Magnetizing nonlinear plasma wakefields for positron acceleration

It is known that only a narrow plasma wakefield sliver in the electron-beam-driven blowout regime suits positron acceleration. Using 3D simulations, we show that matching the cyclotron frequency ${\omega }_c$ with the plasma frequency ${\omega }_p$ forms a stable electron column on axis, expanding the suitable phase space for positron acceleration sizably. For a plasma density $n_p={10}^{16}{\text{ cm}}^{-3}$ in a 35 T field, the interval expands 4.3 times, and a witness positron beam gains 100–150 MeV over 6 cm ($1.6$–$2.5$~GeV/m) with a 92% capture rate.