Motion-induced coherences and density distributions in a Paul-trap

Summary form only given. Application of an ion trap as a frequency standard requires cooling of the ions or an accurate knowledge of the ion motion to compensate for frequency shifts due to the second-order Doppler effect. In this contribution we report on the observation of atomic coherence effects, which originate from the characteristic motion of Paul. Trapped ions and how these effects can be used for high accuracy measurements of the ion motion. Further we present measurements of the ion cloud distribution, which at higher densities is found to form a "hollow ball" and we discuss an expanded model for the motion and space distribution of ions in a large trap.