Modification of the LEP electrostatic separator systems for operation with bunch trains

To meet the LEP2 luminosity requirements for W-pair production, it is planned to operate LEP with bunch trains from 1995 onwards. This new mode of operation entails significant modification both to the existing separator hardware and its control system. The changes have been implemented so as to provide maximum flexibility for the realisation of the bunch train scheme, and also make a return to operation with Pretzel separation possible during 1995. Two LEP Interaction Points (IP) were equipped with new separators in late 1994, enabling first tests with the collision of one train of four e⁺ bunches with one train of four e^- bunches. During the 1994/95 shutdown, four separators have been installed in the two remaining experimental IPs, and eight separators in the non-experimental IP have been displaced to new positions. Details are given of optics requirements for the separator installations, the polarity of the closed orbit separator bumps, system modifications, and performance considerations. Results are presented of investigations into the effects of separator polarity on high voltage performance and on the commissioning of the new hardware and software systems during tests of the bunch train scheme in 1994