title: Chaos of energetic positron orbits in a dipole magnetic field and its potential application to a new injection scheme.
abstract: We study the behavior of high-energy positrons emitted from a radioactive source in a magnetospheric dipole field configuration. Because the conservation of the first and second adiabatic invariants is easily destroyed in a strongly inhomogeneous dipole field for high-energy charged particles, the positron orbits are nonintegrable, resulting in chaotic motions. In the geometry of a typical magnetospheric levitated dipole experiment, it is shown that a considerable ratio of positrons from a ^{22}Na source, located at the edge of the confinement region, has chaotic long orbit lengths before annihilation. These particles make multiple toroidal circulations and form a hollow toroidal positron cloud. Experiments with a small ^{22}Na source in the Ring Trap 1 (RT-1) device demonstrated the existence of such long-lived positrons in a dipole field. Such a chaotic behavior of high-energy particles is potentially applicable to the formation of a dense toroidal positron cloud in the strong-field region of the dipole field in future studies.
authors.affiliation: Max Planck Institute for Plasma Physics, Boltzmannstraße 2, D-85748 Garching and Wendelsteinstraße 1, D-17491 Greifswald, Germany.|Graduate School of Frontier Sciences, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8561, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Saitoh
authors.affiliation: Graduate School of Frontier Sciences, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8561, Japan.
authors.forename: Z
authors.initials: Z
authors.lastname: Yoshida
authors.affiliation: Graduate School of Frontier Sciences, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8561, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Yano
authors.affiliation: Graduate School of Frontier Sciences, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8561, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Nishiura
authors.affiliation: Graduate School of Frontier Sciences, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8561, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Kawazura
authors.affiliation: Max Planck Institute for Plasma Physics, Boltzmannstraße 2, D-85748 Garching and Wendelsteinstraße 1, D-17491 Greifswald, Germany.
authors.forename: J
authors.initials: J
authors.lastname: Horn-Stanja
authors.affiliation: Max Planck Institute for Plasma Physics, Boltzmannstraße 2, D-85748 Garching and Wendelsteinstraße 1, D-17491 Greifswald, Germany.|Ernst Moritz-Arndt University Greifswald, Domstraße 11, 17489 Greifswald, Germany.
authors.forename: T Sunn
authors.initials: TS
authors.lastname: Pedersen