[en] An ion source for generating agglomerated hydrogen ions for an accelerator tube is enclosed by a pressure-resistant container lying on high tension. The container itself is arranged within a pressurized tank filled with SF₆ gas at 10 to 20 bar. The ion source is cooled by liquid He; the vaporizing He gas and N₂ gas is discharged into the interior of an insulating tube. This one contains FC 43 and forms a connection between the pressure-resistant container and the environment of the pressurized tank. The vaporized coolant in the form of bubbles is diffusing through the insulating fluid to the environment. (orig.)