From the December 1973 issue

Keeping control

It is hard to imagine that only four years ago the use of computers in machine control was still a subject for debate. Now the only debate is how best to use them. The SPS team was able to learn from the work of other laboratories, particularly on the 400 GeV synchrotron at NAL and LAMPF at Los Alamos.

One novelty is that instead of a large, central computer overseeing smaller computers, control tasks will be divided between small or medium sized computers, effectively interchangeable. The number crunching ability of a big computer is lost but this is rarely called upon in machine control, and for the few occasions when it is needed a bicycle ride with a magnetic tape to a link to the CERN central computers will not be too arduous.

Novelty number two is in the mysterious realm of software. A major problem in the past has been the interdependence of programs that have to be “compiled” before they can be run. A system has been adopted in which the programs are kept as statements of a specially developed language called NODAL. These statements are interpreted when the program is run and the “interpreter”, resident in each computer, has access to all the information necessary to make the required cross-references and links. Speed of execution is lost, however for almost all control applications a millisecond is not forever and the speed is entirely adequate.

The computers are linked through a Message Transfer System whereby one computer can ask another to perform some measurement, control function or calculation by using a few simple typed statements.

The “operator interface” will also have its novelties. In addition to conventional control aids, such as black and white television screens and computer input keyboards, there will be colour displays, a programmable knob with feedback from the computer and a new type of touch button screen. The whole gamut of lights, switches, etc, which clutter the control rooms of yesteryear, have to be represented on a single console via the touch panel. Each button has a label written on it by the computer. Pressing a button changes the electrical capacity at that point behind the panel and selects a particular function.

• Compiled from texts on pp363–364.

Superconducting magnet operates at AGS

At the beginning of November a large superconducting bending magnet was brought into operation at the Alternating Gradient Synchrotron. It is designed to operate at twice the magnetic field of conventional magnets and has been successfully tested at 4.4 T. The performance seems to have answered several outstanding questions concerning superconducting magnets, an important achievement.

Two magnet sections have been built of standard materials using construction techniques which present no outstanding difficulties. Their magnetic characteristics are identical to 0.01%, in agreement with the design computations, and the mechanical precision compares favourably with the best conventional magnets. This indicates that it should be possible to manufacture such magnets reliably in industry with the expectation that they will be magnetically and mechanically interchangeable.

A second question concerns the ability of superconducting magnets to withstand heavy doses of radiation. The AGS magnet absorbed large beam losses without a problem. This is very significant since future superconducting accelerators depend on a reasonable ability to operate under conditions of heating due to sudden beam loss. This is the first experimental evidence on this fundamental question.

• Compiled from texts on pp374–375.

Compiler’s Note

Bent Stumpe, a Danish engineer working at CERN, invented the revolutionary SPS touchscreen. In keeping with CERN’s ethos, the technology was immediately transferred to industry but take-up was delayed because the considerable computer power it needed was expensive at the time. Today the technology, further developed and commercialised on a large scale, is found everywhere. Bent also invented a trackerball for the SPS consoles, an x–y pointing device that worked on the same principle as the computer mice developed later by industry in the 1980s. The SPS Message Transfer System was an early instance of client/server inter-processor communication, a type of Remote Procedure Call (RPC). All modern distributed computing systems use this request/response mechanism. Tim Berners-Lee, who worked on RPC at CERN in the1980s, employed this paradigm for the HyperText Transfer Protocol of his invention, the World Wide Web. Today, numberless web clients communicate with billions of web servers across the globe.

About the author

Compiled by Peggie Rimmer.