Thursday, May 23, 2019

Mayo goes nuclear: Researchers study dynamics in fusion reactors using mayonnaise

Hold the sriracha, put down the bbq sauce, and toss the mustard, because mayonnaise is finally getting its time to shine. Rather than spreading the condiment colloid on a sandwich though, researchers are using the product to study how materials interact in nuclear fusion reactors. A team of scientists from Lehigh University just published their latest research in Physical Review Fluids, which illustrates how this common household item can be used to explore a surprising question.

Containers of earth temperature, nonradioactive condiments. Credit: Getty

Graduate students Rinosh Polavarapu and Pamela Roach, and professor Arindam Banerjee are fluid dynamicists studying how materials move in biologic and energy systems. In their unique experiment, they investigated the Raleigh-Taylor-instabilities of solid materials with varying initial conditions. In other words, they modeled what happens when a light material, like air, tries to push against a denser material, like metal. Their work is of major interest to national labs, who are currently using these ideas to improve nuclear fusion experiments.

Nuclear energy has long been touted as a (relatively) environmentally-friendly energy alternative; one that could curb our appetite for fossil fuels. The energy produced by nuclear reactors is made possible through a process called fission, the splitting of large atoms into smaller atoms. This releases energy in the form of heat, which then spins a turbine. 

The merging of atoms through fusion can also make energy, but uses much less fuel and produces less waste than fission. Yet, no one has successfully figured out how to harness it for energy. To create fusion, you have to replicate the same conditions as the interior of a neutron star. That’s hard to do on earth because the earth is, in fact, not an incredibly dense and hot neutron star. 

The size of a neutron star compared to the city of Boston. While small, neutron stars can have masses over a million times that of earth's! Credit: NASA Goddard

At Lawrence Livermore and Los Alamos National Laboratories, researchers are developing a method to produce fusion reactions called inertial confinement. Using this technique, frozen gases of hydrogen isotopes are sealed inside metal pellets the size of an M&M, then superheated with sophisticated lasers to about 4 million degrees Fahrenheit.

Here’s where they hit a snag; much like what happens to a raw egg upon being put in a microwave, the superheated gas explodes the pellet, ruining the experiment before fusion can occur. 

“To prevent the mixing,” said Banerjee in a press release, “you have to understand how the molten metal and heated gas mix in the first place.” 

So, why mayonnaise? It turns out that studying molten metal under extreme temperatures and pressure is a bit impractical, unsafe, and most importantly, expensive. While some may search for a spicier material, simple mayonnaise has the right stuff to get the job done (that is, 80% vegetable oil, 8% water, and 12 % other things). Researchers found that both molten metal and room-temperature mayonnaise behave similarly as elastic-plastic materials, allowing scientists to look at the mechanics of this process without needing the high temperatures or nuclear reaction. 

A big question here is how much force does it take for the gas to push through the hot metal, and how can we prevent it from happening in the future? To answer this question, researchers searched for the main drivers of instability; is it based on the initial conditions or localized phenomena? Past research has explored the behavior of liquids in these mixing situations, but this is the first study to address this in a solid. 

In experimental trials, the team poured mayonnaise into a plexiglass container, which was mounted on a cleverly-designed apparatus connected to a rotating wheel. They then used high-speed cameras and image processing software to track the precise motion of the mayonnaise while it accelerated. They repeated the process multiple times using different amplitudes and wavelengths to see what caused the most instability in the mayonnaise. 

Footage of the mayonnaise during the experiments. As the acceleration increased, materials became more and more unstable. Credit: Rinosh Polavarapu, Pamela Roach and Arindam Banerjee

After processing the footage, they concluded that initial conditions, such as the wave amplitude and wavelength, mattered far more than processes at the atomic level when it comes to producing instabilities. By starting the experiments at lower energies, the mayonnaise could withstand higher accelerations. In the future, this could lead to inertial confinement experiments that don’t explode prior to nuclear fusion, because researchers would be able to more precisely adjust the initial conditions of their experiments. By starting their experiments at lower amplitudes, the mayonnaise-air interface has higher stability, meaning it can withstand higher accelerations. 

While condiments have been used in studies of physics before, none have used mayonnaise in such a novel way. So, will the use of condiments easily spread to science fields? Other physicists may need to ketchup. 

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