Controllable nuclear fusion is known as the ultimate energy of the universe. In the big picture, it is a necessary condition for space navigation, and in the small picture, it is an endless treasure that can enable humans to realize unlimited energy and make everyone's life extremely rich!
Therefore, over the years, many countries, including our country, have been working hard to master this technology that can change the way of human life.
This is a recent news that China's new generation of " artificial sun " - China circulator No. 2 M device (HL-2M) has made another breakthrough in scientific research. The plasma current exceeded 1 million amperes, creating a new record for the operation of my country's controllable nuclear fusion device.
However, watching the news that the new record has been broken again and again attract attention, I believe that you in front of the screen are as full of expectations and doubts as me!
Above picture: China's new generation of "artificial sun" (HL-2M)
You should know that in the world, the research on how to use nuclear fusion to generate power has been carried out for more than 60 years. Although news of major breakthroughs have been released from time to time, commercial use has always been hindered by technological difficulties. only sees the records being broken again and again, but what indicators do the "artificial sun" need to meet to be truly commercialized?
If you want to answer the above questions, we have to study the sun first!
First of all, we need to clarify a concept, that is, nuclear fusion is the reaction of two or more atomic nuclei combining to form one or more different nuclei and subatomic particles. However, due to the mass difference between the reactants and products, energy is released or absorbed.
After calculation, the nuclear fusion process that produces a nucleus that is lighter than iron or nickel will usually release energy, and the lighter the element, the easier it is to fusion. However, it should be noted that the so-called "prone to fusion " is only relatively easy.
In general, the conditions for nuclear fusion are always very harsh, requiring the fuel to have a closed environment with sufficient temperature, pressure and time limit to produce plasma that can fusion. The combination of these conditions is called Lawson's criterion, that is, the value obtained by multiplying the three values of temperature, plasma density, and energy constraint time.
common environments that can meet these conditions are only among stars in the universe. The fuel used by stars is hydrogen, and gravity provides a very long constraint time.
Take the sun above our heads as an example. Under the action of gravity, the center of the sun has achieved a high temperature of 15 million K and a high pressure of 200 billion atmospheric pressures, so that hydrogen can be fusion at this "lower" temperature. It is said that the sun can fuse 620 million tons of hydrogen per second and produce 616 million tons of helium, which has been going on for 4.6 billion years.
and there is not such a high pressure on the earth. To fusion occur, the temperature needs to reach hundreds of millions of K. At the same time, in order to reduce the difficulty of fusion reaction , hydrogen isotopes, such as deuterium and tritium, will be used as fuel on the earth, because they are easier to fuse than hydrogen and can meet the requirements of Lawson's criterion.
Since that's the case, how long will it take for us to achieve controlled nuclear fusion?
Take the deuterium-tritium fusion reaction as an example. According to Lawson's criterion, its ignition constant must be greater than 3*10^21KeV s/m³, and the minimum temperature of its fusion reaction is 30 million degrees (2.6keV). According to current data, China's Circuit No. 2 M device (HL-2M) can reach a high temperature of 150 million degrees Celsius (12.9keV), which is enough to meet the temperature requirements required for fusion.
In addition, China Circuiter No. 2 M can theoretically manufacture plasma currents of more than 2.5 megaamps, and has now reached a new operating record of 1 million amperes (1 megaamp).
However, since the cross-sectional area is not clear, we cannot calculate the plasma density for the time being (plasma density is the ratio of plasma current to cross-sectional area), so we cannot calculate whether it meets the Lawson criterion.
However, the author noticed that the news report mentioned: "This new breakthrough means that the device can operate routinely at plasma currents of more than 1 megapipes in the future."
, so it should meet the minimum requirements for plasma density required for fusion. Next, it only needs a long enough constraint time. Therefore, it can be said that it is getting closer and closer to realizing controllable nuclear fusion.
, but only meeting Lawson's criterion is not enough to achieve commercial use, because satisfying Lawson's criterion only reaches the threshold for achieving nuclear fusion. To achieve commercial use, the energy output of nuclear fusion is also required, which is greater than the energy that maintains the input of nuclear fusion. This judgment standard is called Q value, which represents the ratio of the output energy of the nuclear fusion device to the input energy.
above figure: Internal structure of nuclear fusion device
When Q is greater than 0, it can be said that controlled nuclear fusion has been implemented, but the energy output is less than the energy input is not practical. When Q is greater than 1, the energy output is greater than the input, which can be practical, but the output efficiency is too low and the cost is too high. At present, the Q value of most nuclear fusion devices is hovering around 1, and the remaining one is less than 1.
. If you want to achieve commercial use, Q must be greater than 10. Of course, if the conditions are raised to a certain extent, Q will become infinity, which means that only one "ignition" is needed, and the energy emitted by the system is enough to support the continuous progress of nuclear fusion, and no longer need external energy input.
At present, it is expected to realize the controllable nuclear fusion project with Q value greater than 10 as soon as possible. It is the international thermonuclear fusion experimental reactor (ITER) program that has almost gathered global strength. The members are composed of major nuclear countries around the world, including China, covering nearly half of the world's population. However, ITER only barely passed the qualification, and the most efficient one is China's CFETR project. The
CFETR project officially launched engineering design in Hefei on December 5, 2017. It is a next-generation superconducting fusion reactor research project carried out by China on the basis of comprehensively digesting and absorbing ITER-related technologies. It is expected that by 2050, a fusion commercial demonstration reactor will be built. The volume of
CFETR is about 85% of ITER, and is under construction On the one hand, it will adopt 70% of the technology accumulation of ITER, and on this basis, it will make up for the short time of the ITER device, the fuel tritium cannot be self-supported and cannot generate electricity. The Q value is expected to be greater than 25, while the ITER is only 10. The fusion power is as high as 2 million kilowatts, which is 4 times that of ITER.
From this point of view, the seemingly unattainable controllable nuclear fusion technology is actually within reach. If the CFETR project can really proceed smoothly, China will become the first country to move towards the future world. If nothing unexpected happens, we can also witness the arrival of that day!
#China's "artificial sun" has made another breakthrough progress#
