The closed-orbit measurement system for the CERN antiproton decelerator

The closed-orbit measurement system for the new Antiproton Decelerator (AD) employs 59 electrostatic pick-ups (PU). The intensity range from 2&#183;10^{<font size="-1">10</font>} down to 10^{<font size="-1">7</font>} particles poses challenging demands on the dynamic range and noise of the head amplifier. A low noiseamplifier has been developed, having an equivalent input noise of 0.6nV/&#8730;(Hz), allowing beam positions to be measured to &#177;0.5 mm with 5&#183;10^{<font size="-1">6</font>} particles. Two different gains take care of the large dynamic range. After amplification and multiplexing, the PU signals are fed to a network analyser, where each measurement point corresponds to one PU. The network analyser is phase locked to the RF of the AD, thus acting as a &#0147;tracking filter&#0148; instrument. An orbit measurement takes from 0.2 to 12 s depending on the IF-bandwidth of the network analyser, selected according to the beam intensity, and the precision required. At the end of the network analyser sweep the data are read via a GPIB interface and treated by a real-time task running in a VME based Power PC.