Scientists apply boron to tungsten components in fusion facilities

Preliminary research: Scientists apply boron to tungsten components in fusion facilities

Right: Physicist Grant Bodner. Left, clockwise from top left: image of Boron being projected into a WEST tokamak; Diagram showing how the powder dropper works; Western interior. and cut boron solid. Credit: College by Kiran Sudarsanan

What is the relationship between boron, an element in a common household cleaner, and tokamaks, which are ring-shaped fusion facilities that heat fuel to temperatures of up to a million degrees? Scientists at the US Department of Energy’s (DOE) Princeton Plasma Physics Laboratory (PPPL) have conducted research demonstrating that a powder dropper developed with PPPL can successfully drop boron powder into high-temperature plasma inside a tokamak that contains parts made of a heat-resistant material known as tungsten. . The scientists want to emphasize that they can use this process to apply boron to tungsten parts because the bare tungsten walls can harm the performance of the plasma if the plasma damages the tungsten.

Because of that high melting pointAnd the tungsten It is increasingly used in tokamaks to help ingredients withstand the intense heat of the fusion process. Boron partially protects tungsten from plasma It prevents tungsten from leaking into the plasma; It also absorbs any stray elements such as oxygen that may be in the plasma from other sources. These unwanted impurities can cool the plasma and quench fusion reactions.

said Grant Bodner, a postdoctoral researcher at PPPL who was the lead author of the research paper reporting the findings in nuclear fusion. The research was conducted using W Environment in Steady-State Tokamak (WEST), which is managed by the French Atomic Energy Commission (CEA). “WEST is one of the few tungsten environments that can help us test this technology on long pulses,” Bodner said.

Another reason physicists are running their experiments with WEST is that its magnets are made of a superconducting material that will appear in magnets inside future fusion devices. This material conducts electricity with little or no resistance and produces so little excess heat that magnets can operate non-stop for long periods of time, as future fusion reactors should do. The magnets create the forces that hold back the plasma until it can undergo fusion.

Fusion, the force that drives the sun and stars, combines the elements of light in the form of plasma – the hot, charged state of matter made up of free electrons and an atomic nucleus – that generates massive amounts of energy. Scientists are seeking to replicate fusion on Earth for a nearly inexhaustible energy source to generate electricity.

Scientists need a way to regenerate the boron coating while the machines are running because future fusion facilities won’t be able to shut down as much for repainting. “Dumping boron in a tokamak while it’s running is like cleaning your apartment while doing all the other things you normally do in it,” said Alberto Gallo, a CEA scientist who contributed to the research. “It’s very useful – it means you don’t have to take extra time outside of your usual activities to do the cleaning,” he said.

A powder dropper device is installed at the top of the tokamak and uses precision actuators to transfer powdered materials from their tanks to the tokamak’s discharge chamber. This mechanism allows researchers to accurately determine the rate and duration of powder droplets, which at other fusion facilities could include other performance-enhancing materials such as lithium. “Because of this flexibility, the dropper has the potential to be really useful in the future,” Bodner said.

The researchers were surprised to discover that the boron set by the dropper does more than wet the inner tungsten surfaces. “We saw it when we dropped the powder, Plasma confinement increase, which means it retains more of its heat, which helps with the fusion process.”

The increased confinement was particularly useful because it occurred without the plasma entering the state known as H-mode (high confinement mode), where confinement improves but plasma is more likely to explode with what are known as localized edge modes, or ELMs. These ELMs take heat out of the plasma, which reduces the efficiency of fusion reactions and sometimes damages the internal components. “If we could use the dropper to get good H-mode confinement without actually going into H-mode and risking ELMs, that would be great for fusion reactors,” Bodner said.

In the future, researchers want to test dropper use only when necessary to maintain good plasma performance. Adding any additional impurities, even boron, can reduce the amount fusion The energy you get because the plasma becomes less pure, Bodner said. “So, we have to try to use the least amount of boron that can produce the effects we want.”

Future experiments will focus on how much Boron It is actually a tungsten surface coating. “We want to measure these quantities so that we can really define what we’re doing and extend these results in the future,” Bodner said.

Powder not gas: a safer and more effective way to create a star on Earth

more information:
Budner et al., Preliminary results of boron powder injection experiments in low L-mode single plasma in the West, nuclear fusion (2022). DOI: 10.1088 / 1741-4326 / ac70ea

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