Publications associated with Theoretical Astrophysics & Plasma Physics

Chaos of energetic positron orbits in a dipole magnetic field and its potential application to a new injection scheme.

Physical review. E 94 (2016) 043203-

H Saitoh, Z Yoshida, Y Yano, M Nishiura, Y Kawazura, J Horn-Stanja, TS Pedersen

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.

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