Held in a tokamak. What is a "tokamak"? Fusion reactor will open a new era for mankind
The content of the article
TOKAMAK– a device for carrying out a thermonuclear fusion reaction in a hot plasma in a quasi-stationary mode, with the plasma being created in a toroidal chamber and stabilized by a magnetic field. The purpose of the installation is the conversion of intranuclear energy into thermal energy and then into electrical energy. The word “tokamak” itself is an abbreviation of the name “magnetic toroidal chamber”, however, the creators of the installation replaced the “g” with “k” at the end, so as not to evoke associations with something magical.
A person receives 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, but also when light elements are combined. This process is called thermonuclear fusion, it takes place in a hydrogen bomb and a thermonuclear reactor. There are many known thermonuclear reactions, fusion reactions. The source of energy can be those for which there is inexpensive fuel, and there are two fundamentally different ways to start the fusion reaction.
The first way is “explosive”: part of the energy is spent on bringing a very small amount of matter to the required initial state, a synthesis reaction occurs, 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 cannot be “small”. Therefore, it was assumed that a millimetric 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 upper layer of the tablet that 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 fusion reaction. In this case, the pulse must be so short that the substance that has turned into a plasma with a temperature of ten million degrees in a nanosecond does not have time to scatter, but presses on the inside of the tablet. This inner part is compressed to a density one hundred times greater than the density of solids, and heated to a hundred million degrees.
Second way. The initial 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 reached. In order for a thermonuclear reaction to proceed in a mixture of deuterium and tritium and to obtain a positive energy yield (when the energy released as a result of a thermonuclear reaction turns out to be greater than the energy spent 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 up to about 10 9 degrees, while the plasma becomes completely ionized.
Such heating is necessary so that the nuclei can approach each other, despite the Coulomb repulsion. It can be shown that in order to obtain energy, it is necessary to maintain this state for at least a second (the so-called "Lawson criterion"). A more precise formulation of the Lawson criterion is that the product of the concentration and the maintenance time of this state should be on the order of 1015 sCh 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 down.
In 2006, the international community starts building 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 start building "energy", i.e. intended for inclusion in the power grid, thermonuclear reactors. The largest physical projects (accelerators, radio telescopes, space stations) are becoming so expensive that consideration of two options is beyond the means of even humanity, which has united its efforts, so a choice has to be made.
The beginning of work on controlled thermonuclear fusion should be attributed to 1950, when I.E. Tamm and A.D. Sakharov came to the conclusion that it is possible to implement CTS (controlled thermonuclear fusion) 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 only by means of heating due to the passage of current ("ohmic heating") it is impossible to bring the plasma to thermonuclear 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 reached and real experiments were carried out using injectors. Now the most promising are the heating of neutral particles by injection and electromagnetic radiation in the microwave range. In 1988, the T-15 pre-reactor generation tokamak with superconducting windings was built at the Kurchatov Institute. Since 1956, when during the visit of N.S. Khrushchev to Great Britain I.V. Kurchatov announced that these works were being carried out in the USSR. work in this area is carried out jointly by several countries. In 1988, the USSR, the USA, the 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 high. The expected construction period for this plant is eight years, and the operation life is 25 years. The volume of plasma in the installation is about 850 cubic meters. The plasma current is 15 megaamperes. The thermonuclear power of the installation of 500 megawatts 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.
Design.
The device looks like this - the toroidal chamber is put on the core of the transformer, the plasma in the chamber is, in fact, the transformer winding. Atmospheric air is pumped out of the chamber, and then a mixture of gases containing those atoms that will participate in the synthesis is let in. Then, a current pulse is passed through the primary winding of the transformer, sufficient for a breakdown to occur in the secondary "winding" (i.e., in gas) and current begins to flow. When current flows, the plasma heats up, but this method alone fails to heat it above 20 million degrees, since with increasing temperature the plasma resistance and heat release decrease. The current flowing through the plasma creates its own magnetic field, which compresses the plasma, increasing its temperature and concentration, but this is still not enough to achieve the Lawson criterion, so the plasma must be heated additionally. This additional heating can be achieved by electromagnetic radiation with a frequency of 10 MHz to 10 GHz, by a stream of neutral atoms with a high energy of about 0.1 MeV, or by compression by an external alternating magnetic field.
Plasma "lives" in a magnetic field. A constant field could be created by a permanent magnet, although they have their limitations, but in this case the question of a permanent magnet does not arise, because. variable fields are needed, so an electromagnet is used, but when current flows through its winding, heat is generated. When this happens in a plasma, heat is used, but in the winding it is wasted, it must be removed, and the energy intended to ensure the flow of current through the windings must be spent, while a significant fraction of the energy received would be spent on the operation of electromagnets, while the windings will be made of superconducting materials.
One of the important problems of the tokamak is to ensure the purity of the plasma, since impurities entering the plasma stop the reaction. They enter the plasma from the walls of the chamber, since the working substances launched into the volume can be purified, and the chamber wall operates in such conditions that the problem of what and how to make it has received its own name: “the problem of the first wall.” Everything that comes out of the plasma (neutrons, protons, ions and electromagnetic radiation in the range from infrared to gamma rays) destroys the wall, the destruction products enter the plasma. The problem of stability and the problem of "not harmful" are solved in opposite directions, because the heavier the ion, the more harmful it is (the allowable concentration of tantalum and tungsten is a hundred times less than carbon), and most resistant materials are based on heavy metals. At one time, great hopes were placed on carbon materials and composites based on carbides, borides, and nitrides. Porous and profiled (with ribs or needles) walls were considered. In general, it is difficult to say what was not considered, but as a result, beryllium is now chosen as the wall material.
Fuel.
The easiest way is the fusion of nuclei of hydrogen isotopes - deuterium D and tritium T. The deuterium nucleus contains one proton and one neutron. Deuterium is found in water - one part in 6500 parts of hydrogen. The tritium nucleus consists of a proton and two neutrons. During the fusion of deuterium and tritium nuclei, helium He with an atomic mass of four is formed, a neutron n and an energy of 17.6 MeV is released.
D+T=4He+ n+ 17.6 MeV.
The optimal reaction temperature is 2 10 8 K, the Lawson criterion is
0.5 10 15 cm -3 sec.
Another option is the fusion of two deuterium nuclei. It occurs with approximately the same probability according to one of two scenarios: in the first, tritium, proton p and an energy of 4 MeV is released, in the second - helium with an atomic mass of 3, a neutron and an energy of 3.25 MeV.
D+D=T+ p+ 4.0 MeV, D + D = 3He + n+ 3.25 MeV.
The optimum temperature for this reaction is 10 9 K, the Lawson criterion is –10 15 cm–3 s.
The rate of the D + T reaction is hundreds of times higher than that of the D + D reaction, so it is much easier for the D + T reaction to reach conditions where the released thermonuclear energy will exceed the cost of organizing fusion processes. Synthesis reactions involving other nuclei of elements (lithium, boron, etc.) are also possible, but these reactions proceed at the required rate at even higher temperatures.
Tritium is unstable (half-life 12.4 years), but it is supposed to be produced locally from the lithium isotope and the neutrons produced in the reactor
6Li+ n= T + 4He + 4.8 MeV.
At the same time, the same lithium (the system containing it is called a blanket) heats up and can serve as a coolant in the first (radioactive) circuit. Then it transfers heat to the second circuit, in which the water evaporates, and then, as usual, the turbine, generator, wires.
The problem is that the fusion of nuclei is prevented by electric (Coulomb) forces of repulsion; therefore, for synthesis it is necessary to overcome the Coulomb barrier, i.e. do work against these forces, imparting the necessary energy to the nuclei. There are three possibilities. The first is to disperse the ion beam in the accelerator and bombard a solid target with them. This way is inefficient - the energy is spent on ionization of the target atoms, and not on the approach of the nuclei. The second way is to send two accelerated ion beams towards each other, but this way is also inefficient due to the low concentration of nuclei in the beams and the short time of their interaction. Another way is to heat the substance to temperatures of about 100 million degrees. The higher the temperature, the higher the average kinetic energy of the particles and the greater their number can overcome the Coulomb barrier. This method is implemented in the tokamak.
Tokamak (like a nuclear reactor) does not emit any harmful substances - neither chemical nor radioactive - it does not emit. Throughout the history of the tokamak, its main physical (not technical) problem was stability - the plasma column was bent and expanded. By selecting the configuration of the magnetic field, it was possible to increase the stability of the plasma to the possibility of technical implementation. But what happens if the reactor does fail? There is no answer to this question yet, but it is clear that in the event of a tokamak failure, it is less dangerous than a nuclear reactor, and not much more dangerous than a coal-fired station. First, a nuclear reactor contains a supply of fuel for years of normal operation. This is a big plus for a submarine or space flight, but it also creates the fundamental possibility of a major accident. There is no "fuel" in the tokamak. Secondly, since more energy is released during the fusion reaction, then at a comparable power, the quantities of substances themselves will be smaller - the plasma in the tokamak “weighs” less than one hundred grams, and how much does the reactor core weigh? Finally, tritium has a short half-life and is not itself poisonous.
Leonid Ashkinazi
The word "TOKAMAK" is an abbreviation of the words TOROIDAL, CAMERA, MAGNETIC COILS, which describe the main elements of this magnetic trap, invented by A.D. Sakharov in 1950. The scheme of TOKAMAK is shown in Fig.4.
Figure 4. Scheme of principal units of TOKAMAK
The main magnetic field in the toroidal chamber containing hot plasma is generated by toroidal magnetic coils. An important role in plasma equilibrium is played by the plasma current, which flows along the toroidal plasma column and creates a poloidal magnetic field directed along the small bypass of the torus. The resulting magnetic field has lines of force in the form of endless spirals, covering the central line of the plasma torus - the magnetic axis. Thus, the magnetic field lines in TOKAMAK form closed, nested toroidal magnetic surfaces. The current in the plasma is maintained by a vortex electric field created by the primary winding of the inductor. In this case, the plasma coil plays the role of a secondary winding. It is obvious that the inductive maintenance of the current in TOKAMAK is limited by the reserve of the magnetic field flux in the primary winding and is possible only for a finite time. In addition to toroidal coils and the primary winding of the inductor, TOKAMAK should have poloidal windings, which are needed to maintain the equilibrium of the plasma and control its position in the chamber. The currents flowing in the poloidal coils create electromagnetic forces acting on the plasma current and thus can change its position in the chamber and the cross-sectional shape of the plasma column.
The first TOKAMAK was built in Russia at the Institute of Atomic Energy named after I.V. Kurchatov in 1956. Ten years of intense research and improvement of this device led to significant progress in the plasma parameters of TOKAMAKS. By 1968, TOKAMAK T-Z obtained a plasma temperature of 0.5 keV and achieved parameters that significantly exceed those achieved on other magnetic traps. From that moment, the active development of this direction began in other countries. In the seventies, TOKAMAKS of the next generation after T-3 were built: T-7, T-10, T-11 in the USSR, PLT and DIII-D in the USA, ASDEX in Germany, TFR in France, JFT-2 in Japan, etc. Methods for additional plasma heating were developed on TOKAMAKS of this generation, such as injection of neutral atoms, electronic and ion cyclotron heating, various plasma diagnostics and plasma control systems were developed. As a result, impressive plasma parameters were obtained on TOKAMAKS of the second generation: a temperature of several KeV, plasma densities exceeding 1020 m-3. The parameter ntE (Lawson's criterion) has reached the value 5 1018. In addition, TOKAMAK received an additional, fundamentally important element for the reactor - a diverter. With the help of currents in the system of poloidal turns, the magnetic field lines are brought out in a modern TOKAMAK into a special part of the chamber. The plasma divertor configuration is shown in Fig. 5 using the DIII-D TOKAMAK as an example.
Fig.5. Cross-section of a modern TOKAMAK DIII-D with vertically extended plasma and a divertor magnetic configuration.
The diverter makes it possible to better control the energy flows from the plasma and to reduce the influx of impurities into the plasma. An important achievement of this generation of TOKAMAKS was the discovery of modes with improved plasma confinement - the H-mode.
In the early 80s, the third generation of TOKAMAKS, machines with a large torus radius of 2-3 m and a plasma current of several MA, entered service. Five such machines were built: JET and TORUS-SUPRA in Europe, JT60-U in Japan, TFTR in the USA and T-15 in the USSR. The parameters of large TOKAMAKS are shown in Table 2. Two of these machines, JET and TFTR, were designed to work with tritium and obtain a thermonuclear yield at the level of Qfus = Psynthesis / Pcost = 1.
TOKAMAKS T-15 and TORUS-SUPRA have superconducting magnetic coils, similar to those that will be needed in the TOKAMAK reactor. The main physical task of machines of this generation was to study the confinement of plasma with thermonuclear parameters, clarify the limiting plasma parameters, gain experience with a divertor, etc. Technological tasks included: the development of superconducting magnetic systems capable of creating a field with an induction of up to 5 T in large volumes, the development of systems for working with tritium, the acquisition of experience in removing high heat fluxes in a divertor, the development of systems for remote assembly and disassembly of the internal components of the installation, the improvement of plasma diagnostics, etc. .
Table 2. Main parameters of large experimental TOKAMAKS. TOKAMAK TFTR has already completed its program and was stopped in 1997. The rest of the machines continue to work.
1) TOKAMAK T-15 has so far operated only in the regime with ohmic plasma heating and, therefore, the plasma parameters obtained on this facility are quite low. In the future, it is envisaged to introduce 10 MW of neutral injection and 10 MW of electron cyclotron heating.
2) The given Qfus is recalculated from the parameters of the DD plasma obtained in the setup to the DT plasma.
And although the experimental program on these TOKAMAKS has not yet been completed, this generation of machines has practically fulfilled the tasks assigned to it. TOKAMAKS JET and TFTR for the first time received a large thermonuclear power of DT reactions in plasma, 11 MW in TFTR and 16 MW in JET.
This generation of TOKAMAKS reached the threshold value Qfus = 1 and obtained ntE only several times lower than that required for a full-scale TOKAMAK reactor. In TOKAMAKS, they learned how to maintain a stationary plasma current using RF fields and neutral beams. The physics of plasma heating by fast particles, including thermonuclear alpha particles, was studied, the operation of the divertor was studied, and modes of its operation with low thermal loads were developed. The results of these studies made it possible to create the physical foundations necessary for the next step - the first TOKAMAK reactor, which will operate in the combustion mode.
Long-term studies of plasma confinement in TOKAMAKS have shown that the processes of energy and particle transfer across the magnetic field are determined by complex turbulent processes in plasma. And although the plasma instabilities responsible for the anomalous plasma losses have already been identified, the theoretical understanding of nonlinear processes is still insufficient to describe the plasma lifetime based on first principles. Therefore, to extrapolate the plasma lifetimes obtained in modern facilities to the scale of the TOKAMAK reactor, at present, empirical regularities - scalings - are used. One of these scalings, obtained by statistical processing of the experimental database from various TOKAMAKS, predicts that the lifetime increases with the plasma size, plasma current, plasma cross section elongation and decreases with the plasma heating power.
Scaling predicts that TOKAMAK, in which self-sustaining thermonuclear combustion will occur, should have a large radius of 7-8 m and a plasma current of 20 MA. In such a TOKAMAK, the energy lifetime will exceed 5 seconds, and the power of thermonuclear reactions will be at the level of 1-1.5 GW.
Tokamak (TOroidal Chamber with Magnetic Coils) is a toroidal facility for magnetic plasma confinement. The plasma is held not by the walls of the chamber, which are not able to withstand its temperature, but by a specially created magnetic field. A feature of the tokamak is the use of an electric current flowing through the plasma to create the poloidal field necessary for plasma equilibrium. In this it differs from the stellarator, in which both the toroidal and poloidal fields are created using magnetic coils.
Story
The term "tokamak" was introduced by Russian physicists Igor Evgenievich Tamm and Andrei Dmitrievich Sakharov in the 1950s as an abbreviation for the phrase "toroidal chamber with magnetic coils." The first tokamak was developed under the guidance of Academician L.A. Artsimovich at the Institute of Atomic Energy. IV Kurchatov in Moscow and demonstrated in 1968 in Novosibirsk.
Currently, the tokamak is considered the most promising device for controlled thermonuclear fusion.
Device
A tokamak is a toroidal vacuum chamber with coils wound around it to create a (toroidal) magnetic field. Air is first pumped out of the vacuum chamber, and then it is filled with a mixture of deuterium and tritium. Then, with the help of 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 in the plasma chamber.
The current flowing through the plasma performs two tasks:
Heats the plasma in the same way as it would heat any other conductor (ohmic heating).
- Creates a magnetic field around itself. This magnetic field is called poloidal (that is, directed along lines passing through the poles of a spherical coordinate system).
The magnetic field compresses the current flowing through the plasma. As a result, a configuration is formed in which helical magnetic lines of force "wrap around" the plasma column. 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 open, they twist around the torus infinitely many times, forming the so-called. "magnetic surfaces" of 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 have been developed to maintain the current. For this, injection of accelerated neutral deuterium or tritium atoms into the plasma or microwave radiation can be used.
In addition to toroidal coils, additional poloidal field coils are needed to control the plasma filament. They are annular coils around the vertical axis of the tokamak chamber.
Heating by current flow alone is not enough to heat the plasma to the temperature required for a thermonuclear reaction to take place. For additional heating, microwave radiation is used on the so-called. resonance frequencies (for example, coinciding with the cyclotron frequency of either electrons or ions) or the injection of fast neutral atoms.
Controlled thermonuclear fusion
The sun is a natural thermonuclear reactor
Controlled thermonuclear fusion (CTF) is the synthesis of heavier atomic nuclei from lighter ones in order to obtain energy, which is controlled in contrast to explosive thermonuclear fusion (used in thermonuclear weapons). Controlled thermonuclear fusion differs from traditional nuclear energy in that the latter uses a fission reaction, during which lighter nuclei are obtained from heavy nuclei. The main nuclear reactions planned to be used for controlled fusion will use deuterium (2H) and tritium (3H), and in the longer term helium-3 (3He).
The fate of nuclear fusion
The idea of creating a fusion reactor originated in the 1950s. Then it was decided to abandon it, since scientists were not able to solve many technical problems. Several decades passed before scientists managed to "force" the reactor to produce any fusion power.
Diagram of the International Thermonuclear Reactor (ITER)
The decision to design the International Thermonuclear Reactor (ITER) was made in Geneva in 1985. The USSR, Japan, the USA, united Europe and Canada are participating in the project. After 1991, Kazakhstan joined the participants. For 10 years, many elements of the future reactor have been manufactured at the military-industrial enterprises of developed countries. For example, Japan has developed a unique system of robots that can work inside the reactor. In Russia, a virtual version of the installation has been created.
In 1998, the United States, for political reasons, stopped funding its participation in the project. After the Republicans came to power in the country, and rolling blackouts began in California, the Bush administration announced an increase in energy investments. The United States did not intend to participate in the international project and was engaged in its own thermonuclear project. In early 2002, President Bush's technology adviser John Marburger III announced that the US had changed its mind and intended to return to the project.
In terms of the number of participants, the project is comparable to another major international scientific project - the International Space Station. The cost of ITER, which previously reached 8 billion dollars, then amounted to less than 4 billion. As a result of the withdrawal of the United States, it was decided to reduce the reactor power from 1.5 GW to 500 MW. Accordingly, the price of the project “lost weight”.
In June 2002, the symposium "ITER Days in Moscow" was held in the Russian capital. It discussed the theoretical, practical and organizational problems of the revival of the project, the success of which can change the fate of mankind and give it a new type of energy, in terms of efficiency and economy comparable only to solar energy.
If the participants agree on the place of construction of the station and on the start of its construction, then, according to the forecast of Academician Velikhov, by 2010 the first plasma will be obtained. Then it will be possible to start building the first thermonuclear power plant, which, under favorable circumstances, can produce the first current in 2030.
In December 2003, scientists involved in the ITER project gathered in Washington to finally determine the site of its future construction. The France Press news agency reported, citing one of the participants in the meeting, that the decision had been postponed to 2004. The next negotiations on this project will be held in May 2004 in Vienna. The reactor will begin to be built in 2006 and is planned to be launched in 2014.
Principle of operation
Fusion is a cheap and environmentally friendly way to produce energy. For billions of years, uncontrolled thermonuclear fusion has been taking place on the Sun - helium is formed from the heavy isotope of hydrogen deuterium. This releases an enormous amount of energy. However, people on Earth have not yet learned to control such reactions.
Plasma in a fusion reactor
Hydrogen isotopes will be used as fuel in the ITER reactor. During a thermonuclear reaction, energy is released when light atoms combine to form heavier ones. To achieve this, it is necessary to heat the gas to a temperature of over 100 million degrees - much higher than the temperature at the center of the Sun. Gas at this temperature turns into plasma. At the same time, hydrogen isotope atoms merge, turning into helium atoms with the release of a large number of neutrons. A power plant operating on this principle will use the energy of neutrons moderated by a layer of dense matter (lithium)
The construction of the station will take at least 10 years and 5 billion dollars. France and Japan compete for the prestigious right to be the home of the energy giant.
Place of construction
Canada, Japan, Spain and France made proposals to host the reactor on their territories.
Canada justifies the need to place the reactor on its territory by the fact that it is in this country that there are significant reserves of tritium, which is a waste of nuclear energy. The construction of a fusion reactor will make it possible to dispose of them.
In Japan, according to the Kyodo Tsushin news agency, three prefectures were in a desperate struggle for the right to build a reactor at home. At the same time, the inhabitants of the northern island of Hokkaido opposed the construction of it on their land.
In November of this year, the European Union recommended the French city of Cadarache as a future construction site. However, it is difficult to predict how the vote will go. Experts are expected to make decisions based on purely objective scientific facts, but political overtones may also affect voting. The US has already spoken out against giving the construction of the reactor to France, recalling its divisive behavior during the conflict in Iraq.
“We have an already existing scientific and technical structure, competence and experience, which is the guarantor of meeting the deadlines,” said the French Minister of Research.
Japan also has a number of advantages - Rokkasho-mura is located next to the port and next to the US military base. In addition, the Japanese are ready to invest much more money in the project than France. "If Japan is chosen, we will cover all the necessary expenses," said the Minister of Science and Education of Japan.
A French government spokesman told reporters that he had held "very intense high-level talks" ahead of the meeting. However, according to some reports, all countries except the European Union prefer Japan to France.
Environmental Safety
The new installation, according to scientists, is environmentally safer than nuclear reactors operating today. Helium is produced as spent fuel in the ITER facility, and not its isotopes, which must be stored in special storage facilities for decades.
Scientists believe that the fuel reserves for such power plants are practically inexhaustible - deuterium and tritium are easily extracted from sea water. A kilogram of these isotopes can release as much energy as 10 million kg of fossil fuel.
Material from the Uncyclopedia
For many years, science has been developing the problem of using thermonuclear reactions for energy purposes as giant energy sources. Unique thermonuclear installations have been created - the most complex technical devices designed to study the possibility of obtaining colossal energy, which is released so far only during the explosion of a hydrogen bomb. Scientists are striving to learn how to control the course of a thermonuclear reaction - the reaction of the combination (synthesis) of hydrogen isotopes (deuterium and tritium) with the formation of helium nuclei at high temperatures, in order to use the energy released during this for peaceful purposes, for the benefit of people. The magnitude of thermonuclear energy can be judged by the following comparison: the entry into fusion of 1 g of hydrogen isotopes is equivalent to the combustion of 10 tons of gasoline.
Several conditions are necessary for a thermonuclear reaction to take place. The temperature in the zone where thermonuclear fusion takes place should be approximately 100 million degrees. At this temperature, the reacting substance turns into plasma - an ionized gas, a mixture of positive ions and electrons. It is also necessary that during the fusion more energy be released than is spent on heating the substance, or that the fast particles born during the synthesis themselves maintain the required temperature of the fuel. For this, it is necessary that the substance entering into synthesis be reliably thermally insulated from the surrounding and, naturally, cold environment, i.e., that the energy retention time be sufficiently long (at least 1 s). The energy retention time depends on the density of the reactant: the plasma density in the reaction zone should be maintained at least 100,000 billion particles per 1 cm3.
The closest to the conditions required for controlled thermonuclear fusion was achieved with the help of Tokamak installations, created by Soviet physicists. The name of the installation comes from the abbreviation of the words: Toroidal Chamber with Magnetic Coils. The working vacuum chamber of the Tokamak, a toroidal (circular) shape (see Fig.), is equipped with coils that create a strong (several Tesla) toroidal magnetic field. The chamber with coils is placed on an iron yoke and serves as a secondary coil of the transformer. When the current changes in the primary winding wound on the yoke, a vortex electric field is formed in the chamber, breakdown and ionization of the working gas filling the chamber occurs, and a toroidal plasma filament with a longitudinal electric current appears. This current heats the plasma, and its magnetic field, together with the field of the coils, thermally insulates the plasma from the walls.
Oppositely directed currents repel, so the plasma coil tends to increase its diameter. To compensate for this repulsion, the Tokamak has special control coils that create a magnetic field perpendicular to the plane of the torus.
As a result of the interaction of this field with the current in the filament, a radial force arises that keeps the plasma loop from expanding. The current in the coils is regulated by a special automatic system that controls the movement of the plasma filament.
The electrical resistance of the plasma does not increase with increasing temperature, as in other substances, but decreases, and at a given current, the heating of the filament decreases. If, however, the current in the Tokamak is increased above a certain limit, then the magnetic field of the current will become too large compared to the toroidal field of the coils, the cord will begin to wriggle and throw itself onto the wall. Therefore, to heat the plasma to a temperature above 10 million degrees in the Tokamak, additional heating methods are used by injection (input) into the plasma of beams of fast atoms or by introducing high-frequency electromagnetic waves into the chamber. In this case, the plasma in the Tokamak has already been heated up to 70 million degrees.
A large contribution to the development of Tokamak systems was made by a team of Soviet scientists led by Academician L. A. Artsimovich, who was the first to conduct experimental studies of these installations at the I. V. Kurchatov Institute of Atomic Energy. In 1968, a physical thermonuclear reaction was obtained at this institute for the first time. Since the early 1970s Tokamak systems began to play a leading role in research on controlled fusion in other countries of the world - the USA, France, Italy, Great Britain, Germany, and Japan. The largest installation of this type, Tokamak-10, has been built in our country.
Mastering thermonuclear energy is an important task of science and technology. It is even hard to imagine how the construction and use of thermonuclear power plants will change the entire energy sector, energy systems, and entire industries.
a device for carrying out a thermonuclear fusion reaction in a hot plasma in a quasi-stationary mode, with the plasma being created in a toroidal chamber and stabilized by a magnetic field. The purpose of the facility is to convert intranuclear energy into thermal energy and then into electrical energy. The word “tokamak” itself is an abbreviation of the name “magnetic toroidal chamber”, however, the creators of the installation replaced the “g” with “k” at the end, so as not to evoke associations with something magical.
A person receives 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, but also when light elements are combined. This process is called thermonuclear fusion, it takes place in a hydrogen bomb and a thermonuclear reactor. There are many known thermonuclear reactions, fusion reactions. The source of energy can be those for which there is inexpensive fuel, and there are two fundamentally different ways to start the fusion reaction.
The first way is “explosive”: part of the energy is spent on bringing a very small amount of matter into the required initial state, a fusion reaction occurs, 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 cannot be “small”. Therefore, it was assumed that a millimetric 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 upper layer of the tablet that 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 fusion reaction. In this case, the pulse must be so short that the substance that has turned into a plasma with a temperature of ten million degrees in a nanosecond does not have time to scatter, but presses on the inside of the tablet. This inner part is compressed to a density one hundred times greater than the density of solids, and heated to a hundred million degrees.
Second way. The initial 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 reached. In order for a thermonuclear reaction to proceed in a mixture of deuterium and tritium and to obtain a positive energy yield (when the energy released as a result of a thermonuclear reaction turns out to be greater than the energy spent 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 up to about 10 9 degrees, while the plasma becomes completely ionized.
Such heating is necessary so that the nuclei can approach each other, despite the Coulomb repulsion. It can be shown that in order to obtain energy, it is necessary to maintain this state for at least a second (the so-called "Lawson criterion"). A more precise formulation of the Lawson criterion the product of the concentration and the time of maintaining this state should be of the order of 10 15 sCh 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 down.
In 2006, the international community starts building 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 start building “energy”, i.e. intended for inclusion in the power grid, thermonuclear reactors. The largest physical projects (accelerators, radio telescopes, space stations) are becoming so expensive that consideration of two options is beyond the means of even humanity, which has united its efforts, so a choice has to be made.
The beginning of work on controlled thermonuclear fusion should be attributed to 1950, when I.E. Tamm and A.D. Sakharov came to the conclusion that it is possible to implement CTS (controlled thermonuclear fusion) 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 only by means of heating due to the passage of current ("ohmic heating") it is impossible to bring the plasma to thermonuclear 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 reached and real experiments were carried out using injectors. Now the most promising are the heating of neutral particles by injection and electromagnetic radiation in the microwave range. In 1988, the T-15 pre-reactor generation tokamak with superconducting windings was built at the Kurchatov Institute. Since 1956, when during the visit of N.S. Khrushchev to Great Britain I.V. Kurchatov announced that these works were being carried out in the USSR. work in this area is carried out jointly by several countries. In 1988, the USSR, the USA, the 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 high. The expected construction period of this plant is eight years, and the operation life is 25 years. The plasma volume in the setup is about 850 cubic meters. Plasma current 15 megaamperes. The thermonuclear power of the installation of 500 megawatts 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., Science, 1975
Artsimovich L. A., Sagdeev R. Z. Plasma Physics for Physicists. M., Atomizdat, 1979
Hegler M., Christiansen M. Introduction to controlled thermonuclear fusion. M., Mir, 1980
Killin J. Controlled thermonuclear fusion. M., Mir, 1980
Boyko V.I. Controlled thermonuclear fusion and problems of inertial thermonuclear fusion. Soros educational journal. 1999, No. 6
