  One of the key-issues to increase the luminosity in the next generation
particle factories is to reduce the bunch length at the interaction point (IP)
as much as possible. This will allow reducing proportionally the transverse
beta functions at the IP and increasing the luminosity by the same factor. The
strong RF focusing consists in obtaining short bunches by substantially
increasing the lattice momentum compaction and the RF gradient. In this regime
the bunch length is modulated along the ring and could be minimized at the IP.
If the principal impedance generating elements of the ring are located where
the bunch is long (in the RF cavities region) it is possible to avoid microwave
instability and excessive bunch lengthening due to the potential well
distortion.
