Cooling , mass separation and bunching of fusion-evaporation ions with radiofrequency quadrupoles ∗

An RFQ cooler, mass filter and buncher for the SHIPTRAP experiment have been designed and built [1]. This RFQ system will allow for better separation of nuclei of interest from contaminants at SHIPTRAP and thus for improved selectivity and sensitivity of the experiment. Mass filter. A stabilization of the RF amplitude was implemented and thus the achievable mass resolving power of the mass filter for a given transmission improved considerably compared to the values reported previously [1]. A relative transmission of 90% up to a mass reolving power of 240 (FWHM) or 160 (10% peak height) has now been demonstrated for Cs ions (Fig. 1). Similarly, forK ions one has a relative transmission of 90% up to a mass reolving power of 80 (FWHM) or 70 (10% peak height). Figure 2 shows the separation of neighboring masses using an earth-alkaline (Ca, Sr, Ba) ion source. The five most abundant134−138Ba isotopes are separated. An additional line is found at mass 133 and is identified as Cs, which is also present as contamination in the ion source. Figure 2 demonstrates a supression of neighboring mass lines by at least a factor of 10. Buncher. The role of the RFQ buncher is to capture and trap the filtered ion beam delivered by the mass filter. The ions are then extracted in ion bunches and delivered to the Penning trap. Important properties such as energy spread, peak width, storage time, ion temperature and transmission and bunching efficiency were determined. It was found that a peak width (FWHM) of the ejected ions of 40 ns can be