The Core Material of Euro Spallation Neutron Source Target Station is Tungsten, and the Target Weight is 11 Tons

The European Spallation Neutron Source (ESS) is a key project of the EU's large-scale infrastructure construction project, with a total investment of 1.8 billion euros in the construction phase and an annual operation and maintenance cost of about 140 million euros. It is funded by 13 EU member states, including France, Germany, Britain, Hungary, Italy, Latvia, Spain and Sweden. Nearly half of the construction costs are borne by Sweden and Denmark.

The ESS project, located in Lund, Sweden's University city, covers an area equivalent to seven football stadiums. It consumes at least 50,000 cubic metres of concrete, 6,000 tons of steel bars, 40 kilometres of air distribution pipelines and 2,000 kilometres of cables. The project is expected to be completed by 2023. Once fully put into use, it will become the largest spallation neutron source and the most advanced particle physics reality in the world. In the laboratory, 3000 scientists will use ESS neutron beam every year. Like the China Spallation Neutron Source Project, the target material of the neutron target station in this project is tungsten, which weighs 11 tons.

It is known that neutrons are particles that together with protons and electrons make up atoms. Neutrons have a special property: they have no charge, but they do have a "magnetic moment", which means they behave like small magnets. They are dispersed by nuclei, but their interaction with most materials is rather weak, which makes them perfect for studying the magnetic structure and dynamics at the atomic scale.

So neutrons can be used to precisely locate the composition of matter without invasive chemical markers, but at the same time they can pass through most substances in a non-destructive way, which makes them very widely used scientific probes, from medicine to archaeology, from life science to physics and engineering. For example, condensate physics (solid and liquid), chemistry, bioengineering, life science, material science and other fields can also be used to treat cancer, manufacture new nanomaterials, and test the safety performance of aircraft engines. The ESS project will support at least 15 highly specialized instrument projects.

However, to discover and study neutron sources, scientists need a large number of particles to be liberated from their nuclear bonds. This is called "spallation". Further, when energetic particles interact with the nucleus in the process of spallation, due to nuclear reaction, lighter particles will be emitted from the target, most of which are neutrons.

The most ideal material for this process is tungsten target. The method of spallation is to use an accelerator to emit protons on the target, starting with charged molecular hydrogen ions generated by the ion source. Hydrogen is heated by a rapidly changing electromagnetic field, which evaporates electrons from the hydrogen molecule, leaving protons behind, and then injects them into the linear particle accelerator as high-energy pulse releases, thus triggering the spallation target.

In a linear accelerator with ESS up to 600 meters long, particles almost reach the speed of light. At the end of the pipeline, they will hit a huge tungsten target weighing 11 tons and equipped with a three-ton tungsten wheel. This is a new technology for spallation sources, including a cryogenic system cooled by helium and a deceleration-reflection system for neutrons to decelerate to the available speed. After that, the neutron beam guides the neutron to the instrument.

ESS generates a lot of heat, such as for cryogenic systems used to cool superconducting cavities in accelerators. The temperature of the tungsten target will reach several hundred degrees Celsius when it is in operation, but for the heat resistance of tungsten, this is not a trivial matter. These splitting processes generate a lot of waste heat - which will be recovered and used in the renovation of heating facilities for local residents.

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