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Mmw11111m1111111111m11111~11~M1111wh CM-P00043015 CHS-26 '-0 November 1988 N I -VJ CERN LIBRARIES, GENEYA mmw11111m1111111111m11111~11~m1111wH CM-P00043015 STUDIES IN CERN HISTORY The Construction of CERN's First Hydrogen Bubble Chambers Laura Weiss GENEVA 1988 The Study of CERN History is a project financed by Institutions in several CERN Member Countries. This report presents preliminary findings, and is intended for incorporation into a more comprehensive study of CERN's history. It is distributed primarily to historians and scientists to provoke discussion, and no part of ii should be ci1ed or reproduced wi1hout written permission from the author. Comments are welcome and should be sent to: Study Team for CERN History c!o CERN CH-1211 GENEVE 23 Switzerland Copyright Study Team for CERN History, Geneva 1988 CHS-26 November 1988 STUDIES IN CERN HISTORY The Construction of CERN's First Hydrogen Bubble Chambers Laura Weiss GENEVA 1988 The Study of CERN History is a project financed by Institutions in several CERN Member Countries. This report presents preliminary findings, and is intended for incorporation into a more comprehensive study of CERN's history. It is distributed primarily to historians and scientists to provoke discussion, and no part of it should be cited or reproduced without written permission from the author. Comments are welcome and should be sent to: Study Team for CERN History c/oCERN CH-1211GENEVE23 Switzerland " Copyright Study Team for CERN History, Geneva 1988 CERN~ Service d'information scicntifique - 400 - novembre 1988 TABLE OF CONTENTS 8.1 Historical overview 2 8.2 The principle of the bubble chamber 8 8.2.1 The theory of bubble formation 9 8.2.2 The choice of a liquid 13 8.2.3 The technical components of a bubble chamber 15 8.3 CERN's bubble chambers 22 8.3.1 Preparatory steps 23 8.3.2 The hydrogen liquefier 25 8.3.3 The lOcm bubble chamber 27 8.3.4 The 30cm bubble chamber 30 8.3.5 The 2m bubble chamber 34 8.4 Technical elements and construction 42 8.4.1 The buildings 42 8.4.2 The chamber body 45 8.4.3 The vacuum system and the cold shields 48 8.4.4 The cooling system 51 8.4.5 The expansion system 59 8.4.6 The optical system 65 8.4.7 The magnet 69 8.4.8 Security 74 Notes Bibliography 1 The Construction of CERN's First Hydrogen Bubble Chambers Laura Weiss When Donald Glaser received the Nobel prize in 1960 for inventing the bubble chamber the device already had an established place in all high-energy physics laboratories. Not only had small experimental instruments been brought into service in most universities and American and European research centres, but very big chambers were also in use or under construction at Berkeley, Brookhaven, Chicago, Geneva, Dubna, Saclay, London, ... 1 In May 1952 Glaser was looking for a new detection system for cosmic rays, but it was the development and widespread use of particle accelerators in the second half of the 1950s, and notably the Cosmotron and the Bevatron, which made of the bubble chamber the "high-energy nuclear physics counterpart to the low-energy nuclear physics Wilson chamber". 2 The bubble chamber was, in fact, perfectly adapted in its functioning to big accelerators. In addition, like them, it was a powerful and complex device, which required, first for its construction and then for its ultilisation, teams of physicists and engineers who were specialized in different domains, from the physics of materials to optics, from cryogenics to the problems of safety. 3 This chapter begins with a brief historical section intended to situate CERN's achievement in the international context of the day. We then go on to explain in broad outline the theoretical ideas underlying the functioning of the bubble chamber and its different components. Our aim here is to bring out the demands the construction of such a device entails, be that in terms of a knowledge of different fields of physics or of how to develop and organize a number of elements of considerable technical complexity. This is the focus in the body of the chapter, which deals with the construction of the first instruments of this type at CERN, and in which we hope to capture, to the extent that our documents allow, the specificity of the work that was done without continually referring to practices which were widespread at the time. Similarly, to avoid undue repetition in the final section, 2 which describes more carefully the different technical components of CERN's chambers, we have concentrated on the most important of the first chambers built at CERN, and have only referred to the others when a special feature of their construction seemed worth mentioning. We cover then a period stretching from the mid-1950s to the start of the next decade, a period in which CERN brought three increasingly large hydrogen bubble chambers into service. 8.1 Historical overview The bubble chamber was invented in 1952. A census probably taken in 19564 listed chambers built or to be built at universities in Birmingham, Liverpool, London (Imperial College and University College), Oxford and Cambridge, in Great Britain, by Bassi and Mantelli in Italy, and at the Nevis Laboratory in Columbia, by Hildebrand in Chicago, and by Alvarez with his 4'' and 10" instruments and his project for a 72" at Berkeley in the USA. In May 1958, a report written at CERN to evaluate the construction of a big hydrogen chamber remarked that *It is known that bubble chamber projects exist in about 20 separate European centres [ ... ]*. 5 Of course the take off of a new technology is not only to be measured by its general level of acceptance, by the fact that everybody, everywhere, wants to have it (which was doubtless the case with bubble chambers in the early 1950s, when many, even small and dispersed, groups were interested in the instrument, though not to innovate but either to copy what had been done elsewhere or to build small prototypes), but also by the magnitude of the investments big laboratories were prepared to make in it. That granted our aim is not simply to identify all the projects under way in the early 50s but, by describing the achievements of several leading groups, to show the enormous development in this field in less than ten years. The history of the invention starts at the University of Michigan (and is associated with anecdotal details about bubbles in a beer 6 glass! ): in May 1952, Donald Glaser with his student David Rahm began to look at how liquids could be used to detect cosmic rays. By October they had shown that one could photograph the trail of 3 bubbles in a small glass bulb lcm in diameter and lcm long filled with ether. After investigating various systems (sonic, counters, photoelectric cells ... ) for triggering the camera at the moment the particle arrived (when the chambers were later used with accelerators the sequence was reversed, and the beam was to arrive when the chamber was ready), Glaser presented his findings on 2 May 1953 at a meeting of the American Physical Society in Washington. The baton then passed to Luis Alvarez of the Lawrence Radiation Laboratory in Berkeley and Darragh Nagle at the University of Chicago. 7 While Glaser and Rahm went on with their research at Brookhaven , concentrating on the analysis of photographs and so rather losing their leading position in the development of the device itself, the Berkeley group dedicated themselves forthwith to the new idea, and with such efficiency and enthusiasm that by the end of the 1950s one was already speaking of *Alvarez's gamble*. 8 This was no exaggeration: *To make a suitable particle detector, Alvarez had to transcend the intrinsic limitations of Glaser's technique, create several new technologies, walk confidently through unknown terrain, and raise a lot of money*. 9 On 5 May 1953 two of Alvarez's collaborators, F. Crawford and Lynn Stevenson, began to build their first chamber, initially filled with ether, then with liquid nitrogen, and finally with liquid 10 hydrogen , being attracted by the theoretical simplicity of this wonderful *sea of protons* even though it was a long way from 11 practical realization. John Wood , an engineer a point to be noted at a time when physics was only done by physicists, and symbolic perhaps of a change in attitudes and in methods of research soon showed that it was possible to photograph the tracks of bubbles in superheated liquid hydrogen. Wood also studied the possibility of using metallic chambers fitted with glass windows (called *dirty*), since this was the only the practicable way of building big chambers. With a chamber of 2.5" internal diameter Wood showed that the spontaneous ebullition which occurred where metal joined glass did not impede the observation of the tracks if the fall in pressure was very rapid. 4 *By late 1954, it was already clear that Berkeley, at least for 12 some time, was going to dominate bubble chamber technology* • D. Parmentier and A.J. Schwemin continued in June 1954 with a chamber 4" in diameter and 3" deep, of simpler design, built quickly and fitted with a magnet which enabled them to determine the sign and the momentum of particles. In 1955 Alvarez could write provocatively that *all that stood in the way of large, practical chambers, was a series of "engineering details"*. 14 Now he was ready to think big, and he set as his immediate goal a 30" long chamber, whose dimensions he increased to 50"x20"x20" after reflection.
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