Patrick Janot edited Transverse.tex  over 10 years ago

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\subsubsection{Transverse polarization}  Transverse beam polarization builds up naturally in a storage ring by the Sokolov-Ternov effect. A transverse polarization in excess of 5-10\%, which was obtained for beam energies  up to 61 GeV per beam at LEP, is sufficient for beam energy calibration purposes. It is generally accepted that this upper limit is determined by the energy spread, which becomes commensurate with the fractional part of the spin-tune $\nu_s = E_{\rm beam} {\rm [GeV]} /0.440665$. Given that the energy spread scales as $E^2_{\rm beam} / \sqrt{\rho}$ (where \sqrt{\rho}$, where  $\rho$ is the ring bending radius), radius,  it is expected that beam polarization sufficient for energy calibration should be readily available up to and above the WW threshold (i.e., 81 GeV per beam) at TLEP. A new machine with a better control of the orbit should, however, be able to increase this limit. For example, a full 3D spin tracking simulation of the electron machine of the Large Hadron-electron collider Collider  (LHeC) project in the 27 km LHC tunnel predicts 20\% polarization at a beam energy of 65 GeV for typical machine misalignments~\cite{1206.2913}.