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The closed-orbit measurement system for the new
Antiproton Decelerator (AD) employs 59 electrostatic
pick-ups (PU). The intensity range from 2·1010 down to
107 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/√(Hz), allowing beam positions to be
measured to ±0.5 mm with 5·106 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
“tracking filter” 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.
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