Plasma physics and fusion research politics

December 16, 2010

I was recently attracted by an initiative of Focus Fusion: they try to improve the promotion of nuclear fusion among the public and the politicians.  It is well known that this community is not very enthusiastic mainstream fusion (tokamaks or stellerators), it is the least we can say, but they an interesting and broader approach to fusion. Reading one of their article, I found a reference about an article from G. Weisel on “Properties and Phenomena: Basic Plasma Physics and Fusion Research in Postwar America”, in the series “Physics in Perspective”.  This article is of utter interest, if we want to understand some political intricacies of the fusion research. The article focuses on fusion research history till the end of the 90s in the US. Do not try, with this article, to draw definitive conclusions on the present situation of the ITER project: ITER does not play the same role in the US Fusion research than in the European Fusion research; I would even dare to say that ITER is a side-activity, along inertial fusion and other plasma physics topic. It is precisely the complicated links between fusion research and plasma physics which are highlighted in this paper, and the more general perspective of the situation of these two areas in the world of physics.

One interesting point which is developed, is how the scientists have developed the concept of basic plasma physics, and the comparison with elementary particles physics is significant:

Fusion researchers more than once turn from the Properties and Phenomena conception of basic physics and moved toward the Extreme Plasma conception and to the notion of fusion power as the savior of civilization.

There is a lot of stuff hidden in this sentence. The “Properties and Phenomena” conception of basic aspect if a very important notion that can be opposed to the “Big Questions” conception of elementary particles physics. In the latter, physics aims at answering some big mysteries of the universe: what is the ultima structure of matter, what is its origin, simply put, what are the fundamental laws of physics? And they try to address these problems by developing elegant, unifying solutions. Do not expect to find such approach in plasma physics (and I think that we could even extend this to fluid mechanics): most of the work aims at explaining, case by case, the different behaviours of plasma. When I say case by case, I mean for each different conditions of temperature, pressure, magnetic field, space scale, time scale. Plasma physics is a jungle in which most of the physicists are specialized in a tiny area. In Fusion Research, it is not unusual that scientists dealing, for instance, with the plasma center of a tokamak, do not understand, or misunderstand, their colleagues working on the plasma edge.

Why do we have this “dirty physics”. Actually, it could be surprising because the laws governing the plasma are basically very simple: the four Maxwell equations, Lorentz and Newton laws. All these laws govern the behaviour of a plasma particle (electron or ion). Now we have the classical problem of plasma physics: how to apply these laws to the tremendous amount of particles of a plasma system? The solution is to proceed with a statistical averaging of the laws on bigger time and space scale: this process is based on the BBGKY hierarchy which describes  the dynamics of a system of a large number of interacting particles. This process leads to different models according to the adopted scale with a different level of approximation: the Boltzmann model, the two-fluids model, the MHD model.

This is a very simple description of how, starting from a simple set of equations, we quickly fall in the trap of complexity: each model has its own assumptions and its own range of validity. It becomes quickly hard to keep the picture of the whole system in mind and how we derive a model from the basic equations.

This is this difficulty which often urged physicists to promote plasma physics in the domain of “Extreme Plasma”, i.e, the plasma with the temperature and densities useful for fusion.  And this preferential approach for fusion is driven by what Weisel call “the Messianic Fusion”: fusion would be “a discovery as important as the Promethean taming of fire”, quoting Lewis Strauss. And this myth is exactly what is used by proponents of the ITER project, as illustrated by the book of Kenneth Fowler: The Fusion Quest.  The goals of the Grand Quest of Elementary Particles of Physics are replaced here by the idea of messianic fusion.

Now, let us imagine the effect of these two concepts, the messianic fusion and the “Properties and Phenomena” concepts, of plasma physics on the mind of an average fusion researcher: these are two opposite ways of thinking. On one side, what is expected from him, is an accurate, infinitely detailed description and understanding of some simple properties of the plasma, which requires a very specialized knowledge. And on the other side, he is told that he works for the Good of Mankind. The link between the two approaches is difficult to establish. This is an ambivalence that should be addressed, there is clearly a hole in the research on plasma physics: an area where the big picture of plasma physics is studied. This area is investigated, but mostly my mathematicians. There are less and less basic plasma experiments to support this research.


Nuclear fusion: the big picture

December 13, 2010

As an engineer and a physicist, I have to deal most of the time with the details of fusion: how to optimize a particular component of one of the heating systems, how to understand the distribution function of fast ions during some MHD event. Busy with the intricacies of the day-to-day work, I often forget the long term purpose of nuclear fusion: to produce energy for the grid in an effective and rentable way.

A short reminder of the big picture is thus sometimes welcome. I will summarize in this post some guidelines, the reader interested in the topic should refer to the presentations and articles of David Maisonnier from the European Commission or Harmut Zohm from The Max Planck Institute for Plasma Physics who have put a lof of effort in “vulgarizing” fusion research: Power Plant Conceptual Studies in Europe, Overview of Reactor Studies, on the minimum size of DEMO.

The purpose of fusion research is to develop a Fusion Power Plant (FPP).

I will not tackle here the subject of the reason why we need fusion as a source of energy: it si a very controversial issue where emotional and political inclinations play an important role. If you are interested in the subject and want to  make your opinion, please visit the site of the International Energy Agency, where the World Energy Outlook 2008 is free for downloading. A very good basic physics approach is also given by David JC MacKay. If I have time later, I will try to enter this debate more in detail but, for the moment, I consider the three basic assumptions for nuclear fusion. You can agree with them or not, but this is the start of the studies on Fusion Power Plants:

  • Fusion is a relatively clean source of energy
  • Fusion is a safe source of energy
  • Fusion fuels are available for everybody (energy independence)

The EU Fusion Programme is reactor oriented, one of its purposes is to clarify the nature of a FPP (Fusion Power Plant), to identify the technological and conceptual gaps between our present knowledge on fusion and what is required for a FPP and to establish a plant to bridge these gaps.

The European Power Plant Conceptual Study (PPCS), finished in April 2005, identified 5 types of power plants, all based on tokamaks in steady-state mode, ranging from limited to advanced extrapolations in physics and technology.

A typical Fusion Power Plant has to meet the following main requirements:

  • concerning safety and environmental aspects, there shall be no need for emergency evacuation, no active system for safe shutdown and no structure melting down following an accident, minimum wastes to repository . This requirement is the main difference with a fission reactor: an accident of a fusion reactor does not have to impact the  population. The last specification on wastes is, I must admit, vague and it is a weakness of fusion power plants working with Tritium: materials are activated by fast neutrons. But the amount of radioactive wastes will depend on the architecture of the power plant and of the nature of materials used. The purpose is to reduce it as much as possible.
  • The operation of the plant shall make it possible to produce 1GWe as base load with an availability of 75% to 80%, and a few unplanned shutdowns per year.
  • Economically, a fusion power plant shall be more expansive than other “acceptable” energy sources.
  • Last point, the solution should be accepted by the public.

The standard solutions are based on the ITER design with some minor extrapolations IPB98y2 scaling law (this scale “predicts” the confinement of energy in function of the machine parameters).  More advanced solutions  bet on improvements in performance: better confinement, strong shaping for a better current profile control and minimization of divertor loads.

The technology is based on the same coolant for the different of the tokamaks (either water, heliium of even LiPb):  on the divertor with fluxes between 5 and 15MW/m2 (depending on the solution adopted), and on the first wall: 0.5MW/m2 on average 1MW/m2 peak.

The blanket structural material is EUROFER, a low activation ferritic-martensitic steel (550deg max. temperature), with a lifetime of 150dpa (displacement par atom). For an average nuclear load of 2MWa/m2, it corresponds to 5 full-power years.

The vacuum vessel is in stainless steel AISI 316LN, water-cooled and must be re-weldable to allow major repair operation.

The last critical technology concerns the magnets: they are assumed to be like those on ITER: low temperature superconductors Ni3Sn or NiTi cooled with liquid helium. The lifetime is set by the irradiation limit of epoxy insulation.

These are all the basic assumptions used to model Fusion Power Plants: it does not that they define the future design. These models are developed as guidelines, to get order of magnitudes of achievable efficiencies with the present knowledge. In other words, they make it possible a parametric studies of fusion power plants: playing with these models show the weight of the different parameters and help the designer choose the most sensitive.

To give an idea of the results, the most conservative design gives an efficiency of 30%, the most advanced 60%. The problem with the low efficiency of conservative design is the amount of power used for active Helium cooling and for additional heating.

I stop here for today, this should give a small overview of the first steps needed to build not an experimental reactor but a real fusion power plant and how difficulties and technology gaps are evaluated.

Deutsches Museum

December 13, 2010

I must say that I have already been a LOT of time in this museum, one of the biggest in the world for technic. But I had never much time to get interested in all the various or even to take pictures of them. Indeed, most of the time, I was with my children, who have a dedicated section, where they can play with water, with a real fire truck and many other  toys.

Now that they are a bit more autonomous and interested in their environment, I have some free time to enjoy the exhibitions: it is more than both entertaining and  informative: it is an ode to the technical realizations of mankind. Here no shame on engineers and technicians: their genius or even their simple ideas to solve practical problems is presented and explained in a simple and attractive manner.

Naturally, I took a look at the astronautics section: of course, it is not comparable with some museums in the US (for instance, the one in Huntsville, at MSFC), but they are some nice stuff to discover (a small piece of moon rock offered by the US government to Germany), the combustion chamber of an Ariane’s Vulcain 2.

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