Interview: Johan Fremerey
2004 Albert Nerken Award Recipient
Interviewed by Paul Holloway, November 16, 2004
HOLLOWAY: Hello, I'm Paul Holloway, a member of the AVS History Committee. As part of the Society's Historical Archive series, today I'll be talking with Dr. Johan Fremerey from Julich. Johan is the 2004 Albert Nerken Award winner at the 51st International Symposium of the AVS being held in Anaheim, California. Today's date is Tuesday November 16, 2004, and we're very pleased to have Johan here with us. He is being recognized as the Albert Nerken Award winner for the development of the practical spinning rotor gauge and contributions to the understanding of gaseous drag. So Johan, it's a real pleasure to have you here and get to know you a little bit better.
FREMEREY: Thank you.
HOLLOWAY: So tell me a little bit about the history of the spinning rotor gauge. I understand it started with some enabling basic development of bearing structures.
FREMEREY: Yes. In fact, a particular interest of my first teacher, Prof. Wilhelm Groth of Bonn University, was to detect some gravitational effect on spinning rotors as proposed by an American theorist, Jimmy Keith from Detroit. Wilhelm Groth pioneered the uranium ultracentrifuge in the 1930s and '40s, and he was very much interested in this basic physical experiment showing some effects due to centrifugal forces on small rotors. Groth was aquainted with Jesse Beams, well known in the United States as the father of the magnetic suspension system. Beams worked at the University of Virginia, Charlottesville, and in 1937 already devised the first small rotor non-contacting magnetic suspension. This was in fact the beginning of the continuously rotating gas friction gauge as well, although his primary intention was to realize extremely high rotational speeds and accelerations. I think he has reached several hundred million times gravity on his tiny spinning rotors at rotational speeds of several hundred kilohertz, and he brought those tiny balls to explosion.
HOLLOWAY: I bet that was pretty spectacular.
FREMEREY: Pretty spectacular indeed. I will present his results tomorrow in my talk. But maybe, I am not sure about that, but maybe that these high centrifugal fields inspired people at that time to look for gravitational effects on rapidly spinning balls. And so in the late 1950s and at the beginning of the 1960s there was some activity at the University of Detroit by Prof. D. J. Kenney, and one of his students was Jimmy Keith. He was a theorist, who wanted to find out how gravitational dynamics effects could be observed on fast spinning balls. And he published not only on the theoretical gravitational effects but also on the side effects that may affect the experiment, in particular, magnetic drag due to the rotor suspension. The particular effect that he recognized was the influence of Earth's rotation, because a quickly spinning rotor seeks to maintain its spin axis stable in space, and the laboratory moves along with the Earth rotation, so the rotor axis always lags behind the vertical. That means the rotor axis is inclined with respect to the suspension field, and there are eddy currents generated within the rotor.
HOLLOWAY: So that can certainly lead to some error in the design of the experiment. [Yes.] Then I assume that the coefficient of viscosity of the gases in which it was spinning were also part of that error analysis.
FREMEREY: Yes, that's true. And Beams and coworkers were the first to recognize this effect, and they also developed a formal relation between the deceleration of a free-spinning ball due to gaseous friction. They published the respective formula already in 1946 along with spectacular rotor explosion experiments. But this gaseous friction formula is still accurate and is applied in the modern spinning rotor gauge.
HOLLOWAY: This formula is the basis for the spinning rotor gauge today? [Right.] That's remarkable.
FREMEREY: Yes. So they assumed that there is perfect momentum accommodation on the surface of the gas molecules, and this is very close to reality, in fact. So in general we don't have specular reflection, not even on a polished ball.
HOLLOWAY: So it is independent of the finish of the surface?
FREMEREY: Right, presumably because there are always absorbents on the surface, or there is some polycrystalline surface and roughness. Anyway, when you calibrate a spinning rotor gauge against a fundamental standard, then you always have deviations of only a few percent with respect to the formula.
HOLLOWAY: So is that a function of the type of gas as well?
FREMEREY: The friction itself depends on the square root of the molecular weight, but the deviation from perfect momentum exchange is always independent of the gas. Even with helium and hydrogen you have almost perfect momentum accommodation.
HOLLOWAY: Over what sort of pressure ranges does the gauge work?
FREMEREY: Basically within the molecular flow range, which is about up to 0.1 millibars, say. This is the most powerful application for the spinning rotor gauge, and the residual indication is determined by magnetic drags and thermal fluctuations, and this is with the practical spinning rotor gauge, which means with no thermal stabilization you may have stability and readability down to 10-7 millibars.
HOLLOWAY: That's remarkable. The gauge formula was developed in 1946. How long did it take to actually develop something that was commercially available for the spinning rotor gauge?
FREMEREY: For this development, it was very important that George Comsa went into the business and recognized the significance of a spinning rotor gauge for the vacuum community. George became a professor and director of the Julich Institute for Vacuum Physics, together with Harold Ibach, and he promoted the spinning rotor gauge development starting in 1974.
HOLLOWAY: So there was significant time lag between the fundamental formula expression and the development of the commercial gauge.
FREMEREY: Yes.
HOLLOWAY: So where are the commercial gauges predominantly used today?
FREMEREY: They are preferably used for calibration purposes. I would like to have it a more commonly used instrument. For this purpose it should be produced at a lower price, but I think it can well be produced at half the present cost, and then it may be available to everyone's laboratory.
HOLLOWAY: I understand that your name is on all of the patents for the spinning rotor gauge, but no one works in a vacuum with respect to intellectual property. I was wondering if there were other people that worked with you to help develop the gauge.
FREMEREY: Oh yes. As I already mentioned, George Comsa was the initiator of the project, and there was in the first place Bernd Lindenau, and we worked together all the time since the establishment of the vacuum laboratory of George Comsa. And George Comsa himself was involved in the first applications of the spinning rotor gauge, and afterwards mainly Bernd Lindenau significantly contributed to the gauge head design and also to the high pressure extension. Of course the strongest range is within the molecular flow range where this simple formula can be always applied, but it works also up to atmospheric pressure, but there is some deviation from linearity due to viscous flow effects and even to laminar flow. And we have investigated all of these dependencies, and Bernd Lindenau did a lot in this area to make the gauge a high range gauge. The latest version of the gauge was licensed to SAES Getters company, and the range was from 10-6 millibars up to atmospheric pressure, so nine decades of pressure.
HOLLOWAY: That's quite a range! Quite a useful range for pressure measurement. Now you said that the spinning rotor gauge was enabled by development of magnetic bearings, but I'm aware that magnetic bearings are used in turbomolecular vacuum pumps, particularly. What other aspects has magnetic bearing development influenced?
FREMEREY: Well, as you say, the molecular drag pump, and especially turbo pumps. It was in 1990 that the first UHV type magnetic bearing was marketed in a turbo pump. I should mention that the special thing about our UHV magnetic bearings in contrast to say "conventional magnetic bearings" was that these bearings rely on permanent magnet forces, so we are running our permanent magnet bearings at a zero power condition. That is, we stabilize the rotating device on a normally unstable magnetic position. If you have a piece of iron, halfway between two permanent magnets, there's a force equilibrium. But it is unstable. Then we have additional electro magnets to keep it at that point. As long as it stays at that point, the correction current is zero. This is the permanent magnet principle of the UHV type bearings. The Leybold pump was the first one relying on this principle, and it was very successful in the market. There were about 30 Japanese magnetic bearing pumps on the market at that time, and the Leybold pump gained 45% of the marketshare worldwide within only two and a half years.
HOLLOWAY: Very impressive. Great penetration of the market. That means it was performing well.
FREMEREY: It was performing well, yes.
HOLLOWAY: What about other applications besides a vacuum? I understand it's used for a blood pump, for example.
FREMEREY: Yes, the latest development was an application of our permanent magnet bearing in a blood pump. This was done in cooperation with a German company in Berlin. It is also very successful. They have implanted some 150 blood pumps so far, and some patients have already been ex-planted after their heart had recovered due to this device.
HOLLOWAY: That's a wonderful story. Are there other facts that you would like to share about the spinning rotor gauge development with us today?
FREMEREY: Yes, maybe I would like to give some comment on a gravitational effect, because this effect was the motivation for my activities with Wilhelm Groth at Bonn University. In fact I was able to experimentally verify not only the Coriolis effect and other magnetic drag effects predicted by Jimmy Keith, but also detected an effect that followed the predictions of Keith on gravitational radiation interactions. It is funny that these experimental results have never been taken seriously by the community because there were two people who were well known in the field of gravitational theories, and they discarded the gravitational theory that Jimmy Keith used for developing his theory. This was the Birkhoff theory of gravitation. They neither discussed Jimmy Keith's arguments, nor the experimental results or the experimental setup. In fact the basic theory was not well understood yet and was not generally accepted, so they discarded the whole thing.
HOLLOWAY: Well, science is human dynamics in addition to science. Yes, that's an interesting aspect of the story. Are there other facts that you'd like to share with us today?
FREMEREY: There are other applications, yes. We have also made a yarn spinning centrifuge that has been tested up to 60,000 RPM for spinning yarn for textiles. Conventional ring spinning machines are capable of running up to 18,000-20,000 RPM only. A flywheel for energy storage - we have also made a prototype of an energy storage flywheel. And a lot of activity was in the field of chopper wheels for molecular beam analysis, and also for neutron beam conditioning in neutron beam monochromators.
I should also mention the work of Klaus Witthauer. He was the one who made a marketable instrument out of the laboratory-type spinning rotor gauge, and he manufactured all of the commercial spinning rotor gauge controllers for the three licensing companies.
In my opinion the strength of the spinning rotor gauge is, that this gauge does not influence in any way the gas that is being measured. So for this reason it can be used for calibration because it neither pumps, nor creates gases; it is running at ambient temperature and moderate speed compared to the molecular velocities. And so it has not only been used for calibration but also for precise gas accumulation measurement.
HOLLOWAY: Now I understand that in the very beginning that there were some traceable standards that they used to calibrate and check the accuracy of the spinning rotor gauge.
FREMEREY: That's right.
HOLLOWAY: And now what's happened?
FREMEREY: [Laughs] The funny thing is that we were able to calibrate fundamental standard facilities by exactly evaluating the volume ratio of a static expansion apparatus to high accuracy. We have achieved statistical uncertainty of two parts in 104 for the volume ratio determination, and even better. This figure was found for a volume ratio of one to about 250.
HOLLOWAY: That's really remarkable. That's what you call a good standard.
FREMEREY: Yes, indeed. Well, at this time I would also like to thank Gunter Messer, who was head of the German Vacuum Standards Laboratory. He introduced the spinning rotor gauge to the IBPM international comparison program and made it a recognized vacuum transfer standard in cooperation with Charles Tilford from NBS - formerly NBS and now NIST. Messer and Tilford have done a lot to make this gauge a popular standard calibration tool.
HOLLOWAY: It takes a lot of different types of people to actually bring a community together and develop that support for it.
FREMEREY: Yes, that's very true. And opportunities. In particular, George Comsa's personal interest was quite valuable in this development.
HOLLOWAY: Good. It has been a pleasure to have you here today and learn something about the history of the spinning rotor gauge. May I be the latest to add my congratulations for the Nerken Award. Well deserved.
FREMEREY: Thank you very much. Thank you.