M. R. Stoneking

Efficient injection of an intense positron beam into a dipole magnetic field

We have demonstrated efficient injection and trapping of a cold positron beam in a dipole magnetic field configuration. The intense 5 eV positron beam was provided by the NEutron induced POsitron source MUniCh facility at the Heinz Maier-Leibnitz Zentrum, and transported into the confinement region of the dipole field trap generated by a supported, permanent magnet with 0.6 T strength at the pole faces. We achieved transport into the region of field lines that do not intersect the outer wall using the drift of the positron beam between a pair of tailored plates that created the electric field. We present evidence that up to 38% of the beam particles are able to reach the intended confinement region and make at least a 180° rotation around the magnet where they annihilate on an insertable target. When the target is removed and the plate voltages are switched off, confinement of a small population persists for on the order of 1 ms. These results lend optimism to our larger aims to apply a magnetic dipole field configuration for trapping of both positrons and electrons in order to test predictions of the unique properties of a pair plasma.

Manipulation of positron orbits in a dipole magnetic field with fluctuating electric fields

We report the manipulation of positron orbits in a toroidal dipole magnetic field configuration realized with electric fields generated by segmented electrodes. When the toroidal circulation motion of positrons in the dipole field is coupled with time-varying electric fields generated by azimuthally segmented outer electrodes, positrons undergo oscillations of their radial positions. This enables quick manipulation of the spatial profiles of positrons in a dipole field trap by choosing appropriate frequency, amplitude, phase, and gating time of the electric fields. According to numerical orbit analysis, we applied these electric fields to positrons injected from the NEPOMUC slow positron facility into a prototype dipole field trap experiment with a permanent magnet. Measurements with annihilation γ-rays clearly demonstrated the efficient compression effects of positrons into the strong magnetic field region of the dipole field configuration. This positron manipulation technique can be used as one of essential tools for future experiments on the formation of electron-positron plasmas.We report the manipulation of positron orbits in a toroidal dipole magnetic field configuration realized with electric fields generated by segmented electrodes. When the toroidal circulation motion of positrons in the dipole field is coupled with time-varying electric fields generated by azimuthally segmented outer electrodes, positrons undergo oscillations of their radial positions. This enables quick manipulation of the spatial profiles of positrons in a dipole field trap by choosing appropriate frequency, amplitude, phase, and gating time of the electric fields. According to numerical orbit analysis, we applied these electric fields to positrons injected from the NEPOMUC slow positron facility into a prototype dipole field trap experiment with a permanent magnet. Measurements with annihilation γ-rays clearly demonstrated the efficient compression effects of positrons into the strong magnetic field region of the dipole field configuration. This positron manipulation technique can be used as one of essen...

Toward a compact levitated superconducting dipole for positron-electron plasma confinement

This paper describes the design of a compact levitated superconducting coil for the production of a magnetic dipole field to eventually trap positron-electron plasma. The closed 300 turn coil is to be constructed from Bi-2223 high-Tc superconducting tape, directly cooled on a cryogenic cold head (with thermal contact enhanced using helium gas), and inductively energized with a second superconducting coil mounted on the same cold head. Levitation will be achieved from above using a water-cooled copper coil outside the vacuum chamber and its current will be feedback controlled using vertical position information from a laser ranger.This paper describes the design of a compact levitated superconducting coil for the production of a magnetic dipole field to eventually trap positron-electron plasma. The closed 300 turn coil is to be constructed from Bi-2223 high-Tc superconducting tape, directly cooled on a cryogenic cold head (with thermal contact enhanced using helium gas), and inductively energized with a second superconducting coil mounted on the same cold head. Levitation will be achieved from above using a water-cooled copper coil outside the vacuum chamber and its current will be feedback controlled using vertical position information from a laser ranger.