Simulation of Ionization Effects for High-density Positron Drivers in Future Plasma Wakefield Experiments*

The plasma wakefield accelerator (PWFA) concept has been proposed [1] as a potential energy doubler for present or future electron-positron colliders. Recent particle-in-cell (PIC) simulations have shown [2] that the self-fields of the required electron beam driver can tunnel ionize neutral Li, leading to plasma wake dynamics differing significantly from that of a preionized plasma. It has also been shown [3], for the case of a preionized plasma, that the plasma wake of a positron driver differs strongly from that of an electron driver. We will present new PIC simulations, using the OOPIC [4] code, showing the effects of tunneling ionization on the plasma wake generated by high-density positron drivers. The results will be compared to previous work on electron drivers with tunneling ionization and positron drivers without ionization. Parameters relevant to the energy doubler and the upcoming E-164x experiment [5] at the Stanford Linear Accelerator Center will be considered.