Chapter 380: Ideas for Solving the Problem of Tokamak Magnetic Surface Tearing

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

After the Daybreak Fusion Device advanced the high-density plasma magnetic confinement operation time to forty-five minutes, there was no other pioneer who could guide them on the road to controllable nuclear fusion.

Neither the domestic EAST nor the foreign Spiral Stone 7X has reached this height.

The current Dawn Fusion Reactor can be said to be groping forward in darkness and chaos.

While talking about this, Peng Hongxi looked at Xu Chuan and asked: "Speaking of which, the Dawn Device is currently running helium-3 and hydrogen simulations, and will soon touch on real deuterium-tritium fusion."

"In the subsequent deuterium and tritium fusion, how are you going to solve the most difficult problems of internal current and magnetic plane tearing in the tokamak device?"

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

Currently, it is recognized that the most promising route is the magnetic confinement route, but this route has several different implementation methods including tokamak, stellarator, reverse field pinch, cascade magnetic mirror, and spherical ring.

These different methods have different advantages and disadvantages.

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

But correspondingly, it also has shortcomings.

For example, it is difficult to generate plasma current. During operation, the internal current of the plasma will cause problems such as magnetic surface tearing, distortion, and plasma magnetic islands.

In fact, the same goes for stellarators, which have advantages and disadvantages.

Its advantage is that it can operate in a steady state for a longer period of time, without problems such as plasma current generation and magnetic surface tearing;

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

These shortcomings are 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 Daybreak device, it will soon hit the biggest difficulty of the Tokamak device.

That is how to solve the problems of magnetic surface tearing and plasma magnetic islands after conducting real fusion ignition experiments with deuterium and tritium raw materials.

To be honest, he couldn't think of any good solution.

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

If it can be solved, the United States will not give up the more mature magnetic constraint to develop inertial constraint, and Europe will not be more inclined to stellarators.

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

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

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

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

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

Xu Chuan: "Outfield coil and CNC model!"

Peng Hongxi quickly asked: "How to say?"

After thinking for a while, Xu Chuan said: "As we all know, problems such as magnetic surface tearing and plasma magnetic islanding in tokamak devices mainly originate from the way the magnetic field is provided."

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

"This can lead to conflicts between the toroidal field and the poloidal magnetic field and difficulty in balancing, which can cause magnetic surface tearing during operation."

"The stellarator has an advantage in this regard. Its longitudinal magnetic field and poloidal magnetic field are completely provided by the external coil, and magnetic surface tears will not be formed inside."

"So in theory it can operate without plasma current and avoid many instabilities caused by current distribution, which is one of its main advantages."

"I am now considering making a subsequent modification to the Dawning Device. I will combine the advantages of the stellarator and reset the external field coil of the Dawning Device, and combine it with the advantages of the pebble bed's curved surface to try to reduce the magnetic field provided by the poloidal plasma current. to use external field coils to synchronize control and rotation.”

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

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

Or the quasi-cyclosymmetric stellarator studied in China is also using tokamak technology 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 those of tokamak devices.

The stellarator needs to solve fewer problems than the tokamak device.

As for why he still chose to continue working 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 can create plasma performance that is only average and mid-level when compared to a tokamak device.

Tokamak devices can easily achieve high plasma temperatures of hundreds of millions, but stellarators will die if they can achieve temperatures of hundreds of millions.

Anyway, the current star simulator can't do it.

The most advanced stellarator currently is the ‘Helix 7X’ of the Planck Institute for Plasma Research.

Although it had previously set a historical record of 50 million degrees and six and a half minutes, in fact it was only the electron temperature that reached this temperature, and its plasma temperature only reached 20 million degrees.

Although the temperature of 20 million degrees has reached the lowest temperature of deuterium and tritium fusion, which is more than 14 million degrees, in controllable nuclear fusion, the higher the temperature, the easier it is for the fusion phenomenon to occur and the higher the energy it can provide. This is unnecessary Doubtful.

Of course, this is just a simple explanation.

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

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

The greater these three factors, the greater the possibility of fusion.

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

Just like your probability of being stepped on during the Spring Festival travel rush is much greater than your chance of being stepped on when taking a train because there are more 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's also like the Spring Festival travel rush. If everyone sits quietly and waits for the bus, it's not easy to get stepped on. The real risk is that when everyone is walking to get on and off 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 easily collide together when they become active.

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

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

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

Of course, the advantages of the stellarator are still great, and the advantages of controlling the magnetic field are something that the tokamak device deserves to learn from.

He plans to take advantage of this and modify the external field coil of Daybreak to optimize problems such as magnetic surface tearing and plasma islands in the tokamak device.

As for the control model, if the previous issue of resetting the Dawn field coil can be left to other researchers to work together, the latter one can probably only be done by himself.

Fortunately, after his rebirth, he immediately 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 are going to improve Daybreak by referring to the external field coil of the stellarator?"

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

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

Peng Hongxi stood up, walked over and said, "What's wrong with you? You've gone much further than me on the road to controllable nuclear fusion, and you're more capable than a bad old man like me."

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

"In a tokamak, neoclassical tearing modes can be excited by perturbations in the bootstrap current, which is proportional to the pressure gradient."

"When a magnetic island forms, the local pressure gradient within the magnetic island is reduced by transporting parallel to the flux tube of the magnetic field lines, which results in a reduction in the bootstrap current. So in a tokamak, this negative current perturbation causes The island grows further."

"From the data of the first ignition operation experiment, I found some interesting things. Using helium 3 and hydrogen to run the model, it is not that there is no phenomenon such as magnetic surface tearing, but it is much weaker. "

"I analyzed the data before and found that the excitation mechanism of the 2/1 fishbone-like mode is excited by the resonance interaction between high-energy ions and the 2/1 tearing mode. I gave a formula that can explain the energy exchange between the main waves and high-energy ions in the phase space. Resonant relationship.”

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

"If we consider the high-order correction of the poleward drift orbit, the resonance relationship is mathematically corrected to: 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 and the high-energy ion specific pressure βh=0.35%, the perturbation 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 something he had compiled based on 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 islanding, and plasma islanding are very troublesome problems in the real ignition of deuterium and tritium.

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

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

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, high-energy ions escaping from the confinement area and hitting the first wall will also introduce impurities into the plasma, reduce the heating efficiency of high-energy ions, directly affect the plasma performance in future fusion reactors, and become a stumbling block for steady-state long-pulse operation.

This is a problem that has existed since the tokamak was proposed.

The reason why stellarators are now beginning to be favored by various countries again is that after the development of superconducting materials has solved the original magnetic control instability problem of stellarators, it is because it does not have the problems of magnetic surface tearing and plasma magnetic islands of tokamaks, and is more suitable for control.

But if the problems of magnetic surface tearing and plasma magnetic islands can be solved, there is no doubt that tokamaks are more suitable for achieving controlled nuclear fusion than stellarators.

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

But, can it be done?

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

But he saw a glimmer of hope on the blackboard today.

Although 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, and could only roughly understand his ideas from some words.

But scientific development is sometimes like this, especially in mathematics, whether an idea is feasible, sometimes the first glance is quite accurate.

". From these data, it is feasible to explain the main resonance relationship of the 2/1 fishbone mode excited by the interaction of high-energy ions and 2/1 tearing mode resonance."

"As for the specific situation, I'm afraid we need to wait until the Dawn Device realizes the deuterium-tritium fusion experiment and collects enough data to confirm it."

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

The old man did not answer immediately. He thought for a while before he said with a sparkling look in his eyes: "From your analysis and data, the tearing mode can couple with the Alfvén mode driven by high-energy ions to produce new physical phenomena, and the large-scale Alfvén perturbation can nonlinearly drive the tearing mode reconnection and stimulate macroscopic magnetic islands."

"So, how to stabilize the Alfvén perturbation should be your main idea, right?"

Hearing this, Xu Chuan grinned and nodded in praise: "Yes, Mr. Peng is still amazing! He saw through the core idea at a glance."

"If the Alfvén perturbation can be suppressed to a certain extent, Theoretically, the phenomenon of magnetic surface tearing will be much lower. This may be a way to solve the problem of magnetic surface tearing. "

Hearing Xu Chuan's praise, Peng Hongxi shook his head and said: "What's so great about it? I'm old, really old. Even with your detailed explanation, I have to think for a long time to understand it. "

"But from what you said, this may be feasible. "

After a pause, he continued: "I am looking forward to it more and more now. With you, maybe I can really see the spark of controlled nuclear fusion in my lifetime. "

PS: I'm stuck today, so let's just focus on this chapter.

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

If you are not very interested, I will not write so much later. It is too detailed for me to write, and you probably can hardly understand it QAQ. It is better to skip it directly and pretend to be cool?