Superconducting technology is a technology to study the properties and functions of substances in superconducting state, as well as the research, development and application of superconducting materials and superconducting devices. The resistance of some substances will completely disappear when the temperature drops to a certain value, which is called superconductivity. Materials with superconductivity are called superconducting materials or superconductors. Superconducting materials include metallic low-temperature superconducting materials, ceramic high-temperature superconducting materials and organic superconducting materials. The development and application of superconducting technology are of great value to national economy, military technology, scientific experiments and medical care.

Superconductivity was discovered by Dutch scientist H.K. Anis in 19 1 1 year. When he was doing a low-temperature experiment, he accidentally found that the resistance suddenly disappeared when the silver wire was cooled to 4.2K K. Later, scientists found that many metals, alloys and intermetallic compounds also had this characteristic. 1933, German W. meissner discovered that superconductors have high diamagnetism, which makes the magnetic field lines impenetrable. People call it the Mesner effect. 1957, Americans J. Badin, L. N. Cooper and J. R. schrieffer jointly put forward the microscopic theory of superconductivity (BCS theory). 1962, British B.D. Josephson predicted theoretically that superconducting current could pass through an extremely thin insulator and enter another superconductor, forming a tunnel superconducting current. This Josephson effect was later confirmed by experiments. At the beginning of 1986, K.A. Mahler and J.G. Benos of the Institute of International Business Machines Corporation in Zurich, USA, found that barium, lanthanum and copper oxides showed superconductivity at 30 K. The discovery of this ceramic superconducting material has opened up a new way for the development of superconducting technology.

Superconducting materials discovered before 1986 are good conductor metals, alloys and intermetallic compounds, and their highest critical temperature is only 23.2K, while the superconducting materials discovered by Mahler and Benos are oxides, whose critical temperature is much higher than that of low-temperature superconductors, which is of epoch-making significance to superconducting research and has attracted great attention all over the world. 1987, China established an expert committee on superconducting technology and a national joint research and development center for superconducting technology to lead China's superconducting research work. In July of the same year, the President of the United States put forward the Presidential Superconducting Initiative, demanding that the government take necessary measures to support HTS research; The Japanese government, private enterprises and universities have made plans to jointly develop superconducting materials. Superconducting scientists all over the world are looking for superconducting materials with high critical temperature for ceramic materials, which has formed a worldwide superconducting research fever, and high-temperature superconducting materials such as yttrium barium copper oxide, bismuth strontium calcium copper oxide and thallium barium calcium copper oxide are constantly emerging. Since 1986, China has made a series of significant achievements in tackling key problems in high temperature superconducting technology, reaching the international leading level in some fields.

Another characteristic of superconducting materials is Josephson effect or superconducting tunneling effect, that is, an insulating layer (about 10 angstrom thick) is placed between two superconductors, and then the insulating layer becomes a "weak" superconductor, through which current can pass.

The indexes to judge the performance of superconducting materials are critical temperature (TC), critical magnetic field (HC) and critical current (ic). Critical temperature refers to the temperature at which a substance changes from resistance to non-resistance; Critical magnetic field refers to the magnetic field threshold when the superconductivity of superconductor disappears at a certain temperature without current. Critical current refers to the current density value that can make superconductor change from superconducting state to normal state. The larger the values of TC, HC and IC, the better the performance of superconductors.

Superconducting technology is a high-tech with important application value and great development prospect. Its potential military applications can be divided into two categories: strong magnetism and weak magnetism.

Superconducting strong magnetic technology mainly uses superconducting materials to generate high steady-state strong magnetic fields, which can be made into superconducting energy storage devices, superconducting motors and electromagnetic propulsion devices. ① Superconducting energy storage device. This energy storage device will store a lot of energy for a long time and then release it when needed. Large superconducting energy storage system (energy storage 10? Joule) will be used as the power supply for land-based free electron lasers or space-based directed energy weapons. ② Superconducting motor. Compared with the conventional motor, the volume and mass of this motor will be significantly reduced, the power will be doubled, and the efficiency will be greatly improved, which can provide power for weapons and equipment. ③ Electromagnetic propulsion device. The electromagnetic propulsion device made of superconducting ferromagnetic materials can directly convert electric energy into power, and will be able to propel mass objects at high speed. It can be used as the power device of warships in the military, which can eliminate transmission noise and improve concealment. It can also be used as the power device of electromagnetic gun.

The theoretical basis of superconducting weak magnetic technology is Josephson effect. Superconducting electronic devices made by this effect will have the characteristics of low power consumption, low noise, high sensitivity and fast response, which can be used for high-precision electromagnetic measurement of weak signals and also for ultra-high-speed electronic computer components. The main superconducting electronic devices are: ① superconducting weak magnetic detector. Superconducting quantum interferometer, electromagnetic sensor and magnetometer are much more sensitive to magnetic field and electromagnetic radiation than conventional devices, and can be used for military reconnaissance. ② Superconducting computer. Superconducting computers equipped with Josephson devices will be dozens of times faster than ordinary computers, with power consumption reduced to less than one thousandth and good heat dissipation performance. ③ Superconducting high frequency detector. Such as superconducting infrared detectors, parametric amplifiers, mixers, power amplifiers, etc. , will make the performance of space surveillance, communication, navigation, meteorology and weapon systems far exceed that of conventional equipment.