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.