The Vacuum System of the Extra-Low Energy Antiproton Decelerator ELENA at CERN

The Extra-Low ENergy Antiproton decelerator (ELENA) project is under way since 2011. In the past 3 years, it has considerably evolved into a detailed design for the ring and the transfer lines. It is a small machine, ~30 m in circumference, with a rather tight specification for the average pressure seen by the anti-proton beams injected by the anti-proton decelerator (AD). The average pressure in ELENA must be limited to 4x10⁻¹² mbar (H2-equivalent) in order to limit the charge-exchange losses during the rather long deceleration process (several tens of seconds), during which the energy of the beam is reduced and the electron-cooler is used twice in order to decrease the transverse emittance of the anti-proton beam. This paper will discuss the design of the chambers of the injection line, extraction line and the ring. It will also mention the actual status of the vacuum system for the transfer lines to the experiments, LNE, which are under finalisation. The results of detailed 3D simulations made with the test-particle montecarlo code Molflow+ will be discussed, alongside with the choice for the pumping system, mainly distributed NEG-coatings and integrated NEG/ion-pumps.