Projectile fragmentation followed by in-flight separation produces radioactive nuclear beams (RNBs) at energies of 0303100 MeV/u and corresponding velocities of up to half the speed of light at the National Superconducting Cyclotron Laboratory (NSCL). In order to use nuclei produced at these high energies in low-energy experiments, the beams must be slowed to kinetic energies of 03031 eV. Collection and thermalization of rare ions in a gas cell using static electric fields was first demonstrated at the NSCL. Other gas cells have used radio frequency (RF) electric fields coupled to a static drift field to transport the ions through the helium buffer gas instead of a simple electrostatic field . A new so-called "ion surfing" method for ion transport was proposed by Bollen and demonstrated experimentally in this work through detailed measurements with thermal rubidium and potassium ions. These elements were found to be efficiently transported over distances of up to 40 cm in helium gas pressures ranging from 40 to 200 mbar. Transport speeds as high as 75 m/s and 60 m/s were reached for rubidium and potassium ions, respectively, at a gas pressure of 80 mbar. Measured ion speed and transport efficiencies were found to be in good agreement with the results of detailed ion transport simulations. This work validates "ion surfing" as a viable method to transport thermal ions in buffer gas and documents its preparation for use in next-generation beam thermalization devices. -- Abstract.
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