Precision alignment and tolerance of a plasma wakefield accelerator in a laser-ionized plasma source

We present a novel method to align a laser-ionized plasma source with ultrarelativistic electron beams in a plasma wakefield accelerator. The technique relies on analyzing plasma afterglow light at two longitudinal positions as the plasma column is scanned across the beam axis. Using this method, we aligned an 85-cm plasma source to a 10-GeV, 1.6-nC electron beam with better than 10-μm transverse offset and 10-μrad angular error. The alignment was validated by measuring the drive beam energy loss, beam-to-wake energy transfer efficiency, and witness beam energy gain as functions of intentional misalignment. From these measurements, we determined the alignment tolerances required between the laser-ionized plasma source and the electron beams, an essential parameter for the design of plasma-based colliders and advanced light sources.