Beam-driven plasma wakefield acceleration (PWFA) holds considerable promise for next-generation electron-positron colliders and high-energy free-electron lasers, owing to its ultrahigh accelerating gradients. In particular, sustained experimental breakthroughs worldwide indicate that the field is now entering a critical phase toward key advances. To address fundamental physics and technical challenges associated with both electron and positron acceleration in PWFA, the Institute of High Energy Physics (IHEP) has established a plasma wakefield acceleration experimental platform based on the Beijing Electron-Positron Collider (BEPCII). The platform comprises two beamlines and a petawatt laser system. Beamline I deliver electron and positron beams from BEPCII to the experimental area, while Beamline II is a newly constructed 150 MeV high-performance linear accelerator. Together, these beamlines support a range of plasma acceleration experiments, including positron acceleration, electron-cascade acceleration, high transformer-ratio electron acceleration, and external-injection electron acceleration. Notably, Beamline II is capable of generating electron beams with a bunch charge exceeding 5 nC and a peak current above 10 kA. This paper presents a detailed overview of the physics design and current progress of Beamline II.

Plasma acceleration is an innovative principle characterized by high acceleration gradients, which has attracted significant interest from major accelerator laboratories worldwide, because of its potential to increase accelerator energy and reduce size. One promising approach involves using existing conventional accelerators as external injectors for plasma-based accelerators, a topic of considerable interest within the research community. At IHEP, we propose utilizing the BEPCII Linac in conjunction with a new linac based on a photocathode RF gun to develop a new plasma acceleration research platform. The platform consists of two beamlines and a PW laser system. This manuscript presents recent progress of the two beamlines of this platform.