Life and Work of Rolf Wideröe by © Pedro Waloschek, => Contents
12 ETH Zurich, CERN and DESY
My inaugural lecture as an outside lecturer at the Swiss Federal Institute of Technology, Zurich (ETH) took place on December 12, 1953. It's subject was the history of particle accelerators. I prepared the lecture very carefully and I still have the original manuscript.
My lectures were always about `particle accelerators'. Attendance was not compulsory and I had relatively few students. However, some were very studious and sharp. The most important aspect of these lectures for me was in the preparation. At last, I had peace to work through the theories of particle accelerators, and I collected a nice set of formulas which contained everything one would ever need to calculate particle orbits for the various types of accelerators.
I became `Titular Professor' in 1963. I have good memories of my personal contacts at the ETH and I enjoyed my time there. I taught there until 1972.
But let's go back in time a bit, back to the year 1952 or perhaps even a little earlier. As far as I remember, the first definite proposals for a joint European laboratory for nuclear physics came from the French physicist Pierre Auger. From 1948 to 1959 he was the Director of the `Department of Exact and Natural Sciences' at UNESCO which was then concerned with re-establishing research in Europe following the devastation of the War years. Some of the basic ideas may also have come from the famous physicist Isidor Rabi. During the second half of 1951 a `council' (French, `conseil') was set up for this purpose and many influential people from different European countries became involved. The name CERN is an abbreviation of the full title of the council, `Conseil Européen pour la Recherche Nucléaire'. There is now available an in-depth report on these developments by A. Hermann, J. Krige, U. Mersits and D. Pestre, the `History of CERN' in two volumes [He87]. A very interesting `Who's Who' section is included, which, however, contains a few mistakes regarding my life story (Vol. 1, p 565).
The idea of a research centre involving many European countries was discussed during a conference in Copenhagen in June 1952. This is where some projects were planned in greater detail. And I was there - simply because I was interested in this sort of thing. It had little to do with my work for BBC.
In Copenhagen we talked about constructing a synchrotron for 10 GeV protons. I remember some of the participants arguing that I was trying to push things too fast. I on the other hand felt that we should concentrate more on technical questions rather than get bogged down with administrative problems. However, I guess it was necessary to establish precise organisational principles before going any further.
The head of the planning group responsible for this type of accelerator (from which the proton-synchrotron `PS' at CERN emerged) was Odd Dahl, who was working in Bergen and had a very good reputation as a builder of accelerators. He dedicated about a third of his time to the CERN projects. His deputy was Frank Goward. As I already mentioned, he and Barnes, were the first to successfully test the synchrotron principle. H. Alfven, W. Gentner and F. Regenstreif were also in the group, and they were later joined by D. W. Fry, K. Johnsen and Chr. Schmelzer. I was called in as a part-time advisor.
There was a second group, developing a 600 MeV proton-synchrocyclotron, CERN's future `SC'. It was headed by the Dutch physicist Cornelius Bakker, but I didn't really have much to do with them.
After the Copenhagen conference I exchanged several letters with Kjell Johnsen to sort out technical questions on the planned proton-synchrotron. Most of the problems were new and their solutions still unknown. I sent Johnsen my calculations and reprints of some of my publications. I had made a mathematical error at one stage and Johnsen corrected this, but we got together a good basis for the construction of a 10 GeV machine. All my calculations were based on my Norwegian patent of 1946 [Wi46], that is, on my own synchrotron theory.
Soon after that I went to Australia and, as I mentioned earlier, I met in Brookhaven Odd Dahl, Frank Goward and the Americans who had invented the `strong focusing' system on the way back. We spent a whole week in discussions, from August 4 to 10, 1952, and every bit of it was interesting. I understood immediately that their's was a much better idea than my previously proposed `lens-road' for beam focusing. We decided thereupon to upgrade the proposal for a CERN machine to 30 GeV and to fit it with this modern `strong focusing'. And, what's more, the Americans were prepared to help us in this somewhat risky pioneering work.
Looking back it is easy to evaluate the success of this adventure. At the Dubna Research Centre, in the North to Moscow, a 10 GeV proton-synchrotron was being built, still using the traditional method now called `weak focusing'. Their machine was completed in 1957 and 36,000 tons of iron were used to build its magnets. This machine had the highest energy anywhere in the world at that time.
For our strong focusing machine at CERN, which eventually achieved 28GeV, we only used 3,200 tons of iron, that is, less than a tenth of the iron used at Dubna.
This was definite progress - the risk had paid off. On top of this, CERN's machine went into operation before the one built by our friends in Brookhaven. It started operation on November 24, 1959 and it then snatched the world record for particle energy from our Soviet colleagues.
Naturally, we had various problems to deal with, starting with the planning stage. One difficulty consisted in making sure that the betatron oscillations of the protons did not come into resonance with the revolution-frequency of the protons. Because of the large oscillation amplitudes, this would lead to the loss of particles which would then hit the wall of the vacuum chamber.
While a consultant at CERN between 1952 and 1956, I was not given any particular guidelines or set tasks. The consultancy took up a small portion of my time, most of which I spent at BBC in Baden building betatrons. The latter occupation was barely connected to the great CERN project, except perhaps by the fact that a few electrical machines which were needed to excite the CERN magnets were later supplied by BBC. The kinetic energy stored in these machines was then discharged through the magnets.
I received copies of all documents, calculations and comments which were produced for the CERN machine. Every now and then a meeting would be called. For example, on December 18, 1952 I went to Geneva and together with Professor Gentner and Dr.Citron, I visited the site where the machine was going to be built. Citron was working on the planned accelerator's screening. He later became a professor in Karlsruhe. On that occasion, we did choose the sense in which protons had to turn in the machine, in such a way that farms or villages would not be affected by any particles which may escape tangentially. A protective hill had to be thrown up later and it became known as `Mont Citron'.
I remember working on many interesting and useful calculations with Frank Goward, Hildred Blewett and other members of CERN's staff. Now and again I would meet Odd Dahl and Hildred Blewett _ they were good friends. When Odd Dahl returned to Norway for good, John Bertram Adams (from England) came over to Geneva and Kjell Johnsen became his right hand man. But there had been others at CERN before Adams, such as Cornelius Bakker, Lew Kowarski and also Viktor Weißkopf. I knew Weißkopf pretty well.
Odd Dahl has written a very nice book which I mentioned earlier. He describes many things about the beginnings of CERN in this book which is written in Norwegian [Da81] and is now regrettably out of print. On p.191 he writes that one of his friends helped me get to Switzerland after the War. I think he may be referring to Gunnar Randers. As one of the Norwegian delegates, Gunnar Randers was also very active for CERN.
We were looking for a good high frequency specialist for the PS project. I knew Dr.ChristophSchmelzer and persuaded him to join CERN. My memory of how this came to be is quite clear. We had agreed to meet near Waldshut in Germany. I came across from Baden and together we drove on to Höchenschwand in the Black Forest. We sat on a nice meadowy slope and I explained the basic principles of the synchrotron to him. He thought that building such a machine could be an interesting thing to do and so he became a member of the PS group.
See Fig. 12.1: Tunnel of the CERN-PS
My official capacity as consultant for CERN came to an end in 1956. After that I occasionally lent a helping hand and later ceased to have any direct contact with CERN. However, I was invited to the congresses (1956 and 1959) on high energy accelerators.
I met Gerry O'Neill [Wi56] during the 1956 congress. He was working on the small storage ring system with colliding beams which I mentioned in chapter 8. He had apparently not heard of my 1943 patent and had developed the principle from scratch. A year later I visited O'Neill in Stanford and explained my War time patent to him. He was quite astonished.
During the period from 1952 to the end of 1959 I attended a total of 19 meetings and congresses about (or at) CERN. I went to most of the congresses of that era.
This is also when I met Ernest O. Lawrence, the inventor of the cyclotron. I think it may have been at the big congress `Atoms for Peace' at CERN which took place in August 1955. This popular congress would certainly have been a most suitable occasion for a friendly embrace. But it may be that this meeting did not take place until the congress of 1956. Lawrence died of cancer in 1958. I never got to see him in America.
Jan Vaagen told me that there is a picturesque description of the `Atoms for Peace' (1955) conference in a book by Nuel Phair Davis. It concerns Lawrence who, standing on the podium, with his characteristic sense of drama and pathos, celebrated Professor Wideröe seated in the audience as the author of the basic idea for his cyclotron (in the text it apparently says synchrotron, which is wrong). Lawrence may have had good reasons for doing this, but I can't remember his lecture so well.
My next stint as a consultant was for the research centre DESY in Hamburg between 1959 and 1963. I went there several times and would stay for a few days at a time. Mostly I worked with Dr.Werner Hardt on technical problems related to the construction of a 6.4 GeV electron synchrotron which was planned to have a circumference of about 300 metres. Stan Livingston also spent some time at DESY during that period, but I never saw him. I did meet Gustav-Adolf Voss quite often when the synchrotron was being commissioned. And of course I had many conversations with the founder and director of DESY, Professor Willibald Jentschke. We talked a lot about `nuclear mills', that is, storage rings with colliding beams, but Jentschke had not been authorized to build such a machine yet.
See Fig. 12.2: Start of DESY-synchrotron, with Rolf Wideröe.
It wasn't until 1967-68 that collision-machines for electrons and positrons were proposed at DESY and then built and operated _ very successfully, if I may add. The first one, called DORIS, was completed in 1974, and the second one, PETRA, went into operation in 1978. It has a circumference of 2.4 km. DORIS is still being used now (1994), albeit for quite a different purpose. With only one beam, it is a dedicated source of synchrotron radiation. Many interesting research and development projects are being performed there.
And then, between 1984 and 1991, HERA was built at DESY. This is a very special machine. The name stands for `Hadron-Electron-Ring-Anlage' (Hadron Electron Ring Installation) [Wa91]. Electrons (or positrons) of up to 30 GeV are stored in one ring, and protons of up to 820 GeV in another. Both rings were installed in a 6.4 km long underground tunnel. The particles are shot frontally against each other at two points situated within large halls. During one of my Hamburg visits in 1992 Professor Gustav-Adolf Voss, head of the Accelerator Division at DESY, showed me around their impressive installation (see Fig. 12.3). The protons in HERA have to be kept on their course by superconducting magnets. These magnets produce fields which are approximately three times as strong as those of conventional iron magnets fitted with copper coils. A similar type of magnet was also used for a proton-antiproton storage ring called Tevatron, built at Fermilab near Chicago. The Tevatron is about the same size as HERA (6.3km length) and the particles can be stored at an energy of 900GeV.
CERN made relatively early use of colliders with their `Intersecting storage rings' (ISR), a machine in which 30 GeV protons were fired against each other. It went into operation in 1971. This pioneering machine and its use for physics were described by Kjell Johnsen in a CERN-Report with Maurice Jacob [Ja84].
CERN is also where the currently largest storage ring in the world has been built. It is an electron-positron storage ring, which complies exactly with the principle of that patent of mine which was first realised by Bruno Touschek. The ring is called `Large Electron Positron storage ring' or `LEP' for short. It has a circumference of 27 km and the particles inside it will achieve up to 100GeV. In its first phase, when LEP could `only' manage to bring 50 GeV particles to collide, important work was performed on the Z0, the neutral exchange particle of the weak force.
I think that LEP is today regarded as the last stage in the development of this type of storage ring. This is because, when storing electrons or positrons in rings, the achievable energy is limited by the synchrotron radiation which is emitted. This is electromagnetic radiation which spans from infrared and visible light up to extremely hard X-rays. The energy lost this way increases drastically with the particle's energy and at a certain point, it is no longer possible (or just too expensive) to replace it even with the most sophisticated means. Only increasing the radius of the machine can help, which again is limited by the costs. This is why it is most improbable that an electron or positron ring with higher energy (or bigger) than LEP will ever be built.
This problem doesn't occur with protons, antiprotons or even heavier particles (at the energies which are available today). These types of particles can be stored in rings with much higher energies, just as long as it is possible to build magnets which are strong enough to keep the particles on their orbits around the ring (as are those used for the Tevatron and for HERA). Current plans for an accelerator in the LEP tunnel at CERN (LHC) appear to indicate the problems which may arise and the limits of the possible. An even bigger project of the same type in the USA has been cancelled for cost reasons.
Thus I have been able to see the storage rings with
colliding beams make their triumphant progress through the field of
high energy physics. On a personal level, though, I was concerned
with quite different issues during that period, stimulated by my
acquaintance with medical people for whose work most of
the betatrons built at BBC were, after all, intended.