THE TEMPERATURE OF BUFFER-GAS COOLED IONS IN A PAUL TRAP

A measurement of the temperature of a typical ion cloud in a Paul trap with buffer gas cooling has been made using time-of-flight of the extracted ion cloud. A temperature of 0.3 +/- 0.1 eV was obtained for 20 000 K-39 ions in a trap of potential well depth 60 eV with helium buffer gas at 3 x 10(-2) Pa. This value is intermediate by a factor of about 10 in each direction between that of other published works using different observational methods on Paul traps operated under similar conditions. Explanation for the discrepancies are suggested. In any case, the present work indicates that sub-electronvolt temperatures can be achieved, at least for small trap loadings. The result considerably eases the design of transport systems for such ion clouds and greatly enhances the possible uses of a Paul trap collection device for highly sensitive precise experiments.