  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.
