Synthesis and fission: what's the difference?
Fusion and fission are different processes for producing nuclear energy.
This energy produced by nuclearfission, is captured inside reactors and used to heat water to steam, which turns a turbine and generates electricity. But this process creates waste that can remain radioactive for millions of years. The situation in the reactors at Fukushima and Chernobyl showed how this could turn out.
On the other hand, thermonuclear fusion will not leadto the formation of long-term nuclear waste, and the necessary materials can be recycled within 100 years. There is also no danger of an accident, because the process is based on high-temperature reactions that stop in a few seconds if the equipment malfunctions. And since these reactions use a relatively small amount of fuel, there is no danger of using them to produce nuclear weapons.
In the field of nuclear fusion research, there arescientists who strive for one goal - to recreate the processes that the Sun itself uses to produce a huge amount of energy. Enormous gravitational forces trap hydrogen from the sun's atmosphere and use intense heat and pressure to convert the gas into plasma. In it, nuclei collide at high speed, forming helium and releasing energy.
The sun's colossal gravitational forces are about 28 times greater than those here on Earth.Scientists have had to get creative about limiting the fuel for nuclear fusion reactions.The most preferred approach in its current form is to use magnetic fields, which can be used to hold two heavy forms of hydrogen, deuterium and tritium, in a device called a tokamak.
Tokamak - high hopes
The word “tokamak” itself is nothingdoes not denote is just an abbreviation, which later became a full-fledged word. It is used not only in Russia, but also abroad, since it was in our country that this thing was invented and it was here that they actively developed for a long time.
Tokamak is a toroidal chamber with magnetic coils. That's all.
The essence of a tokamak comes down to creatingmagnetic field in which the thermonuclear fusion reaction will occur. Since the temperature of such a reaction is not just high, but literally prohibitive (several million degrees Celsius), it cannot be carried out simply inside some kind of chamber—it will melt long before the operating temperature is reached.
This temperature is achieved due to the fact thatInside the tokamak, the substance is in the fourth state of aggregation, which is achieved at such high temperatures. This state is called plasma. On Earth, plasma in the natural environment is found only in lightning and the northern lights; in space, literally everything consists of it - stars, nebulae, interstellar space.
Inside the building that will house the world's largest tokamak reactor.
The first to propose the use of thermonuclearsynthesis, including for industrial purposes, was the Soviet physicist O.A. Lavrentyev. He did this in his 1950 work. It was with his work that the study of ways to use thermonuclear fusion began.
A year later, other physicists—A.D.Sakharov and I.E. Tamm—developed the idea and said that the thermonuclear reaction should be maintained inside a closed toroidal chamber. To create a magnetic field inside the tokamak, it is made up of sections with coils wound inside them. Since they run the entire length of the chamber and create something like a closed tunnel, the resulting magnetic field is called toroidal. This is the working area of the installation.
Inside the China Experimental Advanced Superconducting Tokamak (EAST).
When the chamber is full, it createsa vortex electric field that maintains the plasma inside the chamber, and at the same time heats it up, bringing it to the same temperature of several million degrees.
Since the field and heating are created due to increasing the current in the inductor, but it cannot increase indefinitely, the lifetime of the plasma in a stable state does not yet exceed several seconds. This is the main reason that we cannot yet use tokamaks as a source of industrial energy production. There are ways to solve this problem, including the use of microwave radiation, but so far work in this direction is still underway.
Many people working to achieve thisgoals, have high hopes for the next generation device that is currently under construction. ITER, or the International Thermonuclear Experimental Reactor, is one of the most ambitious energy projects humanity has ever undertaken, involving scientists and engineers from 35 countries. When completed in 2025, it will be the world's largest nuclear fusion device.
Although most of humanity's ambitionsin the field of nuclear fusion associated with ITER, there are other exciting opportunities. Including another thermonuclear reactor with magnetic confinement - a stellarator.
Stellator - imitating a star
Like tokamaks, stellarators are designed toContaining plasma streams in a closed chamber using magnetic coils, but with some key differences. Instead of a nice, symmetrical donut shape, the stellarator sends plasma out into irregular circles that spin and spin using an incredibly complex series of magnetic coils. This seems counterintuitive, but it actually creates greater stability in the plasma due to differences in internal current, writes New Atlas.
By itself, a stellarator is a type of reactor forimplementation of controlled thermonuclear fusion. The name comes from lat. stella - star, indicates the similarity of the processes occurring in the stellarator and inside the stars. Invented by the American physicist L. Spitzer in 1950, the first prototype was built under his leadership the following year as part of the secret Matterhorn project.
Wendelstein 7-X (W7-X) - experimentalinstallation for research of high-temperature plasma, located in the city of Greifswald in Germany. Its construction was carried out by the Max Planck Institute for Plasma Physics from 2005 to 2014. The purpose of the facility is to test the industrial suitability of a stellarator-type fusion reactor, as well as to research and improve technical components and technologies in the field of controlled thermonuclear fusion.
In such fusion reactorsthe toroidal chamber has a complex, sinuous shape, as do the magnetic fields created around it. This unusual design, according to the theory, helps such reactors operate in a continuous mode, spending much less energy than conventional “even” reactors. tokamak type reactors. In addition, the complex configuration of the magnetic field makes it possible to reliably contain high-temperature plasma, which reduces the risk of its contact with the internal walls of the reactor chamber. However, such advantages come at a price, which lies in the complexity of designing and manufacturing the reactor itself.
In December 2017, W7-X completed its secondstage of experiments in which improved plasma heating and measurement systems were used. The main element that was tested at the second stage was the heat removal system, the operation of which should not affect the plasma cord. This tool consists of a chain of magnets that form complex magnetic fields, causing the plasma to pass close to 10 heat sink plates. Any deviation of the magnetic fields entails a deflection of the plasma cord, which leads to overheating of the plates and to excessive cooling and destruction of the plasma cord.
The work of electromagnets that create a magnetic field is controlled by a complex control system that uses a variety of feedbacks.
Since stellarators do not require so muchinternal current and inherently offer greater stability than tokamaks, Hole says they may well be better suited to power the grid. But this is on condition that the incredibly complex infrastructure can be built in an inexpensive way and with the same constraints, which is not the case in its current form.
Inertial retention is a radical approach
In addition to the magnetic confinement region,other approaches to nuclear fusion that fall under the so-called inertial confinement. Inertial controlled thermonuclear fusion is one of the types of thermonuclear fusion, in which thermonuclear fuel is held by its own inertial forces. The idea is to quickly and evenly heat the thermonuclear fuel, so that the resulting plasma has time to react before scattering. Thus, when using this principle, the reactor will be pulsed. This new line of research in nuclear fusion involves the use of very precisely targeted laser or ion beams to rapidly heat a fuel pellet that will be composed of deuterium and tritium.
The idea is that the impact on thesefuel pellets such a sudden and violent heating will cause enormous compressive forces that set off a chain reaction through the layers of material in which nuclear fusion can occur, releasing enormous amounts of energy. Australia-based HB11 Energy is looking to do away with the traditional deuterium and tritium recipe in favor of a non-radioactive approach that includes hydrogen and boron-b11.
Small pellet of hydrogen boron fuelplaced in a large sphere and hit by two lasers simultaneously to trigger a fusion reaction that directly generates electricity without the use of steam turbines.
The company claims to avoid many problems,which have pursued nuclear fusion for decades, largely because it doesn't try to heat its fuel to insanely high temperatures. He exposes his fuel pellets to two lasers, one to create a magnetic confinement field and the second to trigger a chain reaction of hydrogen and boron fusion that creates particles that can in turn generate an electrical current.
According to experts, this current can be almostdirectly to the existing power system. There would be no need for a steam turbine generator or heat exchanger, and there would be no risk of meltdown. The team is very optimistic about its technology and says its experiments show reaction speeds a billion times better than predicted and believes its development plan will be much faster and cheaper than other approaches.
The energy that is released as a result of suchreaction, is capable of heating the surrounding fuel and, if the temperature is high enough, it can also start a thermonuclear reaction. The purpose of such installations is the ability to achieve thermonuclear "combustion", when the process of heat release causes a link reaction that affects a significant part of the fuel. A typical ball of fuel is the size of a pinhead and contains about 10 milligrams of fuel. In practice, only a small fraction of this fuel can be used in a thermonuclear reaction, but if all of this fuel is used, it will release energy equivalent to burning a barrel of oil.
“This is interesting science,” said Matthew Houle,nuclear fusion expert and Australian National University researcher familiar with HB11 and researchers working on the project at New Atlas - But I would not say there is compelling evidence that you could turn it into a power plant on a faster scale than ITER or toroidal magnetic confinement."
According to Houle, the key problem with suchapproaches is that these reactions occur in the blink of an eye. For the technology to be applied to a practical power plant, it must evolve from short-term, one-time reactions to something that produces a constant supply of energy, such as a burning fire.
Z-pinch - dark horse
Another interesting example of the inertial approachconfinement to nuclear fusion is the Z-pinch. In fusion energy research, it is a type of plasma confinement system that uses an electric current in the plasma to create a magnetic field that compresses it.
In other words, instead of usinglarge and complex magnetic coils to hold plasma streams in place, an approach that uses an electromagnetic field that is generated within the plasma itself. We can say that this is the dark horse in the nuclear fusion race. Since its inception in the 1950s, the pinch effect has promised a simpler configuration than tokamaks or stellarators. But like these devices, it also subject to instability in the plasma that extends beyond the magnetic field lines.
Z-pinch retention system at the University of Washington
Scientists from the University of Washington have come up witha way to smooth out these bulges is by adjusting the plasma hydrodynamics. While a promising solution to the energy problem, like the HB11 laser approach, the Z-pinch still faces major challenges when it comes to delivering continuous power. The problem is that it is also impulsive in nature.
What's the bottom line?
ITER, toroidal magnetic confinementand tokamak design are by far the most advanced. However, nuclear fusion researchers use different approaches, each with its own advantages and disadvantages. Unfortunately, regardless of the approach, the process still requires more energy than it returns. But solving these engineering and physics problems to produce clean energy, incredibly difficult as it may be, will be one of humanity's greatest achievements.
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