Dynamic beam based calibration of orbit monitors at LEP

Modulation of the quadrupole strength of Δk/k < 10-3 was performed parasitically during physics operation of LEP without affecting the luminosity. Wide band BPM offsets for the superconducting quadrupoles were found to be as large as 2 mm and systematically larger than for normal conducting magnets. The wide band type BPM show different offsets for electrons and positrons and for different gain settings. On the other hand, offsets for the wide band BPM system are systematically larger than for the narrow band type. The differences for the two particle types are also smaller for the narrow band type. The offsets measured so far are taken into account by the LEP orbit acquisition. Simulation shows that an increase in the polarization level is expected if all BPM offsets in the arcs are determined. (J.P.N.)