What is a tokamak? The thermonuclear reactor will open a new era for humanity. Technocratic movement Tokamak installation

a device for carrying out a thermonuclear fusion reaction in hot plasma in a quasi-stationary mode, wherein the plasma is created in a toroidal chamber and is stabilized by a magnetic field. The purpose of the installation is to convert intranuclear energy into heat and then into electricity. The word “tokamak” itself is an abbreviation for the name “toroidal magnetic chamber,” but the creators of the installation replaced the “g” at the end with a “k” so as not to evoke associations with something magical.

A person obtains atomic energy (both in a reactor and in a bomb) by dividing the nuclei of heavy elements into lighter ones. The energy per nucleon is maximum for iron (the so-called “iron maximum”), and since maximum in the middle, then energy will be released not only during the decay of heavy elements, but also during the combination of light elements. This process is called thermonuclear fusion and occurs in a hydrogen bomb and a fusion reactor. There are many known thermonuclear reactions and fusion reactions. The energy source can be those for which there is inexpensive fuel, and two fundamentally different ways of starting the fusion reaction are possible.

The first way is “explosive”: part of the energy is spent on bringing a very small amount of substance into the required initial state, a synthesis reaction occurs, and the released energy is converted into a convenient form. Actually, this is a hydrogen bomb, only weighing a milligram. An atomic bomb cannot be used as a source of initial energy; it is not “small”. Therefore, it was assumed that a millimeter tablet of deuterium-tritium ice (or a glass sphere with a compressed mixture of deuterium and tritium) would be irradiated from all sides by laser pulses. The energy density on the surface must be such that the top layer of the tablet, which has turned into plasma, is heated to a temperature at which the pressure on the inner layers and the heating of the inner layers of the tablet itself become sufficient for the synthesis reaction. In this case, the pulse must be so short that the substance, which has turned into plasma with a temperature of ten million degrees in a nanosecond, does not have time to fly apart, but presses on the inside of the tablet. This interior is compressed to a density one hundred times greater than that of solids and heated to one hundred million degrees.

Second way. The starting substances can be heated relatively slowly - they will turn into plasma, and then energy can be introduced into it in any way, until the conditions for the start of the reaction are achieved. For a thermonuclear reaction to occur in a mixture of deuterium and tritium and to obtain a positive energy output (when the energy released as a result of a thermonuclear reaction is greater than the energy expended on this reaction), it is necessary to create a plasma with a density of at least 10 14 particles/cm 3 (10 5 atm.), and heat it to approximately 10 9 degrees, while the plasma becomes completely ionized.

Such heating is necessary so that the nuclei can approach each other, despite Coulomb repulsion. It can be shown that to obtain energy, this state must be maintained for at least a second (the so-called “Lawson criterion”). A more precise formulation of the Lawson criterion: the product of concentration and the time of maintaining this state should be of the order of 10 15 cm cm 3. The main problem is the stability of the plasma: in a second it will have time to expand many times, touch the walls of the chamber and cool.

In 2006, the international community began construction of a demonstration reactor. This reactor will not be a real source of energy, but it is designed in such a way that after it if everything works fine it will be possible to begin the construction of “energy” ones, i.e. thermonuclear reactors intended for inclusion in the power grid. The largest physical projects (accelerators, radio telescopes, space stations) are becoming so expensive that considering two options turns out to be unaffordable even for humanity, which has united its efforts, so a choice has to be made.

The beginning of work on controlled thermonuclear fusion should be dated back to 1950, when I.E. Tamm and A.D. Sakharov came to the conclusion that controlled thermonuclear fusion (CTF) could be realized using magnetic confinement of hot plasma. At the initial stage, work in our country was carried out at the Kurchatov Institute under the leadership of L.A. Artsimovich. The main problems can be divided into two groups: problems of plasma instability and technological problems (pure vacuum, resistance to radiation, etc.) The first tokamaks were created in 1954-1960, now more than 100 tokamaks have been built in the world. In the 1960s, it was shown that heating by passing current (“ohmic heating”) alone could not bring a plasma to fusion temperatures. The most natural way to increase the energy content of plasma seemed to be the method of external injection of fast neutral particles (atoms), but only in the 1970s was the necessary technical level achieved and real experiments were carried out using injectors. Nowadays, heating of neutral particles by injection and electromagnetic radiation in the microwave range is considered the most promising. In 1988, the Kurchatov Institute built a pre-reactor generation tokamak T-15 with superconducting windings. Since 1956, when during N.S. Khrushchev’s visit to Great Britain I.V. Kurchatov announced the implementation of these works in the USSR. Work in this area is being carried out jointly by several countries. In 1988, the USSR, USA, European Union and Japan began designing the first experimental tokamak reactor (the installation will be built in France).

The dimensions of the designed reactor are 30 meters in diameter and 30 meters in height. The expected construction period of this installation is eight years, and the operating life is 25 years. The volume of plasma in the installation is about 850 cubic meters. Plasma current 15 megaamps. The thermonuclear power of the installation is 500 Megawatts and is maintained for 400 seconds. In the future, this time is expected to be increased to 3000 seconds, which will make it possible to conduct the first real studies of the physics of thermonuclear fusion (“thermonuclear combustion”) in plasma at the ITER reactor.

Lukyanov S.Yu. Hot plasma and controlled nuclear fusion. M., Nauka, 1975
Artsimovich L.A., Sagdeev R.Z. Plasma physics for physicists. M., Atomizdat, 1979
Hegler M., Christiansen M. Introduction to Controlled Fusion. M., Mir, 1980
Killeen J. Controlled thermonuclear fusion. M., Mir, 1980
Boyko V.I. Controlled thermonuclear fusion and problems of inertial thermonuclear fusion. Soros educational magazine. 1999, no. 6

TOKAMAK(abbreviated from “toroidal chamber with magnetic coils”) - a device for holding high temperatures using a strong magnet. fields. The idea of T. was expressed in 1950 by academicians I. E. Tamm and A. D. Sakharov; first experiments Research on these systems began in 1956.

The principle of the device is clear from Fig. 1. Plasma is created in a toroidal vacuum chamber, which serves as the only closed turn of the secondary winding of the transformer. When passing a current that increases over time in the primary winding of a transformer 1 inside the vacuum chamber 5 a vortex longitudinal electric force is created. field. When the initial gas is not very large (usually hydrogen or its isotopes are used), its electric power occurs. breakdown and the vacuum chamber is filled with plasma with a subsequent increase in a large longitudinal current Ip. In modern large T. the current in the plasma is several. million amperes. This current creates its own poloidal (in the plane of the plasma cross-section) magnetic field. field IN q. In addition, a strong longitudinal magnet is used to stabilize the plasma. field B f, created using special windings of toroidal magnet. fields. It is the combination of toroidal and poloidal magnets. fields ensures stable confinement of high-temperature plasma (see. Toroidal systems),necessary for implementation controlled thermonuclear fusion.

Rice. 1. Tokamak diagram: 1 - primary winding transformatter; 2 - toroidal magnetic field coils; 3 - liner, thin-walled inner chamber for engravingreduction of the toroidal electric field; 4 - reelki poloidal magnetic field; 5 - vacuum kamera; b-iron core (magnetic core).

Operating limits. Magn. the T field holds high-temperature plasma quite well, but only within certain limits of change in its parameters. The first 2 restrictions apply to the plasma current Ip and her cf. density P, expressed in units of the number of particles (electrons or ions) per 1 m 3. It turns out that for a given value of the toroidal magnet. field, the plasma current cannot exceed a certain limiting value, otherwise the plasma cord begins to twist along a helical line and eventually collapses: the so-called. current interruption instability. To characterize the limiting current, a coefficient is used. stock q by screw instability, determined by the relation q = 5B j a 2 /RI p. Here A- small, R- large radius of the plasma cord, B j - toroidal mag. field, Ip- current in plasma (dimensions are measured in meters, magnetic field - in teslas, current - in MA). A necessary condition for the stability of a plasma column is the inequality q>], so-called. k r i t e r i m K r u-s k a la - Shafranova. Experiments show that a reliably stable holding mode is achieved only at values of .

There are 2 limits for density - lower and upper. Lower The density limit is associated with the formation of the so-called. accelerated, or runaway electrons. At low densities, the frequency of collisions of electrons with ions becomes insufficient to prevent their transition to the mode of continuous acceleration in the longitudinal electric field. field. Electrons accelerated to high energies can pose a danger to the elements of the vacuum chamber, so the plasma density is chosen so high that there are no accelerated electrons. On the other hand, at a sufficiently high density, the plasma confinement mode again becomes unstable due to radiation and atomic processes at the plasma boundary, which lead to a narrowing of the current channel and the development of helical instability of the plasma. Top. the density limit is characterized by dimensionless parameters My-crayfish M=nR/B j and hugella H=nqR/B j (here averaged across the cross section is the electron density n measured in units of 10 20 particles/m 3). For stable plasma confinement it is necessary that the numbers M And H did not exceed certain critical values.

When the plasma heats up and its pressure increases, another limit appears, characterizing the maximum stable value of the plasma pressure, p = n(T e +T i), Where T e, T i-electronic and ion temperatures. This limit is imposed on the value of b equal to the ratio cf. plasma pressure to magnetic pressure. fields; a simplified expression for the limiting value b is given by Troyon's relation b c =gI p /aB j, where g-numerical factor equal to approximately 3. 10 -2.

Thermal insulation. The possibility of heating plasma to very high temperatures is due to the fact that in a strong magnetic field. charging trajectory field particles look like spirals wound on a magnetic line. fields. Thanks to this, electrons and ions are retained inside the plasma for a long time. And only due to collisions and small electrical fluctuations. and mag. fields, the energy of these particles can be transferred to the walls in the form of a heat flow. These same mechanisms determine the magnitude of diffusion fluxes. Magnetic efficiency thermal insulation of plasma is characterized by energy. lifetime t E = W/P, Where W-total energy content of plasma, a P- plasma heating power required to maintain it in a stationary state. Value t E can also be considered as the characteristic cooling time of the plasma if the heating power is suddenly turned off. In a quiet plasma, flows of particles and heat to the walls of the chamber are created due to pairwise collisions of electrons and ions. These flows are calculated theoretically taking into account real charge trajectories. particles per mag. field T. The corresponding theory of diffusion processes is called. neoclassical (see Migration processes). In real plasma T. there are always small fluctuations of fields and particle fluxes, therefore the real levels of heat and particle fluxes usually significantly exceed the predictions of neoclassical ones. theories.

Experiments carried out on many T. decomp. shapes and sizes, made it possible to summarize the results of studies of transfer mechanisms in the form of corresponding empirical studies. dependencies. In particular, energy dependences were found. lifetime t E from main plasma parameters for decomp. hold mod. These dependencies are called s k e l i n g a m i; they are successfully used to predict plasma parameters in newly commissioned installations.

Self-organization of plasma. In plasma T. there are always weakly nonlinear ones, which influence the profiles of the distribution of temperature, particle density and current density along the radius, as if they control them. In particular, to the center. areas of the plasma cord are very often present so-called. sawtooth oscillations reflecting a periodically repeating process of gradual exacerbation and then a sharp flattening of the temperature profile. Ramp-shaped oscillations prevent contraction of current to the magnet. torus axis (see Gas discharge contraction). In addition, in T. from time to time, helical modes are excited (the so-called t i r i n g modes), which are observed outside the cord in the form of low-frequency magnetic waves. hesitation. Tiring modes contribute to the establishment of a more stable distribution of current density along the radius. If the plasma is handled insufficiently carefully, tearing modes can grow so strong that the magnetic disturbances they cause can fields destroy magnets. surfaces throughout the entire volume of the plasma cord, magnetic. the configuration is destroyed, the plasma energy is released to the walls and the current in the plasma stops due to its strong cooling (see. Tearing instability).

In addition to these volumetric oscillations, there are oscillation modes localized at the boundary of the plasma column. These modes are very sensitive to the state of the plasma at the very periphery; their behavior is complicated by atomic processes. Ext. and internal vibration modes can strongly influence the processes of heat and particle transfer; they lead to the possibility of plasma transition from one magnetic mode. thermal insulation to another and back. If in plasma T. the particle velocity distribution is very different from , then the possibility arises for the development of kinetic. instabilities. For example, with the birth of a large number of runaway electrons, the so-called fan instability, leading to the transformation of longitudinal electron energy into transverse energy. Kinetic. instabilities also develop in the presence of high-energy ions that arise when complementary. heating the plasma.

Plasma heating. The plasma of any T. is automatically heated due to Joule heat from the current flowing through it. The Joule energy release is sufficient to obtain a temperature of several. million degrees For the purposes of controlled thermonuclear fusion, temperatures >10 8 K are needed, therefore all large T. are supplemented with powerful systems plasma heating. For this purpose, either electric magnets are used. waves decomposed ranges, or direct fast particles into plasma. For high-frequency plasma heating, it is convenient to use resonances, which correspond to internal. oscillate processes in plasma. For example, it is convenient to heat the ion component in the range of harmonics of cyclotron frequencies or basic. plasma ions, or specially selected additive ions. Electrons are heated by electron cyclotron resonance.

When heating ions with fast particles, powerful beams of neutral atoms are usually used. Such beams do not interact with magnetism. field and penetrate deep into the plasma, where they are ionized and captured by magnetism. field T.

With the help of additional heating methods, it is possible to raise the plasma temperature T. to >3·10 8 K, which is quite sufficient for a powerful thermonuclear reaction to occur. In future T.-reactors being developed, plasma heating will be carried out by high-energy alpha particles arising from the fusion reaction of deuterium and tritium nuclei.

Stationary tokamak. Typically, current flows in plasma only in the presence of an eddy electric current. field created by increasing the magnetic field. flow in the inductor. The inductive mechanism for maintaining current is limited in time, so the corresponding mode of plasma confinement is pulsed. However, the pulsed mode is not the only possible one; heating the plasma can also be used to maintain the current if, along with energy, a pulse that is different for different components of the plasma is also transferred to the plasma. Non-inductive current maintenance is facilitated due to the generation of current by the plasma itself during its diffusion expansion towards the walls (bootstrap effect). The bootstrap effect was predicted by neoclassical scientists. theory and then confirmed experimentally. Experiments show that T. plasma can be held stationary, and Ch. efforts to practically development of the stationary mode are aimed at increasing the efficiency of current maintenance.

Diverter, impurity control. For the purposes of controlled thermonuclear fusion, very pure plasma based on hydrogen isotopes is required. To limit the admixture of other ions in the plasma, in early T. the plasma was limited to the so-called. l i m i t e r o m (Fig. 2, A), i.e., a diaphragm that prevents the plasma from coming into contact with the large surface of the chamber. In modern T. a much more complex divertor configuration is used (Fig. 2, b), created by poloidal magnet coils. fields. These coils are necessary even for plasma with a round cross-section: with their help, the vertical magnetic component is created. fields, edges when interacting with the main. plasma current does not allow the plasma coil to be thrown onto the wall in the direction of a large radius. In the divertor configuration, the turns of the poloidal magnet. the fields are located so that the plasma cross section is elongated in the vertical direction. At the same time, closed magnetic surfaces are preserved only inside; outside, its lines of force go inside the divertor chambers, where the plasma flows flowing from the main are neutralized. volume. In divertor chambers, it is possible to soften the load from the plasma on the divertor plates due to the addition. plasma cooling during atomic interactions.

Rice. 2. Cross section of plasma with a circular cross-section ( A) and vertically elongated to form a divertor configuration ( 6): 1-plasma; 2- limiter; 3 - chamber wall; 4 - separatrix; 5-divertor chamber; 6 - divertor plates.

Tokamak reactor. Ch. The goal of research on T. installations is to master the concept of magnetic. Plasma Containment for Creatures fusion reactor. On T. it is possible to create a stable high-temperature plasma with a temperature and density sufficient for a thermonuclear reactor; laws have been established for thermal insulation of plasma; methods of maintaining current and controlling the level of impurities are mastered. Work on T. is moving from the purely physical phase. research in the phase of creating experiments. .

Lit.: Artsimovich L. A., Managed, 2nd ed., M., 1963; Lukyanov S. Yu., Hot plasma and controlled nuclear fusion, M., 1975; Kadomtsev B.V., Tokamak plasma a complex physical system, L., 1992. B. B. Kadomtsev.

Tokamak (toroidal chamber with magnetic coils) is a toroidal installation for magnetically confining plasma in order to achieve the conditions necessary for controlled thermonuclear fusion to occur. The plasma in a tokamak is held not by the walls of the chamber, which can withstand its temperature only up to a certain limit, but by a specially created magnetic field. Compared to other installations that use a magnetic field to confine plasma, a tokamak feature is the use of an electric current flowing through the plasma to create the poloidal field necessary to compress, heat, and maintain equilibrium of the plasma. This, in particular, differs from a stellarator, which is one of the alternative confinement schemes in which both toroidal and poloidal fields are created using magnetic coils. But since the plasma filament is an example of an unstable equilibrium, the tokamak project has not yet been implemented and is at the stage of extremely expensive experiments to complicate the installation.

It should also be noted that, unlike fissile reactors (each of which was initially designed and developed separately in their own countries), the tokamak is currently being jointly developed within the framework of the international scientific project ITER.

Tokamak magnetic field and flux.

Story

USSR postage stamp, 1987.

The proposal to use controlled thermonuclear fusion for industrial purposes and a specific scheme using thermal insulation of high-temperature plasma by an electric field were first formulated by the Soviet physicist O. A. Lavrentiev in a work in the mid-1950s. This work served as a catalyst for Soviet research on the problem of controlled thermonuclear fusion. A.D. Sakharov and I.E. Tamm in 1951 proposed modifying the scheme, proposing a theoretical basis for a thermonuclear reactor, where the plasma would have the shape of a torus and be contained by a magnetic field.

The term “tokamak” was coined later by Igor Nikolaevich Golovin, a student of Academician Kurchatov. Initially it sounded like “tokamag” - an abbreviation for the words “toroidal magnetic chamber”, but N.A. Yavlinsky, the author of the first toroidal system, proposed replacing “-mag” with “-mac” for euphony. Later this name was borrowed by many languages.

The first tokamak was built in 1955, and for a long time tokamaks existed only in the USSR. Only after 1968, when on the T-3 tokamak, built at the Institute of Atomic Energy. I.V. Kurchatov, under the leadership of Academician L.A. Artsimovich, a plasma temperature of 10 million degrees was reached, and English scientists with their equipment confirmed this fact, which at first they refused to believe, a real tokamak boom began in the world. Since 1973, the research program for plasma physics on tokamaks was headed by Boris Borisovich Kadomtsev.

Currently, a tokamak is considered the most promising device for implementing controlled thermonuclear fusion.

Device

A tokamak is a toroidal vacuum chamber on which coils are wound to create a toroidal magnetic field. The air is first pumped out of the vacuum chamber and then filled with a mixture of deuterium and tritium. Then, using an inductor, a vortex electric field is created in the chamber. The inductor is the primary winding of a large transformer, in which the tokamak chamber is the secondary winding. The electric field causes current to flow and ignite the plasma chamber.

The current flowing through the plasma performs two tasks:

heats the plasma in the same way as any other conductor would (ohmic heating);

creates a magnetic field around itself. This magnetic field is called poloidal (that is, directed along lines passing through the poles of the spherical coordinate system).

The magnetic field compresses the current flowing through the plasma. As a result, a configuration is formed in which helical magnetic field lines “twist” the plasma cord. In this case, the step during rotation in the toroidal direction does not coincide with the step in the poloidal direction. The magnetic lines turn out to be unclosed; they twist around the torus infinitely many times, forming the so-called “magnetic surfaces” of a toroidal shape.

The presence of a poloidal field is necessary for stable plasma confinement in such a system. Since it is created by increasing the current in the inductor, and it cannot be infinite, the time of stable existence of plasma in a classical tokamak is limited. To overcome this limitation, additional methods of maintaining current have been developed. For this purpose, injection of accelerated neutral deuterium or tritium atoms or microwave radiation into the plasma can be used.

In addition to toroidal coils, additional poloidal field coils are required to control the plasma cord. They are ring turns around the vertical axis of the tokamak chamber.

Heating alone due to the flow of current is not enough to heat the plasma to the temperature required for a thermonuclear reaction. For additional heating, microwave radiation is used at so-called resonant frequencies (for example, coinciding with the cyclotron frequency of either electrons or ions) or injection of fast neutral atoms.

Tokamaks and their characteristics

In total, about 300 tokamaks were built in the world. The largest of them are listed below.

USSR and Russia

T-3 is the first functional device.

T-4 - enlarged version of T-3

T-7 is a unique installation in which, for the first time in the world, a relatively large magnetic system with a superconducting solenoid based on tin niobate cooled by liquid helium is implemented. The main task of T-7 was completed: the prospect for the next generation of superconducting solenoids for thermonuclear power was prepared.

T-10 and PLT are the next step in world thermonuclear research, they are almost the same size, equal power, with the same confinement factor. And the results obtained are identical: in both reactors the temperature of thermonuclear fusion was reached, and the lag according to the Lawson criterion was 200 times.

T-15 is a reactor of today with a superconducting solenoid giving an induction field of 3.6 Tesla.

China

EAST - located in Hefei City, Anhui Province. The Lawson criterion for ignition level was exceeded at the tokamak, the energy output coefficient was 1.25

7 billion tenge from the country's budget invested in construction, and 6 years of forced downtime in search of sources of financing. The Kazakh materials science tokamak project was on the verge of closure. However, the situation has changed radically thanks to new directions of international cooperation. Journalist Grigory Bedenko visited Kurchatov and prepared a report specifically for Infromburo.kz about the prospects for research in the field of controlled thermonuclear fusion.

A little history

In the middle of the 20th century, the most developed countries of the world very quickly mastered atomic energy and learned to use it both in military weapons programs and to produce large volumes of thermal and electrical energy for peaceful purposes. However, the process of controlled decay of the atomic nucleus turned out to be extremely unsafe for the environment. Accidents at nuclear power plants and the enormous problem of disposing of high-level waste have deprived this type of energy of its prospects. Then, in the middle of the century, scientists hypothesized that controlled thermonuclear fusion could be an alternative. Experts proposed repeating, under terrestrial conditions, the processes occurring in the depths of stars, and learning not only to control them, but also to obtain energy in the quantities necessary for the existence of civilization. As is known, thermonuclear fusion is based on the principle of fusion of light hydrogen nuclei into heavier ones with the formation of helium. In this case, much more energy is released than during the reverse process, when the nuclei of heavy elements are divided into lighter ones with enormous energy release and the formation of isotopes of various elements of the periodic table. There are no harmful effects or hazardous production waste in thermonuclear reactors.

Diagram of the international experimental thermonuclear reactor ITER

It is curious that the thermonuclear fusion process itself was quite easily recreated for weapons programs, but the development of peaceful energy projects turned out to be an almost impossible task. The main thing for a hydrogen bomb is, in fact, to start the fusion process, which occurs in nanoseconds. But a power thermonuclear reactor requires special conditions. To obtain energy, it is necessary to keep high-temperature plasma in a controlled state for a certain period of time - it is heated from 10 to 30 million degrees Celsius. By confining such a plasma, physical conditions are created for the fusion of light deuterium and tritium nuclei into heavy ones. Moreover, more energy should be released than spent on heating and confining the plasma. It is believed that a single pulse with controlled thermonuclear fusion with a positive energy release coefficient should last at least 500 seconds. But for such a time and at such temperatures, not a single structural material of a promising reactor will withstand it. It will simply evaporate. And scientists around the world have been struggling with the problem of materials science for more than half a century almost to no avail.

Plasma obtained at the Kazakhstan materials science tokamak / Materials provided by the Institute of Atomic Energy of the National Nuclear Center of the Republic of Kazakhstan

Materials provided by the Institute of Atomic Energy NNC RK

This highly slow-motion video shows the formation of plasma in a Kazakhstani tokamak (materials provided by the Institute of Atomic Energy of the National Nuclear Center of the Republic of Kazakhstan)

Plasma formation in CFT

What are tokamak and stellarator?

The abbreviation is Russian, as the first installation was developed in the Soviet Union. A tokamak is a toroidal chamber with magnetic coils. A torus is a three-dimensional geometric figure (shaped like a donut, in simple words), and a toroid is a thin wire wound around a torus-shaped frame. Thus, high-temperature plasma in the installation is formed and retained in the shape of a torus. In this case, the main principle of a tokamak is that the plasma does not interact with the walls of the chamber, but hangs in space, as it were, held by a super-powerful magnetic field. The scheme for thermal insulation of plasma and the method of using such installations for industrial purposes were first proposed by the Soviet physicist Oleg Aleksandrovich Lavrentyev. The first tokamak was built in 1954 and for a long time existed only in the USSR. To date, about two hundred similar devices have been built in the world. Currently, there are operating toroidal chambers for studying controlled thermonuclear fusion in Russia, the USA, Japan, China and the European Union. The largest international project in this area is ITER (more on that later). The initiator of the construction of a materials science tokamak in Kazakhstan was the head of the Russian Kurchatov Institute, Academician Evgeny Pavlovich Velikhov. Since 1975, he headed the Soviet controlled fusion reactor program. The idea to build a facility at the former Semipalatinsk nuclear test site appeared in 1998, when Velikhov met with President of the Republic of Kazakhstan Nursultan Nazarbayev.

Scheme of plasma confinement in a stellarator / Materials provided by the Institute of Atomic Energy NNC RK

A stellarator is an alternative type of reactor to a tokamak for carrying out controlled thermonuclear fusion. Invented by American astrophysicist Lyman Spitzer in 1950. The name comes from the Latin word stella (star), which indicates the similarity of processes inside stars and in a man-made installation. The main difference is that the magnetic field for isolating the plasma from the inner walls of the chamber is created entirely by external coils, which allows it to be used in continuous mode. The plasma in the stellarator is formed in the shape of a “crumpled donut” and, as it were, twists. Today, there are research stellarators in Russia, Ukraine, Germany and Japan. Moreover, the world’s largest stellarator, Wendelstein 7-X (W7-X), was recently launched in Germany.

Kazakhstani materials science tokamak / Grigory Bedenko

These are all research facilities,” says the head of the scientific group of the KTM project. Stellarator differs in the configuration of its magnetic field. In a tokamak, a so-called toroidal winding and a poloidal outer winding are used to contain the plasma. But in a stellarator it’s the other way around - there is a winding wound in a spiral, which performs the functions of both toroidal and poloidal. The tokamak is initially a pulsed installation, and the stellarator is a more stationary installation, that is, the advantage of the twisted winding allows you to hold the plasma indefinitely. Stellarators were developed at the same time as tokamaks, and at one time tokamaks took the lead in plasma parameters. The “procession” of tokamaks has begun all over the world. But nevertheless, stellarators are developing. They are available in Japan; they were recently built in Germany - the Wendelstein 7-X (W7-X) was put into operation. There is a stellarator in the USA. In addition, there are a huge number of all kinds of research installations with partly magnetic plasma confinement - these are various traps. There is also inertial thermonuclear fusion, when a small target is heated by laser radiation. This is such a small thermonuclear explosion.

Units and assemblies of the upper part of the installation / Grigory Bedenko

And yet, the tokamak is considered the most promising as an industrial thermonuclear reactor today.

Technological building in which KTM is located / Grigory Bedenko

Tokamak in Kazakhstan

The Kazakhstan installation was built by 2010 on a specially designated site in the administrative zone of the former Semipalatinsk test site - the city of Kurchatov. The complex consists of several technological buildings that house tokamak components and assemblies, as well as workshops, rooms for data processing, personnel accommodation, etc. The project was developed in Russia on the basis of the National Center for Thermonuclear Research (Kurchatov Institute). The vacuum chamber, magnetic coils, etc. were designed and assembled at the Research Institute of Electrophysical Equipment named after. D.V. Evremov (Research Institute EFA), automation - at the Tomsk Polytechnic Institute. Participants in the project from the Russian side also included the All-Russian Institute of Currents (NII TVCH), TRINITI (Troitsk Institute of Innovative and Thermonuclear Research). The general designer from Kazakhstan was Promenergoproekt LLP, and the Kazelektromontazh UPC complex was directly installed. After all the work was completed, the CTM was launched and produced the first plasma. Then funding for the project was stopped, and the tokamak turned into an expensive high-tech tourist attraction for six long years.

Installation of retrofitting equipment for KTM / Grigory Bedenko

Second life of KTM

The project was rebooted on the eve of EXPO 2017 in Astana. It fit perfectly with the concept of the World Exhibition dedicated to the energy of the future. On June 9, the installation was restarted in the presence of a large number of journalists. Russian developers were present at the launch. As it was stated during the ceremony, the purpose of the first stage of the physical launch is to debug and test the standard KTM systems. Also, according to the head of the National Nuclear Center of the Republic of Kazakhstan Erlan Batyrbekov, on the basis of the Kazakh tokamak, scientists from different countries will be able to conduct a wide range of research, including the modernization of existing industrial reactors.

The AC converter for KTM has a futuristic look / Grigory Bedenko

Then the situation developed in an even more favorable direction. In Astana, during the Ministerial Conference and the VIII International Energy Forum, Kazakhstan received an official invitation to become an associate member of the International Organization ITER. The International Thermonuclear Experimental Reactor is being created by a group of countries to demonstrate the possibility of commercial use of thermonuclear energy, as well as solving physical and technological problems in this area. In essence, ITER is a huge and very complex tokamak. The countries of the European Union, India, China, South Korea, Russia, the USA, Japan and now our country are taking part in the project. From Kazakhstan, research on the topic will be carried out by specialists from the National Nuclear Center, the Research Institute of Experimental and Theoretical Physics of Kazakh National University. Al-Farabi, Institute of Nuclear Physics, Ulba Metallurgical Plant, KazNIPIEnergoprom and Kazelektromash. ITER will be created in France, 60 kilometers from Marseille. Currently, the cost of the project is estimated at 19 billion euros. The launch of the installation is scheduled for 2025.

Baurzhan Chektybaev / Grigory Bedenko

Baurzhan Chektybaev, head of the scientific group of the CT projectM

On June 10, a memorandum was concluded on joint research between ITER and KTM. Within the framework of this agreement, a project for interaction with the International Organization ITER is currently being prepared. They are interested in our installation. The ITER project itself is also not simple; there is a problem of materials. As part of the project, we will study tungsten and beryllium. Certain components and parts of ITER will be made from this material. We will run them in. The entire first wall of the ITER reactor will be lined with tungsten and beryllium tiles. The vacuum chamber itself consists of a diverter, into which plasma flows flow; there is the most intense place - 20 MW per square meter. There will be tungsten. The rest of the first wall will be lined with beryllium.

KTM is a very complex system from a technological point of view / Grigory Bedenko

- Why inITERso interested in our tokamak?

In addition to materials science, the task of our installation is to study plasma physics. CTM is unique in terms of aspect ratio. There is such a parameter, one of the main ones for tokamaks - the ratio of the large radius from the axis to the center of the plasma to the small one, that is, from the plasma axis to its edges. For us this parameter is equal to two. In the same ITER - 3.1. All tokamaks that are more than 3 are classic. There is a modern direction of tokamaks - these are spherical tokamaks, in which the aspect ratio is less than 2 - one and a half and even lower - these are cool, almost spherical chambers. Our tokamak is located, as it were, in a borderline position, between classical and spherical tokamaks. There have not been such installations yet, and here, I think, interesting research will be conducted on the behavior of plasma. Such installations are considered as hybrid future reactors, or volumetric neutron sources.

The lower part of the KTM vacuum chamber / Photo by Grigory Bedenko

- How promising is cooperation withITER?Will it save the project?

In 2010, there was a trial launch using the equipment and the readiness that was available at that time. The task was to show that the installation “breathes” and is capable of working. In the same tenth year, we ran out of funding. Then there were six years of inactivity. All this time we were fighting for the budget. It was previously approved in 2006, and had to be completely revised. About 80% of our equipment is foreign, and in the context of well-known events in the global financial system, the facility has become significantly more expensive than originally planned. In 2016, after adjusting the project budget, additional funding was allocated. The installation has already cost the Kazakh budget 7 billion tenge. This includes construction and installation work, manufacturing of a vacuum chamber and electromagnetic system.

Researchers have to be jacks of all trades / Grigory Bedenko

- What's happening now? There was a trial run in June.

Now the creation of KTM is at its final stage. Currently, installation and commissioning of main and auxiliary systems is underway. We have concluded an agreement with the general contractor who won the tender. There are two companies, one is engaged in construction and installation work, the second - commissioning work. “KazIntelgroup” is engaged in construction and installation work, “Quality Guarantor XXI Century” is engaged in commissioning. Construction of the installation is scheduled to be completed this year. Then, before the end of the year, a physical launch will take place. In 2018, the installation will be put into operation and full-scale experiments will begin. Within 3 years, we plan to reach the nominal design parameters that are included in the installation, and then further research the materials.

In some places the KTM resembles an alien ship / Photo by Grigory Bedenko

- How are you doing with the selection of employees?

Most of the young specialists are graduates of Kazakhstani universities, from Ust-Kamenogorsk, Pavlodar and Semey. Some graduated from Russian universities, for example, Tomsk Polytechnic University. The staffing issue is acute. According to the project, there should be about 120 people, 40 people work. Next year, when the complex is put into operation, then there will be recruitment. But finding specialists in this area is a separate and difficult task.

Dmitry Olkhovik, head of the KTM experiment automation systems department

The peculiarity of the CFT is that it has a rotary-diverter device, that is, all the materials under study can be rotated inside the chamber. In addition, there is also a transport gateway device. This makes it possible to recharge the materials under study without depressurizing the vacuum chamber. On other installations there are certain difficulties: if the chamber has been depressurized, at least a week or two is needed to prepare it again for new launches. We can easily replace test samples in one campaign, without wasting time on depressurization. This is the economic advantage of the installation.

Some types of new equipment are still in original packaging / Grigory Bedenko

- How will the experiments be carried out?

At such installations, two experimental campaigns are carried out per year. For example, we conduct a campaign in the spring, then in the summer we analyze the data obtained and plan further experiments. The second campaign takes place in the fall. The campaign itself lasts from two to three months. There are two main problems on the way to creating a power fusion reactor. The first is to develop the technology for producing and retaining plasma, the second is to develop materials, those that address the plasma directly, because plasma is high-temperature. Huge streams of energy fly and influence the material. The material, in turn, is destroyed and dispersed. And the entry of these particles into the plasma has an extremely negative effect. Plasma is very sensitive to impurities. They cool the plasma and eventually extinguish it. There is also the topic of neutron effects on structural materials. Our tokamak will test materials to determine their heat resistance. This means that they are non-sprayable and compatible with plasma. Tungsten and beryllium will be studied as such materials. We will test them, see how they behave under conditions of high plasma flows, the same as at ITER.

Huge power currents are used in KTM / Grigory Bedenko

- What work is being carried out to retrofit the KTM?

Installation of technological systems for vacuum systems, cooling systems. This is a very complex electrical installation. To get a magnetic field, you need to take a lot of energy from the network. There is a certain complex for energy conversion. Starting from the pulsed power supply system, a lot of carrier transformers are used, and a terristor converter complex is used, that is, a rather complex system in terms of operation, control, and the system is very distributed. That is, all this work is now being carried out, power supplies are being adjusted.

The work is very painstaking / Grigory Bedenko

Working with new KTM equipment

Such installations require a very large amount of electricity to operate. Will KTM consume a lot?

When operating in nominal mode, the electricity intake from the network will be about 80-100 MW. For one experiment. There is also a standard additional heating system, which will also pump energy from the network.

Magnetic coil power supply system / Grigory Bedenko

It is known that in Kazakhstan a significant part of the population has radiophobia. These are the socio-psychological consequences of nuclear tests. How safe will your research be?

It is believed that controlled thermonuclear fusion is an alternative environmentally friendly energy source. Accidents like Chernobyl, Fukushima, etc. simply physically cannot happen here. The most serious thing that can happen is the depressurization of the vacuum chamber where the plasma is contained. In this case, the plasma is quenched and these few grams of thermonuclear fuel that was in the chamber leak out.

Upper part of the installation / Grigory Bedenko

And a few more interesting facts about ITER, the largest international project in the history of such research, on which our experts have high hopes. As mentioned above, ITER is an international organization that includes more than a dozen countries: Russia, France, Japan, China, India, the European Union, Canada, and the USA. Interestingly, each country's contribution to the project is made in the form of finished products. For example, Russia produces some cryogenic windings based on superconductors, power equipment, etc.

Work on setting up the power supply system on KTM / Grigory Bedenko

ITER is not yet an energy installation; it will not provide energy. This is a technology demonstration of the feasibility of producing plasma with energy output. After ITER, when the technologies are developed, a demonstration reactor will be created that will already provide energy. This will happen somewhere in the 40-50s of the 21st century. That is, 100 years after the start of research on this topic.

KTM control room / Grigory Bedenko

The ITER project has about 500 seconds of continuous operation. Pulse reactor. In principle, up to 1000 sec is provided. - how will it go? When all technologies have been selected, materials and design have been approved, DEMO will be created next. It has already been decided that this reactor will be built in Japan.

KTM units / Grigory Bedenko

Apparently, the operating principle of a power thermonuclear reactor will be as follows. The first element, which will absorb the thermal energy of the plasma, will contain channels for heat exchange inside itself. Then everything is the same as at a conventional power plant - heating the secondary circuit coolant, spinning up the turbines and generating electrical energy.

General view of the KTM reactor hall / Grigory Bedenko

The physical launch of ITER will take place in 2025. It will be put into operation in 2028. Based on the results of the work, the option of creating hybrid reactors is being considered - where neutrons from thermonuclear fusion are used to split nuclear fuel.

In order to achieve the conditions necessary for the occurrence. The plasma in a tokamak is held not by the walls of the chamber, which are not able to withstand the temperature necessary for thermonuclear reactions, but by a specially created combined magnetic field - a toroidal external and poloidal field of the current flowing through the plasma cord. Compared to other installations that use a magnetic field to confine plasma, the use of electric current is the main feature of a tokamak. The current in the plasma ensures heating of the plasma and maintaining the equilibrium of the plasma filament in the vacuum chamber. In this way, a tokamak, in particular, differs from a stellarator, which is one of the alternative confinement schemes in which both toroidal and poloidal fields are created using external magnetic coils.

The Tokamak reactor is currently being developed as part of the international scientific project ITER.

Story

Currently, the tokamak is considered the most promising device for implementing controlled thermonuclear fusion.

Device

A tokamak is a toroidal vacuum chamber on which coils are wound to create a toroidal magnetic field. The air is first pumped out of the vacuum chamber and then filled with a mixture of deuterium and tritium. Then using inductor a vortex electric field is created in the chamber. The inductor is the primary winding of a large transformer, in which the tokamak chamber is the secondary winding. The electric field causes current to flow and ignition in the plasma chamber.

The current flowing through the plasma performs two tasks:

heats the plasma in the same way as any other conductor would (ohmic heating);
creates a magnetic field around itself. This magnetic field is called poloidal(that is, directed along lines passing through poles spherical coordinate system).

The presence of a poloidal field is necessary for stable plasma confinement in such a system. Since it is created by increasing the current in the inductor, and it cannot be infinite, the time of stable existence of plasma in a classical tokamak is still limited to a few seconds. To overcome this limitation, additional methods of maintaining current have been developed. For this purpose, injection into the plasma of accelerated neutral atoms of deuterium or tritium or microwave radiation can be used.

In addition to toroidal coils, additional ones are required to control the plasma cord. poloidal field coils. They are ring turns around the vertical axis of the tokamak chamber.

Tokamaks and their characteristics

In total, about 300 tokamaks were built in the world. The largest of them are listed below.

USSR and Russia

Kazakhstan

The Kazakhstan Materials Research Tokamak (KTM) is an experimental thermonuclear installation for research and testing of materials in energy load regimes close to