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

He didn't interfere in the experiments of the stellarator, and almost all of them were arranged by the Energy Research Institute, and the data of the first operation of the Huaxing fusion device was still quite beautiful.

Still, he has some other concerns.

Of course, he is not worried that the stellar will not be able to achieve real ignition operation, he is not worried about this point.

Although there are many things that need to be adjusted in the process of changing the route from a comprehensive tokamak device to an advanced stellar simulator, the core is still based on the theory of magnetic confinement.

The core of magnetic confinement has touched the numerical control model of plasma turbulence, the first wall material and the confined magnetic field.

These three cores, they have already done it on the Daybreak Fusion Device.

Xu Chuan was worried that there were originally two pieces, the first was the feasibility of miniaturization, and the other was that the power of the stellar simulator might be insufficient, that is, after the ignition was realized, the energy that would be guided out may be far from enough.

The first question is not too big of a problem from today's experimental data.

But the second question, I 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 the tokamak device, but its power is also recognized as lower than that of the tokamak device.

Its output is difficult, or almost incomparable, to a tokamak.

This is because of the structure of the stellar, and it is also the place that Xu Chuan is most worried about.

In particular, the power may be lower after miniaturization, to the point that the energy generated is completely insufficient.

After all, the smaller the size, the smaller the amount of plasma that can be contained in the reactor chamber, and the smaller the number of deuterium-tritium plasma, the less likely it is to collide to form fusion.

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

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

This is actually about the concept of how to achieve controlled nuclear fusion.

There may be many people who think that as long as the plasma in the reactor chamber is maintained, it is allowed to fuse and the energy can be channeled to achieve controlled nuclear fusion.

But not in the strict sense of the word.

Nuclear fusion is not something that can be ignited casually, and we need to feed energy to the reactor before we can get the output energy from it (this refers to raising the temperature of the isodeuterium-tritium ion through the ICRF heating antenna, so that it collides with fusion and produces more temperature).

If the input energy is considered as 'input X', then the energy channeled from the reactor on the basis of maintaining the operation of the plasma is 'output Y'.

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

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

If the Q value exceeds 1, it means that the reactor can export energy to the outside, and the higher the Q value, the higher the energy output.

However, due to the current technology, the power station cannot convert 100% of the energy produced by nuclear fusion, and theoretically it can reach 40% to 50%, which is very remarkable, and the Dawn fusion reactor uses a ferrofluid unit + traditional heat engine to reach 73%.

Coupled with various other losses, a rough estimate shows that when the Q value is equal to 2.5, controlled nuclear fusion can "protect the capital", that is, the 'money' invested and the 'money' of power generation output are balanced.

Considering the huge infrastructure and subsequent maintenance costs, scientists generally believe that the "Q value" of controlled nuclear fusion must be at least greater than 50 in order to truly realize controlled nuclear fusion technology.

The Q value of the Daybreak fusion device is more than three digits.

This is also the reason why Xu Chuan chose the tokamak device as the target in the first place, the internal temperature of the tokamak device is higher, the reactor chamber is regular, and it can hold more deuterium-tritium plasma, which will produce a greater Q value.

Listening to Xu Chuan's question, Liang Qu thought for a moment and replied, "Raising the temperature of fusion may solve this problem?" ”

Xu Chuan nodded and said, "This is indeed a method, which can be considered." However, raising the temperature, for the stellar, on the one hand, is more difficult, on the other hand, it may be a bit of a symptom but not a cure. ”

"Charged particles in a toroidal magnetic field typically need to move multiple times along the ring to connect the bottom and top to effectively neutralize charge accumulation. However, this is not good for stellarumers, which have a very large and irregular number of coils of various forms, which will form a large number of local magnetic mirrors. ”

Magnetic mirrors can constrain charged particles to a certain extent, which will cause some particles to be "trapped" in the local magnetic mirror, unable to complete the hoop motion, and thus unable to eliminate the drift caused by the magnetic field curvature and magnetic field gradient, which in turn leads to particle loss. ”

"In particular, the high-energy ions used to heat other particles have a very low collision frequency, and once they are captured by the local magnetic mirror, they can hardly escape, and the loss is very fast. This is extremely important for the self-sustaining heating of fusion reactors (the 3.5 MeV helium nucleus produced by the fusion reaction heats deuterium and tritium). ”

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

But he thinks more about how to solve this problem at the root.

These days, he has been thinking about how to reconstruct the outer field coils and magnet windings of the stellarator, not simply because it is too difficult to produce improved superconductor coils with three-dimensional structures, but also partly because he is trying to find a way to solve this problem.

Hearing this, Liang Qu was also a little big-headed, frowned and thought for a while, and then said, "But the structure of the stellar simulator is too difficult to change. ”

"It itself is to reduce the difficulty of magnetic confinement through extremely high engineering difficulty, and if it is reconstructed, not to mention the difficulty, it is also 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 stellar simulator cannot be greatly adjusted and modified, and if it is adjusted, we need to face problems such as plasma magnetic islands, magnetic surface tearing, and distortion and touching effects." ”

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

Hearing this, Liang Qu frowned and said: "Then it will be difficult to say this, at present, the stellar mimic is the most promising one for miniaturization, if the stellar mimic doesn't work, I really don't know what else can work, pebble?" Or is it inertial constraints? ”

Xu Chuan thought for a while and said: "The pebble bed also needs to face the problem of plasma magnetic surface tearing, and there are almost no solutions to it, and I don't know if the route of inertial restraint can go through fusion, so I will give up for the time being." ”

"What do you think?"

Liang Qu frowned and looked at Xu Chuan and asked, in the field of controlled nuclear fusion, he is the first person known as the 'father of controlled nuclear fusion'.

After thinking for a while, Xu Chuan spoke: "I'm thinking about two things. ”

"What two?"

"The first aspect is to modify the magnet windings and outfield coils of the stellarator."

As he spoke, Xu Chuan sorted out the manuscript paper on the desk and handed it to Liang Qu: "Look at this, it was extremely difficult to produce the external field coil and magnet winding that fed back the three-dimensional structure of the Western Superconductor Group before, and in response to this problem, I combined the problem of low energy efficiency of the stellar simulator I just mentioned to reconstruct the structure of the external field coil and magnet winding." ”

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

"Permanent magnet stellarators?"

Looking at the title on the manuscript paper, Liang Qu muttered a sentence and read it carefully.

Xu Chuan nodded, took a sip of tea and said: "The problem with the stellarator is that there are two aspects, one is that the magnetic field of the traditional stellarum is greater than that of the tokamak, resulting in a higher level of neoclassical transport and high-energy particle loss than the tokamak. ”

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

"Therefore, how to reduce the level of neoclassical transport and high-energy particle loss of the stellarator, and how to generate the required three-dimensional magnetic field with simple engineering permanent magnet blocks are difficult to study."

Hearing this, Liang Qu, who was flipping through the manuscript paper, interjected: "Are you going to use permanent magnets to replace the original magnet winding?" ”

Xu Chuan nodded and said, "From the perspective of theoretical calculations, through the optimization of the magnetic field shape of the stellarator, precise quasisymmetry can be achieved, and then it proves that the stellarator can theoretically achieve the same level of neoclassical transport and high-energy particle loss as the tokamak." ”

"And this can be done by optimizing the outer field coil and magnet windings."

"If the magnet winding is modified first, the size, shape, and remanence of the permanent magnet block are exactly the same, and the magnetization direction is one of the finite specified directions, on the basis of the original spiral stone-7X, the permanent magnet and the quasisymmetry can be combined to form a new permanent magnet stellarator, which may be able to solve these two problems."

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

He continued with Xu Chuan's words: "Compared with the extremely complex three-dimensional twisted coils used in the current stellarizer, the low production cost and low engineering difficulty of the standardized magnet block that can be manufactured in batches and the simple coil greatly weaken the engineering difficulty of the design, construction and maintenance of the stellarator. ”

"Moreover, the uniform size and shape make the permanent magnet blocks can be assembled, which is conducive to the control of assembly accuracy."

"Wonderful!"

"This line of thinking, absolutely absolute!"

In the end, Liang Qudu couldn't help but give a thumbs up, worthy of being the father of controlled nuclear fusion, and his understanding in this field is beyond 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 solution to the difficulty of the project. And the problem of the loss of high-energy particles, or the problem of insufficient fusion energy, I am afraid that we will have to find another way. ”

Liang Qu nodded and asked, "What about another aspect?" I think it's the solution to the problem of loss of high-energy particles, or the lack of fusion energy, right? ”

Since this one has raised the problem, then 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, which makes him more curious about how this person can solve the problem of high-energy particle loss.

The design of the permanent magnet stellar is really amazing in his opinion.

It is not a very large change, which not only retains the advantages of the original stellarator without magnetic surface tearing effect, but also greatly reduces the engineering difficulty, which is a brilliant idea.

Hearing Liang Qu ask about the second aspect, Xu Chuan said with a smile: "The second aspect is to change a fusion raw material. ”

"A different kind of fusion feedstock?" Liang Qu looked at him suspiciously, with some confusion in his eyes.

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

After a pause, he continued: "When we choose raw materials for controlled nuclear fusion, we generally choose isotopes of hydrogen for processing, because the electrostatic repulsion between the lighter nuclei is the least and the most prone to fusion reactions. ”

"Therefore, the substances to achieve nuclear fusion are generally the first to choose the isotopes of hydrogen, deuterium and tritium, which is used in the dawn fusion device."

"The advantage of deuterium-tritium nuclear fusion is that the reaction conditions are the most relaxed and the reaction temperature requirements are the lowest, but the disadvantages are the deterioration of materials brought by neutrons, and the problems that high-energy neutrons take away most of the energy and cannot be used."

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

"So in fact, although it releases a lot of energy, we can use very little of it."

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

"So on the basis of deuterium-tritium fusion, I am ready to change the raw materials for fusion."

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

After a pause, he continued: "In the past, in addition to deuterium-tritium fusion, the mainstream field of controlled nuclear fusion research also included deuterium-helium-triple fusion, helium-tri-helium triple fusion, deuterium-deuterium fusion, hydrogen-boron fusion and other methods. ”

"Compared with deuterium-tritium fusion, these fusion methods are more difficult, and each has its own advantages and disadvantages, I don't know which one you are considering?"

(End of chapter)