A University Professor, and Establishing New Institutes

Abstract

When Herwig arrived in Erlangen in 1956, it was a town of some 60,000 inhabitants, dominated by the university, and the industrial powerhouse, Siemens. Historically, the town had been a seat of nobility, and the Margrave’s castle is still a dominant feature. In 1685, when Louis XIV revoked the Edict of Nantes, the Margrave gave refuge to Huguenots fleeing France, even going so far as to build an entire new quarter, Erlangen Neustadt, to house them. It set the town on a course of growth. Another development that shaped the modern-day town came the following century, with the establishment of the university in 1743. Today, housed in a new modern campus, the Friedrich-Alexander University bears the names of the Margrave who established it, and another who later expanded it, cementing its place in the fabric of the town. Many famous scientists have worked at the university including Georg Simon Ohm, whose name became the unit for electrical resistance, and mathematician Emmy Noether, whose eponymous theorem links symmetry to conservation laws—a tenet that underpins much of modern physics.

The Years at Erlangen

When Herwig arrived in Erlangen in 1953, it was a town of some 60,000 inhabitants, dominated by the university, and the industrial powerhouse, Siemens. Historically, the town had been a seat of nobility, and the Margrave’s castle is still a dominant feature. In 1685, when Louis XIV revoked the Edict of Nantes, the Margrave gave refuge to Huguenots fleeing France, even going so far as to build an entire new quarter, Erlangen Neustadt, to house them. This set the town on a course of growth. Another development that shaped the modern-day town came the following century, with the establishment of the university in 1743. Today, housed in a new modern campus, the Friedrich-Alexander University bears the names of the Margrave who established it, and another who later expanded it, cementing its place in the fabric of the town. Many famous scientists have worked at the university including Georg Simon Ohm, whose name became the unit for electrical resistance, and mathematician Emmy Noether, whose eponymous theorem links symmetry to conservation laws—a tenet that underpins much of modern physics.

Fig. 4.1

Herwig at the carnival at the physics institute in Erlangen in 1958 (Herwig Schopper’s personal collection. ©Herwig Schopper, All rights reserved)

Erlangen was one of the few towns in Germany to emerge from the Second World War relatively unscathed, but that didn’t mean that accommodation was easy to come by. Herwig had been promised an apartment, but when he arrived, he found that it was not ready, and that when it was, the Schoppers would be sharing it with another family. “This was very embarrassing,” Herwig recalled, “because my wife was pregnant and we were expecting the birth of our first child.” After a few weeks in a hotel, they moved in to the new apartment along with a colleague who had also moved from Hamburg, Horst Wegener, and his family. “Each family had two rooms and a little kitchen, but the bathroom was shared, so life was still somewhat limited.” Nevertheless, the apartment was comfortable, and the families got on well.

In March 1954, Doris Schopper was born. Herwig and Ingeborg’s first child went on to forge a remarkable career in public health, earning a degree in medicine from the University of Geneva and a doctorate in public health from Harvard. She held the presidency of the international council of Médecins Sans Frontiers in the 1990s, and went on to become a member of the International Committee of the Red Cross, director of the Geneva Centre for Education and Research in Humanitarian Action and a professor in the faculty of medicine at the University of Geneva. In the 1950s, that was all to come, and Herwig carried her in a little seat attached to his bicycle as they explored the surroundings of Erlangen together.

“At the weekends we would explore the beautiful Bavarian countryside around Erlangen by bicycle,” Herwig recalled. “A little basket was attached to the handlebars for Doris to sit in comfortably, and there was another basket at the back to carry food for the excursion. In this way, we could extend our range of visits and see many of the cultural monuments in the surroundings.” After a few years there was enough money for a car, and the Schoppers bought a Volkswagen. Herwig had passed his driving test when he was serving in the Signals Corps, but he had not converted his military licence into a civilian one. “I never thought I would own a car in my life, so I had to start driving lessons all over again.”

In Erlangen, the young family thrived and Herwig rekindled his love of music by installing a piano in one of the two rooms “But there was a problem. We lived on the ground floor, and above us was a mathematician who was also the dean of the faculty, so in a way, he was my boss. He could not tolerate noise, so I could only play the piano when he went out. My wife would look out of the window and tell me to stop when she saw him coming.”

After the war, the university flourished, and by the time Herwig arrived, its reputation in physics was growing. “There was an experimental physics institute which had become quite well known thanks to the work of Bernhard Gudden,” explained Herwig. “Fleischmann had received his doctorate under Gudden between the wars, and it was when Gudden accepted a chair in Prague that he moved to Erlangen. Gudden was an expert in superconductivity, which was one of the most interesting issues of the time, so the institute had good infrastructure for low temperature experiments.”

Superconductivity, however, was not the main research interest of Fleischmann’s new group, and Herwig found himself taking his first steps into science administration in parallel with his research. Many people had come with Fleischmann from Hamburg but Herwig was the most senior assistant. “I arrived in Erlangen with the main objective of becoming a Dozent,” he explained. “I would translate that as lecturer, but it’s a bit more than that. As a Dozent, you give lectures, of course, but although you don’t have voting rights, you are considered to be a member of the faculty, so it’s an important step in an academic career.” Herwig soon fulfilled all the conditions to achieve such a promotion, and as Fleischmann’s Dozent, he had the additional task of converting the university’s physics research infrastructure to match the needs of the new group.

Measuring the Circular Polarisation of Gamma Rays

In Erlangen, Herwig pursued two lines of research. “I continued the beta decay work that I’d started with Lise Meitner in Stockholm, in particular I started to look at beta gamma correlations, and I also continued the work I’d begun in Hamburg on a polarised proton beam source.”

Sometimes when an atom undergoes beta decay, emitting an electron, the daughter nucleus rapidly emits a gamma ray photon. When this happens, the angular correlation between the beta particles and the gamma ray photons can be used to glean information about the structure of the nucleus that has decayed. This was an established technique by the 1950s, but Herwig wanted to take it a step further by measuring the circular polarisation of the gamma ray photons, which had not been done before. Techniques existed for measuring the circular polarisation of visible light, but not for photons with the much higher energy of gamma rays. Herwig had read a paper by Dutch theoretical physicist, Hendrik Anton Tolhoek, suggesting that it could be done by scattering the photons from magnetised iron, in which the electrons are aligned. While at Erlangen, Herwig established and perfected the technique, publishing several papers shedding light on the structure of beta-emitting nuclei. It was a technique that would serve him well later, when he was a visiting scientist at Cambridge University looking at parity violation in beta decay.

The First Spin-Polarised Proton Beam Source

As a Dozent, Herwig now had a doctoral student of his own, Günther Clausnizer, who would go on to become a professor at Justus Liebig University in Giessen. Together with Fleischmann, the two of them pursued the work Herwig had initiated in Hamburg, building the world’s first polarised proton source, and publishing a paper about it in August 1956 in the German language journal, Zeitschrift für Physik entitled Erzeugung eines Wasserstoffatomstrahles mit gleichgerichteten Kernspins (Generation of a hydrogen atom beam with aligned nuclear spins). At the time it was common practice that the director of the institute co-signed most publications. A significant achievement though it was, the reach of German-language journals was not what it once was, and the paper was little read, leaving polarised proton sources to be re-invented at a later date, and in another place.

Meeting Other Scientists

Erlangen proved to be a stimulating environment for a young research physicist. As well as the experimental group headed by Fleischmann, there was an institute of theoretical physics where Herwig met an assistant of about his age, Hermann Haken, who later founded the discipline of synergetics. There was also an institute of applied physics, with Erich Mollwo and his assistant Gerhard Heiland. With Heiland and Haken being at the same point in their careers as Herwig, the three became firm friends, a relationship that endured long after Herwig’s time in Erlangen.

Industrial research was also very important in Erlangen at the time, with Siemens having a major presence in the town. The company not only had production facilities there, it also ran a research laboratory that had links to the university. Among the scientists that Herwig got to know at Siemens was semiconductor pioneer Heinrich Welker, widely acknowledged as the inventor of type III–V semiconductors, which he developed in Erlangen and are ubiquitous in the electronics industry today. Earlier in his career, while working for Westinghouse in Paris, Welker, along with Herbert Mataré, narrowly lost out on being credited with the invention of the transistor. Welker went on to become director of all of Siemens’ research laboratories, and Herwig recalls one promotion with amusement. “One of the perks of the new rank that Welker had been promoted to was that the doormat in front of his office would be flush to the floor. The works were duly undertaken, but then the promotion was delayed for some administrative reason. The mat had to be raised up, only to be re-sunk into the floor when the appointment was confirmed. There was some silly bureaucracy at Siemens, but in general it was very inspiring to have the Siemens lab close to hand.” Another interesting personality who Herwig met was Wolfgang Finkelnburg, a well-known physicist with whom Herwig later had many contacts concerning the popularisation of physics.

Moving to Mainz and the Foundation of MAMI

Herwig’s stay in Erlangen was a short one. In German physics circles, he was starting to make a name for himself, and in 1958 at the tender age of 34, he was offered a Chair of Nuclear Physics at the University of Mainz. “Fleischmann wanted to keep me in Erlangen, and told me he would do everything he could to get me a chair there,” Herwig recalled. But his mind was made up. “There are two ways to make an academic career—either you stay in an institute under the umbrella of a famous and powerful personality, and eventually move up to a chair, or you move on and become independent. I did not want to stay rooted in one branch of research, so much to Fleischmann’s dismay, I accepted the offer in Mainz.”

When the Schoppers arrived, they found a very different town to the one they’d been living in. Unlike Erlangen, Mainz had been heavily bombed during the war, and some 80% of its historic centre had been destroyed. In the 1950s, archaeologists were still excavating the bomb sites to discover the historic treasures of the city, which dates back to Roman times. The university itself, although having ancient roots, had languished, and was only re-established in 1946, under the French post-war occupancy of the Rhineland Palatinate region. Even though the population of the town had fallen sharply during the war years, accommodation was scarce, and the Schoppers found themselves involved in a long search for somewhere to live. Young Doris, by now four years old, would play a decisive role. “They had promised to provide housing, but there was nothing there. While I was at work, my wife went from one agent to another with my daughter, who eventually decided she’d had enough. She crawled under the agent’s desk and said: ‘mother, I will not move until you’ve found somewhere for us to live!’ Finally we found two rooms under the roof of a little house in the suburbs, a place called Mainz-Gonsenheim. It was a nice part of town, but still it was very modest. One of my former school friends came to visit, and I remember him exclaiming: ‘My God! I thought professors would live differently—what a shabby apartment.’” It was not long, however, before the university lived up to its word, and the Schoppers were able to move into newly built accommodation for university personnel in Göttelmannstrasse. They moved there in 1958, well in time for their second child, a son, to make his entrance.

Andreas Schopper was born in October 1959. “Andreas had a rather eventful childhood, being born in Mainz, but then spending less than a year there before moving to the US, and later coming with me to Karlsruhe, Geneva and Hamburg,” explained Herwig. “He chose to study physics at Basel although I never once tried to influence him, knowing that a career in physics can only be successful if driven by great enthusiasm for the field.” Perhaps some of his father’s own enthusiasm rubbed off on the young Andreas, growing up while Herwig was at DESY and CERN. “Eventually Andreas got a permanent position at CERN after I retired,” continued Herwig. “He worked at the storage ring LEAR and later became a member of the big LHCb experiment at the LHC where he accepted several important tasks in the collaboration. He was also elected president of the Swiss Physical Society in 2012, a rare appointment for a non-Swiss citizen.”

Fig. 4.2

The Schopper family at Geretsried, south of Munich, in the summer of 1966. Left to right, Doris, Herwig’s mother Margarethe, Ingeborg, Andreas and Herwig. (Herwig Schopper’s personal collection. ©Herwig Schopper, All rights reserved)

Mainz University’s physics department was located in a former army barracks that had survived the war, and Herwig’s job was to establish a new institute for research in experimental nuclear physics, which by this time was allowed in West Germany. There was no nuclear physics at Mainz when he arrived, but by the time he left just two years later, the university would be on the way to hosting an important centre for fundamental research in the field. Although the university’s physics department was modest at the time, Mainz was also home to a Max Planck Institute (MPI) that specialised in radiochemistry.

Founded in 1911 as the Kaiser Wilhelm Society, the Max Planck Society got its current name in honour of a former president in 1948, and is a state-funded association of research institutes. “The Max Planck Society’s policy was, it has changed now, but it was to create an institute around a famous personality where they could do what they wanted. When they died, the institute would be dissolved, or converted to another subject.” The MPI for nuclear radiochemistry in Mainz was built around one of the most eminent scientists of the day, Josef Mattauch.

The turmoil imposed on central European science by National Socialism had not bypassed Mattauch, whose career it had very much influenced. After a promising start at the University of Vienna, a Rockefeller Fellowship gave Mattauch the opportunity to work at Caltech in 1927–1928 on the development of mass spectrometry. Returning to Vienna he continued to develop the technique, rising rapidly through the ranks, eventually succeeding Lise Meitner as head of the university’s department of mass spectrometry when she left Austria to go to Berlin. “Mattauch was famous because he had been one of the first to build a powerful magnetic mass spectrometer to analyse the nuclei produced in nuclear reactions,” recalled Herwig. “By the time I got to Mainz, he was head of the MPI. One of the department heads was Fritz Strassmann, who had worked with Otto Hahn and Lise Meitner in Berlin. In the late 40s, they enthusiastically supported an initiative to make Lise Meitner head of the University’s physics department, but she turned the offer down.”

Among the staff at the MPI was Swiss nuclear physicist, Hermann Wäffler. “He had some experience with accelerator physics, and I thought that together we might build up something there. There was a lot of bureaucracy, and an unforeseen hurdle to overcome in the form of a senior member of the university’s management. I had to get authorisation and money to construct a building for the university institute, and I agreed with Wäffler that we would make an application for an electron linear accelerator of about 100 MeV or something like that. We prepared everything, and the first thing was to get approval from the university. There was a lot of resistance, and for a long time I couldn’t work out why. It was not a matter of money, because funds would have to come from the Federal Ministry of Research, in Bonn.” Sometimes it is more difficult to find out why there is resistance and where it comes from than it is to solve the problem itself, and that proved to be the case in this instance. The senior management officer of Mainz University was known as the Kurator, and when Herwig found out that the Kurator too was waiting for university accommodation, things started to fall into place. The new apartment building the Kurator was slated to move into was right next to Herwig’s proposed accelerator laboratory, and that made him nervous. “Not being a physicist, he thought there might be a risk, so I told him that I’d be prepared to move in as his neighbour. Although this never happened, I got the university’s approval. We submitted the proposal to the research ministry, and after going through various committees, the outcome was positive and a linear accelerator was built.”

Today, the laboratory that Herwig Schopper and Hermann Wäffler established in Mainz has evolved to become the Mainz Microtron Laboratory (MAMI), core of the university’s nuclear physics department and among the largest university-based accelerator facilities in Europe. Herwig, however, did not wait for the linear accelerator he’d commissioned to see the light of day. His restlessness, combined with his still-growing reputation as a physicist with a strong managerial and administrative bent, meant that he had no shortage of offers, and two of them proved too good to refuse. “I’m a restless man,” he confessed. “I didn’t stay in Mainz. It was my successor, Professor Ehrenberg, who put the linac into operation and developed nuclear physics in Mainz.” Herwig was heading to Karlsruhe, with a little detour via Ithaca, in New York state.

The Foundation of CERN and DESY Leads to Difficult Decisions

While Herwig had been moving around Germany, there had been an important development in fundamental nuclear research in Europe with the establishment in 1954 of the European Organization for Nuclear Research, CERN, just outside Geneva, Switzerland. With 12 founding member states, CERN was the brainchild of a number of visionary scientists and diplomats who saw fundamental science as the glue that could stick a war-torn continent back together. The idea for a laboratory like CERN was first put forward to the United Nations by the French delegation as early as 1946, and as the idea matured and evolved it gained support from across the continent and further afield.

Fig. 4.3

Wolfgang Gentner (left) architect of CERN’s first accelerator, the Synchrocyclotron, became chair of the Laboratory’s Scientific Policy Committee in 1968. Here he is in discussion with German delegate Wolfgang Paul. Paul went on to win the Nobel Prize for physics in 1989 (©CERN, All rights reserved)

The scientists recognised that European countries could only become competitive again by joining forces, while the diplomats saw science as a neutral language to promote dialogue between nations. “In 1949, the Swiss diplomat and writer, Denis de Rougemont, organised a European cultural conference in Lausanne, bringing together diplomats from countries including the UK, France and Germany,” explained Herwig. “At that meeting a message was delivered from French Nobel Prize-winning physicist, Louis de Broglie, advocating a European laboratory.” It was then that the idea really took hold, and in 1950 at the UNESCO general conference in Florence, an American, Isidor Rabi, tabled the motion that would lead to the establishment of CERN. By the end of the 1950s, CERN had established two important milestones—in 1957, it had brought into operation the highest energy particle accelerator in Europe, a 600 MeV synchrocyclotron (SC), and in 1959, the laboratory commissioned the highest energy particle accelerator in the world, the 28 GeV proton synchrotron (PS). Although the PS would not hold that accolade for long—the American alternating gradient synchrotron (AGS) at Brookhaven on Long Island would soon surpass it—European fundamental physics research was back on the map.

Fig. 4.4

Three of CERN’s founding fathers, left to right: Pierre Auger, Edoardo Amaldi and Lew Kowarski pictured in 1952 (©CERN, All rights reserved)

Fig. 4.5

Auger and Amaldi were together again to celebrate the Laboratory’s 30th anniversary in September 1984. Behind and between them is Denis de Rougemont, who also played a key role in the establishment of CERN (©CERN, All rights reserved)

The creation of CERN transformed fundamental physics research in Europe. The larger, more wealthy member states were able to maintain domestic facilities for fundamental physics in parallel to CERN, and over the years, a policy evolved of developing national or regional laboratories that would be complementary to the big European laboratory in Geneva. By the early 1960s, with the SC and the PS in routine operation, and the tradition of competitive competition between CERN and the US labs firmly established via the PS and AGS, thoughts were turning to the next big machines. In the USSR, a 70 GeV machine was already under construction, while in the US, design work had begun on a 200 GeV machine, with talk of energies as high as 1000 GeV.

CERN’s Director-General, Viki Weisskopf, and the chair of the lab’s Scientific Policy Committee, Cecil Powell, convened a meeting of leading European physicists on 7 January 1963 to thrash out European plans. They agreed that a wider group should be constituted to consider the future of accelerators in Europe. That group met on 17–18 January 1963, and constituted itself as the European Committee for Future Accelerators (ECFA). Among the German delegation was a certain H. Schopper. By this time, the policy of regional labs had been formalised into a ‘summit programme’ at CERN, which would be built around a major facility that would require the efforts of all CERN’s member states, and a ‘base of pyramid’ programme with national and regional labs hosting more modest facilities that would complement the big machines at CERN. An ECFA working party noted that member states that had strong domestic programmes were able to benefit more from their membership of CERN, and flagged up the kinds of facilities that might constitute the base of the pyramid.

Fig. 4.6

Viki Weisskopf was joined by some equally distinguished physicists at a colloquium held in his honour on the occasion of his 80th birthday. Left to right: Val Telegdi, Leon Lederman, Viki Weisskopf, Antonino Zichichi, Herwig Schopper (©CERN, All rights reserved)

This was the context surrounding Herwig’s move from Mainz, and it proved to be decisive in the direction his career would take, largely due to the influence of Willibald Jentschke, an Austrian physicist who had moved to the US after the war and become head of the cyclotron laboratory at the University of Illinois. It had taken the University of Hamburg some time to replace Rudolph Fleischmann when he left for Erlangen, but Jentschke was the person that the university eventually settled on. He proved to be somewhat hard to get, laying down conditions before accepting the post and moving to Hamburg in 1956.

Jentschke originally wanted to establish a base of the pyramid accelerator laboratory at the university in Hamburg. He had gained experience with electron accelerators during his time in the States, and as CERN was a laboratory built around proton machines, his condition for moving was an undertaking from the university that it would support him in a bid to establish an electron accelerator-based facility for high-energy physics, as the emerging field was beginning to be called, in Hamburg. “The authorities in Hamburg agreed to provide, I think it was about 5 million deutschmarks for the accelerator,” said Herwig, “and give support for an application for funding from the Federal Ministry in Bonn. What is five million? Not much for a high-energy physics facility, even at that time.” Jentschke started discussions with influential physicists across Germany—people such as Wolfgang Gentner in Heidelberg, Wolfgang Paul in Bonn, and Wilhelm Walcher in Marburg. “Coming from the States,” explained Herwig, “he was ambitious. He saw an opportunity for something more than just a university laboratory—he wanted to create a national laboratory for high-energy physics in Germany at the base of the ECFA pyramid.” Jentschke secured undertakings from Bonn and the state of Hamburg to fund the facility, and on 18 December 1959, the Deutsches Elektronen-Synchrotron (DESY) was established on an old airfield in the Hamburg suburb of Bahrenfeld.

Jentschke chaired the DESY directorate until 1971, but in the early days, his problem was not just establishing the lab, he also had to build up a community to use it. “There weren’t many high-energy physicists in Germany,” explained Herwig. “He hired some of his former colleagues from the States, among them Martin Teucher and Peter Stähelin, who played decisive roles in setting up an experimental programme at DESY.” But even with experienced people such as Teucher and Stähelin at DESY, Jentschke still needed to build up a user community in Germany. “So he came to me,” said Herwig, “and asked if I’d be prepared to go to the States to learn how to use a high-energy electron accelerator, and set up a user group at Karlsruhe when I got back.” The place to be for circular electron machines at the end of the 1950s was Bob Wilson’s laboratory at Cornell University in upstate New York, and Jentschke offered to arrange a year’s placement for Herwig there.

This left Herwig with some negotiating to do at Karlsruhe. The university had offered him a professorship, and in addition a contract as head of a new Institute at the Kernforschungszentrum (KfK) which had a small cyclotron of about 60 MeV used for radiochemistry.  The university and the KfK were two distinct organisations but worked closely together. Herwig was keen to accept this promising offer, but he did not want to miss the opportunity of a year at Cornell. “I said to Karlsruhe that I’d like to come, but under the condition that I formally start my job with a one-year leave of unpaid absence to go to the United States.” They agreed, and in the summer of 1960, the Schopper family set off for Ithaca. A year later, Herwig took up his position in Karlsruhe. “The University of Karlsruhe had a great tradition in physics. It was there that Heinrich Hertz had discovered electromagnetic waves, for example, and Wolfgang Gaede had developed vacuum pumps. Recently, in a building on the outskirts of the town the university had installed a small accelerator, a betatron, for nuclear and solid-state physics.”

Herwig had another condition for accepting the position at Karlsruhe. “My second condition for accepting the university’s offer was that in addition to being a full professor at the university, they would make me director of the two individual institutes, united under the same name as the Institute for Experimental Nuclear Physics.” Herwig’s condition was accepted by both organisations, and the Institut für Experimentelle Kernphysik (IEKP) was established with Herwig at the helm. “Although the financing and administration were quite different, in daily life it seemed to be just one institute,” recalled Herwig with satisfaction.

Fig. 4.7

(reproduced courtesy of the KIT archives, 28028/04181. ©KIT, All rights reserved)

The Karlsruhe Institut für Experimentelle Kernphysik in 1964

“I thought that by combining the two institutes, we would have the advantages of both: as a university professor, one has great independence with respect to the research you do, and you have close contact with students, which is a great pleasure as well as allowing you to attract the best to the institute. At the research centre, you would have good infrastructure, but less freedom: the research policy would be determined by government, and they wanted more applied research. Combining the two would give me the freedom to do the research I wanted, with the resources that come with a national research centre.” Herwig wanted to ensure that his new position would be right for him, but he also had a bigger picture in mind. “I thought that the stability of both organisations would be improved in the long run by bringing KfK and the university together,” he explained. “In that attempt I was supported by Erwin Becker, director of the Institute of Applied Physics and Walter Seelmann-Eggebert, a former student of Otto Hahn and director of the Institute of Radio Chemistry, both friends of mine and professors at the university.” It was a visionary dream, but it took much longer to realise than any of them could have imagined. “After difficult discussions over many years my initial dream has finally become reality,” said Herwig. “It took until 2009, but today KfK and the university have merged under the name of the Karlsruhe Institute of Technology (KIT), echoing somewhat MIT in the USA.”

Herwig’s concept for the IEKP looked deceptively simple, but in practice Herwig found himself engaged in a battle with industry for the favour of the ministry in Bonn. As chair of the scientific council of KfK he argued for a multidisciplinary research centre developing reactor technology for potential commercial application as its main activity, with a parallel strand in basic research. “It was very hard to convince the Ministry because of the pressure from German industry, so I failed to realign the research centre with basic and applied research,” he recalled. “I’m very sorry about that for two reasons, firstly because I had hoped to create a high-energy physics centre in Karlsruhe, which would provide two legs for KfK to stand on, applied technology and basic research, giving it more stability and independence from fast-changing industrial preferences, and secondly because KfK missed another great opportunity, which was eventually realised in Darmstadt.”

High-Energy Accelerators at Karlsruhe?

Karlsruhe is right next to the border with France close to Strasbourg, and Herwig’s plan was to establish a regional centre for both countries. “There was already DESY,” he explained, “but it was not clear how big DESY would become, and I thought there was room for another base of the pyramid lab in a big country like Germany.” This plan never really got off the ground, but another opportunity soon appeared for KfK.

Among the people Herwig had been talking to about establishing base of the pyramid facilities in Germany was Christian Schmelzer, a professor at the University of Heidelberg who was pushing to set up a centre for heavy-ion physics in Germany. Schmelzer had previously been at CERN, where he played a part in getting the lab’s big machine, the PS, up and running in 1959. Just as Jentschke had chosen an area that CERN was not involved with—electron accelerators, so Schmelzer had chosen another complementary area in the form of heavy ions. “There was no place for such a facility in Heidelberg, and the university was not interested in hosting it anyway, so together with Schmelzer, we considered establishing it at KfK, but because of the resistance from industry, the Ministry turned us down.”

Schmelzer persevered, however, and did eventually get his heavy ion research centre built. In 1969, the Gesellschaft für Schwerionenforschung (GSI) opened its doors for the first time in Darmstadt. For Herwig, however, this was a frustrating period.

When he returned from Cornell, Herwig had a promise to fulfil to Willibald Jentschke: to set up a DESY users’ group at Karlsruhe. This allowed him to pursue his scientific work with the full support of both KfK and the university. He secured two new chairs at the university, and in 1965, recruited Anselm Citron and Arnold Schoch from CERN. After Schoch passed away in 1967, low-temperature physicist Werner Heinz stepped into his shoes two years later, and together, Citron, Heinz and Schopper hatched a plan to design and build a superconducting proton synchrotron with an energy of around 100 GeV in Karlsruhe. “By this time, CERN also had new ideas,” recalled Herwig. “John Adams was proposing a much bigger machine, a Super Proton Synchrotron (SPS) of 300 GeV, and this was being discussed at the international level. It was becoming clear that the ECFA pyramid might no longer be a possibility for Karlsruhe.”

A Second CERN Laboratory and the SPS

CERN’s founding convention specifies that the organisation should be responsible for the construction and operation of “one or more international laboratories,” and with the SPS being seriously considered, many of CERN’s member states had proposed sites for the new CERN facility. Germany was faced with a choice: either support the SPS project, or go ahead with the superconducting facility at Karlsruhe. Both would not be possible.

Eventually, Adams’ argument that it made sense to build the SPS at the Geneva site where it would benefit from the existing infrastructure, notably using the PS as an injector, won the day. “Adams had already been appointed Director-General for the new laboratory before the site was decided, so that was the origin of the two Directors-General for CERN,” said Herwig. “There was a lot of politics at the time, and it was clear that Adams wanted to become Director-General of the new laboratory. If the SPS had been built as a project of the existing CERN laboratory, it’s not clear that he would have become Director-General.” As it was, in 1971 Adams became Director-General of a new CERN laboratory, CERN II, which was established in the French village of Prévessin, just across the border from the original CERN site. “That caused problems for me when it was my turn to become Director-General and I had to unify CERN I and CERN II,” said Herwig, “but I’ll come back to that later.” Germany joined CERN’s SPS project, and Herwig’s last attempt to bring a base of the pyramid facility to Karlsruhe came to nought. “I supported the SPS, and I must admit that I’m a little proud that I could convince my colleagues to abandon the idea at Karlsruhe in favour of the SPS.”

Successes in Science

Herwig’s first forays into scientific administration might have met with varying degrees of success, but his scientific work thrived in Karlsruhe. “These were perhaps my most fruitful scientific years,” he recalled. “I split my work in several ways. I continued with my own nuclear physics work on beta decay with some colleagues who had come with me—I still keep in touch with some of them today. The most senior was Helmut Appel who later became a professor at Karlsruhe. We published important results on internal bremsstrahlung following beta decay by electron capture, which showed that parity violation was 100%.”

Another strand was a polarised proton source for accelerators. “We tested it with the Karlsruhe cyclotron,” explained Herwig. “I must admit I didn’t contribute much to that, but my colleagues got it working.” Herwig also fulfilled his commitment to Willibald Jentschke by setting up a Karlsruhe user group at DESY, which conducted the first experiment by an outside team, and the first at DESY using counter detectors rather than bubble chambers. “It was more or less a copy of what I’d done at Cornell, elastic electron scattering from protons and neutrons, so my year in Ithaca paid off,” he continued. “But at both Cornell and DESY we neglected inelastic electron scattering and thus missed the discovery of ‘partons’, which were later identified as quarks. This discovery was made at SLAC, perhaps because they had a closer relation between theory and experiment.”

Accelerator Technology and Superconducting Cavities

One aspect of his time at Karlsruhe that Herwig is most proud of is the work he initiated there into accelerator technology. “I thought that since KfK was a technical centre, we should do some accelerator technology development. At the time, superconductivity was already being used by industry for medical applications for strong magnetic fields in nuclear magnetic resonance imaging, NMR, which nowadays we call magnetic resonance imaging because people got frightened by the word nuclear, but I’d heard about superconducting cavities to accelerate particles.” When Karlsruhe was bidding for a base of the pyramid facility, a superconducting proton machine was what Herwig had in mind, and by the time they gave up on the bid, they had already invested a lot of effort in this direction. “Some tests had been done with high-frequency superconducting lead cavities—at the time, lead was the favoured superconductor,” Herwig pointed out. “So we started with lead, but later when it became clear that niobium is much better than lead, we switched, first to niobium-coated copper cavities, and later to pure niobium. We were the first group in Europe to investigate superconducting radiofrequency cavities.”

Herwig developed a strong interest in novel accelerator technologies, and although there were some dead ends, the legacy of this work would prove to be significant for future accelerator projects. One curiosity from the annals of the field was a type of machine that rejoiced in the name of the smokatron. “A new idea that had come up and was being developed, above all in the Soviet Union, was the so-called smoke-ring accelerator where one created a ring of electrons in a strong magnetic field. As the ring expanded, the electrons accelerated. The idea was to load these rings with heavy particles like protons that would get accelerated too. They called it a smokatron by analogy to the smoke rings that smokers used to blow. I must admit I wasted a year of work on the smokatron before we realised it would not work. Today, there’s a related principle, wakefield acceleration, that looks promising, but back then, the smokatron was a dead-end.”

The work on superconducting cavities proved far more successful. “After CERN got the SPS, nobody was interested in superconducting linear accelerators, so we started to think about using transverse fields in superconducting particle separators.” To develop such devices, Herwig invited an expert from CERN to spend a year at Karlsruhe applying superconductivity to particle accelerators. “Herbert Lengeler came to us from CERN. He worked with us on superconducting cavities and took that technology back to CERN. This work gave superconductivity an immediate application in separating a mixed particle beam into its components.” The technique was taken up not only at CERN but also at the big Soviet laboratory in Protvino. Years later, Lengeler would become an important member of the group that developed superconducting accelerating cavities for the large electron positron collider (LEP), allowing it to accelerate electrons to 104.5 GeV, a record that still stands to this day.

In His Own Words: Who Cares About Neutrons? The Hadron Calorimeter

“In 1964, I was invited to spend a year at CERN. Well, at that time high, high-energy physics with electrons and protons were completely separate worlds. We hardly spoke to each other. There were separate conferences. There was an international high-energy physics conference for electrons and neutrinos, and a separate one for protons with hardly any communication between the two. One dealt mainly with weak interactions, and the other with the strong interactions. CERN was a proton lab. I arrived there with the stamp of electron high-energy physics, and I was an outsider. So what could I do at CERN? Either I could join an existing group or I could propose something myself. At first, I tried to join a group, but that was hard, since most of the big established groups were not keen to accept an outsider like me who might have his own ideas. So I joined a relatively small group that was led by a Norwegian called Arne Lundby. He was very friendly, and he accepted me in to his group, which was studying pion production. That was a start, but after some time I thought, “Okay, I have the group in Karlsruhe behind me, we could propose something new.” Karlsruhe did not yet have any relationship with CERN, so I had the idea of establishing a user group from Karlsruhe at CERN. A group led by Kai Runge, a professor at Freiburg im Breisgau, joined us and together we submitted a proposal.

Fig. 4.8

Arne Lundby (right), who accepted Herwig into his group, with Kjell Johnsen in November 1974 at an intersection point of the Intersecting Storage Rings, ISR, the world’s first hadron collider. Johnsen was ISR project leader (©CERN, All rights reserved)

Studying the experimental programme of CERN, I discovered that there was no experiment looking at the production of neutrons. There was no detector for neutrons. So I asked myself, “how can one detect neutrons and analyse them?” Neutrons have no electric charge, and so they cannot be deflected and analysed by magnetic fields like charged particles. At Cornell, I had learned how to observe photons, which are also neutral, by using scintillators, which produce light when hit by charged particles. By making the photon convert into a shower of charged particles, and then collecting all the light, you get a signal that is proportional to the original energy of the particle. This method to detect photons was invented by Bob Wilson, who called it, somewhat misleadingly, photon calorimetry, although no calorific effects are involved. I thought, “Why not use that method also for neutrons?” When I looked at the literature, I found that thin scintillation counters had been used to detect neutrons in cosmic rays, but not to measure their energy or direction, just the location where a neutron came down. I asked myself, ‘Why not use the total absorption to measure the energy of neutrons?’ and I decided to make a proposal to build a neutron detector at CERN. All the preliminary work was done with my group at Karlsruhe, where we built the first neutron counter for high-energy physics experiments. We did our first experiment at the proton synchrotron, and later we used this detector at the Intersecting Storage Rings. Finally, the CERN Karlsruhe group made a proposal for the Serpukhov accelerator in the Soviet Union which, at the end of the ‘60s, was the most powerful proton machine in the world with an energy of 70 GeV.

Another important development at that time was that we optimised this spectrometer for our experiment. It sounds pretty obvious today, but at the time I think we were the first group to use a Monte Carlo computer program to optimise a detector. Our neutron calorimeter was built as a sandwich of iron plates and scintillator sheets. In order to stop the neutrons you need a heavy material, like iron, and between the plates of iron you put scintillator plates that collect the light produced by the particle shower produced when the neutrons are absorbed. So we knew we wanted a sandwich of iron and scintillator plates about one metre long, but we needed to find the best distribution of iron and scintillator to get the best energy resolution. I learned that at CERN there was a group responsible for radiation safety under the responsibility of Klaus Goebel, whose job was to make sure that none of the radiation produced in the accelerators could escape. For this purpose the Safety Group had developed a Monte Carlo program to perform calculations for the absorption of radiation. I think it was one of the first Monte Carlo programs ever used at CERN, and we were allowed to use it to model the particle cascades produced in our iron absorber.

Fig. 4.9

The set-up of the first hadron calorimeter built by the Karlsruhe group at CERN (NIM 106 (1973) 189–200). This calorimeter was also the first instrument at CERN to be computer-optimised. Although unfashionable when Herwig proposed it, the calorimeter he built when he was first at CERN proved to be a very useful tool (© Elsevier, All rights reserved, Nucl. Instr. Methods 106 (1973) 189–200 [1])

It was very advanced for its time, even if it looks antiquated now. During my stay at CERN, I learned how to use CERN’s IBM computer and to program it in the Fortran language. I was running around with one-metre-long steel boxes containing IBM punch cards to do the calculations. The trouble was, if you made one little Fortran error, you had to wait for next day to find out. It was very cumbersome, I can tell you. Eventually, we used a calorimeter to study the neutron production at the PS and later at the ISR, and we did an experiment at Protvino in the USSR.

Fig. 4.10

Herwig Schopper (right) with CERN Director-General Willibald Jentschke at Protvino in 1972 discussing CERN-Soviet collaboration in physics with their Soviet counterparts (©CERN, All rights reserved)

With hindsight, that first experience at CERN was very important, but at the time, and much to my dismay, most people laughed at me for my idea of a neutron calorimeter. They said, ‘A calorimeter for neutrons? Complete nonsense. Who cares about neutrons? The only spectrometer you need is a magnetic spectrometer where you can get high precision for charged particles.’ Years later, with the arrival of collider experiments, it turned out that it was not only high resolution that mattered, but that you also need to cover a large solid angle to capture as many of the particles produced as possible. Neutral particles were just as important for the physics, and suddenly calorimeters became fashionable. Nowadays, all collider experiments include large calorimeters that have improved dramatically over the years. I must say, I suffered a lot from being ridiculed by my colleagues, but I got the last laugh.”