Diamond film application: artificial sun
With the improvement of people's living standards, the public's awareness of environmental protection has gradually increased, and the demand for clean energy has become increasingly prominent. At present, the annual development and utilization of renewable energy in China accounts for only about 26% of total energy consumption, and there is still huge room for development. Nuclear energy is one of the most promising new energy sources for human beings. The utilization rate of nuclear energy in developed countries has exceeded 40%, while China only accounts for less than 3%.
There are two ways for people to develop nuclear energy: one is the fission of heavy elements, such as fission of uranium; the other is the fusion of light elements such as antimony, bismuth, and lithium. The fission technology of heavy elements has been practically applied, but heavy elements are radioactive. The lessons of the Fukushima nuclear power plant in Japan have led people to talk about nuclear color change. In contrast, the fusion technology of light elements is non-polluting, and the source of raw materials is rich, which has great potential.
Both strontium and barium are isotopes of hydrogen. Their nuclei can collide with each other under certain conditions to form a heavier nuclei, helium nuclei, and release huge nuclear energy (E=MC2). According to calculations, 0.03 grams of strontium is contained per liter of seawater. The energy released by this 0.03 gram enthalpy is equivalent to the heat of burning 300 liters of gasoline. The total volume of seawater is 1.37 billion cubic kilometers, which contains hundreds of millions of kilograms of plutonium. The energy released by these fusions can guarantee the energy consumption of human beings for tens of billions of years.
However, the nuclear fusion reaction of æ°˜-æ°š needs to be carried out at a high temperature of tens of millions of degrees or even hundreds of millions of degrees. Such a reaction has been achieved on hydrogen bombs (lithium fusion). However, this process is uncontrolled and the conditions required to produce controlled nuclear fusion are very demanding. Our sun relies on nuclear fusion to bring light and heat to the solar system. Its central temperature reaches 15 million degrees Celsius. In addition, there is huge pressure to make nuclear fusion react normally, and the earth cannot get huge pressure. Make up for it by raising the temperature, but in this case the temperature will reach hundreds of millions of degrees. Nuclear fusion is so high that no solid matter can withstand it and can only be constrained by a strong magnetic field. In addition, the ignition of the nuclear reaction is also a problem at such a high temperature, and is generally realized by a microwave gyrotron or a laser beam capable of outputting megawatts of power.
Nuclear fusion reactor
At present, one of the devices capable of completing controlled nuclear fusion in the world is the "Tokamak nuclear fusion reactor", also known as the superconducting Tokamak controlled thermonuclear fusion reactor, commonly known as "artificial sun", which can have an internal temperature of up to 500 million. Degree, more than 30 times the internal temperature of the sun, was invented by scientists in the former Soviet Union in the 1950s. In 2006, I successfully completed the discharge test for the first time in the new generation of thermonuclear fusion device EAST. EAST became the world's first fully-conducted non-circular cross-section nuclear fusion experimental device.
Nuclear fusion reactors need to generate and transmit up to tens of megawatts of microwave energy. Due to the high power generation and transmission, the traditional loss is high, and the thermal conductivity of sapphire, BeO and other microwave window materials can no longer meet the fusion reactor pair. Performance requirements for microwave windows. High-quality diamond film materials have become a good fusion reactor microwave window material because of their low microwave dielectric loss (which is one-tenth of sapphire) and high thermal conductivity (50 times that of sapphire). At present, high-power microwave windows made of high-quality diamond films have been widely used in the international fusion reactor technology.
Foreign-made diamond film microwave window
High-power microwave windows for fusion reactors require diamond membrane diameters of 3-6 inches and thicknesses over 1.8 mm, while requiring high thermal conductivity and low dielectric loss. These characteristics put forward high requirements for the preparation technology of diamond film, which can only be achieved by using 915MHz high power microwave CVD technology.
Regrettably, although element 6 reported its commercialized high-power millimeter-wave transmission window with a diameter of 119 mm as early as 2001, it is still not available in China until today. It is reported that in 2012, in order to adapt to the rapid development of fusion reactor technology, China's EAST plans to order four diamond film microwave windows abroad, with a total contract amount of 4.48 million yuan.
The reason for this situation is the backwardness of China's high-power microwave CVD diamond film preparation technology. Although domestic research has made great progress in 2.45GHz microwave CVD technology in recent years, it has been in the blank of 915 MHz high-power microwave CVD technology research. Until recently, Hebei Institute of Laser Research, Hebei Presman Diamond Technology Co., Ltd. and Professor Tang Weizhong of Beijing University of Science and Technology have successfully developed a 915MHz/75kW high-power microwave CVD device, and prepared a diameter of 127mm for the first time in China. The 1 mm high quality diamond film microwave window material has a thermal conductivity of more than 20 W/cm·K and a dielectric loss of less than tgδ<10-4. Although this indicator can meet the needs of some domestic diamond film users, there is still a big gap in the application requirements of the megawatt microwave window from the nuclear fusion reactor. It is hoped that in the near future, we will be able to realize the localization of this product, help the rapid development of the national nuclear fusion reactor (artificial sun) plan, and realize the large-scale application of China's clean and efficient nuclear energy at an early date, so that the motherland's sky is bluer and the water is clearer. The people's lives are better.
Domestic large-area diamond film window
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