Status of the mixed-signal active feedback damper system for controllingelectron-proton instabilities for the spallation neutron source

As the beam intensity at the Spallation Neutron Source (SNS) in Oak Ridge NationalLaboratory (ORNL) is increased, it becomes necessary to have greater control over theelectron-proton (e-p) instability. This paper presents the design of a mixed-signaltransverse feedback system for active damping of the e-p instability. It describes thedesign, features and results of this feedback damper, and it reviews several experimentalstudies to understand the system performance and its limitations. The mixed-signal feedbackdamper system employs power amplifiers (PAs), analog-to-digital converters (ADCs), multiplefield programmable gate array (FPGA) chips, and digital-to-analog converters (DACs) toprovide feedback damping and system monitoring. Unlike existing analog damping systems,FPGA-based feedback damping systems offer programmability while maintaining high signalprocessing performance. The system gain, delay and digital signal processing components canbe programmed during the experiment to perform timing adjustments, correct for ringharmonics, and equalize magnitude and phase dispersions.