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The extended use of beam loss monitoring has led to a better
understanding of the linear and non-linear physics involved in the single
and multiple particle dynamics at BESSY. This knowledge has been used for
improving the performance of the light source in terms of lifetime, beam
stability, and stability of the energy.
The key to these experiments are loss monitors placed at strategic
locations of the ring with high sensitivity to Touschek or Coulomb
scattered particles.
Coulomb-scattering depends strongly on the transverse dynamics which is
determined by the magnetic guiding fields. Losses occur primarily at the
vertical aperture restrictions imposed by the flat insertion device
vacuum chambers. Tune scan measurements clearly show resonances produced
by the lattice magnets and by some of the insertion devices.
Touschek scattering depends on the 3-dimensional electron density and the
spins of the colliding particles. In transfer function type experiments
these dependencies have been used to observe the effect of resonant
transverse and longitudinal beam excitations. Loss monitors allow to
detect excited head-tail and higher longitudinal modes which are
invisible in the center of mass motion. Another application is the
detection of the resonant destruction of the spin polarization of the
ensemble of electrons. This is used routinely in order to determine the
beam energy with high accuracy.
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