The new low gap BPM system at ELETTRA: Description and prototype tests

A prototype Low Gap BPM system has been installed at ELETTRA and it is now undergoing the first tests. The main purpose of this system is to provide ultra-stable position signals, at the micrometer level, to the Orbit Feedback processors. The system consists of a new Low Gap monitor and a new digital BPM electronics. The monitor was designed at ELETTRA and fits to the 14 mm low gap ID vacuum chamber. Full advantage has been taken from the reduced gap button distance. To reach maximum stability of the BPM itself, a new support system has been designed where, by means of two bellows, the BPM movements are de-coupled from the vacuum chamber slow drifts. Furthermore an external system monitors the BPM position with respect to a reference column made of carbonium. The Low Gap BPM system adopts the digital BPM electronics that was conceived at the Paul Scherrer Institut for the Swiss Light Source (SLS). One of its features is the programmable bandwidth that offers sub-micron position data when set to low bandwidth (<1 kHz). The project evolved into a successful collaborative development between ELETTRA, APL, SLS and the company Instrumentation Technologies. In this paper the first results obtained on the ELETTRA Storage Ring are presented and future system integration is outlined