Injection, confinement, and diagnosis of electrons and positrons in a permanent magnet dipole trap

J. von der Linden; S. Nißl; A. Deller; M. Singer; N. Belmore; C. P. Hugenschmidt; T. Sunn Pedersen; H. Saitoh; E. V. Stenson

doi:10.1140/epjd/s10053-024-00821-x

2024 Impact factor 1.5

Atomic, Molecular, Optical and Plasma Physics

Electron and Positron Interactions and Their Applications-a tribute to Professor Michael Brunger

Open Access

Eur. Phys. J. D (2024) 78: 146
https://doi.org/10.1140/epjd/s10053-024-00821-x

Regular Article

Injection, confinement, and diagnosis of electrons and positrons in a permanent magnet dipole trap

J. von der Linden¹, S. Nißl², A. Deller³, M. Singer⁴, N. Belmore⁵, C. P. Hugenschmidt², T. Sunn Pedersen⁶, H. Saitoh⁷ and E. V. Stenson¹^a

¹ Max Planck Institute for Plasma Physics, 85748 Garching & 17491, Greifswald, Germany
² Technische Universität München, 85748, Garching, Germany
³ University of California San Diego, 92093, La Jolla, CA, USA
⁴ Applied Materials, 85551, Heimstetten, Germany
⁵ TicketSwap, 1012 KL, Amsterdam, The Netherlands
⁶ Type One Energy Group, 53703, Madison, WI, USA
⁷ University of Tokyo, 277-8561, Kashiwa, Chiba, Japan

^a eve.stenson@ipp.mpg.de

Received: 22 November 2023
Accepted: 23 February 2024
Published online: 5 December 2024

Abstract

Prerequisites for the goal of studying long-lived, magnetically confined, electron–positron pair plasmas in the laboratory include the injection of both species into the trap, long trapping times, and suitable diagnostic methods. Here we report recent progress on these tasks achieved in a simple dipole trap based on a supported permanent magnet. For the injection of electrons, both an $E \times B$ $\textbf{E}\times B$ drift technique (of a $\sim$ $\sim$ 2– $μ$ $\upmu$ A, 6-eV beam) and “edge injection” (from a filament emitting a few mA and biased to some tens of volts) have been demonstrated; the former is suitable for low-density beams with smaller spatial and velocity spreads, while the latter employs fluctuations arising from collective behavior. To diagnose the edge-injected electrons, image potentials and currents induced on a wall probe, the magnet case, and wall electrodes were measured. Confinement of drift-injected positrons, measured experimentally, exhibited at least two well-separated timescales. Simulations reproduced this qualitatively, using a simple model of elastic collisions with residual background gas, and point to small adjustments for increasing trapping times. In a major upgrade to diagnostic capabilities, 25 bismuth germanate detectors, placed in three reentrant ports, are able to localize annihilation gammas, which will be used in future experiments to distinguish between different loss channels.

© The Author(s) 2024

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