Fusion: a miracle that happens

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Fusion: a miracle that happens
Fusion: a miracle that happens
Anonim

Despite the fact that the problem of thermonuclear fusion is more than half a century old, man is only approaching its solution. Why did this happen and will we have time to find the key to this reaction before the complete depletion of fossil fuels?

Thermonuclear fusion

Optimism is good, but not self-sufficient. For example, according to the theory of probability, a brick must sometimes fall on every mortal. There is absolutely nothing to 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 at such a turbulent time 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 brick that strives to fall on someone. After all, the employee knows about this brick and can fix everything. It is equally likely that he may not correct, but the main thing is that with any decision, naked optimism will no longer console him.

In the 20th century, an entire industry found itself in this position - the world energy. The people empowered to decide decided that coal, oil and natural gas will always be like the sun in a song, that the brick will sit firmly and will not go anywhere. Let's say it disappears - that's how there is thermonuclear fusion, albeit not yet fully 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 tyrants were forgotten, and thermonuclear fusion did not obey. He just flirted, but demanded more courtesy than mortals had. By the way, they didn’t decide anything, they were quietly optimists for themselves.

The reason to fidget in the chair came when the public began to talk about the finiteness of fossil fuels. Moreover, what kind of limb it is is not clear. Firstly, it is rather difficult to calculate the exact volume of not yet found oil or, say, gas. Secondly, the forecast is complicated by price fluctuations in the market, on which the rate of production depends. And thirdly, the consumption of different fuels is not constant in time and space: for example, in 2015, global demand for coal (this is a third of all existing energy sources) fell for the first time since 2009, but by 2040 it is expected to increase sharply, especially in China and the Middle East.

For clarity, we will take the forecast of the IEA (International Energy Agency) and outline the border in 40-270 years. Imagine then fossil fuels run out.

Another overdue shortcoming of fossil fuels is emissions. When coal, oil and natural gas are burned, carbon dioxide, carbon monoxide and other nasty things are produced that enter the atmosphere. The more such volatiles in the atmosphere, the less sunlight the Earth reflects back into space and the weirder the weather. The emissions situation has become so delicate that recently the IPCC (Intergovernmental Panel on Climate Change) issued an ultimatum to phase out fossil fuels by 2100. Otherwise, climate change will become irreversible.

What happens: in a maximum of 270 years, the world energy industry should go off the rails of oil, coal and natural gas (while 80 percent of electricity is generated thanks to them) and switch to something else - safe, with high efficiency and so that it does not hit the pocket. Price is a paramount issue for developing countries, including Russia, where demand for electricity is growing faster than GDP. It is scary to imagine what awaits those who are not members of OPEC (Organization of Petroleum Exporting Countries) either. But closer to the point, or rather, to the "Nagant" of the coming energy revolution - controlled thermonuclear fusion.

To spite the pendant

As we remember, the simplest atomic nucleus consists of a positively charged proton and a negatively charged electron.If one neutron is "attached" to the atomic nucleus of, say, hydrogen, the isotope is deuterium. If you "attach" two neutrons, you get another isotope - tritium. Moreover, with each new neutron, the charge number and chemical properties of hydrogen will remain the same, but the mass number (the sum of protons and neutrons) and physical properties will change. The ability to design atomic nuclei by controlling their physical properties is of interest to nuclear physics.

To start thermonuclear fusion, two isotopes with a small charge number, for example, deuterium and tritium, must be brought closer to the distance of one atomic nucleus, so that they "stick together" and form a new, heavier nucleus, in our example, helium-4. According to Einstein's formula E = mc2 this will lead to the release of a huge amount of energy, part of which (which is characteristic - large) will go to a lone neutron: when deuterium and tritium collide, it will fly away and never return. By the way, mixing nuclei is the first problem of fusion, and a small charge number simplifies it.

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The fact is that similarly charged atomic nuclei, in general, cannot be brought together - there is a Coulomb repulsion. Therefore, the gas of deuterium and tritium has to be dispersed in a vacuum, heating up to temperatures above 100 million degrees Celsius. As a result, electron shells fly off the atoms, and the gas passes into the state of a plasma, consisting only of charged particles, which allows it to be pushed around with the help of magnetic traps. In fact, for modern installations, 100 million degrees is not the limit, however, the maximum "energy retention time" in the heat, half as long, does not yet exceed 102 seconds.

The trade-off between plasma confinement time and reaction rate is the second problem of thermonuclear fusion. There are as many as two approaches to its solution, according to the number of basic types of reactors: quasi-stationary (stellarators and tokamaks) and inertial. The first are hollow "donuts" in which the gas is heated by current and isolated from the inner walls by magnetic fields. The second are "balls", in which frozen isotopes are simultaneously ignited and squeezed by lasers. The difference is that tokamaks and stellarators are designed for long-term operation with a rarefied plasma, while “pulsed” ones are designed for “shots” at the packed mixture.

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An inquisitive reader, of course, noticed: thermonuclear reactors already exist and even different ones. Then why do we heat the bathhouse with wood and not plasma?

Stars, war and a self-taught physicist

To feel the pain that the solution of the thermonuclear puzzle causes scientists, we mentally walk their path. In 1934, the American physicist of Soviet origin Georgy Gamov, looking at the stars, asked the question: what makes them hot for millions of years? Against the background of the recent discovery of nucleons and the general rise of nuclear thought, he reasonably reasoned that it was a matter of nuclear reactions. Gamow's hypothesis was developed four years later by the American Hans Bethe. In the center of the sun, Bethe believed, hydrogen nuclei collide, turning into isotopes, and then into other elements. The difference in their mass numbers ignites the star.

It was 1938. While the romantics were talking about the world order, politicians were starting the Anschluss and preparing for the Cold War. In 1941, an American of Italian descent, one of the two "fathers" of a nuclear chain reaction, Enrico Fermi suggested that his colleagues in the Manhattan Project think about a bomb not decay, that is, atomic, but fusion, that is, hydrogen. Edward Teller liked Fermi's idea terribly, and for two reasons: he loved difficulties and was curious, and the problem of fission of atomic nuclei at that time was half-solved (the first nuclear reactor started working in the next year, 1942). Not interested.

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Robert Oppenheimer did not share this enthusiasm. But he formed a reserve detachment under the leadership of Teller from the "problem" adherents of the thermonuclear hypothesis. When the "problematic" mathematician Stanislav Ulam described a possible thermonuclear fusion algorithm, the research went into practice.And in 1951, six years after the nuclear test, the United States conducted a preliminary and a year later - a full-scale test of a thermonuclear charge. It was fueled by liquid hydrogen isotopes, which were then replaced with solid-state lithium-6 and -7 deuteride to increase power.

The Soviet prototype of thermonuclear weapons, which received the cozy name "Sloika", was ready by 1949, and in 1950 the self-taught physicist Oleg Lavrentyev - for a change - spoke out in favor of industrial thermonuclear fusion. It would be nice, they say, not only to break. A few months later, simultaneously with the Americans, Igor Tamm and Andrei Sakharov came up with the concept of Lavrentiev, proposing to loop the motion of plasma in a copper "donut" and isolate it with magnetic traps. In the same year, 1951, astrophysicist Lyman Spitzer built the world's first sample of a thermonuclear reactor - a stellarator.

It must be said that the mention of nationalities is not accidental here. The arms race hampered thermonuclear energy no less than optimism and Coulomb repulsion. As a result, the USSR, which was assembling a hydrogen bomb at the positions of the lagging behind, had its own thermonuclear reactor only in 1954, and it was a tokamak. In the types of reactors, ideology is also traced, or, if you will, an existential approach: historically, it turned out that stellarators were more American; tokamaks are more Soviet. Looking ahead, let's say that now this trend is irrelevant.

On the other hand, it was the request of the military that spurred physicists to scientific revolutions. The next few years, the world was shaken mainly by local conflicts, so thermonuclear energy, deprived of that very global courtesy, dangled in free float.

Let's make one more digression. Formally, stellarators were and are considered more advanced than tokamaks. There are several reasons for this. First, in stellarators, plasma is heated and kept only by external currents and coils. In tokamaks, ignition occurs due to an electric current flowing in the plasma and at the same time creating an additional magnetic field. Because of this, free electrons and ions appear in the "donut" of the tokamak, already with their own magnetic fields, which strive to destroy the main field, bring down the temperature and, in general, spoil everything.

Secondly, the chambers of stellarators are not just “donuts”, but “crumpled donuts”: unlike tokamaks, they have no azimuthal symmetry. In this case, the coils on the "crumpled bagels" of stellarators have a helical, nested shape (on tokamaks they are straight and parallel to each other) and "twist" the lines of force, that is, they are subjected to rotational transformation. This also stabilizes the plasma and also pushes the theoretical limit of the optimal pressure in the chamber. And the square of the pressure is roughly proportional to the reaction rate. The higher the pressure, the faster everything will happen.

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Stellarators dominated exactly until 1969, when the plasma temperature (with a volume of only one cubic meter) in the Soviet T-3, the first and only tokamak, reached a record three million degrees Celsius, which is only five times less than the temperature at the center of the Sun. Denying the reality of what was happening, British physicists volunteered to check the results of the experiment, but, alas, a miracle happened. The story of the T-3 introduced the fashion to tokamaks: they are clearer and cheaper in construction. And in 1983 in Great Britain, the largest of the currently existing thermonuclear reactors of this type, the JET, was completed.

The volume of plasma in the JET has already reached about 100 cubic meters. For 30 years, he set a series of records: he solved the first problem of thermonuclear fusion by heating the plasma to 150 million degrees Celsius; generated a capacity of 1 megawatt, and then - 16 megawatts with an energy efficiency index of Q ~ 0.7 … The ratio of consumed energy to received energy 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 is still unconquered.

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The new hope of the industry is the ITER tokamak, which is being built by the whole world in France right now. The ITER Q index should reach 10, the power - 500 megawatts, which, for a start, will simply dissipate in space. Work on this project has been going on since 1985 and was supposed to end in 2016. But gradually the cost of the construction increased from 5 to 19 billion euros, and the date of commissioning was postponed by 9-11 years. At the same time, ITER is positioned as a bridge to the DEMO reactor, which, according to the plan, in the 2040s, will generate the first "thermonuclear" electricity.

The biography of "impulse" systems was less dramatic. When physicists recognized in the early 1970s that the "constant" 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 synchronously "fired" with lasers. The idea is that if the fuel is heated and compressed enough quickly and evenly, the reaction will occur even before the plasma dissipates. And in 1974, the private company KMS Fusion received such a reaction.

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After several experimental installations and years, it turned out that not everything is so smooth with "pulsed" fusion. The uniformity of compression turned out to be a problem: the frozen isotopes turned not into an ideal ball, but into a "dumbbell", which sharply reduced pressure, and hence 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: he was the first in nuclear physics to receive 1.5 times more energy than he used up.

Now, in addition to large ones, the problems of thermonuclear fusion are solved by "pocket", purely experimental, and "start-up" installations of various designs. Sometimes they succeed in performing a miracle. For example, physicists at the University of Rochester recently surpassed the 2013 energy efficiency record by four and then five times. True, the new restrictions on the ignition temperature and pressure did not disappear anywhere, and the experiments were carried out in a reactor about three times smaller than the NIF. And the linear size, as we know, matters.

Why bother so hard, you wonder? To make it clear why thermonuclear fusion is so attractive, let us compare it with "ordinary" fuel. Suppose, at each moment of time, there is one gram of isotopes in the tokamak's "donut". In the collision of one deuterium and one tritium, 17.6 megaelectronvolts of energy are released, or 0, 000 000 000 002 joules. Now statistics: burning one gram of firewood 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. The whole world consumes so much in about 14 minutes.

Refugee neutrons and deadly hydroelectric power plants

Moreover, thermonuclear fusion is almost harmless. “Almost” - because a neutron that will fly away and will not return, taking away 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 blanket sheets - 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 - as luck would have it. Irradiation of a reactor with neutrons is called induced radiation. Because of it, the blanket will have to be changed somewhere every 10-100 years.

It is high time to clarify that the scheme of isotope "coupling" described above was simplified. Unlike deuterium, which can be eaten with a spoon, it is easy to create and find in ordinary seawater, tritium is a radioisotope, and is artificially synthesized for indecent money. At the same time, it makes no sense to store it: the core quickly “falls apart”.At ITER, tritium will be produced locally by colliding neutrons with lithium-6 and separately adding ready-made deuterium. As a result, there will be even more neutrons that will try to "escape" (along with tritium) and get stuck in the blanket than one might think.

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Despite this, the area of ​​the radioactive impact of a fusion reactor will be negligible. The irony is that security is inherent in the very imperfection of technology. Since the plasma has to be kept, and the "fuel" is added again and again, without supervision from the outside, the system will work at most for several minutes (the planned holding time for ITER is 400 seconds) and goes out. But even with a one-time destruction, according to the physicist Christopher Llewellyn-Smith, the cities will not have to be evicted: due to the low density of tritium plasma, it will contain only 0.7 grams.

Of course, the light did not converge like a wedge on deuterium and tritium. For thermonuclear fusion, scientists are 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 vapors. Just for now, at the current stage of technological ignorance, it is a little easier to push deuterium and tritium together.

And simple arithmetic is on the side of the new industry. Over the past 55 years, the world has experienced: five breakthroughs of hydroelectric power plants, as a result of which as many perished as die on Russian roads in eight years; 26 accidents at nuclear power plants, due to which tens of thousands of times fewer people died than from breakthroughs of hydroelectric power plants; and hundreds of accidents on heating power grids with God knows what the consequences. But during the operation of thermonuclear reactors, it seems that nothing, except for nerve cells and budgets, has not yet suffered.

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 well-known chemists, American Stanley Pons and Briton Martin Fleischman, gathered journalists to show the world "cold" nuclear fusion. He worked like that. A palladium electrode was placed in a solution with deuterium and lithium, and a direct current was passed through it. Deuterium and lithium were absorbed by palladium and, colliding, sometimes "adhered" to tritium and helium-4, suddenly heating the solution sharply. And this is at room temperature and normal atmospheric pressure.

The prospect of getting energy without a headwash with temperature, pressure and complex settings was too tempting, and the next day Fleischmann and Pons woke up famous. The Utah state authorities allocated $ 5 million for their research of "cold" fusion, another $ 25 million from the US Congress was requested by the university where Pons worked. Two things added a fly in the ointment to history. First, the details of the experiment did not appear in The Journal of Electroanalytical Chemistry and Interfacial Electrochemistry until April, a month after the press conference. This was contrary to scientific etiquette.

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Secondly, nuclear physicists had many questions for Fleischmann and Pons. For example, why in their reactor the collision of two deuterons gives tritium and helium-4, when it should give tritium and a proton or a neutron and helium-3? Moreover, it was easy to check: provided that nuclear fusion took place in the palladium electrode, neutrons with a predetermined kinetic energy would "fly off" from the isotopes. But neither the neutron sensors, nor the reproduction of the experiment by other scientists led to such results. And due to the 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, 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. Because of the pressure, the nuclei "rubbed" against each other and turned into helium, releasing energy. As in the Fleischmann-Pons experiment, the authors judged about the "neutron-free" synthesis 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 the Italian engineer Andrea Rossi. In 2009, he and physicist Sergio Focardi applied for an apparatus for a "low-energy nuclear reaction". It is a 20-centimeter ceramic tube in 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.

Prior to the Rossi and Fokardi patent, the mechanics of the "reactor" were not disclosed on principle. Then - with reference to a commercial secret. In 2011, the installation began to be checked by journalists and scientists (for some reason the same). The checks were as follows. The tube was heated for several hours, the input and output powers were measured, and the isotopic composition of nickel was studied. It was impossible to open it. The words of the developers were confirmed: the energy comes out 30 times more, the composition of nickel changes. But how? For such a reaction, you need not 200 degrees, but all 20 billion degrees Celsius, since the nickel nucleus is even heavier than iron.

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Not a single scientific journal of the Italian "magicians" has ever been published. Many people quickly gave up on "low-energy reactions", although the method has followers. Rossi is currently suing the patent holder, the American company Industrial Heat, on charges of stealing intellectual property. She considers him a fraud, and checks with experts - "fake".

And yet, "cold" nuclear fusion exists. It really is 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" themselves, 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 about 100 of these "jumps." Then - either a helium mesoatom, or decay (the lifetime of a muon is only 2.2 microseconds). The game is not worth the candle: the amount of energy received from 100 "jumps" does not exceed 2 gigaelectronvolts, and it takes 5-10 gigaelectronvolts to create one muon. For "cold" fusion, more precisely, "muon catalysis", to be beneficial, each muon must learn 10 thousand "jumps" or, finally, stop demanding too much from mortals. In the end, until the Stone Age - with pioneer fires instead of thermal power plants - there are some 250 years left.

However, not everyone believes in the finiteness of fossil fuels. Mendeleev, for example, denied the depletion of oil. She, thought the chemist, is a product of abiotic reactions, and not of decomposed pterodactyls, therefore it self-repairs. Mendeleev imputed rumors to the contrary to the Nobel brothers, who swung at the oil monopoly at the end of the 19th century. Following him, the Soviet physicist Lev Artsimovich expressed his conviction that thermonuclear energy would appear only when mankind “really” needed it. It turns out that Mendeleev and Artsimovich were, though decisive, but still - optimists.

And we do not really need thermonuclear energy yet.

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