Combined remoderation-drift scheme for positron injection into a magnetic trap

Abstract

The efficient transfer of a magnetically guided positron beam into a region of closed magnetic field lines is nontrivial. An E×B-drift technique has previously been used effectively to inject a low-energy (5- to 20-eV) positron beam into the confinement region of a permanent-magnet-based dipole trap. To complement and extend that strategy, we have investigated an approach in which a high-energy (∼350-eV) positron beam is remoderated in a SiC crystal immediately outside the confinement region; the reemitted low-energy positrons are then drift injected. Thus we effectively combine positron remoderation and E×B-drift injection in the same spatial region. Initial tests with this scheme were shown to have an overall efficiency of up to 15(±1)%. Positron trajectory simulations enabled us to account for various loss mechanisms and thereby identify means to improve this in future implementations. This method adds further flexibility to the search for an efficient injection scheme into toroidal magnetic traps with the mission of confining electron-positron pair plasmas.