Under what conditions does nuclear fusion occur? Thermonuclear fusion

Of the four main sources of nuclear energy, only two have currently been brought to industrial implementation: energy radioactive decay is utilized in current sources, and the fission chain reaction - in nuclear reactors. The third source of nuclear energy is annihilation elementary particles until he left the realm of fantasy. The fourth source is controlled thermo nuclear fusion, UTS, is on the agenda. Although this source is less potential than the third, it significantly exceeds the second.

Thermonuclear fusion in laboratory conditions is quite simple to carry out, but energy reproduction has not yet been achieved. However, work in this direction is underway, and radiochemical techniques are being developed, first of all, technologies for producing tritium fuel for CTS installations.

This chapter examines some radiochemical aspects of thermonuclear fusion and discusses the prospects for using installations for controlled fusion in nuclear power.

Controlled thermonuclear fusion- the reaction of the fusion of light atomic nuclei into heavier nuclei, occurring at ultra-high temperatures and accompanied by the release of huge amounts of energy. Unlike explosive thermonuclear fusion (used in a hydrogen bomb), it is controlled. In the main nuclear reactions that are planned to be used to implement controlled thermonuclear fusion, -H and 3 H will be used, and in the longer term, 3 He and “B.”

Hopes for controlled thermonuclear fusion are associated with two circumstances: i) it is believed that stars exist due to a stationary thermonuclear reaction, and 2) the uncontrolled thermonuclear process could be quite simply realized in the explosion of a hydrogen bomb. There appears to be no fundamental obstacle to maintaining a controlled nuclear fusion reaction. However, intensive attempts to implement CTS in laboratory conditions with obtaining energy gains ended in complete failure.

However, CVT is now seen as an important technological solution aimed at replacing fossil fuels in energy production. The global demand for energy, which requires an increase in electricity production and the depletion of non-renewable raw materials, stimulates the search for new solutions.

Thermonuclear reactors use the energy released by the fusion of light atomic nuclei. Napoimeo:

The fusion reaction of tritium and deuterium nuclei is promising for controlled thermonuclear fusion, since its cross section is quite large even at low energies. This reaction provides a specific calorific value of 3.5-11 J/g. The main reaction D+T=n+a has the largest cross section o t ah=5 barn in resonance at deuteron energy E pSh x= 0.108 MeV, compared to reactions D+D=n+3He a,„ a *=0.i05 barn; E max = 1.9 MeV, D+D=p+T about tah = 0.09 barn; E max = 2.0 MeV, as well as with the reaction 3He+D=p+a a m ax=0.7 barn; Eotah= 0.4 MeV. The last reaction releases 18.4 MeV. In reaction (3) the sum of energies p+a equal to 17.6 MeV, the energy of the resulting neutrons?„=14.1 MeV; and the energy of the resulting alpha particles is 3.5 MeV. If in the reactions T(d,n)a and:) He(d,p)a the resonances are quite narrow, then in the reactions D(d,n)3He and D(d,p)T there are very wide resonances with large values cross sections in the region from 1 to 10 MeV and linear growth from 0.1 MeV to 1 MeV.

Comment. The problems with easy-to-ignite DT fuel are that tritium does not occur naturally and must be produced from lithium in the fusion reactor's breeder blanket; tritium is radioactive (Ti/ 2 =12.6 years), the DT reactor system contains from 10 to 10 kg of tritium; 80% of the energy in the DT reaction is released with 14 MeV neutrons, which induce artificial radioactivity in the reactor structures and cause radiation damage.

In Fig. Figure 1 shows the energy dependences of the reaction cross sections (1 - h). The graphs for the cross sections of reactions (1) and (2) are practically the same - as the energy increases, the cross section increases and at high energies the probability of the reaction tends to a constant value. The cross section of reaction (3) first increases, reaches a maximum of 10 barn at energies of the order of 90 MeV, and then decreases with increasing energy.

Rice. 1. Cross sections of some thermonuclear reactions as a function of particle energy in the center of mass system: 1 - nuclear reaction (3); 2 - reactions (1) and (2).

Due to the large scattering cross section when bombarding tritium nuclei with accelerated deuterons, the energy balance of the thermonuclear fusion process in the D - T reaction can be negative, because More energy is spent accelerating deuterons than is released during fusion. A positive energy balance is possible if the bombarding particles, after an elastic collision, are able to participate in the reaction again. To overcome electrical repulsion, nuclei must have a large kinetic energy. These conditions can be created in high-temperature plasma, in which atoms or molecules are in a fully ionized state. For example, the D-T reaction begins to occur only at temperatures above 100 8 K. Only at such temperatures is more energy released per unit volume and per unit time than is expended. Since one D-T fusion reaction accounts for ~105 ordinary nuclear collisions, the problem CTS consists of solving two problems: heating a substance to required temperatures and holding it for a time sufficient to “burn” a noticeable part of the thermonuclear fuel.

It is believed that controlled thermonuclear fusion can be realized if the Lawson criterion is fulfilled (m>10'4 s cm-3, where P - density of high-temperature plasma, t - time of its retention in the system).

When this criterion is met, the energy released during CTS exceeds the energy introduced into the system.

The plasma must be kept within a given volume, since in free space the plasma instantly expands. Due to high temperatures plasma cannot be placed into a reservoir from any

material. To contain the plasma, it is necessary to use a high-intensity magnetic field, which is created using superconducting magnets.

Rice. 2. Schematic diagram tokamak.

If you do not set the goal of obtaining an energy gain, then in laboratory conditions it is quite simple to implement CTS. To do this, it is enough to lower an ampoule of lithium deuteride into the channel of any slow reactor operating on the fission reaction of uranium (you can use lithium with a natural isotopic composition (7% 6 Li), but it is better if it is enriched with the stable isotope 6 Li). Under the influence of thermal neutrons, the following nuclear reaction occurs:

As a result of this reaction, “hot” tritium atoms appear. The energy of the tritium recoil atom (~3 MeV) is sufficient for the interaction of tritium with deuterium present in LiD to occur:

This method is not suitable for energy purposes: the energy costs for the process exceed the energy released. Therefore, we have to look for other options for implementing the CTS, options that provide a large energy gain.

They are trying to implement CTS with energy gain either in quasi-stationary (t>1 s, tg>yu see "Oh, or in pulsed systems (t*io -8 s, n>u 22 cm*w). In the first (tokamak, stellarator, mirror trap, etc.), plasma confinement and thermal insulation are carried out in magnetic fields of various configurations. In pulsed systems, plasma is created by irradiating a solid target (grains of a mixture of deuterium and tritium) with focused radiation from a powerful laser or electron beams: when a beam of small solid targets hits the focus, a successive series of thermonuclear microexplosions occurs.

Among various chambers for plasma confinement, a chamber with a toroidal configuration is promising. In this case, plasma is created inside a toroidal chamber using an electrodeless ring discharge. In a tokamak, the current induced in the plasma is like a secondary winding of a transformer. The magnetic field, holding the plasma, is created both due to the current flowing through the winding around the chamber, and due to the current induced in the plasma. To obtain a stable plasma, an external longitudinal magnetic field is used.

A thermonuclear reactor is a device for producing energy through fusion reactions of light atomic nuclei occurring in plasma at very high temperatures (>10 8 K). The main requirement that a fusion reactor must satisfy is that the energy released as a result

thermonuclear reactions more than compensated for the energy costs from external sources to maintain the reaction.

Rice. h. Main components of a reactor for controlled thermonuclear fusion.

A thermonuclear reactor of the TO-CAMAK type (Toroidal Chamber with Magnetic Coils) consists of a vacuum chamber that forms a channel where the plasma circulates, magnets that create a field, and plasma heating systems. Attached to this are vacuum pumps that constantly pump gases out of the channel, a fuel delivery system as it burns out, and a diverter - a system through which the energy obtained as a result of a thermonuclear reaction is removed from the reactor. Toroidal plasma is in a vacuum shell. a-Particles formed in plasma as a result of thermonuclear fusion and located in it increase its temperature. Neutrons penetrate through the wall of the vacuum chamber into the zone of the blanket containing liquid lithium or a lithium compound enriched in 6 Li. When interacting with lithium, the kinetic energy of neutrons is converted into heat, and tritium is simultaneously generated. The blanket is placed in a special shell, which protects the magnet from escaping neutrons, y-radiation and heat flows.

In tokamak-type installations, plasma is created inside a toroidal chamber using an electrodeless ring discharge. For this purpose, an electric current is created in the plasma clot, and at the same time it develops its own magnetic field - the plasma clot itself becomes a magnet. Now, using an external magnetic field of a certain configuration, it is possible to suspend the plasma cloud in the center of the chamber, without allowing it to come into contact with the walls.

Diverter - a set of devices (special poloidal magnetic coils; panels in contact with plasma - plasma neutralizers), with the help of which the area of ​​direct contact of the wall with the plasma is maximally removed from the main hot plasma. It is used to remove heat from the plasma in the form of a stream of charged particles and to pump out reaction products neutralized on the divertor plates: helium and protium. Clears the plasma of contaminants that interfere with the synthesis reaction.

A fusion reactor is characterized by a power gain, equal to the ratio thermal power of the reactor to the power costs of its production. Thermal power reactor folds:

• - from the power released during a thermonuclear reaction in plasma;
• - from the power that is introduced into the plasma to maintain the combustion temperature of the thermonuclear reaction or the stationary current in the plasma;
• - from the power released in the blanket - a shell surrounding the plasma in which the energy of thermonuclear neutrons is utilized and which serves to protect the magnetic coils from radiation exposure. Fusion reactor blanket - one of the main parts of a thermonuclear reactor, a special shell surrounding the plasma in which thermonuclear reactions occur and which serves to utilize the energy of thermonuclear neutrons.

The blanket covers a ring of plasma on all sides, and those born with D-T synthesis the main carriers of energy - 14-MeV neutrons - release it to the blanket)", heating it. The blanket contains heat exchangers through which water is passed. When the tokamak operates as part of a power plant, the steam rotates steam turbine, and she is the generator rotor.

The main task of the blanket is to collect energy, transform it into heat and transfer it to power generating systems, as well as protect operators and the environment from ionizing radiation created by a thermonuclear reactor. Behind the blanket in a thermonuclear reactor there is a layer of radiation protection, the functions of which are to further weaken the flow of neutrons and y-quanta formed during reactions with matter to ensure the operability of the electromagnetic system. This is followed by biological protection, which can be followed by plant personnel.

An “active” blanket breeder is designed to produce one of the components of thermonuclear fuel. In reactors that consume tritium, breeder materials (lithium compounds) are included in the blanket to ensure efficient production of tritium.

When operating a thermonuclear reactor using deuterium-tritium fuel, it is necessary to replenish the amount of fuel (D+T) in the reactor and remove 4He from the plasma. As a result of reactions in the plasma, tritium burns out, and the main part of the fusion energy is transferred to neutrons, for which the plasma is transparent. This leads to the need to place a special zone between the plasma and the electromagnetic system, in which the burnt-up tritium is reproduced and the bulk of the neutron energies are absorbed. This zone is called the breeder blanket. It reproduces tritium burned in plasma.

Tritium in the blanket can be produced by irradiating lithium with neutron fluxes through nuclear reactions: 6 Li(n,a)T+4.8 MeV and 7 Li(n,n’a) - 2.4 MeV.

When producing tritium from lithium, it should be taken into account that natural lithium consists of two isotopes: 6 Li (7.52%) and 7 Li (92.48%). The thermal neutron absorption cross section of pure 6 Li 0 = 945 barn, and the activation cross section for the reaction (p, p) is 0.028 barn. For natural lithium, the cross section for the removal of neutrons produced during the fission of uranium is equal to 1.01 barn, and the cross section for the absorption of thermal neutrons is a = 70.4 barn.

The energy spectra of y-radiation during radiative capture of thermal neutrons 6 Li are characterized by the following values: the average energy of y-quanta emitted per absorbed neutron, in the energy range 6^-7 MeV = 0.51 MeV, in the energy range 7-r8 MeV - 0 .94 MeV. Total Energy

In a thermonuclear reactor powered by D-T fuel, as a result of the reaction:

y-radiation per neutron capture is 1.45 MeV. For 7 Li, the absorption cross section is 0.047 barn, and the activation cross section is 0.033 barn (at neutron energies above 2.8 MeV). The cross section for the removal of fission neutrons of LiH of natural composition = 1.34 barn, metallic Li - 1.57 barn, LiF - 2.43 barn.

thermonuclear neutrons are formed, which, leaving the plasma volume, enter the blanket region containing lithium and beryllium, where the following reactions occur:

Thus, a thermonuclear reactor will burn deuterium and lithium, and as a result of the reactions will be formed inert gas helium.

During the D-T reaction, tritium burns out in the plasma and a neutron with an energy of 14.1 MeV is produced. In the blanket, it is necessary that this neutron generate at least one tritium atom to cover its losses in the plasma. Tritium reproduction rate To("the amount of tritium formed in the blanket per one incident thermonuclear neutron) depends on the spectrum of neutrons in the blanket, the magnitude of absorption and leakage of neutrons. With 0% plasma coverage by the blanket, the value k> 1,05.

Rice. Fig. 4. Dependence of the cross section of nuclear reactions of tritium formation on neutron energy: 1 - reaction 6 Li(n,t)'»He, 2 - reaction 7 Li(n,n',0 4 He.

The 6 Li nucleus has a very large absorption cross section for thermal neutrons with the formation of tritium (953 barn at 0.025 eV). At low energies, the neutron absorption cross section in Li follows the law (l/u) and in the case of natural lithium reaches a value of 71 barn for thermal neutrons. For 7 Li, the cross section for interaction with neutrons is only 0.045 barn. Therefore, to increase the productivity of the breeder, natural lithium should be enriched in the 6 Li isotope. However, an increase in the 6 Li content in a mixture of isotopes has little effect on the tritium reproduction coefficient: there is an increase of 5% with an increase in the enrichment of the 6 Li isotope to 50% in the mixture. In the reaction 6 Li(n, T) "All the slowed down neutrons will not be absorbed. In addition to strong absorption in the thermal region, there is a small absorption (

The dependence of the cross section for the reaction 6 Li(n,T) 4 He on neutron energy is shown in Fig. 7. As is typical for many other nuclear reactions, the cross section of the 6 Li(n,f) 4 He reaction decreases as the neutron energy increases (with the exception of resonance at an energy of 0.25 MeV).

The reaction with the formation of tritium on the Li isotope occurs with fast neutrons at an energy of >2.8 MeV. In this reaction

tritium is produced and there is no neutron loss.

The nuclear reaction to 6 Li cannot produce expanded tritium production and only compensates for burnt-out tritium

The reaction to ?1l results in the appearance of one tritium nucleus for each absorbed neutron and the regeneration of this neutron, which is then absorbed upon deceleration and produces another tritium nucleus.

Comment. In natural Li, the tritium reproduction rate is To"2. For Li, LiFBeF 2, Li 2 0, LiF, Y^Pbz k= 2.0; 0.95; 1.1; 1.05 and i.6, respectively. Molten salt LiF (66%) + BeF 2 (34%) is called flyb ( FLiBe), its use is preferable due to safety conditions and reduction of tritium losses.

Since not every neutron of the D-T reaction participates in the formation of a tritium atom, it is necessary to multiply primary neutrons (14.1 MeV) using the (n, 2n) or (n, sn) reaction on elements that have a sufficiently large cross section for the interaction of fast neutrons , for example, on Be, Pb, Mo, Nb and many other materials with Z> 25. For beryllium threshold (n, 2 P) reactions 2.5 MeV; at 14 MeV 0=0.45 barn. As a result, in blanket versions with liquid or ceramic lithium (LiA10 2) it is possible to achieve To* 1.1+1.2. In the case of surrounding the reactor chamber with a uranium blanket, the multiplication of neutrons can be significantly increased due to fission reactions and (n,2n), (n,zl) reactions.

Note 1. The induced activity of lithium during irradiation with neutrons is practically absent, since the resulting radioactive isotope 8 Li (cr-radiation with an energy of 12.7 MeV and /-radiation with an energy of ~6 MeV) has a very short half-life - 0.875 s. Lithium's low activation and short half-life facilitate plant bioprotection.

Note 2. The activity of tritium contained in the blanket of a thermonuclear DT reactor is ~*10 6 Ci, so the use of DT fuel does not exclude the theoretical possibility of an accident on the scale of several percent of the Chernobyl one (the release was 510 7 Ci). The release of tritium with the formation of T 2 0 can lead to radioactive fallout, the entry of tritium into groundwater, reservoirs, living organisms, plants with accumulation, ultimately, in food products.

The choice of material and physical state of the breeder is serious problem. The breeder material must ensure a high percentage of conversion of lithium into tritium and easy extraction of the latter for subsequent transfer to the fuel preparation system.

The main functions of the breeder blanket include: formation of a plasma chamber; tritium production with coefficient k>i; conversion of neutron kinetic energy into heat; recovery of heat generated in the blanket during operation of a thermonuclear reactor; radiation protection of the electromagnetic system; biological protection against radiation.

A thermonuclear reactor using D-T fuel, depending on the blanket material, can be “pure” or hybrid. The blanket of a “pure” thermonuclear reactor contains Li, in which tritium is produced under the influence of neutrons and the thermonuclear reaction is enhanced from 17.6 MeV to 22.4

MeV. In the blanket of a hybrid (“active”) thermonuclear reactor, not only tritium is produced, but there are also zones in which waste 2 39Pi is placed and to produce 2 39Pi. In this case, an energy equal to 140 MeV per neutron is released in the blanket. The energy efficiency of a hybrid fusion reactor is six times higher than that of a pure one. At the same time, better absorption of thermonuclear neutrons is achieved, which increases the safety of the installation. However, the presence of fissile radioactive substances creates a radiation environment similar to that existing in nuclear fission reactors.

Rice. 5.

There are two pure breeder blanket concepts based on the use of liquid tritium breeding materials, or on the use of solid lithium containing materials. Design options for blankets are related to the type of coolant chosen (liquid metal, liquid salt, gas, organic, water) and the class of possible structural materials.

In the liquid version of the blanket, lithium is the coolant, and tritium is the reproductive material. The blanket section consists of the first wall, a breeder zone (molten lithium salt, a reflector (steel or tungsten) and a light protection component (for example, titanium hydride). The main feature of a lithium self-cooling blanket is the absence of an additional moderator and neutron multiplier. In a blanket with a liquid breeder you can use the following salts: Li 2 BeF 4 ( T pl = 459°), LiBeF 3 (Twx.=380°), FLiNaBe (7^=305-320°). Among the above salts, Li 2 BeF 4 has the lowest viscosity, but the highest Twl. Prospect Pb-Li eutectic and FLiNaBe melt, which also acts as a self-cooler. Neutron multipliers in such a breeder are spherical Be granules with a diameter of 2 mm.

In a blanket with a solid breeder, lithium-containing ceramics are used as a breeder material, and beryllium serves as a neutron multiplier. The composition of such a blanket includes such elements as the first wall with coolant collectors; neutron breeding zone; tritium production zone; cooling channels for tritium breeding and reproduction zones; iron-water protection; Blanket fastening elements; lines for supplying and discharging coolant and tritium carrier gas. Construction materials- vanadium alloys and steel of ferritic or ferritic-martensitic class. Radiation protection is made of steel sheets. The coolant used is helium gas under pressure yMPa with an inlet temperature of 300 0 and an outlet coolant temperature of 650 0.

The radiochemical task is to isolate, purify and return tritium to the fuel cycle. In this case, the choice of functional materials for fuel component regeneration systems (breeder materials) is important. The breeder material must ensure the removal of thermonuclear fusion energy, the generation of tritium and its effective extraction for subsequent purification and transformation into reactor fuel. For this purpose, a material with high temperature, radiation and mechanical resistance is required. No less important are the diffusion characteristics of the material, which ensure high mobility of tritium and, as a consequence, good efficiency extraction of tritium from breeder material at relatively low temperatures.

The working substances of the blanket can be: ceramics Li 4 Si0 4 (or Li 2 Ti0 3) - a reproducing material and beryllium - a neutron multiplier. Both the breeder and beryllium are used in the form of a layer of monodisperse pebbles (granules with a shape close to spherical). The diameters of Li 4 Si0 4 and Li 2 Ti0 3 granules vary in the ranges of 0.2-10.6 mm and about 8 mm, respectively, and beryllium granules have a diameter of 1 mm. The share of the effective volume of the granule layer is 63%. To reproduce tritium, the ceramic breeder is enriched with the 6 Li isotope. Typical 6 Li enrichment level: 40% for Li 4 Si0 4 and 70% for Li 2 Ti0 3.

Currently, lithium metatitanate 1L 2 TIu 3 is considered the most promising due to the relatively high rate of tritium release at relatively low temperatures (from 200 to 400 0), radiation and chemical resistance. It was demonstrated that granules of lithium titanate, enriched to 96% 6 Li under conditions of intense neutron irradiation and thermal effects, make it possible to generate lithium within two years with almost constant speed. Tritium is extracted from neutron-irradiated ceramics by programmed heating of the breeder material in continuous pumping mode.

It is assumed that in the nuclear industry, thermonuclear fusion installations can be used in three areas:

• - hybrid reactors in which the blanket contains fissile nuclides (uranium, plutonium), the fission of which is controlled by a powerful flow of high-energy (14 MeV) neutrons;
• - combustion initiators in electronuclear subcritical reactors;
• - transmutation of long-lived environmentally hazardous radionuclides for the purpose of radioactive waste disposal.

The high energy of thermonuclear neutrons provides great opportunities for separating energy groups of neutrons for burning a specific radionuclide in the resonant region of cross sections.

Optimism is a good thing, but not self-sufficient. For example, according to the theory of probability, a brick must sometimes fall on every mortal. Absolutely nothing can be done about this: the law of the Universe. It turns out that the only thing that can drive a mortal out into the street in such turbulent times is faith in the best. But for a worker in the housing and communal services sector, the motivation is more complicated: he is pushed into the street by the very same brick that is trying to fall on someone. After all, the worker knows about this brick and can fix everything. It is equally likely that he will not be corrected, but the main thing is that with any decision, naked optimism will no longer console him.

An entire industry found itself in this situation in the 20th century—global energy. The people empowered to decide decided that coal, oil and natural gas would always be there, like the sun in the song, that the brick would sit tight and not go anywhere. Let’s say it goes away - that’s thermonuclear fusion, even if it’s not yet completely controllable. The logic is this: they opened it quickly, which means they will conquer it just as quickly. But the years passed, the patronymics of the tyrants were forgotten, and thermonuclear fusion was not conquered. He just flirted and demanded more courtesy than mortals had. By the way, they didn’t decide anything, they were quietly optimistic.

The reason to squirm in my chair appeared when they began to talk publicly about the finiteness of fossil fuels. Moreover, what kind of limb it is is unclear. Firstly, the exact volume of oil or, say, gas that has not yet been found is quite difficult to calculate. Secondly, the forecast is complicated by fluctuations in market prices, which affect the production speed. And third, fuel consumption varies across time and space: for example, in 2015, global demand for coal (a third of all existing energy sources) fell for the first time since 2009, but is expected to rise sharply by 2040, especially in China and the Middle East.

The plasma volume in JET was already about 100 cubic meters. Over the course of 30 years, he set a series of records: he solved the first problem of thermonuclear fusion, heating the plasma to 150 million degrees Celsius; generated a power of 1 megawatt, and then 16 megawatts with an energy efficiency indicator Q ~ 0.7... The ratio of energy expended to energy received is the third problem of thermonuclear fusion. Theoretically, for self-sustaining plasma combustion, Q should exceed unity. But practice has shown that this is not enough: in fact, Q should be more than 20. Among tokamaks, Q JET remains unconquered.

The new hope for the industry is the ITER tokamak, which is currently being built by the whole world in France. ITER’s Q indicator should reach 10, its power should be 500 megawatts, which, to begin with, will simply be dissipated in space. Work on this project has been going on since 1985 and was supposed to end in 2016. But gradually the construction cost increased from 5 to 19 billion euros, and the commissioning date was pushed back by 9–11 years. At the same time, ITER is positioned as a bridge to the DEMO reactor, which, according to the plan, will generate the first “fusion” electricity in the 2040s.

The biography of “pulse” systems was less dramatic. When physicists recognized in the early 1970s that the “permanent” fusion option was not ideal, they proposed removing plasma confinement from the equation. Instead, the isotopes had to be placed in a millimeter plastic sphere, that in a gold capsule cooled to absolute zero, and the capsule in a chamber. Then the capsule was simultaneously “fired” with lasers. The idea is that if you heat and compress the fuel quickly and evenly enough, the reaction will occur before the plasma dissipates. And in 1974, the private company KMS Fusion received such a reaction.

After several experimental installations and years, it became clear that not everything is so smooth with “pulse” synthesis. Uniformity of compression turned out to be a problem: frozen isotopes turned not into a perfect ball, but into a “dumbbell”, which sharply reduced the pressure, and therefore energy efficiency. The situation led to the fact that in 2012, after four years of operation, the largest inertial American reactor NIF almost closed out of despair. But already in 2013, he did what JET failed to do: he was the first in nuclear physics to produce 1.5 times more energy than he consumed.

Now, in addition to large ones, the problems of thermonuclear fusion are solved by “pocket”, purely experimental, and “startup” installations of various designs. Sometimes they manage to perform a miracle. For example, physicists from the University of Rochester recently exceeded the energy efficiency record set in 2013 by four and then five times. True, new restrictions on ignition temperature and pressure have not gone away, and the experiments were carried out in a reactor approximately three times smaller than NIF. A linear dimension, as we know, matters.

Why bother so much, you wonder? To make it clear why thermonuclear fusion is so attractive, let’s compare it with “ordinary” fuel. Let’s say that at each moment of time there is one gram of isotopes in the tokamak “donut”. The collision of one deuterium and one tritium releases 17.6 megaelectronvolts of energy, or 0.000000000002 joules. Now the statistics: burning one gram of wood will give us 7 thousand joules, coal - 34 thousand joules, gas or oil - 44 thousand joules. Burning a gram of isotopes should lead to the release of 170 billion joules of heat. This is what the entire world consumes in about 14 minutes.

Refugee neutrons and deadly hydroelectric power plants

Moreover, thermonuclear fusion is almost harmless. “Almost” - because the neutron, which flies away and does not return, having taken part of the kinetic energy, will leave the magnetic trap, but will not be able to go far. Soon the fidget will be captured by the atomic nucleus of one of the sheets of the blanket - the metal “blanket” of the reactor. A nucleus that has “caught” a neutron will turn either into a stable, that is, safe and relatively durable, or into a radioactive isotope - depending on your luck. Irradiation of a reactor by neutrons is called induced radiation. Because of this, the blanket will have to be changed somewhere every 10–100 years.

It's time to clarify that the isotope “linking” scheme described above was simplified. Unlike deuterium, which can be eaten with a spoon, is easily created and found in ordinary seawater, tritium is a radioisotope, and is artificially synthesized at an obscene price. At the same time, there is no point in storing it: the kernel quickly “falls apart.” At ITER, tritium will be produced on site by colliding neutrons with lithium-6 and separately adding finished deuterium. As a result, there will be even more neutrons that try to “escape” (along with tritium) and get stuck in the blanket than it might seem.

Despite this, the area of ​​radioactive impact of a thermonuclear reactor will be negligible. The irony is that security is provided for by the very imperfection of technology. Since the plasma has to be retained and the “fuel” added again and again, without outside supervision the system will work for a few minutes at most (ITER’s planned retention time is 400 seconds) and will go out. But even with instantaneous destruction, according to opinion physicist Christopher Llewellyn-Smith, there will be no need to evict cities: due to the low density of tritium plasma, it will contain only 0.7 grams.

Of course, the light did not converge on deuterium and tritium. For thermonuclear fusion, scientists are also considering other pairs: deuterium and deuterium, helium-3 and boron-11, deuterium and helium-3, hydrogen and boron-11. In the last three there will be no “runaway” neutrons at all, and two American companies are already working with hydrogen-boron-11 and deuterium-helium-3 pairs. It’s just that for now, at the current stage of technological ignorance, it’s a little easier to collide deuterium and tritium.

And simple arithmetic is on the side of the new industry. Over the past 55 years, the world has seen: five hydroelectric power failures, which resulted in the death of as many as Russian roads dies within eight years; 26 accidents at nuclear power plants, due to which tens of thousands of times fewer people died than from hydroelectric power plant breakthroughs; and hundreds of incidents on thermal power grids with God knows what consequences. But during the operation of thermonuclear reactors, it seems that nothing has been damaged so far except nerve cells and budgets.

Cold fusion

No matter how tiny it was, the chance to hit the jackpot in the “thermonuclear” lottery excited everyone, not just physicists. In March 1989, two fairly well-known chemists, the American Stanley Pons and the British Martin Fleischman, gathered journalists to show the world “cold” nuclear fusion. This is how he worked. A palladium electrode was placed in a solution with deuterium and lithium and passed through it. D.C.. Deuterium and lithium were absorbed by palladium and, colliding, sometimes “locked together” into tritium and helium-4, suddenly sharply heating the solution. And this is when room temperature and normal atmospheric pressure.

The prospect of obtaining energy without the hassle of temperature, pressure and complex installations was too tempting, and the next day Fleischmann and Pons woke up famous. The authorities of the state of Utah allocated $5 million for their cold fusion research, and the university where Pons worked requested another $25 million from the US Congress. Two points added a fly in the ointment to the story. First, details of the experiment appeared in The Journal of Electroanalytical Chemistry and Interfacial Electrochemistry only in April, a month after the press conference. This was contrary to scientific etiquette.

Secondly, nuclear physics specialists had many questions for Fleischmann and Pons. For example, why in their reactor does the collision of two deuterons produce tritium and helium-4, when it should produce tritium and a proton or a neutron and helium-3? Moreover, it was easy to check: provided that nuclear fusion occurred in the palladium electrode, neutrons with a previously known kinetic energy would “fly off” from the isotopes. But neither neutron sensors nor the reproduction of the experiment by other scientists led to such results. And due to a lack of data, already in May the sensation of chemists was recognized as a “duck”.

Despite this, the work of Pons and Fleischmann brought confusion to nuclear physics and chemistry. After all, what happened: a certain reaction of isotopes, palladium and electricity led to the release of positive energy, or more precisely, to the spontaneous heating of the solution. In 2008, Japanese scientists showed a similar installation to journalists. They placed palladium and zirconium oxide in a flask and pumped deuterium into it under pressure. Due to the pressure, the nuclei “rubbed” against each other and turned into helium, releasing energy. As in the Fleischmann-Pons experiment, the authors judged the “neutronless” fusion reaction only by the temperature in the flask.

Physics had no explanation. But chemistry could have: what if the substance is changed by catalysts - “accelerators” of reactions? One such “accelerator” was allegedly used by Italian engineer Andrea Rossi. In 2009, he and physicist Sergio Focardi submitted an application to invent a device for a “low-energy nuclear reaction.” This is a 20-centimeter ceramic tube into which nickel powder, an unknown catalyst are placed and hydrogen is pumped under pressure. The tube is heated by a conventional electric heater, partially converting nickel into copper with the release of neutrons and positive energy.

Before the patent by Rossi and Focardi, the mechanics of the “reactor” were not disclosed as a matter of principle. Then - with reference to a trade secret. In 2011, journalists and scientists (for some reason the same ones) began checking the installation. The checks were as follows. The tube was heated for several hours, the input and output power was measured, and the isotopic composition of nickel was studied. It was impossible to open it. The words of the developers were confirmed: the energy output is 30 times greater, the composition of nickel is changing. But how? For such a reaction, you need not 200 degrees, but all 20 billion degrees Celsius, since the nickel core is heavier even than iron.

Andrea Rossi during testing of a device for a “low-energy nuclear reaction” (left). / © Vessy's Blog

No one Science Magazine he never published the Italian “wizards”. Many quickly gave up on “low-energy reactions,” although the method has followers. Rossi is now suing the patent holder, the American company Industrial Heat, on charges of theft of intellectual property. She considers him a fraudster, and checks with experts are “false.”

And yet “cold” nuclear fusion exists. It is really based on a “catalyst” - muons. Muons (negatively charged) “kick out” electrons from the atomic orbital, forming mesoatoms. If you collide mesoatoms with, for example, deuterium, you get positively charged mesomolecules. And since a muon is 207 times heavier than an electron, the nuclei of mesomolecules will be 207 times closer to each other - the same effect can be achieved if the isotopes are heated to 30 million degrees Celsius. Therefore, the nuclei of mesoatoms “stick together” on their own, without heating, and the muon “jumps” onto other atoms until it “gets stuck” in the helium mesoatom.

By 2016, the muon had been trained to make approximately 100 such “jumps.” Then - either helium mesoatom or decay (the lifetime of a muon is only 2.2 microseconds). The game is not worth the trouble: the amount of energy received from 100 “jumps” does not exceed 2 gigaelectronvolts, and the creation of one muon requires 5–10 gigaelectronvolts. For “cold” fusion, or more precisely, “muon catalysis,” to be profitable, each muon must learn 10 thousand “jumps” or, finally, stop demanding too much from mortals. After all, there are only 250 years left until the Stone Age - with pioneer fires instead of thermal power plants.

However, not everyone believes in the finiteness of fossil fuels. Mendeleev, for example, denied the exhaustibility of oil. She, the chemist thought, is a product of abiotic reactions, and not of decomposed pterodactyls, and therefore self-regenerates. Mendeleev blamed rumors to the contrary on the Nobel brothers, who at the end of the 19th century aimed at an oil monopoly. Following him, the Soviet physicist Lev Artsimovich completely expressed the conviction that thermonuclear energy will appear only when humanity “really” needs it. It turns out that Mendeleev and Artsimovich, although they were decisive figures, were still optimists.

And we actually don’t need thermonuclear energy yet.

“We said we would put the Sun in a box. The idea is great. But the problem is that we don’t know how to create this box” - Pierre Gilles de Gennes, laureate Nobel Prize in Physics 1991.

While heavy elements There are quite a few elements required for nuclear reactions on Earth and in space in general; there are a lot of light elements for thermonuclear reactions both on Earth and in space. Therefore, the idea of ​​using thermonuclear energy for the benefit of humanity came almost immediately with an understanding of the processes underlying it - this truly promised limitless possibilities, since the reserves of thermonuclear fuel on Earth should have been sufficient for tens of thousands of years to come.

Already in 1951, two main directions for the development of thermonuclear reactors appeared: Andrei Sakharov and Igor Tamm developed a tokamak architecture in which the working chamber was a torus, while Lyman Spitzer proposed an architecture of a more intricate design in shape most reminiscent of an inverted Mobius strip not once, but several times.

The simplicity of the fundamental design of the tokamak allowed long time to develop this direction by improving the characteristics of conventional and superconducting magnets, as well as by gradually increasing the size of the reactor. But with an increase in plasma parameters, problems with its unstable behavior gradually began to appear, which slowed down the process.

The complexity of the stellator design led to the fact that after the first experiments in the 50s, the development of this direction for a long time stopped. It received a new lease of life quite recently with the advent of modern systems computer-aided design, which made it possible to design the Wendelstein 7-X stellator with the parameters and design accuracy necessary for its operation.

Physics of the process and problems in its implementation

Iron atoms have a maximum binding energy per nucleon - that is, a measure of the energy that must be expended to split an atom into its constituent neutrons and protons, divided by their total. All atoms with lower and higher mass have this indicator below iron:

At the same time, in thermonuclear reactions of the fusion of light atoms up to iron, energy is released, and the mass of the resulting atom becomes slightly less than the amount masses of the original atoms by an amount that correlates with the released energy according to the formula E=mc² (the so-called mass defect). In the same way, energy is released during nuclear fission reactions of atoms heavier than iron.

During reactions of fusion of atoms, enormous energy is released, but in order to extract this energy, we first need to make a certain effort to overcome the repulsive forces between atomic nuclei that are positively charged (overcome the Coulomb barrier). After we managed to bring a couple of atoms closer together required distance strong comes into play nuclear interaction, which binds neutrons and protons. For each type of fuel, the Coulomb barrier for the start of a reaction is different, just as the optimal reaction temperature is different:

In this case, the first thermonuclear reactions of atoms begin to be recorded long before reaching average temperature substances of this barrier due to the fact that the kinetic energy of atoms is subject to the Maxwell distribution:

But the reaction at a relatively low temperature (on the order of several million °C) proceeds extremely slowly. So let’s say in the center the temperature reaches 14 million °C, but the specific power of the thermonuclear reaction in such conditions is only 276.5 W/m³, and it takes the Sun several billion years to completely consume its fuel. Such conditions are unacceptable for a thermonuclear reactor, since at such a low level of energy release we will inevitably spend more on heating and compressing thermonuclear fuel than we will receive from the reaction in return.

As the temperature of the fuel increases, an increasing proportion of atoms begin to have energy exceeding the Coulomb barrier and the efficiency of the reaction increases, reaching its peak. With a further increase in temperature, the reaction rate begins to fall again due to the fact that the kinetic energy of the atoms becomes too high and they “overshoot” each other, unable to be held together by the strong nuclear interaction.

Thus, the solution to how to obtain energy from a controlled thermonuclear reaction was obtained quite quickly, but the implementation of this task dragged on for half a century and has not yet been completed. The reason for this lies in the truly insane conditions in which it turned out to be necessary to place thermonuclear fuel– for a positive yield from the reaction, its temperature should have been several tens of millions of °C.

No walls physically could withstand such a temperature, but this problem almost immediately led to its solution: since a substance heated to such temperatures is a hot plasma (fully ionized gas) which is positively charged, the solution turned out to be on the surface - we just had to place such a heated plasma in a strong magnetic field, which will hold the thermonuclear fuel at safe distance from the walls.

Progress towards its implementation

Research on this topic is going in several directions at once:

1. By using superconducting magnets, scientists are trying to reduce the energy spent on igniting and maintaining the reaction;
2. with the help of new generations of superconductors, the magnetic field induction inside the reactor increases, which makes it possible to contain plasma with higher densities and temperatures, which increases power density reactors per unit of their volume;
3. research in the field of hot plasma and advances in the field computer technology allow better control of plasma flows, thereby bringing fusion reactors closer to their theoretical efficiency limits;
4. Progress in the previous area also allows us to keep the plasma in a stable state longer, which increases the efficiency of the reactor due to the fact that we do not need to reheat the plasma as often.

Despite all the difficulties and problems that lay on the way to a controlled thermonuclear reaction, this story is already approaching its ending. In the energy industry, it is customary to use the EROEI indicator - energy return on energy investment (the ratio of the energy expended in the production of fuel to the amount of energy that we ultimately obtain from it) to calculate fuel efficiency. And while the EROEI of coal continues to grow, this indicator for oil and gas reached its peak in the middle of the last century and is now steadily falling due to the fact that new deposits of these fuels are located in increasingly inaccessible places and at ever greater depths:

At the same time, we also cannot increase coal production for the reason that obtaining energy from it is a very dirty process and is literally taking the lives of people right now from various lung diseases. One way or another, we are now standing on the threshold of the end of the era of fossil fuels - and this is not the machinations of environmentalists, but banal economic calculations when looking into the future. At the same time, the EROI of experimental thermonuclear reactors, which also appeared in the middle of the last century, grew steadily and in 2007 reached the psychological barrier of one - that is, this year for the first time humanity managed to obtain more energy through a thermonuclear reaction than it spent on its implementation. And despite the fact that the implementation of the reactor, experiments with it and the production of the first demonstration thermonuclear power plant DEMO based on the experience gained during the implementation of ITER will still take a lot of time. There is no longer any doubt that our future lies in such reactors.

Innovative projects using modern superconductors will soon make it possible to implement controlled thermonuclear fusion, as some optimists say. Experts, however, predict that practical application will take several decades.

Why is it so difficult?

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

Atomic fission is where radioactive isotopes - uranium or plutonium - are split and converted into other highly radioactive isotopes, which must then be disposed of or recycled.

Fusion consists of two isotopes of hydrogen - deuterium and tritium - merging into a single whole, forming non-toxic helium and a single neutron, without producing radioactive waste.

Control problem

The reactions that occur in 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 thermonuclear fusion reactor called Wendelstein 7-X began operation in the northern German city of Greifswald. It is not yet intended 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 installations have common feature- ring-shaped. It is based on the idea of ​​using powerful electromagnets to create a strong electromagnetic field, having the shape of a torus - an inflated bicycle inner tube.

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

Demonstration of capabilities

In Europe there are currently two similar experiment. One of them is the Wendelstein 7-X, which recently generated its first helium plasma. The other is ITER, a huge fusion experimental facility in the south of France that is still under construction and will be ready to start up in 2023.

It is assumed that real nuclear reactions will occur at ITER, although only for short period time and certainly no longer than 60 minutes. This reactor is just one of many steps towards making nuclear fusion practical.

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 manufacturer Lockheed Martin, nuclear fusion can be achieved 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 will allow us to completely change the design of the reactor.

Klaus Hesch, in charge of technology at the Karlsruhe Institute of Technology in southwest Germany, is sceptical. It supports the use of new high-temperature superconductors for new reactor designs. But, according to him, developing 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 Hesch, the MIT students' model shows only the feasibility of the project. But in fact there is a lot in it 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 reels. In the MIT design, the electromagnets can be disassembled to get inside the ring that holds the plasma.

This would be very useful because it would be possible to access objects in 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 comes a more fundamental difficulty: the connections between them are not as simple as the connections between copper cables. No one has even thought about 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 area, which is inner layer metal pipe, in which the tritium necessary for nuclear fusion to occur will be “reproduced”.

Has more big problem- the so-called power output. This is the part of the system into which the used fuel, mainly helium, comes from the synthesis process. The first metal components into which the hot gas enters are called the "divertor". It can heat up to over 2000 °C.

Diverter problem

To help the unit withstand such temperatures, engineers are trying to use the metal tungsten used in old-fashioned incandescent light bulbs. The melting point of tungsten is about 3000 degrees. But there are other restrictions.

This can be done in ITER because heating does not occur constantly. The reactor is expected to 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 they do not have a solution to the diverter problem.

Power plant after 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 expended heating the plasma. The next step will be to build a completely new hybrid demonstration power plant that actually produces electricity.

Engineers are already working on its design. They will need to learn lessons 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 come online much earlier than the mid-21st century.

Cold Fusion Russia

In 2014, an independent test of the E-Cat reactor concluded that the device produced an average of 2,800 watts of power output over a 32-day period while consuming 900 watts. This is more than any chemical reaction can release. The result speaks either of a breakthrough in thermonuclear fusion or of outright fraud. The report disappointed skeptics, who question whether the review was truly independent and suggest possible falsification of test results. Others have set about figuring out the "secret ingredients" that enable Rossi's fusion in order to replicate the technology.

Is Rossi a fraud?

Andrea is impressive. He issues proclamations to the world in unique English in the comments section of his website, pretentiously called the Journal of Nuclear Physics. But his previous failed attempts included an Italian waste-to-fuel project and a thermoelectric generator. Petroldragon, a waste-to-energy project, has failed in part because illegal waste dumping is controlled by Italian organized crime, which has brought criminal charges against it for violating waste regulations. He also created a thermoelectric device for the US Army Corps of Engineers, but during testing the gadget produced only a fraction of the stated power.

Many do not trust Russia, but Chief Editor New Energy Times directly called him a criminal with a string of unsuccessful 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 monitored by a third party who could confirm that heat was indeed being generated. Rossi claims to have spent much of the past year practically living in a container and observing 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 of their hero. But they ended up getting a lawsuit.

Trial

In his filing with the Florida court, Rossi says the test was successful and an independent arbitrator confirmed that the E-Cat reactor produced six times more energy than it consumed. He also claimed that Industrial Heat agreed to pay him US$100 million - US$11.5 million upfront after a 24-hour trial (ostensibly for licensing rights so the company could sell the technology in the US) and another US$89 million upon successful completion of an extended trial. within 350 days. Rossi accused IH of running a “fraudulent scheme” to steal his intellectual property. He also accused the company of misappropriating E-Cat reactors, illegally copying innovative technologies and products, functionality and designs and an improper attempt to obtain a patent on his 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 reenactment involving senior Chinese officials. If this is true, then there is much more than a hundred million dollars at stake. Industrial Heat has rejected these claims as baseless and intends to vigorously defend itself. More importantly, she claims that she "worked for over three years to confirm the results that Rossi allegedly achieved with his E-Cat technology, with no success."

IH doesn't believe the E-Cat will work, 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 serious concerns about the way thermal power was measured. Six days later, the journalist posted his video on YouTube. Experts from all over the world sent him analyzes that were published in July. It became clear that this was a hoax.

Experimental confirmation

Nevertheless, a number of researchers - Alexander Parkhomov from Russian University Friendship of Peoples and the Martin Fleischmann Memorial Project (MFPM) - managed to reproduce Russia's cold thermonuclear fusion. The MFPM report was titled “The End of the Carbon Era Is Near.” The reason for this admiration was a discovery that cannot be explained except by a thermonuclear reaction. According to researchers, Rossi has exactly what he says.

Viable open recipe cold fusion can cause an energy “gold rush”. Can be found alternative methods, which will circumvent Rossi's patents and keep him out of the multi-billion dollar energy business.

So perhaps Rossi would prefer to avoid this confirmation.

Since nuclear forces of attraction act between atomic nuclei at short distances, when two nuclei come closer together, their fusion is possible, i.e., the synthesis of a heavier nucleus. All atomic nuclei have a positive electrical charge and therefore repel each other over large distances. In order for nuclei to come together and enter into a nuclear fusion reaction, they must have sufficient kinetic energy to overcome mutual electrical repulsion, which is greater the greater the charge of the nucleus. Therefore, the easiest way is to synthesize light nuclei with a low electrical charge. In the laboratory, fusion reactions can be observed by firing fast nuclei at a target, accelerated in a special accelerator (see Charged particle accelerators). In nature, fusion reactions occur in very hot matter, for example in the interior of stars, including in the center of the Sun, where the temperature is 14 million degrees and the energy thermal movement some of the fastest particles are sufficient to overcome electrical repulsion. Nuclear fusion occurring in heated matter is called thermonuclear fusion.

Thermonuclear reactions occurring in the depths of stars play a very important role in the evolution of the Universe. They are the source of the nuclei of chemical elements that are synthesized from hydrogen in stars. They are the source of energy for stars. The main source of energy from the Sun is the reactions of the so-called proton-proton cycle, as a result of which a helium nucleus is born from 4 protons. The energy released during fusion is carried away by the resulting nuclei, quanta of electromagnetic radiation, neutrons and neutrinos. By observing the neutrino flow coming from the Sun, it is possible to establish which nuclear fusion reactions and with what intensity occur at its center.

A unique feature of thermonuclear reactions as a source of energy is the very large energy release per unit mass of reacting substances - 10 million times more than in chemical reactions. The entry into synthesis of 1 g of hydrogen isotopes is equivalent to the combustion of 10 tons of gasoline. Therefore, scientists have long been striving to master this gigantic source of energy. In principle, we already know how to obtain thermonuclear fusion energy on Earth today. It is possible to heat matter to stellar temperatures using the energy of an atomic explosion. That's how it works H-bomb- the most terrible weapon of our time, in which the explosion of a nuclear fuse leads to instant heating of a mixture of deuterium and tritium and a subsequent thermonuclear explosion.

But scientists are not striving for such an uncontrollable synthesis that could destroy all life on Earth. They are looking for ways to implement controlled thermonuclear fusion. What conditions must be met for this? First of all, of course, it is necessary to heat the thermonuclear fuel to a temperature where fusion reactions can occur with a noticeable probability. But this is not enough. It is necessary that more energy is released during fusion than is expended on heating the substance, or, even better, that the fast particles created during fusion themselves maintain the required temperature of the fuel. To do this, it is necessary that the substance entering the synthesis be reliably thermally insulated from the surrounding and, naturally, cold environment on Earth, i.e., that the cooling time, or, as they say, the energy retention time, is sufficiently long.

Temperature and retention time requirements depend on the fuel used. The easiest way to carry out synthesis is between the heavy isotopes of hydrogen - deuterium (D) and tritium (T). In this case, the reaction results in a helium nucleus (He 4) and a neutron. Deuterium is found on Earth in huge quantities in seawater (one deuterium atom for every 6,000 hydrogen atoms). Tritium does not exist in nature. Today it is produced artificially by irradiating lithium in nuclear reactors with neutrons. The absence of tritium, however, is not an obstacle to the use D-T reactions synthesis, since the neutron produced during the reaction can be used to reproduce tritium by irradiating lithium, the reserves of which are quite large on Earth.

For implementation of D-T The reaction is most favorable at temperatures of about 100 million degrees. The requirement for energy retention time depends on the density of the reacting substance, which at such a temperature will inevitably be in the form of plasma, i.e., ionized gas. Since the intensity of thermonuclear reactions is higher, the higher the plasma density, the requirements for energy retention time are inversely proportional to the density. If we express the density in the form of the number of ions per 1 cm 3, then for the D-T reaction at the optimal temperature the condition for obtaining useful energy can be written in the form: the product of density n and energy retention time τ must be greater than 10 14 cm −3 s, i.e. That is, a plasma with a density of 10 14 ions per 1 cm 3 should noticeably cool down no faster than in 1 s.

Since the thermal speed of hydrogen ions at the required temperature is 10 8 cm/s, the ions fly 1000 km in 1 s. Therefore, special devices are needed to prevent plasma from reaching the walls that insulate it. Plasma is a gas consisting of a mixture of ions and electrons. Charged particles moving across a magnetic field are subject to a force that bends their trajectory and forces them to move in circles with radii proportional to the momentum of the particles and inversely proportional to the magnetic field. Thus, a magnetic field can prevent charged particles from escaping in a direction perpendicular to the field lines. This is the basis for the idea of ​​magnetic thermal insulation of plasma. The magnetic field, however, does not prevent the movement of particles along the lines of force: in the general case, particles move in spirals, winding around the lines of force.

Physicists have come up with various tricks to prevent particles from escaping along field lines. You can, for example, make “magnetic plugs” - areas with a stronger magnetic field that reflect some of the particles, but it is best to roll the field lines into a ring and use a toroidal magnetic field. But one toroidal field, it turns out, is not enough.

A toroidal field is inhomogeneous in space - its intensity decreases along the radius, and in an inhomogeneous field a slow movement of charged particles occurs - the so-called drift - across the magnetic field. This drift can be eliminated by passing a current through the plasma along the circuit of the torus. The magnetic field of the current, adding to the toroidal external field, will make the overall field helical.

Moving in spirals along the lines of force, charged particles will move from the upper half-plane of the torus to the lower and back. At the same time, they will always drift in one direction, for example upward. But, being in the upper half-plane and drifting upward, the particles move away from the middle plane of the torus, and being in the lower half-plane and also drifting upward, the particles return to it. Thus, drifts in the upper and lower halves of the torus are mutually compensated and do not lead to particle losses. This is exactly how the magnetic system of Tokamak-type installations is designed, on which best results on heating and thermal insulation of plasma.

In addition to thermal insulation of the plasma, it is also necessary to ensure its heating. In a Tokamak, current flowing through a plasma cord can be used for this purpose. In other devices, where confinement is carried out without current, as well as in the Tokamak itself, other heating methods are used to heat to very high temperatures, for example, using high-frequency electromagnetic waves, injection (introduction) into the plasma of beams of fast particles, light beams generated by powerful lasers, etc. The greater the power of the heating device, the faster the plasma can be heated to the required temperature. Development in recent years has been very powerful lasers and sources of beams of relativistic charged particles made it possible to heat small volumes of matter to thermonuclear temperatures in a very short time, so short that the matter has time to heat up and enter into fusion reactions before scattering due to thermal motion. In such conditions additional thermal insulation turned out to be unnecessary. The only thing that keeps particles from flying apart is their own inertia. Fusion devices based on this principle are called inertial confinement devices. This new direction of research, called inertial thermonuclear fusion, is being rapidly developed at the present time.