Twelfth International Conference on Plasma Physics
Nice, 12-19 October 1988
C. MAISONNIER
Director of the Fusion Programme
Commission of the European Communities
Brussels
The memory of Lev Andreevich Artsimovich certainly does not need to be kept alive by the lecture that I have the honour to deliver today. Indeed, Artsimovich's name is clearly engraved on two cornerstones of controlled thermonuclear fusion research: the tokamak, so far the most successful magnetic confinement concept, and international co-operation.
What better monument to his memory could be thought of than ITER, the international thermonuclear experimental tokamak reactor? Since April 1988, ITER conceptual design activities have been bound together under the auspices of the International Atomic Energy Agency as the work of four equal partners: the United States of America, the Soviet Union, Japan and the European Community, the latter including in its contribution Sweden and Switzerland and now Canada.
The ITER quadripartite initiative has become a reality not only because of support at the highest political level but also because of the proven ability of fusion scientists to work together concretely on complex tasks, which has been progressively and successfully developed through a variety of schemes: from the setting up of an integrated European Fusion Programme (the masterpiece of my predecessor, Professor Palumbo) which made possible a large joint undertaking such as JET, to bilateral agreements between nations or groups of nations, to multilateral implementing agreements in the framework of the International Energy Agency (to quote only one, let me mention the agreement on the large tokamaks which has established strong links between TFTR, JET and JT-60), and through the INTOR Workshop.
The Artsimovich Memorial Lectures are a most appropriate occasion for the fusion community worldwide to think over its work in a broad perspective.
Why fusion?
The world fusion effort evolves in an evolving world. The population on earth, now five billion, was about three billion when fusion research was first declassified and will be eight billion or more when fusion could start contributing substantial energy. What the world energy requirement will be then is hard to guess given the extremely uneven global distribution of primary energy consumption levels over the various economies. Depending on the degree and rate of levelling out of this distribution as well as on the extent of success in enhancing the efficiency of energy end use worldwide, the total energy needs could increase enormously.
Whatever the quantity of energy which will be necessary, there will more and more be the requirement of quality: energy must be produced in a manner that is not only economically but also environmentally acceptable, even if what is and will be environmentally acceptable is a moving target difficult to define. Every source of energy has its own economic, health and environmental costs and risks. Reliance on fossil fuels, apart from problems linked with global or local availability, carries the risk of global warming (the greenhouse effect) and acidification, which is perceived with increasing acuteness both in public opinion and at governmental level. A possible large scale use of the renewable energy sources (sunlight, biomass, etc.) depends on local conditions and seems to be confronted with high costs and substantial environmental consequences. Nuclear power from fission reactors is facing three main concerns: safety and accidental radioactive releases, waste disposal and nonproliferation. The degree of concern in these three areas will most probably be lower in the case of nuclear power from future fusion reactors, for which, however, it is too early to tell whether eventually they will be economically competitive.
As to the question "When will the first fusion power plant be built?", Academician Velikhov reported that Artsimovich once gave the sibylline but probably sound reply: "When there is great need for it." Against the background of recent experiences, the need for the development of a diversity of widely accessible long term energy sources which show promise of being not only technologically feasible but also acceptable from the economic, safety, environmental and non-proliferation points of view is being perceived more and more acutely. It can be objectively argued, I think, that fusion has the potential of becoming one of these sources.
The technological problems associated with deuterium-tritium fusion reactors, which will have to breed their own fuel (tritium) in a lithium blanket surrounding the reacting plasma, have gradually been revealed by the many conceptual reactor designs produced within the world fusion community over more than a decade. These studies have also evidenced that the achievement of the potential environmental and safety advantages of fusion will not materialize automatically but will depend to a large measure on designs specifically tailored to this end, in which the use of low activation materials could play an important role. The studies have also shown how economic competitiveness will depend on attaining plasma and engineering performances such as high beta, high wall loading and ease of maintenance - performances which are not yet assured.
However, there are fundamental reasons why future fusion reactors have the potential to reach a high degree of passive safety and to have only a moderate impact on the environment:
-The reacting chamber of a fusion plant will contain only that quantity of fuel which is required for immediate use (a few seconds). The energy content of the fuel will therefore be very small and the amount of energy which will be susceptible to fast release in a fusion reactor in case of accident can in principle be reduced to very low levels by adequate design, as it is not linked with the fundamental process of energy production but only with auxiliary systems.
-The radioactivity in a DT fusion plant arises only from the intermediate tritium fuel and from the interaction between neutrons and the structural materials of the plant; the reaction products themselves are not radioactive. The development of an environmentally benign DT fusion reactor is, therefore, a question of engineering aimed at maintaining a low tritium inventory and, together with materials development, at keeping the activation of structural materials to a low level; it has no basic limit due to the fundamental process of energy production itself. Moreover, one could even conceive of using, in a later stage, instead of the DT reaction, reactions such as deuterium-helium 3 (D-3He) which, at the cost of more demanding plasma parameters, would have the potential for removing most of the environmental concerns. The availability of 3He, once considered an insuperable problem, might find solutions in the distant future.
These potential advantages of future fusion reactors, together with the abundance and wide availability of the primary fuel (lithium), should, if properly understood, be of substantial weight in determining the public attitude towards fusion.
Past achievements
Let me now briefly consider our past achievements. Fusion research has only recently emerged from the intimacy of the laboratories into highly visible Big Science public programmes and is still mostly in a scientific stage of development, although a growing fraction of the R&D; effort is being devoted to fusion technology.
Successive generations of tokamaks continue to occupy the forefront of magnetic fusion research, thus contributing most of the papers at these conferences; new devices of this kind are still under construction. Wisely, however, the major fusion programmes have maintained the necessary breadth in the toroidal confinement approach by experimenting with alternative configurations - stellarators, reversed field pinches and others - which are complementary to the tokamaks and could potentially have intrinsic advantages over them for the ultimate reactor. And then there is the inertial approach to controlled fusion, which is also making good progress, as will be reported at this conference, but which belongs to a slightly different world, traditionally not covered by the Artsimovich Memorial Lectures.
The most impressive result so far in controlled thermonuclear fusion research has been obtained with tokamaks. The value of the product of central ion temperature, central ion density and global energy confinement time, which is the best figure of merit on the way to the reactor, has increased by almost four orders of magnitude during the past twenty years. It is now only a factor of four away from breakeven and slightly more than an order of magnitude away from ignition, which is our longed for milestone marking the achievement of the proof of the scientific feasibility of fusion power.
The principal key to such progress has been the increase in gross machine parameters, and it is the relative simplicity of the tokamak concept which has allowed us to build the large devices we have today. An example of the virtue of size, and of course I do not mean only geometrical size, is given by JET, which is the largest tokamak in the world and which is, I think, second to none in scientific output.
Progress has also been made using smaller devices. For instance, substantial insight into the complexity of cross-field diffusion in reactor relevant plasmas was brought about by the discovery of the H-mode in ASDEX with a divertor magnetic separatrix, pointing to the strong influence of edge localized phenomena on global confinement. Enhanced confinement regimes have also been achieved, with intense neutral beam heating and pellet injection, on tokamaks without divertors. But I cannot resist quoting the slightly provocative statement of Dr. Furth that "in this context of programmatic success, it is sobering to reflect that identification of the specific physical phenomena responsible for anomalous transport in toroidal configurations has not progressed decisively since 1956."
Other reactor relevant critical physics issues are under intense investigation both in theory and in experiments; they concern limits to stable tokamak operation such as the elongation dependent plasma beta limit, the density limit and the control of disruptions, and also the so-called innovative ideas, such as current drive (demonstrated at the megampere scale in JT-60) and various impurity control schemes.
The last untouched physics problem, alpha particle heating, should become accessible to experimentation about three years from now, when TFTR, JET and TSP (which is the new name of T-14) will enter into their phase of tritium operation.
So we can say that, while mysteries still remain in some or most of these issues, the conclusion of the scientific phase of fusion is now in sight. It is therefore timely to plan for the Next Step device on the road towards a prototype reactor, a Next Step which should complete the demonstration of the scientific feasibility of fusion and confront the problems linked with its technological feasibility.
The Next Step
The pace of the major fusion programmes, as they are geared at present, is such that in some three years from now we will, we hope, have a sufficient scientific and technical basis to propose to our authorities the launching of the detailed design of one or more of the various possible incarnations of a Next Step device, national or international, with a view to its construction.
Next Step devices are at present in the predesign phase both within the large fusion programmes (for example NET in the European Community, which is the one I am most familiar with) and in the quadripartite venture, ITER. ITER, whose definition phase will be formally concluded in November 1988, is conceived as a tokamak device which, to quote from its terms of reference, "will provide the database in physics and technology necessary for the design and construction of a demonstration fusion power plant." It is estimated that three decades of R&D; will be required before such a demonstration reactor can become operational.
With the Next Step, we should not only develop, test and demonstrate technologies applicable to future fusion reactors but also define safety standards for these reactors. And it will be only with the Next Step that we will establish a sufficient basis to evaluate with some certainty the overall potential of fusion as an energy source. As in the case of any major decision on high technology, the decision to embark on the detailed design of the Next Step will have a strong political component. By that time, the fusion community will have to be able to make a good case on three different grounds:
-Firstly, we should have a sound scientific and technical basis. Work in progress makes us reasonably confident about this point. I am sure that at this conference we will have a good opportunity to confirm this confidence not only on the basis of outstanding scientific results but also on the technological side, thanks, for instance, to the appearance of the first large superconducting tokamaks: Tore Supra, which is now in operation, and T-15, which is in the final stage of construction.
-Secondly, we should be able to present convincing safety, environmental and, as far as possible, economic arguments in favour of fusion. So, already now, long before the characteristics of a practical reactor are known in any detail, it is essential, even if very challenging, to undertake a systematic and continuous assessment of fusion's potential to achieve attractive combinations of environmental, safety and economic characteristics. International collaboration should be used to its maximum extent to make progress in these fields, where it could be particularly helpful. Indeed, first steps are already being taken in this direction in the framework of the International Energy Agency.
-Thirdly, we should have concrete plans on how the major fusion programmes could take full advantage of a wide international co-operation, co-operation which could lead to a single device or to the joint planning of Next Step activities. Indeed, international co-operation will become more and more a necessity if we want to make the most efficient use of the resources of the world fusion community. These include, as a particularly precious element, a highly qualified staff, whose dedication will be a necessary condition for the success of the Next Step but whose full utilization requires that the Next Step be undertaken as soon as technically feasible.
Now, at the end of my talk, I would like to stress that international co-operation, even if extrapolated to an unprecedented level, cannot substitute for strong 'domestic' programmes. The four large fusion programmes of the world are at present working together in the ITER conceptual design activities to provide, by the end of 1990, a design which will then be available for all ITER Parties to use, either in their own national programme or as part of a larger international co-operative programme.
Some of the ITER Parties also have national plans to embark, at about the same time, on the detailed design of a similar Next Step. I will not attempt to make any prediction on the framework in which the Next Step(s) will eventually be built. What is clear to me is that we will have to work hard, keeping open all options, to prepare the ground for a decision to start the realization of the Next Step(s) early in the 1990s.
