Injection of positrons into a dense electron cloud in a magnetic dipole trap

M Singer,E V Stenson,H Saitoh,M R Stoneking,S Nißl,J Horn-Stanja,T Sunn Pedersen,A Card,A Deller,C Hugenschmidt

doi:10.1063/5.0050881

Abstract

The creation of an electron space charge in a dipole magnetic trap and the subsequent injection of positrons have been experimentally demonstrated. Positrons (5 eV) were magnetically guided from their source and injected into the trapping field generated by a permanent magnet (0.6 T at the poles) using a cross field E × 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 −42 V, which is consistent with an average electron density of (4±2)×1012 m−3 and a Debye length of (2±1) 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 toward the production of a confined electron–positron pair plasma.

Highlights

Efforts to create pair plasmas consisting of quasi-neutral combinations of particles of an opposite charge and an equal mass are being pursued across a wide range of regimes
We find that the presence of an electron cloud with densities and space charge potentials relevant to future experiments does not negatively impact the efficiency of positron injection
An important step toward this goal is the injection of low–energy positrons into an electron cloud

Summary

Introduction

Efforts to create pair plasmas consisting of quasi-neutral combinations of particles of an opposite charge and an equal mass are being pursued across a wide range of regimes. Successful trapping of pair plasmas would create a novel and very likely stable system. In particular, production of a low-temperature magnetically well-confined electron–positron plasma would offer numerous opportunities for experimental tests of the theoretical predictions. Production of a low-temperature magnetically well-confined electron–positron plasma would offer numerous opportunities for experimental tests of the theoretical predictions It is, a significant experimental challenge to achieve the density threshold for plasma phenomena in the laboratory with a collection of electrons and positrons. Established devices for confining either positrons or electrons are called Penning–Malmberg traps, and nested combinations of such devices have been used to bring particles of an opposite charge into interaction with one another.11–16 Such traps are not suitable for long confinement of quasi-neutral pair plasmas with small Debye lengths. Other efforts have employed non-neutral plasmas or dense beams as electrostatic traps for particles of the opposite sign of charge.17,18 These experiments did not seek to produce quasi-neutral combinations of particles that are of interest here Other efforts have employed non-neutral plasmas or dense beams as electrostatic traps for particles of the opposite sign of charge. these experiments did not seek to produce quasi-neutral combinations of particles that are of interest here

Objectives

Methods

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Conclusion