The beta-beam decay ring design

The aim of the beta-beams is to produce highly energetic beams of pure electron neutrino and antineutrino, coming from β-decays of the 18Ne10+ and 6He2+, both at gamma = 100, directed towards experimental halls situated in the Fréjus tunnel. The high intensity ion beams are stored in a ring until the ions decay. Consequently, all the injected ions will be lost anywhere in the ring, generating a high level of irradiation. Since they come from the SPS, the ring circumference has to be a multiple of the SPS one. The straight sections must be as long as possible in order to maximize the useful neutrino flux. The straight section length is chosen to be about 36% of the circumference length, which imposes 1-km-long arcs. The bend field in the arcs is then achievable. The arc has been chosen as a2Pi phase advance insertion, which improves the optical properties (dynamic aperture and momentum acceptance) and allows the easy determination of the working point bythe optics of the straight sections.