High Accuracy Field Mappings with a Laser Monitored Travelling Mole

The LEP Spectrometer is an alternative method adopted to predict the LEP beam Energy. A bending magnet is flanked on either side by tgree beam position monitors /BPM) used to determine thedeflection angle of the beam. In order to reach the desired accuracy on the beam energy a relative precision of a few 10-5 on the magnetic field intefral is necessary. The magnet is a full-iron core dipole, 5.75 m long, of the MBI type used in the LEP injection region. It has been specially designed in order to have high field uniformity.