  In this Letter, I report on a novel scheme for beam stacking without any beam
emittance dilution using a barrier rf system in synchrotrons. The general
principle of the scheme called longitudinal phase-space coating, validation of
the concept via multi-particle beam dynamics simulations applied to the
Fermilab Recycler, and its experimental demonstration are presented. In
addition, it has been shown and illustrated that the rf gymnastics involved in
this scheme can be used in measuring the incoherent synchrotron tune spectrum
of the beam in barrier buckets and in producing a clean hollow beam in
longitudinal phase space. The method of beam stacking in synchrotrons presented
here is the first of its kind.
