The ultimate energy that humans pursue is hidden in this terrifying weapon

Recently, with the major scientific and technological progress made by my country's new generation of artificial sun "China Tollux 3", as well as the occurrence of some events related to nuclear technology, many people have begun to pay attention to mankind's "ultimate energy" technology - controlled nuclear fusion.

Many people are curious about why nuclear fusion is considered the "ultimate energy" technology for mankind? What is the history of nuclear fusion? Why is controlled nuclear fusion so "difficult to control"? To what extent does nuclear fusion need to be achieved to truly solve the energy problem? Let's talk about these questions below.

Kuzka's mother

At the United Nations General Assembly in 1960, Khrushchev promised the United States that he would let Americans see "Kuzka's Mother". On October 30, 1961, Americans saw it.

On this day, the US Geological Survey Bureau discovered that an earthquake of about 5 on the Richter scale occurred near Novaya Zemlya. But soon, a US reconnaissance plane discovered that this was not an earthquake, but "Kuzka's mother".

"Kuzka's mother" is a Soviet colloquialism, just like the Chinese "give you some color to see". This time, the Soviets wanted to show the Americans the bomb AN602, so this bomb was nicknamed "Kuzka's mother" in the Soviet Union, and it was called "Tsar Bomb" in the West.

Image source: Wikipedia

The Soviet Union originally planned that "Kuzka's Mother" would be a super nuclear bomb with a TNT equivalent of 100 million tons.

But the design of a 100 million ton nuclear bomb at the time could cause a relatively large area of ​​radioactive fallout. In addition, after dropping a bomb of this magnitude, the pilot would not have enough time to escape the explosion site, and would basically have no way back. So the Soviet Union modified the bomb design and reduced the explosive equivalent by half.

What the Americans saw was a weakened version of "Kuzka's Mother". But even in a weakened version, it is still the most powerful bomb in human history, with an explosive equivalent of 50 million tons , 3,800 times that of the "Little Boy" atomic bomb and 10 times the total energy of all conventional bombs in World War II.

When Kuzka's Mother exploded, a fireball with a diameter comparable to the height of Mount Everest (8 km in diameter) was produced, and the flash of the nuclear explosion could be seen 1,000 km away. The explosion produced a giant mushroom cloud, nearly 8 times the height of Mount Everest (67 km high), and the mushroom head was 97 km wide.

The reason why it has such power is that it utilizes the energy produced by another kind of nuclear reaction - nuclear fusion energy .

Image source: Wikipedia

What is nuclear fusion?

Nuclear fusion is the fusion of the nuclei of two lighter atoms into a heavier nucleus. This process also releases huge amounts of energy. The same weight of nuclear fusion fuel (usually deuterium and tritium, isotopes of hydrogen) can produce four times the energy of nuclear fission, which is 4 million times more than burning oil or coal. [1]

The sun's energy is generated by nuclear fusion. Image source: Wikipedia

But nuclear fusion doesn't happen easily.

When we talked about atomic structure, we mentioned that atomic nuclei are all positively charged. If two atomic nuclei want to collide and fuse, they must overcome the repulsive force and bring their nuclei close enough.

This requires providing ultra-high temperature and ultra-high pressure to press a large number of atomic nuclei together to increase the chance of their fusion.

Such conditions are not difficult to find in the universe, such as the huge pressure and high temperature inside the sun and other stars that can sustain nuclear fusion reactions. But on the surface of the earth, it is not easy to create such conditions.

Using an atomic bomb to trigger nuclear fusion

When an atomic bomb explodes, the center of the bomb can generate temperatures of tens of millions of degrees and pressures of billions of atmospheres.

Therefore, people naturally think that placing nuclear fusion materials next to the core of the atomic bomb and using the energy from the atomic bomb explosion may be able to trigger nuclear fusion.

In May 1951, an experimental bomb called "George" was put on the test bench. In the core of the atomic bomb, in addition to the material used to trigger nuclear fission, there was also liquid deuterium. Scientists hoped to use it to test whether the atomic bomb could trigger nuclear fusion. As a result, it emitted an explosion power far exceeding that of an atomic bomb, which confirmed that it was feasible to use an atomic bomb to trigger nuclear fusion .

The scene when George exploded, Image source: Wikipedia

Because the most commonly used nuclear fusion reaction comes from the fusion reaction of hydrogen isotopes deuterium and tritium, this type of nuclear fusion weapon is also called a hydrogen bomb.

Although hydrogen bombs utilize nuclear fusion, it is uncontrolled nuclear fusion and can be used as a weapon but not as an energy source .

If you want to use it as energy, you also need to "tame" this powerful energy.

Controlled nuclear fusion

Nuclear fusion can only occur under extremely extreme conditions, so it is extremely difficult to "tame" this energy. This is mainly reflected in the following aspects:

First, the conditions for using nuclear fusion to generate electricity are too harsh. According to Fermi’s calculations, in order to use nuclear fusion to generate electricity, the temperature of the plasma must be heated to about 50 million degrees Celsius or more [2]. However, such a high temperature environment does not exist in the natural environment of the earth.

Of course, scientists can use technical means to create such a high-temperature environment, such as through electric fields, particle beams, radio wave oscillations (similar to the principle of microwave ovens), magnetic oscillation heating, etc.

But creating such an environment requires a lot of energy on the one hand, and on the other hand, it brings a problem that no substance can hold the heated plasma .

The substance with the highest melting point known so far is tantalum hafnium carbide (Ta4HfC5), which has a melting point of 4215 degrees Celsius. This melting point is far lower than that of heated plasma.

To solve this problem, the most mature method at present is to use a tokamak device to confine plasma, which is also the most promising container for a nuclear fusion reactor.

The principle of the tokamak device. Image source: Wikipedia

The tokamak device uses magnetic field confinement to confine the plasma inside the device, forming a continuously flowing ring. Of course, current technology is not enough to make the nuclear fusion reaction self-sustaining, and an auxiliary heating system is required to continuously heat the plasma flow (usually using a neutral particle beam).

At present, our country is at the forefront of the world in the development of tokamak devices.

In May 2021, the fully superconducting tokamak nuclear fusion experimental device of the Hefei Institutes of Physical Science, Chinese Academy of Sciences, achieved a record of running for 101 seconds at 120 million degrees and for 20 seconds at 160 million degrees.

On December 30, 2021, it operated for 1056 seconds at nearly 70 million degrees Celsius, setting a record for the longest operation of high-temperature plasma.

In April 2023, the fully superconducting tokamak nuclear fusion experimental device once again set a new world record, successfully achieving steady-state high confinement mode plasma operation for 403 seconds.

Image source: Xinhua News Agency

Despite this groundbreaking achievement, we are still a long way from using nuclear fusion to generate electricity.

After running, there is another key value

In the field of nuclear fusion power generation, there is a very important indicator - the Q value.

The ratio of energy released by a nuclear fusion reactor to the external energy consumed is called Q. When Q is equal to 1, it means that the energy produced by the nuclear fusion reaction is equal to the external energy it consumes.

But this does not mean that it can sustain its own power generation. It is generally believed that when the Q value is greater than 5, the nuclear fusion reactor can sustain itself. [3]

However, considering the conversion between heat, kinetic energy and electrical energy, it is internationally recognized that a nuclear power plant can only be profitable if the Q value reaches above 10. And if it wants to become a commercial nuclear fusion power plant, the Q value needs to reach above 30 .

So far, the highest Q value that humans have achieved is 0.67, and the theoretical maximum value is 1.25 (Japan's JT-60 uses deuterium-deuterium for experiments, and if converted to deuterium-tritium, the theoretical value is 1.25). This value is still far from the self-sustaining nuclear fusion reactor and using it to generate electricity.

But the temptation of nuclear fusion power generation is too great. The difference between it and traditional energy is like the difference between stars and planets. As long as we master this stellar-level energy, human civilization will take a big step forward.

Therefore, scientists in many countries around the world are also actively developing this energy source. For example, the ITER project, in which 35 countries around the world are participating, has begun to build laboratories and various equipment in France. Once completed, it will be the world's largest nuclear fusion device. It is expected to start full-power nuclear fusion experiments in 2036, and is planned to be able to achieve a Q value of more than 10 for 5 to 10 minutes. [3]

ITER construction site on June 2, 2023. Image source: iter.org

However, the ITER project is currently facing huge challenges in engineering technology (click to view: "156.5 billion yuan! The most expensive research project in history, what exactly is it for?").

It can be seen that controlled nuclear fusion, as the "ultimate energy" pursued by mankind, still has a long way to go. Even if scientists from various countries come together to work together, they still face many unforeseen difficulties. Whether mankind can "tame" this energy in this century, we will have to wait and see.

References
[1] https://www.iaea.org/newscenter/news/what-is-nuclear-fusion
[2] McCracken, Garry; Stott, Peter (2012). Fusion: The Energy of the Universe. Academic Press. ISBN 978-0-12-384657-0.
[3] https://www.iaea.org/sites/default/files/6211011zt.pdf

Planning and production <br /> Author丨Science scraps popular science creation team Editor丨Cui Yinghao