The 400 GeV proton synchrotron c£«A//s/3-PU Hie European Organization for Nuclearbelow Research, ground and the accelerator construction has CERN, has built a 400 GeV proton synchrotron,thus caused known minimum disturbance to the environment. as the Super Proton Synchrotron or TheSPS. diameterIt provides of the ring is 2.2 km, the maximum the physicists of Europe with world-classwhich could facilities be accommodated on the available site. for research in particle physics. Although the construction programme initially Construction has been financed by elevenenvisaged CERN a peak energy of 300 GeV, it proved pos­ Member States — Austria, Belgium,. Denmark,sible, Federal by using accelerator magnets with a high peak Republic of Germany, France, Italy, Netherlands,field, to increase the energy to 400 GeV. The de­ Norway, Sweden, Switzerland, and the Unitedsign Kingdom. intensity is 1013 protons per pulse at a pulse Tlie total estimated cost, spread over repetitionan eight-year rate of aboutevery one 6 s. pulse construction programme which began inThe 1971,parameters is of energy and intensity are tiie key 1150 million Swiss francs (at 1970 costs).features Protons of an accelerator from the point of view were first accelerated to full energyof in thethe experimentalSPS in programme which it can sustain. 1976 but provision of the full range of machine facilities, particularly, in the experimentalProtons areas, from the CERN 28 GeV proton synchrotron, is scheduled for completion at the beginningPS, are injected of into the SPS at an energy of 10 GeV. 1979, After acceleration they can be ejected towards two experimental areas (West and North). Tire West ex­ TL'? accelerator is built undergroundperimental on an ex­ area is scheduled to receive particles tension of the previously existingearly CERN site in located1977, and the North experimental area on the Franco-Swiss border near Geneva. aboutThe site 18 months later. The areas are being equipped area now comprises 109 hectares in Switzerlandwith a range and of hadron, electron, muon, and neutrino 451.5 hectares in France. Tire ring tunnelbeams, in which many of them of the highest energy, intensity, the machine is built is an average of aboutand quality40 m ever achieved. History of the SPS project Tire coming into operation about 20out years by agohigh ofenergy physicists and accelerator ex­ accelerators which could achieve particleperts energies from throughout Europe. This resulted in 1967 in the GeV range, opened up a new era in ourin a secondunder­ ECFA report which strongly recommended standing of the nature of matter. Asthe so building often of a 300 GeV proton synchrotron on the happens, this increased knowledge provokedlines aof series the CERN design study of 1964. of further questions, and it was obvious that many of them might be answered by access to stillBy thehigher end of 1968, letters of intent to sup­ energies. In the early 1960s, followingport the re­the project had been received from six Member markably successful operation of theStates, CERN 28 GeVand a Project Director was appointed by the Proton Synchrotron and its twin, theCERN 33 GeVCouncil. The Project Director, together with Alternating Gradient Synchrotron at Brookhavenexperts from USA, CERN and Laboratories in the Member it became clear that the techniques used inStates, tire set about revising the 1964 design to in­ construction of these machines could corporatebe extended toimprovements in accelerator technology much higher energies. which had subsequently arisen. Meanwhile, the CERN Convention was ammended to take account of the ex­ In 1963 a committee (the European Committeeistence forof two separate Laboratories (the revised Future Accelerators, ECFA) was set up toConvention study the actually coming into force in 1971). whole field of high-energy physics in EuropeHowever, and authorization to of the project by all the nake recommendations concerning futureMember experimental States was not forthcoming because of dif­ facilities. It presented a report to theficulties CERN in the selection of the site for the new Council in the same year, in which the majorLaboratory recom­ and because of the high costs involved mendation was the construction of "a inneu' the proton project as it stood at that time. accelerator of a very high energy". In this situation, the Project Director pre­ In 1964 a detailed design of a 300 GeV protonsented in 1970 an alternative project for construc­ synchrotron was produced by CERN. It wastion envisaged of the accelerator. Tire crucial change was that the accelerator would be constructedthe proposalin a new to build the new machine alongside the CERN Laboratory elsewhere in Europe, andexisting the Council CERN Laboratory. This circumvented the invited the CERN Member States to proposeproblems possible of site selection and, at the same time, sites. Twenty-two site offers were received,greatly and reduced the cost. The savings came from about half of them were the object of a usingcareful the PS as injector, from using the existing examination by CERN to see if they met theWest criteria experimental area which already had large- laid down in the design study. scale particle detectors installed and, particularly, from using the existing "infrastructure" of the CERN From the end of 1965 a further studyLaboratory was carried (administrative and technical services, 0 J vic-j j;' ike CSRli give, 'jiih the 3PS ajoeler- ator picked out in white, against the background of Geneva and the Alps. The Franco-Swiss frontier which crosses the site is also indicated. (Photo Swiss Air) etc.). The now project also included several op­ The participation of the full community of tions concerning future development of the accelera­ European high energy physicists in designing the ex­ tor. For example, by beginning with a "missing perimental facilities for the accelerator was en­ magnet" lattice of conventional magi.ets, higher sured from the outset. ECFA organized two major energies could have been achieved later by the in­ study sessions in 1971 and 1972, which established troduction of superconducting magnets in the gaps the basis of the experimental hall layout, the left in the lattice. available particle beams, and features of the major detection systems. In 1972 an SPS Experiments The new proposal was worked out in detail in Committee was set up to decide on the in it ia l ex­ the course of 1970 and presented as a two-volume re­perimental programme. This early start on preparing port "A Design of the European 300 GeV Research the experimental programme was necessary to ensure Facilities". It received support from the scienti­ that the large and complex detection systems needed fic community and in political circles throughout for physics at high energies would be built in time Furope. for the start of operation of the machine. On 19 February' 1971, ten of the CERN Member As the design and construction of machine com­ States approved the "Programme for the Construction ponents progressed at CERN, it was realized that the and Bringing into Operation of the 300 GeV Labora­ technology of superconducting magnets had not ad­ tory". (Denmark joined at the beginning o f 1 9 72 .) vanced far enough for them to be incorporated in The project cost was set at 11S0 million Swiss the SPS. On the other hand, it iras found possible francs (at 1970 costs) over a construction period to build the full ring with convention?1, magnets of eight years. A new Laboratory, known as CERN which, given the ring diameter of 2.2 km and a mag­ Laboratory II, with its own Director General was net design allowing peak fields of 1.8 tesla, would set up to build the accelerator. (The two CERN give the accelerator a peak energy capability of Laboratories were unified at the beginning of 1976.)400 GeV. The construction schedule was fixed so as The s it e , which straddles the frontier, was made to provide beams into the West experimental area in available by France and Switzerland. The supply of the sixth year of the construction programme and electrical power was ensured by France and the into the second (North) experimental area in the supply of cooling water by Switzerland. The formal eighth year. design description of the accelerator, entitled "The 300 GeV Programme", was published in January The SPS first accelerated protons to the design i9~ :. energy of 400 GeV in lt'76. 3 Générai features of the SPS design Several of the major features of theas SPS"continuous de­ transfer" and consists of debunching sign c*re set by the decision to locate thethe machinePS beam and peeling it off during ten turns by alongside the existing CERN Laboratory.a systemThe land inof kicker magnets, an electrostatic deflec­ this area is not flat, the surface heighttor, varying and a septum magnet so that a ribbon of even from place to place by several tens ofintensity metres, andis ejected towards the SPS. The ejection/ the bed rock underneath is a ridge of molasseinjection (a is done at a momentum which can be varied mixture of sandstone and marl) whosebetween depth varies 10 and 14 GeV/c. This is high enough to over the site from a metre to 30 metresavoid below problems ground of quality of the injection field in level. Since the SPS had to be built in thethe bedrock SPS magnets and to limit the necessary frequency for stability reasons, it was not possibleswing in to the use SPS radio-frequency accelerating sys­ the cut and fill method for making thetem. tunnel It also to reduces the time for which the PS is house the machine. It was decided to bore occupiedthe tun­ filling the SPS. This keeps the time for nel using a full-face boring machine suitablewhich the forPS is occupied with injection into the SPS sand type rocks.