Great Country Academician

In the office, Xu Chuan and Liang Qu chatted for a while and listened to the follow-up work arrangements.

He has no longer intervened in the stellarator experiments, leaving almost all arrangements to the Energy Research Institute. The first operation of the Huaxing Fusion Device, the data was quite beautiful.

But he still has some other concerns.

Of course, he is not worried that the stellarator cannot achieve real ignition operation. He is not worried about this.

Although there are many things that need to be adjusted during the route change from a comprehensive tokamak device to an advanced stellarator device, the core is still based on the magnetic confinement theory.

As for the core of magnetic confinement, we have touched on the three major parts of the CNC model of plasma turbulence, the first wall material and the confinement magnetic field.

They have already completed these three cores in the Dawn Fusion Device.

Xu Chuan was originally worried about two things. The first was the feasibility of miniaturization, and the other was that the power of the stellarator might be insufficient, that is, the energy guided after ignition was achieved might not be enough.

Judging from today's experimental data, the first question is no longer a big problem.

But for the second question, I still don’t know what the situation is.

The advantage of the stellarator is that the control of plasma turbulence is much stronger than that of a tokamak device, but its power is also recognized to be lower than that of a tokamak device.

Its output is difficult, or almost incomparable, with that of a tokamak device.

This was destined because of the structure of the stellarator, and it was also what Xu Chuan was most worried about.

Especially after miniaturization, the power may be even lower, so low that the energy generated is completely insufficient.

After all, the smaller the volume, the less amount of plasma that can be accommodated in the reactor chamber. If the amount of deuterium and tritium plasma is small, the probability of collision to form fusion will be smaller.

A controllable nuclear fusion reactor does not mean that it has achieved ignition, stabilized the operation of plasma turbulence, completed deuterium and tritium fusion and can guide energy out.

These are just the basics of fusion, and on top of that, there is something called the Q value.

This actually involves the concept of "achieving controllable nuclear fusion".

Many people may think that controllable nuclear fusion is achieved as long as the plasma in the reactor chamber is maintained, allowed to fuse, and energy can be directed out.

But actually it's not strictly speaking.

Nuclear fusion cannot be ignited casually. We need to input energy into the reactor first before we can get the output energy (this refers to raising the temperature of equal deuterium and tritium ions through ICRF heating antenna, allowing them to collide and fuse. generate more temperature).

If the input energy is regarded as ‘input X’, then the energy directed out of the reactor on the basis of maintaining the plasma operation is ‘output Y’.

The difference between Y-X is the so-called Q value.

Only when the Q value is equal to one, the reactor can maintain stability without external energy input and rely on its own fusion reaction.

When the Q value exceeds 1, it means that the reactor can output energy to the outside. The higher the Q value, the higher the energy output.

However, due to current technology, power stations cannot convert 100% of the energy generated by nuclear fusion. In theory, it would be great to achieve 40% to 50%. The Dawn Fusion Reactor uses a magnetic fluid unit + a traditional heat engine. Just reached 73%.

Coupled with various other losses, a rough estimate shows that when the Q value is equal to 2.5, controllable nuclear fusion can "guarantee", that is, the "money" invested and the "money" generated by the power generation are balanced.

What is obvious is that just "guaranteing capital" is not enough. Considering the huge infrastructure and subsequent maintenance costs, scientists generally believe that the "Q value" of controllable nuclear fusion must be at least greater than 50 before it can be truly realized. Controlled nuclear fusion technology.

The Q value of the Daybreak Fusion Device exceeds three digits.

This is also the reason why Xu Chuan originally chose the tokamak device as the target. The internal temperature of the tokamak device is higher, the reactor chamber is regular, it can accommodate more deuterium and tritium plasma, and the Q value generated will be greater.

Listening to the question raised by Xu Chuan, Liang Qu thought for a moment and replied: "Maybe raising the temperature of fusion can solve this problem?"

Xu Chuan nodded and said: "This is indeed a method that can be considered. However, raising the temperature is more difficult for the stellarator, and on the other hand it may treat the symptoms rather than the root cause."

"Charged particles in a ring magnetic field generally need to move along the ring for many times to connect the bottom and the top, so as to effectively neutralize the charge accumulation. But this is very detrimental to the stellarator, which has a very large number of coils in various forms. They are numerous and extremely irregular, forming a large number of local magnetic mirrors.”

"Magnetic mirrors can restrain charged particles to a certain extent. This will cause some particles to be "captured" in local magnetic mirrors and cannot complete the circular motion completely, and thus cannot eliminate the effects caused by magnetic field curvature and magnetic field gradient. Drift, which in turn leads to particle loss.”

"Especially high-energy ions used to heat other particles. Due to the low collision frequency, once captured by the local magnetic mirror, they can hardly escape and are lost quickly. This is very important for the self-sustaining heating of the fusion reactor (the 3.5 MeV helium produced by the fusion reaction The heating of atomic nuclei (deuterium and tritium) is extremely important."

Liang Qu's suggestion is indeed feasible, because the higher the temperature, the more active the particles are, and the more active they are, the greater the probability of collision.

But what he was thinking more about was how to solve this problem from the root.

These days, he has been thinking about how to reconstruct the external field coil and magnet winding of the stellarator. It is not just because it is too difficult to produce an improved superconductor coil with a three-dimensional structure, but also partly because he is also trying to find a way to solve this problem.

Hearing this, Liang Qu also felt a little big-headed. After thinking for a while, he frowned and said, "But the structure of the stellarator is too difficult to change."

"It itself uses extremely high engineering difficulty to reduce the difficulty of magnetic confinement. If it is re-constructed, not to mention the difficulty, it will also be very troublesome to change its structure and whether it can continue to be miniaturized."

Xu Chuan shook his head and said: "No, the overall structure and shape of the stellarator cannot be significantly adjusted or modified. If we do, we will need to face problems such as plasma magnetic islands, magnetic surface tearing, and distortion effects."

"We currently have no means to solve these problems during the miniaturization process, so we can only rely on the special structure of the stellarator to avoid them."

Hearing this, Liang Qu frowned and said: "That would be difficult. At present, the star simulator is the most promising one for miniaturization. If the star simulator doesn't work, I really don't know what else. Would that work, a ball bed? Or inertia constraints?”

Xu Chuan thought for a while and said: "The pebble bed also needs to face the problem of plasma magnetic surface tearing. There are almost no solutions. I don't know whether the inertial constraint route can lead to fusion, so I will give up for now. "

"What do you think?"

Liang Qu frowned and looked at Xu Chuan and asked. In the field of controllable nuclear fusion, he is the first person known as the 'Father of Controlled Nuclear Fusion'.

After thinking for a while, Xu Chuan said: "I am considering two aspects."

"Which two aspects?"

"The first aspect is to transform the magnet windings and external field coils of the stellarator."

With that said, Xu Chuan sorted out the papers on his desk and handed them to Liang Qu: "Look at this. Previously, the Western Superconducting Group reported that it was extremely difficult to produce three-dimensional structure field coils and magnet windings. To address this problem, , I combined the problem of low energy efficiency of the stellarator just mentioned and reconstructed the structure of the external field coil and magnet winding."

Looking at the manuscript paper that was pushed over, Liang Qu's eyes flickered a little, and he took it with a little curiosity.

"Permanent magnet stellarator?"

Looking at the title on the manuscript paper, Liang Qu muttered something and started reading it carefully.

Xu Chuan nodded, took a sip of tea and said: "The problem with stellarators lies in two aspects. First, the ripples of the magnetic field of traditional stellarators are larger than that of tokamak, which leads to its neoclassical transport level and high-energy particles. The level of losses is higher than for a tokamak.”

"The second is that it requires a three-dimensional structure of the coil, which is complex in structure, difficult to manufacture, and quite costly."

"So how to reduce the neoclassical transport level and high-energy particle loss level of the stellarator, and how to use a simple engineering permanent magnet block to generate the required three-dimensional magnetic field is a difficult research problem."

Hearing this, Liang Qu, who was flipping through the manuscript, interrupted: "Are you planning to use permanent magnets to replace the original magnet windings?"

Xu Chuan nodded and said: "From a theoretical calculation point of view, through the optimization of the magnetic field configuration of the stellarator, precise quasi-symmetry can be achieved, which proves that the stellarator can theoretically achieve neoclassical output comparable to that of a tokamak. transport levels and high-energy particle loss levels.”

"This aspect of the design can be accomplished by optimizing the external field coil and magnet windings."

"If the magnet windings are modified first so that the size, shape and remanence of the permanent magnet blocks are exactly the same and the magnetization direction is one of the limited specified directions, the permanent magnets and the quasi-quasi-magnets can be combined on the original basis of Helixite-7X. Combining symmetrical configurations to reconstruct a new permanent magnet stellarator may be able to solve these two problems."

Looking through the manuscript paper in his hand and listening to Xu Chuan's explanation, Liang Qu's eyes became a little brighter.

He followed Xu Chuan's words and continued: "Compared with the extremely complex three-dimensional twisted coils used in current stellarators, the low production cost and low engineering difficulty of standardized magnet blocks that can be manufactured in batches and simple coils have a great impact on the development of stellarators. Design, construction, and maintenance have greatly reduced the engineering difficulty.”

"And the unified size and shape allow the permanent magnet blocks to be assembled, which is conducive to assembly accuracy control."

"Wonderful!"

"This idea is amazing!"

At the end of the sentence, Liang Qu couldn't help but give a thumbs up. He is worthy of being the father of controllable nuclear fusion. His understanding in this field exceeds that of ordinary people for at least ten years.

Xu Chuan smiled, shook his head slightly, and said: "Even if it is feasible, this is only a way to solve the engineering difficulty. As for the problem of high-energy particle loss, or the problem of insufficient fusion energy, I'm afraid we have to solve it separately. Think of ways to."

Liang Qu nodded and asked: "What about another aspect? I guess it is the solution you are considering to solve the problem of high-energy particle loss, or the problem of insufficient fusion energy, right?"

Since this person raised the issue, he must have considered a solution.

And he just said that he has considered both the engineering difficulty and the loss of high-energy particles. Now he is more curious about how this person solves the problem of loss of high-energy particles.

The design of the permanent magnet stellarator was really amazing in his opinion.

It is not a very drastic change. It not only retains the advantage of the original stellarator without the magnetic surface tearing effect, but also greatly reduces the engineering difficulty. This idea is incomparable.

When Liang Qu asked about the second aspect, Xu Chuan smiled and said, "The second aspect is to change the fusion raw material."

"Change the fusion raw material?" Liang Qu looked over doubtfully, with some confusion in his eyes.

Xu Chuan nodded and said, "That's right, change the fusion raw material."

After a pause, he continued: "When we choose raw materials for controllable nuclear fusion, we usually choose hydrogen isotopes, because the electrostatic repulsion between lightweight nuclei is the smallest and fusion reactions are most likely to occur."

"So to achieve nuclear fusion, the material is generally the first choice of hydrogen isotopes deuterium and tritium, which is what the Dawn fusion device uses."

"The advantage of deuterium-tritium fusion is that the reaction conditions are the most relaxed and the reaction temperature requirements are the lowest, but the disadvantage is that neutrons cause material degradation, and high-energy neutrons take away most of the energy that cannot be used."

"Although the reuse of neutrons can be used to complete tritium self-sustainment, most of the energy taken away by high-energy neutrons is wasted."

"So actually it releases a lot of energy, but we can use very little of it."

"Moreover, the deuterium-tritium fusion device also needs to use first wall materials and peripheral protective materials to cope with the impact of high-energy neutrons, which further increases the volume of the fusion reactor."

"So based on deuterium and tritium fusion, I am going to change the raw materials for fusion."

Hearing this, Liang Qu nodded in agreement and said, "These are indeed the shortcomings of deuterium and tritium fusion, but if you change the fusion raw material."

After a pause, he continued: "Previously, in addition to deuterium-tritium fusion, the mainstream areas of controllable nuclear fusion research also included deuterium-helium fusion, helium-3-helium fusion, deuterium-deuterium fusion, hydrogen-boron fusion, etc. way."

"Compared to deuterium and tritium fusion, these fusion methods are more difficult. Each has its own advantages and disadvantages. Which one are you considering?"