  We are considering a RF cavity with Beryllium disk installed in the middle of
the cavity as an ionization cooling element for the muon/pion beam. Specially
arranged wedge-type shape of the disk together with nonzero dispersion allows
6D cooling of muon beam. Technical aspects of this system and conceptual design
are discussed in this paper also. This type of cooler demonstrates advantages
if compared with the RF cavity filled with pressurized gas or with the helical
cooler.
