Performance of ion surfing rf-carpets for RI beam gas catcher

High-energy RI beams produced in-flight by fragmentation or fission are used in ion trap-based precision experiments after being stopped in a gas catcher. The stopped ions can be extracted from the gas catcher as a low energy ion beam. In order to transport and extract ions quickly and efficiently, an rf-carpet (RFC) method utilizing a dc potential gradient has been the standard technique [1]. However, such a method is restricted by the transport time to longer half-life isotopes due to the maximum dc gradient that can be supported before electric discharges occur in the gas catcher. To avoid that limitation, a hybrid technique wherein the dc gradient is replaced by a traveling potential wave was proposed, called ``ion surfing'' [2,3]. Recently, we have demonstrated ion extraction using a circular RFC under low [4] and intermediate pressures. For the first time we demonstrated the ion extraction using an rf-carpet in high-pressure He gas. An efficiency of nearly 100\% was obtained at 200 mbar He gas pressure for $K^{+}$ ions.\\[4pt] [1] M. Wada et al., Nucl. Instr. Meth. B204 (2003) 570.\\[0pt] [2] G. Bollen, Int. J. Mass Spectrom. 299 (2011) 131.\\[0pt] [3] M. Brodeur, et al., Int. J. Mass Spectrom. 336 (2013) 53.\\[0pt] [4] F. Arai, et al., Int. J. Mass Spectrom. 362 (2014) 56.