SLAC, Menlo Park, California, USA
CERN, Geneva, Switzerland
The feedback control of intra-bunch instabilities driven by electron-clouds or strong head-tail coupling requires bandwidth sufficient to sense the vertical position and apply correction fields to multiple se ctions of a nanosecond-scale bunch. These requirements impose challenges and limits in the design of the feedback channel. We present experimental measurements taken from CERN SPS machine development studies with an intra-bunch feedback channel prototype. The performance of a 3.2 GS/s digital processing system is evaluated, quantifying the effect of noise and limits of the feedback channel in the bunch stability as well as transient and steady state motion of the bunch. The controllers implemented are general purpose 16 tap FIR filters and the impact on the bunch stability of controller parameters are analyzed and quantified. These studies based on the limited feedback prototype are crucial to validate reduced models of the system and macro-particle simulation codes including the feedback channel. These models will allow us predicting the beam dynamics and controller limits when future wide-band hardware is installed in the final prototype to stabilize multiple bunches.
