Recent developments in the improvement campaign for the high voltage converter modulator at the Spallation Neutron Source

The High Voltage Converter Modulator (HVCM) systems at the Spallation Neutron Source (SNS) are the primary power sources for the klystrons that supply RF power to the H-beam. The availability of the HVCMs exceeds 99% due to numerous improvements that have been implemented since SNS operations began in 2006. However, the HVCMs continue to operate in open-loop mode that results in significant voltage droop within each pulse. Control margin in the low-level RF control system is becoming a limitation as beam intensity and pulse length are increased to raise the beam power on target to 1.4 MW. This paper will discuss recent progress towards improving the pulse characteristics delivered by the HVCM systems and additional steps being pursued to further improve the system reliability. Alternative modulation schemes for switching the IGBTs, alternative system topologies and various enabling technologies to accomplish these goals will be the primary focus. The motivation, design details, test results and implementation will be presented.