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The CERN Antiproton Decelerator (AD) provides antiproton beams with a kinetic energy of 5.3 MeV to an active user community. The experiments would profit from a lower beam energy, but this extraction energy is the lowest one possible under good conditions with the given circumference of the AD. The Extra Low Energy Antiproton ring (ELENA) is a small synchrotron with a circumference a factor of 6 smaller than the AD to further decelerate antiprotons from the AD from 5.3 MeV to 100 keV. Controlled deceleration in a synchrotron equipped with an electron cooler to reduce emittances in all three planes will allow the existing AD experiments to increase substantially their antiproton capture efficiencies and render new experiments possible. ELENA ring commissioning is taking place at present and first beams to a new experiment installed in a new experimental area are foreseen in 2017. The transfer lines from ELENA to existing experiments in the old experimental area will be installed during CERN Long Shutdown 2 (LS2) in 2019 and 2020. The status of the project and ring commissioning will be reported.This article is part of the Theo Murphy meeting issue 'Antiproton physics in the ELENA era'.

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The deceleration of the beam down to 0.1 GeV/c in the ring previously used as Antiproton Collector (AC) at 3.5 GeV/c, requires a number of modifications to the lattice. The insertion of the electron cooling, needed to cool the antiproton beam at low energy, implies the re-arrangement of quadrupoles. The optical functions then need to be readjusted in order to keep the large acceptance and to cope with the electron and stochastic cooling environment. Calculations of the linear optics and of the acceptance are reported. Tests of beam deceleration in the AC show the need for closed-orbit correction at low momentum in addition to the static correction by the movement of the quadrupoles available in the present configuration. The deceleration tests will be discussed and a correction system, which includes trim supplies on the main bending magnets, will be described. THE ELECTRON COOLING INSERTIONThe present AC lattice [1] is made of 28 FODO cells with two straight sections of about 28 m length each, two of 15 m length and four densely packed arcs. The 28 m straight sections have no orbit dispersion whereas the 15 m sections have a small dispersion. To satisfy the topology imposed by the injection and ejection lines special 'half-quadrupoles' are used in the injection/ extraction section and some quadrupoles are transversally displaced in the other 28 m straight section in order to maintain symmetry.For efficient operation as an Antiproton Decelerator [2,3] electron cooling is needed at low energy. The electron cooling device should be located in a straight section where the dispersion is zero and beta functions of 5-10 m are desired. To gain space for the cooler, the central quadrupole of the long straight section opposite to the injection section is removed and the two adjacent Fquadrupoles are shifted towards the next D-lenses. The rematching of the optics is done by decreasing the distance between the closest two lenses on either side of the cooler.The required strength for these new D-lenses is beyond the values obtainable with the AC quadrupoles, so two identical quadrupoles are needed side by side using AC spares. The new layout of this section in shown in Fig. 1. AD LATTICEThe very large acceptance requirements are 'p/p = ±3%