Wolfgang Paul: inspired scientist, Nobel laureate, father figure

Wolfgang Paul was born 100 years ago on 10 August 1913 at Lorenzkirch, a village in Saxony, Germany, as the fourth child of Theodor and Elisabeth Paul. Descended from generations of Lutheran ministers, they preferred a humanistic education for their family, so as a child Paul learnt Latin and Greek and could quote the Bible by heart. However, his father was professor in pharmaceutical chemistry at the university in Munich, where Paul grew up. Although Theodor Paul died when his son was only 15, he had implanted in him a strong interest in sciences – a path that the young Paul decided to follow.

Before Paul began his study of physics in Munich, in 1932 the theoretician Arnold Sommerfeld advised him to start an apprenticeship in practical mechanics. So in 1934 he moved to the Technical Highschool in Berlin. There he joined the group of Hans Kopfermann, who became not only his teacher but also a fatherly friend. In the following years, Paul followed Kopfermann first to Kiel and later to Göttingen, where he worked and taught until 1952. During the 16 years that Paul stayed with Kopfermann, his work concerned mainly the optical measurement of hyperfine-splitting in atomic spectra to determine nuclear magnetic moments. In his PhD thesis – interrupted for a short time by a call to the Luftwaffe at the beginning of the Second World War – Paul improved this method using atomic beams.

By the end of 1952 Paul had accepted a chair at the University of Bonn, where he became director of the Institute of Physics. The institute had suffered war damage and financial means were still scarce. As Paul put it, to perform competitive research in such a situation "one has to have new ideas". Continuing earlier work, he developed a mass spectrometer using a quadrupole lens with an oscillating field instead of a magnetic field – an interesting example of cross-fertilization between different fields because at the time Paul also became interested in the new idea of strong focusing in particle accelerators. Knowledge of orbit stability in accelerators led him to the "Paul mass filter", which found many applications.

The mass filter provides stability in two transverse dimensions, but by adding a ring-shaped electrode with an oscillating field, particles are also caught in the longitudinal direction. This is the ingenious idea behind the "Paul trap" or "Ionenkäfig" as he called it. The device realized a long-cherished dream – the free suspension of individual atoms or molecules for lengthy periods of time, enabling extremely precise measurements of fundamental constants (e.g. the magnetic moment of an electron), as well as the construction of ultraprecise clocks and other instruments. For this work, Paul shared the Nobel prize with Norman Ramsey and Hans Dehmelt in 1989, followed by many other distinctions.

The second activity that Paul started in Bonn concerned the construction of particle accelerators. A crew of bright young students and assistants – some having followed Paul from Göttingen – but with no experience in accelerator technology, jumped into the adventure of building Europe’s first electron synchrotron with strong focusing and an energy of 500 MeV. Even to their own surprise, it worked well. A 2.5 GeV electron synchrotron followed 10 years later and, before retiring, Paul helped to gain approval for a beam-stretcher storage ring – ELSA.

These machines transformed the institute in Bonn to one of the most important laboratories in Europe. More than 100 students were trained there and transferred their knowledge to many universities, countries and industries. The experience gained in Bonn was also essential in the founding of DESY where Paul played a major role.

Active in research even after retiring, Paul had the idea to extend his trap, which was for charged particles, to neutrons. In this case, sextupole rather than quadrupole fields were needed to act on the magnetic moment of the neutron. He built such a trap, NESTOR, which was installed in a neutron beam at the Institut Laue–Langevin, Grenoble. Being short of manpower, Paul recruited his two sons and they measured the half-life of the neutron with high precision and determined its gravitational mass by seeing the neutrons fall inside the trap.

In addition to his scientific insight, Paul was aware of the responsibility that scientists owe to society. He co-signed the famous Göttingen declaration advising against the nuclear armament of Germany. He also refused a limitation on scientific research, since "scientific knowledge, which means understanding, is no risk. Non-understanding is the risk when acting."

Paul played important roles as an organizer. Having spent a year as a guest at CERN in 1959, he became director of the Nuclear Physics Division (1964–67) and later served as chair of the Scientific Policy Committee and as a member of the German delegation. He also was director of DESY from 1971 to spring 1973 (where I had the pleasure to succeed him). However, he did not feel "at home" in large organizations, which are necessarily more formal than a university institute, where he could be a paternal boss, following his intuition and taking care of his flock. He was not a polished orator, but his talking was full of content and people listened carefully. In meetings, his pertinent questions, starting with "one should be allowed to ask…", were feared.

Wolfgang Paul died in Bonn, almost 10 years ago on 7 December. Not only was he an eminent scientist, everyone who had the chance to work with him benefited from his human qualities.

Herwig Schopper, former CERN director-general and one of the speakers at the Wolfgang Paul Symposium to be held at the University of Bonn on 11–13 November.


Advanced accelerator physics in Norway

The CERN Accelerator School (CAS) and the Norwegian University of Science and Technology (NTNU) organized a course on advanced accelerator physics this year, which took place in Trondheim on 18–29 August.

The course followed an established format with lectures in the morning and practical courses in the afternoon. The lecture programme consisted of 32 lectures, supplemented by discussion sessions, private study and tutorials. The practical courses provided "hands-on" experience in three topics: RF measurement techniques, beam instrumentation and diagnostics, and optics design and corrections. Participants selected one of the three courses and followed the chosen topic throughout the school. Seminars and a poster session completed the programme.

The course was attended by 70 students selected from more than 90 applicants. Representing 21 nationalities, most of the participants came from European countries with a few from beyond. Their positive feedback reflected the high standard of the lectures and teaching.

CERN, NTNU, the Research Council of Norway and Radiabeam Technologies sponsored the school. NTNU also provided excellent facilities and invaluable support for the highly technical courses, which are a key feature of the advanced school.

The next CAS courses will be a specialized school on power converters in Switzerland in May 2014 and an introductory course on accelerator physics in the Czech Republic in September 2014.

• For more about CAS, visit www.cern.ch/schools/CAS.


Elsevier comes on board SCOAP3 open-access initiative

As of January 2014, Elsevier’s premier high-energy physics journals Physics Letters B and Nuclear Physics B will be published under the model of the Sponsoring Consortium for Open Access Publishing in Particle Physics (SCOAP3), which was launched at CERN a year ago (CERN Courier November 2012 p6). In a letter of intent that was signed on 8 July, Elsevier and CERN formalized their commitment to move these journals from a subscription model to an open-access model, in which the content is available to anyone who would like to access it free of charge and the open-access article publishing charges are paid by libraries rather than authors.

SCOAP3 was initiated by CERN in 2007, following the report of a task force on open-access publishing in particle physics. In addition, all of the LHC experiments strongly encouraged publishing results in open-access journals. The objective of SCOAP3 is to grant unrestricted access to articles appearing in scientific journals in the field of particle physics. While open dissemination of preprints has been the norm in particle physics for two decades, the SCOAP3 initiative brings the peer-review service that is provided by journals into the open-access domain.

How does the redirecting of funds work? Under the subscription model, libraries purchase journal subscriptions to cover publishing costs and allow their researchers to access articles. In contrast, under SCOAP3, libraries contribute to the consortium, which pays centrally for the publishing charges of the open-access article – freeing the libraries from paying subscriptions.


Virdee receives honorary degree

Tejinder (Jim) Virdee went back to his alma mater, Queen Mary University of London (QMUL), on 18 July to receive an honorary degree at the summer graduation ceremonies. Here he is seen signing the Honorary Graduates Book with the university’s principal, Simon Gaskell. Virdee, who is professor of physics at Imperial College, London, played a critical role in the design, research and development, prototyping, construction, installation, commissioning, data taking and physics exploitation of CMS – all leading to the discovery of a Higgs boson in July last year. He has been with the CMS experiment at CERN from the start and was deputy spokesperson (1993–2006) and then spokesperson (2007–2009).