| Radiofrequency ion traps are used to hold ions in a small, undisturbed region of space for the purpose of ultra stable frequency standards. To attain the highest possible degree of stability while preserving a high signal-to-noise ratio, it is necessary to utilize large ion clouds and cool the ion motion as much as is allowed by fundamental limits. A model of trapped ion motion including trap electric fields, inter-ion electric forces, laser cooling forces, and background thermal excitation is developed for several trap geometries, including the rf/dc linear trap geometry which provides a compact electrode configuration for containing large clouds of ions. Using this model in a supercomputer simulation, laser cooling is examined for solid-like, liquid-like, and gas-like ion clouds for various laser and trap parameters, and recommendations for effective cooling of rf-trapped ions are made. In an rf/dc linear trap, the radius of the dc endpins should be smaller than the nominal cloud radius. The laser should be as close to saturating the atomic cooling transition as possible, aligned at a shallow (... |
