The ion circus

The ability to prepare radioactive beams to study nuclear structure and dynamics has seen important developments in recent years. The use of ion traps and buffer-gas cooling now routinely enables the accumulation and purification of even short-lived nuclides [1]. This is a key point for future installations such as EURISOL [2] and SPIRAL2 [3] since higher intensity also brings an increase of isobaric contamination which can be disastrous considering background and even radioprotection. Until now, the development of beam coolers and bunchers has relied on linear (radiofrequency quadrupole) Paul traps. In this contribution we describe the progress in developing a cooling scheme based on a miniature radiofrequency storage ring, formed by bending a linear trap into a circle (see Fig.1). The ion circus, so named for its ability to trap ions at different positions along the ring circumference and to eject them in either tangential or perpendicular direction, has also been designed to operate in an adiabatic mass separation mode in which the resolving power is increased as the ions are cooled during the many turns in the ring. The ion circus has now be built and is under test in Orsay. Details of the concept and design were reported in [3]. Here, we report on the results of the first tests and the future program.(author)