'FOCUS' on computing at CERN

The latest addition to CERN's central computer complex is a CDC 3100 for FOCUS, the "Facility for On-line Computations and Up-dating Services". lts main purpose is to manage data-links to the central computers from smaller computers used on-line in electronics experiments.

The on-line computers carry out preliminary checks and record the data on magnetic tape for full processing later on the central CDCs 6600 and 6400. Some have been connected to the central computers via separate data-links to access this processing directly. Unfortunately, this is an inefficient use of central computer memory and the demand for such links would soon overload the machines.

The solution is to use the 3100 as an intermediary, to receive all the on-line computer data-links and manage their access to the central computers via one link. Another advantage of the intermediate computer is that a typewriter console can be added to each on-line computer to allow the physicists to select and modify their programs in the central computers and receive their results printed out by the console.

Better than one part in a million

CERN has given considerable attention to the problems of metrology because of the immediate requirement for aligning the intersecting storage rings ISR and the future requirement for aligning the 300 GeV machine, ten times the diameter of the 28 GeV proton synchrotron PS.

An automatic measuring device, the Distinvar, has been developed for rapid and accurate measurements of distances up to 55 m. lt was tested in one of the PS tunnels for a thousand measurements over a distance of 50 m and gave a relative precision of better than one part in a million.

The Distinvar uses a calibrated invar wire attached to a special reading head which reads off the difference between the calibrated length and the actual distance between the measured points. ln the head, a "balance beam" oscillates between two electrical contacts fixed to a carriage that moves along a precision micrometer screw until the tension in the wire is balanced by a weight. The position of the carriage (and hence the distance to be measured) is then transferred via a potentiometer to be read at the recording station or passed to a computer.

The absolute precision is obtained by calibrating the invar wire before and after a measurement against a 4 m-long invar rule calibrated by the International Bureau of Weights and Measures (Sèvres). Each measurement takes three minutes, is entirely automatic and could be performed by remote control, for example in radioactive areas.

The Distinvar will be used in the alignment of the ISR magnets. Because of its speed and reliability it has not been necessary to allocate time for alignment in the construction programme.

Separators for Serpukhov

CERN is busy studying a radiofrequency particle-separator system [and a fast-ejection system] to be used on the 70 GeV proton synchrotron, which came into operation at the Serpukhov Institute for High Energy physics in October. The designs are at an advanced stage and only minor extensions of the techniques used on the CERN proton synchrotron PS have been necessary to meet the requirements of the higher-energy machine. The spirit of collaboration is excellent and the practical aspects of such an extensive collaboration between two high-energy physics Laboratories are working well.

The purpose of a particle separator is to sift out a particular type of particle at a particular momentum from the spray of particles with a wide momentum range coming from a target bombarded by the accelerated proton beam.

A two-cavity radio-frequency separator, brought into operation at CERN in 1965 by a group led by B W Montague, was already designed for possible extension to three cavities, an idea first put forward by W Schnell. With three cavities it is possible to overcome a limitation of the two-cavity system, namely that the separation of one type of particle from two other types is only possible for very narrow momentum regions.

The proposed design for Serpukhov is based on a new three-cavity system and covers a momentum region from 17 to 36 GeV/c. It completed a very successful test run in June when P Bernard, P Lazeyras, H Lengeler and V Vaghin [from Serpukhov] succeeded in separating antiprotons with a momentum of 12 GeV/c, about twice as high as previously achieved and about the highest momentum that can be reached with the CERN PS.

• Compiled from texts on pp250–252.

Compiler's Note

CERN's achievement in bringing together people from all corners of the world in a sustained common endeavour is unsurpassed. For more than half a century, the organization has remained almost immune to the vicissitudes of the Cold War, international conflicts and civil strife. Today, CERN's 10,000 users, drawn from 95 countries, represent almost half of the nations on the planet. That these young scientists and engineers regard this motley mix as seemingly normal bodes well for the future as the first decade of the new millennium draws to a close (or was that last December?).