An arc chamber for an ion implantation system includes an exit aperture positioned at a wall of the arc chamber, filaments respectively positioned at two opposing sides within the arc chamber, and repeller structures respectively positioned at two opposing walls within the arc chamber between the filaments and the arc chamber. The repeller structure includes a repeller substrate with a screw axis for fitting the repeller structure to the arc chamber, an insulator positioned underneath the repeller substrate providing an electrical isolation between the repeller substrate and the arc chamber, and a conductive spacer covering a portion of the insulator positioned in between the insulator and the arc chamber.