The acceleration and storage of radioactive ions for a neutrino factory

Abstract

The term beta-beam has been coined for the production of a pure beam of electron neutrinos or their antiparticles through the decay of radioactive ions circulating in a storage ring. This concept requires radioactive ions to be accelerated to a Lorentz gamma of 150 for 6 He and 60 for 18 Ne. The neutrino source itself consists of a storage ring for this energy range, with long straight sections in line with the experiment(s). Such a decay ring does not exist at CERN today, nor does a high-intensity proton source for the production of the radioactive ions. Nevertheless, the existing CERN accelerator infrastructure could be used as this would still represent an important saving for a betabeam facility. This paper outlines the first study, while some of the more speculative ideas will need further investigations.

The Technical challenges of Beta-beams

“…The first objective is to establish the maximum annual rate of (anti-)neutrinos from a given the production rate [2] and with the re-use of the PS and SPS for acceleration. The next step, which has already started [3], will be to identify possible measures to increase the annual rate within the framework of the existing and possible future infrastructure at CERN.…”

“…The numbers presented in ref. [2] were compiled from general parameters for beam current and targets taken from the EU-supported EURISOL RTD project [9]. The possibility of increasing these numbers has been discussed ever since then.…”

“…A similar set-up in Louvain-La-Neuve operates with high efficiency for the production of a radioactive ion beam where the ions are produced on-line in a thick target [12]. The He ions would, in the proposed 60 GHz ECR source, be extracted almost exclusively in the highest charge state (2 + ) but Table 2 The assumed possible production [2] (for atoms at the entrance to the ECR) compared to a theoretically required production [8].…”

“…A first study [2,3] of the possibility of using the existing CERN machines for the acceleration for radioactive ions to a relativistic gamma of roughly 100, for later storage in a new decay ring of approximately the size of SPS, was made in 2002. The results from this very first short study were very encouraging, but as no resources could be allocated at CERN for this work, it was not continued.…”

Low-energy neutrinos at off-axis from a standard beta beam

“…The calculations we present are performed assuming parameters from the currently ongoing feasibility study [40,41]. For the original beta-beam scenario, we assume a storage ring of total length L = 6580 m with straight sections of length Z = 2501 m. The 6 He expected intensity to produce antineutrino fluxes is f = 2.53 × 10 13 ions/s.…”