First application of the Laser Ion Source and Trap (LIST) for on-line experiments at ISOLDE

•First application of LIST target for on-line experiments at ISOLDE.•Reliable operation of LIST together with a strongly outgassing UCx target.•Suppression of isobaric contaminants by a factor of more than 10000 achieved.•Laser ionization efficiency of LIST improved by factor 2.5 compared to 2011 LIST. The Laser Ion Source and Trap (LIST) provides a new mode of operation for the resonance ionization laser ion source (RILIS) at ISOLDE/CERN, reducing the amount of surface-ionized isobaric contaminants by up to four orders of magnitude. After the first successful on-line test at ISOLDE in 2011 the LIST was further improved in terms of efficiency, selectivity, and reliability through several off-line tests at Mainz University and at ISOLDE. In September 2012, the first on-line physics experiments to use the LIST took place at ISOLDE. The measurements of the improved LIST indicate more than a twofold increase in efficiency compared to the LIST of the 2011 run. The suppression of surface-ionized francium contaminants has enabled the first in-source laser spectroscopy of 217Po and 219Po.