Oral-History:René Flükiger

About René Flükiger

René Flükiger was born in Monaco, the son of an Italian mother and a French father who died in war. Leaving France at four years old, Flükiger grew up in Italy until his mother remarried when he was ten, at which point he moved to Switzerland. He graduated from the ETH in Zurich with a degree in Experimental Physics, and finished his Ph.D. thesis at the University of Geneva in 1972. Over his thirty year career, Flükiger conducted research at the University of Geneva, at MIT, in Karlsruhe, and in industrial applications. Additionally, he has held several positions in various research departments, successfully underwent Habilitation and nominated as a full professor at the University of Geneva, and been presented with several awards in recognition of his accomplishments in the development of superconducting materials and applications. Currently, he serves as Vice Chairman of the Implementing Agreement “HTS Superconductors” of the International Energy Agency (IEA), and is working on an irradiation program as a Resident Associate at CERN.

In this interview, Flükiger discusses his early interest in physics and metallurgy leading him to his work in superconductors and applications. Involved in both the research and industrial aspect of the field for over thirty years, he stresses the importance of quality of materials, and of hard work and hands on experience in order to gain a further understanding. Reflecting on his various experiences and research ventures on superconducting materials, he comments on how small progresses contribute to a general progress of the field, to remain motivated in the face of difficulties and disappointments, and on the evolution of the field over his career.

About the Interview

RENÉ FLÜKIGER: An Interview Conducted by Sheldon Hochheiser for the IEEE History Center, 13 August 2014.

Interview #656 for the IEEE History Center, The Institute of Electrical and Electronic Engineers Inc.

Copyright Statement

This manuscript is being made available for research purposes only. All literary rights in the manuscript, including the right to publish, are reserved to the IEEE History Center. No part of the manuscript may be quoted for publication without the written permission of the Director of IEEE History Center. Request for permission to quote for publication should be addressed to Oral History Program, IEEE History Center at Stevens Institute of Technology, Samuel C. Williams Library, 3rd Floor, Castle Point on Hudson, Hoboken NJ 07030 USA or ieee-history@ieee.org. It should include identification of the specific passages to be quoted, anticipated use of the passages, and identification of the user.

It is recommended that this oral history be cited as follows:

René Flükiger, an oral history conducted in 2014 by Sheldon Hochheiser, IEEE History Center, Hoboken, NJ, USA.

Interview

INTERVIEWEE: René Flükiger
INTERVIEWER: Sheldon Hochheiser
DATE: 13 August 2014
PLACE: Charlotte, North Carolina

Introduction

Hochheiser:

This is Sheldon Hochheiser of the IEEE History Center. It is the 13th of August 2014. I am here at the ASC Conference in Charlotte, North Carolina with Professor, René Flükiger, forgive me if I didn't pronounce your name correctly.

Flükiger:

It is exactly right.

Hochheiser:

Good. I did learn something from my college German.

Flükiger:

[Laughter] Good.

Early Life and Background

Hochheiser:

If we could begin, let's start with a little background. Where in Switzerland were you born and raised?

Flükiger:

Oh, I am a complicated person. I was born in Monaco in France as the son of a French father and an Italian mother and got the French nationalship. I never saw my biological father; he died in war. I was four years old, just after the end of the war, when we left France for Italy. I grew up in Italy and Italian is my mother tongue. Meanwhile I also speak fluently German and English. I was 10 years old when my mother was remarried to a Swiss, after which I moved to Switzerland. Her new husband adopted me officially and gave me his name. I do not like this name at all, it doesn't fit to me, but of course, I had no choice. My original name is Rosati, but it doesn't play a role here. Then I stayed all the time in Switzerland, where I made all the schools. After getting my diploma as physicist at the ETH, the Federal Technical School in Zurich. I moved to Geneva, where I finished my PhD thesis in 1972, just after getting married. We have two daughters.

Hochheiser:

Okay, if I can go into some of those things in a little more detail. What led you to the ETH for college? Why did you choose to go there rather than some other place?

Flükiger:

At that time I was living in Zurich with my parents and it was most convenient for me to accomplish my studies in the same town. The ETH is an engineering school, and I discovered soon that I was not too much inclined toward engineering: I was more attracted by physics. During my whole career, my occupations always covered the range between physics and engineering or both, if possible. The event which gave me the idea to study physics was the atomic exhibition in Geneva in 1956. Many companies dealing with the nuclear industry, but also uranium mining companies came from all of the world and presented their activities in a very suggesting way: at this time, nobody had the hostile attitude towards the atomic business one generally encounters today. I was very much impressed, so much, that I rapidly knew I had to go in that direction – at the beginning more subconsciously, but with time, more and more convinced. I liked this exhibition very much. I saw how the ore is extracted from the earth and is refined to uranium metal by various companies in Mexico and the United States. At the same exhibition were also many scientists, and when I realized how they calculated the energy produced by the reactors and the destructive one produced by the bombs I said to myself: "This is interesting". Several years later, I studied physics at ETH. In my diploma work I analyzed the Sondheimer oscillations in very pure Indium wires. After the diploma I found that pure physics was still not exactly what I wanted, and added one year at ETH where I followed various lectures about metallurgy: indeed, after practical work in a company during the summer holidays, I had understood that metallurgical problems was attracting me very much. At that time (begin of sixties) the ETH did not have a metallurgy department: this is the reason why I had to wait until the end of my four and a half years in physics before I could at least be inscribed to metallurgy lectures. Later on, during my two years at MIT, I had the chance to deepen my knowledge in metallurgy. Finally, I am now both a physicist and a metallurgist. During my whole life, I took advantage of this double formation. As an example, the Plenary Talk I just gave this morning at the ASC (I was invited to discuss the present state of MgB₂ superconductors) combined elements of fundamental physics with processing steps involving metallurgy.

Hochheiser:

And then after that year, you went on to Geneva?

Flükiger:

Yes, I moved to the university in Geneva. I was engaged in the Department of Condensed Matter (Solid State Physics), but what attracted me there was the combination with practical metallurgy: During my PhD thesis work, I have grown single crystals and have also built furnaces for high temperature treatments for the study of phase diagrams: it was exactly what I like.

Hochheiser:

One thing I found interesting, is that you were in the department of condensed matter physics. Were there multiple physics departments?

Flükiger:

Yes. In Geneva there are five departments: a Department of Astronomy, one of Applied Physics, one of Solid State Physics, one of Nuclear Physics, and finally one of Theoretical Physics.

Hochheiser:

Because that's very different from the schools in the United States I'm familiar with.

Flükiger:

Well, in Switzerland, it’s like that. They have a faculty of science with various sections, e.g. physics, chemistry, biology, geology, and others. The physics section comprises the just mentioned 5 departments.

Introduction to Superconductivity

Hochheiser:

How did you first get interested in the field of superconductivity?

Flükiger:

The main subject of the group of Prof. J. Muller who engaged me in Geneva was superconductivity: here I had my first contact with this research field. My task consisted in melting the materials, homogenizing and measuring them at low temperatures. I found the work so interesting, that I passed many nights working in the laboratory. We tried to find new superconducting materials with higher transition temperatures, by means of new preparation and testing methods. At that time, all the work of the group was directed towards the fundamental mechanisms of superconductivity and, more generally, of solid state physics. Applications were no subject; at Swiss universities, the main accent was traditionally set on the fundamental properties.

Hochheiser:

Right.

Flükiger:

Applications came later. A slow evolution during several decades has led to the situation of today, with an opening of the universities for applied subjects.

Hochheiser:

How were you melting the materials?

Flükiger:

At the beginning with an arc furnace; later with a high frequency oven. I built myself an electron bombardment furnace for single crystal growth, including the electronic control.

Hochheiser:

Was that how you prepared the substances?

Flükiger:

In my whole life, I have prepared all samples myself, always following high quality standards. I always found that only a good material allows good measurements. I am so convinced by that statement that even now, as a senior scientist, in the spare time, I prepare my samples myself simply because I love this activity. In metallurgy, you have to touch materials to get the feeling and to understand them. I think that's my way.

Hochheiser:

And what led you to work with the A15 phases in particular?

Flükiger:

This was the main subject of my professor in Geneva. At that time, A15 type materials exhibited the highest known critical fields, which was interesting in view of high field solenoids.

Hochheiser:

Who was that?

Flükiger:

Professor Jean Muller (this name is written without accent, for historical reasons). The whole group made superconductors. The main goal was to measure the superconducting transition temperature, Tc, trying to get higher values. The low temperature specific heat was an important subject, giving an indication about the homogeneity of the sample and of the electronic density of states. I found a special research subject which I treated in my Ph.D. thesis and which is still important for my research today: the measurement of the atomic order parameter of A15 type compounds. This quantity describes the probability of the various atoms to be on their equilibrium position in crystallographic structure. If you change the degree of atomic order, you also change the interactions between them, which in turn affects the superconducting properties. I measured the amount of atoms being outside of their equilibrium lattice sites by means of X ray diffractometry.

Hochheiser:

Of the A15 crystal structure?

Flükiger:

Of the A15 structure, yes. I specialized my knowledge in crystallography and in superconductivity, and determined the electronic density of states, which was analyzed in the frame of the current theories.

Hochheiser:

Now I understand. The better job you could do of producing a pure substance with less disorder.

Flükiger:

The reality is more subtle; the material should first of all be homogenous and this at different ordering states. To introduce a partial disorder in the material, you heat it up to a very high temperature, and then splash it against a cooled metallic wall in order to get cooling rates between 10⁵ and 10⁶ degrees per second. With this technique, you get states of the material which cannot be obtained at room temperature, of course: you create nonequilibrium states.

Hochheiser:

So your, your dissertation then was part of Professor Müller's work?

Flükiger:

Yes, exactly, it was the effect of atomic ordering on the superconducting properties of A15 compounds.

Hochheiser:

Any particular A15 compounds?

Flükiger:

No, we tried to study all the most interesting ones (several dozen). As I already mentioned, at that time in Geneva we're not linked to any application and just studied most of them, not taking care of a possible application. We studied those A15 type compounds with very low T_c as well as those with the highest T_c, e.g. Nb₃Al or Nb₃Sn, including also ternary systems, as Nb₃(Al₁-_xGe_x). I think that during my Ph.D. time I melted more than a thousand samples.

Hochheiser:

Now am I correct that you stayed at the University of Geneva after receiving your doctorate?

Flükiger:

Yes, I got the task to build up the material preparation laboratory and I realized that. So we built ourselves machines for doing differential thermal analysis, for establishing phase diagrams up to 2’300 °C. I specialized myself in methodological problems having to do with the phase diagrams, stability of the various crystallographic phases and so on. In addition I built several high vacuum furnaces, for single crystal growth and for heat treatments. In the sixties, high vacuum was not yet at the level of today: we had 10^-8 mm Hg of pressure in a vessel which was at that time quite exceptional. Today, ultrahigh vacuum systems can be encountered in most laboratories.

Hochheiser:

Did building up a laboratory also mean building up a staff?

Flükiger:

Prof. Muller was Dean of the faculty and had very little time for leading his group. He was grateful that I took over several of his tasks, in particular organizing the research work of the younger assistants. He just let me do it.

Hochheiser:

Right.

Flükiger:

I have built an electron beam bombardment furnace for growing single crystals of high temperature materials (e.g. Ta, Nb). And also large size furnaces for a variety of quenching experiments as well as for heating experiments with different furnaces. We also built or modified devices for low temperature experiments for fundamental research (measurement of T_c, of the electrical resistivity and of the specific heat).

Hochheiser:

And you're still working with A15?

Flükiger:

Yes, among many other subjects, I still work at present with the superconductor Nb₃Sn, an A15 type compound. This material will be used for the quadrupole magnets in LHC Upgrade, which will produce fields of the order of 12 T.

Hochheiser:

Now was Professor Muller’s group at Geneva at the forefront of European research on superconductivity?

Flükiger:

The reputation of the group was built on the metal physics of superconductors and in the study of phase diagrams. You can call it “at the forefront”, I would rather say the group was at a top level.

Hochheiser:

You have to be more specific?

Flükiger:

Yes, you cannot do everything; the field of superconductivity is very broad. Theories of superconductivity mean a deep understanding of electronic states. It is a very different discipline than for example the measurement of exotic superconducting properties. And there is the metal physics of superconductors, which is a combination of both. One has to make the samples, to study their metallurgical properties, to measure them and finally to analyze in the light of the current theories. I must say it was a good group, and the excellent results obtained there are the reason why I was asked to act as an Invited Scientist for two years at MIT.

Hochheiser:

Okay. While you were in Geneva, how much contact did you have with other groups both in Europe and here in the United States?

Flükiger:

We had very good contacts with the Naval Research laboratory in Washington, who were treating similar problems. At that time, we were also in contact with Professor Bernd Matthias of the University in San Diego, La Jolla: he was very famous for his discoveries of new superconductors. We had strong contacts with the Bell Laboratories in Murray Hill (which don't exist anymore), in particular with Professor Ted Geballe, who is now at Stanford University. We had also good contacts with Russian and German scientists. Prof. Saemann-Ischenko, in Erlangen was particularly interested in our order parameter measurements, for explaining his results on irradiated materials. All my life I had intense contact with researchers from many countries: maybe this facility of contact corresponds to my character. I love contacts, as a person coming from the South of Europe, I appreciate very much talking with people.

Developing Superconducting Wires at MIT

Hochheiser:

[Laughter] During this period, did you start looking at wires made of these materials?

Flükiger:

Not at the University. I changed completely during my stay at MIT, 1977/78. There I started to prepare wires in the group of Professor Simon Foner at the Magnet Laboratory in Boston. I was really enthusiastic about the fact to fabricate myself a superconducting wire. From there on, an important part of my work was always devoted to the development of superconducting wires of various structures. The superconducting wires I have studied in all these years were based on a variety of compounds: Nb₃Sn (T_c = 18K), PbMo₆S₈ (Chevrel phases, T_c = 15K), then the High Temperature Superconductor Bi-2223 (T_c = 110K) and finally, MgB₂ (T_c = 39K). This all was still physics, still metallurgy, still superconductivity, but on wires and tapes.

Hochheiser:

Okay. What led to your going to the magnet lab at MIT in the first place?

Flükiger:

Yeah, [laughter] it's very simple, I got invited because they knew my papers quite well, as my competitors. This was for me the big chance of my life: First of all to get contact with the American way of working, which is quite different from the European, but even more important, the direct contact with well-known laboratories and researchers in this country.

Hochheiser:

In what ways is it different?

Flükiger:

It is different because in the United States, the contact between laboratories is very much alive and the contact is an open one. In Europe, you're more behind your own subjects. And, in the US, everybody in the field knows each other; all are depending on the same funding agencies and this creates some knowledge about the activities of the others, which in turn creates contacts, and so on. Here, you have contacts, but you work more by yourself. In Europe, you have maybe less general contacts, but the work in a team is more developed. In the States it's still a team but each one is working more decoupled, so the personality is much more important. At MIT, I was completely alone in the corner of a big laboratory. If you ask something to somebody, they don't have time because they are under stress. So yes, maybe that was the point. At that time in Europe, we had some kind of quiet working (if not today then I will come tomorrow….), while in the US there was a constant pressure. This is at least partly because the funding periods here are considerably shorter: three or six months, or one year at the maximum. In Europe we have funding for two years, sometimes for three years, and so one has more time. And I must say, in the US, the efficiency is certainly higher due to a higher pressure. People here are used to it. I accepted this pressure without problems: it corresponds very well to my character. However, I had some difficulties coming back to Europe after that stage. In Karlsruhe, Germany, I was pushing my group for more efficiency, but they didn't understand why I was pushing like that. Let me say that in the meantime, things have changed.

Hochheiser:

I also noticed that around this time, 1977 or so you were working with some more complex systems, ternary Molybdenum Sulfides (or Chevrel phases).

Flükiger:

Yes, we developed new methods for the preparation of wires with high critical current density. Unfortunately, the upgrade of the know-how to an industrial scale failed.

Hochheiser:

Now you're getting away from just the A15s?

Flükiger:

Oh, we never got away from those, but included also many other compounds in our study.

Hochheiser:

That's another aspect maybe.

Flükiger:

But the ternary Molybdenum Sulfides were quite interesting: T_c was not so high, 15 K, but the critical field B_c2 was absolutely extraordinary for a LTS superconductor: 60 tesla, twice as much as for the A15 compounds. And so I started to all use all my knowledge and methodology on phase diagrams and deformation technology for realizing these Chevrel phase wires. I started the work on Chevrel phases during the year I passed in Geneva between the stage at MIT and the engagement in Karlsruhe, Germany. There I continued this work: we were quite successful, reaching the highest critical current densities ever published, with my coworker, Dr. Wilfried Goldacker.

Hochheiser:

I also noticed in looking through your publications the paper in this area was the first thing you published in an IEEE journal.

Flükiger:

Oh, I forgot that.

Hochheiser:

No, I was just curious at what led to that.

Flükiger:

Maybe it was from one of the ASC conferences, they publish always in IEEE.

Hochheiser:

Yes, of course. So was the year you spent at MIT the first time you went to one of these ASC conferences?

Flükiger:

No. I was there before in the year ' 76, attending the ASC at the University in Stanford. I met very interesting research people there and some of them invited me later in their laboratories. The ASC in Stanford was very special because the posters were not inside the room but outside, the weather being always beautiful there.

Hochheiser:

[Laughter] Yes, any other recollections of those ASC meetings in the 70s?

Flükiger:

That was the first one, and then the second one was in '78 in Pittsburgh. At the end of my stage at MIT, I presented my new results. I developed a new process for the fabrication or Nb₃Sn wires, based on powder metallurgy, which raised a considerable interest.

Hochheiser:

And what was that?

Flükiger:

If you make a superconducting wire, you just start with rods, many, many rods for getting a multifilamentary configuration. You bundle these rods and introduce them into a copper tube (the matrix) and then deform them to a wire with smaller diameter. In order to get a multifilamentary wire, you perform the bundling process a first time, followed by wire drawing and by a second, then a third bundling process: at the end you have a wire of 1 mm diameter with 10,000 filaments. My idea was to replace this long process by a one-step procedure, consisting in mixing niobium and copper powders of 40 micron size together, to enclose them in a Cu tube and deform it to a wire of the final diameter. The last process consisted in electroplating Sn at the wire surface, followed by a reaction at 550°C to form the superconducting Nb₃Sn phase. This process worked out quite nicely, I would say. Well, after the very hard work at MIT - I must admit I didn't sleep very much during this time – my process was successful. Unfortunately it was not appropriate for an industrial application: the process of coating the Cu wire by a Sn layer as thin as a few microns revealed to be very demanding, the homogeneity becoming a problem. That was the handicap: the values of J_c were satisfactory, but the fluctuation was too important. Another disadvantage was the low T_c values of these wires. After I left MIT, the group of Professor Simon Foner continued this work for several years, but this technique never reached an industrial level.

Hochheiser:

Anything else on your time at MIT before we go back to Geneva?

Flükiger:

Not for the moment, no.

Research in Karlsruhe

Hochheiser:

Okay, so after a year at MIT you went back to Geneva?

Flükiger:

In reality I stayed almost two years at MIT; the first year I was there with my family, but during the second year I made not less than 10 short stages at MIT: I was engaged to continue the experiments I had begun during the first year, nobody else being available there. This was physically a very hard year: sometimes, I arrived at the airport in Boston at 3:00 pm from Geneva but was already in the laboratory around 4:00 pm!

Hochheiser:

[Laughter]

Flükiger:

I got a lot of friends with that kind of work. [Laughter]

Hochheiser:

As well as lots of experience in airports [laughter].

Flükiger:

Yes, but also experience in organizing my time under stress. I was always a hard worker.

Hochheiser:

So you spent a little more time in Geneva and then you moved.

Flükiger:

One year, just to look for another job, seeing no possibility to get a faculty position in Geneva. Yes, I would have had the possibility to stay there as a kind of assistant, some kind a postdoc of a higher degree. But I refused, being terrified about the idea to be still a postdoc at 65. I would never have accepted that, and told to myself: "I must find something else". Quite soon, I got an offer from the Nuclear Research Center in Karlsruhe, Germany: they wanted to build up a new laboratory for the development of high field superconductors. It was exactly what I was looking for and I accepted right away. I got a stable position there as a department leader. The conditions were very good: my group comprised 25 coworkers and I got sufficient funding to build up the laboratory, with a high field magnet, various high temperature furnaces and a whole set of deformation machines. Thanks to these sets of equipments and to dedicated coworkers, this was the real beginning of my career in the field of superconducting wires. At the Institut for Technische Physik in Karlsruhe, the first material studied was the A15 type compound Nb₃Sn.

Hochheiser:

And what was the second?

Flükiger:

Chevrel phases, or lead molybdenum sulfide, with the formula PbMo₆S₈.

Hochheiser:

So you built up a laboratory at Karlsruhe

Flükiger:

Yes, a laboratory comprising all facilities to fabricate multifilamentary wires and to characterize them at high magnetic fields, in view of their use in NMR and fusion magnets. For the laboratory we bought a Helmholtz magnet from Intermagnetics producing the high field of 15 tesla in a bore of 50 mm - I think it was the first magnet of its kind in the world. A Helmholtz magnet is not a simple solenoid where the sample length is very limited, the wire being perpendicular to the field produced by the magnet. The Helmholtz magnet configuration consists of two parallel coils producing a horizontal magnetic field, the wire being located vertically. The physical data, e.g. the voltage, are measured in the homogeneous field zone determined by the distance between the two magnets and the bore diameter.

The advantage of this particular configuration is that long wire samples can be introduced, and that different locations along the wire length can be measured.

Instead of a wire, it is also possible to introduce a cable in the space between the two magnets and to apply strong tensile forces on it, in order to simulate the effect of Lorentz forces in a magnet during high field operation. In Karlsruhe, I was also responsible for the design and construction at a reduced scale of a prototype cable for a tokamak magnet for the NET fusion project (NET = Next European Torus was the name of the fusion project in 1980). Note that the cable for NET was designed for 20 kA only, while the cable for today’s tokamak magnets in ITER reach 67 kA).

Hochheiser:

So it sounds like another thing you had during your years at Karlsruhe, now you're starting to really work on applications.

Flükiger:

Yes, on applications.

Hochheiser:

Your early work in Geneva was much more fundamental?

Flükiger:

Yes, and I switched over to wires during my stay at MIT. In Karlsruhe I maintained the activity on wires but in addition I started to develop cables with the industry, in particular with Vacuumschmelze in Hanau (D), (today Bruker). We had a strong collaboration with them, and it was an extremely positive experience. Hanau can be reached in one and a half hour by car from Karlsruhe, so I was quite often there.

Hochheiser:

Who were the people in the company that you were working with?

Flükiger:

Today they are all retired.

Hochheiser:

Well of course. [Laughter]

Flükiger:

[Laughter] The main contacts were with Dr. Hillman, the director, and Dr. Springer, both being directly responsible for the manufacture of the superconductors. My task was to discuss the new developments with them and to test the wires or cables they fabricated for us. We also participated in developing new techniques for improving the wire production. So it was quite a wide range of tasks, if you want.

Hochheiser:

And then they took your work and then, manufactured the cables?

Flükiger:

Yes. They did not apply all my ideas but were receptive for some of them, I would say. You cannot have only good ideas…... If you want to have one good idea, you need 10 other ideas. And you have to continue and to start again. Never lose the impact, never stop, that's the way. If it doesn't work it doesn't matter, just try once more, or try another thing. It doesn't work try another one. That's life. And that's the pleasure also. Somehow, some day it will work.

Hochheiser:

Well basically you're making intelligent assumptions as to what things are even worth trying.

Flükiger:

Yes, exactly.

Hochheiser:

And of course some of them will work and some of them won't.

Flükiger:

Yes, but for that you must believe in what you're doing and you have to believe in yourself. That is what I had to learn with time.

Hochheiser:

I'm sure it must be frustrating when you think something will work and when you'll actually try it doesn’t.

Flükiger:

There is something which I didn't say before. In Switzerland, before I left, I made a lot of military service and I ended up as a captain with the army, in the artillery. The military service was accomplished in several lengths of 3 to 6 months (mainly during the semester holidays, but also during the semester, which caused troubles in recovering the lost time……..), plus three weeks a year, the total being two years. It was a hard time, but I learned not only discipline, I learned to talk to 30 people who absolutely don't want to listen and also learned to push people who don't want to run. There I learned not to give up.

Hochheiser:

Another thing I'd like to ask you about, while you were in Karlsruhe you went for the habilitation. I'm curious about that because that's something we don't have here in the United States.

Flükiger:

Yes. In Europe, if you want to become a professor either you are directly nominated or you apply for an open position. In the second case, you are invited, together with other candidates, to present yourself by giving a talk. In addition, you are tested during several hours by the nomination committee. Universities in Europe would like (in older times more than today) to have an important work of the candidates. Required would be a publication which is crossing fields, not a simple PhD thesis. They wish an important work, which has your hand, your fingerprints on it. Once a university has accepted your Habilitation work, you have the right to give lectures, the title being “Private docent” (which does not exist in the USA). In my case, I had already written a major publication based partly on my own results in the field of high temperature phase diagrams: R. Flükiger, "Phase Diagrams on Superconducting Materials", in "Superconductor Material Science”: Metallurgy, Fabrication and Applications" Ed. S. Foner and B. B. Schwartz, Plenum Press, 1981, pp. 511-604. However, in the first half of the eighties, there were no open professor positions in my special domains. During several years I looked for openings, and was even close to give up: after all, I was happy with the working conditions in Karlsruhe. However, I wanted to come back to university, being attracted by the combination of teaching and research.

Since time had passed since the first major publication mentioned above, I decided to write a second one, just in case. I wrote this new work, the Habilitation work, during the evenings; during the days I did my work on different matters. This new work had the title “Atomic ordering, phase stability in bulk and in filamentary A15 type compounds”, KfK Nr. 4204, May 1987, pp. 1 - 306, and was internally published at the Kernforschungszentrum Karlsruhe (D). This work was very well accepted in Geneva, the University I had left more than 10 years before! It turned out that they were looking for exactly someone like me with a background in metal physics and in applied superconductivity. Among the 29 candidates applying for the position of an Ordinary Professor, 4 selected ones were asked to represent themselves for a second time, after which I was finally nominated.

Hochheiser:

Let's get back to Karlsruhe for a minute. Are there other things about your work through those years in Karlsruhe that are significant?

Flükiger:

Yes, I did some neutron irradiation work on Nb₃Sn wires. Neutron irradiation was at that time important in view of fusion magnets, especially in Karlsruhe, where important fusion activities were located. Indeed, the scope of my high field laboratory was to develop superconductors for a fusion magnet. A series of short wires was irradiated at the 14 MeV neutron facility in Berkeley and I measured them myself up to 20 tesla in Grenoble at the high field laboratory. Due to strict safety prescriptions, this is the highest field at which superconducting irradiated samples have been measured up to the present day. This small irradiation activity I experienced has been quite important for me in 2009, when I was asked to lead the irradiation activities at CERN, in view of the next accelerator, LHC Upgrade. Since irradiation causes a decrease of the degree of ordering in the A15 Nb₃Sn structure, and thus a change of the electronic properties and also of the current carrying capacity, I found myself back in the subject of my Habilitation work. Indeed, irradiation caused indeed similar effects to those I had analyzed many years before by means of quenching techniques: the circle was closed.

Hochheiser:

Do you recall your reaction on learning about Müller and Bednorz’ discovery of high temperature superconductivity?

Flükiger:

Yes, I recall very well because the referee of this first paper was a certain Professor Buckel at the University of Karlsruhe. I attended a seminar where he told us that he was the referee of a paper mentioning a new superconductor with the record transition temperature of 28K. At that time, this was almost unbelievable, and it looked unserious. As a referee, he had of course to treat the whole thing as a secret. Nevertheless, he wrote the names of the elements in the oxide compound, Ba, La, Cu and O on the blackboard, not mentioning the formula. He asked, "What do you think about this compound if you could do it?" I remember that we all laughed: that crazy compound, a superconductor? Impossible! Later, after learning the importance of this discovery, I started immediately with the reaction of some samples, but the effort was limited since I had simultaneously to continue my work for the NET cable. However, powder metallurgical techniques (the only available ones in my laboratory) are not the appropriate ones for preparing highly textured tapes of the HTS compound Yttrium Barium Copper Oxide (YBa₂Cu₃O₇, T_c = 92K) with high critical current densities. For this reason, I entered only later in the game, after the discovery of the compound Bi₂Sr₂Ca₂Cu₂O₃ (T_c = 110K). In spite of the failure of powder metallurgy for the preparation of YBa₂Cu₃O₇ tapes, this technique is still the only applicable one for producing other industrial superconductors, based on Bi₂Sr₂Ca₂Cu₂O₃, Bi₂Sr₂Ca₁Cu₂O_x, MgB₂ and more recently, Fe based pnictides.

Hochheiser:

Yes and a lot of things I'll ask you more about. Did you know, Müller and Bednorz?

Flükiger:

Yes.

Hochheiser:

Before the discovery?

Flükiger:

No. Before I had heard about Alex Müller as a professor in a Swiss university, but Bednorz was completely unknown to me before their discovery. I had the opportunity to meet Alex Müller for the first time when he acted as one of the official referees for my Habilitation in Geneva (the work was written in Karlsruhe, but was accepted by the university of Geneva). This was at the end of 1987; it was after the discovery, but he was not yet awarded with the Nobel Prize, so I’m just proud of that. [Laughter]

Hochheiser:

Anything else on the years at Karlsruhe before we move back to Geneva?

Flükiger:

Not really, I would say. Well, during that time I was elected as an advisor of the High Field Laboratory in Grenoble.

Hochheiser:

Now what did you do as an advisor?

Flükiger:

We had regular meetings, where we discussed the impact on physical properties of the research at very high magnetic fields (50 tesla and more). Another task was also to select possible experiments where measurements at very high fields could lead to the observation of new effects. Finally, we also studied the future state of art of producing very high magnetic fields.

Hochheiser:

And then as you described you succeeded among many applicants in getting the professorship

Flükiger:

Yes, it was quite late for me because I was already 49 at the nomination date. I was chosen for my scientific profile, combining solid state physics and metallurgy. The choice of an experienced material scientist is explained by the need for new, high quality materials for the research of the other groups in the physics institute. To centralize the material preparation was certainly a good idea, and allowed a considerable savings of manpower and funding.

Hochheiser:

I don’t know enough about how the European system works differently from the American systems, I would have no idea about it.

Flükiger:

Yes, they wanted my specialties so I was elected.

Hochheiser:

And did that typically happened to people who are younger?

Flükiger:

Yes, for example my successor in Geneva (Prof. Carmine Senatore) was 38 at his nomination in 2013. There is nothing in Europe which forbids the nomination of younger people, but sometimes they prefer people with experience. Sometimes you have to react fast. Indeed, it can happen that you wanted to engage somebody of a certain age in view of his scientific profile, but that this person was already engaged by another university. In this case, you have to search for another candidate, and will choose a younger one. As you see, the whole nomination procedure is quite flexible.

Teaching and Research in Geneva

Hochheiser:

So you came back to Geneva in 1990, now as a professor?

Flükiger:

Yes. After an absence from Geneva of more than 11 years, I was not anymore considered as an insider. For an insider, the chances to get a promotion are quite low in Europe.

Hochheiser:

So what is involved with being a professor?

Flükiger:

I think that another argument may have worked in my favor was my experience as a group leader in Karlsruhe. Very soon after my nomination in Geneva, I was asked to act as the Director of the Département de Physique de la Matière Condensée (the Solid State Physics Department), a task which I took over during 8 years, in addition to my daily research work. Later, from 2000 to 2005, I acted as president of the Physics Faculty.

Hochheiser:

How much time did that take away from your research?

Flükiger:

I would say, as director from one to two days a week, and as president, at least two days a week.

Hochheiser:

So it still allowed plenty of time

Flükiger:

Plenty of time is not the right expression. Indeed, I had to prepare lectures, two two-hour lectures a week. In addition, two hours of a facultative lecture and at least two hours exercises with students. The subject of lectures changed all 2 or 3 years: as you know, to prepare a new lecture for a semester requires an intense effort.

Hochheiser:

I've done that myself, and yes I know what goes into preparing a lecture. [Laughter]

Flükiger:

The first year is just hard. You don't sleep very much. I went to bed at two o'clock and was up at seven. That's it.

Hochheiser:

What level were your courses?

Flükiger:

In today’s scale, it is for Bachelor and for Master's classes, for both. For the first year I got for Bachelor’s students and later I got lectures for the older ones.

Hochheiser:

And in the meantime were you building a research group?

Flükiger:

Yes. I was particularly lucky because one of the professors, Professor Martin Peter, a theoretician and former rector of the university, liked my experimental approach, we had many discussions together. He was interested by our search for new fabrication methods for wires and tapes conductors based on HTS superconductors. At that time, thanks to my metallurgical background, my group was one of the first ones worldwide to fabricate Ag sheathed, thin Bi2223 tapes with high critical current densities at the temperature of liquid nitrogen, 77K. In 1991, the National Research Foundation decided to support the research on the High T_c superconductors (which were discovered in Switzerland) with an exceptional, one-time funding. Thanks to the support of Martin Peter, I obtained the equivalent of more than 1.5 million US$, which were used for buying a 17 tesla magnet and a series of deformation machines for the preparation of long superconducting wires and tapes. It should be mentioned that the rest of money for completing this laboratory came from my activities linked to industries, in particular from a collaboration with Rolex, the watch manufacturer.

Hochheiser:

Yeah, I was going to ask you about that because it seems far from superconductivity.

Flükiger:

Yes and no. The common point is the deformation laboratory, as I will explain in the following. Rolex is a worldwide known manufacturer of high quality (and expensive) mechanical watches. In these watches there are two types of springs: the first one is a source of energy for the movement, the second one oscillates periodically with a highly controlled period, thus determining the precision of the watch. The spring for the time regulation is a magnetic alloy containing eight components constructed in Switzerland by Nivarox. A careful study of the market convinced Rolex that Nivarox, who belonged to the main competitor, would eventually stop selling these springs to other companies. It must be said that these high quality springs are essential for the precision and thus for the quality of a mechanical watch. Without high quality springs, a watch company cannot survive. The decision to fabricate in-house a new type of time springs was a strategical one. Since Rolex is only a watch maker and has no experience in complex metallurgy, I was asked to collaborate in solving the problem. We knew that years ago there was a development about a material, NbZr (Niobium-Zirconium). (This material is superconducting, with T_c = 10K, but this is not of importance here). It has peculiar elastic properties: the variation of the elastic modulus of NbZr with temperature presents a nonmonotonic behavior, with a peak at room temperature. The problem consisted in finding a way to transform this peculiar behavior of the elastic modulus into a strictly constant value around room temperature. With a spring with such a flat elastic modulus between +30°C and -30°C, one could get out from his heated house into a “Siberian” winter with -30°C without affecting the high precision in time of the watch!

An important point for Rolex was to submit patents on a new process, in order to be independent of any other company. For this reason, a generous funding was provided by Rolex, which allowed us building up an exceptionally well equipped laboratory. With a 300 ton extrusion machine and various swaging and drawing machines for deformation, the Geneva laboratory became - also thanks to Rolex - one of the biggest laboratories for wire deformation worldwide. The fabrication of NbZr springs starts with the zone melting of long rods of 12 mm diameter by means of electron bombardment. I had built such a furnace during my PhD thesis, and knew the process: this accelerated the construction of the present furnace. During deformation to finer rods, NbZr exhibits a marked work hardening, which leads to breakages. In contrast to previous attempts by other researchers, I solved this problem by introducing sophisticated deformation sequences including surface oxidation and heat treatments. After a number of steps, a 40 micron thick tape was formed. This tape is the basis for the final spring, which has to be mounted in the watch by specialists. The whole process is very time consuming, but the result, a new nonmagnetic time spring with excellent metallurgical properties, was the reward. Several patents were submitted by Rolex, who has reached the strategic goal: today, most Rolex watches have our time spring. I got the number two of the new prototype watches. However, I keep it at home because it's too heavy for me (200 grams!). My watch is not cheaper than a Rolex (a Blancpain), but it is simpler and three times lighter. The whole collaboration with Rolex lasted 5 years and finished in 2001.

Hochheiser:

Right, the project was finished.

Flükiger:

Yes, for me it was finished.

Hochheiser:

Now it's an issue of production.

Flükiger:

That is something else, yes. But many of the deformation steps for this successful development are the same ones as for tapes based on Bi-2223 tapes and for wires based on Nb₃Sn or MgB₂.

Hochheiser:

Right. [Laughter] I wondered, how does that fit in with his work? Now I know.

Flükiger:

NbZr is a superconductor. Everyone with a Rolex has thus a superconductor in his watch but doesn't know it! The reason is that the superconductor properties are not used, only the anomaly of the elastic modulus at room temperature.

Hochheiser:

And meanwhile while you're doing this you're continuing the work on Bi-2223

Flükiger:

Bi-2223, right. Three people of Rolex worked all the time in the same laboratories in our institute as the other members of my group. A problem consisted in maintaining the whole spring development work as a secret. We succeeded, surprising the Rolex managers, who initially claimed that it would be impossible to maintain secrets in a university laboratory. I must say that the possibility to maintain secret a development was the key for a number of other industrial projects in my group.

Hochheiser:

And as a professor were you also training doctoral students?

Flükiger:

Oh yes. In my career, I have directed the PhD theses of 25 physicists. My present Ph.D. student will finish at the beginning 2015. I had quite an intense life with that, but I must say that the work with Ph.D. students was maybe the most interesting thing of my whole career. When you meet these young men or girls the first time, they do not anything about their future subject. But after three or four years, at the end of their work, they know many things better than you.

Hochheiser:

Her name?

Flükiger:

Tiziana Spina, she's an Italian, in the last year of her thesis work (she works at CERN, but will submit the thesis at the University of Geneva). A few years ago, she didn't know anything about superconductivity, but yesterday, she gave a marvelous talk here at the ASC conference. And that’s the pleasure of a professor, to see how their knowledge continues to grow. You give a lot to these young people in their first years, but then it comes back: they contribute with their ideas and knowledge to the work of your group: that's the reward. I love that. It's good for you to deal with young people and to take part of their lives. I am now 75, I don't know if you remarked that [Laughter]. I work exactly as I worked, say, 40 years ago, only my face has changed. At CERN I'm leading a whole activity, and still feel young at the daily contact with these young researchers.

Hochheiser:

How has your work with BISCO 2223 evolved? You’ve been working on it for many years.

Flükiger:

Bi-2223 was indeed one of my subjects during almost 10 years. I can say that my group was among the top research laboratories. At the EUCAS conference in Veldhoven (Netherlands), our contribution was awarded as “Best Paper”. The author of this paper was Dr. Yibing Huang, who is now responsible for the fabrication of Bi-2212 wires at OST (Oxford Superconducting Technology), USA. The development of Bi-2223 tapes in my laboratories found an end almost 7 years ago: the Japanese company Sumitomo developed a new technique based on a large high pressure/high temperature apparatus requiring large investments, their wires having critical current densities much higher than ours. With our limited means, we could not compete anymore. A further reason was the strong anisotropy of J_c at 77K: if the field is applied parallel to the tape, the latter can carry high currents up to very strong magnetic fields. However, a field applied perpendicular to the tape surface, a field as low as 1 T is sufficient to destroy superconductivity in the tape. This problem still subsists, even after intense research activity in many laboratories. It follows that at 77K, Bi-2223 tapes cannot be used for magnets, the only possible application being in current carrying cables. At low temperatures, e.g. 4.2 or 20K, the anisotropy of J_c is much smaller, and there is still a market for Bi-2223 tapes.

Hochheiser:

What is the market for that?

Flükiger:

With the exception of cable applications at 77K for Bi-2223 cables (example: the superconducting 1 km cable in Essen (D)), there is a market for magnet applications at low temperature. At 4.2K, the current carrying capacity of Bi-2223 tapes is lower than the competing HTS tapes based on YBa₂Cu₃O₇ (yttrium barium copper oxide). But this handicap is more than compensated by the considerably lower cost of Bi-2223 and the possibility to produce much longer tape lengths, exceeding 2 km.

Hochheiser:

I also noted some work on a related compound, Thallium 1223.

Flükiger:

My group participated in a European project having the goal to investigate the possibilities to prepare Tl-1223 tapes with high critical current densities. This material looked extremely interesting, its transition temperature being as high as 120 degrees Kelvin. Unfortunately, it's an extremely complex material and we did not succeed, the J_c values of these tapes being more than one order of magnitude below those of Bi-2223. Other laboratories also failed in producing high quality Tl-1223 tapes, no solution being found to the weak link behavior between neighbor grains. This difficulty arises from the fact that the last layer of a HTS grain is insulating, thus constituting an obstacle for the transport of supercurrents. The situation is very different in MgB₂: you can just press MgB₂, powders together, and current transport is possible.

Hochheiser:

Which I guess brings us, so then you moved on from Bi-2223 to magnesium boride.

Flükiger:

Yes, when MgB₂ was discovered in 2001, my laboratory was already well equipped for the development of wires based on powder metallurgy. We started right away and were in 2002 the first group who published critical densities above 10⁶ A/cm² at 4.2K in MgB₂ wires. In the following, several new techniques were introduced, but we managed to remain at the top of the developments: this is also the reason why I was invited to give the Plenary talk about the progress in MgB₂ just two hours ago at the ASC conference here in Charlotte.

Hochheiser:

And how has that worked progressed? What have you accomplished in your and your group's work on MgB₂?

Flükiger:

In the first step we used the so-called “ex situ” technique for the MgB₂ wire fabrication. However, since the critical current densities obtained by this technique were somewhat limited, we changed to another technique, called “in situ”, where the reaction to MgB₂ occurs at the end of the wire deformation process. In addition to the wire fabrication processes, a good part of our work was also dedicated to the study of physical properties, by means of low temperature specific heat and magnetic relaxation. By specific heat it was possible to visualize the homogeneity of the MgB₂ phase in the wires. Our magnetic relaxation measurements revealed in 2005 that MgB₂ wires could be used in magnets operating in the “persistent mode”; today, this property found an application in MRI (magnetic resonance imaging). I realize that maybe my biggest accomplishment in this field was a consequence of the observation that the MgB₂ grains in the filaments were packed with a too low density, with = 50% voids. The idea was: “Well, if you apply pressure on the wire, there will be more contacts between the grains and the critical currents will be higher”. However, how to apply high pressures on a wire? First experiments with flat tapes revealed that pressures as high a 1 GPa (Gigapascal) were necessary to obtain a sizeable effect. However, a market for industrial applications requires a wire rather than a tape configuration. I constructed a machine based on four different anvils which were simultaneously pressing against each other. After deforming the round wire into a square one, the wire was submitted to the quasi-hydrostatical pressure exerted by the four anvils. The operation was a success, the critical current density of our wires at 4.2 K degrees being enhanced by a factor of two, at 20 K by a factor of four (2008). This was really exciting, and we continued the study, the question being whether it was possible to transform this result into a machine for the production of long wire lengths for applications. For this purpose I applied the same principle using a 20 ton press which was available in the laboratory and constructed a new machine. Four different anvils push simultaneously against each other all few tenths of a second. Between two pushes, the wire is travelling, the displacement length being equal to the anvil length, resulting in long lengths of wire after a certain number of pushes. This patented procedure yielded quite exciting results with the highest critical densities reported so far (2009).

Here I must make a personal remark. The just mentioned results were published 2009, while my official retirement date at the university was 2005. Fortunately for me, the department had serious difficulties in finding a successor, the development of new superconducting materials for applications being a very special domain requiring a combination of fundamental and applied physics. As a consequence, I got from the rector of the university the right to act five years longer as an ordinary professor, but with a small difference: without salary. Since I had already my pension money, in addition to the honorarium from the ongoing collaboration with a Swiss company working in the superconducting field (Bruker, Fällanden), I had almost the same salary as before so I enthusiastically accepted the opportunity. In the retrospective, I see that it was a win for the University, but a much bigger one for me, who loves the scientific work. This explains why I was still responsible for the applied superconductivity group in Geneva up to 2010. The number of my publications in these 5 years was somewhat reduced, since I had no access anymore to various funding agencies.

CERN

At that time, CERN was looking for somebody willing to work with high energy irradiations of superconducting wires in view of the next accelerator, the LHC Upgrade (LHC: Large Hadron Collider)). I took profit from my 30 years old experience with neutron irradiation of Nb₃Sn wires and could convince them that I was the right person. Since 2010, I am now active at CERN as an Associate Researcher (At CERN, one cannot be engaged full time after 65). As an Associate, I can carry out my research as a full member. I have no signature for funding nor for the engagement of people, which I do not feel as a handicap. I'm responsible for the study of the effect of irradiation by several high energy sources on the superconducting properties of Nb₃Sn and MgB₂ wires in the quadrupole magnets of the LHC Upgrade, which will be operational around 2022. The radioactive load in will be much higher than in the present LHC accelerator. Since the magnets will get radioactive, one has to move many installations from the magnet location, at a depth of 100 meters to the surface. A high current cable has to be developed which can carry a current of 20’000 Amperes to the magnets. These quadruples are made of Nb₃Sn, a material I know very well. My task consists in estimating the effect of the total radiation load on the magnets during the accelerator life time (~ 10 years). In other words will the quadrupoles survive the life time of the accelerator? This is what I’am doing at present; I don't know if I should go further in the details, the field being quite complicated.

Hochheiser:

Let me put it this way, yes you should but we need to stop for a minute because I need to change the tape.

End tape 1; begin tape 2.

Hochheiser:

We're going to continue on with your work at CERN.

Flükiger:

At CERN the LHC accelerator is an extremely complex, large scale installation. The next step, LHC Upgrade, will even add to the complexity. You don't have only neutrons; you have also protons, ions, photons, and finally gamma rays and electrons. These are five different kinds of irradiation with very, very high energies. They are produced simultaneously after the proton-proton collisions at 14 TeV (tera electronvolt). The magnets are 35 meters away from the collisions, but are still exposed to quite a large radiation load which has been calculated by my colleagues and which constitute the baseline of my studies. Unfortunately, there is no installation in the world where I can simultaneously study all the five energy sources, so I have to study all of them separately. The neutron irradiations were done in collaboration with the group at the Atom Institute (ATI), in Vienna (Austria). The proton irradiation work is still going on, in collaboration with the Kurchatov laboratory in Moscow, as well as with the cyclotron in Louvain-La-Neuve in Belgium. The measurements are performed partly at CERN and partly at Kurchatov: it's a complex program. A Ph.D. student, Tiziana Spina from Italy, is working with me at CERN in this field. Our first result is that in spite of the fact that there are 30 times less protons than neutrons, the damage caused by them is comparable. The present results suggest that the magnet will survive the expected 10 years of lifetime of the accelerator. But we need more indications; as you know the financial investment for the accelerator system is enormous and we should really be sure that all effects have been taken into account. A particular care has to be given to the irradiation by charged particles, as protons and pions: along their penetration path in the material, their energy slowly decreases up to a given point where all the remaining energy is suddenly lost in a restricted area, the effect being generally called the Bragg peak. This effect is today used for cancer therapy: A proton irradiation treatment can be applied on a patient having a localized cancer. In contrast to X-rays, which just kill everything along their path through the body, protons can be adjusted to undergo the Bragg peak precisely in the cancerous region, the region behind it being not damaged. Now you understand why today, proton irradiation is getting more attention in the treatment of cancers. In the Bragg peak regions inside the quadrupole magnets, the energy is locally lost, thus inducing a local decrease of the atomic order and thus of the transition temperature and possibly also of the critical current density. Since my Habilitation work was centered on the effects of ordering, I am back in my preferred research subject! I am very excited about the further studies in this field. However, due to the induced radioactivity, this subject cannot be studied in our laboratory. We can measure superconducting properties, but the X-ray diffraction measurements and the TEM analysis have to be carried out in Kurchatov. We are now waiting for the first results, hoping that the surprises we will meet will remain manageable. That's the scope of my work.

Reflection

Hochheiser:

Now that we've gone through your career step by step, looking back how would you evaluate your career as a whole?

Flükiger:

[Laughter] Through all of my career, I had a lot of pleasure. I really love to be involved in research tasks and worked quite hard to solve the problems I encountered. About the output, there have been a number of small progresses which may have contributed to the general progress in the field. We did not display big discoveries, but think that our results contributed to some extent to further understanding. This is particularly true for our metallurgical studies at a top level, as the phase diagrams up to 2’200°C of binary systems comprising superconducting A15 phases, as Nb₃Al and Nb₃Ge, established using new methods developed in our laboratory (1973 - 1977). The variation of the properties in the stable A15 composition range in these systems as well as the studies on the degree of ordering in many A15 compounds were the basis for the understanding of the electronic properties in A15 type systems (1987).

Between 1980 and 2000, I have contributed to an improvement of J_c in industrial bronze route Nb₃Sn wires extending the Sn content of the Cu-Sn bronze to 16wt.% Sn. By means of neutron diffraction at temperatures between 10 and 600 degrees K at the reactor in Grenoble (France), I was the first to visualize the elastic tetragonal deformation induced by the matrix in Nb₃Sn wires (1985).

A very interesting thing was the introduction of high pressure treatments at room temperature to enhance the mass density inside of superconducting wires. In 2008, I have reported the first strong enhancements of J_c obtained in MgB₂ wires with the CHPD method (Cold High Pressure Densification). This method has to be considered as a pioneering process, since it has been in the meantime applied by other laboratories which extended it to wires based on other superconducting compounds, as Bi-2212 and MgB₂. It will certainly also be applied on new superconducting materials which may be discovered in future. The merit of the principle of high pressure application lies in the fact that no one of the superconductors discovered in the last decades is ductile: this means that with the exception of NbTi and Nb₃Sn, all other materials being promising for industrial application require powder metallurgical techniques to be formed in a wire configuration. Wires based on the new superconductors based on Fe-As (the pnictides), a subject about which I didn't talk today, can also only be prepared by powder metallurgical processing under room temperature pressure, too. Powder metallurgy includes automatically the presence of voids, and to overcome these voids you need pressure, which can be applied either at room or at high temperature. Now that everybody's has accepted that, it may sound strange that I had problems getting my paper accepted because the referee found this “brute force” somewhat primitive.

Hochheiser:

Were there anythings that you were working with that as opposed to satisfaction were disappointments?

Flükiger:

Well, there were not many disappointing facts, except in the Bi-2223 system: we were a leading laboratory before the interest faded away quite suddenly because of this low field in the perpendicular field direction. That meant we had to start rapidly with something else, which was somehow frustrating. That was the biggest deception.

Hochheiser:

In what ways has your field as a whole evolved over your many years of activity?

Flükiger:

Everything has progressed and in particular, what progressed today is the analysis at the microscopic and nanoscopic level. 20 or 30 years ago people just made an X-ray measurement, identified the structure and made a SEM (Scanning electron microscopy) picture, but it was not really clear what was happening in the material. Today you have many new technologies which have been developed for analyzing the conditions at the nanometric level. You cannot see the atoms directly but you can recalculate back how they look like. In a region of 10 or 20 nanometers you can get detailed information with some different kinds of very advanced TEM installations (Transmission electron microcopy). That gives us information on properties which were out of reach before. What is new is we don't fear to attack very complex problems today, also thanks to very sophisticated calculation programs. Reality is much more complex than it was years ago because at that time the limited means of observation made it appear simple. I have learned something in the past years: when sometimes people laugh about fundamental physics, saying: “Nice, but it doesn't help you for application”, I do not agree with them: my advice is that you have to do both! Since today the research in materials is performed at a nanometric level, the deeper insight in the fundamental processes helps you to better understand what you see in your material: this is a condition for a progress in applications. That combination is the key of most progresses in the last years.

Hochheiser:

In what ways, if any, have these fields become more globalized, so that the relationship between your research in Europe and research in North America and Asia has become different than it was when you were a young scholar?

Flükiger:

Asia is now a competitor and it was not there 30 years ago. It started in Japan, then came China and Korea. In the meantime, these countries are strongly promoting the research in the field of applied superconductivity. Two decades ago, China sent many young researchers to the US or to Europe for learning. These people now came back to China and their laboratories have achieved a top level. I had four Chinese coworkers in my group, and all of them made their way: three of them are professors in China: Timing Xu (Xinhua University, Beijing), Hongli Suo (Techn. University, Beijing and Xiaodong Su (Soochow University, Suzhou) and one is production manager at Oxford (OST) in the USA. Today, high level research in superconductivity in view of applications is performed in many countries, in the U.S. certainly, but also in Europe, in particular in Germany, England and Italy (In Switzerland, a strong activity is carried out at CERN, in connection with the next accelerators). In Japan, China and Korea, large funding has been attributed in the last years for developing applied superconductors, e.g. cables and current limiters. One should also mention Russia and India: both countries were included in the ITER project (ITER: International Thermonuclear Experimental Reactor). The ITER program has now seven different countries which participate and construct some of the parts: U.S., Europe, Japan, China, India, Russia and Korea.

Hochheiser:

You've been attending these ASC conferences for many years.

Flükiger:

Yes. All of them since '76.

Hochheiser:

In what ways have these conferences evolved or changed over the many years?

Flükiger:

An evolution took place, I think through the quality of the people who are in charge of the organization. The ASC conference is driven by a professional organization which takes care of the meetings, while a number of known scientists watch about the technical level of the contributions. In the last years, the criteria for the acceptation of a submitted paper have been tightened. As a member of the board, I know the organization very well; the people there are all devoted to ASC and accomplish a lot of free work. I must thank them, sincerely. The scientific level has been strongly improved: you will not find a paper which is not of high quality among the submitted ones, their number now exceeding 1,000. Last year they started a program for antiplagiarism and all the papers are analyzed to see if they were copied from somewhere. I was even co-author of one which was rejected because my PhD student copied more than 20% of his own article which was just published 1 month before the ASC conference! You could do that 20 years ago, and it has been largely accepted, but today, it doesn't work anymore. And this is certainly a point for improving the quality. Also the quality for referees and has been improved. The requirements lead to the fact that a paper accepted by the ASC is today considered as a good paper, in general.

Hochheiser:

As you can see, we started, I started with a large stack of cards face up, now they're pretty much face down.

Flükiger:

Good.

Hochheiser:

So I ask finally, is there anything that you'd like to add that I neglected to ask you about?

Flükiger:

Oh, about my supplemental activities, I worked five years for Charmilles on spark erosion machines.

Hochheiser:

For what kind of machines?

Flükiger:

Electric discharge (or spark erosion) machines. Spark erosion is used when you want to cut a piece of tungsten carbide, one of the hardest materials on earth. What do you do? Perhaps you don't know. Okay. Cutting by electric discharge consists in approaching a fine Cu wire to the surface of your working piece and to provocate a series of small discharges on the Cu surface in a dielectric liquid. It's like a small lightning, with the difference that these ones have the size of a cubic micron or even smaller. Then you have 20,000 degrees at the location of the discharge: approaching it to the sample, you will melt away a large number of very small parts of it: the Cu wire will now go down through the superhard tungsten carbide piece like through butter. Complex metallurgical processes take place during this process: since the spark temperature is so high, the sample surface will locally melt within a very thin layer, but will be cooled by the dielectric liquid, with the consequence that the quenching rate at the sample surface is of the order of 1,000,000 degrees per second. This rapid quenching induces structures which are unstable and which cause some dendrites and from the dendrites you can say how fast the cooling was. This technique is widely used worldwide; Charmilles Switzerland being the market leader. Unfortunately, the ultra-rapid quenching causes the formation of nano-crack at the sample surface, and thus cannot yet be used in aeronautics. We had a project to reduce or even to fill up these nano-cracks. I was involved in this work, but had not enough time to solve all problems. But at least, in the five years of collaboration with Charmilles, we have contributed in accelerating the spark erosion cutting process. This was the result of better understanding of the fundamental processes occurring after the discharges.

Hochheiser:

Anything else you would like to add?

Flükiger:

I don't know. We have talked about many things.

Hochheiser:

I think we have. Well in that case, I think we're finished. I thank you for your time and for sharing your recollections of your career.

Flükiger:

Thank you or listening and for the excellent preparation of the interview. I think I am quite surprised that I still remember everything. [Laughter] I have a very good memory.

Hochheiser:

I noticed.