The Wuhan National Pulse Magnetic Field Science Center, the attack of electromagnetic storms once and for all, forced the material to reveal secrets that were unknown. State-of-the-art power supplies, magnets and control systems create the world's top level magnetic field devices.
"The magnetic field is proportional to the current, and the force and heat that the magnet is subjected to is proportional to the square of the magnetic field. So the harder it is to go up. It is as difficult as the 100-meter run from 9.9 seconds to 9.8 seconds." Li Liang, director of the Science Center, said.
"The United States has gone from 70T (Tesla) to 90T for 20 years, Germany for 15 years, and China for 4 years." Li Liang said.
Coil life is nearly double that of international counterparts
In 1820, the Dane Oster inadvertently discovered that the wires were energized and the small magnetic needles in the vicinity would jump. Since then, people have been using energized coils to create magnetic fields. A strong magnetic field of a few milliseconds generated by an instantaneous high current is called a pulsed strong magnetic field, which is higher than a steady-state magnetic field.
Researchers at the National Pulsed Magnetic Field Science Center told us that they use a small finger-thick wire to wind a coil, connect a voltage of 25,000 volts, and flow through a transient current of 40,000 amps to generate a pulsed magnetic field of tens of T. .
However, the energized coil is elongated and crushed by the internal stress of the magnet. Li Liang said that the stress on their coils is 50 times the pressure of the "Zhenlong" on the seabed at 7000 meters. Moreover, the magnet generates a large amount of heat during the discharge process, and the coil is bubbled with liquid nitrogen to cool the temperature; the liquid nitrogen at a temperature of minus 200 degrees Celsius is evaporated at the instant of energization.
The energy of the magnets introduced into the magnets in a few milliseconds, such as the energy of 10 kilograms of TNT, is often broken up. Russian and Japanese scientists have used extreme methods to create magnetic fields of thousands of T, which is the strongest magnetic field currently available to humans. But the coil must be sacrificed, it is disposable, and the magnet coil cannot be reused.
The record coil of the National Strong Magnetic Field Laboratory is made of copper beryllium alloy, the strongest - the biggest hero of the 100T magnetic field record. The Chinese team uses the domestically developed copper-bismuth alloy, which is only 2/3 of the former.
The Chinese have taken a different approach and explored the potential from theoretical analysis. Through accurate calculations, the effect of the layering and reinforcement of polymer fiber layers was greatly improved, just like a hoop hoops the barrel. It is stronger than Kevlar and is the toughest fiber in the world. The fiber soaks the epoxy and acts as an insulating layer for the coil.
Professor Peng Tao is full-time winding. "If the resin is not enough, the reflection is different." Peng Tao said that from the texture and color of the coil, the veteran can see it.瑕疵 Let the coil crash earlier.
The magnet coil of the United States is one meter in diameter, much larger than China's, with lower stress and less damage. However, the average coil of the US coil will be broken 500 times; the coil made by Peng Tao can be used 800 times.
China's power supply is cheap and powerful
Li Liang has worked in Europe and the United States for many years. Most of the world's strongest magnets since 1992 have been involved in design.
"We are overtaking in a corner." Li Liang said, "We have never been there, summing up the experience of each family, so the design is more integrated and systematic."
The United States National Strong Magnetic Field Laboratory generator power supply, two-story high, huge flywheel energy storage, instant discharge - this is the second largest player in the nuclear fusion experiment, 100T record.
China's power supply is divided into three parts: generator power supply (less than 1/10 of the US); 20 capacitor energy storage type power modules; lead-acid battery pack. Through structural optimization, only a few capacitor energy storage type power modules are used, and a magnetic field pulse peak of 90.6T is superimposed. The United States needs 115 megajoules of energy to achieve 100T, and China only achieves 10 megajoules of 90T.
Professor Ding Hongfa, who specializes in power supply, said: "The switching time difference of dozens of modules should be limited to microseconds. Components should also be screened to make the circuit delay consistent."
Construction started in 2008, most of the equipment was self-developed, and the localization rate was 85%. "People are outsourced to professional companies, we are doing it ourselves." Li Liang said.
Each group of capacitor energy storage type power supply is 1 million yuan. The entire power system investment is only a fraction of the Americans. The liquid helium recovery system only has a price of 1/4 of the foreign similar equipment, and the recovered helium gas can save 5 million to 6 million yuan of experimental consumption per year.
Pulsed flat-top magnetic fields are very important, but Americans do flat-top pulsed magnetic fields, which can only be used 50-60 times a year. The Chinese have improved the power and control system, just as simple as opening a microwave oven.
"International experts said that we spent 120 million yuan and did 120 million US dollars of work." Li Liang said.
Measurement needs to be extremely fine
In October 2013, under the witness of experts from all over the world, the Chinese installation was the first show. The international authority reports that China's magnets and power technology are among the best in the world; the control system is internationally leading.
Although the highest magnetic field record is not as good as the United States, the advantages of the Chinese device are obvious – a central control system enables a flexible combination of Category 3 power supplies and 8 experimental stations. This is a killer of the Chinese magnetic field, which is more favorable for experiments. Professor Han Xiaotao, the person in charge of the control system, said: "Others are all magnets that send a waveform. We can generate multiple waveforms from a single magnet."
The United States achieved 100.75T in 2013, Germany achieved 94T, and China became a member of the 90T Club with 90.6T. At present, only the United States and China are expected to set a new record.
Strong magnetic fields will examine new material properties and lead to the next generation of electronic materials and chips. Professor Zhu Zengwei said: "Semi-metals such as bismuth and antimony are suitable for studying extreme conditions under strong magnetic fields."
In November 2018, Peking University discovered that “the number is concussed” and the experiment was done in Wuhan. The logarithmic law was discovered by clearly observing 5 oscillations under the 58T magnetic field.
The "storm eye" of the strong magnetic field is only 20 mm long, and all the samples and sensors are arranged in the almond-sized space, similar to the micro-carving.
"Vortex, thermal effects, vibration, electromagnetic interference... Measurements are always accompanied by noise," said Zuo Huakun engineer.
It is difficult to measure a high quality signal at a time because there are too many interference factors. The sample rod is immersed in the liquid helium and is also separated from the outside by a layer of vacuum, but the high temperature of the coil for a moment will still cause the sample to have a thermal disturbance of zero degrees and zero degrees. The line of the sensor may also vibrate by a few micrometers under the action of a pulsed magnetic field.
There are also many unpredictable factors, such as the instability of the ground zero voltage and the difference in humidity, which may cause different measurement results.
"If it is not so unpredictable, those physics problems will not be left to the present." Zuo Huakun said that the Wuhan National Pulse Strong Magnetic Field Science Center is no weaker than any peers.
"After the completion of the center, not only domestic scientists basically did not go abroad to do experiments, but also attracted many foreign users such as Cambridge and Stanford." Li Liang said.
(Original title The world's leading strong magnetic field Chinese built like this)