Experimental Demonstration of Multi-Joule Energy Transfer, Total Charge Capture, and Positron-Compatible Wakefields in Laser-Ionized Plasma Channels

Plasma wakefield accelerators (PWFA) promise acceleration gradients orders of magnitude higher than conventional radiofrequency accelerators, offering a pathway toward compact, high-energy colliders. Realizing this potential requires efficient multi-joule energy transfer and high-quality acceleration of both electrons and positrons. Using laser-ionized hydrogen plasma sources at FACET-II, we demonstrate significant progress toward these goals. In a single-bunch configuration, we achieve at least 5.6 J of energy transfer from a 1.52 nC, 10 GeV electron beam, corresponding to a drive-to-wake efficiency of 37±3%. In a two-bunch setup, we demonstrate complete charge capture of an externally injected 300 pC witness beam while maintaining high overall efficiency. Additionally, we experimentally realize PWFA in a laser-ionized narrow plasma channel. In this regime, the wake elongates, and sheath electrons form an extended filament providing both acceleration and focusing for positrons. Comparative wake-structure mapping between narrow and wide channels demonstrates these wake characteristics.