High Resolution and Low Charge Button and Strip-Line Beam Position Monitor Electronics Upgrade at FLASH

Historically the FLASH (Free Electron Laser in Hamburg) facility at DESY (Deutsches Elektronen-Synchrotron)in Germany has foreseen operation in a charge range from1 nC-3 nC for which a VME based BPM (Beam Position Monitor) system has been in operation since 2005 with a later upgrade to lower charges. In the past few years the standard machine operation settled at a few hundreds ofpC with a tendency to smaller charges down to 100 pC and less. The performance of the BPM system at charges below300 pC was in many locations along the machine unsatisfactory,making the operation of the linac more unstableand less reliable. Therefore a new BPM electronic system based on the utca (Micro Telecommunication ComputingArchitecture) for physics MTCA.4 standard has been developed to overcome the limitations of the old electronics and has already been successfully in operation in FLASH 2. A substantially improved version of the RF (radio frequency)front-end and digital electronics/firmware has been developed in 2016 and tested successfully. The peak detector electronics have been extended to a double peak detection in four channels and the fully customized Firmware is working machine synchronous. In summer 2017 all old button and strip-line BPM electronics have been replaced with the newtype. This paper summarizes the features and performance of the new BPM system, compares the beam jitter free resolution of the old and new BPM system and highlights its high single shot resolution of better than 10 $\mu$m rms at acharge of 15 pC