The Revised Skew Quadrupole System for Coupling Compensation in the CERN Intersecting Storage Rings (ISR)

With the existing and proposed installations of solenoid detector magnets and low-ß schemes, the original coupling compensation scheme in the ISR was no longer sufficiently versatile to provide adequate compensation under all conditions. A brief description of the new scheme, which was installed early in 1978, is given. This scheme can excite coupling vectors at any phase so that it is able to compensate solenoids and large localized quadrupole errors in low-ß schemes as well as random magnet tilts. The design of the scheme is also strongly influenced by the fact that there are no regions with zero horizontal dispersion in the ISR and the skew quadrupoles have to be specially arranged so as to avoid exciting vertical dispersion. The experience gained with this scheme and the methods used for measurement and correction of the machine are illustrated by practical examples.