Düsseldorf 2007 – scientific programme
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SYCP: Symposium Strongly coupled plasmas
SYCP 1: Symposium Strongly Coupled Plasmas
SYCP 1.5: Invited Talk
Tuesday, March 20, 2007, 16:30–17:00, 5D
Three-dimensional long-range ordered structures in RF confined ion Coulomb crystals — •Michael Drewsen — Inistitute of Physics and Astronomy, University of Aarhus, DK-8000 Aarhus C, Denmark
When an ensemble of trapped ions is cooled below a certain critical temperature it forms a very sparse and fragile type of solid, often referred to as a Coulomb crystal. The spatially ordered structures of such solids depend critically on the actual trapping fields as well as on the number of the trapped ion species. Recently, we have observed three-dimensional long-range ordered structures in near-spherically symmetric single-species Coulomb crystals of 40Ca+ ions confined in a linear rf Paul trap. The long-range ordered structures appeared as soon as the number of ions exceeded ∼1000 ions. Though this result is unexpected from molecular dynamics (MD) simulations of the systems ground states, it is found to be in agreement with MD simulations of metastable ion configurations. We have as well observed three-dimensional long-range ordered structures in the central 40Ca+ ion component of 40Ca+-44Ca+ two-species ion Coulomb crystals in a linear Paul trap. The structures here are strikingly more persistent (lifetimes of 10 s) and always of one specific type in one particular orientation. Molecular dynamics simulations strongly indicate that these characteristics are a consequence of an effective anisotropy in the inter-ion interaction induced by the radio frequency quadrupole trapping field.