Vacuum leak problem in low energy of pelletron

During unit wise conditioning of unit # 8, the vacuum started deteriorating inside the tube after a spark. The RGA leading was taken and it was found out that residual gas inside tube was sulphur hexafluoride. A leak was dete cted in second tube of unit number eight in between electrode 6 to 8. Leak was sealed with the sealant. Again leak check was done and no leak was foun d. The tank was closed and conditioning was started again. During the same unit number eight conditioning, leak developed again followed by a spark. S o the damaged tube was replaced with a new accelerator tube. During the ins tallation time the alignment of the machine was taken care. Again leak chec king was done and the tube was baked properly. The tank was closed again an d this particular unit was conditioned for about four days. The maximum vol tage it has attained was 1.1 MV.