  We propose a novel positron beam loading regime in a hollow plasma channel
that can efficiently accelerate $e^+$ beam with high gradient and narrow energy
spread. In this regime, the $e^+$ beam coincides with the drive $e^-$ beam in
time and space and their net current distribution determines the plasma
wakefields. By precisely shaping the beam current profile and loading phase
according to explicit expressions, three-dimensional Particle-in-Cell (PIC)
simulations show that the acceleration for $e^+$ beam of $\sim$nC charge with
$\sim$GV/m gradient, $\lesssim$0.5% induced energy spread and $\sim$50% energy
transfer efficiency can be achieved simultaneously. Besides, only tailoring the
current profile of the more tunable $e^-$ beam instead of the $e^+$ beam is
enough to obtain such favorable results. A theoretical analysis considering
both linear and nonlinear plasma responses in hollow plasma channels is
proposed to quantify the beam loading effects. This theory agrees very well
with the simulation results and verifies the robustness of this beam loading
regime over a wide range of parameters.
