A neutral atom storage ring and intense cold atom source




Huntington, William D.

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Presented in this thesis is a proposed design for a continuously loaded permanent magnet meter scale storage ring for confining neutral atoms and molecules. Confinement is generated by neodymium magnets arranged to produce hexapole fields. The ring is in the shape of a “racetrack” with two bending sections of 1 meter radius and is composed entirely of linear segments of magnets. A permanent magnet injection system continuously guides particles from an existing source into the ring using an optical pumping scheme. The dynamics of the design are well explained by charged particle accelerator theory extended to neutral particles. The proposed design is over an order of magnitude larger than previous neutral atom storage rings and provides over 2 orders of magnitude greater trapping depth. An extensive simulation was developed to characterize and optimize the ring and injector system. The design is optimized for our existing source of ⁷Li atoms, although theory and simulation indicate it will work well with other paramagnetic species. With our source it is expected to build up a circulating flux of around 5 × 10¹⁴ atoms/s and an atom number of about 2 × 10¹³. It has previously been suggested that such a design is unstable, but in this work it is shown that an essential stability criteria was neglected. Also presented is the improvement and characterization of an intense, continuous cold atom beam to be used to load the storage ring. The beam is generated via post nozzle seeding of a supersonic cryogenic ⁴He jet with hot ⁷Li atoms. The atomic beam is brought to a focus 176 cm from the nozzle by a 10 cm bore diameter permanent magnet hexapole lens. At the focus the beam is measured to have a flux of 2.3(4) × 10¹² atoms/s, brightness of 1.8(6) × 10¹⁹ m⁻²s⁻¹sr⁻¹, forward velocity of 210(2) ms⁻¹, and longitudinal temperature of 7(3) mK. An improved vacuum design should yield around 10 times higher flux.



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