The 600 MeV synchro-cyclotron (SC) was shut down for several weeks at the beginning of this year, partly for routine maintenance but mainly to enable work to be carried out on a number of alterations to the machine. Altogether, 217 men took part in the work, the largest numbers being drawn from the central workshop and the cleaning staff, apart from the various SC groups.
The major task was to make preparations for the installation at a later stage of a polarized-proton source. A fundamental property of every proton is its "spin", a concept of quantum mechanics analogous to the spinning of a top about its central axis. In a normal proton beam the axes of spin are oriented in all directions, but in many cases experimental results (of proton–proton scattering, for example) could be interpreted much more clearly if all the protons were spinning in the same direction. The polarized-proton source, under development in the MSC Division, aims at producing such a "polarized" beam.
Various studies at CERN and elsewhere have shown that the intensity and quality of the accelerated beam is highly dependent on the precise conditions at the centre, where the protons have low energy and need to be guided carefully onto the right orbit. Protons produced in the centre spiral outwards, in a horizontal plane, under the joint influence of a magnetic field and an accelerating electric field. Although the magnetic field of the SC was thoroughly surveyed in 1955–56 during construction, many changes have been made since then, the effects of which have had to be estimated. Moreover, much more accurate magnetic-field measurements are now possible, and so the long shut-down was seized upon as a good opportunity for a new survey of the central area.
With every new improvement in the SC the amount of associated radiofrequency equipment has increased and the space available has become ever more crowded. During this shut-down, the complex switching system for starting up the equipment was rearranged, and some of it replaced by new units, so as to occupy much less space. Extensive changes included modifications to the main control desk, with a revised arrangement of control buttons and interlock indications, linked with a new alarm system.
The whole of the work in or near the accelerator was complicated by the radioactivity that is always present after the machine is switched off. Because no-one is allowed to receive more than a certain dose of radiation over a given period of time, many of the jobs had to be shared among a number of people and everything had to be planned very carefully in advance, with close supervision during the actual shut-down. Close cooperation between the MSC groups, Health Physics and the Workshops enabled the programme of work to be drawn up, and when the time came everything went ahead smoothly.
• Compiled from the article on pp44–47.
Compiler's note
The design of the SC started in 1953, before CERN came into existence. Building and construction began in 1954, aiming at 600 MeV proton beams with an average intensity of 1 μA. This was achieved in August 1957, and in April 1958 an experimental programme began that was to last for more than 30 years. One of the first achievements was the long-awaited observation of pion decay into an electron and a neutrino.
Emphasis swung to nuclear physics in the mid-1960s with the construction of the Isotope Separator On-Line Detector (ISOLDE). The vast range of short-lived nuclei that became available attracted hundreds of nuclear physicists. The SC was adapted to provide beams for ISOLDE, delivering the first beam in October 1967.
The decision to shut down the SC for good came in 1990 when much of its research programme could continue at the booster of CERN's Proton Synchrotron.