Finally, a practical use of nuclear fusion

There are a few hundred such reactors, known as tokamaks, at state-funded research facilities around the world, including the UK’s European joint Torus, and ITER, the International Experimental Thermonuclear Reactor, a 35-nation collaboration in southern France. For decades, researchers have used it to meet the challenges of nuclear fusion, a potentially revolutionary technology that could provide essentially unlimited energy. Inside the tokamak, powerful magnets are used to hold the rotating plasma at high pressure, enabling it to reach the tens of millions of degrees required for atoms to fuse together and release energy. Pessimists argue that nuclear fusion is doomed to forever remain the energy source of the future — for now, fusion experiments still consume more electricity than they generate.

But Kostadinova and her collaborator Dmitriy Orlov were more interested in the plasma inside these reactors, which they realized could be the perfect environment to simulate a spacecraft’s entry into the atmosphere of a gas giant. 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.

Together they used the DIII-D facilities to perform a series of ablation experiments. Using a port at the bottom of the tokamak, they inserted a series of carbon rods into the plasma flow, and used high-speed, infrared cameras and spectrometers to track how they disintegrated. Orloff and Kostadinova also fired tiny carbon pellets into the reactor at high speed, simulating on a small scale what a heat shield would encounter on the Galileo probe in Jupiter’s atmosphere.

Conditions inside the tokamak were remarkably similar in terms of plasma temperature, velocity of flow over the material, and even composition: the Jovian atmosphere is composed mostly of hydrogen and helium, while the DIII-D tokamak uses deuterium, an isotope of hydrogen. “Instead of shooting something at very high speed, we are instead putting a stationary object in a very fast flow,” Orloff says.

The experiments, presented at a meeting of the American Physical Society in Pittsburgh this month, helped validate the ablation models developed by NASA scientists using data sent from the Galileo probe. But it also serves as a proof of concept for a new type of testing. “We’re opening up this new area of ​​research,” Orloff says. “No one has done it before.”

It is something much needed in the industry. “There has been a delay in the new testing procedures,” says Yanni Barghouti, founder of Cosmic Shielding Corporation, a start-up that makes radiation shields for spacecraft. “It allows you to prototype much faster and at a lower cost – there is a feedback loop.”

It remains to be seen whether fusion reactors will be a practical test ground – highly sensitive devices designed for another purpose entirely. Orlov and Kostadinov were given time at DIII-D as part of a special effort to use the reactor to expand scientific knowledge, using a port built into the tokamak for the purpose of safely testing new materials. But it is an expensive process. It cost them a day on the machine half a million dollars. As a result, it is likely that this type of experiment will be carried out sparingly in the future, when the opportunity arises, to modify and improve the computer simulations.

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