RF System Calibration Using Beam Orbits at LEP

The target for beam energy calibration at LEP 200 is to achive a relative accuracy of approximatively 10-4 for energies above the W pair production threshold. A variety of calibration methods have been used for that purpose, one of them being based on a spectrometer magnet. The spectrometer is using six dedicated high resolution BPMs to measure the beam energy through the deflection angle around a dedicated and calibrated dipole magnet. To obtain the average beam energy, local deviations at the spectrometer due to the energy sawtoothing must be taken into account. The local energy shift depends on the energy loss in each arc as well as on the details of the RF voltage distribution. Local phase errors and longitudinal misalignements affect the local energy and must be taken into account. This note describes a method to determine some overall RF parameters for each interaction point of LEP to improve the accuracy of the local energy prediction. It is based on a MAD model of the RF system which is calibrated by dedicated experiments.