Great Country Academician

On the other side, in the office, Xu Chuan and Peng Hongxi were chatting about the problems in controllable nuclear fusion technology.

After the Dawn fusion device advanced the high-density plasma magnetic confinement operating time to forty-five minutes, on the road of controllable nuclear fusion, there were no other pioneers who could guide them.

Neither the domestic EAST nor the foreign Helix 7X have ever reached this height.

The current dawn fusion reactor can be said to be groping forward in darkness and chaos.

Talking about this, Peng Hongxi looked at Xu Chuan and asked: "Speaking of which, the dawn device is currently running helium-III and hydrogen simulations, and will soon touch the real deuterium-tritium fusion."

"In the subsequent deuterium-tritium fusion, how do you plan to solve the most difficult problems in the tokamak device, the current and magnetic surface tearing inside the plasma?"

In the field of controllable nuclear fusion, different routes have different implementation methods and technologies.

At present, it is recognized that the most promising route is the magnetic confinement route, but this route has several different implementation methods such as tokamak, stellarator, reverse field pinching, cascaded magnetic mirrors, and spherical rings.

These different approaches have different advantages and disadvantages.

For example, the tokamak device has simple technology and low cost; low neoclassical transport; and has the advantages of strong annular rotation and related flow shear and weak damping of latitudinal flow.

But correspondingly, it also has disadvantages.

For example, the generation of plasma current is difficult, and the internal current of plasma will cause problems such as magnetic surface tearing, twisting, and plasma magnetic islands during operation.

In fact, the stellarator is the same, with advantages and disadvantages.

Its advantage is that it can operate in a steady state for a longer period of time, and there is no problem of plasma current generation and magnetic surface tearing;

But the disadvantages are the high level of neoclassical transmission, the complex manufacture and assembly of coils and coil support structures, etc.

These shortcomings are the inevitable difficulties on the road to controllable nuclear fusion, and each one is no less than a world-class problem.

And with the progress of the dawn device, the biggest difficulty of the tokamak device will soon be touched.

That is how to solve the problems of magnetic surface tearing and plasma magnetic island after the real fusion ignition experiment is carried out on the deuterium-tritium raw material.

To be honest, he couldn't think of a great solution.

Let alone him, there is currently no good solution in the world to solve the problems of magnetic surface tearing and plasma islands in the tokamak device.

If it can be solved, the United States will not give up the more mature magnetic confinement to engage in inertial confinement, and Europe will not be more inclined to stellarator.

But maybe this young man in front of him has a unique way of thinking and can create miracles?

Hearing this question, Xu Chuan thought for a while, and then said: "To be honest, it is quite difficult to fully solve these problems on a certain route."

"Problems such as magnetic surface tearing and plasma islands are one of the biggest problems of tokamak devices and tokamak-like devices."

"To solve this problem, in my personal opinion, we have to start from two aspects."

Hearing this, Peng Hongxi's eyes suddenly showed interest, and he asked curiously, "Which two aspects?"

Xu Chuan: "Outfield coils and NC models!"

Peng Hongxi quickly asked: "How do you say?"

After thinking for a while, Xu Chuan said: "As we all know, the magnetic surface tearing and plasma magnetic islands in the tokamak device mainly come from the way the magnetic field is provided."

"In the tokamak, the rotational transformation of the helical magnetic field is jointly formed by the annular field generated by the external coil and the poloidal magnetic field generated by the plasma current."

"This leads to conflicts and difficulties with balancing between the toroidal and poloidal fields, which can cause tearing of the magnetic surfaces during operation."

"The stellarator has an advantage in this regard. Its longitudinal magnetic field and polar magnetic field are completely provided by the external coil, and the tearing of the magnetic surface will not form inside."

"So theoretically it can operate without plasma current, and it can avoid a lot of instabilities caused by current distribution, which is one of its main advantages."

"I'm now considering a follow-up remodeling of the dawn device, combining the advantages of the star imitator, resetting the outer field coil of the dawn device, and combining the advantages of the curved surface of the pebble bed, to try my best to reduce the magnetic field provided by the polar plasma current. to the use of external field coils to synchronize control and rotation."

Judging from Xu Chuan's experience after his rebirth, from around 2025, countries have actually gradually begun to abandon single-type fusion devices and start researching fusion devices.

For example, the Planck Institute of Plasma, Helix 7X will choose to cooperate with the PPPL laboratory in Princeton, and use the magnetic mirror control technology of the PPPL laboratory to optimize the neoclassical transmission of the stellarator.

Or the quasi-ring symmetric stellarator researched in China is also using the technology of tokamak to optimize the stellarator.

It has to be said that after superconducting materials are applied to controllable nuclear fusion technology, the advantages and future of stellarators are actually greater than that of tokamak devices.

Stellarators also have fewer problems to solve than tokamaks.

As for why he still chooses to go on the tokamak device, the biggest reason is that the plasma performance of the tokamak device far exceeds that of the stellarator.

That's right, at present, even the most advanced Helix 7X, the plasma performance that can be created on a tokamak device is just an ordinary mid-level one.

The tokamak device can easily achieve the high temperature of the plasma with a temperature of 100 million, but the stellarator needs to achieve a temperature of 100 million.

Anyway, the current stellarator cannot do it.

Currently the most advanced stellarator is the 'Spiralite 7X' of the Planck Institute for Plasma Research.

Although the historical record of 50 million degrees and 6.5 minutes was created before, in fact, it is only the temperature of electrons that reaches this temperature, and its plasma temperature only reaches 20 million degrees.

Although the temperature of 20 million degrees has reached the lowest temperature of deuterium-tritium fusion above 14 million degrees, in controllable nuclear fusion, the higher the temperature, the easier the fusion phenomenon will occur, and the higher the energy can be provided. Doubtful.

Of course, this is just a simple explanation.

In fact, what really affects the fusion efficiency is the reaction cross section, that is, the probability of collisions between positively charged atomic nuclei in the plasma.

The factor that affects the collision probability is the fusion triple product, that is, the product of the reacting material density, reaction temperature and confinement time.

The greater this triple factor, the greater the likelihood of fusion.

For example, the greater the plasma density, the higher the probability of collisions between plasmas.

It's like the probability of your foot being stepped on during the Spring Festival travel season is much higher than the probability of being stepped on when you take the train because there are too many people;

The higher the plasma temperature, the higher the activity of the plasma.

After all, the temperature itself reflects the intensity of particle motion. The more active the particles, the higher the possibility of collision and fusion.

It is also like Spring Festival travel, if everyone sits quietly and waits for the bus, it is not easy to be stepped on. The real risk is that when everyone walks up and down the train, the probability of stepping on their feet is high.

Raising the temperature is to make the particles active. The particles are like a crowd, and they are easy to collide with each other when they are active.

As for controlling time, let's not talk about it.

In terms of these three factors, the tokamak has an advantage in the first two, and the stellarator has an advantage in the latter.

This is also one of the reasons why Xu Chuan chose to start with a tokamak-like device instead of a stellarator.

Of course, the advantages of the stellarator are still great, and the advantage of controlling the magnetic field is something that the tokamak device is worth learning from.

He is going to take advantage of this, and start from this aspect to modify the external field coil of the dawn, so as to optimize the magnetic surface tearing and plasma islands in the tokamak device.

As for the control model, if the problem of resetting the dawn field coil can be handed over to other researchers to cooperate with each other, the latter one can only be done by himself.

Fortunately, after returning from rebirth, he decisively chose to major in mathematics, which gave him enough mathematical ability to do this.

On the sofa, Peng Hongxi thought for a while, and said, "So you plan to improve Daybreak by referring to the outer field coil of the stellarator?"

Xu Chuan smiled and nodded and shook his head, got up and dragged out a blackboard from a corner of the office.

"Yes, but that is the transformation of the outer field coil. As for the mathematical model control, I have some ideas here. It happens that you are always here this year. Can you help me take a look?"

Peng Hongxi stood up, walked over and said, "You don't have eyes, you have gone farther than me on the road of controllable nuclear fusion, and you are more capable than me, a bad old man."

Xu Chuan smiled, took out a piece of white chalk from the chalk box hanging beside the blackboard, and said while writing mathematical formulas on the blackboard:

"In a tokamak, the neoclassical tearing mode can be excited by perturbation of the bootstrap current, which is proportional to the pressure gradient."

"When magnetic islands are formed, the local pressure gradient within the magnetic islands is reduced by transport parallel to the flux tubes, which leads to a reduction in the bootstrap current. So in a tokamak, this negative current perturbation leads to The island grew further."

"And from the data of the first ignition operation experiment before, I found some interesting things. Using helium three and hydrogen to run the model, in fact, it is not without phenomena such as magnetic surface tearing, but it is much weaker. .”

"Before I analyzed the data, I found that the high-energy ion interacts with the 2/1 tearing mode resonance to excite the excitation mechanism of the 2/1 fishbone mode, which can explain the energy exchange between the main wave and the high-energy ion in the phase space. resonant relationship."

"The resonance relationship between waves and ions can be written mathematically as: nωt+pωp-ω=0"

"If the high-order correction of the poloidal drift orbit is considered, the resonance relationship is mathematically corrected as: ωt+(m+l)ωp-ω=0"

"That is, co-passingωt+ωp=ω, co-passingωt+2ωp=ω"

"When the high-energy ion distribution center ejection angle Λ0=0.6, the high-energy ion specific pressure value βh=0.35%, the disturbance distribution function δf near the magnetic moment μ=0.554 in the Pφ-E phase space"

"."

In the office, Xu Chuan stood in front of the blackboard and wrote some things he had sorted out based on the experimental data.

On the side, Peng Hongxi also got up from the sofa and walked over, silently looking at the calculations on the blackboard and listening to Xu Chuan's explanation.

In the tokamak device, problems such as magnetic surface tearing, electromagnetic islands, and plasma islands are very troublesome problems in the actual ignition of deuterium-tritium.

Even among the various problems encountered in the whole of controlled nuclear fusion, it is one of the most troublesome problems.

The severity is not weaker than the first wall material, tritium recovery, neutron radiation and other issues.

Because the loss and redistribution of high-energy ions will directly affect the density of high-energy ions in the core and affect the fusion efficiency.

Secondly, when high-energy ions escape from the confinement region and hit the first wall, impurities will be introduced into the plasma, which will reduce the heating efficiency of high-energy ions, directly affect the performance of plasma in future fusion reactors, and become a stumbling block to the steady-state long-pulse operation.

This has been a problem with the tokamak ever since it was proposed.

The reason why stellarators are now beginning to be favored by various countries is that, on the one hand, the development of superconducting materials has solved the original problem of magnetic control instability of stellarators, because it does not have the tokamak’s magnetic surface tearing, plasma Problems such as magnetic islands are more suitable for control.

However, if the problems of magnetic surface tearing and plasma magnetic islands can be solved, there is no doubt that tokamak is more suitable for achieving controllable nuclear fusion than stellarator.

Because it has a huge advantage in increasing the plasma temperature.

Just, can it be done?

To be honest, Peng Hongxi didn't know about this issue.

But on today's blackboard, he saw a glimmer of hope.

Even though he was standing in front of the blackboard, listening to the explanation and looking at the formulas, he couldn't keep up with the rhythm, so he could only roughly understand his train of thought from some words.

But the development of science is sometimes like this, especially in mathematics, whether an idea is feasible or not, sometimes the first intuition is quite accurate.

".From these data, by changing the central ejection angle parameter Λ0 in the high-energy ion distribution function to change the high-energy ion species and their share in the simulated system, explain the resonance between high-energy ions and 2/1 tearing mode It is feasible to interact to excite the main resonance relationship of the 2/1-like fishbone model."

"As for the specific situation, I'm afraid we need to wait until the dawn breaker implements the deuterium-tritium fusion experiment and collect enough data to confirm it."

In front of the blackboard, Xu Chuan threw the end of the chalk back into the chalk box, and turned to look at Peng Hongxi.

The old man didn't answer immediately, he thought for a while, and then said with gleaming eyes: "From your analysis and data, the tearing mode can be coupled with the Alphen mode driven by high-energy ions to produce new physical phenomena, and the large Amplitude Alfvén perturbations can nonlinearly drive tear-mode reconnection and excite macroscopic magnetic islands."

"So, how to stabilize the Alphen disturbance should be your main idea?"

Hearing this, Xu Chuan grinned, nodded in praise and said, "That's right, Mr. Peng is still amazing! You can see through the core idea at a glance."

"If the occurrence of Alphen disturbance can be suppressed to a certain extent, theoretically, the phenomenon of magnetic surface tearing will be much reduced. This may be a solution to the problem of magnetic surface tearing."

Hearing Xu Chuan's praise, Peng Hongxi shook his head, and said, "What's so amazing, I'm old, I'm really old. With your detailed explanation, I'd have to think for a long time to figure it out."

"But from what you've said, it might be possible."

After a pause, he continued: "I'm looking forward to it even more now. With you here, maybe I can really see the spark of controllable nuclear fusion light up in my lifetime."

PS: It's very calm today, so let's start with this chapter.

In addition, I would like to ask if you are interested in this detailed solution to the principle process of controllable nuclear fusion?

If you're not very interested, I won't write so much later, it's too detailed for me to write, and it's rare for you to understand QAQ, so it's better to just skip the pretending?