Presentation on theme: "PROPERTIES OF TRAPPED Ca+ IONS"— Presentation transcript:
1PROPERTIES OF TRAPPED Ca+ IONS James Oldham, University of Oxford63rd Molecular Spectroscopy Symposium17th June 2008
2Introduction Motivation and Experimental Apparatus Simulation Model Findings from SimulationsMotions of Trapped IonsIon Temperature DependenciesBi-component CrystalsConclusions
3MotivationProvide theoretical data about Coulomb crystals in context of current experiments.Determine thermal properties of ions in a crystal which will affect collision energies:Dependence on trap parameters.Dependence on ion positions.Determine extent that time-dependent potential changes ion energies.Investigate positions of reactant and product ions in bi-component crystals seen during a reaction.
4Experimental Apparatus Photo-ionised Ca+ trapped with linear RF (Paul) trap.Primarily cooled with 397nm diode laser.866nm diode laser used to repump ion population from metastable 2D3/2.
5Coulomb Crystals ‘Condensed’ state of a one-component plasma Arises from equilibrium between trapping and repulsive Coulomb forces.Molecular dynamics (MD) simulations provide details such as ion energies, positions of non-fluorescing ions.
7Simulation of a Coulomb Crystal Simulated image of 1080 Ca+ Coulomb crystal
8Types of Ion Motion Ion motion comprised of : secular motion, random thermal motion of ions;micromotion, high frequency ordered motion induced by RF field.In adiabatic regime, types of motion are independent of one another.
9How hot are the ions?Two different kinetic energies can be attributed to ions:Secular energyEffective energySecular distributions match Boltzmann distributions at equal Tsec.No match between effective energy and Boltzmann distributions.Secular velocity distribution of a 2685Ca+ Coulomb crystal with mean secular temperature of 15mK, and corresponding Boltzmann distribution.
10Ion Secular Temperatures Varying magnitude of heating force alters Tsec in simulations.Tsec of experimental crystals obtained by comparing experimental and simulated images.Micromotion has negligible impact on images.
11Effective Energies of Ions Experimental images of an ion string and prolate and oblate crystals.For a trapped ion,Average radial ion displacement increases for larger or more oblate crystals.Greater range of energies expected for large/oblate crystals.
12Effective Energy Distributions Distributions formed by taking ion effective energies over many timesteps in simulation.Distributions dependent on number of ions and shape of crystalClear shell structures of crystals seen.Changing secular temperature of ions has little effect on distribution.
13Reaction ProgressionSimulated images of bi-component crystals replicate experimental images.Imply product ions formed and trapped experimentally.CaF+ reside at greater radial distances than Ca+.
14ConclusionsExperimental crystals accurately reproduced by use of time-dependent MD simulation, allowing greater knowledge of crystals, including kinetic energy profiles including and excluding micromotion.Trap parameters and shape/size of crystal strongly affect effective energies of ions, although secular temperatures not significantly dependent.Micromotion generally dominates kinetic energy of a radially displaced ion.Simulations of bi-component crystals indicate that product ions are formed when CH3F is present in chamber.
15Acknowledgements Alex Gingell Martin Bell Dr. Stefan Willitsch Prof. Tim SoftleyEPSRC