SNS LEBT Chopper improvements

The Low Energy Beam Transport (LEBT) Chopper for the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory has experienced failures of the power semiconductors within the tri-state pulsed power supplies. These power supplies deliver a +/- 3 kV pulse or ground potential to an electrostatic einzel lens split into four quadrants to deflect the beam for 200 ns to 1 us. The four power supplies are ac coupled to a -50 kV dc supply for steering offset of the lens. This paper discusses the failure modes and improvements to mitigate future failures.