In the Qixia Mountain Controlled Nuclear Fusion Research Institute, standing in the laboratory, Xu Chuan looked at the images and data on the display.
On one side of the laboratory, there is an isolated experimental room.
Inside, scanning electron microscopes, metal in-situ analyzers, mass spectrometers and other equipment are analyzing the materials in the equipment.
The second extreme experiment of the Daybreak Fusion Device not only set a two-hour high-density plasma operation record, but also a deuterium-tritium raw material fusion ignition operation experiment.
The real deuterium and tritium raw material fusion ignition operation experiment brings data and value that cannot be compared with the simulation of high-density plasma flow operation with helium 3 and hydrogen.
Although the latter can also be close to the former in terms of temperature, density, etc., it is ultimately unable to produce fusion phenomena.
The former, even if it is only one milligram, can achieve true deuterium and tritium fusion to release energy, release neutrons, increase the temperature of the plasma, disrupt the operation of the plasma, etc.
These are things that cannot be accomplished by helium-3 and hydrogen simulations.
In particular, neutron irradiation damage to the first wall material is the next world problem in controllable nuclear fusion relay control of high-temperature plasma turbulence in the reactor chamber.
The material of the first wall not only has to face the high-temperature deuterium and tritium plasma in the reactor chamber, which is hundreds of millions of degrees, but also faces the neutron beam generated during the fusion of deuterium and tritium raw materials.
In addition, the first wall material may even perform the tritium self-sustaining function.
The two raw materials for dt controlled nuclear fusion are deuterium and tritium.
The content of deuterium on the earth is huge. There are about 40 trillion tons of deuterium in seawater alone, and its preparation is relatively simple.
But compared to deuterium, the amount of tritium stored on the earth is quite scarce.
The amount of tritium in global natural resources is almost negligible, and the amount in nature is only about 3.5 kilograms.
At present, the storage of tritium raw materials in various countries does not exceed 25 kilograms in total.
On the one hand, tritium will autonomously emit beta rays and decay, with a short half-life of only 12.5 years.
On the other hand, its preparation can generally only be done through nuclear reactions.
Currently, the industrial preparation of tritium mainly uses neutrons from reactors and lithium-6 compounds as targets to produce tritium, and then uses thermal diffusion methods to enrich tritium to more than 99% before collecting and storing it.
The neutron beam is uncontrollable, and the amount produced in a nuclear fission reactor is not large, so the output is very low.
Therefore, in controllable nuclear fusion technology, how to maintain a self-sustaining cycle of tritium is also one of the key issues.
Some people may think that particle accelerators can be used to accelerate neutrons to bombard lithium materials to produce tritium raw materials, but to be honest, those who have this idea are basically those who did not study physics seriously in high school.
Neutrons carry no electrons, and the magnetic field of the accelerator has no effect on them at all.
If magnetic fields could confine neutrons, materials for the first wall of a controllable fusion reactor wouldn't be so hard to find.
Fortunately, a large number of neutrons are produced during the fusion of deuterium and tritium. If neutrons are used to bombard a lithium-6 compound target, tritium can theoretically be self-sustaining.
During the last operation of the Dawn Fusion Reactor, Xu Chuan conducted such an experiment.
On the first wall, he had people install lithium-6 compound targets, tungsten alloys, molybdenum alloys, graphite, carbon composites, beryllium alloys and other materials.
Among them, the lithium-6 compound target material is used to test whether the neutrons released during the deuterium-tritium fusion process can really bombard the lithium material to produce enough tritium raw materials as theoretically.
As for other materials, it is to find the most suitable first wall material.
Neutron irradiation is no joke.
As of now, it can produce extremely strong transmutation effects on most materials and most metal materials.
This will not only destroy the structure of the material, but also act like a foaming agent, turning the material into an extremely fragile foam.
Imagine how it would feel if a piece of steel as thick as a foam box was broken into slag by your hands.
Neutron irradiation in controlled nuclear fusion reactors can do this.
In fact, this is exactly the case. Although the last dawn fusion device used only one milligram of deuterium and tritium raw materials, the neutrons produced during the fusion process still affected the various test materials deployed on the first wall to varying degrees.
of damage.
Fortunately, however, the lithium-6 compound target did play a corresponding role during the experiment. The neutron beam produced by deuterium-tritium fusion hit it and produced some tritium elements.
Therefore, theoretically speaking, it is possible to solve the problem of tritium self-sustainment by using lithium-6 compound target material as a reactant.
This can be considered a major breakthrough.
After all, in the past, no experimental institution or research institution could actually use an experimental reactor to conduct a deuterium-tritium fusion reaction to test neutrons and lithium materials to synthesize tritium raw materials.
This must be their first time.
There is good news, but there is more bad news.
The damage degree of various test materials installed on the first wall material to resist neutron irradiation is higher than what Xu Chuan calculated.
Looking at the images on the computer screen, Zhao Guanggui, a professor of materials science standing on the other side of Xu Chuan, sighed softly and said: "Judging from the experimental data, there are many more problems than we imagined."
Xu Chuan looked at the images on the computer and said, "No matter how many there are, we have to solve them one by one, right?"
Hearing this, Zhao Guanggui sighed: "That's true, but we have a lot of troubles. And we have now entered a new field. In the area of controllable nuclear fusion, no other research institution or laboratory can
Provide us with experience as a reference.”
Hearing this, Xu Chuan smiled and said: "Referring to other people's experiences and ideas can indeed provide us with great convenience, but after all, we are just walking on other people's paths. In this aspect of scientific research, if we want to achieve something
, after all, you have to have your own thoughts and ideas."
This chapter is not over, please click on the next page to continue reading! "The lazy method may be suitable for other fields, but for us who are engaged in academic research, what to do and how to solve problems ultimately require our own independent thinking.
.”
On the side, Xing Xuexing, a professor of materials science who was transferred from Shuimu University, smiled and said: "Being able to go ahead and expand the boundaries is what every researcher and scholar hopes for."
After a pause, he brought the topic back to the experimental data: "But Professor Zhao is right, we are in a lot of trouble this time."
"Whether it is tritium self-sustaining or various damage to neutron irradiation-resistant sample materials, they are far lower than expected before the experiment."
"Using neutrons to bombard lithium targets can indeed generate tritium. However, the amount generated and the amount we collect are not as much as theoretically."
"On the one hand, not all of the neutron beam generated by fusion in the chamber acts on the lithium-6 compound target. The energy it carries is too high and will directly penetrate the target, causing the number of reactions to be far lower than expected."
"On the other hand, the energy level carried by these neutrons is too high. At a temperature of 120 million degrees, the energy level of the neutron beam released by deuterium and tritium fusion is comparable to that of a medium and large particle collider. This will have a negative impact on the target material and the third
It has had a very serious impact on every side.”
Xu Chuan thought for a while and said: "The first problem can be easily solved. At worst, the thickness of the target can be increased. In addition, it can be made into a fully covered type, wrapping the reaction chamber as a whole, so that the neutron beam can be
It’s not a waste.”
"As for the second one, it's a bit troublesome."
Controlled nuclear fusion is not nuclear fission, and the temperature of nuclear fission is far inferior to that of nuclear fusion.
Even if a large-yield nuclear bomb explodes, the core temperature will reach the level of one million degrees Celsius.
When Little Boy was dropped on Hiroshima, the temperature in the core area of the explosion was only over 6,000 degrees. In comparison, this value is simply not worth mentioning in controllable nuclear fusion.
More than 6,000 degrees, this data is not even a fraction of the plasma temperature at which the Daybreak fusion device operates.
The temperature at which a nuclear bomb explodes is only this, so the temperature of a nuclear power plant that uses the nuclear fission effect to generate electricity is even lower.
Therefore, most of the anti-irradiation materials that can be used in nuclear fission reactors cannot be used in controllable nuclear fusion reactors.
Not only the lithium target used for tritium self-sustainment was damaged during the experiment, but other experimental materials deployed on the first wall were also damaged.
On the side, Zhao Guanggui said tentatively: "How about lowering the fusion temperature?"
"The temperature at which deuterium and tritium fusion can occur is around 12 million degrees, or 120 million degrees. This is a full ten times increase."
"Although lowering the temperature will affect the activity of the deuterium-tritium plasma, which will in turn affect the amount of fusion and the energy generated. It is not undesirable to sacrifice part of the heat and energy in exchange for the stability of the first wall material."
Xu Chuan thought for a while, shook his head and said, "It's not feasible."
"Although thermal motion can cause neutrons to collide inelastically, and the higher the thermal motion speed, the greater the impact on matter, the energy level of the neutron beam in the fusion reactor does not come solely from temperature."
"Its main source is the energy generated during the fusion of deuterium and tritium nuclei. Each fusion of deuterium and tritium atoms will produce a 14.1ev neutron. This part is destined in high energy physics, and lowering the temperature only reduces part of the external force.
.”
Zhao Hongzhi nodded and said: "Well, from this aspect, it is basically impossible to lower the temperature to reduce the damage of neutrons to the first wall material."
"Judging from the material analysis data after neutron irradiation, molybdenum, tungsten, and graphene are on the first step and are less affected by neutron irradiation. Austrian steel and ceramics are on the second step, and other materials are on the second step.
worse."
On the side, Professor Xing Xuexing from Shuimu University shook his head and said: "Molybdenum is not good. Shuimu has done research before. Molybdenum will transmute into radioactive elements when it is irradiated by neutrons. As for molybdenum alloys, more are needed.
tried."
"On the other hand, there may be some hope for tungsten and tungsten alloys. Currently, tungsten alloy is used as the first wall material for ter and est. It has good heat resistance and the transmutation products are osmium and rhenium, so there is no radioactivity problem."
Xu Chuan shook his head and said: "Tungsten probably won't work either."
"There are no problems with tungsten's heat resistance and transmutation products, but problems such as differences in its physical plasticity and thermal expansion coefficient, as well as the accumulation of thermal stress, can cause cracks within the material."
"This would be fatal for a controlled fusion reactor."
Hearing that Xu Chuan vetoed the tungsten alloy, the laboratory fell into silence again.
The problem of the material of the first wall is indeed very troublesome, so troublesome that no one in the world can find a suitable one.
After all, in a controlled fusion reactor, the first wall material is strongly affected by high-energy neutrons, electromagnetic radiation and high-energy particles (deuterium, tritium, helium and other impurities) emitted from the plasma.
For a commercial tokamak reactor, theoretically speaking, the general neutron wall load must reach at least 5/2.
Neutron wall load is a design indicator related to the power density of the fusion reactor, which is numerically equal to the product of the fusion neutron source intensity and the neutron energy on the first wall material per unit area.
The vast majority of heat-resistant materials simply fail to meet these extremely stringent property challenges.
But then again, if this problem had been so easy to solve, it wouldn't have persisted until now.
After all, controllable nuclear fusion is something that everyone in the world can do if they can, and the various technical problems and material issues must have been discussed countless times.
Staring at the data on the computer screen, Xu Chuan pondered for a while and then said: "I think we may need to change our thinking about the material selection for the first wall."
Hearing this, everyone else in the laboratory looked over.
Zhao Hongzhi asked: "How to say?"
Xu Chuan thought for a while, organized his words, and then said: "Each d-t fusion will produce a 14.1ev neutron. Since neutrons are not charged, they cannot be restrained by a magnetic field and will directly bombard the first wall material and cause damage.
.”
"14.1ev is a very, very large energy. You must know that the atoms in the material are bound by various chemical bonds, and their bond energies are approximately between 1 and 10ev."
"In other words, the energy carried by a 14.1ev neutron is enough to destroy millions of ordinary chemical bonds, which will undoubtedly cause irreparable damage to the material."
"In a fusion reactor, high-energy neutrons are like bullets fired at materials, constantly hitting metal atoms, breaking the chemical bonds around them, forcing the atoms to leave their original positions, thereby destroying the regular atomic arrangement."
"If you simply want to resist neutrons, perhaps structures made of materials such as beryllium gold, graphite, graphite and uranium 238 can do it. Aren't these materials used in nuclear fission reactors to reflect neutrons?"
"But if you put it in a controllable nuclear fusion reactor, it won't work."
"The reason is simple, because we need neutrons to make tritium self-sustaining, otherwise the currently stored tritium raw materials cannot support the commercial use of controllable nuclear fusion."
"So I personally feel that instead of looking for a resistant material in metal materials, why not try other materials?"