Oral-History:Michael Green

About Michael Green

Michael Green received a B.S., M.S., and Doctor of Engineering, all in Mechanical Engineering, from the University of California, Berkeley, in 1962, 1964, and 1977 respectively. He is a licensed mechanical engineer in the State of California; holds a patent (US patent No. 5131488, issued 21 July 1992) for a variable wave form, variable frequency, variable phase, down hole seismic source for use in old and gas exploration; and has approximately 400 papers to his credit. Green has been elected as a full member of the International Academy of Electrotechnical Sciences (Moscow, Russia) and he has served on the board of the IEEE Council on Applied Superconductivity since its founding.

In this interview Michael Green discusses his education and career, especially his posts at the Lawrence Radiation Laboratory, Kernforschungszentrum Karlsrue, Lawrence Berkeley Laboratory, and Oxford University.

About the Interview

MICHAEL GREEN, An interview conducted in 2014 by Sheldon Hochheiser, IEEE History Center, Hoboken, NJ, USA.

Interview #563, for the IEEE History Center, The Institute of Electrical and Electronics Engineers, Inc.

Copyright Statement

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

Interview

INTERVIEWEE: Michael Green

INTERVIEWER: Sheldon Hochheiser

DATE: 11 August 2014

PLACE: Charlotte, North Carolina

Introduction

Hochheiser:

This is Sheldon Hochheiser of the IEEE History Center. It's Monday, August 11th, 2014. I'm here at the ASC conference in Charlotte, North Carolina with Mike Green. Good afternoon.

Green:

Good afternoon.

Hochheiser:

If we could start with just a little background, where were you born and raised?

Green:

I was born in San Jose, California. After that, I was raised in the New Idria Quicksilver Mine in San Benito County, California, seventy miles southeast of Hollister California, on mostly dirt road. I lived there until I was ten. Then I lived in Los Gatos, California for six months. Then my father became an Oldsmobile dealer in Santa Cruz, California, so I lived in Capitola for five years. However, being a car dealer in the early 1950s during the Korean War was not a good thing, particularly if you were an Oldsmobile dealer and you had the Hydramatic transmission plant burn down and a steel strike and all of that stuff. I ended up back in Los Gatos where I graduated from high school in 1957.

Hochheiser:

Were you interested in science and technical things as a youth?

Green:

I knew what I was going to do when I was ten. As a kid I used to explore old mine tunnels. My father taught me how to tell whether a tunnel was reasonably safe to go into. I loved things like rattlesnakes. I loved things like rocks, so I had a rock collection. I knew geologists. I knew mining engineers. I loved going into the furnace as a kid and dipping my hand in liquid mercury up to my arm pit, so my excuse for becoming a scientist is I grew up in a mercury mine. It's true, I grew up in a mercury mine and that's why I became a scientist. It helped that I was dyslexic (I didn’t know that until I was 20 years older.), so I wasn't good at things like reading and writing and spelling. I went to a one-room school for the first four years and learned eighth grade math by the time I was in the fourth grade. I knew how a bill became a law and I knew all of the states and the state capitols, but I couldn't read and I couldn't write very well. My penmanship was lousy. This kind of nudged me into the sciences anyway.

Education at UC Berkeley

Hochheiser:

What led you to Berkeley rather than some other school in California?

Green:

I went to Berkeley mostly because my father did. My family is one of those families in California that has graduates of both Stanford and Berkeley. My grandfather graduated from Berkeley in 1892 and he never went to high school. He was an Irish kid from San Francisco and he had a propensity for the medicine and that sort of thing, so he went straight to pharmacy school without ever going to high school and became a Berkeley graduate and eventually a pharmacist in Los Gatos, California. Another part of my family went to Stanford. My father was a second generation Berkeley graduate. I applied to Stanford and I was admitted. My father said there's no way in hell you're going there. He couldn't afford it anyway. I went to Berkeley as was preordained, and I'm a loyal Golden Bear. I still give my Stanford friends a bad time, but it's a friendly rivalry between two great universities.

Hochheiser:

Did you go there with a plan to major in mechanical engineering?

Green:

No.

Hochheiser:

How did you end up there?

Green:

Well, I went to Berkeley planning on majoring in physics. In high school, I was a Westinghouse [Science Talent Search finalist]. I was second or third in northern California. I was really into rockets. The television wanted some of us on TV. This guy in my high school and I were second and third in the state, I don't know which order we were. We weren't the top one, but we were close. We decided that since we were both building rockets together, we would talk about that rather than talk about Foucault pendulums and trees of the Santa Cruz Mountains, so we did a demonstrations of rockets on TV. That led to more than one television show, the last of which was “Ask the Professors.”

There were two professors from Berkeley by the names of Anthony Oppenheim and Edmund Laitone who were aeronautical science professors. We were asking them serious questions about fuel-to-oxidizer ratios and how solid rockets worked because we were interested in getting our rockets to go up further, which was a very explosive thing. We were doing firsthand experiments with fuel and various chemical mixtures some of which were explosives and some of which actually made good rocket fuel and others that completely fizzled altogether. These professors remembered that TV show and I ended up getting into graduate school in Berkeley because they remembered that TV interview.

I started out in physics. I was really interested in physics. I wanted to go into particle physics or nuclear physics. My problem was I couldn't pass German. German as well as English were requirements. I took bonehead English and I hadn't started the English requirement yet. Then I took German and flunked it. Then the dean of Letters and Science at Berkeley said, “If you don't pass German, I'm going to kick you out. It doesn't matter what your grade point is.” I put my hands up and thanked God that this was an omen to go into engineering which didn't require any English or any foreign language.

So, I lost a year, but I became a mechanical engineer with an emphasis on aerodynamics of fluid mechanics and heat transfer. That turns out to be a good combination when you're dealing with cryogenics and things of that nature. I was going to work in the aerospace industry and I had a number of job offers when I was getting my master's degree January of 1964. However, John F. Kennedy was assassinated and Lyndon Johnson became the president. Within two months of the assassination of John F. Kennedy, there were no jobs available in a place that I wanted to work. I didn't want to go to Texas, Louisiana, Alabama, or Mississippi. In March 1964, I took a temporary job at the University of California Radiation Laboratory [UCRL], which later became the Lawrence Berkeley Laboratory (LBL). I'm still associated with LBL fifty years later as a retiree now. I still write papers for them without pay.

Lawrence Berkeley Laboratory

Hochheiser:

When you went to Lawrence, you thought this was just going to be a short-term job?

Green:

That's kind of what I thought. I remember what I was doing when Kennedy was assassinated. I was sitting at the Radiation Laboratory library on the hill, working for a professor trying to get together materials for a civil defense course that would be related to nuclear explosions and that sort of thing. I was there listening to the reports of the president being assassinated, not knowing who did it or any of this stuff. I said, “Oh my God”, because the Cuban Missile Crisis had been the previous year. I'm sitting there reading classified documents about 5-megaton bombs and all of that kind of stuff, which I probably shouldn't've been reading, but I was reading them and I was helping with this course material. This guy said why not come to work for the lab, so I did. I interviewed in mechanical engineering, but they told me they weren't hiring. Then a week later I got a job offer. I worked most of my career at LBL. I was involved in particle physics. I loved that, but I also loved all of the adjunct stuff, one of which happened to become superconductivity and cryogenics.

Superconductivity Research

Hochheiser:

How and when did you first become interested in superconductivity?

Green:

Literally a year after I started working at LBL, I was asked to look at thin septum magnets. These are magnets where you've got a kicker and you kick the beam from one side of the septum coil to other. You have to kick it across the septum. Could we use superconductivity to make a magnetic field, with a very thin, conductor in it? I wrote a paper on it in 1965. It's a terrible paper. That was one of the first papers I ever wrote in the field. I also wrote about stability issues and how we could make one of these magnets more stable and other things. Then, of course, I went and worked part-time for the superconductivity group. I built my first superconducting magnet in the fall of 1965 and had that wonderful feeling that all people in superconductivity have. You say, “Oh my God, the resistance really did go to zero. You can't measure it.” It still sends a chill up my spine every time I cool down a magnet and all of a sudden the resistivity slowly goes from a flat so many ohms and then drops to zero.

Hochheiser:

Was this first magnet part of a larger project?

Green:

No. It was just an experimental magnet that was testing a conductor that was built by James Wong of Supercon. It was called 15-30 conductor. It was 30 mils of copper with a 15 mil single core superconductor down the middle. We insulated it with Ebonol (a copper oxide insulation). You could get the cooling through the Ebonol much better than an organic insulation and there was just enough copper to be stable, not intrinsically stable, but dynamically stable. This was a material you could take up to short sample in a magnet. It was a pretty good conductor; 1,200 amps per square millimeter at 5 Tesla, which in those days was phenomenal performance. I built a magnet a single-layer magnet that was wound on a tube six inches in diameter made of phonolic resin plastic. We wound this coil and we powered it up with a truck battery through a pair of copper tube leads that were gas-cooled. We couldn't run the magnet very long because the acid in the battery was boiling, but that was my first superconducting magnet. Then I got involved in a whole bunch of programs. They were all basically physics-related. I did the first measurements that I know about of magnetization and the effect on magnetic fields in a dipole.

Hochheiser:

When was this?

Green:

This was late 1969 or early 1970. People didn’t believe me when I told them that I thought it was superconductor magnetization. They said oh, no, no, it's magnetization of the stainless steel. I said no, no, no, this doesn't behave like magnetization of the stainless steel. Magnetization of the stainless steel would be the same even after the magnet went normal and you measure it. No, was different. The measured magnetization field went up as you put current into the conductor and it changes when you brought the current back down in the conductor. If the superconductor goes normal, it disappears. You have the small residual magnetization from the stainless steel. It took me a long time to convince people that it was, in fact, magnetization of the superconductor. I finally wrote a paper concerning that in 1971. I wrote a number of engineering notes. It wasn't a perfect theory, but it became the basis of a number of papers that I wrote on magnetization of superconductors. I wasn't a physicist, so I didn't know much about this. But, I was using doublet theory, basically magnetization in a filament of superconductor is one current that's going this way and one current that's going that way and there's a distance between them and that's a current doublet. It has a very different field structure, such as excessive sextapole, decapole, and multipoles found in a symmetric dipole. There was a dipole term, too, but it was very different than the behavior of a single current going through that wire. I worked with people in Europe at CERN and other places on how you get rid of that effect if you're going to actually build useful superconducting magnets for accelerators. That was in the early 1970s when I was working in Germany.

Hochheiser:

Let's step back a little bit before you talk about Germany.

Green:

Yes.

Accelerator Design Research

Hochheiser:

I noticed that from fairly early in your career you were part of a group working on a 200-billion electron-volt accelerator design.

Green:

Yes, it became Fermilab [Fermi National Accelerator Laboratory]. Edward Lofgren and Edwin McMillan wanted this project for Berkeley. Lofgren, was the head of the accelerator group at Berkeley, was the head of the project. McMillan was the director of the Lawrence Berkeley Lab. Lawrence died and it had become the Lawrence Radiation Lab at that point. They wanted to build the next generation of accelerators. AGS at Brookhaven had opened up in 1965. That was about 35 GeV and this was to take proton accelerators up to 200 GeV. They wanted to build it in the Livermore Valley. Our plans were all based on that, but then politics got involved. The Midwesterners had been denied MURA. Dirksen [Senator Everett McKinley Dirksen of Illinois] was on one side and Mayor Daley [Richard Joseph Daley] on the other side, and a bunch of Midwestern congressman and senators decided this had to be opened up to the whole country. Due to the politics it went to Batavia, Illinois. Robert Wilson, who, in fact, was a graduate of Berkeley and one of Lawrence's graduate students, decided he would build the machine in a very innovative way, far different than the design our people proposed. Wilson ended up building Fermilab as a separated function machine where the dipoles are pure dipoles and the quadrupoles are pure quadrupoles whereas the AGS and other machines at CERN [the European Organization for Nuclear Research] were built with shaped pole magnets that had both quadrupoles and dipoles built into them.

Hochheiser

Right. What part in the project were you doing while it was still in Berkeley?

Green:

I worked on what was called the booster accelerator. It was a machine that was similar to a machine that was at DESY [Deutsche Electron Synchrotron] in Germany and another one at the Daresbury Laboratory in England. In the U.S. it was a 60-hertz machine. In Europe it was a 50-hertz machine. They were built with transformer steel and you had to deal with the magnetization effects in stainless steel and in the transformer steels as well. We developed the codes for shaping the poles and then we developed ways of trying to account for the magnetization of the steel and what it might do to the quality of the field. My first job literally was to come up with a design for a mechanically tuned RF cavity for energies up to 200 MeV, so this is definitely non-relativistic for protons. It had to tune over a 2:1 ratio. We ultimately ended up using ferrite, but this was one of the alternative designs. My first paper published, “Transactions on Nuclear Science,” in 1965, was on this, basically a loudspeaker coil tuned cavity that would run at 60 hertz. In later years, I found out this was a good idea.

Hochheiser:

This was not superconductivity?

Green:

No, no, this was before superconductivity.

Hochheiser:

That's what I gathered, but I just wanted to double-check.

Superconductivity Research Projects

Green:

Well, my first paper in superconductivity was, written for the first Magnet Technology Conference, which was at Stanford in 1965. I did not go to the first Applied Superconductivity Conference, but I went to the second in 1967, and, of course, I got really involved in superconductivity. I wrote a couple of paper for the Brookhaven Summer Study in 1968, which is where everything sort of jelled and came together, including the whole concept of multi-filamentary and twisted conductors. Most of that work had been done in Britain.

Hochheiser:

Did you spend a period of summers in Brookhaven?

Green:

No, I only was there for one summer study. It was six weeks long.

Hochheiser:

One summer?

Green:

I was there for two or three weeks. I went to a number of different sessions. I gave talks at a number of sessions. This led to more work toward building accelerator dipoles and quadrupoles. I worked with Bill Hassenzahl on a quadrupole from Los Alamos. I worked with various people in Berkeley. We started looking at superconducting accelerator designs and, at some point, I was asked by Werner Heinz whether I would come and join the group at Karlsruhe, which was a brand-new group in Germany.

Hochheiser:

Did you go to Karlsruhe? Did you take leave from Berkeley?

International Superconductivity Research

Green:

I took what started out as a year-and-a-half of leave and ended up being away from Berkeley for two years to work at Karlsruhe. I didn't have my Ph.D. yet, so what were the Germans going to call me? They gave me the title of Dr. Physiker, which meant I got paid more, which was good. I didn't have a doctorate, although most people thought I did. I had enough knowledge in the field, so I suppose I could've had one, but I hadn’t earned it yet. I was taking course work part-time after my master's, so I didn't get my doctorate until 1977.

Hochheiser:

What did you do at Karlsruhe? Were you a part of the group at this new institution?

Green:

Yes, I was part of the group. I was on a machine design committee that was organized by Hans-Otto Wüster at CERN. He later became a director general of CERN. He liked Americans because he had been a German POW during World War II. He was captured as a young man in Normandy and sent to a POW camp where he learned English. He was an interesting guy. For a while, he headed up JET, a fusion project in England. I also worked on a committee on the magnets and the magnet problems, which included superconductor magnetization.

Hochheiser:

This was a committee from a number of institutions?

Green:

Yes, CERN, CEN-CEA Saclay in France, the Rutherford lab in England, and, the Institute fur Kernphysik IEKP at the Kernforschungszentrum Karlsruhe (KfK), a nuclear research center [established in 1956]. They no longer call it that. It's Karlsruhe Institute of Technology (KIT) now. It's closer with the university now than it was then, It is still a separate lab that's about thirteen kilometers north of Karlsruhe. [KIT was created in 2009 by the merger of the University of Karlsruhe and the Karlsruhe Research Center Forschungszentrum Karlsruhe, a national nuclear research center (Kernforschungszentrum Karlsruhe, or KfK).]

Hochheiser:

What were these two international committees trying to achieve?

CERN

Green:

What they were trying to achieve was CERN had a very good idea of how they wanted to upgrade the SPS.

Hochheiser:

The SPS?

Green:

This was the super proton synchrotron. It was a machine that was like Fermilab and they were talking about upgrading it. They were trying to talk about whether to take the magnets out and put in superconducting magnets. Those of us on the machine design committee thought this idea was absolutely nuts. We were right, but, you had to convince some very high-up people in the European physics community and some thirty-year-old was not going to do that. I was part of a distinguished panel that looked at that issue because I had started looking at designs for superconducting accelerators in the 1960s. We came up with the obvious solution that you have the SPS as an injector and you go into a superconducting ring and you double the energy like they did in Fermilab, but that wasn't really done until later at CERN. We ended up with a competition between the three labs, Karlsruhe, Saclay, and Rutherford, to build a magnet, a 1-meter long dipole.

In Germany this was a political problem because Siemens felt that they should be getting the money to do this and that German industry should do this. “Fine”, said the Ministry of Science or Physics, I don't remember what ministry it was in those days, so they gave Siemens a bunch of money to build one of these magnets with the proviso that we at Karlsruhe were supposed to share everything we knew with Siemens. The professor I was working for asked, “What do you think about this”? I said, “We'd be crazy if we did it, because you don't want to share your information with somebody who's out to cut your throat.” He agreed.

We had to be part of a collaboration with Siemens, but we didn’t share every bit of information we had. Siemens was proposing a superconductor that was like a shoelace. It was a woven fine filament conductor. We were proposing a stiff cable conductor. We didn't propose a Rutherford cable, but we proposed another kind of cable. We decided that we had to make certain compromises. First of all, on the machine design side, I knew that they were never going to build a fast-cycling machine. One of the requirements for the dipole was it had to go from 0 to 4.5 T and back to 0 in 2 seconds. This was nonsense from an accelerator standpoint. It had to go to 4.5 T. It had to have a required field uniformity of 1 part in 100. Since I was on the machine design committee, I strongly suggested to the professor that our goal should be going up in 15 seconds and coming down in 15 seconds, it should also go to the 4.5 T full field, and the field uniformity should be at 1 part in 1000, because it was becoming very clear at that point the field uniformity was an important issue. That was our goal as we built the magnet.

The French decided that the short pulse time was ridiculous, but they said that a 10 percent field uniformity was good enough. I don't know why they said that, but they did. The British stuck to their guns because they're the ones who set the original standards, so the British magnet was 1 part in 100 field uniformity. It went up to 4.5 T in a second and back down in a second. It didn't go much more than a pulse up and pulse down, but it did generate 4.5 T. In Karlsruhe, it got to full field in the time that we had allotted. We did achieve a field uniformity of better than 1 part in 1,000, except for a systematic 3 part in 1000 quadrupole error that may be due to the placement of the measurement coil in the magnet bore. It was realized that that was really more important than anything else by that point. The Siemens magnet went to 2.9 Tesla once but never any higher, but you couldn't pulse it at all and the field uniformity was terrible. As a result, Karlsruhe ended up getting a lot of the fusion research work in Germany.

Siemens’ nose was pushed out of shape because we hadn't exactly shared our design with them, and, of course, they complained bitterly to the government that we were not using the Siemens superconductor, which was Vacuumschmelze at the time. I told the professor that we should buy the best superconductor you could get; the best superconductor in the world at that time was being made by Imperial Metals Industries in Birmingham England. The second-best conductor was being made in the United States. The Germans clearly couldn't buy the American conductor, which was cheap, so they bought IMI conductor, which was more expensive. It was a good conductor and it was stable; that was what was really important for our magnet.

I worked with a good group of people; some really great guys. I learned to speak German and I learned to play cards in German because if you were in Europe, except for trips to England, you didn't fly. You took the long train trips, so drank beer and played cards while you were on the train. This was the German way.

Hochheiser:

Did you notice any differences in style between the research groups in America and the research groups in Germany?

Green:

There were some differences. In the research groups in Germany, if the professor expressed a view, everybody in the group went with the professor. This was even truer in France. England was more like the U.S. In fact, in France at that time, you almost couldn't go to the loo [restroom] without asking somebody's permission. At least that was my feeling. The French actually have loosened up over the years. They have become much more like us because of their working with a lot of people in CERN and all of that. Things have changed in France immensely. The British were very much like us and I found that the Germans were very much like us in a lot of ways, too. We could speak the same language. I just had to be very careful about how I interacted with people in the group. In time, I was on a first-name basis with the professor, but nobody else of the group knew it because it was agreed that it was not my place to call him by his first name except in private because that implied a different relationship. I knew if he had made up his mind, the only way you were going to change it was privately. Then it would be his suggestion that we make the change this way. That kind of diplomacy was something that I really had to learn. Of course, with your colleagues you could make suggestions, but you had to be very careful to understand that their views would change immediately if the professor said otherwise. Since then Germany has changed a lot, too.

Hochheiser:

Did the synchrotron get built using the magnets you've been describing?

Green:

Ultimately yes. I ended up working with a graduate student of Prof. Werner Heinz by the name of C. H. Dustmann. He ended up working for Brown, Boveri [BBC] in Mannheim, West Germany. In the late 1970s, he sent me a letter and suggested that I call him. He wanted me to come to Germany and talk to him about magnet design for a machine that was going to be built at DESY. At the time, I was really into cold iron magnets, using the iron as part of the support structure to carry the magnetic forces. You could put in stainless steel collars between the coil and the iron, but the iron had to be cold. This is what Fermilab was doing except that Fermilab had warm iron. I was proposing the collars, the iron, you bring everything in. The collars provided the space, so you didn't saturate the iron too much. I went to Mannheim, talked to him, and we came up with a proposal. He wrote it up for his company. It was submitted to DESY, Deutsche Electron Synchrotron, at Hamburg for the HERA machine. The opposing company was Siemens, which was interesting. They were proposing a magnet that looked very much like the Fermilab energy-doubler magnet. It was very clear that the BBC design would be a lot cheaper to build and had a lot of potential, so it was suggested by DESY that Siemens build a magnet and BBC build a magnet. Both companies built their magnets. The BBC magnet was markedly better; with better in field uniformity and the whole bit. By that point I understood a lot more about magnetization and I knew how we could adjust for this and all of that sort of thing. Again, Siemens was not happy. Then, of course, the politics came into play, so it this had to be a more inter-European experimental and facility. The Italians, Ansaldo in Genoa, built half the dipoles. The quadrupoles were being built by Alstom in France. We had this interesting mixture, but I was only a consultant on the project.

Hochheiser:

Right, and this was long after your work in Karlsruhe?

Green:

It had been six or seven years.

Hochheiser:

Sometimes projects take a long time.

Green:

I think HERA was the first superconducting machine in Europe. Half the magnets were built by Ansaldo, so half the ring was Ansaldo. They didn’t even bother to shuffle the magnets. Half the ring was one type and half the other and each half had different magnetization characteristics. Each group put a magnet out. They were measuring the field in real-time and then adjusting the correction elements based on the measurements of the field in that one magnet. It worked; the machine's still running.

Hochheiser:

Backing up a bit, so your two years in Karlsruhe were done and you were going back to Berkeley.

Green:

I went back to Berkeley.

Hochheiser:

Did you bring anything back from Karlsruhe that was of use?

MHD Research

Green:

The LBL was going on a different course. I didn't really rejoin the group. I did some alternative work; I looked at MHD [magneto fluid dynamics or hydromagnetics]

Hochheiser:

MHD?

Green:

Yes. I looked at whether we should go into liquid metal MHD or something like that for topping cycles for coal. Nothing really came of it. Then I got involved with a group that was interested in geothermal, so I set up a group that would model geothermal power cycles. In the meantime, I was still working on superconductivity with the group. I also got involved in another group that wanted to build detector magnets; not the main Berkeley group focus. I was working and writing papers on geothermal energy and in superconductivity at the same time. What's interesting is that ResearchGate has never discovered my geothermal papers. It discovered other papers, which I wrote but I didn't know I was a co-author of. I was writing papers in both fields. I suggested using this code to model liquid nitrogen plants and refrigeration cycles. The code could do it. We got rid of our 7600 computers and all of the coding that was associated with it.

Hochheiser:

A Control Data 7600?

Green:

Yes, Control Data. We had a couple of 7600s. The lab would not pay to convert the codes over to a more modern machine and so they died. These codes would optimize a thermal cycle of some sort in 12-dimensional space. We were using Minuie, a CERN optimization code, and a number of other things. I could design a multistage refrigerator, the whole bit, with this, as long as I had good fluid properties. I was doing that and superconductivity, so I got involved in what became the PEP4 project.

Dissertation on Superconductivity

Hochheiser:

Somewhere along the line in the 1970s you managed to complete an academic degree.

Green:

Yes, I managed to get a doctorate and my thesis was on superconductivity.

Hochheiser:

What exactly was your thesis about?

Green:

I proposed writing about, a series of test coils that we'd built. There were two 1-meter diameter coils and there were 2-meter diameter coils that were leading to a detector magnet. My thesis advisor says well this sounds interesting, but I would have to get someone from LBL on the committee who knew what I was doing.

Hochheiser:

Who was your thesis advisor?

Green:

My thesis advisor was Edmund Laitone, at Berkeley. He was a fluid mechanics engineer and got his Ph.D. at Stanford after the World War II. He worked for the aircraft companies during the war. He could tell you all of the stories about why certain aircraft in the United States’ military didn't fly very well. He said I think you should go for a doctor of engineering because your thesis doesn't sound like it's got enough original work in it. I didn't care one way or another whether it was a Ph.D. or a Doctor of Engineering. Berkeley is one of the few schools in the country that gives a Doctor of Engineering, so I went that way.

When he finally read my thesis, he said you've come up with at least two very original ideas here. It could've been a Ph.D. thesis. The two ideas had to do with using a shorted and a secondary as a way of quench protection of a thin solenoid magnet where I'm operating the superconductor at current densities of about 650 amps per square millimeter. In fact, we built one magnet that ran at 1,250 amps per square millimeter. That was a low field magnet. It was unheard of to be able to safely quench a magnet with that kind of current density in it. I did it through a process that I coined as quench-back. Basically you form a shorted secondary in the magnet mandrel and that quenches the whole coil. We also came up with a lot of other schemes that involved using varistors and some other things where we could quench the coil rapidly. One method was discharging a large capacity at say 450 V into the center tap in a two-layer coil. We could quench a coil in something like, 30 microseconds. I'm talking about a big coil. It behaved like a delay line. We actually used that method on a magnet. It turned out to be far more expensive than we thought it was going to be, but we used it. The second thing was the concept of using two-phase flow for helium instead of single-phase flow.

This all came out of an experiment that I reported on at the 1971 particle accelerator conference in March of 1971 (before I went to Germany) It was published IEEE Transactions on Nuclear Science in 1972 I think. I ran a potted coil (potted in wax) with tubes around it and I set it up so that I could run it with either super-critical helium or two-phase helium. It ran better with two-phase helium.

Then I began to look at what we had to do to make it stable. I came up with a concept of using a control dewar to shift the helium entering the coil from 60% gas and 40% liquid down to 0% liquid. It turns out that you could run long lengths of two-phase flow over a garden hose without any oscillations as long as you put yourself in the right place in the Baker diagram. The Baker diagram, of course, came out from Ovid Baker, who was in the oil-and-gas industry. He wrote this paper in the late 1940s. It worked very well with helium. Helium is a wonderful fluid because the ratio of densities from liquid to gas is only 6. It would be 8 or 4.2 K, but typically it's around 6 at 4.4 K. It makes things better for two-phase flow. It makes it almost very easy to do. The first big magnet I ever built was cooled work without appreciable flow oscillations with two-phase helium. It had 250 to 450 meters of pipe that were like a garden hose, and the magnet had a horizontal bore. It was stable and it became a way of cooling large detector magnets. The CMS [Compact Muon Solenoid] at CERN is cooled using two-phase helium flow.

Hochheiser:

CMS?

Green:

This is the largest superconducting magnet in the world. It is 2.7 GJ of stored energy (800 sticks of dynamite) and it's cooled with two-phase flow. There are others that use a thermal siphon circuit. That’s also two-phase flow. Everybody in the world said that two-phase helium won't work, but it did. However, I had done enough of experiments and I was convinced I could make it work.

Hochheiser:

Right. This was in the late 1970s?

Green:

This was back in the mid to late 1970s. I wrote my thesis about the quench back as a method of quench protection for high current density coils and about two-phase helium flow through a cooling circuit. We had a number of other ideas, but that was basically what it was. A career goes in cycles. Originally, I was a proponent of single-phase super-critical helium flow and even wrote my first paper in that in the 1960s. Later I became convinced that the temperatures were too high. You had to run the helium through heat exchangers too many times whereas if you used a two-phase flow, you could use the compressor of the refrigerator to provide the pressure to run everything through. As long as you had a constant source of pressure, you didn't get the garden hose effect. That was a key element. The other element was to make sure that the flow per unit area of the tube was at the right level and that the helium entered the tube sub-cooled or at the saturated liquid line. You had to get the right flow regime so that you either got something that was mostly mist or something that was bubbles and liquid. That was my mechanical engineering side. The other was kind of an electrical engineering thing. Ultimately, I ended up becoming a member of IEEE. It fit me better.

Superconductivity Projects

Hochheiser:

What was ESCAR?

Green:

ESCAR [Experimental Superconducting Accelerator Ring] was an accelerator that was supposed to be built before the Fermilab energy doubler. It was an accelerator that had, if I remember rightly, twelve dipoles and six quadrupoles, and it was a test proposal to test a number of different things, including cold iron. We had a disaster when the quench protection system on ESCAR was disabled. The magnet quenched [and burned much of the equipment] and the funding for it got canceled, so we'd built half the machine. It was just a test platform, but still, it was a disappointment. It was a machine that really was not needed because Fermilab was moving so well. Anyway, that's a description of ESCAR. I was involved in it on the refrigeration side. We had a 1,500-watt machine that we bought from CTI. The company was later was owned by Koch Industries. Then they got rid of it. What was left made GM coolers. The part that makes the large refrigerators went to Linde. The only part that's left in the United States is the part that makes the 1400 machines. These are perfectly decent machines. In fact, for many applications they're ideally-suited, and they're a lot cheaper than the Linde, bigger machines. Yes, I got interested in that side of it, too.

Hochheiser:

This was still in the 1970s?

Green:

Yes, still in the 1970s. We tested the first TPC magnet [Time Projection Chamber magnet] on the 1,500-watt machine. It was fine until we were blowing out seltzer gas-bearing turbines on a regular basis. We had to learn why those were not successful. Rod Burns, who was from our lab, ultimately figured out how to make them work and people at SLAC [SLAC National Accelerator Laboratory was originally named Stanford Linear Accelerator Center] particularly learned how to rebuild the turbines because every time you blew one, it was $40,000. Let's put it this way; the turbines have improved considerably since those days. The turbine was a reasonable design; however there was a problem. If you quenched a magnet and took the cold gas up into the lower end of the refrigerator heat exchanger, the thrust bearing reversed in the second-stage turbine. The thrust bearings were designed for the thrust only going in one direction, so these turbines were extremely sensitive to the temperature of the gas that was in the lower heat exchangers. I was used to piston machines that didn't care about the gas temperature. I could quench the magnet and I could take as much of the gas through the cold mass of the refrigerator as the refrigerator could take. In a sense that stored cold into the cold mass of the refrigerator, allowed you to recover from it, and quench a lot faster. But you couldn't do that with these turbines. You still can't do it with most turbine machines. Although I did do it with a Linde oil-bearing turbine machine at Karlsruhe and it worked fine. I should say I suggested it, they said no, and when they did by accident, it worked, but that was a case where the oil-bearing turbine had thrust going both ways. In any event, the designs have improved considerably. Those machines are far more reliable than they used to be and far more expensive than they used to be, too.

Hochheiser:

That’s a tradeoff for you.

Green:

Yes, large refrigeration systems are a European monopoly, which is another issue. The only manufacturers of big machines left in the world are in Europe. The US got out of the business when the SSC [Superconductor Super Collider] was shut down. In the US, nobody builds big machines. Yes, we kluge big machines together as we buy turbines and other pieces here and there. That's what they're doing at Michigan State. They've been doing that at Jefferson Lab. But, that's not really building integrated refrigeration systems.

Hochheiser:

What was the MINIMAG project?

Green:

MINIMAG was what led to the PEP-4 project. This was supposed to be a 1.5 or 2-meter-long detector that was 1 meter in diameter. It was supposed to be less than a half a radiation length thick, but that was determined to be too small. It became a magnet that was over two meters in diameter with an 11-atmosphere TPC. This meant you had to have an 11-atmosphere vessel on the inside, so the radiation thickness increased to three-quarters of a radiation length. It was one of the first thin detector magnets, so MINIMAG was just a way of getting there.

Hochheiser:

Okay. This led to the PEP-4 solenoid.

Green:

Yes. MINIMAG started out as two test solenoids 1 meter in diameter. Then we knew we had to go to 2 meters and so we built a 2-meter diameter solenoid and realized that we scaled things the wrong way. Well, you learn. We were going for high current density windings, because the aluminum matrix conductors we bought from Alcoa didn’t draw well. We didn’t try copper-based superconductors in a pure aluminum matrix, which turns out is a far better way of doing it. I took the high current density approach, but some of the others including Akira Yamamoto and the French, Jean Royet decided to use ultra-pure aluminum co-extruded with copper matrix niobium titanium conductor. Yamamoto, of course, took it further because he could show that if you use the pure aluminum in the right way, you got very, very long, minimum propagation zones and therefore the magnets became very stable. They didn't quench at all. But all of these machines use some form of two-phase cooling, either a thermal siphon circuit or a forced two-phase system (mostly the latter). It became very clear to me that the low current density, ultra-pure aluminum conductor approach, was better until you got to be so big that the forces cause the conductor to yield too much. CMS [Compact Muon Solenoid] at CERN is a hybrid. It's got a section of very pure aluminum in it. An aluminum alloy that is quite robust is on either side of it and that's what carries the magnetic forces.

Hochheiser:

How does the PEP-4 fit into it?

Green:

PEP-4 was an experiment on the first PEP accelerator at SLAC. It had a magnet that operated at 65,000 amps per square centimeter and a quench back from a mandrel. We later proved that it was true, but nobody really believed you could quench this magnet without having a quench-protection circuit. You could it was eventually proven, but that was sort of after the fact. We engaged in this very expensive system that you discharged a capacitor bank, you do a center tap between the two layers of the coil, and you could turn the whole coil normal in about 30 microseconds. Then you just literally dump the energy into the end of the coil and the mandrel that it was wound around. This was fine as quench protection method. We never burned out any coils, but you could've done the same thing and put the mandrel material in the conductor. If it were very pure aluminum, then you got very long minimum propagation zones and you weren't going to get it to quench at all. Look at CMS and ATLAS, these are huge magnets with huge stored magnetic energies and they all have that aluminum matrix conductor with copper-based niobium/titanium co-drawn or co-extruded with the aluminum. I had little to do with that, but Akira Yamamoto in Japan became the big proponent of it.

Berkeley Electrosciences

Hochheiser:

How did you get involved in the commercial venture, Berkeley Electrosciences?

Green:

Well, it was one of these things where I knew somebody on campus who knew somebody on campus. A fellow by the name of Jay Singer came up to me and said I'm going to start this company to make MRI magnets. It was nuclear magnetic resonance magnets; MRI came later. I thought well, okay I could get involved and four of us set up a company called Berkeley Electrosciences. While working at LBL by day, I was out raising money and searching for venture capital for our new company by night. I traveled a lot, leaving the lab, jumping on an airplane to New York, and returning to the lab the next day. I don't know how my family put up with me. We got some funding, but the deal was killed because the venture capitalists proposed selling us to Technicare. We didn't really want to move to Mayfield, Ohio, so the deal didn't sit well with us. Then Osborne Computer went broke and the venture capitalists took a real bath, so the venture capital people in New York and San Francisco were reluctant. When General Electric announced that they were going to get into the superconducting magnet business, the four of us decided it was better to walk away and we did.

Hochheiser:

Good.

[End of tape 1; begin tape 2]

SSC, Superconductivity, and Magnetism Research

Hochheiser:

When did you first become involved with the SSC?

Green:

I guess I got involved around 1984.

Hochheiser:

That sounds about right.

Green:

Yes. There was a group at Berkeley.

Hochheiser:

What was your role in the group?

Green:

I was a member of the superconducting magnet group, but only part of the time.

Hochheiser:

Yes.

Green:

I was interested in things like magnetization issues.

If you went to too fine a filament superconductor, the coherence length through the copper was too short and you'd start getting tunneling from one filament to another. How could you prevent that? How could I model it? I looked at using passive correctors made from superconductors to correct the sextapole and the decapole in a dipole. I actually did some experiments and could reduce them about an order of magnitude. We didn't understand terribly well all of the coupling effects from a cable. We could even do some of those. In fact, I may still be doing some work with some people at Ohio State on that. The codes I have may still work. They may have to be updated, but I think a good graduate student could upgrade them. We could get them to work and we could then model this tape conductor and all of this other stuff.

I was interested in that and I was also interested in large detector magnets because I had worked with William M. Fairbank at Stanford University. He is dead now. He actually had a patent for a really nifty design for an MRI magnet; it was like two big beach balls. There was an outer beach ball and an inner beach ball. The coils that generated the magnetic field for the MRI were on the inner beach ball and the coils that were to buck the field and make the linkage flux almost zero, were on the outside. I tried to convince people that this might be an interesting approach for a detector magnet because you could get fairly large fields on the inside in large volumes and not have to have thousands of tons of iron to return the flux. It didn't really get anywhere, but that was one of the things that I worked on. I worked on magnetization, too. I did not go to Texas, although I did go down there every once in a while. I was sorry to see the project killed. I think [President Bill] Clinton basically gave Congress the choice of killing it or the space station. From a technical standpoint and in terms of the science that is going to come out of it, they should've killed the space station, but that's neither here nor there. It certainly did irreparable harm to American physics. The ball is clearly in the European court. It doesn't look like it's going to be in our court for a long time; not with the current funding situation and the lack of any direction politically in this country.

Hochheiser:

Do you recall what you and your colleagues' reaction was when the SSC was killed?

Green:

I looked at it incredulously because literally 70 percent or 80 percent of the tunnel had already been drilled. They had forty miles, something like that, of tunnel, maybe more, that they had to filled in. What wasn't filled in is growing mushrooms, I think. They spent $600 million just closing the project down. That machine would've been on by the year 2000. I thought about a lot of decisions that had been made. I was one who favored a lower-field superconducting magnet like 4 Tesla with the idea that you would build a longer tunnel, and you could upgrade the machine later when the technology got ripe so that you could do it. They ultimately went with 6.6 T, and had they even designed at 4.5 T, everything would've been easier, the project would've been further along, and it would've been much more difficult to kill. But that's 20/20 hindsight, too. I fully admit that. You know, my role was relatively minor. I was working on a project called ASTROMAG at the same time.

Hochheiser:

Right. What was ASTROMAG?

Green:

ASTROMAG was a magnet that was supposed to go on the space station. The idea was to be able to do two kinds of experiments. One was to look for antimatter, not just positrons and antiprotons, but possibly anti-helium. The other experiment was aimed towards heavier ions. I worked on an experiment with Buford Price that was supposed to go up on Challenger. We were a long way on that project when Challenger blew up. The project was canceled within two weeks because the bird that was going to fly us and bring the LDEV that our panels were going to be mounted on, was dead, so therefore the project was dead.

I was asked to get involved with ASTROMAG by George Smoot, who later won the Nobel Prize in physics for his work on the structure of the Big Bang after light, the 3-degree Kelvin light out there. He was a very good guy to work with, just a great physicist. I was looking at long-life dewars, because the cryocoolers were there at that time. We were looking at whether we could come up with a magnet that could be mounted on the space station or out in a free orbiter that would have a lifetime in the neighborhood of seven to ten years. We could see going to three with superfluid helium, dewars maybe. I said no, let's use solid hydrogen and superfluid helium, so we did a bunch of calculations. We suggested we could get seven to ten years on a cryostat like that, but there was no way of getting that bird out there.

After the Challenger accident, NASA made the bureaucratic decision not to allow any hydrogen on the shuttle, never mind that you've still got the same liquid oxygen, liquid hydrogen engines that are taking it up there and the same solid rocket boosters with the bad O-rings in them. No, we couldn’t have any hydrogen in the shuttle bay. No, we were talking about relatively little hydrogen compared to the tanks a couple of tons of hydrogen in the solid state. While it is on the bird it's being kept cold with liquid helium. By the time the liquid helium is gone the magnet is either on the space station or it's free flying. But, no, there was no way that NASA was going to buy into it. They made a bureaucratic decision and it was a bureaucratic decision that cost NASA immensely. First of all, there was an orbiter that was going out to Jupiter that was supposed to be sent out in 1986. It had a Centaur engine that had to be in the shuttle bay and it wasn't flying on Challenger. But, no, they made the decision; no, there's going to be no hydrogen on the shuttle.

The Jupiter mission missed the collision of a comet with Jupiter. You have to look at hydrogen from the standpoint of an oxidizer next to it, as well as an ignition source. The Challenger had all three in very close proximity. I just shook my head because there was an experiment that involved using solid hydrogen to measure the effects of global warming early on. Instead, they used liquid neon and solid CO2. They got very little data because the detector only ran for seven months whereas the solid hydrogen cooling system was destined to go for about four years. I sometimes shake my head at some of the decisions that are made for bureaucratic reasons, frankly. You don't change them.

ASC

Hochheiser:

Yes. To shift gears a minute and talk about the ASC, you had mentioned briefly that your initial ASC meeting was the organizations second meeting.

Green:

The second ASC meeting was in Austin, Texas. In those days, Austin was dry, so if you wanted to drink, you had to join a club. I remember going out with Charlie Laverick [spelling?]. You will hear about him from some other people. He was one of the early pioneers in the U.S. He's dead as far as I know. The last time I saw him, he was living in Virginia about one mile from where Stonewall Jackson's arm is buried. If you're a Civil War buff, you know that Stonewall Jackson's arm is buried separately from the rest of his body. Charlie was a character who liked to drink and tell stories. He truthfully claimed that he personally got caned by the Archbishop of Canterbury when he was going to a church school in Durham, England. Of course, the Archbishop was a young priest then. I went to a club in Austin Texas with Charlie, and as we were leaving, he was negotiating for a bottle of bourbon so we could continue drinking. By the time we left the club taxis were gone and we ended up going back to the hotel with the strippers in their Volkswagen. We didn't do anything with the strippers. All we were going to do was drink, so we finished off the bourbon in Charlie's room. He chided me as a young engineer because I was a little fragile in the morning while I was giving my paper in the session that he was chairing. Well that was Charlie and that was the first ASC I attended.

Hochheiser:

I assume the ASC was a lot smaller then.

Green:

I think sixty attended the first ASC and about one hundred went to the second. The paper [I presented] was published in the Journal of Applied Physics. I did not go to another ASC until 1974. I was living in Germany. I don't know why I didn't go to the 1968 or 1970 ASCs. The 1972 ASC was held in Annapolis. I was in Germany and I had a choice to either go to the ASC or the MT in Brookhaven. I went to MT. In 1974 it was in Oakbrook and I went to that one. I attended the 1976 ASC at Stanford and the ASC in 1978, but I did not go in 1980 or 1982. Since 1984, I have attended every ASC.

Hochheiser:

How did you come to be on the board of the ASC?

Green:

I got talked into being the editor.

Hochheiser:

Okay, that's the next question. How did you get talked into being the editor?

Green:

A fellow by the name of Steve St. Lorant, asked me to be editor. He is a very interesting character from SLAC and somebody you ought to interview, He is truly an Oxbridge person because he got his Ph.D. from Oxford and his undergraduate degree from Cambridge, or vice versa. I can't remember exactly. He was born in in Czechoslovakia right after the Germans invaded Sudetenland. His mother was Hungarian and his father English and living in England. Steve didn't get out of Czechoslovakia until 1947. He said he learned how to roll a joint because he collected cigarette butts on the streets, turned the tobacco into cigarettes, and sold them to get money during the period after the war. He talked about things like that. Steve and I were good friends, and he said he’d like me to do the editing. I didn't know what I was getting into. He said he would help me, but he was not at the ASC in San Diego in 1984. Where was Steve? Well, Steve was off in India, so I edited 225 papers myself.

Hochheiser:

Well, that must've been quite a job.

Green:

It was, and everything was on mats in those days and everything was done by mail. The papers were published in IEEE Transactions on Magnetics. Steve edited the previous five conferences. The previous one had been in Tennessee, Knoxville I think. He and John Alcorn, another character in the field, were the traveling together. John Alcorn decided to buy an old Chevrolet he found on a farm in Tennessee. It still ran, so they drove it across the country. The 1984 proceedings included a picture of the car after it had been fixed up. In the previous proceedings he published a picture of the car and all of the papers flying out the back. It was a drawing, of course, as this car was being driven across the country. The 1984 proceedings actually had a photograph of Clarabelle, the car, after she'd been fixed up. She was a beautiful 1956 Chevrolet.

I edited the papers in 1984 and in 1986 when ASC was chaired by Ed Edelsack. I was on the editorial committee with Jim Schooley, Bob Soulen, and Vickie Bardos. I was the editor in chief in 1988 in San Francisco with Vickie Bardos. By 1990, we had three editors Vicky Bardos, Bob Fagaly, and myself. As the conference grew so did the number of editors. By then the system sort of developed and I became quest editor, or I should say editor-in-chief, a number of times, the last time was 2010. I also edited for a number of MT conferences over the years as well.

I actually enjoyed editing because it's a way of finding out what's going on in the field. It has its bad moments and its good moments, particularly when you have these awful papers that people really want to save. In any event, it's been very positive. I chaired the ASC conference in 1998.

Hochheiser:

My next question is about being on the ASC board.

Green:

I've been on the board almost continuously actually since 1984. I'm a nonvoting member of the board today, but I never ran for the board. That was interesting. I just served in various capacities with the organization.

I got involved in the council the same way. I wasn't even a member of IEEE when I joined the [Superconductivity] council. I figured oh, maybe I better belong to IEEE. It's been a very satisfactory relationship. I have enjoyed the relationship with the people. My first wife went to all of the ASCs from 1984 on, she liked the people. I was going to marry my second wife, and I said, well, why don’t you come up to Portland and see me get my award. We married in 2012. One month after the ASC meeting we were married in Australia and went on an around the world. I love to travel.

STAR and Other Experiments

Hochheiser:

Back to science.

Green:

Right.

Hochheiser:

Okay. What was the STAR experiment?

Green:

STAR was an experiment on a heavy ion collider at Brookhaven. STAR was a 6-meter diameter solenoid. It only had to be about 0.5 T field, so I was a proponent of using a superconducting magnet. In fact, I was a proponent of doing it the way Akira Yamamoto, the British, and others were doing it.

We came in with a series of estimates. We had to go out and get budgetary quotes. One guy, working for a company in California, came in at $3 million. I knew his bid was low, but he said he would build it for that fee. General Dynamics submitted the high bid at $15 million. Later, I talked to the engineer who prepared the estimate for General Dynamics. He told me, “I came in at $7.5 million and I think we could've built it for that, but then I was told to double it because it was a budgetary quote, If they could get $15 million, they wanted to get it. I went to four or five different vendors. I felt that I knew what it was going to cost. My range was in the $5 million to $7 million range.

I came up with an algorithm for calculating the cost of superconducting magnets. If you use the right technique, the algorithm actually works pretty well, particularly with detector magnets. The physicist in charge wouldn't have it, so Brookhaven proposed using conventional coils. They came in and said we could use conventional coils. Then they were going to use aluminum coils, which would've been cheaper, but they didn't have enough space. So the changed to copper coils. The copper coils came in. The current density was higher. Then all of a sudden, the iron didn't fit and the magnet ended up costing $15 million anyway and it cost $3 million a year to run. While this was going on some of the people at Brookhaven that were on their side said we've got another experiment. Would you work with us on the Muon g-2 [pronounced gee minus two] experiment? That's how I ended up doing that.

Hochheiser:

Okay, so what was the Muon g-2 experiment?

Green:

The Muon g-2 experiment is an experiment that, in fact, fairly recently was moved across the country to Fermilab. This is a ring that's fifty feet in diameter, I guess. It is a muon storage ring that stores muons at energy of 3.1 GeV, which is roughly thirty-one times the at-rest energy of a mass of a muon.

The g-2, I can't explain the physics exactly except that this g function is supposed to have theoretical value of 2 according to the standard model, but it doesn't. They've been trying to measure this property out to as many decimal places as possible because it gives them some insight about things that don't fit the standard model like dark energy and dark mass and things of this nature.

When the experiment ran at Brookhaven, they extended the g-2 coefficient out a long ways. Then the DOE [the U.S. Department of Energy] decided that Brookhaven was going to be a nuclear physics lab, but its not going to do any more high-energy physics such as the Muon g-2 experiment. They shut the whole thing down instead of paying a little bit of money and upgrading the system so that they could get much more data. This was another bureaucratic decision.

As their machines were shutting down, the Muon g-2 experiment was shipped to Fermilab. Now they've got a better injector for putting in maybe 100 or 1,000 times more muons, so they could get the kind of statistics needed to calculate the g-2 coefficient to enough decimal places to be really useful. Now maybe we would have better insight into what might be wrong with the standard model. In all of the time I've been involved in physics were we not at a time in physics like we were 100 or 120 years ago when the standard model of the time, which was Maxwell's equations and Newton's equations, was falling apart. Why were we getting these x-rays? What's this radioactive decay; and so forth. Maybe we were at a similar time in physics again. The standard model works today, but it doesn't explain everything. Now we have this conundrum of dark mass, dark energy. Why is the universe accelerating instead of slowing down? All of these things that we're seeing, and the g-2 coefficient is a relatively cheap way to maybe get some insight. It isn't going to answer the question, but it might tell you how wrong the standard model is. Only a theoretician really knows what the g-2 variation might mean.

Hochheiser:

Then you became the only engineer on the muon collider.

Green:

I wasn't the only engineer, but I was the only one at the lab working on it.

Hochheiser:

Which was about when?

Green:

Oh, I started working on muon collider in 1995. Virtually everybody was a physicist and I was the only engineer. I was the only one who really knew anything about superconductivity, so a lot of the early magnet designs were mine. However, other people worked on them, too. I have not worked with the MAP collaboration in some time. I'm semiretired. I'm still involved in MICE the Muon Ionization and Cooling Experiment).

Hochheiser:

What is MICE and when did you first involved with this work?

Green:

MICE is the Muon Ionization and Cooling Experiment. We had our first discussion about actually doing an experiment, which was based on a model that we came up with for a muon collider or a neutrino factory. You know, they're both kind of related.

Post-Retirement from LBL Work

Hochheiser:

Yes.

Green: We had a particular lattice in mind. I said okay, we'll create the lattice and we'll demonstrate cooling. We started talking about that in 2001. I wrote my first, LBL reports on it in the 2001/2002/2003 time frame.

In 2003, I retired full-time from the lab and went to work for Oxford University.

Hochheiser:

This was simply a matter of your turning 65 or was there another reason for retiring at that time?

Green:

First of all, one reason was that my retirement benefits weren't going to go up. I'd been there a long time and I also was offered a financial incentive to retire. It didn't mean I wanted to quit working. I also knew that as soon as I met the IRS constraints about taking this financial incentive I could come back to work at the lab part-time. This plan suited me fine.

In the meantime, I decided take a full-time job at Oxford University’s physics department. I worked exclusively on the MICE magnets; did the basic design on the focusing magnets, the coupling magnets; and I worked with the Italians on the spectrometer solenoid. The Italians eventually couldn't get the funding to stay in the collaboration, so they bowed out. In turn, LBL got the spectrometer solenoid.

Now as a part-time engineer at LBL, I was working on it. I couldn't be in charge, so another younger engineer was in charge. Yet, I provided a lot, I won't say all because, you know, you can't say that, but I provided a lot of insight. I did a lot of the basic design calculations and we turned it over to a vendor in Livermore. Then I got involved with the Chinese. The Chinese hired me and wanted to be involved. We needed somebody who might come up with some money and some manpower. It seemed like a group that might work. If the director of the institute had not gotten into trouble, it would have worked. I think he ended up losing the institute directorship. I've got to say partly it was business as usual in China, but it certainly seemed unseemly to the average American. If you're used to dealing with the Chinese, you know that what the director was doing was not unusual at all. In any event, without him at the helm, the project sort of fell apart. We're still working with some Chinese companies. We're still working with people in China a little bit, but I quit going to China in 2012.

Hochheiser:

Does it look like this was no longer a fruitful collaboration?

Green:

The collaboration is still going, but I am not very active in the collaboration. My wife, my first wife, had been dead for three years, and I connected with my wife Nancy so we married in 2012. My life has changed and I am traveling for pleasure a lot more. My second wife is a retired schoolteacher. We can both afford to travel, let's put it that way.

Hochheiser:

Today, are you still involved with the MICE project now?

Green:

I still am in a peripheral sort of way, but now my work is basically with Michigan State. I've been working on various conventional and superconducting magnets at FRIB and I've been working on something called a cyclotron gas stopper magnet, which is a standalone magnet that weighs 167 tons and the IR-to-load is 167 tons. The two cold masses 1.25 tons each, but the cryostats, all of the coolers and the vacuum vessels, and all of that stuff, everything, is installed in two warm iron poles that separate so that they put the guts of the machine into it. Then they come together. The two coils cannot be connected physically except through the iron poles, which would be the way you would normally do it. All of the forces are carried to the iron through cold mass supports. This magnet is cooled with six Cryomech PT450 cryocoolers. They are a remote valve design, so they produce 4.05 watts at 4.2 K while producing 36 watts at 40 K in each cooler. We decided to go one step further. I said it should be possible to cool this magnet down with the coolers using a thermal siphon cooling loop. You've got cold here, it goes down a pipe and into the magnet to the bottom; it comes around the outside; and it goes back to the cooler. As of this last week, we have one of the coils cold and full of liquid helium or nearly full with liquid helium. We cooled it and liquefied the helium with the coolers. The second coil is in the process of being cooled down. Now each coil may behave differently, so we don't know exactly how they're going to behave. But, it's at least looking like it works. The magnet takes 3.5 times longer to cool down than I had originally calculated because the structure of the flow passages of the magnet is far tighter than I thought it was. This is a typical cryogenic problem. You know, you've got 20/20 hindsight. But, you don't realize the fact that you ended up using a half-inch pipe here to this cooler and the rest of them are three-quarters of an inch. Now this might be a bad thing, but it cuts this cooler off from cooling things down, so only these coolers over here are working. That's not a good thing, so we have to redesign some of the piping. But, we've got the magnet coil cold without redesigning the piping, so that's good news for at least one coil. We hope that in two weeks we'll know where the second coil will get cold. Then we can turn the magnet on and see how it quenches and all that sort of thing. I've got a couple of papers here about that. It's been a very good project. We may end up building another one for FRIB, in which case we will redesign the cooling system around the magnet.

Hochheiser:

What is FRIB?

Green:

FRIB is the Facility for Rare Isotope Beams that's being built at Michigan State.

Hochheiser:

Well, that's quite a change from working on muons.

Green:

Yes. These particles only live a little bit longer; I mean, they are rare isotopes. They might have half-lives of seconds instead of 20 milliseconds. It is interesting work and I can do it on a part-time basis. I do some telecommuting and I commute to Michigan about eight times per year, staying one week or one-and-a-half weeks. My wife is happy, I'm keeping my mind active, and we have time to travel. In January we're going to Antarctica, all around the southern tip of South America, and Machu Picchu. I am an eclipse chaser, so I am trying to convince my wife that we've got to go see a solar eclipse at the Faroe Islands. I particularly want to see this one because the first eclipse, solar eclipse, total eclipse I ever saw was in Oregon in 1979. It's the same SAROS as the eclipse in the Faroe Islands. Now I don't fully expect to see the sun in the Faroe Islands, but at least I'd like to be there.

Hochheiser:

Well, we've now reached the present.

Green:

Yes.

Hochheiser:

Can you think of any superconducting projects I neglected to ask you about?

Green:

Oh boy, superconducting projects.

Hochheiser:

Yes, are there any additional superconducting projects that you'd like to say something about?

Green:

Well, you know, one of the things that I worked on with some people at UCLA was a compact light source. This was one that was supposed to be able to provide fairly intense x-rays for etching chips, that sort of thing. It would've been an interesting machine to have at a university campus. I worked with some physicists and we created a machine that would generate 1.5 GeV electrons, accelerate them, and run it as a storage rig. It involved having six 7.5 Tesla superconducting dipoles, conventional quadrupoles, and stuff in between so that you can get the beams out. It was based on a Russian design by Pavel Vobly at Novosibirsk. We did some studies of the design and got the kinds of field uniformity we wanted. We could get the edge focusing off the dipoles that we wanted. In fact, it was an iron magnet with superconducting coils that went to very high fields. You expect the iron saturates. Well, it does, so you put in extra windings to provide the amp turns for the saturated portion of the iron. If you end up with a very uniform field, that was really acceptable for the kind of acceleration that we wanted to do. We got a building to do it in, but we couldn't get the funding. I was involved in a couple of little projects with UCLA that way.

I've been involved in stupid little things like going to talk to some guy in Tulsa, Oklahoma with an eighth grade education who was making some of the most interesting electric motors that I've ever seen in my life. He couldn't get any funding. He said, “I keep telling them about my monopole.”, so I told him there is no such thing as a monopole. He persisted: “Oh, no, you've got a pole here, and there's a pole over here.” I said, “You've got two poles. Believe me.” I had to explain to this guy that if you wanted a university professor to listen, you don’t call them monopoles. He had a brilliant intuition. I saw a golf cart system that he built. If you ran that thing on ice and a wheel that would start slipping, all of the power went to the other wheels. It would've been a very good design for an electric car. He built the most unusual electric motors that I've ever seen. I was asked to look at it and I didn't think he was crazy at all. I think he was onto something. He just didn't have the way of explaining it to somebody who was really technical, so I tried to write up what he did and explain it in technical terms. I'm not an expert on motors. I learned what I know about electric motors in electrical engineering 101 at Berkeley.

Since you are with the IEEE, you'll love this story. I belong to Sigma Phi Epsilon fraternity. The president of GM, Robert Stempel, belonged to my fraternity. I was in a meeting of alumni and donors, I'm a donor, and I asked him about the EV1. I said what kind of a drive, what kind of a motor do you use? Oh, he says we use a 60-hertz synchronous motor. I looked at him and said why the hell do you do that? I mean, you've got a battery, you convert it to 60 hertz, and you run a 60-hertz motor. “Well,” he said, “I’ve got to keep my automatic transmission factory in business. I'm thinking to myself, oh no, because electric motors are very well-suited for any kind of transportation. You want high torque at low speeds and low torque at high speeds. I just shook my head, and I guess that was the way the EV1 was built. I've only seen one of them and it's in a museum in Lansing, Michigan. It still runs, I understand.

Hochheiser:

Now we’ve talked about your activities with the ASC. You were also, involved with the IEEE CSC.

Green:

I was program chair for the ICMC, International Cryogenic Materials Conference in 1999. I became involved with CSC because I publish in IEEE Transactions. If you were to look at my resume or papers, you'd find that more of my refereed papers were published with IEEE than any other place. The Cryogenic Engineering Conference (CEC) papers are not considered to be refereed, but, in fact, they are pretty well refereed and it's a recognized publication for cryogenics. I've been active in that community as well. In fact, when I got into superconductivity, I felt that the cryogenic side was every bit as important as the superconducting side. If you're going use the word "applied," you have to think about the two together. That's why I talked about it when you're making a thin magnet. You can't put a thick helium vessel on it. You've got to cool this magnet with tubes and you're thinking in terms of its function, so the cryogenics has to be part of the process. The style of engineering that I developed over the years is to look at the cryogenics every bit as much as the superconducting part of it. Now with the shortage of liquid helium, the shortage of helium, period, people are beginning to realize that you've got to go to systems that have very little helium. You can't go with no helium, particularly with big devices, but you can reduce your helium inventory by an order of a magnitude or two by rather simple engineering and you end up with a better solution. It has lower mass and it will withstand much higher pressures. With superconducting magnets you used to quench them and you got this big plume of helium. You don't have to have that anymore at all. You can get the magnets to eat up their own boiling helium. You just store it in tanks if you have so little helium or hydrogen. I've even argued that HTS magnets would be far better cooled with hydrogen than helium. However, you have the Hindenburg Syndrome and you have a lot of other things. For example, people forget that large generators for generations have been cooled with hydrogen. Hydrogen is not nearly as bad an animal as propane, gasoline or a number of other things that I have looked at. I’ve done some work in that area, too.

Hochheiser:

You've also just described how the cryogenics has evolved over the many years.

Green:

I was working in the pulp-and-paper industry and we wanted it use NMR [nuclear magnetic resonance spectroscopy] to measure the water content of woodchips. They said we don't want to know just the water content. We want to know whether it's ice. I said fine, we ought to be able to do that with NMR, so we built an experiment in Berkeley where we could take wet woodchips just picked up and put them in the machine. We could get a water content measurement in about three seconds. The standard method takes a couple of hours. The standard in the pulp-and-paper industry is you heat it up, you get the water out, you weigh it before it goes in and you weigh it afterwards, going through this cycle with dry air and all of that stuff. We were doing it with NMR and our points were like right on the line. What was even more interesting was that we could tell you where the water was. If the water was in the wood, it had a different signature than if it was on the outside of the wood. If the water was frozen outside of the wood, it had a different signature than it did if it was frozen inside the wood. You would see samples at minus 50 degrees Centigrade where you had water inside of the wood, ice inside of the wood, and ice outside of the wood; you'd have three different signatures; and you could tell the percentage of each. The total water content numbers came out right.

Hochheiser:

In what ways have superconducting magnets and their applications evolved over your many years of working with them?

Green:

Let me put it this way; I've looked at the whole power industry issue. Roger Boom, for example, was famous because he was a big proponent of superconducting energy storage. I wasn't a big proponent because of the cost. I When I was pointing it out at the time, I said, just use a Sears truck battery, it costs 0.00001 dollars per joule to store the energy. Yes, there's some problems about how often you can get the energy in and out and at what rate, whatever, but a superconducting energy storage system couldn't touch it. In the 1970s, I saw all of the things that were going on in motors, generators, power transmission lines, the whole thing. You see the same thing all over again with HTS [high-temperature superconductivity]. The question is, will it be used in the industry if it is the only technology in town or if it's the cheapest technology in town that will do the job? That's what I have seen. That's been the biggest problem with commercializing superconductors.

Hochheiser:

What do you see as your greatest achievements of your career and things that brought you the most satisfaction?

Green:

Certainly working in physics has given me a great deal of satisfaction, working with physicists and knowing that working in superconductivity in particular really has helped that field go. I’ve got a great deal of satisfaction from some of the things I’ve done outside of superconductivity, cryogenics in general. I think that, for example, the pulp-and-paper industry made a serious mistake in not letting us go further with it because had we been in three years later, we could've said we can put everything on coolers. We could do NMR as the black liquor is flowing through the magnet, going on the way to the burner. We could've done all of these things. We were just a little bit too early.

I wasn't allowed to report on any of this stuff, but when I was finally allowed to report on this stuff it was very clear that we could've done a lot of these industrial applications in 2003 that we couldn't do in 1998 just because of the change in technology in coolers alone. If you're looking at lignins and stuff like that and black liquor, you might want five tests in the field so that if you're looking at woodchips you might go anywhere from 0.2 to 2 Tesla. We're not talking about fantastic, we're talking about being able to commercialize something that you can build, you could cost, and you could get companies to build the units.

As I was saying, the coolers have made a big difference, and HTS [current] leads they're not perfect, but boy, they've made a real difference. They're making a real difference on how NMR [nuclear magnetic resonance spectroscopy] and MRIs [magnetic resonance imaging] are being cooled. They're making a difference on how NMR magnets are being built. So, most superconductivity and the cryogenic side, we've made some real progress.

I think for many applications the big refrigerators are not needed, but there are applications such as large accelerators and any kind of a plant where you have many, many units of something that are very close together, where it's much cheaper to cool them with a large refrigerator. But you'd better do it right. You'd better use some kind of a two-phase cooling system or something that doesn't have a lot of helium in it. Having large tanks of helium in this day and age is foolish. I think that that's just the direction that things are going to move. In the electric power industry, I'm not sure what the role or superconductivity is going to be. We're going to see a much more diverse system.

I'm disappointed that a lot of countries are rejecting the nuclear option because there are reactor designs out there. In fact, I was involved with one as a student fifty years ago which showed that reactors could be built much smaller. If you could cool the reactor or particularly cool the reactor in the event of a water failure by natural convection, you would get rid a lot of safety problems and you could perhaps build reactors that were in smaller unit sizes. I still consider nuclear power to be part of the mix. Fusion I'm not so convinced that it will ever be economic. ITER [International Thermonuclear Experimental Reactor] is an extremely expensive project. The first thermal nuclear power plant will be hellishly expensive. Frankly, they're going to have the same radiation problems as fission plants. They're different. We could reduce the radioactive nuclei of fission plants if we're willing to accelerate particle beams into the nuclear waste to get it to low half-life isotopes. It's hard to say what the role of superconductivity is in physics, maybe also in electronics, maybe in computers ultimately. It maybe large scale, but for any form of a large magnetic field, you would never do it with a conventional magnet in this day and age. If you wanted, 20 cubic meters of field at a tenth of a Tesla, you'd be able to build superconducting magnets to do it. But 40 cubic meters or whatever, it's just going to be less expensive to do it, and a much more open structure.

Hochheiser:

All of my cards are now face down. Is there anything you would like to add that I neglected to ask you?

Green:

You know, I can't think of anything.

Hochheiser:

In that case, I guess we've done a good job.

Green:

I think you did a good job of interviewing me.

Hochheiser:

I think you did a good job of talking about your career.

Green:

In my career, I've got to say part of it was luck and part of it is I had very good people that I worked with over the years. I will say most of them were really good people and not jerks. There have been a few, but not very many, and, you know, I don't care. People are still very important in terms of getting things done. I don't particularly like web conferencing. If I'm going to have a conference with somebody overseas, I'd just as soon be on the telephone because I don't have to see them. I can't see their slides anyway, so what's the point? I've certainly done a lot of that over my career where. Many times my wife said why are you getting up at this hour of the morning? I said I have a meeting in England, so she said you're not there. Well, I'm here. At other times I had a late at night because I had a meeting in China. That's life, too. My first wife and my second wife reacted the same way. Why is it I check my email at least three times a day? I check it early in the morning, so I can answer the Europeans. I check it late at night, so I can answer the Chinese or the Japanese. That's less now than it used to be because I don't work full-time anymore, but we are a very connected world these days. I have a few more years left.

Hochheiser:

I'm sure you do.

Green:

I think that we're done, aren't we?

Hochheiser:

Okay, thank you.

Green:

Thank you.

[End Tape 2]