Tenth International Conference on Plasma Physics
London, 12-19 September 1984

E.P. VELIKHOV
USSR Academy of Sciences
Moscow, Union of Soviet Socialist Republics

Mr. Chairman, Ladies and Gentlemen,

I am deeply touched by your invitation to deliver the fourth Artsimovich Memorial Lecture at the 10th International Conference on Plasma Physics and Controlled Nuclear Fusion Research. All my life in science has been connected in some way with Artsimovich and his department at the I.V. Kurchatov Institute of Atomic Energy, which I joined first as a student of theoretical physics. Those were the fascinating years in which the principles of plasma physics were created. Many of those present here will remember the dramatic situation at the Salzburg Conference in 1961 and the wonderful early life story of tokamaks, which is so reminiscent of the tale of the Ugly Duckling. In those years, which were so hard for fusion studies, I was among the deserters and became engaged in the study of MHD generators. At that time I shared the opinion of many of those present here that the stellarator approach was more reliable than the tokamak one; a point of view stemming from the purely speculative opinion that the field structure, shear, etc., in the stellarator was strictly pre-set whereas in the tokamak it depended on the plasma. Moreover, for reasons concerned with dimensionality, I believed in Bohm diffusion.

In spite of all these difficulties, I was lucky then, both as a human being and as a scientist, to be on friendly terms with Lev Andreevich: it looked as if I had overcome the strong barrier of repulsion which surrounded him and had entered the potential well of human and scientific charm of his enormous intelligence and his beautiful soul. To my surprise, Lev Andreevich asked me in 1969 to be the head of a Committee which would, in essence, decide on the next step in fusion. The problem was as hard then as it is now, and people were afraid to approach it. The main document at the Committee's disposal was a report by L.A. Artsimovich and B.B. Kadomtsev in which, on the basis of theoretical and experimental considerations that are now well known, the authors came to the conclusion that, very probably, the tokamak approach would pave the way to the reactor' in the engineering sense of the phrase, of course. The Committee supported the idea that the T-10 tokamak should be built, and Lev Andreevich asked me to be the administrative leader.

Artsimovich's conclusions were confirmed by further research. Work on next-generation tokamaks, including that reported at this Conference, shows that modern tokamaks "possess an ideal vacuum technology, highly developed magnetic configurations with an accurately pre-set geometry of the field lines and programmed regimes of electric circuits and carry a quiet, stable, high-temperature plasma" and that "the door to the desired region of superhigh temperatures", and, let us add, of the necessary confinement time, "is about to open". In this approach, many detailed ideas of Lev Andreevich have been confirmed: that the ion heat conduction should be determined by the current field; that the electron heat conduction is explicitly anomalous; that it is possible to control the plasma position by transverse fields and control winding;' that non-circular plasma column cross-sections are of great advantage, etc.

I should like to speak in particular about Lev Andreevich's idea of possible plasma heating by adiabatic compression along the major radius, which for two reasons is of special importance now. First, we are all aware of the improved plasma confinement with density rise on Alcator. The suppression of electron losses allows an approach towards, and a study of, the neoclassical regime of confinement. In this case, a heating problem arises. Ohmic heating needs too high fields, i.e. 16 T; the auxiliary heating - by RF or beam energy - has very severe limitations. Although the required power decreases with the square of the field, the power density rises proportionally to the field square. Therefore, the adiabatic approach is a natural one.

Second, in passing to the next stage, the study of fusion plasma burn, we should retain the possibility of carrying out a flexible experiment. This is of particular importance since we need precise information on a number of parameters, as the INTOR design analysis shows, for the construction stage of the next-generation devices. The opportunity must be provided for an operative experiment: the construction of the compactest and cheapest devices with rated neutron yield, i.e. with a minimum amount of particles within the volume. Depending on the nature of the losses, the energy and the number of particles drop in inverse proportion to the square of the field or to its first power, and, with due account of the geometry and stress limitations in the winding, the optimum field is close to 12 T.

Taking both of these aspects into account, we are continuing work on the application of adiabatic compression. The Proqramme includes studies on two tokamaks, T-13 and Tuman-3, and a full-scale experiment with a high-field tokamak (the parameters are given in Table I). Preliminary experiments, some of which are reported at this Conference, confirm the validity of the high-field tokamak concept. These experiments refer to discharge initiation (T-13), to the initial stage of plasma production, to the efficiency of compression along the minor radius (Tuman 2-A, Tuman 3), and to the possibility of automatically controlling the plasma column position under compression along the major radius. The experimental results achieved in TFTR also gave us encouragement, and we therefore ordered the equipment for a high field.

It can be shown that the attainable nt value is proportional to the energy in the plasma and to the average mechanical stresses in the winding. We choose the latter, of course, according to our possibilities of production. During the first stage of the experiments, about 150 MJ will be deposited within the tokamak. Later on, it will be possible to increase the contribution two to three times in order to enter the burn range with sufficient reliability.

Fast heating and the possibility of varying the compression regime allow us to hope for a better understanding of the beta-limits, which is a must for us at this stage.

The possibility of applying this approach to technological studies and its reactor prospects are determined by the so far unknown dependence of the effective electron heat conduction and of b on the temperature. This conclusion will therefore depend on the results of future experiments.

Thus an idea conceived by Lev Andreevich Artsimovich is being developed and we are counting very much upon its success.

Artsimovich held the opinion that our technological possibilities would enable us to pass to the DEMO stage of controlled fusion feasibility within one or two decades. The INTOR design has, since 1979, confirmed these assumptions. Today, we may maintain that it is widely agreed internationally that a fusion reactor providinq deuterium-tritium plasma burn will be constructed and put into operation at the beginning of the next decade.

According to the engineering requirements suggested by the IFRC, the INTOR programme should provide or demonstrate the following features: physics and engineering basis for a DEMO fusion reactor, achievement of the necessary physical parameters, design and test of the fusion reactor components, their integration into the reactor set, an efficiency test of the reactor as a whole, reliability and service life of the components and the reactor as a whole, test of the power - and tritium-producing systems as well as proof that the device is safe and fulfils the conditions posed by environmental protection. Discussions on the concept design have shown that this goal is realistic, provided that some supplementary scientific research programmes are carried out. In the USSR we are currently organizing a widespread publicity campaign on the results of INTOR design and optimization, in order to inform the power engineering community. The experience gained in maintaining the T-7 tokamak with superconducting coils, in designing and testing the superconducting parts of the T-15 magnetic system, in addition to a widespread fusion study programme on the tokamaks that are already operative or being put into operation, are a valuable support for the INTOR design. We are sure that Soviet industry, in particular, possesses the experience and technology necessary for the construction of INTOR. We can be even more certain of this when the entire international potential is being utilized.

New advances in the physics basis will undoubtedly be reported at this Conference. To begin with, I should like to congratulate our US and European colleagues on the startup of TFTR and JET and on the first results obtained from these machines. Between the last two Conferences, we witnessed not only a continuous advance in plasma confinement (nt = 1014 on Alcator), in heating (ICRH on PLT and other tokamaks, ECRH on T-10), and in induction-free sustainment of the current at elevated densities, but we also gained - treater confidence in the possibility of achieving the necessary beta-value.

Admittedly, the latter point needs further experimental verification, in particular the cardinal theoretical conclusion that the limiting b grows quadratically with decreasing aspect ratio.

This last conclusion may substantially affect all our concepts, even the choice of superconducting or 'warm' windings. All these achievements, as well as the information to be gained at this Conference, will be included in optimizing INTOR (Phase Two A), which is expected to be brought to a conclusion in summer 1985. My feeling is - and it also seems to be the opinion of the whole fusion community - that work on INTOR constitutes a great and undoubtedly unprecedented success on an international scale and is of great value to all participants. We should like to express our gratitude to the INTOR Group and to the Director General of the IAEA and his colleagues for their true support and assistance. Most of all, we should be proud that, during the years of difficult international relations (I hope they will never be worse), we managed to keep our sense of proportion and, by combined effort, to do something small but useful for mankind. Of course, in a lecture dedicated to Artsimovich I should mention that this is one more brick in the structure of our co-operation, our common cause in supplying power to humanity, a building for whose foundations Artsimovich worked so hard and successfully.

What shall we do after Phase Two A?

This is a crucial and difficult problem, and it is high time to think it over because it is not going to solve itself. Whatever happens, it will remain a useful piece of work, but a joint construction of INTOR would be a marvelous achievement, from every point of view. Otherwise, we shall lose a unique chance on such a scale in this century because no similar projects are to be seen on the horizon.

The national designs of the next big step in controlled fusion may differ from INTOR, in accordance with the nations' own scientific and engineering programmes. In the Soviet Union, the next step has been developed within the framework of the T-20 design: a large tokamak with 'warm' windings. T-20 should serve as a testbed for designing and testing commercial fusion reactor components. The engineering parameters of T-20 are somewhat conservative.

The success achieved in the tokamak studies, the successful operation of the T-7 tokamak with superconducting windings and the T-15 design (large tokamak, also with superconducting windings) encouraged us to use superconducting windings in the OTR design and to revise its parameters.

(1) Demonstration of feasibility of reliable and safe electricity and fissile fuel production by a fusion reactor

(2) Experience in design, construction and maintenance of the tokamak reactor in duration and specific-load regimes that are close to those of a commercial reactor;

(3) Construction of an experimental testbed for scientific and engineering research,

(4) Test of materials and verification of fundamental engineering solutions for building a fusion power plant in the future.

In the process of maintaining the OTR, problems of remote servicing and replacement of reactor parts and units during scheduled operation and repair periods must be solved.

The OTR reactor is at a stage of conceptual design now (reference parameters are given in Table II). The OTR is expected to have a partial uranium blanket (on the outside of the torus). This will enable us to demonstrate the production of a substantial amount of electricity and plutonium.

It is clear that we are counting on the first, quite definite application of fusion in a hybrid system, producing electricity and fissile fuel for atomic power plants. Recently we have been aware of definite support for this idea from the USA. I am thinking here of an analysis made by Claire E. Max from LLNL which, with arguments familiar to us, confirms the economic advantage of this approach, provided, of course, that atomic power Production develops in a normal manner. One figure from this report illustrates very well the difference between the scenario of power supply to thermal reactors and that of their replacement, which will be necessary for world power production: either to construct breeders, 65 per year from 2010 until 2050, or to construct hybrid reactors, ten per year from 2025 until 2050, having in mind the existing gap in the development of both technologies. Hence, the author comes to the most important conclusion that the fusion hybrid reactor is needed, and very soon, for the development of power production. Artsimovich meant the same when, to the question: "When will the first fusion power plant he built?" he replied: "When there is great need for it".

Has this time come? I think, it has and it coincides with the time when we are almost ready for it from the point of view of science and technology. But this is only my private opinion, which is not decisive. We should discuss it seriously within the fusion and scientific power engineering communities. At the same time, I do not, of course, reject the pure reactor concept. Moreover, there is some hope now of using tokamaks even for D-D reactions. But it will all require the solution of still more serious problems in physics and technology. This will be the next step in the development of fusion power production.

To conclude: I should like to explain why in this Artsimovich Memorial Lecture I have spoken only about tokamaks. There are two reasons. First, the tokamak is Artsimovich's main contribution to the development of plasma physics and controlled nuclear fusion research. Second, if we want to achieve something real this century, it will be possible only on the basis of tokamaks. Other concepts, even the most promising ones, require at least the same scale of collective effort for their foundation and verification. Artsimovich always supported a reasonable pluralism, in conjunction with a realistic assessment of the current situation.

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