The ion-catcher device for SHIPTRAP

An ion-catcher device consisting of a buffer-gas stopping cell and a radio-frequency quadrupole (RFQ) has been built for the SHIPTRAP facility at GSI. Results of characterisation measurements with the buffer-gas cell and the extraction RFQ performed at GSI in Darmstadt and at the MLL (Maier-Leibnitz-Laboratory) in Garching are presented. The set-up was tested off-line using laser-produced ions and on-line using stable beams and fusion–evaporation products. During the on-line measurements the ions with total energies of around 200keV/u were thermalised in helium buffer gas at 40–60mbar. In the following they were guided by a combination of electric RF- and DC-fields until they were transported by the gas flow through the extraction nozzle. After being extracted by a supersonic gas jet the ions were separated from the buffer gas and guided by the extraction RFQ towards subsequent detection systems. Depending on the electric-field strength average extraction times of around 10ms and an overall efficiency (including stopping and extraction) between 4% and 8% have been achieved.