies and operation for physics. At the end of this period a total of over 1.7 inverse picobarns of integrated luminosity had been recorded per experiment, resulting in a total of more than 70000 Z/sup 0/s detected. The energy of each fill was varied, and half the number of fills were at the Z/sup 0/s peak. During 1990, LEP was operated in the same way as in 1989; 12.1 inverse picobarns and three quarters of a million Z/sup 0/s were produced. Physics fills of 6-h duration in 1989 were increased to 10-12 h in 1990 as the lifetimes of the beams increased with the steadily improved vacuum in the ring.<<ETX>>

Overview of LEP operation in 1998

After the installation of 32 additional RF cavities in the 1997-1998 shutdown LEP was operated at a beam energy of 94.5 GeV. The total integrated luminosity for the year 1998 clearly surpassed its target and reached 198 pb/sup -1/. Vertical beam-beam tuneshifts of more than 0.07 were obtained. The performance did not seem to be beam-beam limited, but the total beam current was limited by power dissipation problems to around 6 mA. A high phase advance optics (102/spl deg/, 90/spl deg/), with a smaller natural emittance, was used for regular operation in 1998. This contributed to the excellent performance of LEP, together with the further reduction of both the horizontal and vertical beta function at the interaction points. No dynamic aperture problems were encountered.

High intensity proton beams in a multi-cycled SPS

The SPS ran for 247 days during 1994; 64% of this was with high intensity proton beam for physics data taking in the Fixed Target mode of operation, 12% was for a lead run at the end of the year, with the remaining 24% spent in setting up and machine development. The SPS supplied LEP with 8 bunches of electrons and 8 bunches of positrons either in the 14.4 or 19.2 seconds interleaved cycling mode during the operation with protons or lead ions respectively. The new record peak intensity during the year was 3.9/spl times/10/sup 13/ protons per pulse at 450 GeV. A total of 11/spl times/10/sup 18/ proton were delivered to all targets with an overall average during physics of 2.5/spl times/10/sup 13/ protons per pulse at 450 GeV. Some 6/spl times/10/sup 18/ protons were delivered to both neutrino experiments.