New Automatic Bunch Current Sensitive Fast Attenuator for RF Front-end of Bunch-by-Bunch Feedback System at SPring-8
K.Kobayashi*, T.Nakamura (JASRI/SPring-8)
We currently developing a new bunch current sensitive automatic attenuation system for the RF front-end of the bunch-by-bunch feedback system in the SPring-8 storage ring. It controls the attenuation of high current bunch signal to avoid the saturation of RF front-end and for equalization of the feedback gain for hybrid beam filling modes consist of few-mA singlet bunches and sub-mA bunch trains. We have already developed and installed a bunch current sensitive automatic attenuator with a simple mixer, a discriminator and FPGA based 1-turn delay with the attenuation level of 15 dB. However this attenuation level is not enough for hybrid filling modes with higher bunch current singlets and lower bunch current trains which are recently requested by users. To achieve more attenuation level and more flexible operation, we are now developing an attenuation system with a voltage variable attenuator controlled by a digital bunch current measurement device which is converted from a SPring-8 bunch-by-bunch feedback processor. This paper describes the new attenuation system and its test results.