Speaker
Prof.
Desmond Barber
(DESY)
Description
The attainable equilibrium polarisation in electron/positron storage rings depends on a balance between polarisation build-up due to the Sokolov-Ternov effect and depolarisation resulting from the stochastic nature of the emission of photons in the synchrotron radiation. The rate of depolarisation rises faster with energy than the rate of polarisation, with the ratio scaling at least like the square of the energy. It can then be very difficult to obtain high equilibrium polarisation at high energy unless the ring is extremely well aligned. Moreover, the depolarising effects can become prohibitive if the polarisation has been made longitudinal in parts of the ring, unless the optical state of the ring
can be arranged appropriately. The beam-beam interaction can also have strong direct and indirect effects on the polarisation.
Thus before a ring is built, the attainable polarisation should be estimated on the basis of well known theory, backed-up by detailed Monte-Carlo spin-orbit tracking simulations.
In this talk I give a brief overview of the theory and illustrate the phenomenology with the results of calculations for various rings including for the ring-ring option of the LHeC.
Primary author
Prof.
Desmond Barber
(DESY)
