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Plasma immersion ion implantation into inner surfaces of tubes has practical importance, but intrinsic drawbacks such as poor dose uniformity and small equivalent ion flux have limited wider applications. In this paper, a new technique utilizing a moving auxiliary electrode inside the tube to improve the dose uniformity and ion implantation efficiency is described. The effects of the moving auxiliary electrode are investigated by 2-D particle-in-cell simulation. The results show that, when the grounded auxiliary electrode is withdrawn along the axis of the tube, external ions are continuously attracted into the tube and implanted into the interior wall. It is verified by the incident dose peak when the auxiliary electrode is kept at a certain location inside the tube. Uniform ion implantation into a cylindrical bore can be accomplished by physical translation of the electrode, and this technique is suitable for implantation of long tubes without an internal plasma source.