Injection of Positrons into a Dense Electron Cloud in a Magnetic Dipole Trap

TL;DR

This paper experimentally demonstrates the creation of an electron space charge in a magnetic dipole trap and successful injection of positrons into this environment, advancing the understanding of electron-positron plasma formation.

Contribution

It introduces a method for injecting positrons into a dense electron cloud within a magnetic dipole trap, showing the feasibility of creating a confined electron-positron pair plasma.

Findings

Electron space charge potential reaches -42V

Positron injection remains efficient despite space charge

Electron density estimated at (4 ± 2) × 10^{12} m^{-3}

Abstract

The creation of an electron space charge in a dipole magnetic trap and the subsequent injection of positrons has been experimentally demonstrated. Positrons (5eV) were magnetically guided from their source and injected into the trapping field generated by a permanent magnet (0.6T at the poles) using a cross field E $\times$ B drift, requiring tailored electrostatic and magnetic fields. The electron cloud is created by thermionic emission from a tungsten filament. The maximum space charge potential of the electron cloud reaches -42V, which is consistent with an average electron density of ($4 \pm 2$) $\times 10^{12}$ $\text{m}^{-3}$ and a Debye length of ($2 \pm 1$) $\text{cm}$. We demonstrate that the presence of this space potential does not hamper efficient positron injection. Understanding the effects of the negative space charge on the injection and confinement of positrons represents an important intermediate step towards the production of a confined electron-positron pair plasma.