  We study the dynamic behavior of ultracold neutral atoms in a macroscopic ac
electric trap. Confinement in such a trap is achieved by switching between two
saddle-point configurations of the electric field. The gradual formation of a
stably trapped cloud is observed and the trap performance is studied versus the
switching frequency and the symmetry of the switching cycle. Additionally, the
electric field in the trap is mapped out by imaging the atom cloud while the
fields are still on. Finally, the phase-space acceptance of the trap is probed
by introducing a modified switching cycle. The experimental results are
reproduced using full three-dimensional trajectory calculations.
