Current Tolerances for LEP Magnet Power Converters

The excitation tolerances for the LEP power converters are important in the machine design. Three types of tolerances are discussed. The short term stability includes setting error, short-term current drift and current ripple. The long-term reproducibility corresponds to the overall error over a time scale of one week. Lastly, the field tracking error covers the current variation during energy ramping. The implications of excitation tolerances of the different types of LEP magnets on the machine performance are studied in order to establish the retained criteria, for instance on the tune and chromaticity variations. Possible means of control, such as field measurement systems, tune control loop and transverse feedback are considered to prevent the risk of defining too restrictive tolerances.