A NEW LA7TICE FOR THE BETA-BEAM DECAY RING TO REDUCE THE HEAD-TAIL EFFECTS

The beta-beam concept relies on the production, by beta decay of radioactive ions of a very high flux, of an electron neutrino and anti-neutrino beam towards a distant detector. In this aim, the radioactive isotopes are stored in a long racetrack-shaped ring, called the decay ring, where they orbit until they decay or are lost. The intensities to store in the decay ring to obtain the required neutrino fluxes are very high (several amperes in average). Therefore, collec- tive effects occur. Among them, the head tail effect, caused by transversal resonance impedance, is one of the main is- sues: the beam was shown to be unstable with the previ- ous decay ring lattice. The transition gamma was reduced to mitigate this problem. For this purpose the lattice was changed by removing the injection from the arc to put it in a chicane which is added in one of the long straight sections. After presenting the limitation due to head tail effects, we will present the modification in the lattice and their impact on the dynamic aperture in the decay ring. Then the im- provement on the beta-beam performance with respect to the lower transition gamma will be shown.