If a part (11) at a specific electrical potential is intended to be located in a vacuum container, it is necessary to pass an electrical conductor through the wall of said vacuum container (10). An insulating body (14) must be mounted in the wall (10) for this purpose. If physical or chemical processes take place in the container which lead to the separation (precipitation) of conductive material, there is a risk of the insulating bodies (14) in the interior of the container being coated and of the conductive coating forming a link between the conductor (13) and the container (10). In order to avoid material deposits on the insulating body (14), a gas flow is produced which flows along wall parts of the insulating body.
