Reviews of Accelerator Science and Technology: Volume 5 – Applications of Superconducting Technology to Accelerators
By Alexander W Chao and Weiren Chou (eds.)
Reviews of Accelerator Science and Technology is a journal series that began in 2008 with the stated aim “to provide readers with a comprehensive review of the driving and fascinating field of accelerator science and technology” – in a “journal of the highest quality”. It made an excellent start, with the first volume presenting the history of accelerators, followed by one that focused on medical applications (CERN Courier May 2010 p51). With one volume published a year, there are now five in the series, which appears to show no signs of failing in its original goals. Each has communicated a specific topic through the words of highly respected experts in articles that are well illustrated and presented. The books they form hold the promise of becoming an unrivalled encyclopaedia of accelerators.
This latest volume is no exception. It looks at the role of superconductivity in particle accelerators and how this intriguing phenomenon has been harnessed in the pursuit of ever-increasing beam energy or intensity. It also considers the application of superconducting technology beyond the realm of accelerators, for example in medical scanners and fusion devices. As well as containing much technical detail it is also full of fascinating facts.
Exactly 100 years ago, Heike Kamerlingh Onnes speculated that a 10 T superconducting magnet “ought not to be far away” (CERN Courier April 2011 p46). The first contributions to this volume, in particular, outline some of the steps to 10 T – and why it took longer than Onnes had originally hoped for the industrial-scale production of high-field superconducting magnets to become reality. A major problem lay in finding superconducting materials with physical properties that allow large-scale fabrication into wires. The first commercially produced wires were of niobium-zirconium, as used in early superconducting magnets for bubble chambers. However, this alloy was soon superceded by niobium-titanium (NbTi) – the material of choice in high-energy physics for the past 40 years, culminating today in the superconducting magnets for the LHC, as well as the huge toroidal and solenoidal magnets for the ATLAS and CMS detectors. Now, R&D effort is turning to Nb3Sn, which can allow higher magnetic fields, for example for the High Luminosity LHC project (CERN Courier July/August 2013 p41).
In this context, it is worth realizing that the biggest market for superconducting magnets is for nuclear magnetic-resonance spectroscopy – and it is here that a field as high as 23.5 T has been reached in a magnet based on Nb3Sn. There is also interest in high magnetic fields for magnetic resonance imaging (MRI) in medicine. In MRI the signal strength is related to the polarization of the protons in whatever is being scanned. Increasing the magnetic field from the 1.5 T that is currently used routinely to 10 T results in a polarization that is almost seven times higher, as well as improved signal-to-noise, leading to a clear improvement in image quality. Upcoming developments include 6 T magnets based on Nb3Sn.
The application of superconductivity in particle accelerators extends of course to the acceleration system, with the use of superconducting RF technology, first proposed in 1961 (CERN Courier November 2011 p33). In this case, an important part of the R&D has focused on the physics and materials science of the surface – the surface resistance being a key parameter. So far there are no commercial applications for superconducting RF, but it has a role in many types of particle accelerators, from high-current storage rings at light sources to the high-energy machines of the future, such as the International Linear Collider (ILC).
Jefferson Lab’s Continuous Electron-Beam Accelerator Facility (CEBAF) is in a sense the “LHC” of superconducting RF, employing originally 360 five-cell 1.5 GHz cavities. It is currently undergoing an upgrade to 12 GeV (CERN Courier November 2012 p30) with cavities that will operate at 19.2 MV/m. The European X-ray free-electron laser project, XFEL at DESY, will use 800 nine-cell 1.3 GHz cavities operating at more than 22 MV/m, but it would be dwarfed by an ILC with more than 15,000 cavities.
Besides the contributions on the major topics of superconducting magnets and RF, others are dedicated to cryogenic technology, industrialization and applications in medicine. In addition, following the journal’s tradition, there are articles that are not related to the overall theme but are of concern to the accelerator community worldwide. In this case, one article discusses the education and training of the next generation of accelerator physicists and engineers, while another reviews the history of the KEK laboratory in Japan. Altogether, this makes for more than a journal volume – in my opinion, it is a book, well worth reading.
• Christine Sutton, CERN.
Doing Physics: How Physicists Take Hold of the World (2nd edition)
By Martin H Krieger
Indiana University Press
Paperback: £16.99 $24.00
E-book: £14.99 $21.99
First published over two decades ago, Doing Physics has recently been released as a second edition. The book relates the concepts of physics to everyday experiences through a carefully selected series of analogies. It attempts to provide a non-scientific description of the methods employed by physicists to do their work, what motivates them and how they make sense of the world.
Martin Krieger began his academic career in experimental particle physics but quickly realised that he was not suited to working in large groups on experiments. Following his PhD, he moved into the social sciences and began working on computing models for city planning. He uses this experience to reflect on the way science is done from a social science viewpoint. His aim is to explain how doing physics is part of familiar general culture.
Krieger claims that physicists employ a small number of everyday notions to “get a handle on the world” experimentally and conceptually. He argues further that these models and metaphors describe the way physicists actually view the world and that to see the world in such terms is to be trained as a physicist. The analogies he chooses to support his ideas are drawn from the diverse areas of economics, computing, anthropology, theatre and engineering. Each of the first five chapters of the book is devoted to exploring each of the analogies in detail.
The book begins with a discussion on division of labour according to the economist Adam Smith’s model of a pin factory. The description of physical situations in terms of interdependent particles and fields is analogous to the design of a factory with its division of labour among specialists. The second chapter considers physical degrees of freedom as the parts of a complex model such as a clockwork mechanism or a computer. Chapter three is devoted to the anthropological theory of kinship and marriage, comparing the rules of relationships to the rules of interaction for the families of elementary particles or for chemical species – who can marry whom is like what can interact with what. The conclusion is that anything that is not forbidden will happen. The theatrical world provides an analogy to creation, where a vacuum is represented by a simple stage setting on which something arises out of nothing. Finally, machine-tool design is used to describe the physicist’s toolkit, where the work of doing physics is like grasping the world with handles and probes.
In the second edition, Krieger has provided some minor revisions to the text and has added a brief chapter on the role of mathematics and formal models in physics. This additional discussion is based on work from two other books he has written in the intervening years. It is questionable whether the second edition is warranted. In this highly technical chapter Krieger goes so far as to discern an analogy of analogies in physics and mathematics – a so-called syzygy.
Krieger claims that the book is for high-school students and upwards. However, it seems more appropriate for a specialized audience. Doing Physics is aimed at sociologists and philosophers of science, rather than at the science community itself. Indeed, for some the experience of reading the book could bring to mind a well known quote by Richard Feynman: “Philosophy of science is about as useful to scientists as ornithology is to birds.” For others, however, the book might provide some useful insights into patterns or relationships between physics and the everyday world that they have not previously considered.
• Theresa Harrison, Warwick University.