Researchers have turned liquid metal into a plasma, opening a new approach to achieving nuclear fusion.
What is a Plasma?
Everyone is familiar with the common phases of matter we’ve known since elementary school: solids, liquids, and gases. There are other states of matter, and the most common state of the Universe’s observable matter is plasma.
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Plasma is a mass of free moving electrons and ions—positively charged atoms that are missing their electrons—that easily conducts electricity. While not usually found naturally on Earth, we can generate artificial plasmas. The most common way to do this is to heat a gas to thousands of degrees Fahrenheit, which strips the atoms of their electrons.
This is how neon lights operate; an electric current flows through and excites the normally inert neon gas inside a tube, which then emits photons as its electrons peel off.
Heating up a gas is not the only way to create a plasma though. The researchers at the University of Rochester’s Laboratory for Laser Energetics (LLE) were able to create a dense plasma of deuterium by creating a high-density liquid deuterium by first lowering its temperature to 21 degrees Kelvin (-422 degrees Fahrenheit) and then rapidly increasing the liquid deuterium’s temperature to almost 180,000 degrees Fahrenheit.
They accomplished this using LLE’s OMEGA lasers to initiate a strong shockwave through the supercooled deuterium liquid that compressed the liquid to as many as 5 million atmosphere’s of pressure.
In its initial liquid state, deuterium exhibits classical properties of a liquid, but at higher densities, the electrons and protons of the deuterium need to take on certain properties described only in quantum mechanics, rather than in classical physics. The exception to this, however, is in the case of a plasma.
The researchers were able to monitor the transition then from a superdense liquid to a plasma as the sample began completely transparent but transformed into a highly-reflective substance that took on a traditional metallic appearance.
"By monitoring the reflectance of the sample as a function of its temperature, we were able to observe the precise conditions where this simple lustrous liquid metal transformed into a dense plasma," said Mohamed Zaghoo, a research associate at LLE.
Potential for Fusion
The fundamental nature of these materials matter because this new information can give researchers developing models for how materials conduct electricity as well as a better understanding of how matter in the extreme environments of the Universe operate, which could open the door to understanding how to achieve the Universe’s most common energy source: nuclear fusion.
"This work is not just a laboratory curiosity. Plasmas comprise the vast interiors of astrophysical bodies like brown dwarfs and also represent the states of matter needed to achieve thermonuclear fusion. These models are essential in our understanding of how to better design experiments to achieve fusion," Zaghoo said.
The research was published in Physics Review Letters last month.