ELENA is a compact ring for cooling and further deceleration of 5.3 MeV antiprotons delivered by the CERN Antiproton Decelerator. The AD physics program is focused on trapping antiprotons in Penning traps where antihydrogen is formed after recombination with positrons. The ultimate physics goal is to perform spectroscopy on antihydrogen atoms at rest and to investigate the effect of the gravitational force on matter and antimatter.
In today’s set-up, most (99.9%) of the antiprotons produced are lost due to the use ofdegrader foils needed to decelerate them from the AD ejection energy down to around 5 keV; an energy suitable for trapping. By using a ring equipped with beam cooling, high deceleration efficiency and an important increase in phase-space density can be obtained, resulting in an increased number of trapped antiprotons. For the ATRAP and ALPHA experiments, improvements of up to 2 orders of magnitude can be expected. The same holds for the AEGIS experiment which is currently being installed and has foreseen to also use a thick degrader to reduce the antiproton energy. ASACUSA, on the other hand, presently uses an RFQD for deceleration to 100 keV followed by an ultra-thin degrader (1 micron thick) for deceleration to 5 keV. In this case a 10-fold increase in the trapping efficiency can be expected primarily due to reduced transverse and longitudinal emittances. ASACUSA will also benefit from more real physics beam time as in the present situation tuning of the RFQD is very delicate and time consuming.
In addition to the increased number of antiprotons, ELENA will be able to deliver beams almost simultaneously to all four experiments resulting in an essential gain in total beam time for each experiment. This also opens up the possibility to accommodate an extra experimental zone.
With a circumference of about 30 m, ELENA can be located in the AD hall where assembly and commissioning would not disturb the current AD operation.
Decelerating to these low energies is new and will be very challenging both in the design of the different elements and for the operation of the ring. ELENA will provide a unique facility that will deliver low energy antiproton beams of the highest quality.
ELENA is to be located inside of AD Hall with a circumference as small as possible to minimize space requirements and to reduce intensity limitations due to the space-charge induced tune shift. The new ring is located such that its assembly and commissioning will have a negligible impact on the current AD operation. In fact, the commissioning of the ELENA ring could take place in parallel with the present physics program with short periods dedicated to commissioning during the physics run.
The AD experimental area layout will not be significantly modified, but the much lower beam energies require the design and construction of completely new electrostatic transfer lines.
The new ELENA location has been chosen based on:
- Modifications to the ELENA circumference and ring layout as compared to the study presented in 2007 (CERN-AB-2007-079).
- Use of the existing AD ejection line for the transfer of antiprotons from AD to ELENA.
- Possibility to install an additional optional ELENA ejection line and a new experimental area to serve future experiment(s).
- Considerations for safety and crane access.
- Location of the new AEGIS experiment.
- Minimizing the cost and complications of creating floor space.