The regimes of polarization in a high energy e+e−e^{+}e^{-} storage ring

Several regimes of polarization must be considered for high-energy e /sup +/e/sup -/ storage rings. Based on a theoretical paper by Derbenev, Kontratenko and Skrinsky from 1979 we describe the different cases. Particularly, it is shown that from a certain high energy onwards the polarization degree is expected to increase with energy. This is in sharp contrast to the usually considered regime where the expected polarization level decreases for higher beam energies. The theory of Derbenev, Kontratenko and Skrinsky is applied to the LEP storage ring with its energy range from the Z at 91 GeV to the W at 200 GeV. Though the theoretical expectations for beam polarization at the highest beam energy remain low, it is shown that the depolarization can move into a new regime for LEP above 60 GeV. The high energy LEP is the first storage ring that operates in this new and experimentally unknown regime of beam spin dynamics. (6 refs)

Review of ultra high-gradient acceleration schemes, results of experiments

A dramatic improvement in energy gain per unit cost is mandatory for the future of very high energy accelerators, for which RF-acceleration would be replaced by new tech-niques. Several schemes have been proposed (laser driven, beam driven accelerators) and tested. A critical review of these schemes and experimental results is presented, with considerations on the most promising techniques and the effort still needed. Important parameters for high luminos-ity (efficiency, emittance preservation, ...) are discussed

Measurements of heavy ion beam losses from collimation

The collimation efficiency for Pb ion beams in the LHC is predicted to be lower than requirements. Nuclear fragmentation and electromagnetic dissociation in the primary collimators create fragments with a wide range of Z/A ratios, which are not intercepted by the secondary collimators but lost where the dispersion has grown sufficiently large. In this article we present measurements and simulations of loss patterns generated by a prototype LHC collimator in the CERN SPS. Measurements were performed at two different energies and angles of the collimator. We also compare with proton loss maps and find a qualitative difference between Pb ions and protons, with the maximum loss rate observed at different places in the ring. This behavior was predicted by simulations and provides a valuable benchmark of our understanding of ion beam losses caused by collimation.Comment: 12 pages, 20 figure

The Beam-Beam Interaction in the Presence of Strong Radiation Damping

The beam-beam interaction in electron-positron storage rings depends strongly on the radiation damping. It has been shown before that the achievable beam-beam tune shift (the beam-beam limit) is a function of the damping decrement (the damping rate per beam-beam interaction). The LEP collider has been operated and has delivered luminosity in the range of 45 GeV to 101 GeV. The beam-beam performance data from LEP is revisited and fitted with a simple model. The scaling of the beam-beam limit with the damping decrement is estimated

Polarization Issues at CLIC

We review polarization issues for CLIC at 3 TeV centre-of-mass energy. An electron beam with about 80% polarization can be produced by an SLC-type photo-injector. Compton scattering off a high-power laser beam may provide a source of positrons with 60%-80% polarization. If the spin transport is taken into account in the geometric layout of the facility and in the choice of local beam energy, no significant depolarization is expected to occur on the way to the collision point. We demonstrate this explicitly by spin tracking through the beam delivery system. During the beam-beam collision itself, due to beamstrahlung and the strong fields at 3 TeV, about 7% of effective polarization will be lost. A polarimeter for the spent beam appears indispensable