LISE 3: a magnetic spectrometer—Wien filter combination for secondary radioactive beam production

Abstract

The doubly achromatic spectrometer LISE installed at GANIL has been running since six years for the study of exotic nuclei and the production of secondary beams obtained by the interaction of high energy heavy ions ( E/ A < 100 MeV) with thick targets (up to 1 g/cm 2). Essentially it is composed of two dipole magnets selecting the nuclear reaction products according to A/ Z at 0°. Combined with an achromatic degrader located in the intermediate focal plane, it provides a selection in A 3/ Z 2. Recently we have upgraded LISE by two major improvements: i) The angle of entry of the primary beam with respect to the axis of the spectrometer has been made variable (0° to 3.5°). This allows the suppression of remaining incompletely stripped beam-charge-states in experiments with heavy beams ( Z > 30). ii) A velocity filter based on an electrostatic field crossed with a magnetic one has been installed. This filter provides a third selection which is powerful in suppressing contaminants. Furthermore, the flight path between the target and the final focus is now increased to 43 m, which allows easy time-of-flight measurements also for heavy species. LISE 3 provides separated secondary beams of increased intensity and isotopic purity. We shall review the essential properties and present some recent experimental results for illustration.