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

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

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

Simulations on a potential hybrid and compact attosecond X-ray source based on RF and THz technologies

We investigate through beam dynamics simulations the potential of a hybrid layout mixing RF and THz technologies to be a compact X-ray source based on Inverse Compton Scattering (ICS), delivering few femtoseconds to sub-femtosecond pulses. The layout consists of an S-band gun as electron source and a dielectric-loaded circular waveguide driven by a multicycle THz pulse to accelerate and longitudinally compress the bunch, which will then be used to produce X-ray pulses via ICS with an infrared laser pulse. The beam dynamics simulations we performed, from the photocathode up to the ICS point, allows to have an insight in several important physical effects for the proposed scheme and also in the influence on the achievable bunch properties of various parameters of the accelerating and transverse focusing devices. The study presented in this paper leads to a preliminary layout and set of parameters able to deliver at the ICS point, according to our simulations, ultrashort bunches (around 1 fs rms), at 15 MeV, with at least 1 pC charge and transversely focused down to around 10 um rms or below while keeping a compact beamline (less than 1.5 m), which has not yet been achieved using only conventional RF technologies. Future studies will be devoted to the investigation of several potential ways to improve the achieved bunch properties, to overcome the limitations identified in the current study and to the definition of the technical requirements. This will lead to an updated layout and set of parameters.Comment: To be published in Nucl. Inst. Meth. A as proceedings of the EAAC17 conference 9 pages, 11 figure