Performance of Ion Surfing Rf-carpets for High-Energy RI Beam Gas Catcher

High-energy radioactive isotopes have been used in ion trap-based precision experiments after being stopped in a large gas cell. The stopped ions of these isotopes can be extracted from the large gas cell as a low-energy ion beam. To transport and extract these ions quickly and efficiently, electric fields are required to guide them. In this respect, an rf-carpet (RFC) method utilizing a dc potential gradient is a standard technique. However, such a method is restricted to longer half-life isotopes because of the transport time owing to the upper limit on the dc gradient that can be supported before electric discharges occur in the large gas cell. To study short half-life isotopes, an RFC featuring faster transport is required. Recently, a hybrid technique wherein the dc gradient is replaced by a traveling potential wave was proposed, called ion surfing. Recently, we have demonstrated the transport and extraction of K ions using a circular RFC in 20 mbar of He gas pressure. However, in a practical gas cell, the gas pressure is higher by one order of magnitude. In this study, the transport and extraction of K and Cs ions with the ion surfing method were tested in high pressure He gas using a 100 mm cylinder electrode to create a push electric field Epush and a circular RFC of 80 mm diameter. In addition, we compared the effect of an RFC of a fine pitch with one of a rough pitch. The fine pitch RFC consists of 0.08 mm wide ring electrodes with 0.16 mm pitch and 0.32 mm diameter orifice, whereas the rough pitch RFC consists of 0.16 mm wide ring electrodes with 0.32 mm pitch and 0.64 mm diameter orifice.