Efficient cooling and pre-acceleration of positron beams via a surface-plasmon wakefield

Phase-space control of positron beams is essential for compact, high brightness positron sources, yet efficient capture and early stage acceleration remain challenging. Here we propose and numerically investigate a surface-plasmon driven wakefield scheme in a dense plasma micro-tube, in which wakefield excitation is sustained by the oscillation of a nanometric electron layer at the inner wall. Coupled Geant4 and particle-in-cell simulations show that this single stage configuration links positron generation to wakefield injection, enabling positron capture, longitudinal phase-space cooling, transverse geometric compression, and pre-acceleration with an average accelerating gradient of about 0.5 TV/m. At about 10 mm (33.4 ps), the positron beam reaches a peak energy of 5.68 GeV with a minimum relative energy spread of 10.3%, while the beam divergence is reduced and the longitudinal capture efficiency exceeds 95%. These results support dense plasma micro-tubes as compact platforms for positron pre-acceleration and phase-space control in future high brightness positron injectors.