Abstract
Recent moment theories of ion motion in devices where the external fields vary with position and time are applied to non-ideal ion traps. In first approximation, the theories give differential equations with collision frequencies that vary with the effective temperature characterizing the relative kinetic energy of the ion-neutral collisions. Solutions of the set of coupled differential equations provide the ion number density, average velocities, average energies, and average temperatures as functions of time and of position in the apparatus. Solutions of the coupled equations are discussed for the Maxwell model, rigid spheres, and general ion-neutral interactions. A surprising finding is that ac fields on the end caps lead to changes in the stability region for ion motion in traps, changes that can cause ion injection both for small and large values of the ac field applied to the rings.