To the ionization cooling in a RF cavity with absorber
  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. 
Alexander A. Mikhailichenko (Cornell University, LEPP, Ithaca, New   York)
physics.acc-ph