Abstract: Numerical simulation on plasma ion implantation of a trapezoid tube is conducted in a MATLAB based Particle-in-cell model.It shows that "anodic-sheath" appears around internal electrode,where there is no ion.Some ions gather at the edge of "anodic-sheath" leading to a high-ion-density ring.It makes an m-shaped dose distribution on upside wall and downside wall of the tube.Due to asymmetry of the trapezoid tube,"anodic-sheath" expands faster toward long-wall of the tube.Implantation energy is relatively low at initial stage and becomes higher with time.This is attributed to the position of ions in the tube before they are implanted into the tube wall.The tube configuration determines sheath shape and final distribution of implantation dose and energy.

Key words: trapezoid tube, plasma ion implantation, temporal and spatial evolution, particle-in-cell, MATLAB