TEMPORAL INVARIANCE AND ENERGETIC AND SPATIAL PROPERTIES OF STORED IONS IN A QUADRUPOLE RF TRAP .3. FUNDAMENTAL FREQUENCIES IN PRESENCE OF SPACE-CHARGE

A method (applied to a tridimensional model) for evaluating the dynamic properties of strongly confined ions submitted to space charge is introduced. This method is used for a trap, the characteristics of which are: a equals 0, q equals 0. 2 but can be extended to other conditions. It is shown that the space charge induces a perturbation of the individual motion which depends on the average energy of ion. Above the number of 10**4 ions, one can observe a variation of fundamental frequencies which is not constant for the whole population. The domain of values of these frequencies is not negligible. The method described permits to define an ″effective″ fundamental frequency from which the behavior of the whole can be inferred. The results are compared to those predicted by other authors.