  Positron creation and acceleration is one of the major challenges for
constructing future lepton colliders. On the one hand, conventional technology
can provide a solution, but at a prohibitive cost and scale. On the other hand,
alternative, reduced-scale ideas for positron beam generation could bring this
dream closer to reality. Here we propose a novel plasma-based positron
acceleration method using a powerful laser propagating through a dense and
narrow plasma channel. A large amount of electrons is injected within the
channel during laser propagation. This electron loading creates static fields
in the plasma, enabling positrons to be guided transversely while they directly
gain energy from the laser field itself. Within this context, we present a
theoretical model to describe how the laser injects the electrons and estimate
the beam-loaded effective electron density. We validate our theoretical
predictions through Quasi-3D PIC simulations and demonstrate the robustness of
this guiding and direct laser acceleration process for positrons. Our approach
could pave the way for testing this new positron acceleration scheme at
ELI-Beamlines, showcasing unprecedentedly high average energy gain rate of a
few TeV/m. The fireball jet produced contains GeV-level electrons, positrons,
and x-rays, opening the path towards potential laboratory astrophysics
experiments using these beams.
