According to modern astrophysical concepts, the main source of energy for the Sun and other stars is thermonuclear fusion occurring in their depths. Under terrestrial conditions, it is carried out during the explosion of a hydrogen bomb. Thermonuclear fusion accompanied by a colossal energy release per unit mass of the reacting substances (about 10 million times greater than in chemical reactions). Therefore, it is of great interest to master this process and, on its basis, create a cheap and environmentally friendly source of energy. However, despite the fact that studies of controlled thermal nuclear fusion(TCF) employs large scientific and technical teams in many developed countries, there are still many complex problems to be solved before the industrial production of thermonuclear energy becomes a reality.

Modern nuclear power plants using the fission process only partially satisfy the world's electricity needs. The fuel for them is the natural radioactive elements uranium and thorium, the prevalence and reserves of which in nature are very limited; therefore, for many countries there is a problem of their import. The main component of thermonuclear fuel is the hydrogen isotope deuterium, which is found in sea water. Its reserves are publicly available and very large (the world ocean covers ~ 71% of the Earth's surface area, and deuterium accounts for about 0.016% of the total number of hydrogen atoms that make up water). In addition to the availability of fuel, fusion power sources have the following important advantages over nuclear power plants: 1) the UTS reactor contains much less radioactive materials than a nuclear fission reactor, and therefore the consequences of an accidental release of radioactive products are less dangerous; 2) thermonuclear reactions produce less long-lived radioactive waste; 3) TCB allows direct electricity generation.

PHYSICAL FOUNDATIONS OF NUCLEAR FUSION

The successful implementation of the fusion reaction depends on the properties of the atomic nuclei used and the possibility of obtaining a dense high-temperature plasma, which is necessary to initiate the reaction.

Nuclear forces and reactions.

The energy release during nuclear fusion is due to extremely intense attractive forces operating inside the nucleus; these forces hold together the protons and neutrons that make up the nucleus. They are very intense at distances of ~10–13 cm and weaken extremely rapidly with increasing distance. In addition to these forces, positively charged protons create electrostatic repulsive forces. The radius of action of electrostatic forces is much greater than that of nuclear forces, so they begin to dominate when the nuclei are further apart.

As G. Gamov showed, the probability of a reaction between two approaching light nuclei is proportional to , where e – base of natural logarithms, Z 1 And Z 2 are the numbers of protons in interacting nuclei, W is the energy of their relative approach, and K is a constant multiplier. The energy required to carry out a reaction depends on the number of protons in each nucleus. If it is more than three, then this energy is too high and the reaction is practically impossible. Thus, with increasing Z 1 and Z 2 the probability of a reaction decreases.

The probability that two nuclei will interact is characterized by a “reaction cross section” measured in barns (1 b = 10–24 cm 2). The reaction cross section is the area of ​​the effective cross section of the nucleus, into which another nucleus must “get” in order for their interaction to occur. The cross section for the reaction of deuterium with tritium reaches its maximum value (~5 b) when the interacting particles have a relative approach energy of about 200 keV. At an energy of 20 keV, the cross section becomes less than 0.1 b.

Out of a million accelerated particles hitting the target, no more than one enters into nuclear interaction. The rest dissipate their energy on the electrons of the target atoms and slow down to speeds at which the reaction becomes impossible. Consequently, the method of bombarding a solid target with accelerated nuclei (as was the case in the Cockcroft-Walton experiment) is unsuitable for CTS, since the energy obtained in this case is much less than the energy spent.

Thermonuclear fuels.

Reactions involving p, which play the main role in the processes of nuclear fusion in the Sun and other homogeneous stars, are of no practical interest under terrestrial conditions, since they have a too small cross section. For the implementation of thermonuclear fusion on earth, a more suitable type of fuel, as mentioned above, is deuterium.

But the most probable reaction is realized in an equal component mixture of deuterium and tritium (DT-mixture). Unfortunately, tritium is radioactive and, due to its short half-life (T 1/2 ~ 12.3 years), is practically never found in nature. It is obtained artificially in fission reactors, and also as a by-product in reactions with deuterium. However, the absence of tritium in nature is not an obstacle to the use of DT - fusion reactions, since tritium can be produced by irradiating the 6 Li isotope with neutrons produced during fusion: n+ 6 Li ® 4 He + t.

If the thermonuclear chamber is surrounded by a layer of 6 Li (natural lithium contains 7%), then it is possible to carry out complete reproduction of the consumable tritium. And although in practice some of the neutrons are inevitably lost, their loss can be easily replenished by introducing such an element as beryllium into the shell, the nucleus of which, when one fast neutron hits it, emits two.

The principle of operation of a thermonuclear reactor.

The fusion reaction of light nuclei, the purpose of which is to obtain useful energy, is called controlled thermonuclear fusion. It is carried out at temperatures of the order of hundreds of millions of kelvins. This process has only been implemented in laboratories so far.

Time and temperature conditions.

Obtaining useful thermonuclear energy is possible only if two conditions are met. First, the mixture intended for synthesis must be heated to a temperature at which the kinetic energy of the nuclei ensures a high probability of their fusion upon collision. Secondly, the reacting mixture must be very well thermally insulated (i.e., the high temperature must be maintained long enough for the required number of reactions to occur and the energy released due to this exceeds the energy spent on heating the fuel).

In quantitative form, this condition is expressed as follows. To heat a thermonuclear mixture, one cubic centimeter of its volume must be supplied with energy P 1 = knt, Where k- numerical coefficient, n- the density of the mixture (the number of nuclei in 1 cm 3), T- required temperature. To maintain the reaction, the energy imparted to the thermonuclear mixture must be conserved for a time t. In order for a reactor to be energetically profitable, it is necessary that during this time more thermonuclear energy be released in it than was spent on heating. The released energy (also per 1 cm 3) is expressed as follows:

Where f(T) is a coefficient depending on the temperature of the mixture and its composition, R is the energy released in one elementary act of synthesis. Then the condition of energy profitability P 2 > P 1 will take the form

The last inequality, known as the Lawson criterion, is a quantitative expression of the requirements for the perfection of thermal insulation. The right side - "Lawson's number" - depends only on the temperature and composition of the mixture, and the larger it is, the more stringent the requirements for thermal insulation, i.e. the more difficult it is to create a reactor. In the region of acceptable temperatures, the Lawson number for pure deuterium is 10 16 s/cm 3 , and for an equal-component DT mixture it is 2×10 14 s/cm 3 . Thus, the DT mixture is the preferred fusion fuel.

In accordance with the Lawson criterion, which determines the energetically favorable value of the product of density and confinement time, in a thermonuclear reactor, as large as possible should be used. n or t. Therefore, studies of CTS diverged in two different directions: in the first, researchers tried to keep relatively rarefied plasma with the help of a magnetic field for a sufficiently long time; in the second, with the help of lasers for a short time to create a plasma with a very high density. Much more work has been devoted to the first approach than to the second.

Magnetic confinement of plasma.

During the fusion reaction, the density of the hot reactant must remain at a level that would provide a sufficiently high yield of useful energy per unit volume at a pressure that the plasma chamber can withstand. For example, for a mixture of deuterium - tritium at a temperature of 10 8 K, the yield is determined by the expression

If accept P equal to 100 W / cm 3 (which approximately corresponds to the energy released by fuel elements in nuclear fission reactors), then the density n should be approx. 10 15 cores / cm 3, and the corresponding pressure nt- about 3 MPa. The retention time in this case, according to the Lawson criterion, should be at least 0.1 s. For deuterium-deuterium plasma at a temperature of 10 9 K

In this case, when P\u003d 100 W / cm 3, n» 3×10 15 cores/cm 3 and a pressure of approximately 100 MPa, the required holding time will be more than 1 s. Note that these densities are only 0.0001 of atmospheric air, so the reactor chamber must be evacuated to a high vacuum.

The above estimates of retention time, temperature, and density are typical minimum parameters required for the operation of a fusion reactor, and are more easily achieved in the case of a deuterium-tritium mixture. As for the thermonuclear reactions that occur during the explosion of a hydrogen bomb and in the interiors of stars, it should be borne in mind that, due to completely different conditions, in the first case they proceed very quickly, and in the second - extremely slowly compared to the processes in a thermonuclear reactor.

Plasma.

When a gas is heated strongly, its atoms partially or completely lose electrons, resulting in the formation of positively charged particles called ions and free electrons. At temperatures above a million degrees, a gas consisting of light elements is completely ionized, i.e. each atom loses all of its electrons. A gas in an ionized state is called a plasma (the term was introduced by I. Langmuir). The properties of a plasma differ significantly from those of a neutral gas. Since there are free electrons in the plasma, the plasma conducts electric current very well, and its conductivity is proportional to T 3/2. Plasma can be heated by passing an electric current through it. The conductivity of a hydrogen plasma at 10 8 K is the same as that of copper at room temperature. The thermal conductivity of the plasma is also very high.

To keep the plasma, for example, at a temperature of 10 8 K, it must be reliably thermally insulated. In principle, the plasma can be isolated from the walls of the chamber by placing it in a strong magnetic field. This is provided by the forces that arise when the currents interact with magnetic field in plasma.

Under the action of a magnetic field, ions and electrons move in spirals along its lines of force. The transition from one line of force to another is possible in collisions of particles and in the imposition of a transverse electric field. In the absence of electric fields, high-temperature rarefied plasma, in which collisions rarely occur, will only slowly diffuse across magnetic field lines. If the lines of force of the magnetic field are closed, giving them the shape of a loop, then the plasma particles will move along these lines, being held in the region of the loop. In addition to such a closed magnetic configuration, open systems (with field lines extending outward from the ends of the chamber) were also proposed for confining the plasma, in which particles remain inside the chamber due to magnetic “plugs” that restrict the movement of particles. Magnetic mirrors are created at the ends of the chamber, where a narrowing beam of field lines is formed as a result of a gradual increase in the field strength.

In practice, magnetic confinement of a sufficiently high density plasma turned out to be far from simple: magnetohydrodynamic and kinetic instabilities often arise in it.

Magnetohydrodynamic instabilities are associated with bends and breaks in magnetic field lines. In this case, the plasma can begin to move across the magnetic field in the form of bunches, leave the containment zone in a few millionths of a second and give off heat to the chamber walls. Such instabilities can be suppressed by giving the magnetic field a certain configuration.

Kinetic instabilities are very diverse and have been studied in less detail. Among them are those that disrupt orderly processes, such as the flow of a constant electric current or a stream of particles through a plasma. Other kinetic instabilities cause a higher plasma transverse diffusion rate in a magnetic field than that predicted by collision theory for a quiet plasma.

Systems with a closed magnetic configuration.

If a strong electric field is applied to an ionized conducting gas, then a discharge current will appear in it, simultaneously with which a magnetic field surrounding it will appear. The interaction of the magnetic field with the current will lead to the appearance of compressive forces acting on the charged particles of the gas. If the current flows along the axis of the conducting plasma filament, then the resulting radial forces, like rubber bands, compress the filament, moving the plasma boundary away from the walls of the chamber containing it. This phenomenon, theoretically predicted by W. Bennett in 1934 and experimentally demonstrated for the first time by A. Ware in 1951, is called the pinch effect. The pinch method is applied to plasma confinement; its notable feature is that the gas is heated to high temperatures by the electric current itself (ohmic heating). The fundamental simplicity of the method led to its use in the very first attempts to contain a hot plasma, and the study of a simple pinch effect, despite the fact that it was subsequently supplanted by more advanced methods, made it possible to better understand the problems that experimenters face today.

In addition to plasma diffusion in the radial direction, there is also a longitudinal drift and its exit through the ends of the plasma column. Losses through the ends can be eliminated if the chamber with plasma is shaped like a donut (torus). In this case, a toroidal pinch is obtained.

For the simple pinch described above, the magnetohydrodynamic instabilities inherent in it are a serious problem. If a small bend occurs at the plasma column, then the density of magnetic field lines with inside bending increases (Fig. 1). The magnetic lines of force, which behave like strands resisting compression, will quickly begin to "bulge", so that the bend will increase until the entire structure of the plasma filament is destroyed. As a result, the plasma will come into contact with the walls of the chamber and cool down. To exclude this disastrous phenomenon, before the passage of the main axial current, a longitudinal magnetic field is created in the chamber, which, together with the circular field applied later, “straightens” the incipient bending of the plasma column (Fig. 2). The principle of stabilization of a plasma column by an axial field is the basis for two promising projects of thermonuclear reactors - a tokamak and a pinch with a reversed magnetic field.

Open magnetic configurations.

inertial hold.

Theoretical calculations show that thermonuclear fusion is possible without the use of magnetic traps. To do this, a specially prepared target (a ball of deuterium with a radius of about 1 mm) is rapidly compressed to such high densities that the thermonuclear reaction has time to complete before the fuel target evaporates. Compression and heating to thermonuclear temperatures can be performed by super-powerful laser pulses, uniformly and simultaneously irradiating the fuel ball from all sides (Fig. 4). With the instantaneous evaporation of its surface layers, the emitted particles become very high speeds, and the ball is under the action of large compressive forces. They are similar to the reactive forces driving a rocket, with the only difference being that here these forces are directed inward, towards the center of the target. This method can create pressures of the order of 10 11 MPa and densities 10,000 times higher than the density of water. At this density, almost all thermonuclear energy will be released in the form of a small explosion in ~10–12 s. Occurring microexplosions, each of which is equivalent to 1–2 kg of TNT, will not cause damage to the reactor, and the implementation of a sequence of such microexplosions at short intervals would make it possible to realize an almost continuous production of useful energy. For inertial containment, the arrangement of a fuel target is very important. A target in the form of concentric spheres made of heavy and light materials will make it possible to achieve the most efficient evaporation of particles and, consequently, the greatest compression.

Calculations show that at the energy laser radiation of the order of a megajoule (10 6 J) and a laser efficiency of at least 10%, the thermonuclear energy produced must exceed the energy expended for pumping the laser. Thermonuclear laser facilities are available in research laboratories in Russia, the USA, Western Europe and Japan. The possibility of using a heavy ion beam instead of a laser beam or a combination of such a beam with a light beam is currently being studied. Thanks to modern technology, this method of initiating a reaction has an advantage over laser, since it allows you to get more useful energy. The disadvantage is the difficulty in focusing the beam on the target.

INSTALLATIONS WITH MAGNETIC RETENTION

Magnetic plasma confinement methods are being studied in Russia, the USA, Japan and a number of European countries. The main attention is paid to toroidal-type devices, such as tokamak and pinch with reversed magnetic field, which appeared as a result of the development of simpler pinches with a stabilizing longitudinal magnetic field.

For confining plasma with a toroidal magnetic field B j it is necessary to create conditions under which the plasma would not be displaced to the walls of the torus. This is achieved by "twisting" the magnetic field lines (the so-called "rotational transformation"). This twisting is done in two ways. In the first method, a current is passed through the plasma, leading to the configuration of the already considered stable pinch. Magnetic field current B q J - B q along with B j creates a total field with the required twist. If B j B q , we get a configuration known as a tokamak (an abbreviation of the expression "TOROIDAL CAMERA WITH MAGNETIC COILS"). Tokamak (Fig. 5) was developed under the leadership of L.A. Artsimovich at the Institute atomic energy them. I.V. Kurchatov in Moscow. At B j ~ B q the pinch configuration with reversed magnetic field is obtained.

In the second method, special helical windings around the toroidal plasma chamber are used to ensure the equilibrium of the confined plasma. The currents in these windings create a complex magnetic field, which leads to twisting of the lines of force of the total field inside the torus. Such an installation, called a stellarator, was developed at Princeton University (USA) by L. Spitzer and his co-workers.

Tokamak.

An important parameter on which the confinement of a toroidal plasma depends is the “stability margin” q, equal to rB j / R.B. q , where r And R are the small and large radii of the toroidal plasma, respectively. At a small q a helical instability can develop, which is analogous to the instability of the bending of a straight pinch. Scientists in Moscow experimentally showed that when q> 1 (i.e. B j B q) the possibility of helical instability is greatly reduced. This makes it possible to effectively use the heat released by the current to heat the plasma. As a result of many years of research, the characteristics of tokamaks have improved significantly, in particular, by increasing the field uniformity and efficient cleaning of the vacuum chamber.

The encouraging results obtained in Russia stimulated the creation of tokamaks in many laboratories around the world, and their configuration became the subject of intensive research.

The ohmic heating of the plasma in the tokamak is not sufficient to carry out the thermonuclear fusion reaction. This is due to the fact that when the plasma is heated, its electrical resistance, and as a result, the heat generation during the passage of current is sharply reduced. It is impossible to increase the current in the tokamak above a certain limit, since the plasma column can lose stability and be transferred to the chamber walls. Therefore, various additional methods are used to heat the plasma. The most effective of them are the injection of beams of high-energy neutral atoms and microwave irradiation. In the first case, ions accelerated to energies of 50–200 keV are neutralized (to avoid their “reflection” back by the magnetic field when introduced into the chamber) and injected into the plasma. Here they are again ionized and in the process of collisions they give up their energy to the plasma. In the second case, microwave radiation is used, the frequency of which is equal to the ion cyclotron frequency (the rotation frequency of ions in a magnetic field). At this frequency, the dense plasma behaves as an absolutely black body, i.e. completely absorbs the incident energy. On the JET tokamak of the countries of the European Union, a plasma with an ion temperature of 280 million Kelvin and a confinement time of 0.85 s was obtained by injection of neutral particles. A thermonuclear power reaching 2 MW was obtained on deuterium-tritium plasma. The duration of the reaction is limited by the appearance of impurities due to the sputtering of the chamber walls: impurities penetrate into the plasma and, being ionized, significantly increase energy losses due to radiation. Currently, work on the JET program is focused on research on the possibility of controlling impurities and their removal, the so-called. "magnetic diverter".

Large tokamaks were also created in the USA - TFTR, in Russia - T15 and in Japan - JT60. The research carried out at these and other facilities laid the foundation for the next stage of work in the field of controlled thermonuclear fusion: in 2010, it is planned to launch a large reactor for technical tests. It is assumed that this will be a joint work of the United States, Russia, the countries of the European Union and Japan. see also TOKAMAK.

Reversed field pinch (FOP).

The POP configuration differs from the tokamak in that it has B q~ B j , but the direction of the toroidal field outside the plasma is opposite to its direction inside the plasma column. J.Taylor showed that such a system is in a state with a minimum energy and, despite q

The advantage of the POP configuration is that the ratio of the volumetric energy densities of the plasma and the magnetic field (value b) in it is greater than in the tokamak. It is fundamentally important that b be as large as possible, since this will reduce the toroidal field and, consequently, reduce the cost of the coils that create it and the entire supporting structure. The weakness of POP is that the thermal insulation of these systems is worse than that of tokamaks, and the problem of maintaining the reversed field has not been solved.

Stellarator.

In a stellarator, a closed toroidal magnetic field is superimposed by a field created by a special helical winding wound around the camera body. The total magnetic field prevents the plasma from drifting away from the center and suppresses certain types magnetohydrodynamic instabilities. The plasma itself can be created and heated by any of the methods used in a tokamak.

The main advantage of the stellarator is that the method of confinement used in it is not related to the presence of current in the plasma (as in tokamaks or in devices based on the pinch effect), and therefore the stellarator can operate in a stationary mode. In addition, the helical winding can have a "divertor" effect, i.e. purify the plasma from impurities and remove reaction products.

Plasma confinement in stellarators is being comprehensively studied at facilities in the European Union, Russia, Japan, and the United States. On the stellarator "Wendelstein VII" in Germany, it was possible to maintain a non-current-carrying plasma with a temperature of more than 5x10 6 kelvin, heating it by injection of a high-energy atomic beam.

The latest theoretical and experimental studies showed that in most of the described installations, and especially in closed toroidal systems, the plasma confinement time can be increased by increasing its radial dimensions and confining magnetic field. For example, for a tokamak, it is calculated that the Lawson criterion will be fulfilled (and even with some margin) at a magnetic field strength of ~ 50 ± 100 kG and a small radius of the toroidal chamber of approx. 2 m. These are the installation parameters for 1000 MW of electricity.

When creating such large installations with magnetic plasma confinement, completely new technological problems arise. To create a magnetic field of the order of 50 kG in a volume of several cubic meters using water-cooled copper coils, a source of electricity with a capacity of several hundred megawatts is required. Therefore, it is obvious that the windings of the coils must be made of superconducting materials, such as alloys of niobium with titanium or with tin. The resistance of these materials electric current in the superconducting state is zero, and, consequently, to maintain the magnetic field will be spent minimal amount electricity.

reactor technology.

Prospects for thermonuclear research.

Experiments carried out on installations of the tokamak type have shown that this system is very promising as a possible basis for the UTS reactor. The best results to date have been obtained on tokamaks, and there is hope that with a corresponding increase in the scale of installations, they will be able to implement an industrial controlled fusion. However, the tokamak is not economical enough. To eliminate this shortcoming, it is necessary that it does not work in a pulsed mode, as it is now, but in a continuous mode. However, the physical aspects of this problem are still poorly understood. It is also necessary to develop technical means that would improve the parameters of the plasma and eliminate its instabilities. Considering all this, one should not forget about other possible, although less developed options for a thermonuclear reactor, for example, a stellarator or a reversed field pinch. The state of research in this area has reached the point where there are conceptual reactor designs for most high temperature plasma magnetic confinement systems and for some inertial confinement systems. An example of the industrial development of a tokamak is the Aries project (USA).

Innovative projects using modern superconductors will soon allow controlled thermonuclear fusion, some optimists say. Experts, however, predict that practical use will take several decades.

Why is it so difficult?

Fusion energy is considered a potential source. It is the pure energy of an atom. But what is it and why is it so difficult to achieve? First you need to understand the difference between classical and thermonuclear fusion.

The fission of the atom consists in the fact that radioactive isotopes - uranium or plutonium - are split and converted into other highly radioactive isotopes, which then must be buried or recycled.

Synthesis consists in the fact that two isotopes of hydrogen - deuterium and tritium - merge into a single whole, forming non-toxic helium and a single neutron, without producing radioactive waste.

Control problem

The reactions that take place on the Sun or in a hydrogen bomb are thermonuclear fusion, and engineers face a daunting task - how to control this process at a power plant?

This is something scientists have been working on since the 1960s. Another experimental fusion reactor called Wendelstein 7-X has started operation in the northern German city of Greifswald. It is not yet designed to create a reaction - it is just a special design that is being tested (a stellarator instead of a tokamak).

high energy plasma

All thermonuclear plants have common feature- ring-shaped. It is based on the idea of ​​using powerful electromagnets to create a strong electromagnetic field shaped like a torus - an inflated bicycle tube.

This electromagnetic field must be so dense that when it is heated in a microwave oven to one million degrees Celsius, a plasma must appear in the very center of the ring. It is then ignited so that thermonuclear fusion can begin.

Demonstration of possibilities

Two such experiments are currently underway in Europe. One of them is the Wendelstein 7-X, which recently generated its first helium plasma. The other is ITER, a huge experimental fusion facility in the south of France that is still under construction and will be ready to go live in 2023.

Real nuclear reactions are expected to take place at ITER, albeit only for a short period of time and certainly no longer than 60 minutes. This reactor is just one of many steps on the way to making nuclear fusion a reality.

Fusion reactor: smaller and more powerful

Recently, several designers have announced a new reactor design. According to a group of students from the Massachusetts Institute of Technology, as well as representatives of the weapons company Lockheed Martin, fusion can be carried out in facilities that are much more powerful and smaller than ITER, and they are ready to do it within ten years.

The idea of ​​the new design is to use modern high-temperature superconductors in electromagnets, which exhibit their properties when cooled with liquid nitrogen, rather than conventional ones, which require a new, more flexible technology that will completely change the design of the reactor.

Klaus Hesch, who is in charge of technology at the Karlsruhe Institute of Technology in southwestern Germany, is skeptical. It supports the use of new high-temperature superconductors for new reactor designs. But, according to him, to develop something on a computer, taking into account the laws of physics, is not enough. It is necessary to take into account the challenges that arise when putting an idea into practice.

Science fiction

According to Hesh, the MIT student model only shows the possibility of a project. But it's actually a lot of science fiction. The project assumes that serious technical problems thermonuclear fusion solved. But modern science has no idea how to solve them.

One such problem is the idea of ​​collapsible coils. Electromagnets can be dismantled in order to get inside the ring that holds the plasma in the MIT design model.

This would be very useful because one would be able to access objects during internal system and replace them. But in reality, superconductors are made of ceramic material. Hundreds of them must be intertwined in a sophisticated way to form the correct magnetic field. And here there are more fundamental difficulties: the connections between them are not as simple as the connections of copper cables. No one has even thought of concepts that would help solve such problems.

too hot

High temperature is also a problem. At the core of the fusion plasma, the temperature will reach about 150 million degrees Celsius. This extreme heat remains in place - right in the center of the ionized gas. But even around it it is still very hot - from 500 to 700 degrees in the reactor zone, which is the inner layer of a metal pipe in which the tritium necessary for nuclear fusion to occur will "reproduce".

It has an even bigger problem - the so-called power release. This is the part of the system that receives used fuel from the fusion process, mainly helium. The first metal components that the hot gas enters are called the "divertor". It can heat up to over 2000°C.

Diverter problem

In order for the installation to withstand such temperatures, engineers are trying to use the metal tungsten used in old-fashioned incandescent lamps. The melting point of tungsten is about 3000 degrees. But there are other limitations as well.

In ITER, this can be done, because heating in it does not occur constantly. It is assumed that the reactor will operate only 1-3% of the time. But this is not an option for a power plant that must operate 24/7. And, if someone claims to be able to build a smaller reactor with the same power as ITER, it is safe to say that he does not have a solution to the divertor problem.

Power plant in a few decades

Nevertheless, scientists are optimistic about the development of thermonuclear reactors, although it will not be as fast as some enthusiasts predict.

ITER should show that controlled fusion can actually produce more energy than would be spent on heating the plasma. The next step is to build a brand new hybrid demonstration power plant that actually generates electricity.

Engineers are already working on its design. They will have to learn from ITER, which is scheduled to launch in 2023. Given the time required for design, planning and construction, it seems unlikely that the first fusion power plant will be launched much earlier than the middle of the 21st century.

Cold Fusion Rossi

In 2014, an independent test of the E-Cat reactor concluded that the device averaged 2,800 watts of power output over a 32-day period with a consumption of 900 watts. This is more than any chemical reaction is capable of isolating. The result speaks either of a breakthrough in thermonuclear fusion, or of outright fraud. The report disappointed skeptics, who doubt whether the test was truly independent and suggest possible falsification of the test results. Others have been busy figuring out the "secret ingredients" that enable Rossi's fusion to replicate the technology.

Rossi is a scammer?

Andrea is imposing. He publishes proclamations to the world in unique English in the comments section of his website, pretentiously called the Journal of Nuclear Physics. But his previous unsuccessful attempts included an Italian waste-to-fuel project and a thermoelectric generator. Petroldragon, a waste-to-energy project, failed in part because illegal dumping is controlled by the Italian organized crime, which initiated a criminal case against him for violating the rules for waste management. He also created a thermoelectric device for the Corps of Engineers ground forces USA, but during testing, the gadget produced only a fraction of the declared power.

Many do not trust Rossi, but Chief Editor The New Energy Times bluntly called him a felon with a string of failed energy projects behind him.

Independent Verification

Rossi signed a contract with the American company Industrial Heat to conduct a year-long secret test of a 1-MW cold fusion plant. The device was a shipping container packed with dozens of E-Cats. The experiment had to be controlled by a third party who could confirm that heat generation was indeed taking place. Rossi claims to have spent much of the past year practically living in a container and overseeing operations for more than 16 hours a day to prove the commercial viability of the E-Cat.

The test ended in March. Rossi's supporters eagerly awaited the observers' report, hoping for an acquittal for their hero. But in the end they got sued.

Trial

In a Florida court filing, Rossi claims the test was successful and an independent arbitrator confirmed that the E-Cat reactor produces six times more energy than it consumes. He also claimed that Industrial Heat agreed to pay him $100 million - $11.5 million upfront after the 24-hour trial (ostensibly for licensing rights so the company could sell the technology in the US) and another $89 million after the successful completion of the extended trial. within 350 days. Rossi accused IH of running a "fraudulent scheme" to steal his intellectual property. He also accused the company of misappropriation of E-Cat reactors, illegal copying innovative technologies and products, features, and designs and inappropriately attempting to obtain a patent on its intellectual property.

Goldmine

Elsewhere, Rossi claims that in one of his demonstrations, IH received $50-60 million from investors and another $200 million from China after a replay involving Chinese officials. top level. If this is true, then a lot more than a hundred million dollars is at stake. Industrial Heat has dismissed these claims as baseless and is going to actively defend itself. More importantly, she claims that she "worked for more than three years to confirm the results that Rossi allegedly achieved with his E-Cat technology, all without success."

IH doesn't believe in the E-Cat, and the New Energy Times sees no reason to doubt it. In June 2011, a representative of the publication visited Italy, interviewed Rossi and filmed a demonstration of his E-Cat. A day later, he reported his serious concerns about the method of measuring thermal power. After 6 days, the journalist posted his video on YouTube. Experts from all over the world sent him analyzes, which were published in July. It became clear that this was a scam.

Experimental confirmation

Nevertheless, a number of researchers - Alexander Parkhomov from Russian University Friendship of Peoples and the Martin Fleishman Memorial Project (MFPM) - managed to reproduce the cold thermonuclear fusion of Russia. The MFPM report was titled "The End of the Carbon Era Is Near". The reason for such admiration was the discovery, which cannot be explained otherwise than by a thermonuclear reaction. According to the researchers, Rossi has exactly what he is talking about.

Viable open recipe cold nuclear fusion can cause an energy "gold rush". Alternative methods may be found to bypass Rossi's patents and keep him out of the multi-billion dollar energy business.

So perhaps Rossi would prefer to avoid this confirmation.

Mass is a special form of energy, as evidenced by the well-known formula of Einstein E = mc 2 . From it follows the possibility of converting mass into energy and energy into mass. And such reactions at the intra-atomic level of matter really take place. In particular, part of the mass of the atomic nucleus can be converted into energy, and this happens in two ways. First, a large nucleus can break up into several small ones - this process is called a reaction decay. Secondly, several smaller nuclei can combine into one larger one - this is the so-called reaction synthesis. Nuclear fusion reactions in the universe are very widespread - suffice it to mention that it is from them that stars draw energy. Nuclear fission today serves as one of the main sources of energy for mankind - it is used in nuclear power plants. Both in the decomposition reaction and in the synthesis reaction, the total mass of the reaction products is less than the total mass of the reactants. This difference in mass is converted into energy according to the formula E = mc 2 .

Decay

In nature, uranium occurs in the form of several isotopes, one of which - uranium-235 (235 U) - spontaneously decays with the release of energy. In particular, when a sufficiently fast neutron hits the nucleus of a 235 U atom, the latter decays into two large pieces and a number of small particles, usually including two or three neutrons. However, having summed up the masses of large fragments and elementary particles, we will miss a certain mass in comparison with the mass of the original nucleus before its decay under the impact of a neutron. This missing mass is released in the form of energy distributed among the resulting decay products - first of all, kinetic energy(energy of motion). Rapidly moving particles scatter from the place of decay and collide with other particles of matter, heating them up.

They are particles rapidly flying away from the place of decay, while they do not fly far, crashing into neighboring atoms of the substance and heating them up. Thus, the energy generated by nuclear decay is converted into the heat of the surrounding matter.

Uranium mined from natural uranium ore, the uranium-235 isotope, contains only 0.7% of the total mass of uranium - the remaining 99.3% is the relatively stable (weakly radioactive) 238 U isotope, which simply absorbs free neutrons without decaying under their influence. Therefore, to use uranium as fuel in nuclear reactors, it must be preliminarily enrich - that is, to bring the content of the radioactive isotope 235 U to a level of at least 5%.

After that, uranium-235 as part of enriched natural uranium in a nuclear reactor decays under the influence of neutron bombardment. As a result, on average, 2.5 new neutrons are released from one 235 U nucleus, each of which causes the decay of another 2.5 nuclei, and the so-called chain reaction. The condition for the continuation of the undamped uranium-235 decay reaction is the excess of the number of neutrons released by the decaying nuclei of the number of neutrons leaving the uranium conglomerate; in this case, the reaction continues with the release of energy.

In the atomic bomb, the reaction is deliberately uncontrolled, as a result of which, in a fraction of a second, a huge number of 235 U nuclei decays and explosive energy, colossal in its destructiveness, is released. In nuclear reactors used in the power industry, the decay reaction must be strictly controlled in order to dose the energy released. A good neutron absorber is cadmium - it is usually used to control the decay rate in nuclear power plant reactors. Cadmium rods are immersed in the reactor core to the level necessary to reduce the rate of free energy release to technologically reasonable limits, and in the event that the energy release falls below the required level, the rods are partially removed from the reaction core, after which the decay reaction is intensified to the required level. The released thermal energy is then converted into electrical energy in the usual way (by means of turbogenerators).

Synthesis

Thermonuclear fusion is a reaction directly opposite to the decay reaction in its essence: smaller nuclei are combined into larger ones. The most common reaction in the Universe in general is the reaction of thermonuclear fusion of helium nuclei from hydrogen nuclei: it continuously proceeds in the bowels of almost all visible stars. In its pure form, it looks like this: four hydrogen nuclei (protons) form a helium atom (2 protons + 2 neutrons) with the release of a number of other particles. As in the case of the decay reaction of an atomic nucleus, the total mass of the formed particles turns out to be less the mass of the initial product (hydrogen) - it is released in the form of the kinetic energy of the reaction product particles, due to which the stars are heated up.

In the interiors of stars, the thermonuclear fusion reaction does not occur at once (when 4 protons collide), but in three stages. First, a deuterium nucleus is formed from two protons (one proton and one neutron). Then, after another proton hits the deuterium nucleus, helium-3 is formed (two protons and one neutron) plus other particles. Finally, two helium-3 nuclei collide to form helium-4, two protons, and other particles. However, in aggregate, this three-stage reaction gives a net effect of the formation of a helium-4 nucleus from four protons with the release of energy carried away by fast particles, primarily photons ( cm. evolution of stars).

The natural fusion reaction takes place in stars; artificial - in a hydrogen bomb. Alas, man has not yet been able to find the means to direct thermonuclear fusion into a controlled channel and learn how to obtain energy from it for peaceful purposes. However, scientists do not lose hope for achieving positive results in the field of obtaining "peaceful and cheap" thermonuclear energy in the foreseeable future - for this, the main thing is to learn how to keep high-temperature plasma either by means of laser beams or by means of super-powerful toroidal electromagnetic fields ( cm.

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Nuclear fusion reactions are called thermonuclear because the only way to initiate reactions is to heat the nuclear fuel to a high temperature.

The nuclear fusion reaction can also serve as a source of energy.

Nuclear fusion reactions require extremely high temperatures and pressure.

Hydrogen-3 is the easiest to enter into the nuclear fusion reaction, but it is present in earth's atmosphere in such small quantities, and its production is associated with very high costs, that the very feasibility of using it as a fuel is called into question.

This reaction is called a nuclear fusion reaction, since the result of the combination of nuclei is a heavier nucleus.

In order for a nuclear fusion reaction to begin, it is necessary to reach a temperature of the order of a million degrees. Since the only currently known means of achieving such temperatures are nuclear fission reactions, a fission-based atomic bomb is used to excite the hydrogen fusion reaction. It is assumed that the energy released by stars, including our Sun, is formed as a result of nuclear fusion reactions, similar to the above reactions. Depending on the age and temperature of the star, carbon, oxygen, and nitrogen nuclei, as well as hydrogen and helium isotopes, can take part in such reactions.

The main problem with the fusion reaction is to develop a technology that can hold a gas of charged particles, a plasma at a temperature of the order of many millions of degrees for quite a long time in order to release the required amount of energy, while the plasma is in an isolated state. . There are two methods by which this process is controlled: the method of magnetic fields and the method of holding heavy hydrogen atoms with the help of powerful lasers. This method represents the easiest way to carry out nuclear fusion, which involves deuterium and tritium and which takes place in a plasma held by magnetic fields at a temperature of more than 100 million C. end products fusion reactions are helium ions (He-4) and neutrons. About 80% of the energy released as a result of fusion comes from neutrons. The systems for heat transfer and conversion to heat, which are the next step, are similar to those used in nuclear fission reactors.

Learning how to generate useful energy through nuclear fusion is important primarily because thermonuclear fusion is an almost inexhaustible source of energy. The cost of fusion fuel is small compared to the cost of fossil fuels; it is available everywhere, and the process of obtaining it has only a minor impact on the environment. Further, although thermonuclear energy is also one of the types of atomic energy, it differs significantly from conventional atomic energy, which is released during the fission of uranium, plutonium, and thorium. Compared to nuclear fission reactors and the dangers they create, a fusion reactor appears to be far less dangerous.

The rate of energy release as a result of all the reactions of nuclear fusion occurring in every second turns out to be a strikingly small value, if expressed in calories per gram of matter. It will be more than 100 times less than the rate at which the human body releases heat in one second during its metabolism. Of course, the total amount of heat given off by the Sun cannot be compared with the heat of our body due to the extremely huge amount of the total mass of the Sun. But the question arises how the Sun can be so hot if the rate of heat release per gram of mass in it is 100 times less than in our body.

It is generally accepted that generating energy through nuclear fusion should cause less pollution. environment than by nuclear fission. However, it should be taken into account that construction materials for the internal parts of a fusion reactor must become very radioactive and often have to be replaced. What is the cause of these complications.

The abundance of an element is related to the stability of its nucleus and the course of nuclear fusion reactions of elements. In accordance with this, there are approximate rules that determine the abundance of an element. Thus, it has been observed that elements with small atomic masses are more common than heavy elements. Further, atomic masses the most common elements are expressed in multiples of four; elements with even ordinal numbers are several times more common than their neighboring odd elements.

Truly immense prospects for the development of the energy basis of production promises society the mastery of a controlled nuclear fusion reaction. The solution of the problem of controlling thermonuclear reactions is on the agenda of Soviet science. Among its tasks is the discovery of ways to directly convert thermal, nuclear, solar and chemical energy into electrical energy.

If the protons manage to get close to distances r r0, then a nuclear fusion reaction occurs, the nucleons form a bound system - the nucleus of the deuterium atom. The bound state corresponds to the model of a particle in a potential well. But such approach of particles is prevented by a potential barrier. To elucidate the possibility of a reaction, it is necessary to solve the problem of the passage of particles through a barrier at different energies.

Lithium is a source of the heavy isotope of hydrogen, tritium, which is used in nuclear fusion reactions.

As a child, I loved to read the magazine "Science and Life", in the village there was a file starting from the 60s. There they often talked about thermonuclear fusion in a joyful way - it's almost there, and it will be! Many countries, in order to be in time for the distribution of free energy, built Tokamaks (and set up a total of 300 of them around the world).

The years have gone by... It's 2013 and humanity still gets most of its energy from burning coal, like it did in the 19th century. Why did it happen, what prevents the creation of a thermonuclear reactor, and what can we expect in the future - under the cut.

Theory

The nucleus of an atom, as we remember, consists in the first approximation of protons and neutrons (= nucleons). In order to tear off all neutrons and protons from an atom, a certain energy must be expended - the binding energy of the nucleus. This energy is different for different isotopes, and naturally, in nuclear reactions, the energy balance must be maintained. If we plot the binding energy for all isotopes (per 1 nucleon), we get the following:


From here we see that we can get energy either by separating heavy atoms (like 235 U), or by connecting light ones.

The most realistic and interesting in practical terms are the following synthesis reactions:

1) 2 D+ 3 T -> 4 He (3.5 MeV) + n (14.1 MeV)
2) 2 D+ 2 D -> 3 T (1.01 MeV) + p (3.02 MeV) 50%
2 D+ 2 D -> 3 He (0.82 MeV) + n (2.45 MeV) 50%
3) 2 D+ 3 He -> 4 He (3.6 MeV) + p (14.7 MeV)
4) p+ 11 B -> 3 4 He + 8.7 MeV

These reactions use Deuterium (D) - it can be obtained directly from sea water, Tritium (T) - a radioactive isotope of hydrogen, now it is obtained as a waste product in conventional nuclear reactors, it can be specially produced from lithium. Helium-3 - like on the Moon, as we all already know. Boron-11 - natural boron consists of 80% boron-11. p (Protium, hydrogen atom) - ordinary hydrogen.

For comparison, the fission of 235 U releases ~202.5 MeV of energy, i.e. much more than with a fusion reaction based on 1 atom (but based on a kilogram of fuel - of course, thermonuclear fuel gives more energy).

According to reactions 1 and 2, a lot of very high-energy neutrons are obtained, which make the entire structure of the reactor radioactive. But reactions 3 and 4 - "without neutron" (aneutronic) - do not give induced radiation. Unfortunately, side reactions still remain, for example, from reaction 3 - deuterium will react with itself, and there will still be a small neutron radiation.

Reaction 4 is interesting because as a result we get 3 alpha particles, from which, theoretically, energy can be directly removed (because they actually represent moving charges = current).

In general, there are enough interesting reactions. The only question is how easy it is to implement them in reality?

On the complexity of the reaction Mankind has mastered the fission of 235 U relatively easily: there is no difficulty here - since neutrons do not have a charge, they can literally "crawl" through the nucleus even at a very low speed. In most fission reactors, just such thermal neutrons are used - in which the speed of movement is comparable to the speed of the thermal movement of atoms.

But during the fusion reaction - we have 2 nuclei that have a charge, and they repel each other. In order to bring them closer to the distance necessary for the reaction, it is necessary that they move at a sufficient speed. This speed can either be achieved in an accelerator (when all atoms move at the same optimal speed as a result), or by heating (when atoms fly randomly in random directions and at a random speed).

Here is a graph showing the reaction rate (cross section) versus the speed (=energy) of the colliding atoms:

Here is the same, but constructed from the plasma temperature, taking into account the fact that the atoms there fly at a random speed:


We immediately see that the D + T reaction is the “easiest” (it needs a miserable 100 million degrees), D + D is about 100 times slower at the same temperatures, D + 3 He goes faster than the competing D + D only at temperatures of the order 1 billion degrees.

Thus, only the D + T reaction is at least remotely accessible to a person, with all its shortcomings (radioactivity of tritium, difficulties in obtaining it, radiation induced by neutrons).

But as you understand, taking and heating something up to one hundred million degrees and leaving it to react will not work - any heated objects emit light, and thus quickly cool down. Plasma heated to hundreds of millions of degrees - shines in the X-ray range, and what is most sad - it is transparent to him. Those. Plasma with such a temperature fatally cools down quickly, and in order to maintain the temperature, it is necessary to constantly pump in gigantic energy to maintain the temperature.

However, due to the fact that there is very little gas in a thermonuclear reactor (for example, in ITER - only half a gram), everything turns out not so bad: to heat 0.5 g of hydrogen to 100 million degrees, you need to spend about the same amount of energy as to heat 186 liters of water per 100 degrees.

The project ended on September 30, 2012. It turned out that there were inaccuracies in the computer model. According to the new estimate, the pulse power achieved at NIF is 1.8 megajoules - 33-50% of what is required to release as much energy as was expended.

Sandy Z-machine The idea is: take big pile high-voltage capacitors, and sharply discharge them through thin tungsten wires in the center of the machine. The wires instantly evaporate, and a huge current of 27 million amperes continues to flow through them for 95 nanoseconds. Plasma, heated to millions and billions (!) degrees, emits X-rays, and compresses a capsule with a deuterium-tritium mixture in the center (the energy of an X-ray pulse is 2.7 megajoules).

It is planned to upgrade the system using the Russian power plant(Linear Transformer Driver - LTD). In 2013, the first tests are expected, in which the energy received will be compared with the energy spent (Q=1). Perhaps this direction in the future will have a chance to compare and surpass tokamaks.

Dense Plasma Focus-DPF- "collapses" the plasma running along the electrodes to obtain gigantic temperatures. In March 2012, a temperature of 1.8 billion degrees was reached at an installation operating according to this principle.

Levitated Dipole- "inverted" tokamak, in the center of the vacuum chamber hangs a toroidal superconducting magnet which holds the plasma. In such a scheme, the plasma promises to be stable on its own. But the project does not currently have funding, it seems that the synthesis reaction was not carried out directly at the facility.

Farnsworth–Hirsch fusor The idea is simple - we place two spherical grids in a vacuum chamber filled with deuterium, or a deuterium-tritium mixture, apply a potential of 50-200 thousand volts between them. In an electric field, atoms begin to fly around the center of the chamber, sometimes colliding with each other.

There is a neutron yield, but it is rather small. Big loss energy into bremsstrahlung X-rays, the inner grid quickly heats up and evaporates from collisions with atoms and electrons. Although the design is interesting from an academic point of view (any student can assemble it), the efficiency of neutron generation is much lower than linear accelerators.

Polywell is a good reminder that not all fusion work is public. The work was funded by the US Navy, and was classified until negative results were obtained.

The idea is a development of the Farnsworth–Hirsch fusor. The central negative electrode, which had the most problems, we replace with a cloud of electrons held by a magnetic field in the center of the chamber. All test models had regular, not superconducting, magnets. The reaction produced single neutrons. In general, no revolution. Perhaps the increase in size and superconducting magnets would have changed something.

Muonic catalysis- a radically different idea. We take a negatively charged muon and replace it with an electron in an atom. Since the muon is 207 times heavier than an electron, 2 atoms in a hydrogen molecule will be much closer friend to a friend, and a fusion reaction will occur. The only problem is that if helium is formed as a result of the reaction (chance ~ 1%), and the muon flies away with it, it will no longer be able to participate in reactions (because helium does not form a chemical compound with hydrogen).

The problem here is that the generation of a muon at the moment requires more energy than can be obtained in a chain of reactions, and thus energy cannot be obtained here yet.

"Cold" thermonuclear fusion(this does not include "cold" muon catalysis) - has long been a pasture of pseudoscientists. There are no scientifically confirmed and independently repeatable positive results. And sensations at the level of the yellow press were more than once before Andrea Rossi's E-Cat.