Computation for ions stored in a quadrupole R.F. TRAP cooled by a buffer gas. Influence of working conditions on space-charge effects

Abstract

We have studied the influence of the confinement parameters (a, q, Ω) on the perturbations, caused by space-charge, of the statistical properties of strongly confined Cs+ ions cooled by helium buffer gas. The formalism, using a 3D-model, is briefly recalled. The spatial and energy dispersions and the evolution of the fundamental frequencies of the movement are computed as a function of increasing ion number, n. A variation of the parameters a and q does not influence the magnitude of the upper limiting values for "weak space-charge" (highest value of n for which the Gaussian properties are conserved); however, the driving frequency, Ω, strongly modifies these values. In each case, the space-charge increases the ion-cloud dimensions and decreases the fundamental frequencies, but the velocity distributions remain constant. © 1985.