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- E. Barbero, B. Dehning, J. Prochnow
CERN, Geneva, Switzerland
- J. Bergoz, K. Unser
Bergoz, Bergoz Instrumentation, St. Genis Pouilly, France
- J. Matheson
RAL, Rutherford Appleton Laboratory, Chilton, UK
- E. Torrence
UChicago, University of Chicago, IL, USA
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At the LEP e+/e- collider, a spectrometer is used to determine
the beam energy with a target accuracy of 10-4.
The spectrometer measures the lattice dipole bending angle
of the beam using six beam position monitors (BPMs).
The required calibration error imposes a BPM accuracy of
1 æm corresponding to a relative electrical signal variation
of 2×10-5. The operating parameters have been compared
with beam simulator results and non-linear BPM response
simulations. The relative beam current variations between
0.02 and 0.03 and position changes of 0.1mm during the
fills of last year lead to uncertainties in the orbit measurements
of well below 1μm. For accuracy tests absolute
beam currents were varied by a factor of three. The environment
magnetical field is introduced to correct orbit readings.
The BPM linearity and calibration was checked using
moveable supports and wire position sensors. The BPM
triplet quantity is used to determine the orbit position monitors
accuracy. The BPM triplet changed during the fills
between 1 and 2μm RMS, which indicates a single BPM
orbit determination accuracy between 1 and 1.5μm.
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