November 30, 2021

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Finally, there is a practical use of nuclear fusion.  But this is not what you expect

Finally, there is a practical use of nuclear fusion. But this is not what you expect

Researchers have used the infernal temperatures of an experimental nuclear fusion reactor for a surprising purpose: to test spacecraft heat shield materials. To write the British scientific site wired.

Why is this important?

Nuclear fusion is a potentially revolutionary technology that could provide essentially unlimited energy. Skeptics argue that nuclear fusion is doomed to forever remain the energy source of the future — for now, fusion experiments still use up more electricity than they generate. But projects can also serve another purpose…

On December 7, 1995, a NASA probe penetrated the atmosphere of Jupiter. While the probe, the Jupiter’s Atmospheric Probe, at a speed of more than 100,000 km / h. Humming through the drag, the friction heated the air around the craft to more than 28,000 degrees Fahrenheit. This split the atoms into charged particles and created an electric soup called plasma. Plasma explains natural phenomena such as lightning or the northern lights; The sun is a giant burning ball of plasma.

Plasma made its way through Jupiter’s heat shield much faster than anyone at NASA expected. When the agency’s engineers analyzed data from the sensors in the heat shield, they realized their exact models were wrong. The shield disintegrated in some areas much more than expected, and much less in others. The probe barely survived, the only reason being that they built up a margin of error in the design by making it thicker. “This has remained an open question,” said Eva Kostdinova, a plasma expert from Auburn University. wired. “But if you want to design new tasks, you have to be able to model what happens.”

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Connected to a billion dollar spacecraft

It is very difficult to accurately simulate entry conditions for a high-speed spacecraft in a pressurized atmosphere, so it is difficult to test precision models designed for such space missions.

This also hampers new heat shield materials that could be lighter or better than the carbon-based heat shields in use today. If you can’t test them, it’s very hard to be sure they’ll work when attached to a billion dollar spacecraft.

Previous tests have used lasers, plasma beams and high-speed projectiles to simulate heat from entering the aircraft. But none of them are quite right. “There is no space facility on Earth that can reach the high temperatures it encounters in atmospheric conditions.” breakthrough for something like Jupiter,” says Kosdinova.

scorching heat from the reactor

New research by Kostadinova and collaborator Dmitriy Orlov of the University of California, San Diego, has revealed a possible alternative: the scorching heat inside an experimental nuclear fusion reactor.

Several hundred such reactors, known as tokamaks, are located in government-funded research facilities around the world. The most famous of these is the European Common Ring in the UK, and ITERInternational Experimental Thermonuclear Reactor, a 35-nation cooperative in southern France.

Researchers have been using this tokamak for decades to tackle challenges nuclear fusion. In tokamak, powerful magnets are used plasma So that it can reach the tens of millions of degrees needed to fuse atoms and release energy.

plasma

But Kostadinova and her collaborator Dmitriy Orlov were more interested in the plasma inside these reactors. They realize that this is just a perfect simulation of a spacecraft penetrating the atmosphere of a gas giant, a planet made up mostly of gases. Orloff works at the DIII-D fusion reactor, an experimental tokamak at a US Department of Energy facility in San Diego, but his background is in aerospace engineering.

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Together they used the DIII-D facilities to perform a series of experiments. Through a port at the bottom of the tokamak, they inserted a series of carbon rods into the plasma stream, and used high-speed, infrared cameras and spectrometers to see how they disintegrated. Orloff and Kostadinova also fired tiny, high-velocity carbon grains into the reactor, simulating on a small scale what the probe’s heat shield would have experienced in Jupiter’s atmosphere.

Conditions in the tokamak were remarkably similar in terms of plasma temperature, the speed with which it flows over the material, and even its composition. For example, the Jovian atmosphere consists mainly of hydrogen and helium, and the tokamak uses DIII-D deuterium, an isotope of hydrogen. “Instead of shooting something at a very high speed, we put a stationary object in a very fast current,” Orloff says.

The experiments, presented this month at a meeting of the American Physical Society in Pittsburgh, helped validate models developed by NASA scientists using data returned from the probe. But it also works as a file proof of concept for a new type of test.

experimental garden

It remains to be seen whether fusion reactors will be a practical test ground – incredibly sensitive devices designed for an entirely different purpose. Orlov and Kostadinov were given time at DIII-D as part of a special effort to use the reactor to expand scientific knowledge. They were able to do this using a port built into the tokamak to safely test the new material. But it is an expensive process. Their day in the machine cost half a million dollars. As a result, these types of experiments are likely to be performed only sporadically in the future.

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With more experiments, Orlov and Kostadinova hope the models can be improved and used to improve the heat shield design for future missions. By applying more material when needed, but also removing it where it is not needed. NASA’s DAVINCI+ mission, which will be launched to Venus by the end of this decade, may be the first to take advantage of this.

In addition, this technique can be used to test new materials, such as silicon carbide. Or newer forms of heat shields, which use a combination of passive materials that burn and other components that don’t.

If an error occurs

Research can also help with design fusion reactors yourself. So far, understandably, most research has focused on plasma interactions in the tokamak core. But with nuclear fusion becoming increasingly important for commercial purposes, more attention must be paid to building reactors. And designing materials that can absorb the fusion reaction and safely dissipate energy if things go wrong…

(Javed)