MAYO used to see how molten metals act under fusion reactor pressures

Could MAYONNAISE hold the key to unlocking unlimited emission-free power? Physicists use the condiment to study how molten metals behave under the type of pressures found in nuclear fusion reactors

  • Inertial confinement fusion reactors are currently unable to reach fusion ignition
  • This is due to the metal capsules that hold energy-producing plasma popping 
  • The capsules pop because the plasma and the hot metal mix into each other 
  • Researchers used mayo as a substitute for molten metal to explore the mixing 
  • They filmed a box containing mayo and a lighter material layer spinning around
  • Experts found that way the layers mix depends on the starting conditions 

Mixing condiments might be unpleasant on the dinner plate but in the lab it is helping experts explore a problem that is stopping nuclear fusion.

Researchers from the US spun a box containing a layer of mayonnaise around and watched how the condiment gradually bled into another lighter material.

Mayonnaise behaves like an elastic-plastic material, just like the molten metal capsules found in active inertial confinement fusion reactors.

These prototype power generators fail to work because the metal capsules mix with the plasma they’re built to contain and burst — before fusion can ignite.

Researchers found that the mayonnaise surface remained intact for longer if initial disturbances to the materials were kept to a minimum.

These findings are being fed into a computer model currently under development at the Los Alamos National Laboratory in New Mexico.

Combined with other research this model may hold the key to unlocking unlimited emission-free power. 

Mixing condiments might be unpleasant on the dinner plate but in the lab it is helping experts explore a problem that is stopping nuclear fusion. Using a high-speed camera, the team monitored how the mayonnaise’s surface reshaped (pictured) 

Lehigh University mechanical engineer Arindam Banerjee and colleagues studied how materials act in extreme environments, which call for creative substitutions.

In this study, Hellman’s Real Mayonnaise was used as a stand-in for molten metal because the condiment at room temperatures has similar properties to metals at high temperatures, with both behaving like an elastic-plastic material.

Researchers poured the mayo into a plexiglass container, along with a second, lighter material, both of which were then subjected to wave-like disturbance before being accelerated on a rotating wheel. 

The team used a high-speed camera to monitor how the mayonnaise’s surface responded to the acceleration.

They then used a computer algorithm to analyse the changes.

‘In the presence of gravity — or any accelerating field — the two materials penetrate one another like “fingers”,’ Professor Banerjee said. 

Researchers call the point where the mayonnaise surface begins to mix with the other material the ‘instability threshold’.

The onset of this instability is related to both the size and the frequency of the initial wave-like disturbances applied to the two materials, they found.

With both two- and three-dimensional disturbances, the surface interface between the materials was more stable if the initial disturbances were smaller and higher in frequency.

This means that, under such starting conditions, the materials can be spun faster before they begin to mix. 

‘There has been an ongoing debate in the scientific community about whether instability growth is a function of the initial conditions or a more local catastrophic process,’ Professor Banerjee added. 

‘Our experiments confirm the former conclusion: that interface growth is strongly dependent on the choice of initial conditions, such as amplitude and wavelength.’ 

Mayonnaise behaves like an elastic-plastic material, just like the molten metal capsules found in active inertial confinement fusion reactors. These prototype power generators fail to work because the metal capsules mix with the plasma they’re built to contain and burst (stock)

The mixing of materials of different densities like this, where unstable layers form because the density and pressure changes involved are opposite in direction, is an example of what scientists call a Rayleigh-Taylor instability.

Until now, studies of the instability had mostly been limited to working with liquids and gases — and little had been known about how accelerated solids mix.

This was because accelerated solids mix so quickly and are challenging to measure.

Better understanding how the Rayleigh-Taylor instability emerges could help to solve various challenges in the fields of astrophysics and geophysics, in industrial processes such as explosive welding, and in high-energy density physics problems relating to inertial confinement fusion.

The latter is something Professor Banerjee and colleagues are directly involved with addressing, in tandem with both the Lawrence Livermore National Laboratory’s National Ignition Facility, in California, and the Los Alamos National Laboratory in New Mexico.

Inertial confinement fusion is a type of nuclear reactor concept in which energy-producing atom fusion reactions are set off by heating and compressing a fuel target.

These targets are typically pin-head-sized pellets that contain the hydrogen isotopes deuterium and tritium.

Inertial confinement fusion is a type of nuclear reactor concept in which atom fusion reactions are set off by heating and compressing a fuel target. Each of these targets (pictured, stock image) are typically tiny pellets that contain the hydrogen isotopes deuterium and tritium

Nuclear fusion is an attractive energy source, having the potential to offer vast amounts of power without harmful emissions or the long-lived radioactive waste that is generated by conventional, fission-based nuclear power stations.

In ‘indirect drive’ fusion setups, the fuel targets are surrounded by metal casings, the inner sides of which are heated up to around 222 million degrees Celsius (400 million degrees Fahrenheit) in a matter of nanoseconds using high-powered-lasers.

Unfortunately, the process has a flaw — the laser heating causes the metal capsules to melt, allowing the compressed gas to burst out, exploding the capsule before the reactor reaches the necessary ignition point of the fusion process. 

Professor Banerjee likened this issue to what happens when you squeeze a balloon. 

‘As the balloon compresses, the air inside pushes against the material confining it, trying to move out,’ Professor Banerjee said.

‘At some point, the balloon will burst under pressure,’ he added.

‘The same thing happens in a fusion capsule; the mixing of the gas and molten metal causes an explosion.’

If researchers could stop these two parts from mixing in the first place, this hurdle to developing a working nuclear fusion reactor would be removed. 

To do this, Professor Banerjee explained, you must first understand exactly how the molten metal and the heated gas are mixing in the first place. 

The researchers’ mayonnaise-based experimental setup is a step towards this — one that allows them to explore how accelerated materials mix in isolation, freed from the complicating factors of extreme temperatures and incipient nuclear reactions. 

The team’s device, which took four years to build, is the first of its kind that can study the mixing between two materials under conditions that are relevant to those seen in inertial confinement fusion reactor prototypes.

The data from the mayo tests will ultimately be fed into a model of the exploding fuel capsule problem that is being developed by experts at the Los Alamos National Lab.

‘They have taken a very complicated problem and isolated it into six or seven smaller problems,’ said Professor Banerjee, explaining that different groups of researchers are tackling the different parts of the issue.

‘There are materials scientists working on certain aspects of the problem’ he added, and ‘there are researchers like me who are focused on the fluid mechanics.’ 

Together, these threads are ‘all feeding into different models that will be combined in the future,’ he said.

The full findings of the study were published in the journal Physical Review E.

HOW DOES A NUCLEAR FUSION REACTOR WORK? 

 Fusion is the process by which a gas is heated up and separated into its constituent ions and electrons. 

It involves light elements, such as hydrogen, smashing together to form heavier elements, such as helium. 

For fusion to occur, hydrogen atoms are placed under high heat and pressure until they fuse together.  

When deuterium and tritium nuclei – which can be found in hydrogen – fuse, they form a helium nucleus, a neutron and a lot of energy.

This is done by heating the fuel to temperatures in excess of 150 million°C and forming a hot plasma, a gaseous soup of subatomic particles.

 For energy production, plasma has to be confined for a sufficiently long period for fusion to occur.

When ions get hot enough, they can overcome their mutual repulsion and collide, fusing together. 

When this happens, they release around one million times more energy than a chemical reaction and three to four times more than a conventional nuclear fission reactor.

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