PARTICLE CONFINEMENT IN TIME-DEPENDENT FIELDS

The confinement of charged particles by linear, time-dependent fields with arbitrary pulse shape is studied. It is assumed that the trapped particles are perturbed by collisions with a neutral background gas. T he spatial dispersion and energy of the trapped particles are determin ed using an asymptotic expansion based on a singular perturbation appr oach in terms of the momentum exchanged during collisions. Parametric instabilities, which result in the destruction of the confinement, are identified for different pulse shapes.