Transport analysis of rf drift-velocity filter employing crossed DC and AC electric fields for ion swarm experiments

The operational characteristics of the RF drift-velocity filter developed to separate a mixture of gaseous ions are examined theoretically. The solutions of the appropriate transport equations provide an analytical formula for the transmission efficiency of the filter in terms of the mobility and diffusion coefficient of the ions, the electric field strength, the RF frequency and the filter dimension. Using the experimental transport data for Li+/Xe and Cs+/Xe, the formula was tested and it was found that it adequately accounts for the degree of ion separation achieved by the filter at high gas pressures. The variation of the profiles of the arrival time spectra for Li+, Na+ and Cs+ ions in CO2, obtained by drift-tube experiments, also supports this analysis. 4 refs., 10 figs