What is a Superconducting Magnet?

A superconducting magnet is an electromagnet made of a coil made of a second type of superconductor with a high transition temperature and a particularly high critical magnetic field at low temperatures. Its main characteristic is that there is no electrical loss caused by the resistance of the wire, and no magnetic loss caused by the existence of the iron core, which has a strong practical value. It is widely used in industry and scientific research, but it must work at the temperature of liquid helium, which is costly.

Since the discovery of superconductivity in 1911, researchers have been trying to use superconducting materials to wind superconducting coils, superconducting magnets. But the initial disappointment was that the superconducting magnet was quenched with only a small current, that is, the superconducting coil transitioned from a superconducting state with zero resistance to a normal state with relatively high resistance. Until 1961, JEKunzler and others used Nb ₃ Sn superconducting materials to wind superconducting coils that can generate a magnetic field close to 9T, which opened the prelude to the practical application of superconducting magnets. The discovery of high-temperature superconducting materials has produced

Superconducting magnets are superior to conventional magnets in many ways:

(1) There is no Joule heat loss when the superconducting magnet runs stably. This is especially true for magnets that require a strong DC magnetic field in a large space. It can save a lot of energy and the required excitation power is very small. No large water supply and purification equipment like conventional magnets is required. In nuclear physics and high-energy physics research, large superconducting magnets have been used as core components. The significance of high-temperature superconducting magnets in this regard is even more obvious.

(2) Superconducting materials can have high current density, so superconducting magnets are small in size and light in weight, and can easily meet special requirements regarding high uniformity or high magnetic field gradients.

(3) If a superconducting switch is connected in parallel to make the superconducting magnet work in a continuous current state, an extremely stable magnetic field can be obtained, and in principle, no additional power is required, which avoids the need for ordinary magnets Consumes a lot of electricity.

(4) The manufacture and use of small superconducting magnets are very convenient, and small and medium superconducting magnets have become the basic equipment of many laboratories. ^[1]

Superconducting magnet systems are divided into two types: traditional cylindrical superconducting magnets and open superconducting magnets. Traditional superconducting magnets are mainly divided into two grades of 1.5T and 3.0T according to the field strength. 1.5T is the mainstream magnet and 3.0T

The application of superconducting magnet energy storage in power systems was first proposed by Ferrier in 1969. The initial idea was to meet the needs of the French power system to regulate load changes. In the 1970s, making a superconducting coil was easier than making a power electronic device. In 1974, the Los Alamos National Laboratory in the United States developed the first operational superconducting magnet energy storage system with a three-phase inverter. The principle of superconducting magnet energy storage is to use the magnetic field generated by the direct current of the superconducting coil to store energy. In order to reduce energy loss, the energy storage coil must be made of superconducting material and immersed in liquid nitrogen or helium. The key technology of superconducting coils is their manufacturing and cooling.

Because energy conversion is not required, superconducting magnet energy storage has very good dynamic characteristics compared to mechanical energy storage devices, and its response time is on the order of seconds. In addition, because there is virtually no resistance in the coil, superconducting magnet energy storage can produce very high

The high-temperature superconducting coil can be used as the winding of the device, can also directly constitute a magnet, and can also be used as an inductor. A superconducting magnet generally refers to a superconducting coil that can generate a strong magnetic field wound with a superconducting wire. As a device, it also includes a low-temperature thermostatic container necessary for its operation. Compared with ordinary permanent magnets and conventional wire electromagnets, superconducting magnets have great advantages. Generally, the magnetic field near the poles of a permanent magnet is within a few thousand Gauss, and it is very difficult to increase its magnetic field strength. An electromagnet is a magnet made of insulated copper or aluminum wires wound on an iron core. When a strong magnetic field is generated, it needs to pass a large current in the coil, which generates high temperature and emits huge heat. Due to magnet resistance and magnetic circuit losses, a large amount of electrical energy is wasted due to conversion into thermal energy. To obtain a strong magnetic field using conventional conductors, you must use a magnetic core with high permeability, or increase the number of coil turns and increase the current. However, the magnetization characteristics of magnetic cores have saturation limits and the magnetic cores are too heavy. It is difficult to generate a stable strong magnetic field in a large range. Increasing the number of coil turns will increase the volume and weight. Efficiently generate strong magnetic fields. The stronger the magnetic field of the electromagnet, the more power it consumes, and the higher the temperature of the electromagnet. This will cause the copper or aluminum wires or insulators to melt, which will limit the application of high magnetic fields. ^[1]