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

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.

Annihilation-gamma-based diagnostic techniques for magnetically confined electron–positron pair plasma

“…2018) and injection of positrons into the dipole field populated with a dense cloud of electrons (with electron density, ) (Singer et al. 2021 b ).…”

“…Pedersen et al (2012) and Stoneking et al (2020) map out a path towards a magnetically confined pair plasma involving accumulating positrons in non-neutral plasma traps from the NEPOMUC positron beam , the world's highest flux positron source, and injecting them (in combination with electrons) into a magnetic confinement geometry suitable for low plasma densities such as a dipole field or a stellarator. Recently, significant progress has been made towards confining positrons in a permanent magnet dipole trap including lossless injection of a positron beam (Stenson et al 2018), confinement of positrons for longer than 1 second ) and injection of positrons into the dipole field populated with a dense cloud of electrons (with electron density, n e − ∼ 10 12 m −3 ) (Singer et al 2021b).…”

Ion-driven destabilization of a toroidal electron plasma -- A 3D3VPIC Simulation

“…Such an electron plasma in inhomogeneous magnetic field is useful to understand nonlinear coupling 45,46,66 between different toroidal Diocotron modes, collisional/non-collisional transport mechanisms 47 of electron plasma energy and also crucial to initiate an ongoing construction of electron-positron plasma experiment using dipole magnetic field 49,50 . These systems can often serve as test-beds to understand plasma dynamics in curved magnetic field which are often found in astrophysical phenomena 48 .…”