Gargamelle CERN's new heavy liquid bubble chamber

ratory and the selection of experiments In the April issue of CERN COURIER we ment was already in use, to 'see' about for the research programmes take account reproduced a photograph of the arrival one neutrino an hour from the millions of what is happening elsewhere and a of the first piece of the new heavy liquid that the accelerator produced. This will fairly logical list of complementary bubble chamber 'Gargamelle'. The 140 ton have increased by the early 1970s to machines and programmes have been base-plate for the magnet was towed onto something like 10 000 per day and the established. But, as costs and manpower the site by two tractors in a 48-wheel study of neutrinos will be on the same requirements rise, and as machines and convoy on 31 March. It seems an appro­ footing as that of most other particles. At their related instrumentation become more priate time to say something about this CERN, Gargamelle will be one of the and more sophisticated, the time seems significant addition to CERN's research important contributors to this advance. ripe for fuller integration. equipment. For neutrino experiments, a heavy liquid

The practical difficulties are consider­ bubble chamber has two advantages over able. The research programmes of national Its use a hydrogen bubble chamber: machines are at present almost entirely i) It presents a more dense target so that Gargamelle has been conceived principally filled from the local Universities — would there are more particles with which as an instrument for research on neutrinos. the national Universities suffer from inter­ the neutrino can interact; The fascination of these elusive particles nationalization of the Laboratories? How has been brought out in several previous ii) The distance a neutral particle travels would the financing of a Laboratory be articles in CERN COURIER (see particu­ in the liquid before producing charged organized, if one country were encouraged larly the article by C.A. Ramm, vol. 6, p. particles (which leave tracks giving to build a particular machine there, while 211). They are the most abundant particles information about the parent neutral other countries made extensive use of it? in the universe and their study will tell us particle) is shorter. Many important How would Laboratories cope with large much about the weak interaction, the neutrino interactions — such as the teams of foreign scientists in terms of only one in which they take part. Their elastic scattering of an antineutrino language, education of children, accommo­ interactions are so rare that ten years and a proton producing a neutron — dation etc., without being geared to meet ago, our present ability to observe neu­ yield neutral particles, and the ability these problems almost to the extent of trinos was unimaginable. By 1963, it had of the heavy liquid chamber to give CERN itself? What body would recommend become possible at high-energy acceler­ information on them is therefore a particular machine for a particular coun­ ators, where large, refined detection equip­ invaluable. try? Would that body ever be able to tell a country that it ought to shut a machine down? Who would control the research programmes in such Laboratories?....

But to confront these problems may prove to be very important. Faced with limited resources, some overall plan should ideally operate. Let us hope that when the sun of the 300 GeV machine finally rises it will be surrounded by an orderly array of satellites.

An aerial view of part of the CERN site. The wheel shape of the proton synchrotron itself is fairly obvious and, pointing from it towards the bottom of the picture, is the tunnel housing the neutrino beam-line. The large new building (bottom centre of the picture) is the one which will house Gargamelle. In the background top left can be seen some of the excavation work for the Booster (the new higher-energy synchrotron injector) and for the Intersecting Storage Rings. A heavy liquid chamber is less favour­ A 1/8 scale model of Gargamelle has been Description of the chamber constructed of transparent coloured plexiglas so able than the hydrogen chamber in the that the way In which the different components complexity of the target it presents to the fit together can be seen. On the right are the The main features of the chamber are as incoming beam and in the accuracy with units of the pressure system culminating in the follows: the body (which is almost ready diaphragms in the chamber (they look like two which the particle tracks can be for delivery) is a welded cylinder with pistons pointing in directions almost along the measured. Also, it is worth adding here dished ends, 1.85 m in diameter and 4.5 m diagonals of the photograph). that modified hydrogen chambers are now The optical system views the chamber through long, with the axis of the cylinder in the coming into vogue containing hydrogen/ fish-eyes lenses set in the diaphragms. The direction of the beam. It is constructed of chamber, magnet and coils can be picked out neon mixtures or a hydrogen target sur­ low carbon steel, 60 mm thick increasing and on the left is the illumination system. rounded by a hydrogen/neon mixture, to 150 mm in the region of the ports. Its which compromise between the advan­ total volume is 12 m3 of which 10 m3 is tages and disadvantages of pure hydrogen 'useful volume', i.e. can be seen by two and heavy liquid. cameras. Two diaphragms, made of poly- urethane elastromer 4 m by 1 m, running The main detector in the neutrino experi­ in the direction of the axis on one side of ments previously carried out at CERN has the chamber are used to vary the pressure been the CERN heavy liquid bubble on the liquid. The liquid can be pure pro­ chamber, which has a volume of 1180 pane (when the chamber would contain 5 litres. Gargamelle is much bigger with tons of liquid) to freon (15 tons) or any 10 000 litres of useful volume. In a uniform intermediate mixture. Four fish-eye lenses, ciation of headaches with Gargamelle is neutrino beam the event rate would be with an angle of view of 110° are set in appropriate even in modern times. The proportional to the volume for the same apertures in each diaphragm; each set of construction of the new chamber has liquid. In fact, Gargamelle will contribute four have their images recorded on a created many problems for its makers. about a factor of seven to the rate at single film. There are 21 xenon flash Bringing forth the data from Gargamelle which neutrino interactions can be tubes distributed over the chamber behind will also cause some headaches. The observed. diaphragms to give 'dark field' illumination direct interpretation of the events recorded (see CERN COURIER vol. 7, p. 144). on the two films will be much more The new chamber is being designed The chamber is surrounded by a complicated than with smaller bubble and built at the Saclay Laboratory in magnet designed to produce a field of chambers. New scanning and measuring France, with help from Ecole Polytech­ 19 kG. The magnet yoke, weighing 800 techniques will be essential and already, nique, Orsay and industry and is being tons, serves as support for the chamber, under the auspices of the Gargamelle given to CERN who are providing its the expansion system and the coils. The Users' Committee, much development is buildings and supplies. As mentioned two sets of coils weigh 80 tons each and in progress. above, the first piece arrived recently and are mounted vertically; the field direction the other components will arrive during is horizontal. Gargamelle, in combination with the the course of the next year. The magnet is increases in repetition rate and intensity coming directly to be assembled at CERN. The name Gargamelle is taken from the per pulse of the proton synchrotron and The other components will be first satirical novel 'Gargantua' by Rabelais the refinements incorporated in the new assembled and tested at Saclay. It is (1534) in which Gargamelle was the mother neutrino beam-line, should make the hoped to have the chamber in operation of the giant Gargantua. She gave birth to coming years of neutrino research at at the end of 1969. Gargantua through her ear. The asso- CERN very fruitful ones.

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