Peter J. Bryant

Operational Experience with the Superconducting High-Luminosity Insertion in the CERN Intersecting Storage Rings (ISR)

The eight superconducting quadrupoles and their cryogenic equipment for this insertion were installed in the ISR at the end of 1980. The insertion has been used to assess the problems of running a superconducting insertion in a storage ring as well as to provide high luminosity for physics. The luminosity is increased at intersection 8 by a factor of 7. By means of dedicated collimators and orbit corrections, safe working conditions could be established for the superconducting magnets during injection, accumulation, stable beam periods and when dumping the beams. Quenches were mainly caused by large accidental beam losses. Operating parameters for all standard beam energies, including acceleration to 31.4 GeV/c, have been established. At 26.6 GeV/c, with currents of 30.6 A in ring 1 and 30.3 A in ring 2, a luminosity of 1.4 1032 cm-2s-1 was obtained in the insertion. This is the highest luminosity reached so far in storage rings and it was obtained during a physics run. Satisfactory beam conditions could also be provided for antiproton physics at 26.6 GeV/c in ISR with both low-ß insertions on, in I1 and I8, respectively.

Antiprotons in the ISR

A brief account is given of the events leading up to antiprotons in the Intersecting Storage Rings (ISR) followed by a synopsis of the characteristics and parameters of the physics runs made to date. Experience gained with critical operations, such as transfer line steering, injection optimization, stacking and phase displacement acceleration is reviewed bearing in mind the extremely low beam intensities. Special reference is made to the various machine improvements, namely the vertical transverse stochastic cooling for proton beams of up to 12 A, the transverse and longitudinal stochastic cooling for the antiprotons, the new antiproton beam position monitoring system in the transfer lines and ring and the use of two high-luminosity insertions. At the end of June 1982, a scheme for reaching higher luminosities by making multiple transfers from the Antiproton Accumulator (AA) and using longitudinal stochastic cooling in the ISR was demonstrated. The absence of any measurable loss rate during long periods of stable beam conditions has been used to set a new lower limit of 1000 h on the antiproton lifetime at rest. Finally, preparations are in progress to collide 3.5 to 6.5 GeV/c antiprotons with a hydrogen gas jet target.

Measurement of the Excitation of the Coupling Resonance Qh - Qv = 0

To take advantage of the large resonance-free regions close to the diagonal Qh = Qv in the tune diagram, the Intersecting Storage Rings (ISR) operate with nearly equal tunes. Thus, the excitation of the coupling resonance Qh - Qv = 0 is of importance and this has stimulated the study of its effects, the measurement of its excitation by axial and skew quadrupole fields and its compensation. A complex coupling coefficient C can be defined in terms of axial and skew quadrupole fields, and the unperturbed machine parameters. An electronic device has been built to measure |C| by kicking a small beam and analysing the coherent oscillation. By combining different coupling vectors, phase measurements are also possible. Examples are given of coupling vectors measured in the ISR for magnet tilts, skew quadrupoles and solenoids. The outlines of two methods for directly measuring both amplitude and phase are also given. Some ideas are extended to higher order resonances.

A Project to Operate the CERN Intersecting Storage Rings (ISR) with Antiprotons

The storage of antiprotons in the ISR for proton - antiproton physics is planned for 1981, using the 3.5 GeV/c, cooled, antiproton source, which is currently being built at CERN. Two schemes have been studied for achieving this aim. Firstly, the antiprotons could be injected at 3.5 GeV/c from the cooling ring and accelerated in the ISR or secondly, they could be injected into the ISR at 26 GeV/c after acceleration in the CERN Proton Synchrotron (PS). Although the latter scheme is more expensive, since it requires a new transfer line, it has been adopted as it is operationally more reliable and as it makes it possible to stack the antiprotons. With five full-intensity pulses, the circulating antiproton current would be 0.15 A, which, with a 30 A proton beam, would yield a luminosity of 1.3 × 1029 cm-2s-1 in a standard intersection and 9.2 × 1029 cm-2s-1 with the planned superconducting low-ß scheme.

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.