Vacuum chamber for treating workpieces with beams

Apparatus is described for directing a beam at a workpiece in vacuum has a special planar sliding multiple seal arrangement that enables repeated scanning movement of the workpiece across the beam. The seal includes a planar slide plate and an opposed relatively movable seal support member, also preferrably a plate parallel to the slide plate. Aligned apertures are in the members, one of which is larger in the direction of relative movement than the other enabling the relative movement while maintaining the alignment. A plurality of concentric resilient seals, which may be of oval race track configuration, bear with a sliding contact against the planar surface, these seals preferably comprising composites of a thin high density polyethylene seal element and a soft and only milding compressed backing element that applies a feather-light seal pressure. Between-seal pumping is provided to reduce the differential pressure across any seal to to remove gas that may leak into the space. The embodiment shown incorporates the seal between a moving target chamber and a fixed ion beam chamber