  A luminosity of a circular collider can be increased by squeezing the bunch
length at the interaction point (IP). A natural way to decrease the bunch
length is to decrease the momentum compaction factor and/or to increase the RF
voltage. However, in such a way we cannot obtain short bunches with high
currents since wakefields prevent this due to the potential well distortion and
the microwave instability. In present paper we propose to use a strong RF
focusing (with high RF voltage and high momentum compaction factor) to obtain
very short bunches at the IP with progressive bunch elongation towards the RF
cavity. This allows placing the most important impedance generating elements
near the RF cavity where the bunch is longest thus minimizing the effect of the
wakefields.
