Yves Baconnier

The Large Hadron Collider (LHC) in the LEP tunnel

After the remarkable start-up of LEP, the installation of a Large Hadron Collider, LHC, in the LEP tunnel will open a new era for the High Energy Physics. This report summarizes the main LHC parameters and subsytems and describes the more recent studies and developments.

Extraction from the CERN SPS

The experimental programme requires three different modes of extraction from the SPS : fast extraction (burst duration from 3 ¿s to 23 ¿s), slow resonant extraction (spill duration 0.5 s to 2 s) and fast resonant extraction (spill duration shorter than 3 ms). All three modes have been successfully tested and brought into operation. Fast extraction of the full beam is 100% efficient. By fast beam shaving, fractions as low as 1% of the circulating beam can be extracted in a fairly stable way. Third-integer extraction is used to produce slow spills of 700 ms or more. The efficiency of resonant extraction is currently some 97%. The spill duty factor at present amounts to about 40%. Fast resonant spills of less than 2 ms were achieved with both integer and half-integer extraction. The different modes of extraction are consecutively performed during each accelerator cycle. At present, a 1 s third-integer spill at 200 GeV/c is followed by a fast shaving extraction at 210 GeV/c and by a fast or fast resonant extraction of the remaining protons at 400 GeV/c.

Electron Beam Dynamics in the CERN PS

The 28 GeV proton synchrotron (PS) forms part of the chain of LEP injectors with the rôle to accelerate positrons and electrons from 0.6 GeV, the operating energy of the Electron/Positron Accumulator (EPA), to 3.5 GeV, the positron/electron injection energy of CERNs 400 GeV proton synchrotron (SPS) which then accelerates the particles to 20 GeV. The PS used as an electron synchrotron has to supply the SPS with 8 bunches at an intensity of Nb = 8 × 109 particles per bunch. Bunch length and energy spread must be chosen carefully to avoid transverse and longitudinal single-bunch instabilities (turbulence) associated with high peak currents in the SPS. Analysis of the beam dynamics in the combined function lattice of the PS shows that this requirement can be fulfilled if the damning-partition numbers are changed. A Robinson Wiggler is proposed for this purpose and a new additional RF system is needed to produce the required bunch dimensions in longitudinal phase space.

High Intensity Phenomena Observed in the CPS

A review of high intensity phenomena observed in the CPS is presented. At injection an attempt is made to describe the combined effect of space charge and resonances, which result in a loss of 70% of the injected beam intensity and a reduction by a factor of 3 of the central core brilliance. Results of measurements on the effect of a localised bad vacuum are given. The situation at transition is briefly described. Seven different instabilities observed in the CPS in longitudinal or transverse phase plane are analysed. The compensation techniques are described in all cases. Whenever possible an attempt has been made to give some qualitative explanation of the mechanism.

B factory with a finite crossing angle

The RD this way, the bunches fully overlap when they collide. The commisonning of the machine would begin with symmetric energies where the beam‐beam effect is known and be progressively extended to asymmetric energies, a regime for whi...