Chapter 381: Ideas to solve the problem of magnetic surface tearing in tokamak
On the other side, in the office, Xu Chuan and Peng Hongxi were chatting 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 EST nor the foreign Spiral Stone 7 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 surface 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 the generation of plasma current and the tearing of the magnetic surface;
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 of them 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 come from the way the magnetic field is provided."
"In a tokamak, the rotational transformation of the helical magnetic field is formed by the annular field generated by the external coil and the poloidal magnetic field generated by the plasma current."
"This will lead to conflicts between the annular field and the poloidal magnetic field and difficulty in balancing, and will cause the problem of 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. This 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 utilizing 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 for Plasma Research, Helix 7 will choose to cooperate with the pppl laboratory at Princeton, using the magnetic mirror control technology of the pppl laboratory 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 work 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 7 can create plasma performance that is only average and medium-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 want to reach temperatures of hundreds of millions.
Anyway, the current star simulator can't do it.
The most advanced stellarator currently is the ‘Helix 7’ of the Planck Institute for Plasma Research.
Although it previously set a historical record of 50 million degrees and six and a half minutes, in fact what reached this temperature was only the electron temperature, and its plasma temperature only reached 20 million degrees.
This chapter is not finished yet, please click the next page to continue reading the exciting content! 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 greater the fusion
The easier it is for a phenomenon to occur, the higher the energy it can provide, there is no doubt about it.
Of course, this is just a simple explanation.
In fact, what really affects the 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 the probability of being stepped on during the Spring Festival travel rush is much greater than the probability of being stepped on when taking the 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 is also like the Spring Festival travel rush. If everyone is sitting quietly waiting for the train, it is not easy to get stepped on. The real risk is when everyone is walking to get on and off the train, the probability of getting stepped on is higher.
Raising the temperature makes the particles active. Particles are like a crowd of people, and they tend to 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 instead of 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 islanding 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 with, the latter one can probably only be done by himself.
Fortunately, after he was reborn, 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 modification 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 this 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, the neoclassical tearing mode 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 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 are no phenomena 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.
Resonance relationship.”
"The resonance relationship between waves and ions can be mathematically written as: nt pp-=0"
"If we consider the high-order correction of the poleward drift orbit, the resonance relationship is mathematically corrected to: t (l)p-=0"
"That is co-pssngt p=,co-pssngt 2p="
"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.
The severity is no less serious than problems such as first wall materials, tritium recycling, and neutron radiation.
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 zone and encounter the first wall, impurities will be introduced into the plasma, reducing the heating efficiency of high-energy ions, directly affecting the plasma performance in future fusion reactors, and becoming a stumbling block to steady-state long pulse operation.
This is a problem that has existed since tokamak was proposed.
The reason why stellarators are now beginning to be viewed favorably by various countries again is that, on the one hand, the development of superconducting materials has solved the problem of unstable magnetic control of stellarators. This is because it does not have the magnetic surface tearing of tokamak, and the plasma
Problems such as magnetic islanding are more suitable for control.
But if problems such as 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 stellarators.
Because it has huge advantages in increasing the plasma temperature.
But, can it be done?
This chapter is not over yet, please click on the next page to continue reading! To be honest, Peng Hongxi doesn’t know about this issue.
But on today's blackboard, he saw a glimmer of hope.
Although now he is standing in front of the blackboard, listening to the explanation and looking at the calculations, he can't keep up with the rhythm. He can only roughly understand his ideas from some words.
But scientific development 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 projection angle parameter Λ0 in the high-energy ion distribution function to change the high-energy ion species and their share size loaded into the simulation system, it can explain the resonance of high-energy ions with the 2/1 tearing mode
It is feasible that the interaction excites the dominant resonance relationship of the 2/1-like fishbone model."
"As for the specific situation, I'm afraid we need to wait until the Dawn Device implements the deuterium-tritium fusion experiment and collects enough data to confirm."
In front of the blackboard, Xu Chuan threw the chalk 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 and then said with shining 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
Amplitude Alfvén perturbations can nonlinearly drive tearing mode reconnection and excite macroscopic magnetic islands."
"So, how to stabilize the Alfvén disturbance should be your main idea, right?"
Hearing this, Xu Chuan grinned, nodded and praised: "Yes, Mr. Peng is still awesome! He can see through the core idea at a glance."
"If the occurrence of Alfvén disturbance can be suppressed to a certain extent, theoretically, the phenomenon of magnetic surface tearing will be reduced a lot. 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 a great thing! I'm old, really old. With your detailed explanation, it would take me a long time to figure it out."
"But judging from what you said, this may indeed be feasible."
After a pause, he continued: "I am 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: I’m stuck 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 and 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 probably hard for you to understand QQ. It's better to be straightforward and skip the pretense?