Abstract: An ion beam implanter includes an ion beam source for generating an ion beam moving along a beam line and a vacuum or implantation chamber wherein a workpiece is positioned to intersect the ion beam for ion implantation of a surface of the workpiece by the ion beam. The ion beam implanter includes workpiece support structure having a scan arm extending through an opening in a wall of the implantation chamber into the implantation chamber interior region. The workpiece support structure further includes a spherical sliding vacuum seal assembly having a spherical support rotatably supported in the opening in a wall of the implantation chamber. The spherical support includes a central throughbore for slidably supporting the scan arm. The spherical sliding seal assembly further includes a first seal disposed between an outer surface of the spherical support and the wall of the implantation chamber and a second seal disposed between the scan arm and the throughbore of the spherical support.