Investigation of periodic acceleration tube discharges with a capacitive pickup array

Several diagnostic techniques are described, which were used to determine the cause of periodic tube discharges and consequent fast terminal voltage drops in an FN tandom accelerator which were observed to occur at high beam intensities for the voltage range 7 to 9 MV. Terminal voltage drops were first monitored with a generating voltmeter (GVM). As a result of this study it was decided to install an array of four capacitive pickups (mushrooms) along the length of the pressure vessel. Information obtained from these pickups and analysis of beam fluctuation data permitted the source of the difficulty to be identified as a high transmission grid installed at the entrance to acceleration tube 1