Performance of the new coupled bunch feedback system at HERA-P

A longitudinal broadband damper system to control coupled bunch instabilities (LMBF) has been installed in the 920 GeV proton accelerator HERA-p at the Deutsches Elektronen-Synchrotron DESY in Q4/2005. This was one of the attempts to increase the specific luminosity at HERA by reducing the bunch length. The feedback system is based on a single board FPGA (field programmable gate array) with two ADCs and 2 DACs (each 14 bits resolution) at 52 MHz sampling rate. It was fully automated, in order to relief the operator from manual control during system operation. During commissioning in Q1/2006 it turned out that the performance goals were reached and the noise introduced due to the feedback corrections and the 1 kW power amplifier was not as much a problem as expected. The proton bunch length is significantly reduced as well as the lengthening of the bunches over runtime since all formally occurring coupled bunch instabilities could sufficiently be suppressed during the enegergy ramp and the following luminosity run. System optimization points were found in automatic gain adjustment during acceleration ramp, oscillation level triggering and timing of kicker pulse to bunch.