AUTOMATIC EXTERNAL FILLING FOR THE ION-SOURCE GAS BOTTLE OF A VAN DE GRAAFF ACCELERATOR

We describe a fully automatic system we developed to fill, from an ext ernal gas bottle, the ion sourer terminal gas storage bottle of a 2 MV Van de Graaff accelerator without depressing the 25 bar insulating ga s. The system is based on a programmable automate ordering electropneu matical valves. The only manual operation is the connection of the ext ernal gas cylinder. The time needed for a gas change is reduced to typ ically 15 min (depending on the residual pressure wished for the gas r emoved from the terminal bottle). To check this system we study the io nic composition of the ion beam delivered by our accelerator after dif ferent gas changes. The switching magnet of our accelerator was used t o analyse the ionic composition of the accelerated beams in order to v erify the degree of elimination of the previous gases in the system. ( C) 1997 Elsevier Science B.V.