I N 1920 Arthur Eddington, an English astrophysicist, gave a lecture to the British Association for the Advancement of Science on the inner structure of stars. He guessed that what makes the sun shine – then a matter of many debates – was a kind of nuclear reaction. "This reservoir," he said, "can hardly be anything other than the sub-atomic energy that is known to be abundant in all things, and sometimes we dream that man will someday learn how to release him and use him for his ministry. The store is almost inexhaustible if only it could be tapped. "
Eddington suspected that the energy in question was released from the nuclei of the hydrogen atoms that fused into helium atomic nuclei, and he knew that a helium nucleus weighs just under four hydrogen nuclei and he surmised that the difference, which was converted into energy according to the recently discovered formula E = mc 2 was enough to power the sun, he was right, he was right in the dreams of the People began to exploit them, they started looking for Eddington's speculations, and they still dream about it ̵
In one important aspect, however, the dream of man-controlled nuclear fusion has changed in recent years. From Zeta, the first attempt to build a fusion reactor to build a fusion reactor in Harwell in southern England in the 1950s, to Iter, the latest over budgetary overreaching frog in southern France (see article), the merger was carried out by the provincial governments. No longer. Now there is an economic interest. Companies in North America and Europe are planning and planning the construction that they hope will be profitable fusion reactors. Your projects have different approaches and different amounts of money. However, they all have one thing in common: the desire to bury the old joke that commercial merger power is 30 years away – and always will be.
Given the work of Eddington and his successors, fusion power on Earth is often described as an imitation of the process that drives the sun. That is not completly correct. In solar fusion helium nuclei are formed, which are composed of two protons and two neutrons, each consisting of a particle of individual protons. The nuclei of the hydrogen atoms are thereby flung away by the positive particles, which are referred to as positrons. The average time required to complete this reaction is about a billion years.
Luckily, there is a shortcut. Here, neutrons pre-loaded hydrogen atoms are used – either one (deuterium) or two (tritium). One out of 6,000 hydrogen atoms on earth is actually deuterium, meaning that the substance can be extracted from water. Tritium, which is radioactive, is much rarer and needs to be synthesized. But the process is simple and the raw material lithium is abundant.
Deuterium and tritium react much more easily together than naked protons – and no positrons are involved. The result is helium and a replacement neutron. All you have to do to create a fusion reactor is to design and build a device that can contain a mixture of deuterium and tritium at the temperatures and densities that are needed long enough for the reaction to deliver more energy than is intended for promotion. In each machine, these parameters temperature, density and time can be weighed against each other. Their optimal mix under certain circumstances is known as Lawson's criterion, after John Lawson, who was associated with Zeta.
Nowadays, most attempts to reach the Lawson criterion are made using machines called Tokamaks in the 1950s by Andrei Sacharov, a Soviet physicist who later became famous as a human rights activist. And it's the tokamak route that drives some of the commercial wannabe fusion forces. One of them is Commonwealth Fusion Systems ( CFS ), a spin-out from the Laboratory of Plasma Physics of the Massachusetts Institute of Technology in Cambridge, Massachusetts. Another is Tokamak Energy, a spin-out from the British research laboratory of the Atomic Energy Authority in Culham – Harwell's successor.
The Lawson and the Winnings
A conventional tokamak is a hollow torus reminiscent of a donut or a bagel, wrapped in superconducting electromagnets. This torus contains the fuel, a plasma (a gas in which electrons and atomic nuclei are separated) that consists of deuterium and tritium. The magnets serve both to heat and to confine the plasma, which maintains the density and keeps it away from the torus wall, because when it touches the wall, it immediately cools down.
Tokamaks are usually large machines. For example, the torus of Iter has a volume of 830 cubic meters. However, the reactor of the CFS reactor will be about one-sixty-fifth of the volume of Iter. It can get away with such a small volume because it has stronger magnets that compress the plasma more tightly. As a bonus, these magnets become superconducting at relatively high temperatures, so that they can be cooled with liquid nitrogen, which is cheap, and not with liquid helium, which is expensive.
Tokamak Energy researchers also use nitrogen-cooled superconducting magnets. However, the company has avoided the conventional form of a tokamak in favor of something that, while still having a hole in the middle, is more like a pitted apple. The theory is that the plasma in such "spherical" torus is more stable and thus easier to handle than that in the donut form. Unlike CFS Tokamak Energy has already built a number of functional prototypes. The last, ST 40, has reached a plasma temperature of 15m ° C. The goal of the company is to reach 100m ° C in the next few years. That's two-thirds of the way to the 150m ° C that a tokamak needs to reach the Lawson criterion.
Tokamaks are not the only reactors in the city. In Vancouver, Canada, a company called General Fusion is working on a company that uses a phenomenon called field-reverse configuration ( FRC ). The limiting magnetism is generated by the movement of the electrically charged particles in the plasma itself, as this plasma rotates in a vortex similar to a smoke ring.
In General Fusion's machine, the spinning plasma, after being fired into a spherical reaction chamber, is rapidly compressed by the simultaneous release of hundreds of pistons attached to the outside of the chamber. These induce a shockwave that compresses the deuterium tritium fuel, increases its density by a thousandfold, and increases its temperature from 5 to 150 ° C. The improvement of these two parameters of the Lawson calculation means that the shortness of the third time does not matter anymore. At least that's the theory. Christofer Mowry, head of General Fusion, hopes to demonstrate the truth within five years by building a pilot plant.
Another company using the approach of FRC is TAE Technologies of Foothill Ranch, California. The latest device from TAE which was unveiled in July 2017, is a 25-meter-long machine called Norman, according to Norman Rostoker, a plasma physicist at the University of California, Irvine, the founder of the company and who died in the year 2014.
Norman is a cylindrical reactor. Plasma injectors at each end of the cylinder firing FRC are simultaneously directed towards each other at approximately 1 m kilometers per second. When the eddies meet, they merge into a cigar-shaped cloud that is three meters long and about half a meter wide. This is maintained by rays of deuterium atoms that are shot into them from the outside, and thus kept hot and stable.
Norman has made vortexes with temperatures of 3.5m ° C, which take about ten milliseconds, and not the microseconds of a conventional FRC . TAE hopes to raise this temperature to about 30 ° C by the end of this year and triple the lifetime of the plasma. Everything is smart. The special feature of the company, however, is that it intends to dispense with deuterium and tritium in favor of the normal hydrogen (the nucleus of which is a lone proton) and boron. Instead of a helium nucleus and a neutron, three helium nuclei are formed in this reaction. In fact, TAE was originally known as Tri Alpha Energy because naked helium nuclei in the field of nuclear physics are called alpha particles.
The lack of neutrons is crucial. When the deuterium-tritium fusion occurs in a tokamak, about 80% of the released energy is carried along by the neutrons. In a practical power plant, this kinetic energy would be collected by absorbing the neutrons in a suitable material and releasing the kinetic energy as heat. This heat would be used to generate steam and drive a turbine. If lithium was chosen as the absorbing material, this arrangement would have the advantage of producing new tritium in order to be able to re-enter the reaction.
The disadvantage of such an approach is that the remainder of the reactor also absorbs neutrons, creating what is radioactive (though not as radioactive as a conventional cleavage reactor) and ultimately damaging its structure. In addition, every step of the process loses energy. The proton-boron method offers a more elegant method of generating electricity, since alpha particles are positively charged and thus can induce current directly in an outer conductor. There is no warming, and the alpha particles never escape to cause damage elsewhere.
Of course there is a catch. Proton-boron fusion requires billions of degrees of temperature. This is an order of magnitude that is hotter than anything that has been achieved so far in a fusion experiment. And although such plasma temperatures have been produced under other circumstances in laboratories, it is unclear how TAE manages the equipment they use.
The mighty shrimp
TAE is radical in the choice of fuel. But other forms of fusion radicalism are possible. In the actual design of its reactor, the most radical part is probably the path that First Light Fusion pursued – leaving Oxford University. Although the First Light process aims to extract energy from a conventional mixture of deuterium and tritium, the technology they want to use is inspired by a shrimp.
Pistol shrimp are among the noisiest animals in the world. Its sound is generated by a specialized claw half the length of the creature's body, and is used to stun the prey. When the claw closes, the rapidly changing pressure causes vapor-filled cavities, so-called cavitation bubbles, in the surrounding water. When these bubbles collapse, the shock waves produce a sound as powerful as the sound of a Saturn V rocket. That's enough to kill small fish – the shrimp will eat then.
Pistol prawns were the subject of the doctorate awarded by Oxford to the founder of First Light, Nicholas Hawker. Armed with the results of his study, Dr. Hawker, whether he could increase the shrimp technique to produce plasmas that meet the Lawson criterion.
The core of First Lights reactor design is a device that holds one half of a pistol shrimp. The claw is replaced by a bullet consisting of a small disc of aluminum or copper. This is fired at a speed of about 30 km per second, replacing the other half of the claw, a 10 mm cube containing a fuel-filled cavity. The impact of the projectile generates shock waves in the fuel and thus cavitation bubbles. When these bubbles collapse the deuterium and the tritium, computations force them into a small space long enough to connect. Whether these calculations are correct will be tested later this year.
Put your money where your mouth is
So there is a lack of ideas on how to build a practical fusion reactor. However, every investor is also faced with the question of how long it takes for a new idea to work. In terms of merger, the most important milestone on this path is likely to be profit. This is the point where more energy comes from a merging plasma than from its creation.
Everyone has a good story about it. CFS wants to make a profit by 2025. Likewise Tokamak Energy. The next device from TAE Copernicus will, according to the company, not only make a profit, but also be a power plant demonstrator. In fact, TAE is aiming to deliver fusion-based electricity to the grid by 2030. This year, Tokamak Energy is also set to begin producing large-scale electricity – from power plants with a capacity in the order of 100 MW . First Light Fusion predicts that reactors using its technology will be used in the 2030s.
All this optimism should be considered carefully, especially by companies that need to raise funds for future experiments. However, capital is raised. The TAE has so far raised $ 600 million in private funds. General Fusion has raised over $ 100 million, Tokamak Energy £ 50 million ($ 65 million) and First Light, which is still in the early stages of progress, £ 25 million.
Undoubtedly there are challenges ahead. Stephen Dean of Fusion Power Associates, a foundation following the field, states, "The history of the merger does not give you much assurance that there is no problem. They know that we have been there for 50 years and there has always been a problem. "Nevertheless, he also says that he knows no showstoppers for private companies. "They are all based on good physics. These are all good people who make these programs. "And the price is huge. If only one of the fusion startups succeeds, the world's power supply will be forever guaranteed and free of carbon.