By Academician Vasily GLUKHIKH, Director, Scientific Research Institute of Electrophysical Equipment named after D.V. Yefremov (NIIEFA); Anatoly MINEEV, Vitaly MURATOV, Oleg FILATOV, Candidates of Sciences (Phys. & Math.), researchers of the same Institute

Within a decade the first international experimental thermonuclear reactor is scheduled to go into operation. A major contribution to its development is being provided by researchers and engineers of St. Petersburg.

This could be startling news for an average layman to be told that we are all swimming in plasma-gas in ionized state. The proofs and manifestations of that in nature are strokes of lightning and also your own domestic lighting, in industry- welding equipment and devices for surface finishing, and in technical and medical fields- these are lasers. As a matter of fact, 90 percent of the matter of the Universe is plasma and synthesis reactions within it are the main source of energy of stars. And that means that there is no denying the fact that the world around us is a world of plasma. Having said that, we know but very little about how to "tame" plasma and put it at the service of our global and also daily needs and requirements.

Scientific research in this field has been going on since the end of WW2. A new science was born-plasma physics, and researchers have developed new methods of diagnostics of matter in what they call its extreme state. The main problem consists in heating deuterium-tritium plasma to temperatures appro-

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aching 100 mln degrees and maintain it at this temperature long enough for the synthesis reaction with the release of large amounts of energy. Solving this problem will mean solving the problem of controlled thermonuclear fusion.

Research in this general field is proceeding along the two main lines: retention of plasma with the help of strong magnetic fields, and what we call inertial retention with the help of successive microexplosions of targets heated by energy supplied from outside-from lasers or beams of particles. The present article focuses attention on systems of magnetic retention, commonly known as tokamaks.

The scientific guidance of the project, including determination of unit parameters, is the responsibility of the "Kurchatovsky Institute Research Center" (Moscow)-former Institute of Atomic Energy named after I. V. Kurchatov. A significant contribution to the studies of plasma behavior in magnetic retention systems has been provided by the RAS Physical-Technical Institute named after Joffe (FTI). The "Chief Designer" of practically all of big magnetic plasma retention units is our own Institute located a stone's throw away from our "Northern Palmyra". The Institute is surrounded by a cooperative of Leningrad enterprises which are putting the ideas of physicists into practice.

In 1958, NIIEFA (then Special Design Bureau) embarked on the development of the ALFA unit which became the responsibility of a team of experts with Acad. Vasily Glukhikh at the head. Components of the unit were produced by several Leningrad plants and we assembled them later. Among the major problems before our collective at that time was reaching high vacuum, prevention of breakdowns of insulation, development of systems of regulation of intensity of the vortex electric field, establishment of the principle of discharge current changes in time and reducing the level of magnetic fields scatter for improving the stability of plasma discharge.

ALFA experiments, conducted in conjunction with FTI specialists, make it possible to obtain data on the regimes and properties of powerful electrical discharge in toroidal chamber in the presence of a weak stabilizing longitudinal magnetic field. Many methods of plasma diagnostics were suggested which have since become part and parcel of measuring techniques in such units all over the world.

It should be noted at this point that ALFA dimensions were rather big for that time, unlike the size of the longitudinal magnetic field. The more promising turned out to be the approach according to which for the heating and retention of plasma its own current was used (generated by lengthwise vortical electric field), and for the suppression of the main plasma instabilities - a strong lengthwise magnetic field. This trend of research continued to develop at IAE under the name of "tokamak" (toroidal chamber with magnetic coils).

In the late 1950s we designed and produced at the ELEKTROSILA Plant in Leningrad the tokamak T-3 unit which has since been used for testing a number of technical solutions which were later used in the construction of other units. Later on we modernized T-3 (T-3A, T-4) boosting considerably the magnetic field.

One important result obtained by Soviet scientists and engineers at that time was the retention of high-temperature plasma much better than was suggested by pessimistic prognostications of our foreign colleagues. Subsequent verifications by British physicists of the T-3A data with the help of the instruments they brought with them confirmed the high plasma parameters-something that triggered the development of toka-mak-like units in other countries.

On the basis of the above it became possible to progress towards the parameters of a thermonuclear reactor. It had been demonstrated in theory that plasma retention should be improved considerably if the dimensions of the unit and the strength of the magnetic field are increased. This, however, could increase considerably the losses on the heating of conductor (copper) windings of the toroidal system. This being so, they were replaced with superconducting ones of the subsequent generations of "homemade" tokamaks.

The T-10 unit was completed in 1968 - 1971 and was put into operation in the middle of 1975. The complex and challenging project involved scores of R&D

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and design organizations, including NIIEFA where the work was supervised by its director, Prof. E. Komar, and after his death by the newly appointed director Prof. V Glukhikh. The Chief Engineer of the project was Prof. V. Muratov, and the construction of T-10 involved the staffs of a number of Leningrad enterprises, including the Pilot Plant of the Institute, KRASNY VYBORZHETS, ELEKTROSILA, SEVKABEL and Izhora Plant amalgamations, etc.

The starting impulse of plasma ignition in the new tokamak was much greater than in T-3 and T-4. The quality of the toroidal magnetic field was higher, and experiments on this unit, which continue to this day, provide a source of new and important data promoting the progress of the thermonuclear program. Thus, using super-high methods it became possible for the first time in the world to heat plasma electrons to thermonuclear temperatures (90 mln ^o C).

The next step was the building in the 1980s of two biggest tokamaks which were expected to attain plasma parameters of a nuclear reactor. The first of them-T-14 (or TSP-tokamak with a strong field)-was planned in order to sharply raise the temperature and density of plasma to use the principle of its adiabatic compression by a growing magnetic field by moving the plasma pinch in the toroidal chamber along a greater radius towards the unit center and implement reactions of synthesis of deuterium and tritium, investigating the impact of the obtained products on the combustion regime.

The task put before the chief designer of TSP (NIIEFA) was to produce an extremely tense structure with a giant power supply system (over 10 GVt). The scale of problems resolved by the Institute staff can be demonstrated by the following example. It has been possible to produce a toroidal winding in which, in the course of repeated working pulses, bronze passed from the elastic state into plastic one without destruction in the course of repeated working impulses.

The second unit, T-15-is the result of consistent improvements of T-3, T-4 and T-10 in boosting the geometric dimensions and the strength of the magnetic field. To reduce the capacity of the power supply it was decided to use the phenomenon of superconductivity in the making of the electromagnetic system.

The implementation of a project of this scale required the pooling of resources of some 30 research centers and enterprises. Among the first to be mentioned in St. Petersburg are NIIEFA (chief designer), its pilot plant (superconducting winding coils of toroidal field), Izhora Plant (special steel) and Admiralteisky Plant (heat screens), ELEKTROSILA amalgamation (coils of toroidal magnetic system and power structure), R&D Association KOM INTERN (system of ionic-cyclotron heating) and R&D Association BUREVESTNIK, to mention but a few.

Plasma experiments were commenced on both of these units in the late 1980s. By that time scientists in the United States, Japan and member states of the European Union, and also Russia, working on controlled thermonuclear fusion came to the conclusion that it would be more expedient and less expensive to tackle the problems by their combined efforts, making the best of each other's knowledge and experience. And combined efforts were launched for designing what was called an International Thermonuclear Experimental Reactor-ITER. And it should be pointed out at this stage that out of the total of 75 Russian centers and organizations engaged on this program 10 belong to St. Petersburg.

At the present stage design work on ITER has been completed and experts are choosing an appropriate building site. But the search continues for new solutions and approaches to the problem of controlled thermonuclear fusion. In the late 1990s, for example, specialists of the "Capital on the Neva" produced a rather small, but very promising unit-spherical tokamak GLOBUS-M. This is the fruit of the combined efforts of FTI (scientific direction), NIIEFA (electromagnetic system) and Leningradsky Severny Plant (vacuum chamber). This ongoing research can be crowned in time with a "harvest" of compact energy-intensive units in which the attainment of thermonuclear combustion will be a much simpler matter.

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