Brian William St. Leger Montague

Polarized Beams in High-Energy e+e- Storage Rings

The polarization of electron/positron beams in storage rings is fundamentally governed by the quantized nature of synchrotron radiation. On the one hand, beams can become polarized by the Sokolov-Ternov spin-flip asymmetry of the photon emission, whereas on the other hand, the abrupt energy loss excites orbit oscillations which perturb the spin motion and give rise to depolarizing effects. It is the balance between these two aspects of the same phenomenon that determines the degree of beam polarization that can be built up and maintained in a machine.

Depolarisation in large electron storage rings

Abstract It is shown from elementary considerations that polarised beams of electrons or positrons are unlikely to be obtained in storage rings much above about 30 GeV in top energy. Normal design criteria in such machines result in large energy spreads which straddle depolarising resonances. The requirement that such resonances be weak enough as not to cause substantial depolarisation, imposes control of vertical closed-orbit errors and beam size beyond what is currently believed to be feasible.

An E-P Facility in the CERN SPS

A 25 GeV electron (or positron) storage ring installed in the SPS tunnel above the proton synchrotron would provide e-p collisions with a luminosity in the range of 10/sup 31/ to 10/sup 32/ cm/sup -2/ s/sup -1/. The collisions would normally take place at an intermediate plateau of the SPS-cycle up to 270 GeV, and could be followed by acceleration and extraction of the proton beam for fixed target experiments. The feasibility of such a facility is demonstrated and the essential features presented.

Polarization of Beams in LEP

Plans are presented for the implementation of polarized beams in LEP Phase 1 up to about 50 GeV. They include polarimeters, enhancement of polarization rate, error correction methods.

Beam-Beam-Driven Coupling Resonance of Fourth Order

The non-linear force of the beam-beam interaction in storage rings excites coupling resonances between radial and vertical betatron oscillations. In beams of unequal emittances the coupled motion, though stable, can increase the smaller emittance. The behaviour of single-particle motion driven by a periodic beam-beam force near the resonance 2Qv−2Qh = m is examined and it is shown that the tune difference between vertical and horizontal planes plays an important role. The criteria for avoiding increase of vertical emittance are of particular interest for e+e− storage rings and are evaluated for the Large Electron Positron (LEP) machine.

Studies of 400 GeV superconducting proton storage rings

A study has been made of the feasibility of building Large Storage Rings (LSR) at CERN using superconducting dipoles and quadrupoles with the 400 GeV proton synchrotron, SPS, serving as injector. Proton-proton collisions at centre-of-mass energies of up to 800 GeV can be obtained in six interaction regions. Two of these provide luminosities exceeding 1033 cm−2 s−1 and would be dedicated to large-transverse-momentum physics. The other four p-p intersections offer much experimental flexibility at somewhat lower luminosity. Provision is made to add an electron storage ring of 20–25 GeV to obtain e-p collisions at up to 200 GeV centre-of-mass energy with a luminosity of 1032 cm−2 s−1 in each of two special e-p interaction regions. Antiproton-proton collisions could be obtained by a minor rearrangement of some elements in two of the interaction regions.

Very-high-luminosity insertions for the CERN intersecting storage rings

Abstract The luminosity of the CERN ISR could be brought into the range of 0.5 to 2×10 33 cm −2 s −1 by modification in the vicinity of one interaction region. The high luminosity is obtained by a combination of near-zero crossing angle, low-beta and vanishing momentum compaction at the intersection point. The attainable performance will depend on whether or not superconducting magnetic elements are used, the maximum tolerable level of the electromagnetic beam-beam interaction and the available stacked proton current. Provision is made in the design for adjusting the crossing angle to achieve the optimal conditions.