Abstract: Disclosed is ion implantation apparatus in which an ion source is coupled to a semiconductor or workpiece holder which is mounted for rotation and reciprocation in a first chamber in the path of the ion beam. A second chamber is releasably coupled to the first chamber with means connected to the second chamber in such a manner as to enable displacement between the first and second chamber, the chambers being in fluid communication with one another when the apparatus is in operation. Vacuum drawing means are provided to effect a vacuum in both the first and second chamber when the apparatus is in operation, and when it is desired to withdraw the holder from the apparatus by disconnecting the second chamber from the first chamber, venting the first chamber automatically actuates a check valve which seals the second chamber permitting the retention of a vacuum in the second chamber while allowing the first chamber to be exposed to atmospheric pressure.