The REX-ISOLDE project

Abstract

REX-ISOLDE is a pilot experiment at ISOLDE/CERN to study the structure of neutron-rich nuclei (N=20, N=28) with post-accelerated radioactive ion beams (1). Therefore radioactive ions with charge state 1+, which are delivered by the online mass separator ISOLDE, are accelerated up to 2.2 MeV/u by means of a new concept. The radioactive ions are first accumulated in a Penning trap, then charge breeded to a charge-to-mass ratio of 1/4.5 in an Electron Beam Ion Source (EBIS) and finally accelerated. The LINAC consists of three components, namely a Radio Frequency Quadrupole (RFQ) accelerator, which accelerates the ions from 5 to 300 keV/u, an interdigital H-type structure (IH) with a final energy between 1.1 and 1.2 MeV/u and three seven gap resonators, which allow to vary the final energy between 0.8 and 2.2 MeV/u. Pulsing of the EBIS high voltage platform allows deceleration of the ions from the trap, which leads to a rather low injection energy of the RFQ. Thus a more efficient, adiabatic bunching and better output emittances than in the proposal design of the RFQ are the results. The IH-structure is now similar to that of the GSI HLI-structure (2), because of the increased exit energy in comparison to (1). An overview of the project, emittances of beam dynamics calculations for the design of the accelerator components and the present state of the accelerator are presented.