Ellipsoidal Coulomb crystals in a linear radio-frequency trap -: art. no. 073506

A static quadrupole potential breaks the cylindrical symmetry of the effective potential of a linear rf trap. For a one-component liquid plasma at low temperature, the resulting equilibrium charge distribution is predicted to be an ellipsoid. Laser-cooled Be-9(+) ellipsoidal ion crystals were produced and good agreement was found between their shapes and the cold fluid prediction. In two-species mixtures, containing Be-9(+) and sympathetically cooled ions of lower mass, a sufficiently strong static quadrupole potential produces a complete spatial separation of the species. (C) 2005 American Institute of Physics.